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   1407篇
  免费   125篇
  国内免费   17篇
安全科学   60篇
废物处理   22篇
环保管理   67篇
综合类   964篇
基础理论   186篇
污染及防治   54篇
评价与监测   168篇
社会与环境   17篇
灾害及防治   11篇
  2025年   1篇
  2024年   7篇
  2023年   14篇
  2022年   8篇
  2021年   18篇
  2020年   15篇
  2019年   12篇
  2018年   5篇
  2017年   13篇
  2016年   16篇
  2015年   18篇
  2014年   37篇
  2013年   63篇
  2012年   49篇
  2011年   123篇
  2010年   98篇
  2009年   84篇
  2008年   66篇
  2007年   111篇
  2006年   90篇
  2005年   85篇
  2004年   90篇
  2003年   83篇
  2002年   80篇
  2001年   58篇
  2000年   41篇
  1999年   25篇
  1998年   22篇
  1997年   33篇
  1996年   33篇
  1995年   50篇
  1994年   43篇
  1993年   10篇
  1992年   9篇
  1991年   6篇
  1990年   11篇
  1989年   5篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   4篇
  1984年   5篇
  1983年   3篇
  1982年   1篇
排序方式: 共有1549条查询结果,搜索用时 15 毫秒
41.
We studied the validity of mid-trimester amniotic fluid testosterone and FSH in the diagnosis of fetal sex in abnormal fetuses and in twins. It was found that the testosterone/FSH ratio, but not the level of the individual hormones, was an excellent criterion for fetal sex diagnosis. In a control group of 32 female and 34 male fetuses, the testosterone/FSH ratio was diagnostic. In two cases the values were indeterminate and fetal sex could not be predicted, but there were no false diagnoses. The abnormalities of the fetuses were diagnosed by karyotype analyses or raised levels of α-fetoprotein. It was found that neither autosomal trisomies nor X-chromosome aneuploidy or neural tube defect interfered with the diagnostic value of the hormonal approach. The twin study included 14 pairs, three of whom were discordant for sex. In all twins the fetal sex diagnosis was appropriate. In co-twins of the same sex the hormone levels were very close to each other.  相似文献   
42.
43.
Fetal akinesia deformation sequence (FADS) is a rare condition characterized by intrauterine growth retardation (IUGR), congenital limb contractures, pulmonary hypoplasia, hydramnios and craniofacial abnormalities. The present report comprises an autopsy study of three fetuses to illustrate the variable clinical manifestations and neuropathological findings. Fetus 1 had arthrogryposis and no movement on fetal ultrasound examination. Aborted at 21 weeks, the fetus showed micrognathia, bilateral joint contracture with pterygia at the elbow and axilla. Growth retardation and pulmonary hypoplasia were not major features. Neuropathologic examination revealed anterior horn cell loss and lateral corticospinal tract degeneration in spinal cord, with marked muscular atrophy. Fetus 2, 20 weeks' gestation, had fetal akinesia, nuchal thickening, left pleural effusion, and Dandy-Walker malformation on ultrasound examination. Autopsy showed low-set ears, ocular hypertelorism, cleft palate, flexion contractures with pterygia over axilla, elbow and groin, pulmonary hypoplasia, Dandy-Walker malformation, unremarkable spinal cord and skeletal muscle. Fetus 3, 21 weeks' gestation, was aborted for fetal akinesia, neck and limb webbing and severe arthrogryposis. At autopsy, similar facial abnormalities, contracture and pterygia in neck and multiple major joints were found. Borderline pulmonary hypoplasia and severe lumbar scoliosis were also present. The brain, spinal cord and muscle were unremarkable. In these three fetuses, the prenatal ultrasound and autopsy findings were characteristic of FADS. Neurogenic spinal muscular atrophy was the basis of fetal akinesia in Case 1. Dandy-Walker malformation was present in Case 2, but the pathogenetic mechanism of fetal akinesia was not clear as spinal cord and muscle histology appeared normal. The etiology of akinesia was undetermined in Case 3; no extrinsic or intrinsic cause was identified. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
44.
45.
46.
    
Although fetal cells have been known to escape to the maternal circulation for a number of years, research attempts to use them for prenatal diagnosis have not had any consistent success. This review attempts to trace the history of such attempts and to document their progress and reasons for success or failure. The opinions of recent conferences including that of the US National Institute of Child Health and Human Development, a sponsor of major US research in the field, are reported and discussed. It is concluded that although basic work has demonstrated the biologic availability of both fetal cells and their free DNA representatives in the maternal circulation at gestational ages relevant to prenatal diagnosis, much work remains to develop practical technology for their consistent recovery and assay. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
47.
48.
49.
50.
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