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   42938篇
  免费   364篇
  国内免费   250篇
安全科学   874篇
废物处理   2012篇
环保管理   5520篇
综合类   8317篇
基础理论   11573篇
环境理论   14篇
污染及防治   10077篇
评价与监测   2863篇
社会与环境   2102篇
灾害及防治   200篇
  2021年   228篇
  2018年   1762篇
  2017年   1656篇
  2016年   1725篇
  2015年   605篇
  2014年   730篇
  2013年   2530篇
  2012年   1330篇
  2011年   2431篇
  2010年   1636篇
  2009年   1575篇
  2008年   2059篇
  2007年   2447篇
  2006年   1225篇
  2005年   1025篇
  2004年   1014篇
  2003年   1079篇
  2002年   1020篇
  2001年   1176篇
  2000年   880篇
  1999年   555篇
  1998年   435篇
  1997年   438篇
  1996年   445篇
  1995年   510篇
  1994年   491篇
  1993年   438篇
  1992年   437篇
  1991年   442篇
  1990年   464篇
  1989年   446篇
  1988年   401篇
  1987年   371篇
  1986年   353篇
  1985年   355篇
  1984年   397篇
  1983年   366篇
  1982年   409篇
  1981年   361篇
  1980年   325篇
  1979年   335篇
  1978年   314篇
  1977年   273篇
  1976年   255篇
  1975年   242篇
  1974年   285篇
  1973年   278篇
  1972年   260篇
  1971年   234篇
  1967年   233篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
721.
722.
723.
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   
724.
725.
726.
727.
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   
728.
This article reports the results of a retrospective study designed to examine the responses of couples to genetic amniocentesis and subsequent therapeutic abortions due to birth defects. Fourteen women and 12 men were interviewed by experienced interviewers using a structured format designed by the authors, and each interview was audiotaped for later rating. The 5 raters (all women) were instructed to independently rate each interview using forms designed by the authors to elicit information about many aspects of the participant's individual responses as well as perceptions of spouse's responses to the process of pregnancy, amniocentesis, therapeutic abortion, and sequelae. Ratings of all 5 raters were conjoined and an homogeneous narrative was constructed for each interview. Results indicate, in general, that the respondent couples coped well with this experience. In fact 70 per cent of the respondent couples described their marital relationships as becoming closer as a result of their experience. Only a few participants reported long-term deleterious effects. Most couples coped by relying on relatives, friends, and occasionally, professional counsellors. In addition, most participants in this study suggested ways to improve the medical and psychological aspects of this experience.  相似文献   
729.
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   
730.
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   
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