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   30259篇
  免费   344篇
  国内免费   250篇
安全科学   1031篇
废物处理   1476篇
环保管理   4125篇
综合类   4500篇
基础理论   7863篇
环境理论   8篇
污染及防治   7429篇
评价与监测   2170篇
社会与环境   2066篇
灾害及防治   185篇
  2023年   133篇
  2022年   262篇
  2021年   322篇
  2020年   199篇
  2019年   249篇
  2018年   445篇
  2017年   474篇
  2016年   729篇
  2015年   545篇
  2014年   862篇
  2013年   2499篇
  2012年   1031篇
  2011年   1372篇
  2010年   1120篇
  2009年   1160篇
  2008年   1442篇
  2007年   1348篇
  2006年   1234篇
  2005年   1104篇
  2004年   1058篇
  2003年   1013篇
  2002年   943篇
  2001年   1109篇
  2000年   782篇
  1999年   493篇
  1998年   368篇
  1997年   394篇
  1996年   406篇
  1995年   474篇
  1994年   402篇
  1993年   356篇
  1992年   385篇
  1991年   362篇
  1990年   333篇
  1989年   325篇
  1988年   299篇
  1987年   249篇
  1986年   252篇
  1985年   255篇
  1984年   274篇
  1983年   262篇
  1982年   275篇
  1981年   227篇
  1980年   170篇
  1979年   183篇
  1978年   169篇
  1977年   139篇
  1975年   139篇
  1973年   167篇
  1972年   144篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
601.
Foci of calcification were observed at autopsy in the liver of a fetus with complete trisomy 9 on which two cordocenteses had been performed. It is suggested that liver calcifications are a possible complication of the procedure. As several other cases of calcifications in the liver and other organs of fetuses with autosomal trisomies have been described without a history of cordocentesis, further studies should be carried out to determine whether fetuses with chromosomal anomalies are more prone to thrombus formation and embolization.  相似文献   
602.
Prenatal diagnosis on chorionic villous tissue was performed for a woman with the karyotype 46,XX,t(2;18)(q32;q12)—a subtle ‘difficult’ translocation. The case illustrates the necessity of good quality cytogenetics for accurate prenatal diagnosis. For chorionic villi this can be obtained only with long-term culture.  相似文献   
603.
604.
Serum PAPP-A measurements taken from 254 women in the first trimester are reported. Eleven chromosomal abnormalities were detected. The mean serum PAPP-A levels in cases of Down syndrome were 0.44 MOM at 9 weeks gestation, 0.15 MOM at 10 weeks, and 0.29 MOM at 11 weeks. The PAPP-A level at 10 weeks was below those of pregnancies which aborted spontaneously. At 11 weeks, the pregnancies with Down syndrome recorded the lowest PAPP-A levels at that gestation. On this small sample, offering chorionic villus sampling to women with singleton pregnancies and a PAPP-A level below 0.3 MOM (approximately 6.5 per cent of this at-risk group) would have detected all the Down syndrome fetuses at 10 weeks and 50 per cent at 11 weeks without selecting those cases destined to abort. This suggests that serum PAPP-A should continue to be investigated as a potential first-trimester screening test for Down syndrome.  相似文献   
605.
A laboratory scale study was conducted to assess the feasibility of the new coupling of rotating biological contactor (RBC) plus porous biomass support system (PBSS) using polyurethane foam as porous support media to biodegrade petroleum refinery wastewater. Polyurethane foam was attached on disks of two four-stage laboratory scale cascade connected RBC units.The two RBC units were operated simultaneously at different but constant, flowrates giving hydraulic loading rates of 0.01, 0.02, 0.03, 0.04 m3/m2/d in two runs keeping the same rotational speed 10 r/min throughout. Organic loading was a less controllable factor in this study.For all of the hydraulic loadings, it was found that the removal efficiency of total chemical oxygen demand (TCOD) and oil were above 80 percent. Ammonia nitrogen and phenol removal were above 90 and 80 percent respectively. The maximum biomass concentration within polyurethane foam was about 30 g/m2 in the first stage for 0.03 m3/m2/d hydraulic loading.The results show that t  相似文献   
606.
An efficient, reproducible and rapid fused silica capillary column gas chromatographic method, in splitless mode, for analysing of the three chloroanthracene isomers is described. The method affords efficient separation and good linearity for each isomer in the range of 0.2 -200 μg/ml. The method can also be used in separation and determination of another thirty three aromatic and their halosubstituted compounds. This paper also presents the applications of the method in analysing of complex products mixture from reaction of the selected aromatic compounds with hydrogen chloride on fly ash surface from municipal incinerator.  相似文献   
607.
608.
Bilateral cleft lip and cleft palate can be diagnosed by ultrasonography prior to 20 weeks of pregnancy. The anomaly produces an abnormal facial profile and, on cross-section, the clefts in the maxilla are demonstrable. The method is illustrated by sonograms from a fetus in which the defect was diagnosed before trisomy 13 became known by karyotyping.  相似文献   
609.
610.
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