首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1998篇
  免费   282篇
  国内免费   280篇
测绘学   89篇
大气科学   271篇
地球物理   321篇
地质学   698篇
海洋学   365篇
天文学   3篇
综合类   126篇
自然地理   687篇
  2024年   3篇
  2023年   26篇
  2022年   61篇
  2021年   91篇
  2020年   70篇
  2019年   84篇
  2018年   46篇
  2017年   97篇
  2016年   93篇
  2015年   78篇
  2014年   120篇
  2013年   131篇
  2012年   78篇
  2011年   109篇
  2010年   88篇
  2009年   84篇
  2008年   136篇
  2007年   119篇
  2006年   98篇
  2005年   79篇
  2004年   81篇
  2003年   107篇
  2002年   86篇
  2001年   103篇
  2000年   102篇
  1999年   86篇
  1998年   56篇
  1997年   55篇
  1996年   52篇
  1995年   38篇
  1994年   32篇
  1993年   19篇
  1992年   7篇
  1991年   14篇
  1990年   9篇
  1989年   7篇
  1988年   1篇
  1987年   3篇
  1986年   4篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1978年   1篇
排序方式: 共有2560条查询结果,搜索用时 15 毫秒
91.
This paper evaluates the international agreements in place for the protection of the environment and the regulation of human activities taking place in world's oceans and seas. 500 multilateral agreements were reviewed against a framework of reference, grounded on the theoretical approaches of Adaptive Management and Transition Management. According to this framework, oceans complex systems management should: (1) consider the global oceans as a Social-Ecological System (SES); (2) aim to achieve or maintain their ecological resilience; and (3) implement iterative, learning-based management strategies, supported by science-based advice to policy and management. The results show that the present international legal framework for the global oceans does not require countries to adopt an adaptive, complex systems approach for global oceans ecological resilience. Instead, this study supports the perspective of a double fragmentation among international agreements. First, global agreements focus on issue-based objectives for determined human activities, ecological components or anthropogenic pressures. Second, regional agreements have a wider scope, but also a varying level of inclusion of ecological resilience considerations. There is the need to foster the inclusion of such an approach into existing and future international agreements and their implementation, including through soft-law, project-based initiatives at global and regional scales.  相似文献   
92.
针对广东孔江国家湿地公园出现的库周村民生产生活污染、农业面源污染、植被群落单一等问题,开展湿地生物多样性保护与生态恢复工程,为湿地公园后期建设规划提供依据。  相似文献   
93.
广东海丰湿地是中国华南亚热带滨海湿地的典型代表,也是南中国海生态系统的重要组成部分,为多种珍稀、濒危鸟类和候鸟提供重要栖息地和迁徙中转站,具有重要的保护价值。在野外湿地资源调查的基础上,阐述了海丰自然保护区湿地类型与特点、湿地动植物资源、湿地利用现状等生态特征,分析了湿地面临的主要威胁,提出湿地生态系统保护与管理的主要对策和措施。  相似文献   
94.
根据国内碳汇发展现状,分析了张掖黑河湿地发展碳汇的优势与劣势,提出了发展湿地碳汇的对策。  相似文献   
95.
引入湿地旅游资源"资产化管理"和"生态承载能力"两个概念,通过资源资产化管理厘清湿地生态资源所有权和经营权关系,着眼于源头市场化监管,责任约束;通过生态承载能力监控,将湿地生态旅游开发限制在生态良好可控范围之内,从而形成以生态向好带动旅游开发,以旅游开发促进生态投入的良性均衡形态。  相似文献   
96.
Family farms have long generated income from agricultural tourism including U‐picks, wagon rides, corn mazes and petting zoos, but contemporary agricultural tourism reflects much greater sophistication in terms of product variety, services, activities, and marketing. In Michigan, farm operators have moved beyond classic products and activities and the traditional consumer base. New sources of revenue derive from classes on beer, cider, mead and wine making, yarn spinning, perfume/soap‐making, farm markets, fishing, educational classes, school tours and hospitality including weddings and on‐farm restaurants. This case study of Michigan agricultural tourism reports results from a systematic survey of 154 agritourism operations conducted throughout the state during summer and fall of 2013 with a focus on the economic benefits of the fast‐changing sector. This study summarizes tax revenues, sales and employment trends for the farm operations participating in the survey but also quantitatively assesses the contribution of agricultural tourism to Michigan's economy through an extrapolation of the sample to estimate state‐wide totals. Results from OLS multivariate regression analysis intended to identify relationships between employment, advertising and scale to gross sales per day are also reported. These analyses show the importance of agricultural tourism to rural and peri‐urban places in Michigan and throughout the nation, while raising concerns about a growing division between large and small operators and what this growing gap may mean for the future of the sector.  相似文献   
97.
