Using CNKI database as the data source, domestic academic journals were searched to identify papers related to this theme, for the further analysis of research in this area. With “natural resources”, “sustainable development” and “China” as the keywords, the logical multiplier (“and”) as the operator, and the literature search timeframe from January 1, 2000 to December 31, 2019, a total of 379 academic journal papers were retrieved. In addition, in order to ensure the accuracy and scientific integrity of the research results and eliminate the interference of irrelevant literature, 64 non-academic items, such as relevant information, brief interviews, conference notifications and topic selection notices, were manually eliminated. Ultimately 315 valid papers were finally obtained and were used as the data analysis basis for the subsequent research.

CiteSpace is a knowledge map drawing tool that is very influential in the field of information visualization software, as its capability for the analysis of the research object through the whole development course, research hot spots and the future development trends of applications is very extensive (Yang and Hang, 2012). Through scientific visualization analysis of the knowledge map, CiteSpace can be short and concise in presenting the history of the research content and the main body structure (Li and Wang, 2016). As a classic software for visualization analysis in this field, its application mainly focuses on management science, library and archives management, economics, etc. (Sui and Pang, 2017). More recently, it has gradually appeared in the analysis and research of knowledge maps of pedagogy, architecture and other disciplines. In this paper, a visual atlas of natural resources and sustainable development in China from 2000 to 2019 is drawn using CiteSpace, and keywords in the literature are comprehensively studied, so as to further interpret the research status and evolutionary path, clarify the knowledge structure, and detect the development trends. Based on China's natural resource and sustainable development related academic journals in econometric analysis, we can accurately understand the research status of the research target, we can be more objective in our understanding of current research gaps and mining, as well as the domestic natural resource protection and sustainable development research perspective, and we can derive the projections on the trends of future development.

Statistical analysis was conducted on the number of published papers of natural resources and sustainable development in China in the past two decades, and the annual distribution of the number of research documents was obtained (Fig. 1). According to the changing trend of literature quantity in this research field, the research process of natural resources in China can be roughly divided into three stages: the stage of progressive improvement, the stage of stable development, and the stage of deepening maturity.

The first stage (2000-2005): Phase of gradual improvement. In 1997, due to the over-exploitation of resources, the Yellow River was cut off for 226 days throughout the whole year, and the appearance of the catastrophic flood disaster in 1998 made people increasingly realize the importance of resource protection and sustainable utilization (Huang, 2004). In 2002, the 16th CPC National Congress gave new instructions on this, emphasizing resource conservation, and taking it to the national level. At the same time, that meeting also pointed out the country's future development direction on resource development and utilization (Gao, 2003). Subsequently, the scientific development concept which was derived on this basis began to consider the subject status of human beings, emphasizing that development should be people-oriented (Li, 2006). These are promotive factors in the national field which have a great impact on the area of natural resources, and they are also the main reason for the increase in the number of publications in this period. In this stage of development, although natural resources have received some attention, domestic scholars still focused on discussing the relationship between resources and economic development, and most of them are on qualitative research topics, such as theoretical concepts and case introductions.

The second stage (2006-2014): Stable development stage. As the first year of the 11th Five-Year Plan, 2006 marked a change in the economic situation and that Plan proposed to change the traditional development model, abandon the development path of over-exploitation of resources, and it emphasizes realizing the common progress of resources and society (Zhou, 2007). Subsequently, in 2013, the state began to further explore the issue of resource protection and made new policy guidance for the development of resource-based cities (Zhang, 2013), which gave an orientation for the exploitation of natural resources in resource-based cities and emphasized the sustainability of development. This document made an important contribution in further prompting scholars to strengthen research in the field of natural resources. As can be seen from Fig. 1, the amount of research literature on the sustainable development of natural resources in this stage does not increase or decrease significantly compared with the previous stage, but it is generally stable.

The third stage (2015-2019): The deepening maturity stage. The research content at this stage was still affected by national policies and guidelines, and The National Sustainable Agricultural Development Plan (2015-2030) was issued in 2015 (Du and Jin, 2016). This document began to introduce the concept of sustainable development into agricultural development from the industrial and urban aspects, emphasizing the sustainability of agricultural development. In 2018, the reorganization of the resources sector shows the importance of the management of natural resources to national development (Li et al., 2006). During this period, the research on natural resources and sustainable development had undergone a great change. On the whole, although the number of academic papers published in this stage decreased compared with the previous stage, the research on natural resources and sustainable development in this stage was more mature than in the previous stage. It no longer only paid attention to the problems and difficulties existing in natural resources, but paid more attention to the systematic nature and integrity of the research, and constantly expanded the width and breadth of the research on natural resources and sustainable development in theory and practice.

