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   41786篇
  免费   469篇
  国内免费   573篇
安全科学   1290篇
废物处理   1851篇
环保管理   5402篇
综合类   6830篇
基础理论   11141篇
环境理论   22篇
污染及防治   10897篇
评价与监测   2775篇
社会与环境   2350篇
灾害及防治   270篇
  2022年   400篇
  2021年   415篇
  2020年   318篇
  2019年   390篇
  2018年   636篇
  2017年   640篇
  2016年   1008篇
  2015年   724篇
  2014年   1124篇
  2013年   3314篇
  2012年   1362篇
  2011年   1866篇
  2010年   1527篇
  2009年   1539篇
  2008年   1895篇
  2007年   1938篇
  2006年   1709篇
  2005年   1422篇
  2004年   1382篇
  2003年   1417篇
  2002年   1279篇
  2001年   1698篇
  2000年   1164篇
  1999年   712篇
  1998年   518篇
  1997年   500篇
  1996年   518篇
  1995年   595篇
  1994年   603篇
  1993年   513篇
  1992年   536篇
  1991年   508篇
  1990年   559篇
  1989年   514篇
  1988年   435篇
  1987年   395篇
  1986年   340篇
  1985年   368篇
  1984年   409篇
  1983年   398篇
  1982年   383篇
  1981年   356篇
  1980年   282篇
  1979年   312篇
  1978年   272篇
  1977年   215篇
  1975年   229篇
  1974年   204篇
  1972年   247篇
  1971年   208篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
721.
722.
723.
724.
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   
725.
726.
727.
We describe our experience of prenatal diagnosis of non-ketotic hyperglycinaemia in four at-risk pregnancies using the glycine/serine ratio in amniotic fluid obtained between 18 and 20 weeks of gestation. All glycine levels were in the normal range. Serine levels were normal in two patients and borderline in the others. Glycine/serine ratios were normal in two patients, moderately increased in one patient ( + 3 SD), and highly increased in one patient ( + 8 SD). All the children were perfectly normal at birth. Because of this false-positive prediction and the false-negative prediction recently reported, we suggest that this unreliable method should not be used.  相似文献   
728.
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   
729.
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   
730.
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   
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