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   20336篇
  免费   157篇
  国内免费   122篇
安全科学   410篇
废物处理   951篇
环保管理   2444篇
综合类   2544篇
基础理论   5697篇
环境理论   5篇
污染及防治   4764篇
评价与监测   1518篇
社会与环境   2206篇
灾害及防治   76篇
  2022年   157篇
  2021年   154篇
  2020年   102篇
  2019年   120篇
  2018年   737篇
  2017年   713篇
  2016年   768篇
  2015年   310篇
  2014年   435篇
  2013年   1232篇
  2012年   688篇
  2011年   1368篇
  2010年   928篇
  2009年   1019篇
  2008年   1285篇
  2007年   1523篇
  2006年   674篇
  2005年   648篇
  2004年   564篇
  2003年   665篇
  2002年   647篇
  2001年   739篇
  2000年   516篇
  1999年   277篇
  1998年   212篇
  1997年   199篇
  1996年   192篇
  1995年   238篇
  1994年   181篇
  1993年   152篇
  1992年   173篇
  1991年   168篇
  1990年   195篇
  1989年   178篇
  1988年   135篇
  1987年   123篇
  1986年   104篇
  1985年   133篇
  1984年   147篇
  1983年   120篇
  1982年   123篇
  1981年   106篇
  1980年   104篇
  1979年   110篇
  1977年   82篇
  1976年   73篇
  1975年   79篇
  1974年   77篇
  1973年   84篇
  1972年   75篇
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
31.
The distribution pattern of the gastropod Bradybaena fruticum has been studied in a forest-steppe landscape. Analysis of the frequencies of polymorphic biochemical and conchological characters has yielded preliminary results on the characteristics of the species population structure whose formation was determined by a set of natural and anthropogenic factors.Translated from Ekologiya, No. 1, 2005, pp. 39–47.Original Russian Text Copyright © 2005 by Snegin.  相似文献   
32.
33.
Aspects of the trophic attributes of the mudskipper,Periophthalmus barbarus occurring in the mangrove swamps of ImoRiver estuary, Nigeria, were investigated during a 12-month period(April, 1992-March, 1993). Feeding intensity increased with size;it was higher in the dry season (November-April) than in the wetseason (May-October); monthly changes in the indices of feedingintensity were significantly correlated. Major food objectscomprised detritus and benthic algae; crustaceans, insects,macrophyte matter and sand grains were minor food objects whilefish, molluscs, Chilopoda, nematodes and fungi were unconsciouslydevoured objects. Diet varied seasonally; algae and sesarmid crabswere generally more in the dry season than during the rains whereasFPOM and fish increased in the wet over dry season. The mudskipperdisplay a high degree of euryphagy and can be considered as ageneralist and an omnivore. The lower trophic status of P. barbarusqualifies it as a good aquaculture candidate. Food richness washigher in big-sized class (BSC) than small-sized class (SSC).Size-based and seasonal variations were not apparent in foodrichness. Diet breadth was higher in the BSC than the SSC; therewas dry season increase in diet breadth.  相似文献   
34.
35.
The effect of industrial air pollution on natural small mammal populations has been studied in the northern taiga subzone of the boreal forest zone. The results of long-term monitoring have been used to demonstrate the possibility of predicting changes in the main population and community characteristics of the animal species studied as dependent on the degree of anthropogenic impact.  相似文献   
36.
37.
Four introduced and one aboriginal species of the genus Pinus L. have been studied in the middle taiga subzone of southern Karelia. Significant interspecific differences in the dates of onset, cessation, and peak of the growth of shoots and needles have been revealed. It has been shown that their annual increment depends on the rate of growth, rather than on its duration. The dynamics of shoot and needle growth in introduced and aboriginal species, though largely similar, differ in some respects. These differences reflect species-specific responses to hydrothermal conditions in a certain growing season.  相似文献   
38.
39.
40.
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   
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