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   9265篇
  免费   66篇
  国内免费   68篇
安全科学   215篇
废物处理   419篇
环保管理   823篇
综合类   1459篇
基础理论   1915篇
环境理论   5篇
污染及防治   2394篇
评价与监测   782篇
社会与环境   1342篇
灾害及防治   45篇
  2023年   47篇
  2022年   153篇
  2021年   186篇
  2020年   90篇
  2019年   98篇
  2018年   219篇
  2017年   239篇
  2016年   290篇
  2015年   179篇
  2014年   333篇
  2013年   710篇
  2012年   369篇
  2011年   450篇
  2010年   346篇
  2009年   373篇
  2008年   438篇
  2007年   469篇
  2006年   357篇
  2005年   382篇
  2004年   401篇
  2003年   374篇
  2002年   305篇
  2001年   320篇
  2000年   229篇
  1999年   122篇
  1998年   84篇
  1997年   103篇
  1996年   76篇
  1995年   104篇
  1994年   82篇
  1993年   64篇
  1992年   69篇
  1991年   74篇
  1990年   78篇
  1989年   65篇
  1988年   47篇
  1987年   46篇
  1986年   54篇
  1985年   56篇
  1984年   60篇
  1983年   47篇
  1982年   51篇
  1981年   43篇
  1980年   45篇
  1979年   51篇
  1975年   33篇
  1973年   33篇
  1972年   40篇
  1971年   31篇
  1969年   33篇
排序方式: 共有9399条查询结果,搜索用时 15 毫秒
11.
Cornus stolonifera, Salix petiolaris, and Spiraea alba clones already located within the corridor of an electrical power line. To establish the efficiency of treatments, we examined the statistical differences of growth traits between species and treatments. An analysis of the effects of layering shows, after the first growth season, differences for all growth traits in only one species, Spiraea alba. After the second growth season, we observed the development of new aerial stems. Layering favors horizontal expansion of shrubs over height development. The third year after treatment, the effect of layering is reduced except for Cornus stolonifera, which continuously increases, as shown by the significant progression of the clone issued from the layer even five years after treatments. With the cutting back technique, we expected a distinct vertical growth of the shrubs at the expense of increasing the crown diameter. This technique would be best associated with the rejuvenation of clones, followed by a layering of new shoots to allow a horizontal expansion of the shrubs. Therefore, the formation of a dense shrub community by layering should be considered a valuable approach for the biological control of undesirable trees in powerline rights-of-way.  相似文献   
12.
The most widely used method for fetocide in late termination of pregnancy for fetal abnormalities (TOPFA) consists of injecting of potassium chloride (KCl) into the fetal heart and is likely to be painful after 22 weeks of gestation. We studied ten consecutive women undergoing TOPFA between 22 and 38 weeks. This technique for fetocide consisted of a single umbilical vein puncture under ultrasound guidance with injections of sufentanil 5 µg followed by KCl 2 g. No electrocardiographic modifications could be observed and maternal plasma potassium levels did not show any significant variation throughout the procedure. Fetal umbilical phlebotomy for fetal analgesia followed by fetocide therefore appears to be a safe procedure for the mother and allows the fetus to die without pain when late termination of pregnancy (TOP) is indicated. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
13.
The abundance and trophic structure of zooplankton along the longitudinal profile of two typical rivers in the Yaroslavl sector of the Volga region are determined by anthropogenic and zoogenic factors. The distribution of zooplankton under the influence of these factors is described by the concept of patch dynamics. The abundance of zooplankton reaches the highest values in the ameliorated upper reaches of rivers and in beaver ponds.  相似文献   
14.
Male phenotype associated with a 45,X karyotype is an infrequent finding. We present a case diagnosed prenatally on amniocentesis performed for maternal age. The male phenotype was associated with a translocation of a distal part of Yp including the pseudoautosomal SHOX gene and SRY gene on the short arm of a chromosome 21. By DNA analysis we could show that the X chromosome was of maternal origin and that the breakpoint was in interval 3 of the Y chromosome. Mechanisms and genetic counselling are discussed based on a review of published cases of 45,X and XX males. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
15.
16.
17.
18.
19.
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