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   44280篇
  免费   468篇
  国内免费   367篇
安全科学   1297篇
废物处理   1682篇
环保管理   5972篇
综合类   7393篇
基础理论   12313篇
环境理论   33篇
污染及防治   11231篇
评价与监测   2702篇
社会与环境   2194篇
灾害及防治   298篇
  2022年   324篇
  2021年   324篇
  2020年   264篇
  2019年   348篇
  2018年   670篇
  2017年   701篇
  2016年   1020篇
  2015年   755篇
  2014年   1026篇
  2013年   3259篇
  2012年   1598篇
  2011年   1959篇
  2010年   1457篇
  2009年   1514篇
  2008年   1801篇
  2007年   1895篇
  2006年   1697篇
  2005年   1701篇
  2004年   1792篇
  2003年   1630篇
  2002年   1277篇
  2001年   1626篇
  2000年   1158篇
  1999年   742篇
  1998年   571篇
  1997年   565篇
  1996年   592篇
  1995年   644篇
  1994年   588篇
  1993年   540篇
  1992年   564篇
  1991年   519篇
  1990年   518篇
  1989年   526篇
  1988年   454篇
  1987年   396篇
  1986年   389篇
  1985年   417篇
  1984年   405篇
  1983年   431篇
  1982年   428篇
  1981年   395篇
  1980年   368篇
  1979年   373篇
  1978年   317篇
  1977年   278篇
  1976年   256篇
  1974年   249篇
  1973年   246篇
  1972年   276篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
731.
732.
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   
733.
734.
735.
736.
737.
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   
738.
The natural desire for couples to be parents and the medical practitioner's inability to treat most genetic diseases have been responsible for some of the most exciting research into infertility and genetic disorders. This has led in the United Kingdom to the establishment of the Warnock Committee of Inquiry into Human Fertilization and its report in 1984, and to a Review of the guidance on Research Use of Fetuses and Fetal Material published in 1989 and known as the Polkinghorne Report. The Warnock Report, among other ethical issues, considers the most fundamental question which has been debated for thousands of years, namely, What is life and when does it begin? More recently, the report has been responsible for new legislation which imposes ethical and legal restrictions on the scientific and medical community. The Polkinghorne Report recommends a voluntary code of practice which is morally and ethically acceptable within our society. We are also fortunate in the U.K. to have a parliamentary structure which allows debate on such important human issues and is prepared to impose ethical restrictions.  相似文献   
739.
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   
740.
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