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   39286篇
  免费   710篇
  国内免费   3211篇
安全科学   1395篇
废物处理   1696篇
环保管理   4463篇
综合类   12132篇
基础理论   8530篇
环境理论   12篇
污染及防治   10559篇
评价与监测   2080篇
社会与环境   1806篇
灾害及防治   534篇
  2023年   265篇
  2022年   667篇
  2021年   569篇
  2020年   448篇
  2019年   499篇
  2018年   659篇
  2017年   778篇
  2016年   978篇
  2015年   877篇
  2014年   1270篇
  2013年   3173篇
  2012年   1490篇
  2011年   1829篇
  2010年   1505篇
  2009年   1550篇
  2008年   1750篇
  2007年   1663篇
  2006年   1551篇
  2005年   1245篇
  2004年   1162篇
  2003年   1198篇
  2002年   1103篇
  2001年   1296篇
  2000年   1038篇
  1999年   773篇
  1998年   598篇
  1997年   569篇
  1996年   567篇
  1995年   568篇
  1994年   535篇
  1993年   502篇
  1992年   499篇
  1991年   475篇
  1990年   457篇
  1989年   415篇
  1988年   335篇
  1987年   296篇
  1986年   317篇
  1985年   318篇
  1984年   346篇
  1983年   327篇
  1982年   335篇
  1981年   343篇
  1980年   299篇
  1979年   302篇
  1978年   237篇
  1977年   232篇
  1974年   232篇
  1972年   225篇
  1967年   245篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
841.
842.
843.
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   
844.
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   
845.
846.
847.

Naturwissenschaften Aktuell

Großforschung mit anderen Namen  相似文献   
848.
Dedicated to Prof. Dr. A. Buchs, University of Geneva, on the occasion of his 60th birthday.  相似文献   
849.
850.
Cysts of the choroid plexus of the lateral ventricle can be detected in the fetus during routine scanning at 16–18 weeks' gestation with an approximate incident of one in every 120 pregnancies. It is likely that in a high percentage of cases cysts are bilateral and that their recent discovery is mainly due to improvements in imaging technology. Although the great majority of cases resolve and do not result in any morbidity, five cases of trisomy 18 and one case of trisomy 21 associated with fetal choroid plexus cysts have been reported. In this prospective study, choroid plexus cysts were detected in 42 fetuses, resulting in 40 normal infants and 2 cases of trisomy 18. It is concluded that there may be a relationship between fetal choroid plexus cysts and trisomy 18. In order to obtain a more precise and accurate result, a multi-centre prospective study is being organized.  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