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   32082篇
  免费   430篇
  国内免费   460篇
安全科学   1051篇
废物处理   1341篇
环保管理   4692篇
综合类   4855篇
基础理论   8466篇
环境理论   10篇
污染及防治   8695篇
评价与监测   1943篇
社会与环境   1687篇
灾害及防治   232篇
  2022年   259篇
  2021年   289篇
  2020年   262篇
  2019年   251篇
  2018年   477篇
  2017年   455篇
  2016年   723篇
  2015年   586篇
  2014年   863篇
  2013年   2663篇
  2012年   1079篇
  2011年   1502篇
  2010年   1157篇
  2009年   1329篇
  2008年   1478篇
  2007年   1562篇
  2006年   1332篇
  2005年   1128篇
  2004年   1128篇
  2003年   1063篇
  2002年   1023篇
  2001年   1238篇
  2000年   928篇
  1999年   570篇
  1998年   406篇
  1997年   409篇
  1996年   445篇
  1995年   481篇
  1994年   427篇
  1993年   389篇
  1992年   339篇
  1991年   337篇
  1990年   348篇
  1989年   331篇
  1988年   308篇
  1987年   281篇
  1986年   272篇
  1985年   270篇
  1984年   326篇
  1983年   291篇
  1982年   320篇
  1981年   306篇
  1980年   252篇
  1979年   285篇
  1978年   179篇
  1977年   180篇
  1976年   153篇
  1975年   167篇
  1973年   164篇
  1972年   186篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
281.
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   
282.
283.
The prenatal diagnosis of cystinosis is currently based on the increased amount of free-cystine present in amniotic fluid cells. Amniocyte cultures must be grown for at least 2 weeks to obtain sufficient cells for such measurements. Thus, the diagnosis cannot be made until close to 20 weeks gestational age by this method. We report a case in which chorionic villi were used for direct cystine measurement resulting in the in utero diagnosis of cystinosis at 9 weeks gestational age. The diagnosis was confirmed by the study of cultured chorionic villus cells, and of the 10-week abortus.  相似文献   
284.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling.  相似文献   
285.
286.
 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   
287.
288.
289.
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   
290.
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur.  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