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   44946篇
  免费   650篇
  国内免费   1429篇
安全科学   1589篇
废物处理   2077篇
环保管理   5895篇
综合类   8250篇
基础理论   11518篇
环境理论   26篇
污染及防治   11952篇
评价与监测   2810篇
社会与环境   2515篇
灾害及防治   393篇
  2023年   227篇
  2022年   528篇
  2021年   534篇
  2020年   440篇
  2019年   444篇
  2018年   745篇
  2017年   770篇
  2016年   1135篇
  2015年   900篇
  2014年   1376篇
  2013年   3666篇
  2012年   1711篇
  2011年   2266篇
  2010年   1811篇
  2009年   1883篇
  2008年   2166篇
  2007年   2187篇
  2006年   1901篇
  2005年   1574篇
  2004年   1465篇
  2003年   1527篇
  2002年   1376篇
  2001年   1674篇
  2000年   1247篇
  1999年   801篇
  1998年   548篇
  1997年   577篇
  1996年   552篇
  1995年   633篇
  1994年   607篇
  1993年   525篇
  1992年   517篇
  1991年   500篇
  1990年   529篇
  1989年   476篇
  1988年   408篇
  1987年   385篇
  1986年   348篇
  1985年   358篇
  1984年   418篇
  1983年   372篇
  1982年   376篇
  1981年   342篇
  1980年   276篇
  1979年   306篇
  1978年   246篇
  1977年   203篇
  1975年   207篇
  1974年   196篇
  1972年   211篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
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   
18.
Abstract:  Introduction of artificial light into wildlife habitat represents a rapidly expanding form of human encroachment, particularly in coastal systems. Light pollution alters the behavior of sea turtles during nesting; therefore, long-wavelength lights—low-pressure sodium vapor and bug lights—that minimize impacts on turtles are required for beach lighting in Florida (U.S.A.). We investigated the effects of these two kinds of lights on the foraging behavior of Santa Rosa beach mice (  Peromyscus polionotus leucocephalus ). We compared patch use and giving-up densities of mice for experimental food patches established along a gradient of artificial light in the field. Mice exploited fewer food patches near both types of artificial light than in areas with little light and harvested fewer seeds within patches near bug lights. Our results show that artificial light affects the behavior of terrestrial species in coastal areas and that light pollution deserves greater consideration in conservation planning.  相似文献   
19.
Introduced and cryptogenic species in Port Phillip Bay, Victoria, Australia   总被引:4,自引:0,他引:4  
Port Phillip Bay (PPB) is a large (1,930 km2), temperate embayment in southern Victoria, Australia. Extensive bay-wide surveys of PPB have occurred since 1840. In 1995/1996 the Commonwealth Scientific and Industrial Research Organization (CSIRO) Centre for Research on Introduced Marine Pests (CRIMP) undertook an intensive evaluation of the region with the aims of developing a comprehensive species list of native and introduced biota and contrasting previous bay-wide assessments with a current field survey in order to detect new incursions and discern alterations to native communities. Two methods were used to meet these aims: a re-evaluation of regional museum collections and published research in PPB to identify and determine the timing of introductions; and field surveys for benthic (infauna, epifauna and encrusting) organisms between September 1995 to March 1996. One hundred and sixty introduced (99) and cryptogenic (61) species were identified representing over 13% of the recorded species of PPB. As expected, the majority of these are concentrated around the shipping ports of Geelong and Melbourne. Invasions within PPB appear to be increasing, possibly due to an increase in modern shipping traffic and an increase in aquaculture (historically associated with incidental introductions); however the records of extensive biological surveys suggest that this may, in part, be an artefact of sampling effort. In contrast to Northern Hemisphere studies, PPB (and Southern Hemisphere introductions in general) have significantly different suites of successfully invading taxa. PPB is presented as one of the most invaded marine ecosystems in the Southern Hemisphere.Communicated by M.S. Johnson, Crawley  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