《China Geology》2021,4(3):421-432
The Badain Jaran Desert is the third largest desert in China, covering an area of 50000 km2. It lies in Northwest China, where the arid and rainless natural environment has a great impact on the climate, environment, and human living conditions. Based on the results of 1∶250000 regional hydrogeological surveys and previous researches, this study systematically investigates the circulation characteristics and resource properties of the groundwater as well as the evolution of the climate and ecological environment since the Quaternary in the Badain Jaran Desert by means of geophysical exploration, hydrogeological drilling, hydrogeochemistry, and isotopic tracing. The results are as follows. (1) The groundwater in the Badain Jaran Desert is mainly recharged through the infiltration of local precipitation and has poor renewability. The groundwater recharge in the desert was calculated to be 1.8684×108 m3/a using the water balance method. (2) The Badain Jaran Desert has experienced four humid stages since the Quaternary, namely MIS 13-15, MIS 5, MIS 3, and the Early–Middle Holocene, but the climate in the desert has shown a trend towards aridity overall. The average annual temperature in the Badain Jaran Desert has significantly increased in the past 50 years. In detail, it has increased by about 2.5°C, with a higher rate in the south than in the north. Meanwhile, the precipitation amount has shown high spatial variability and the climate has shown a warming-drying trend in the past 50 years. (3) The lakes in the hinterland of the Badain Jaran Desert continuously shrank during 1973–2015. However, the vegetation communities maintained a highly natural distribution during 2000–2016, with the vegetation cover has increased overall. Accordingly, the Badain Jaran Desert did not show any notable expansion in that period. This study deepens the understanding of groundwater circulation and the climate and ecological evolution in the Badain Jaran Desert. It will provide a scientific basis for the rational exploitation of the groundwater resources and the ecological protection and restoration in the Badain Jaran Desert.© 2021 China Geology Editorial Office.  相似文献   
98.
There is an increasing need for transformational changes in the global food system to deliver healthy nutritional outcomes for a growing population while simultaneously ensuring environmental sustainability. However, such changes are subject to political and public constraints that usually allow only gradual, incremental changes to occur. Drawing inspiration from the British cycling team’s concept of marginal gains, we show how transformation might be reconciled with incremental changes. We demonstrate that a set of marginal food system changes acting to increase production efficiency, to reduce losses or to adjust diets could collectively reduce the agricultural land required globally for food production by 21%, or over a third given higher adoption rates. The results show that while all categories of action are important, changes in consumer choices in Europe, North America and Oceania and in the supply-chain in Africa and West and Central Asia have the greatest potential to reduce the land footprint of the food system.  相似文献   
99.
Despite significant technological advances in emerging economies, the further development of clean energy technologies in developing countries remains crucial to reducing the greenhouse gas emissions associated with economic development. In this paper we address two significant gaps in the growing body of literature that has assessed the role of the Clean Development Mechanism in promoting the transfer of clean technologies to developing countries. First, we present a qualitative analysis of the governance of the Clean Development Mechanism in India. This provides a basis for understanding the extent to which and the ways in which governance may impact upon the likelihood that projects promote technology transfer. Second, we provide a novel quantification of the level and nature of technology transfer that has occurred in Indian Clean Development Mechanism projects, based on insights from literature on technological capability building. We find that the Clean Development Mechanism in India has produced a negligible number of projects that promote technology transfer if technology transfer is understood as a process of learning about technology. Together these qualitative and quantitative analyses show how politics and governance have contributed to the current form of the Clean Development Mechanism market in India, in which processes of building indigenous technological capabilities have been neglected.  相似文献   
100.
最近十年来中国地理科学的进展   总被引:10,自引:0,他引:10  
最近十年来中国地理科学的最重要进展有:自然地理学与人文地理学的平衡发展,人口、资源、环境的研究,遥感的应用与地理信息系统的建立,自然地理定位观测,青藏高原隆起对自然环境的影响,城市与城市规划,中国历史地理研究等。最近,并已开始研究气候变化与海平面上升对中国的影响,使我国地理科学研究紧紧跟上世界发展的步伐。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号