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   28551篇
  免费   186篇
  国内免费   163篇
安全科学   520篇
废物处理   1564篇
环保管理   3785篇
综合类   3414篇
基础理论   8089篇
环境理论   4篇
污染及防治   6928篇
评价与监测   2177篇
社会与环境   2291篇
灾害及防治   128篇
  2022年   126篇
  2021年   156篇
  2020年   101篇
  2019年   145篇
  2018年   1762篇
  2017年   1669篇
  2016年   1597篇
  2015年   461篇
  2014年   522篇
  2013年   1558篇
  2012年   1074篇
  2011年   2153篇
  2010年   1409篇
  2009年   1368篇
  2008年   1784篇
  2007年   2236篇
  2006年   766篇
  2005年   737篇
  2004年   705篇
  2003年   748篇
  2002年   782篇
  2001年   773篇
  2000年   572篇
  1999年   316篇
  1998年   257篇
  1997年   223篇
  1996年   273篇
  1995年   267篇
  1994年   256篇
  1993年   228篇
  1992年   209篇
  1991年   187篇
  1990年   206篇
  1989年   192篇
  1988年   181篇
  1987年   171篇
  1986年   148篇
  1985年   147篇
  1984年   194篇
  1983年   185篇
  1982年   168篇
  1981年   171篇
  1980年   138篇
  1979年   159篇
  1978年   108篇
  1977年   100篇
  1976年   88篇
  1975年   94篇
  1973年   92篇
  1972年   100篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
192.
Cytogenetic study of chorionic villi sampled because of advanced maternal age revealed, after overnight culture, an apparently non-mosaic trisomy 7. Amniocentesis showed exclusively normal mitoses, and the pregnancy continued normally. One hundred mitoses from cord blood of the normal newborn revealed a non-mosaic 46,XX complement. No cells with a proven trisomy 7 were found in cultures from either of two biopsies of the morphologically normal placenta, but the peripheral biopsy showed in multiple cultures an abnormal clone: 47,XX, + 20,-2,-21, + t(2;21)(p13;q22). To our knowledge, this is the first case of non-mosaic trisomy 7 detected on CVS which has had follow-up studies of amniotic fluid, cord blood, and term placenta.  相似文献   
193.
194.
 Ants have a well developed olfactory sense, which they need both for the perception of environmental chemicals, and for a highly sophisticated intraspecific communication system based on pheromones. The question arises therefore as to how different odors are coded in the antennal lobe, the first central neuropil to process olfactory information. We measured odor-evoked activity patterns using in vivo neuropil calcium recording in the antennal lobe of the ant Camponotus rufipes. We found that (a) odors elicit focal activity spots (diameter ca. 20 μm) which most probably represent the olfactory glomeruli; (b) different odors are coded in odor specific patterns of such activated spots, and a particular spot can participate in the pattern for different odors; (c) calcium increased in the activated spots within the 2-s stimulation period and slowly declined thereafter. Received: 10 March 1999 / Accepted in revised form: 5 July 1999  相似文献   
195.
196.
197.
198.
During a 7-year period, 117 fetal karyotypes were available from 131 genetic amniocenteses. These procedures were performed between 14 and 37 weeks' gestation for the following abnormal ultrasound findings: (1) intrauterine growth retardation (IUGR)—61 cases; (2) fetal malformation—71 cases; and (3) amniotic fluid volume (AFV) abnormality—60 cases. Chromosomal abnormalities were identified in 19 cases (16.2 per cent). Aneuploidy was 2.5 times as frequent in the presence of malformations than in their absence. No correlation was demonstrated between specific fetal malformations and specific chromosomal abnormalities. Aneuploidy was also twice as frequent in the presence of symmetrical IUGR than in its absence. No chromosomal abnormalities were found among eight cases of asymmetrical IUGR. Four cases of aneuploidy presented with isolated IUGR, three of these involving the X chromosome. The frequency of aneuploidy was the same with or without abnormalities of AFV (14.3 versus 16.4 per cent). No chromosomal abnormality was found associated with isolated AFV abnormalities.  相似文献   
199.
The excellent technical assistance of H. Führer and I. Leib is appreciated. Part of the work was supported by the Bundesministerium für Forschung und Technologie, the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and from the Leitz and Hoechst companies. This paper is part of the M. D. thesis of Ch.L.  相似文献   
200.
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