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   20840篇
  免费   240篇
  国内免费   122篇
安全科学   541篇
废物处理   899篇
环保管理   2823篇
综合类   3411篇
基础理论   5863篇
环境理论   11篇
污染及防治   5342篇
评价与监测   1298篇
社会与环境   878篇
灾害及防治   136篇
  2021年   137篇
  2019年   133篇
  2018年   244篇
  2017年   263篇
  2016年   416篇
  2015年   314篇
  2014年   481篇
  2013年   1620篇
  2012年   583篇
  2011年   825篇
  2010年   674篇
  2009年   669篇
  2008年   849篇
  2007年   873篇
  2006年   776篇
  2005年   675篇
  2004年   653篇
  2003年   637篇
  2002年   616篇
  2001年   767篇
  2000年   577篇
  1999年   328篇
  1998年   264篇
  1997年   283篇
  1996年   284篇
  1995年   332篇
  1994年   306篇
  1993年   288篇
  1992年   279篇
  1991年   280篇
  1990年   298篇
  1989年   277篇
  1988年   251篇
  1987年   240篇
  1986年   223篇
  1985年   203篇
  1984年   255篇
  1983年   210篇
  1982年   273篇
  1981年   222篇
  1980年   184篇
  1979年   202篇
  1978年   185篇
  1977年   154篇
  1976年   139篇
  1975年   143篇
  1974年   159篇
  1973年   163篇
  1972年   148篇
  1971年   146篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
351.
352.
353.
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   
354.
355.
356.
Scheffler  H.  Witkowski  S.  Becke-Goehring  M.  Bock  R.  Schuster  P.  Habermehl  G.  Jaenicke  L.  Schröder  F. A.  Tritsch  M. F.  Creutzfeldt  O.  Ziegler  H.  Hölldobler  B. 《Die Naturwissenschaften》1984,71(10):540-543
The Science of Nature -  相似文献   
357.
We studied the validity of mid-trimester amniotic fluid testosterone and FSH in the diagnosis of fetal sex in abnormal fetuses and in twins. It was found that the testosterone/FSH ratio, but not the level of the individual hormones, was an excellent criterion for fetal sex diagnosis. In a control group of 32 female and 34 male fetuses, the testosterone/FSH ratio was diagnostic. In two cases the values were indeterminate and fetal sex could not be predicted, but there were no false diagnoses. The abnormalities of the fetuses were diagnosed by karyotype analyses or raised levels of α-fetoprotein. It was found that neither autosomal trisomies nor X-chromosome aneuploidy or neural tube defect interfered with the diagnostic value of the hormonal approach. The twin study included 14 pairs, three of whom were discordant for sex. In all twins the fetal sex diagnosis was appropriate. In co-twins of the same sex the hormone levels were very close to each other.  相似文献   
358.
Necrotic brown lesions developing on leaves and fruits of lemon, and other plants, near fossil-fuel-burning power plants emitting vanadium-rich ash, were reproduced experimentally by inoculating leaves with this type of ash, which is strongly acidic. Comparable lesions were formed when drops of vanadium oxide, dissolved in NaOH, were put on leaves and fruits. Neutralizing, or adding excess H2SO4 (to pH 3), did not alter lesion formation. The histology of these lesions was similar to that of lesions attributed to vanadium-rich ash.  相似文献   
359.
360.
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