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   31345篇
  免费   262篇
  国内免费   326篇
安全科学   825篇
废物处理   1420篇
环保管理   3633篇
综合类   5468篇
基础理论   7888篇
环境理论   9篇
污染及防治   8187篇
评价与监测   2365篇
社会与环境   1956篇
灾害及防治   182篇
  2022年   310篇
  2021年   302篇
  2020年   191篇
  2019年   258篇
  2018年   477篇
  2017年   474篇
  2016年   760篇
  2015年   530篇
  2014年   868篇
  2013年   2483篇
  2012年   1010篇
  2011年   1299篇
  2010年   1131篇
  2009年   1169篇
  2008年   1312篇
  2007年   1390篇
  2006年   1244篇
  2005年   1073篇
  2004年   1033篇
  2003年   1018篇
  2002年   965篇
  2001年   1326篇
  2000年   901篇
  1999年   588篇
  1998年   381篇
  1997年   374篇
  1996年   413篇
  1995年   420篇
  1994年   391篇
  1993年   335篇
  1992年   363篇
  1991年   349篇
  1990年   351篇
  1989年   332篇
  1988年   316篇
  1987年   242篇
  1986年   233篇
  1985年   244篇
  1984年   271篇
  1983年   255篇
  1982年   287篇
  1981年   237篇
  1980年   193篇
  1979年   230篇
  1978年   207篇
  1977年   180篇
  1976年   179篇
  1975年   161篇
  1974年   176篇
  1972年   150篇
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
441.
442.
443.
444.
445.
446.
We report a 16-month-old boy with delayed psychomotor development, dysmorphic features, and failure to thrive. He had a mosaic karyotype detected prenatally: mos 46,XY/47,XY,+r(20)/47,XY,+20. After birth, the abnormal cell lines were confirmed in a number of tissues. The small ring chromosome was identified using fluorescence in situ hybridization as derived from chromosome 20. We compared our patient with previously reported cases of mosaic trisomy 20 detected prenatally and associated with an abnormal phenotype. In an attempt to characterize an r(20) syndrome, we also compared our case with two similar reports in the literature.  相似文献   
447.
Multiple placental passes during chorionic villus sampling (CVS) increase the risk of fetal loss; however, specific factors that predispose to repeat aspiration have not been delineated. To identify anatomic and technical variables associated with multiple-pass procedures, a detailed review of 205 videotaped CVS procedures (single pass = 163; multiple pass = 42) was performed, blinded to pregnancy outcome. The route of sampling did not influence the need for multiple aspiration attempts (transabdominal—30/ 135; transcervical—12/70), nor was placental location alone discriminatory. However, the combination of a posterior placenta and uterine retroversion was observed more frequently in the multiple-pass cohort (8/42 vs. 9/163; p<0.05). In transabdominal cases, suboptimal needle placement (e.g., perpendicular to the placental long axis) was more common in the initial aspiration of a multiple-pass procedure (21/30 vs. 38/105;p<0.01), while limited penetration of the catheter tip (e.g., just inside the placental edge) characterized a majority of multiple-pass cases in the transcervical subset (7/12 vs. 3/58; p<0.0001). A case-control cohort was constructed to evaluate the impact of these technical variables on sampling efficacy, independent of the influence of uterine position and placental site. In that analysis, suboptimal location and/or orientation of the sampling device remained characteristic of multiple-pass cases. We conclude that further reduction in the frequency of multiple-pass procedures might be achieved by consistent placement of the device tip in the central placental mass. Unlike amniocentesis, where any point of amnion entry will suffice, this technical nuance should be emphasized with CVS to maximize the single-pass success rate.  相似文献   
448.
449.
IntroductionChengdu KunmingRailwayLineislocatedonthemountainregionofsouthwesternChina .Therearealotofdebrisflowgulliesspreadingbesidethisrailwayline .Onsummer,thedebrisflowoftenburstsandthreatensthesafetyoftherailwaytransportation.In 1981,alarge scaledebris…  相似文献   
450.
Ten out of the 12 new EU members, used to belong to the so-called “former eastern block”, with a post WWII environmental policy radically different from the tendencies followed in Western Europe. The lack of conservation regulations has resulted in a rather harmful industrialization, regarding natural resources and environmental quality. While air pollution transfer is a phenomenon of transboundary level, there is a particular interest in examining the contribution of the new EU member states to the environmental pressure faced by the older member states and vice versa. The current study utilises the official data for almost 20 years published by the European Monitoring and Evaluation Program concerning the transboundary transfer of NOx and SO2 in order to analyse the situation and discuss the present and future environmental policy regarding air pollution.  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