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   42722篇
  免费   451篇
  国内免费   539篇
安全科学   1222篇
废物处理   1900篇
环保管理   5225篇
综合类   7912篇
基础理论   11142篇
环境理论   23篇
污染及防治   10774篇
评价与监测   2802篇
社会与环境   2497篇
灾害及防治   215篇
  2022年   392篇
  2021年   390篇
  2020年   280篇
  2019年   357篇
  2018年   647篇
  2017年   637篇
  2016年   1016篇
  2015年   746篇
  2014年   1109篇
  2013年   3226篇
  2012年   1417篇
  2011年   1874篇
  2010年   1487篇
  2009年   1573篇
  2008年   1840篇
  2007年   1907篇
  2006年   1683篇
  2005年   1618篇
  2004年   1633篇
  2003年   1648篇
  2002年   1286篇
  2001年   1654篇
  2000年   1113篇
  1999年   703篇
  1998年   483篇
  1997年   512篇
  1996年   524篇
  1995年   588篇
  1994年   598篇
  1993年   508篇
  1992年   507篇
  1991年   506篇
  1990年   529篇
  1989年   459篇
  1988年   419篇
  1987年   388篇
  1986年   347篇
  1985年   361篇
  1984年   389篇
  1983年   378篇
  1982年   386篇
  1981年   330篇
  1980年   280篇
  1979年   297篇
  1978年   281篇
  1977年   213篇
  1975年   224篇
  1974年   217篇
  1972年   202篇
  1971年   214篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
Following the renewed effort at achieving a new green revolution for Africa, emphasis has been placed on modernizing smallholder agriculture through the deployment of improved inputs especially mechanized technologies. In Ghana, the government has in the last decade emphasized the provision of subsidized mechanized ploughing services to farmers alongside a rapidly growing private sector tractor service market. While mechanized technology adoption rates have increased rapidly, the deployment of these technologies has been without critical analysis of the impacts on production patterns and local agrarian systems. This paper examines the distributional impacts of agriculture mechanization on cropping patterns and farm sizes of smallholder farmers in northern Ghana using Geographic Information Systems (GIS) techniques, and semi-structured interviews with smallholder farmers (n=60). Specifically, comparative analysis of the field sizes and cropping patterns of participant farmers prior to and after the adoption of mechanized technologies was conducted. In-depth interviews were used to contextualize the experiences of smallholder farmers toward understanding how mechanization may be impacting traditional agriculture. Our findings reveal a mechanization paradox in which farm sizes are expanding, while cropping patterns are shifting away from traditional staple crops (pearl millet and sorghum bicolor) to market-oriented crops (maize, rice and groundnuts). This transition we argue, has adverse implications on the cultural dimension of food security, the organization of social life, and climate change adaptation. We recommend a retooling of the current agricultural policy focus to ensure context sensitivity for a more robust battle against food insecurity.  相似文献   
12.
Environmental Science and Pollution Research - Zinc is an essential nutritional trace mineral required for growth and health. The aim of the current work is to compare the effects of bulk zinc...  相似文献   
13.
14.
15.
16.
17.
18.
Biomethane production through biogas upgrading is a promising renewable energy for some industries which could be part of the equilibrium needed with fossil fuels consumption to achieve a sustainable society. This paper presents a comprehensive list of biogas upgrading technologies focused on carbon dioxide removal as well as recent advances reported by researcher with wide expertise in this topic. Additionally, an extensive costs–performance comparison among the technologies studied is discussed. Among the different alternatives, chemical scrubbing stood out to achieve high biomethane purities while cryogenic technologies proved to be effective against methane losses. Regarding the different costs, water scrubbing and membrane separation seem to be the most affordable techniques.  相似文献   
19.
Journal of Material Cycles and Waste Management - The present research work focused on fabricating Biodegradable Plate (BD plate) composed of rice husk ash, bagasse and corn starch which is...  相似文献   
20.
Quantitative methods have been applied to the study of floristic structure and diversity in Samarskaya Luka. The results show that Samarskaya Luka is a floristically heterogeneous area in which six elementary floras can be distinguished. This area has been assessed as a floristically autonomous formation, and its floristic representativeness was estimated.  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