The study of keywords co-occurrence in a certain field can reflect the research basis of the field. Based on the keywords of natural resources and sustainable development, this paper analyzes the co-occurrence of keywords in the recent 20 years, and draws a map of keyword co-occurrence in the field. A total of 469 nodes and 759 links are obtained, as shown in Fig. 2.

In the keyword co-occurrence spectrum, the keyword frequency is proportional to the corresponding node size (Ye et al., 2014). Experience shows that keywords with high word frequency and strong centrality are of great significance to the research status of the field. According to the node size of the responses of the co-occurrence map, keywords such as nature resource, sustainable development, ecological civilization, circular economy, ecological compensation, ecological environment and environment accounting have large nodes, which shows that the research on natural resources and sustainable development in China focused on these aspects. On the basis of the above analysis, the top ten keywords by word frequency were selected, and their centrality is analyzed in depth, as shown in Table 1.

It can be seen from Table 1 that, excluding thematic keywords such as sustainable development and natural resource, keywords such as China, resource, ecological civilization and natural resource have the largest nodes in the co-occurrence map, and their word frequencies appear the most, at 17, 16 and 11 times, respectively. In addition, according to the data, the keyword centrality should be compared with 0.1. If the keyword centrality exceeds 0.1, the node is called a key node. The higher the centrality of the node, the higher the correlation between the keyword and other keywords should be (Wang, 2020). The above table shows that there are few key nodes in this study, and only the central degrees corresponding to sustainable development, natural resource and ecological civilization are greater than 0.1, while the centrality degrees of the other keywords are relatively low, which indicates that Chinese scholars have diverse and scattered research interests in the field of natural resources and sustainable development. In addition, the initial year of the emergence of keywords indicates that the major keywords in the field of natural resources and sustainable development appeared earlier, indicating that the relevant research in this field started earlier and the early results have strong representative and academic values. Therefore, based on the comprehensive analysis of the above results, the research results on natural resources and sustainable development in China can be summarized into three main aspects from the perspectives of research objects, application methods and solution strategies.

From the perspective of research objects, GDP, environment protection, ecological deficit and carrying capacity are hot research topics in the field of natural resources and sustainable development. Among them, GDP has a relatively high degree of centrality and frequency, indicating that GDP has a strong correlation with other keywords in the field.

From the perspective of application methods, such methods as ecological compensation, ecological footprint, indicator system, institutional innovation, information, and national economic accounting system have been widely applied in the field of natural resources and sustainable development. However, the centrality of ecological footprint was low, indicating that the correlation between ecological footprint and other research topics was weak. It can also be seen that the studies on ecological footprint have a strong special property compared with other studies. Therefore, when applying the ecological footprint method, scientific analysis should be carried out based on data differences such as biological production area type and annual output of consumption items (Akadiri et al., 2020).

From the perspective of solution strategies, keywords such as environment accounting, circular economy, countermeasures, Chinese society of natural resources, ecological construction and so on, are hot spots in this research field. As can be seen from the keywords involved in this field, Chinese scholars in the field of natural resources and the sustainable development countermeasures were proposed to repair recovery, and under the guidance of China natural resources society and other organizations, while the research on moderate exploitation and utilization of resources has made increasing contributions to promoting social stability and coordinated economic development.

3.3.1 The authors distribution

According to the analysis of the data, there are 428 authors in 315 journals, and the top five authors with the most papers are Sun X H, Cheng J H, Xiao G X, Niu W Y and Du Q. These authors published about 5% of the total literature. In addition, 408 of the 428 authors published only one paper, accounting for about 95.3% of the total literature. According to Lotka's Law (Chi and Wu, 2019), the ratio of low-yield authors in this study far exceeds the numerical standard of the Law. These results show that in the past two decades, many different scholars have been involved in the studies related to natural resources and sustainable development, but they are extremely scattered, and although the research content is broad, it is not deep enough.

Table 2 gives some basic characteristics of the authors who published two or more papers in the field of natural resources and sustainable development between 2000 and 2019. Sun X H topped the list with four published papers, accounting for 1.26% of the total sample. The authors Cheng J H, Xiao G X, Niu W Y, Du Q each published three papers, while the other authors each published two papers. The publication earliest year of these authors is roughly between 2000 and 2005, and most of them are published separately, while the joint publications are less common and more scattered. Sun X H is the author with the most papers, and his research focuses on discussing the relationship between resources and economic sustainability from the perspective of micro-enterprise green accounting supervision (Zhao and Sun, 2003; Sun, 2006).

