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   19130篇
  免费   165篇
  国内免费   122篇
安全科学   396篇
废物处理   750篇
环保管理   2015篇
综合类   4817篇
基础理论   4344篇
环境理论   13篇
污染及防治   4755篇
评价与监测   1139篇
社会与环境   1137篇
灾害及防治   51篇
  2022年   130篇
  2021年   135篇
  2019年   133篇
  2018年   266篇
  2017年   261篇
  2016年   390篇
  2015年   304篇
  2014年   442篇
  2013年   1226篇
  2012年   477篇
  2011年   768篇
  2010年   566篇
  2009年   641篇
  2008年   788篇
  2007年   810篇
  2006年   719篇
  2005年   595篇
  2004年   607篇
  2003年   598篇
  2002年   587篇
  2001年   684篇
  2000年   442篇
  1999年   325篇
  1998年   217篇
  1997年   238篇
  1996年   257篇
  1995年   268篇
  1994年   270篇
  1993年   239篇
  1992年   227篇
  1991年   238篇
  1990年   227篇
  1989年   196篇
  1988年   185篇
  1987年   174篇
  1986年   174篇
  1985年   168篇
  1984年   185篇
  1983年   182篇
  1982年   193篇
  1981年   163篇
  1980年   145篇
  1979年   137篇
  1978年   148篇
  1977年   136篇
  1976年   121篇
  1975年   121篇
  1974年   133篇
  1967年   128篇
  1965年   122篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
105.
106.
107.
The diagnosis of Freeman–Sheldon syndrome was made by ultrasonographic evaluation of a 20-week fetus with a positive family history. The ultrasonographic features were abnormalities of the extremities and mouth.  相似文献   
108.
No clear answer concerning whether multivitamin/folate supplementation prevents neural tube defects (NTDs) is provided by three studies in the United States. All these studies are occurrence in nature, no recurrence studies having been conducted. The Atlanta Birth Defects Study is subject to pronounced memory and recall biases, the length between event and interview being as long as 16 years. In a second study (Boston University), objections can be raised to certain aspects of the experimental design, and the claim that 22 per cent of women started vitamins sufficiently early after pregnancy diagnosis to influence NTD formation is suspicious. Our NICHD case control study of 541 women in California and Illinois revealed no evidence for multivitamins or folic acid preventing NTDs. U.S. public policy-makers face difficulties in applying results of recurrence or occurrence studies in high-risk areas to low-risk areas in the U.S.  相似文献   
109.
Using a modified procedure by Solomons and Styner (1969), an evaluation of inorganic pyrophosphate (PPi) was performed on the amniotic fluid of two fetuses at risk for osteogenesis imperfecta (OI) at 14½ weeks gestation. The parents of both cases had a previous child with OI, Type II. The normal control group at 14–16 weeks gestation had PPi values ranging from 22.0–59.2 ug/100 ml, with a mean of 38.6±9.51 ug/100 ml. In each at-risk fetus, the amniotic fluid PPi value was within normal range. The first baby was born phenotypically normal at term. Intrauterine radiographic and fetal sonograms were done on the second fetus at approximately 19 weeks gestation. Both showed evidence of OI, Type II. The pregnancy was terminated at 21 weeks. Radiologic studies of the aborted fetus were consistent with OI, Type II. Our results indicate that the evaluation of PPi levels in amniotic fluid is not the method of choice for prenatal diagnosis of IO.  相似文献   
110.
With the advent of more stringent controls on wastewater treatment, sewage sludge production in Europe and many parts of the world is increasing. With this increase comes the problem of sludge disposal, and recycling to land arguably offers an economically and environmentally sustainable option. However, a major limitation of sewage sludge reuse is the potential release of heavy metals from the sludge and heavy metal accumulation to toxic levels in topsoils. The properties of the sludge play a crucial role in determining the initial release and subsequent availability of heavy metals in amended soils. Bioavailable forms of heavy metals in recently amended soils are most likely to be those that are bioavailable in the sewage sludge. In this paper, published research on the importance of sewage sludge characteristics on metal release and bioavailability will be reviewed and contrasted with original research. A selection of sludges from around Australia has been collected for this purpose. Through the use of incubation studies, isotope dilution techniques, ion-selective electrode measurements and 13C-NMR spectroscopy, the importance of a range of sludge properties on heavy metal behaviour in sludges and sludge-amended soils is addressed.  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