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   20749篇
  免费   242篇
  国内免费   127篇
安全科学   539篇
废物处理   897篇
环保管理   2800篇
综合类   3404篇
基础理论   5856篇
环境理论   10篇
污染及防治   5333篇
评价与监测   1285篇
社会与环境   860篇
灾害及防治   134篇
  2022年   130篇
  2021年   141篇
  2018年   234篇
  2017年   254篇
  2016年   406篇
  2015年   310篇
  2014年   469篇
  2013年   1610篇
  2012年   578篇
  2011年   823篇
  2010年   673篇
  2009年   666篇
  2008年   835篇
  2007年   875篇
  2006年   769篇
  2005年   664篇
  2004年   651篇
  2003年   635篇
  2002年   616篇
  2001年   764篇
  2000年   574篇
  1999年   329篇
  1998年   264篇
  1997年   281篇
  1996年   280篇
  1995年   335篇
  1994年   302篇
  1993年   286篇
  1992年   281篇
  1991年   278篇
  1990年   295篇
  1989年   280篇
  1988年   251篇
  1987年   241篇
  1986年   226篇
  1985年   202篇
  1984年   257篇
  1983年   212篇
  1982年   274篇
  1981年   219篇
  1980年   185篇
  1979年   203篇
  1978年   187篇
  1977年   154篇
  1976年   138篇
  1975年   144篇
  1974年   159篇
  1973年   164篇
  1972年   149篇
  1971年   148篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
341.
342.
Cysts of the choroid plexus of the lateral ventricle can be detected in the fetus during routine scanning at 16–18 weeks' gestation with an approximate incident of one in every 120 pregnancies. It is likely that in a high percentage of cases cysts are bilateral and that their recent discovery is mainly due to improvements in imaging technology. Although the great majority of cases resolve and do not result in any morbidity, five cases of trisomy 18 and one case of trisomy 21 associated with fetal choroid plexus cysts have been reported. In this prospective study, choroid plexus cysts were detected in 42 fetuses, resulting in 40 normal infants and 2 cases of trisomy 18. It is concluded that there may be a relationship between fetal choroid plexus cysts and trisomy 18. In order to obtain a more precise and accurate result, a multi-centre prospective study is being organized.  相似文献   
343.
Dr. Mertin haben wir für seine Hilfe bei der Interpretation der elektronenmikroskopischen Aufnahmen, der Deutschen Forschungsgemeinschaft und dem Fonds der Chemischen Industrie für ihre finanzielle Unterstützung zu danken.  相似文献   
344.
345.
346.
347.
We have documented the presence of five mitochondrial enzymes in samples of chorionic villus tissue and measured the levels of activity. Three of the enzymes catalyse biotindependent reactions. These are propionyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase and pyruvate carboxylase. the other enzymes. 4-aminobutyric acid aminotransferase and succinic semialdehyde dehydrogenase, are involved inthe degradation of the central inhibitory neurotransmitter GABA. Distinct diseases in whichthere is deficiency of each of these enzymes have been documented in man. Significant levels of activity were observed for all five enzymes in chorionic villus tissue. This methodology should permit early prenatal diagnosis of deficiencies of these enzymes by chorionic villus biopsy in the first trimester.  相似文献   
348.
349.
350.
Prenatal diagnosis of the cerebro-hepato-renal (Zellweger) syndrome has been performed in 10 pregnancies at risk by measuring both the activity of acyl CoA: dihydroxyacetonephosphate acyltransferase (DHAP-AT) and the de novo plasmalogen biosynthesis, either in cultured amniotic fluid cells or in fibroblasts cultured from a chorionic villus biopsy. In 7 of the pregnancies both tests indicated no abnormality. All 7 continued to term and normal infants were delivered. However, in amniotic fluid cells from 2 fetuses affected by Zellweger syndrome unequivocal differences from control values were found. The activity of DHAP-AT was clearly deficient and the de novo plasmalogen biosynthesis was impaired. In one pregnancy at risk prenatal diagnosis was performed during the first trimester by measuring both the DHAP-AT activity and the de novo plasmalogen biosynthesis in fibroblasts cultured from a chorionic villi biopsy. From the deficient DHAP-AT activity and the impaired de novo plasmalogen biosynthesis it was concluded that the fetus was affected. This was confirmed biochemically after induced abortion. It can be concluded that measurement of the DHAP-AT activity and the de novo plasmalogen biosynthesis provides convenient methods for the early prenatal detection of Zellweger syndrome.  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