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   33453篇
  免费   675篇
  国内免费   1487篇
安全科学   1161篇
废物处理   1255篇
环保管理   4395篇
综合类   7005篇
基础理论   9232篇
环境理论   21篇
污染及防治   8806篇
评价与监测   2007篇
社会与环境   1414篇
灾害及防治   319篇
  2023年   196篇
  2022年   375篇
  2021年   365篇
  2020年   339篇
  2019年   363篇
  2018年   560篇
  2017年   577篇
  2016年   736篇
  2015年   679篇
  2014年   967篇
  2013年   2543篇
  2012年   1203篇
  2011年   1604篇
  2010年   1327篇
  2009年   1348篇
  2008年   1541篇
  2007年   1588篇
  2006年   1416篇
  2005年   1191篇
  2004年   1118篇
  2003年   1090篇
  2002年   1044篇
  2001年   1324篇
  2000年   953篇
  1999年   623篇
  1998年   504篇
  1997年   493篇
  1996年   505篇
  1995年   528篇
  1994年   470篇
  1993年   422篇
  1992年   447篇
  1991年   384篇
  1990年   392篇
  1989年   419篇
  1988年   350篇
  1987年   305篇
  1986年   280篇
  1985年   312篇
  1984年   288篇
  1983年   323篇
  1982年   323篇
  1981年   275篇
  1980年   244篇
  1979年   271篇
  1978年   229篇
  1977年   195篇
  1976年   201篇
  1975年   192篇
  1972年   199篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
571.
572.
The de-O-sulphation of α-linked glucosamine-6-sulphate residues in heparan sulphate requires a specific sulphatase, glucosamine-6-sulphatase, which has been shown to be deficient in tissues of Sanfilippo D, or mucopolysaccharidosis type IIID (MPS IIID), patients. MPS IIID fibroblasts cultured in Basal Eagle's medium supplemented with either fetal calf serum or heat-inactivated fetal calf serum, MDCB or Ultraserg media had residual glucosarnine-6-sulphatase activities towards a heparin-derived trisaccharide substrate, O-(α-N-acetylglucosamine-6-sulphate)-(1→4)-L -O-(α-iduronic acid-2-sulphate)-(1→4)-D -O-2,5-anhydro [1-3H]mannitol-6-sulphate, GlcNAc6S-IdoA2S-anM6S, which were less than 1 per cent of the normal range for fibroblasts cultured in Basal Eagle's medium supplemented with fetal calf serum. However, the glucosamine-6-sulphatase activities of MPS IIID fibroblasts grown in Chang's medium were similar to the activities in normal control fibroblasts which were cultured in Basal Eagle's medium. These results indicate that caution is required for prenatal diagnosis of MPS IIID patients using chorionic villi or amniotic cells cultured in Chang's medium.  相似文献   
573.
574.
We describe our experience of prenatal diagnosis of non-ketotic hyperglycinaemia in four at-risk pregnancies using the glycine/serine ratio in amniotic fluid obtained between 18 and 20 weeks of gestation. All glycine levels were in the normal range. Serine levels were normal in two patients and borderline in the others. Glycine/serine ratios were normal in two patients, moderately increased in one patient ( + 3 SD), and highly increased in one patient ( + 8 SD). All the children were perfectly normal at birth. Because of this false-positive prediction and the false-negative prediction recently reported, we suggest that this unreliable method should not be used.  相似文献   
575.
This research was supported by a grant from the National Council for Research and Development, Israel, and the KFK, Karlsruhe, Germany.  相似文献   
576.
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   
577.
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   
578.
579.
580.
We present a case of fetal abdominal cystic hygroma that presented at 19 weeks of gestation. Ultrasonographic evaluation of the fetus revealed soft tissue enlargement of the left leg and a retroperitoneal mass in the left pelvis and abdomen. This represents the first reported case of prenatal diagnosis of abdominal cystic hygroma.  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