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   44408篇
  免费   498篇
  国内免费   343篇
安全科学   1386篇
废物处理   2066篇
环保管理   5963篇
综合类   7028篇
基础理论   11969篇
环境理论   18篇
污染及防治   10976篇
评价与监测   2973篇
社会与环境   2582篇
灾害及防治   288篇
  2022年   345篇
  2021年   416篇
  2020年   276篇
  2019年   330篇
  2018年   595篇
  2017年   653篇
  2016年   1002篇
  2015年   728篇
  2014年   1150篇
  2013年   3601篇
  2012年   1395篇
  2011年   1892篇
  2010年   1553篇
  2009年   1603篇
  2008年   1945篇
  2007年   1925篇
  2006年   1720篇
  2005年   1526篇
  2004年   1468篇
  2003年   1418篇
  2002年   1338篇
  2001年   1616篇
  2000年   1160篇
  1999年   690篇
  1998年   548篇
  1997年   585篇
  1996年   603篇
  1995年   707篇
  1994年   617篇
  1993年   555篇
  1992年   564篇
  1991年   553篇
  1990年   544篇
  1989年   524篇
  1988年   482篇
  1987年   427篇
  1986年   397篇
  1985年   401篇
  1984年   461篇
  1983年   416篇
  1982年   474篇
  1981年   395篇
  1980年   311篇
  1979年   348篇
  1978年   309篇
  1977年   267篇
  1975年   251篇
  1974年   251篇
  1973年   288篇
  1972年   261篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
731.
732.
733.
734.
735.
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   
736.
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   
737.
738.
The index patient is a female fetus in which prenatal diagnosis of 8p trisomy was established after amniocentesis at 16 weeks of gestation. This fetus was the unbalanced product of a maternal translocation of 5q/8p (karyotype: 46,XX,t(5;8)(q35;pl 1). Internal malformations include an anomalous lobature of the right lung, a little and high atrio-ventricular communication, and an anomaly in the number and shape of the aortic semilunar valves. The possible relationship between the phenotype and the chromosomal abnormality is briefly discussed.  相似文献   
739.
This research was supported by a grant from the National Council for Research and Development, Israel, and the KFK, Karlsruhe, Germany.  相似文献   
740.
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