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   24311篇
  免费   357篇
  国内免费   616篇
安全科学   755篇
废物处理   1065篇
环保管理   3372篇
综合类   4152篇
基础理论   6179篇
环境理论   7篇
污染及防治   6293篇
评价与监测   1524篇
社会与环境   1771篇
灾害及防治   166篇
  2023年   145篇
  2022年   289篇
  2021年   262篇
  2020年   244篇
  2019年   239篇
  2018年   402篇
  2017年   405篇
  2016年   588篇
  2015年   468篇
  2014年   661篇
  2013年   2019篇
  2012年   846篇
  2011年   1208篇
  2010年   942篇
  2009年   1030篇
  2008年   1148篇
  2007年   1207篇
  2006年   980篇
  2005年   840篇
  2004年   860篇
  2003年   805篇
  2002年   759篇
  2001年   926篇
  2000年   697篇
  1999年   408篇
  1998年   279篇
  1997年   301篇
  1996年   309篇
  1995年   374篇
  1994年   290篇
  1993年   273篇
  1992年   252篇
  1991年   263篇
  1990年   249篇
  1989年   242篇
  1988年   210篇
  1987年   199篇
  1986年   199篇
  1985年   201篇
  1984年   241篇
  1983年   197篇
  1982年   221篇
  1981年   216篇
  1980年   171篇
  1979年   192篇
  1978年   122篇
  1977年   127篇
  1974年   125篇
  1973年   124篇
  1972年   138篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling.  相似文献   
222.
The nature and origin of two de novo small marker chromosomes found at prenatal diagnosis were determined by fluorescence in situ hybridization using chromosome centromere-specific probes and chromosome-specific plasmid libraries. One marker was found in a mosaic state and was shown to be an i(18p). The second marker was characterized as an inv dup(22). We conclude that molecular cytogenetic analysis contributes to the identification of marker chromosomes and therefore facilitates genetic counselling and decision-making for the parents.  相似文献   
223.
224.
225.
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur.  相似文献   
226.
 This study investigated the influence of cat urine odour in suppressing development and fertility in Campbell's hamster males. Exposure to this odour from postnatal day 11 until day 45 (sexual maturation) resulted in reduced sex organ weights, reduced testosterone levels and in an increase in abnormalities of the synaptonemal complex in both sex chromosomes and autosomes. Subsequent breeding experiments revealed a significant decrease in litter size. All these data indicate a severe effect of predator odour on the breeding success of potential prey species. It is assumed that these effects are caused by the sulphurous compounds in the urine; however, the underlying mechanisms are not yet known. Received: 31 January 2000 / Accepted in revised form: 6 June 2000  相似文献   
227.
The abundance patterns of ant communities were monitored with pitfall traps during 14 weeks in four northern California, dry farmed, apple orchards: an abandoned orchard undisturbed for 25 years, two ‘organically’ managed orchards, one with a cover crop of bell beans (Vicia faba) and grasses and the other kept clean of cover by discing, and a ‘commercial’ clean cultivated orchard sprayed with organophosphate insecticides. Six species of ants coexisted in the abandoned orchard, whereas only two species were found in the managed orchards. In both the organic and sprayed, clean cultivated systems, ants were more abundant in the orchard edges than in the vegetation-free centers. This trend was not apparent in the abandoned or organic cover orchards, where plant diversity in the center was similar to that of the edges. Ant predation on potato tuberworm larvae, Phthorimaea operculella, artificially placed on the orchard floor, declined with the intensity of management and vegetational simplication. A higher incidence of larval removal occurred in the edges than in the centers of the clean cultivated orchards. No noticeable populations of ants were detected on the trees in any of the orchards. Increased vegetational diversity and lack of disturbance appeared to affect ant locomotory activity and foraging efficiency by creating preferred sheltering and feeding sites.  相似文献   
228.
229.
230.
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