3.3.2 Distribution of research institutions

A total of 327 research institutions have participated in China's natural resources and sustainable development research, according to the data. Among them, 13 institutions each published two or more papers, and the remaining 314 institutions each published one paper, accounting for 96% of the total literature among research institutions. This indicates that in the past two decades, the literature on natural resources and sustainable development has involved many different research institutions, but on the whole, the research literature of each institution is relatively small, so the research content is not in-depth enough, and it is relatively dispersed. Table 3 shows a ranking of the top 10 institutions

by number of papers in the field of natural resources and sustainable development in China over the past twenty years. According to the statistics, there are nine universities and one research institute in total. The results show that universities are the key research institutions in this area.

The institution with the largest number of publications is the Institute of Geographical Sciences and Nature Resources of the Chinese Academy of Sciences. This institution published total of 10 papers, focusing on the summary of China's existing academic contributions to the construction of natural resources and ecological civilization (Li and Liu, 2013), and emphasizing the disciplinary value of resource economics and its role and contribution to the construction of ecological civilization (Dong et al., 2013). However, this institution generally publishes its papers separately from others, so it does not have close links with other institutions and lacks academic exchanges. There are some joint publications among other individual research institutions. Although they are closely related, overall, the research contents of each institution are still relatively dispersed, and there is a lack of cross-regional or interdisciplinary collaborative research mechanisms and platforms.

Statistical analysis was conducted on the literature retrieval results, and the top 10 cited references in the field of natural resources and sustainable development were identified (Table 4) to explore and analyze their roles as important knowledge bases in the research process of natural resources and sustainable development. The results showed that the author with the highest citation frequency was Huang N S, who was cited 269 times in total. In addition, among the top 10 cited references, eight were published between 2000 and 2005, indicating that the early research results in this field have important theoretical and research values. In addition, these 10 top-cited studies focus on the issue of natural resources and economic development, and involve relevant legislation (Lv, 2000; Cai, 2001), policy adjustments (Lin et al., 2012), sustainable development mechanisms (Cheng et al., 2005) and other aspects of this research field. The research contents of natural resources and sustainable development are discussed from multiple perspectives and aspects. In addition, the most frequently cited papers are from Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, which indicates that their research on natural resources and sustainable development started earlier and has strong application and guiding significance. From the aspect of source institutions, the highly cited papers are not only from the research institutes of Geographical Sciences and resources, but also from the political, legal and economic institutions. This shows that Chinese scholars attach great importance to the legal protection and economic benefits of natural resources and sustainable development.

With the wide application of sustainable development theory, the number of publications about natural resources and sustainable development in China is also on the rise. In the development process of nearly 20 years, the aspect of the content has become more and more profound and presents a diversified research trend. In order to more accurately grasp the research frontier and dynamics in the field of natural resources and sustainable development, based on the analysis of keyword co-occurrence, the evolutionary trend of research hot spots in the past two decades can be further analyzed, and the results are shown in Fig. 3 (Ye and Zhang, 2018). This figure shows that the research on natural resources and

sustainable development in China has a long and rapid development span, and is in an important period of qualitative transformation. The path can be divided into three main phases of the theoretical development stage (2000-2005), protection adjustment period (2006-2015), and control and optimization phase (2016-2019). Theoretical development stage (2000-2005): Hot keywords mainly include legislative proposal, ecological environment, GDP, accounting system, consumption, agriculture resource, etc. During this period, the CPC Central Committee held five central symposia on work related to population, resources and the environment, and the relevant legal system for resource management was further improved (Gu et al., 2011). Therefore, many scholars gradually took the idea of sustainable development as the guiding ideology of research in the field and carried out research on the legislative protection of natural resources. In 2003, with the introduction of the basic state policy of resource protection, Chinese scholars attached great importance to the environ mental effects in the stage of city development and resource utilization. Consequently, the research on energy crisis, energy consumption, environmental accounting and other aspects were gradually increasing. On the whole, at this stage of development, the research on natural resources and sustainable development in China had just begun. The research direction followed the national policies and focused mainly on meeting the needs of the country. The research content mainly focused on the macro-level of resource protection and utilization, environmental legislation and other aspects. For example, Niu (2000) started with the ancient sustainable development thought, and through the systematic analysis of the formation and practice of this theory in ancient times, this paper studied its application in contem porary times. In order to improve the application level of sustainable development thought in China's economy, society, legislation, ecology and so on, Li (2003) made a deep discussion on the relevant issues of China's sustainable development legislation.

