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   41463篇
  免费   435篇
  国内免费   548篇
安全科学   1231篇
废物处理   1842篇
环保管理   5038篇
综合类   7806篇
基础理论   10722篇
环境理论   29篇
污染及防治   10570篇
评价与监测   2704篇
社会与环境   2239篇
灾害及防治   265篇
  2023年   203篇
  2022年   425篇
  2021年   415篇
  2020年   314篇
  2019年   375篇
  2018年   642篇
  2017年   610篇
  2016年   954篇
  2015年   734篇
  2014年   1117篇
  2013年   3185篇
  2012年   1384篇
  2011年   1836篇
  2010年   1516篇
  2009年   1601篇
  2008年   1867篇
  2007年   1915篇
  2006年   1644篇
  2005年   1450篇
  2004年   1288篇
  2003年   1392篇
  2002年   1236篇
  2001年   1597篇
  2000年   1141篇
  1999年   708篇
  1998年   483篇
  1997年   506篇
  1996年   493篇
  1995年   596篇
  1994年   613篇
  1993年   487篇
  1992年   486篇
  1991年   491篇
  1990年   520篇
  1989年   473篇
  1988年   408篇
  1987年   379篇
  1986年   326篇
  1985年   336篇
  1984年   348篇
  1983年   351篇
  1982年   337篇
  1981年   315篇
  1980年   270篇
  1979年   292篇
  1978年   249篇
  1977年   191篇
  1975年   202篇
  1972年   197篇
  1971年   185篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
921.
922.
923.
924.
925.
926.
927.
IntroductionAtmosphericnitrousoxide (N2 O)isaveryradioactivelyactivegreenhousegas,alsocontributingtothedepletionofozonelayerofstratosphere .AtmosphericN2 Omainlyoriginatedfromnitrificationanddenitrificationinterrestrialecosystems.Grasslandecosystem ,accoun…  相似文献   
928.
Environmental managers at U.S. Department of Defense (DoD) installations overseas are faced with the challenge of managing contaminated sites at these installations with little information on the extent of contamination or the risk posed by the site. In this regard, DoD managers overseas encounter a situation quite similar to the situation faced by decision makers in the U.S. who are managing brownfields. Innovative site characterization and risk-based decision-making methods, which are currently being developed for expeditious application at brownfield sites in the U.S., may also be appropriate for application at overseas DoD sites. In this paper, the analytic hierarchy process (AHP) is used by DoD decision makers to evaluate and rank innovative site characterization technologies and risk-based decision-making and management methods, for use at installations in Korea. Results indicate that for sites with high potential risk the decision makers preferred site characterization technologies that produce data of high quality and a method that can be used to establish credible risk-based remediation goals. This study provides a framework for applying characterization technologies and risk management to poorly characterized contaminated sites in developing countries, where resources for remedial actions may be limited.  相似文献   
929.
This study provides data on the incidence of fetal trisomies 21, 18, and 13 at 9–14 weeks' gestation in women aged 35–45 years and estimates of maternal age-specific risks in women aged 20–45 years. Our data from 5814 singleton pregnancies undergoing first-trimester karyotyping for the sole indication of maternal age ⩾ 35 years were combined with those from two previous reports and the incidence of the trisomies was calculated from a total of 15 793 pregnancies. Comparison of incidences at 9–14 weeks' gestation with published data at 15–20 weeks' gestation and in livebirths demonstrated that at birth the maternal age-specific incidence of trisomy 21 is 33 per cent lower than at 15–20 weeks' gestation and 54 per cent lower than at 9–14 weeks' gestation. Furthermore, the relative frequency of trisomies 18 and 13 decreases from 30 per cent at 9–14 weeks to 22 per cent at 15–20 weeks and 14 per cent at birth.  相似文献   
930.
In this paper we describe the use of five-colour fluorescence in situ hybridization for prenatal diagnosis of aneuploidy using uncultured amniotic fluid cells. The analysis is based on ratio mixing of dual-labelled probes and digital imaging for the detection and visualization of five different probes specific for the five target chromosomes, 13, 18, 21, X, and Y. A retrospective blind analysis of 30 coded uncultured amniotic fluid samples correctly detected fetal sex and five trisomy 21 cases. Multicolour fluorescence in situ hybridization used in this way allows rapid and simultaneous detection of the most frequent aneuploidies.  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