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   40764篇
  免费   445篇
  国内免费   322篇
安全科学   1174篇
废物处理   1473篇
环保管理   5660篇
综合类   6491篇
基础理论   11548篇
环境理论   24篇
污染及防治   10568篇
评价与监测   2451篇
社会与环境   1868篇
灾害及防治   274篇
  2022年   260篇
  2021年   278篇
  2019年   322篇
  2018年   556篇
  2017年   547篇
  2016年   816篇
  2015年   663篇
  2014年   942篇
  2013年   3077篇
  2012年   1154篇
  2011年   1694篇
  2010年   1400篇
  2009年   1401篇
  2008年   1710篇
  2007年   1794篇
  2006年   1642篇
  2005年   1348篇
  2004年   1350篇
  2003年   1280篇
  2002年   1246篇
  2001年   1655篇
  2000年   1145篇
  1999年   731篇
  1998年   588篇
  1997年   577篇
  1996年   583篇
  1995年   651篇
  1994年   623篇
  1993年   535篇
  1992年   561篇
  1991年   530篇
  1990年   545篇
  1989年   573篇
  1988年   480篇
  1987年   423篇
  1986年   385篇
  1985年   421篇
  1984年   426篇
  1983年   457篇
  1982年   452篇
  1981年   401篇
  1980年   342篇
  1979年   375篇
  1978年   321篇
  1977年   271篇
  1976年   258篇
  1975年   267篇
  1974年   256篇
  1973年   245篇
  1972年   292篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
701.
The fluxes of heavy metals and magnetite, a fly-ash component, from coal burning, to sediments of the Kunming Lake in Beijing have increased measurably over the last fifty years. Ages were introduced to the sediment strata through Pb-210 geochronologies. Even with a doubling of coal usage by the year 2000, the anthropogenic metal fluxes will still be less than those recorded in metropolitan Tokyo and U.S. lakes.  相似文献   
702.
703.
704.
705.
The nature of the cosmic redshift is one of the most fundamental questions in modern science. Hubble's discovery of the apparent Expansion of the Universe is derived from observations on a small number of galaxies at very low redshifts. Today, quasar redshifts have a range more than 1000 times greater than those in Hubble's sample, and represent more than 100 times as many objects. A recent comprehensive compilation of published measurements provides the basis for a study indicating that quasar observations are not in good agreement with the original predictions of the Expanding Universe theory, but are well fit by the predictions of an alternative theory having fewer adjustable parameters.  相似文献   
706.
707.
708.
709.
A population of 1639 patients were seen for chorionic villus sampling (CVS). Embryonic death was identified at ultrasound in 5.3 per cent of patients. The number of patients undergoing CVS was 1551, with 1416 transcervical procedures and 135 transabdominal procedures. The most common indication for CVS was advanced maternal age. Spontaneous pregnancy losses identified by increased risk of pregnancy loss with increasing aspiration attempts. The total fetal loss for this population was 5.4 per cent with the pregnancy loss estimated due to procedure being 1.2 per cent. Analysis of placentae from patients having CVS and amniocen-tesis showed no differences. Microbiological assessment prior to CVS was similar to previous publications.  相似文献   
710.
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   
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