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   99040篇
  免费   1231篇
  国内免费   1135篇
安全科学   3902篇
废物处理   3647篇
环保管理   15049篇
综合类   21514篇
基础理论   27648篇
环境理论   75篇
污染及防治   18854篇
评价与监测   5901篇
社会与环境   4167篇
灾害及防治   649篇
  2022年   828篇
  2021年   815篇
  2020年   666篇
  2019年   879篇
  2018年   1250篇
  2017年   1306篇
  2016年   2267篇
  2015年   1869篇
  2014年   2601篇
  2013年   9290篇
  2012年   2554篇
  2011年   3132篇
  2010年   3425篇
  2009年   3574篇
  2008年   2757篇
  2007年   2670篇
  2006年   2860篇
  2005年   2715篇
  2004年   2996篇
  2003年   2866篇
  2002年   2443篇
  2001年   2909篇
  2000年   2327篇
  1999年   1645篇
  1998年   1417篇
  1997年   1420篇
  1996年   1549篇
  1995年   1637篇
  1994年   1532篇
  1993年   1379篇
  1992年   1376篇
  1991年   1349篇
  1990年   1296篇
  1989年   1277篇
  1988年   1113篇
  1987年   1030篇
  1986年   1010篇
  1985年   1095篇
  1984年   1190篇
  1983年   1194篇
  1982年   1189篇
  1981年   1121篇
  1980年   958篇
  1979年   961篇
  1978年   844篇
  1977年   739篇
  1976年   675篇
  1974年   655篇
  1973年   688篇
  1972年   698篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
We present a case of ultrasonographic prenatal diagnosis at 24 weeks of femur—fibula—ulna (FFU) complex. To our knowledge, this is the first report of an early prenatal diagnosis of FFU.  相似文献   
102.
103.
104.
105.
Benthic organisms can significantly alter the physical properties of marine sediments, but it has hitherto been difficult to assess and quantify the effects of bioturbation. In situ geophysical techniques offer new methods for measuring these effects: measurement of acoustic shear-wave velocity and electrical resistivity allows nondestructive assessment of the properties of the grain framework and pore-fluid matrix, respectively, of the seabed sediment. The influence of burrowing invertebrates on the structural properties of sandy sediments at intertidal locations on the coast of Wales (UK) was investigated during the periol 1986–1987 using these techniques. Three species (Arenicola marina, Corophium arenarium and Lanice conchilega) were selected on the basis of their contrasting styles of burrow construction. All three species produced measurable and significant, although different, changes in bed properties. They modified shear-wave propagation through the bed by changing bed rigidity: while A. marina and C. arenarium decreased rigidity by creating open burrows, L. conchilega increased rigidity by building shell-lined tubes. All produced a decrease in electrical resistivity by altering porosity and/or tortuosity, which implies an increase in permeability; these changes were attributable not only to the presence of the burrows but also to modification of the between-burrow sediment texture and bed properties.  相似文献   
106.
107.
108.
Early non-invasive fetal sexing is widely available over the Internet, leading to concerns about its possible use for sex selection. The aim of this review is to summarise the results of surveys describing lay attitudes towards sex selection for non-medical reasons to help address or inform such concerns. A search of electronic databases and key journals was supplemented by an Internet search and citation-tracking. Twenty-one quantitative studies were identified. Most were conducted in the US, with five recent studies in the UK and Germany. Most studies found that, overall, people were not in favour of sex selection. However, this varied from 94 to 18%. People may hold more negative attitudes when the method of sex selection is specified, particularly if this involves termination of pregnancy (TOP). Attitudes towards the general availability of sex selection are less negative than those towards personal use. Attitudes were consistently negative in German surveys. Little is known of such attitudes outside the US, the UK and Germany, and how such attitudes may change as new sex selection technologies become available. Studies of use of early non-invasive fetal sexing for sex selection for non-medical reasons are needed to assess the extent to which concerns about usage are justified and to assist in debates on how these might be most appropriately addressed. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
109.
110.
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