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   34595篇
  免费   231篇
  国内免费   225篇
安全科学   637篇
废物处理   2011篇
环保管理   3960篇
综合类   4296篇
基础理论   9249篇
环境理论   13篇
污染及防治   9065篇
评价与监测   3054篇
社会与环境   2627篇
灾害及防治   139篇
  2023年   158篇
  2022年   377篇
  2021年   406篇
  2020年   223篇
  2019年   259篇
  2018年   1784篇
  2017年   1706篇
  2016年   1825篇
  2015年   631篇
  2014年   896篇
  2013年   2299篇
  2012年   1448篇
  2011年   2422篇
  2010年   1681篇
  2009年   1549篇
  2008年   1988篇
  2007年   2396篇
  2006年   1146篇
  2005年   939篇
  2004年   925篇
  2003年   915篇
  2002年   894篇
  2001年   1021篇
  2000年   711篇
  1999年   446篇
  1998年   310篇
  1997年   272篇
  1996年   302篇
  1995年   313篇
  1994年   279篇
  1993年   249篇
  1992年   258篇
  1991年   222篇
  1990年   227篇
  1989年   231篇
  1988年   203篇
  1987年   165篇
  1986年   130篇
  1985年   146篇
  1984年   179篇
  1983年   165篇
  1982年   199篇
  1981年   134篇
  1980年   122篇
  1979年   157篇
  1978年   120篇
  1977年   109篇
  1976年   100篇
  1975年   87篇
  1974年   89篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
12.
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   
13.
14.
The purpose of the research is to identify the critical challenges that are impeding the adoption of e-mobility in India. It also aims to give a roadmap how to address these challenges while taking into considerations concerns of all the relevant stakeholders. Based on an in-depth literature review, an exploratory research design is employed to delve deep into various aspects of e-mobility. This is followed by a three-phase Delphi technique to identify and rate the e-mobility challenges in the Indian context. The study successfully identifies four different categories of challenges and proposes integrative framework for e-mobility. Further, the research goes on to lay out the future roadmap for mass adoption of electric vehicles (EVs) in India. The research is novel in terms of presenting a holistic viewpoint on e-mobility in India. Its originality lies in identifying the major inhibitors obstructing EVs adoption in India and then suggesting the roadmap how to overcome these impediments for mass adoption of e-mobility.  相似文献   
15.
16.
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   
17.
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   
18.
19.
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   
20.
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