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   35011篇
  免费   267篇
  国内免费   222篇
安全科学   749篇
废物处理   1711篇
环保管理   4754篇
综合类   5216篇
基础理论   9849篇
环境理论   11篇
污染及防治   8285篇
评价与监测   2543篇
社会与环境   2201篇
灾害及防治   181篇
  2022年   202篇
  2021年   213篇
  2020年   174篇
  2019年   230篇
  2018年   1734篇
  2017年   1630篇
  2016年   1656篇
  2015年   512篇
  2014年   606篇
  2013年   2036篇
  2012年   1173篇
  2011年   2279篇
  2010年   1518篇
  2009年   1443篇
  2008年   1881篇
  2007年   2221篇
  2006年   1030篇
  2005年   864篇
  2004年   886篇
  2003年   876篇
  2002年   868篇
  2001年   1074篇
  2000年   758篇
  1999年   452篇
  1998年   351篇
  1997年   334篇
  1996年   367篇
  1995年   404篇
  1994年   422篇
  1993年   349篇
  1992年   348篇
  1991年   358篇
  1990年   374篇
  1989年   358篇
  1988年   290篇
  1987年   267篇
  1986年   259篇
  1985年   239篇
  1984年   286篇
  1983年   280篇
  1982年   288篇
  1981年   268篇
  1980年   215篇
  1979年   243篇
  1978年   190篇
  1977年   181篇
  1975年   180篇
  1974年   165篇
  1973年   167篇
  1972年   180篇
排序方式: 共有10000条查询结果,搜索用时 794 毫秒
261.
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   
262.
263.
Prenatal real-time ultrasonographic diagnosis of microphthalmia is presented. Diagnosis was made at 18 weeks' gestation in a fetus of a patient with a previous infant affected with the syndrome of cryptophthalmia with absence of septum nasi and ambiguous genitalia (Fraser syndrome). Recognition of microphthalmia as a part of Fraser syndrome and the easy visualization of fetal facial bones and orbits in the second trimester made the diagnosis possible.  相似文献   
264.
265.
 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   
266.
Metasedimentary garnet-mica schists are interlayered with metabasic garnet–omphacite schists and enclose eclogite boudins in the high-pressure metamorphic Maksyutov complex in the Southern Urals, Russia. These three rock types were investigated in one outcrop and compared chemographically and thermobarometrically. The Fe/Mg distributions between garnet rim–omphacite and garnet rim–phengite pairs indicate different equilibration temperatures for the three samples, with the lowest temperature (500°C, >1.5 GPa) for the eclogite boudin, an intermediate temperature (630°C, >1.7 GPa) for the foliated eclogite and the highest temperature (650°C, >1.7 GPa) for the garnet-mica schist. The garnets in garnet-mica schist enclose abundant chloritoid relics and the Fe/Mg distribution between chloritoid and garnet records an earlier high-temperature stage (650°C, >2.0 GPa) before the garnet rim–phengite temperatures were reached. Together with some minimum- and maximum-pressure estimates three different prograde pressure–temperature paths and a common retrograde metamorphic evolution are interpreted from the chemographic and thermobarometric data. The different early metamorphic evolutions and conditions confirm the variability of protoliths, which are also indicated by different U/Pb zircon and rutile ages.  相似文献   
267.
268.
269.
270.
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