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   43683篇
  免费   489篇
  国内免费   315篇
安全科学   1238篇
废物处理   1706篇
环保管理   5944篇
综合类   7180篇
基础理论   12484篇
环境理论   30篇
污染及防治   11121篇
评价与监测   2660篇
社会与环境   1818篇
灾害及防治   306篇
  2022年   274篇
  2021年   291篇
  2019年   310篇
  2018年   561篇
  2017年   569篇
  2016年   858篇
  2015年   698篇
  2014年   997篇
  2013年   3273篇
  2012年   1249篇
  2011年   1813篇
  2010年   1485篇
  2009年   1494篇
  2008年   1814篇
  2007年   1903篇
  2006年   1684篇
  2005年   1443篇
  2004年   1390篇
  2003年   1367篇
  2002年   1336篇
  2001年   1702篇
  2000年   1224篇
  1999年   768篇
  1998年   587篇
  1997年   614篇
  1996年   624篇
  1995年   690篇
  1994年   640篇
  1993年   583篇
  1992年   591篇
  1991年   555篇
  1990年   573篇
  1989年   594篇
  1988年   507篇
  1987年   459篇
  1986年   428篇
  1985年   439篇
  1984年   477篇
  1983年   479篇
  1982年   513篇
  1981年   440篇
  1980年   377篇
  1979年   415篇
  1978年   360篇
  1977年   302篇
  1976年   296篇
  1975年   285篇
  1974年   283篇
  1973年   291篇
  1972年   298篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
651.
652.
 The “Linh Duong” (Pseudonovibos spiralis), a newly described Vietnamese bovid, has been shown to be related to the Caprinae on the basis of the mitochondrial cytochrome b gene sequencing from horn fragments. To integrate the greatest available biodiversity we performed a new phylogenetic analysis including all genera of Caprinae. Unexpectedly, Pseudonovibos is found to be robustly associated with Rupicapra, and closer to the Alpine than to the Pyrenean chamois. Several clues led us to interpret this result as a carry-over DNA contamination of Pseudonovibos by Rupicapra. Received: 19 July 1999 / Accepted in revised form: 20 October 1999  相似文献   
653.
 Self-diffusion coefficients were studied for the highly polar liquid N-methylformamide at pressures up to 200 MPa between the melting pressure curves and 420 K by the spin-echo method. N-Methylformamide exists as a mixture of two conformers in the neat liquid. These conformers have large differences at lower temperatures in their dynamic and structural properties. The self-diffusion coefficient of the cis-conformer being 17% lower than that of the trans-conformer at the same T and p. This is the first observation of such an effect. The experimental study is supported by Monte Carlo (MC) calculations which show that the first neighbors around a cis conformer are arranged differently than in an all trans liquid. The difference leads in the simulations to a much lower dielectric constant for the trans-cis mixture and might also explain the retardation of diffusion for the cis conformer. Received: 15 November 1999 / Accepted in revised form: 28 February 2000  相似文献   
654.
Two types of fermented organic waste (trade and industry waste and fruit and vegetable waste) were successfully used as a sole carbon source to produce poly-3-hydroxybutyrate-co-valerate (PHBV) by Ralstonia eutrophus (formerly Alcaligenes eutrophus) via oxygen limitation.The production of PHBV could be optimized by optimizing the oxygen transfer through the fermentor. Thereby, a peak concentration of 1.1 g PHBV per liter cell suspension, 40 w% of cell dry weight, was obtained at an aeration rate of 0.24 mol O2/h·kg biomass. The yield of PHBV on the fatty acid concentration in the organic waste was 0.16 g polymer/g volatile organic matter. The process obtained, compares well with the commercial production process of PHBV based on glucose.  相似文献   
655.
656.
One hundred and fifty-one women of advanced maternal age who underwent genetic termination of pregnancy (TOP) were studied for their reproductive behaviour and the type of procedure for prenatal diagnosis in a subsequent pregnancy. A total of 59 women (39 per cent) had a further pregnancy. In all continuing pregnancies prenatal diagnosis was performed, of which 75 per cent consisted of chorionic villus sampling (CVS). Reproductive behaviour following a genetic termination was negatively correlated with maternal age and parity. Both reproductive behaviour and the choice to undergo a diagnostic procedure in the next pregnancy were independent of the type of diagnostic procedure in the previous affected pregnancy.  相似文献   
657.
658.
659.
660.
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