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   32593篇
  免费   383篇
  国内免费   273篇
安全科学   1171篇
废物处理   1555篇
环保管理   4723篇
综合类   4731篇
基础理论   8441篇
环境理论   15篇
污染及防治   7947篇
评价与监测   2305篇
社会与环境   2155篇
灾害及防治   206篇
  2023年   155篇
  2022年   281篇
  2021年   341篇
  2020年   213篇
  2019年   274篇
  2018年   472篇
  2017年   514篇
  2016年   790篇
  2015年   587篇
  2014年   916篇
  2013年   2810篇
  2012年   1125篇
  2011年   1483篇
  2010年   1202篇
  2009年   1247篇
  2008年   1529篇
  2007年   1479篇
  2006年   1315篇
  2005年   1164篇
  2004年   1129篇
  2003年   1086篇
  2002年   1015篇
  2001年   1142篇
  2000年   829篇
  1999年   527篇
  1998年   412篇
  1997年   420篇
  1996年   449篇
  1995年   509篇
  1994年   446篇
  1993年   388篇
  1992年   415篇
  1991年   392篇
  1990年   355篇
  1989年   347篇
  1988年   331篇
  1987年   271篇
  1986年   277篇
  1985年   272篇
  1984年   290篇
  1983年   288篇
  1982年   308篇
  1981年   261篇
  1980年   189篇
  1979年   207篇
  1978年   184篇
  1977年   157篇
  1975年   146篇
  1973年   170篇
  1972年   151篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
46.
This work, carried out within the framework of the PRISMA II project, aims at evaluating the effects of the Po River flow on primary productivity, measured by C with in situ sample incubations. A total of four cruises was carried out in late winter and early summer (1996-1998) along transects from the coast offshore. In both seasons, the highest primary productivity was found in the most oligohaline stations. The effects of the Po River inputs were therefore clearly evident in the westernmost area, both in high productivity values and in the shape of productivity profiles. In late winter, extensive blooms of Skeletonema costatum and Pseudo-nitzschia delicatissima resulted in productivity values that were sometimes higher than in early summer. In early summer 1996, greatly reduced river flow clearly influenced productivity which was much lower than in 1997.  相似文献   
47.
48.
49.
Three monoclonal antibodies (MAbs) against trophoblast (GB17, GB21, and GB25) and flow cytometry were used to sort trophoblast-like cells (TLCs) from peripheral blood of pregnant women. Sorted TLCs were processed for electron microscopy and fetal DNA amplification of the Y-specific sequences from mothers carrying male fetuses. At the ultra-structural level, most of the nucleated cells had the morphology of leucocytes, suggesting maternal contaminants, and we did not find the characteristic features of the free inter-villous trophoblast cells. Nevertheless, polymerase chain reaction (PCR) analysis showed an amplification of Y-specific sequences in two out of three samples of sorted TLCs. These results suggest that besides the maternal leucocytes, sufficient trophoblast nucleated fetal cells can be obtained using cell enrichment by sorting. This sensitive method holds promise for non-invasive prenatal diagnosis of fetal sex and if sufficient Y(positive) nuclei are found, for the diagnosis of selected numerical chromosome abnormalities.  相似文献   
50.
Sustainable development of the earth's limited water and land resources is of paramount importance because of rising world population and existing conflicting demands for these resources. Enormous capital investment has been made in developing these resources, but now there is irrefutable evidence that such developments have led to major resource degradation. This includes problems of salinisation and damages to ecosystems. The countries predominantly affected by human induced salinisation are located in arid and semi-arid regions of the world and include Australia, China, Egypt, India, Pakistan, USSR, and USA. This paper describes the processes of salinisation, its impacts and the use of quantitative methods in salinity investigation and management. Australia is used as a case study of typical salinity problems and as a demonstration of the fruitful application of quantitative methods. The paper concludes that quantitative methods such as surface water and groundwater models are powerful design, management and predictive tools in salinity investigation. However, application of some models, such as those for unsaturated flow and transport and groundwater solute transport, are not widespread due to uncertainties in describing the complexity of the processes and the lack of hydrodispersive data.  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