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   39966篇
  免费   437篇
  国内免费   340篇
安全科学   1296篇
废物处理   1704篇
环保管理   5456篇
综合类   7185篇
基础理论   10131篇
环境理论   14篇
污染及防治   9873篇
评价与监测   2543篇
社会与环境   2307篇
灾害及防治   234篇
  2022年   307篇
  2021年   369篇
  2019年   304篇
  2018年   534篇
  2017年   549篇
  2016年   855篇
  2015年   665篇
  2014年   995篇
  2013年   3223篇
  2012年   1236篇
  2011年   1677篇
  2010年   1337篇
  2009年   1455篇
  2008年   1739篇
  2007年   1694篇
  2006年   1531篇
  2005年   1320篇
  2004年   1297篇
  2003年   1276篇
  2002年   1178篇
  2001年   1430篇
  2000年   1007篇
  1999年   653篇
  1998年   475篇
  1997年   489篇
  1996年   538篇
  1995年   593篇
  1994年   543篇
  1993年   485篇
  1992年   510篇
  1991年   497篇
  1990年   482篇
  1989年   477篇
  1988年   424篇
  1987年   363篇
  1986年   360篇
  1985年   375篇
  1984年   384篇
  1983年   373篇
  1982年   394篇
  1981年   351篇
  1980年   296篇
  1979年   301篇
  1978年   278篇
  1977年   239篇
  1976年   234篇
  1975年   231篇
  1974年   247篇
  1973年   271篇
  1972年   244篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Ligustrum lucidum Ait. f. tricolor (Rehd.) Rehd. in relation to atmospheric pollutants in Córdoba city, Argentina. The study area receives regional pollutants and was categorized taking into account traffic level, industrial density, type of industry, location of the sample point in relation to the street corner, treeless condition, and topographic level. Dried weight/fresh weight ratio (DW/FW) and specific leaf area (SLA) were calculated, and concentrations of chlorophylls, carotenoids, total sulfur, soluble proteins, malondialdehyde (MDA), and hydroperoxy conjugated dienes (HPCD) were determined in leaf samples. Sulfur content correlates positively with traffic density and SLA correlates negatively with some combinations of the categorical variables; MDA correlates positively with topographic level and total protein concentration correlates negatively with treeless condition. On the basis of our results, traffic, location of trees, type of industry, situation of a tree with respect to others, and topographic level are the environmental variables to bear in mind when selecting analogous sampling points in a passive monitoring program. An approximation to predict tree injury may be obtained by measuring DW/FW ratio, proteins, pigments, HPCD, and MDA as they are responsible for the major variability of data.  相似文献   
12.
13.
14.
15.
16.
17.
18.
19.
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   
20.
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