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   17738篇
  免费   146篇
  国内免费   121篇
安全科学   410篇
废物处理   677篇
环保管理   1953篇
综合类   5371篇
基础理论   3678篇
环境理论   2篇
污染及防治   4275篇
评价与监测   932篇
社会与环境   640篇
灾害及防治   67篇
  2018年   213篇
  2017年   207篇
  2016年   311篇
  2015年   231篇
  2014年   339篇
  2013年   1199篇
  2012年   398篇
  2011年   557篇
  2010年   521篇
  2009年   573篇
  2008年   605篇
  2007年   626篇
  2006年   542篇
  2005年   483篇
  2004年   510篇
  2003年   466篇
  2002年   452篇
  2001年   628篇
  2000年   421篇
  1999年   290篇
  1998年   209篇
  1997年   197篇
  1996年   199篇
  1995年   231篇
  1994年   244篇
  1993年   209篇
  1992年   226篇
  1991年   232篇
  1990年   254篇
  1989年   231篇
  1988年   182篇
  1987年   180篇
  1986年   181篇
  1985年   182篇
  1984年   199篇
  1983年   187篇
  1982年   196篇
  1981年   208篇
  1980年   169篇
  1979年   180篇
  1978年   147篇
  1977年   139篇
  1974年   147篇
  1973年   147篇
  1968年   156篇
  1967年   184篇
  1966年   154篇
  1965年   148篇
  1964年   152篇
  1963年   139篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
431.
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   
432.
A technique is described for measuring pressure within the amniotic cavity and within fetal vessels and/or body compartments. Two saline-filled catheters were connected at one end to needles inserted during indicated invasive procedures and at the other to silicon strain gauge transducers. In 36 pregnancies with normal liquor volume, stable intra-amniotic pressure (IAP, range 1–14 mmHg) increased with gestation (r=0·48, p<0·01). In pregnancies complicated by severe oligohydramnios, IAP was ≤ 1 mm Hg and rose to normal levels with saline amnioinfusion. Raised IAP (range 17–26 mm Hg), found in pregnancies with gross polyhydramnios, fell with drainage of amniotic fluid. Subtraction manometry was used to determine supra-amniotic pressure within the intervillus space, umbilical vein, umbilical artery, abdominal and thoracic cavities, and the urinary tract in normal and/or pathological fetuses. Low intravesical and intrapelvicalyceal pressures (median 6·5, range 2–10 mmHg) were noted in fetuses with obstructive uropathies. Intrauterine subtraction manometry appears to be a useful tool in the understanding of fetal pathophysiology and may be of clinical benefit in the therapeutic drainage and infusion of amniotic fluid and in the assessment of certain fetal disease states.  相似文献   
433.

Naturwissenschaften Aktuell

Nachholbedarf in multidisziplinärer Forschung  相似文献   
434.
435.
436.
437.
438.
439.
440.
Prenatal diagnosis of the cerebro-hepato-renal (Zellweger) syndrome has been performed in 10 pregnancies at risk by measuring both the activity of acyl CoA: dihydroxyacetonephosphate acyltransferase (DHAP-AT) and the de novo plasmalogen biosynthesis, either in cultured amniotic fluid cells or in fibroblasts cultured from a chorionic villus biopsy. In 7 of the pregnancies both tests indicated no abnormality. All 7 continued to term and normal infants were delivered. However, in amniotic fluid cells from 2 fetuses affected by Zellweger syndrome unequivocal differences from control values were found. The activity of DHAP-AT was clearly deficient and the de novo plasmalogen biosynthesis was impaired. In one pregnancy at risk prenatal diagnosis was performed during the first trimester by measuring both the DHAP-AT activity and the de novo plasmalogen biosynthesis in fibroblasts cultured from a chorionic villi biopsy. From the deficient DHAP-AT activity and the impaired de novo plasmalogen biosynthesis it was concluded that the fetus was affected. This was confirmed biochemically after induced abortion. It can be concluded that measurement of the DHAP-AT activity and the de novo plasmalogen biosynthesis provides convenient methods for the early prenatal detection of Zellweger syndrome.  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