Protection adjustment period (2006-2015): Compared with the previous period, this period shows a significant increase in the number of publications, more targeted research directions and more in-depth research levels. The hot keywords for this period are ecological construction, biodiversity, annual academic conference, ecological carrying capability, ecological footprint, fissure and suggestion, etc. In 2006, the request to establish a master's and doctor's discipline system in resource science and engineering was reintroduced (Feng, 2003). Since then, China's research system on natural resources has undergone a transformation. In 2010, with the support of the China Natural Resources Society, Beijing Normal University and the Graduate School of the Chinese Academy of Sciences together submitted to the academic degree Office of the State Council a proposal on the adjustment of the first level disciplines of natural resources science. In 2012, the Ministry of Education divided the major of “Resource Environment and Urban and Rural Planning Management” into two majors, including “Human Geography and Urban and Rural Planning” and “Natural Geography and Resource Environment” (Cheng et al., 2020). Under this background, the research of Chinese scholars in the field of natural resources and sustainable development became further deepened. Research on natural resource protection, environmental carrying capacity, strategy formulation and other aspects increased significantly, and related research methods such as evaluation system and ecological footprint were continuously expanded. For example, Du et al. (2006) analyzed China's ability to maintain a good environmental status with the help of environmental sustainability index, providing a direction for China's sustainable development. Xie et al. (2008) took natural resources as an important indicator for judging China's sustainable development ability, and evaluated China's sustainable development ability, which served as a valuable lead for the reasonable uses of natural resources and the further development of a sustainable development strategy in China.

Control and optimization phase (2016-2019): After 2016, China's research on natural resources and sustainable development has gradually matured. Under the guidance of General Secretary Xi Jinping's “two mountains theory”, many development strategies have achieved great results. Therefore, compared with the previous two stages, this stage shows a transition from research hot spots to resource abundance, quantitative evaluation, citation analysis, and extended consumption. Thus, it can be seen that in the current development stage, the main research directions of natural resources and sustainable development will focus on three aspects: resource reduction, conservation of natural resources and efficient utilization of technology. For example, against the background of resource constraints, Zhang (2019) established a macro model to realize the coordinated development of economic growth and carbon emission reduction, aiming at a series of problems in China, such as the shortage of natural resources, energy shortage, low energy utilization rate, and great pressure on carbon emission reduction, and put forward relevant suggestions. Du et al. (2019) established the conditional relaxation measure (SBM) model to measure the ecological efficiency of different cities or regions, and empirically analyzed the relationship between resource abundance and urban sustainable development, providing a direction for solving the problem of the low degree of urban sustainable development in China. Huang (2018) systematically combed the rising process of resource and environment carrying capacity assessment, summarized its existing problems, and provided effective suggestions for the future research directions of resources and environment carrying capacity, providing important support for regional sustainable development and serving the national strategy.

The emergence of environmental problems such as epidemic, locust plague and fire in 2020 has once again attracted the research focus of scholars due to the mutualism between human and nature. In the field of natural resources and sustainable development, Chinese scholars will continue to broaden their thinking for solving problems and exploring diversified solutions. In recent years, the state has issued a number of policy documents related to the protection and management of natural resources. From the establishment of the Ministry of Natural Resources in 2018, to the Fourth Plenary Session of the 19th Central Committee in 2019, and then to 2020, when the state proposed to supervise land and resources and formulate a land space planning system, the country tends to adhere to and improve the ecological civilization system in the field of natural resources, so as to promote the harmonious coexistence of man and nature health. The analysis results show that the research system of natural resources and sustainable development in China is relatively complete and the research focus is concentrated. As can be seen from the evolutionary path chart, due to different policy orientations in different periods, there are also differences in research emphases on management means and protection mechanisms. Therefore, the future research efforts of Chinese scholars on the improvement of management capacity and the construction of protection mechanisms should be guided by national policies, on the premise of sustainable development and utilization of resources, give countermeasures and suggestions for realizing the modernization of the natural resource governance system and governance capacity and promoting the sustainable development of cities.

As words related to the ecological environment, such as environmental protection and haze, once again become the hot words of the two sessions in 2020, China should take natural resources as the foundation and strengthen the protection of resource elements and the ability to protect resources. Therefore, future research on natural resources and sustainable development should focus on strengthening compensation mechanisms and improving the administration system. First of all, to improve the administration system in the field, relevant scholars of high quality should be developed, natural resources studies should focus on topics such as the reform of supply side keywords as the research point, to clear the responsibility and improve the protection and restoration system, continue to increase the protection consciousness of the main body of management, and to provide theoretical guidance for the sustainable development of natural resources. Secondly, in terms of strengthening the natural ecological compensation mechanism, we should focus on scientific planning, use control, compensation protection, shared development and other directions, and discuss how to establish and optimize the supervision system of stakeholders, so that the management subject can use the natural resources in a sustainable way.

