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   26457篇
  免费   421篇
  国内免费   1575篇
安全科学   830篇
废物处理   1256篇
环保管理   3594篇
综合类   5379篇
基础理论   6985篇
环境理论   8篇
污染及防治   6573篇
评价与监测   1557篇
社会与环境   2027篇
灾害及防治   244篇
  2023年   141篇
  2022年   330篇
  2021年   288篇
  2020年   290篇
  2019年   235篇
  2018年   919篇
  2017年   920篇
  2016年   986篇
  2015年   641篇
  2014年   704篇
  2013年   1792篇
  2012年   1098篇
  2011年   1870篇
  2010年   1275篇
  2009年   1440篇
  2008年   1642篇
  2007年   1843篇
  2006年   898篇
  2005年   813篇
  2004年   804篇
  2003年   814篇
  2002年   791篇
  2001年   828篇
  2000年   669篇
  1999年   444篇
  1998年   348篇
  1997年   343篇
  1996年   341篇
  1995年   355篇
  1994年   280篇
  1993年   270篇
  1992年   229篇
  1991年   209篇
  1990年   202篇
  1989年   200篇
  1988年   168篇
  1987年   146篇
  1986年   160篇
  1985年   155篇
  1984年   209篇
  1983年   159篇
  1982年   177篇
  1981年   162篇
  1980年   135篇
  1979年   153篇
  1978年   97篇
  1977年   99篇
  1975年   96篇
  1974年   102篇
  1972年   107篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
53.
Uterine lavage affords the potential for non-invasive human blastocyst recovery, with obvious potential for preimplantation genetic diagnosis. In an effort to duplicate in women the multiple blastocyst recovery per cycle that can be achieved in several other species, we initiated a programme in which fertile women underwent superovulation, followed by lavage and embryo collection. We superovulated 15 fertile women, aged 21–40, in 29 cycles using one of four regimens. Insemination was by either intercourse or artificial intracervical donor insemination with cryopreserved sperm from men of proven fertility. In 28 of 29 cycles, the uterus was lavaged daily for 1, 2, or 3 days between 5 and 10 days after human chorionic gonadotropin (hCG) administration or luteinizing hormone (LH) surge. Almost total fluid volume was recovered in every lavage. There were no retained pregnancies and no complications. Surprisingly, only two morulae, one blastocyst, and four unfertilized ova were recovered. Thus, alterations in ovulation induction, insemination timing, or lavage techniques must be contemplated in order to increase the blastocyst yield and thus fulfil the potential of uterine lavage for preimplantation diagnosis.  相似文献   
54.
We are very grateful to A. Gessner for his great help in the construction of the apparatus and A. Meyer for performance of some pressure bomb experiments. This work was supported by grants of the Deutsche Forschungsgemeinschaft (Forschergruppe Ökophysiologie) to U.Z. and O.L.L.  相似文献   
55.
56.
We have documented the presence of five mitochondrial enzymes in samples of chorionic villus tissue and measured the levels of activity. Three of the enzymes catalyse biotindependent reactions. These are propionyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase and pyruvate carboxylase. the other enzymes. 4-aminobutyric acid aminotransferase and succinic semialdehyde dehydrogenase, are involved inthe degradation of the central inhibitory neurotransmitter GABA. Distinct diseases in whichthere is deficiency of each of these enzymes have been documented in man. Significant levels of activity were observed for all five enzymes in chorionic villus tissue. This methodology should permit early prenatal diagnosis of deficiencies of these enzymes by chorionic villus biopsy in the first trimester.  相似文献   
57.
58.
We report relatively high citrulline concentration in amniotic fluid of a citrullinemic fetus suggesting that prenatal detection of this condition could be done on this basis in conjunction with a direct or an indirect determination of argininosuccinate synthetase activity in amniotic fluid cells.  相似文献   
59.
60.
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