Since 2016, with the rise of the big data boom, data access has become more convenient. Therefore, quantitative means have been widely applied in the field of natural resources and sustainable development, which has promoted the scientific development of research results. From the analysis results of keyword co-occurrence and the evolutionary path, quantitative analysis will be more widely applied in the research field. Therefore, a comprehensive application of various big data processing, analysis and mining technologies, combined with natural resources and sustainable development of the focus issues to be solved (Zhou and Li, 2016), the establishment of corresponding scientific evaluation systems in different research directions will become an important starting point for controlling the development direction of natural resources and sustainable development in China.

With quantitative analysis becoming the mainstream in the research field, the study of countermeasures for natural resources and sustainable development can be changed into optimization and decision problems. From the perspective of optimization, the establishment of a scientific evaluation system can provide targeted solutions to existing problems in the field. At present, high investment and high consumption in exchange for high growth is still the current development mode of China's construction industry. This uneconomic development mode has brought serious damage to China's ecological environment, and also deeply affected people's production and lives. However, the construction of the built environment impact assessment system can provide a clear direction for alleviating the contradiction between building development and environmental deterioration, which is extremely important for regulating the ecological environment and improving the quality of space. The extensive application of forecasting models, such as time series methods and sustainable forecasting systems, has clarified the primary tasks of natural resources and sustainable development at the present stage. Besides, it has forecasted the future direction of this field. For instance, relevant scholars can scientifically predict the frequency and location of natural disaster occurrences by means of quantification, so that people can respond quickly and effectively in the face of sudden disasters, and reduce the harm caused by emergencies as much as possible, and thus promote the sustainable development of the society.

Scientific and technological research is an important basis for the research on natural resources and sustainable development (Liu et al., 2013). In early 2018, the State Council released Some opinions on Comprehensively Strengthening basic scientific research, to comprehensively strengthen basic scientific research, and it placed an emphasis on the important role of basic scientific research on natural resources protection and utilization (Tao et al., 2019).

As can be seen from the evolutionary path chart of natural resources and sustainable development, scientific and technological research has received a growing amount of attention since 2016. Relevant research results are increasing, and relevant technological means are playing an increasingly important role in saving energy consumption, developing energy-saving resources, and reducing the consumption of natural resources in industry, agriculture, transportation and other fields. In the future, if we want to really achieve the goal of sustainable development of natural resources by means of science and technology, we need to start from two aspects. On the one hand, we need to strengthen the basic theoretical research on science and technology, and deeply explore the application of this technology in the sustainable development of natural resources, find the causes from the root, and provide a solid research foundation and accurate practice guidance for the wide application of related technologies. This requires Chinese scholars not only to continue to attach importance to this research, but also to improve the relevant theoretical research work. On the other hand, in this field, it is necessary to establish a systematic research framework with sustainable development as the principal component, and bring the sustainable development research of agriculture, forestry and industry into this unified framework, so as to continuously enrich the theoretical system of sustainable development and improve the application level of scientific and technological achievements.

It can be seen from the co-occurrence map and evolutionary path map of keywords that the relevant research on natural resources and sustainable development in China has made numerous achievements and become increasingly mature. However, due to its complex content and the many fields involved, the relevant research within the field still remains relatively scattered, and a perfect research system cannot be formed. In addition, there is a lack of cooperation between scholars, and there is a serious lack of corresponding academic exchanges and cooperation, which affects the depth and breadth of the research in this field.

Therefore, the future research content of natural resources and sustainable development should place an emphasis on the interactions and integration between different authors, different institutions and various disciplines, and then continuously promote the establishment of interdisciplinary research systems. First of all, we should attach great importance to the exchanges and cooperation between different institutions and scholars, break the existing regional barriers, cross disciplinary barriers, and actively make use of cross-disciplinary and cross-field research methods. Secondly, we should explore innovative research directions from multiple perspectives and fields, explore diversified and multilevel in-depth research content, and transform the focus from single research perspectives such as economics and management to muti-disciplinary integrated research, so as to establish a comprehensive and systematic scientific research system. The multi-disciplinary research perspective is constantly improved, so not only can it promote the development of natural resources protection and sustainable use theory, but it can also provide some new guidance for the application of natural resources in China.