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   31529篇
  免费   341篇
  国内免费   229篇
安全科学   884篇
废物处理   1188篇
环保管理   4399篇
综合类   6146篇
基础理论   8411篇
环境理论   14篇
污染及防治   7910篇
评价与监测   1801篇
社会与环境   1156篇
灾害及防治   190篇
  2018年   334篇
  2017年   354篇
  2016年   560篇
  2015年   439篇
  2014年   637篇
  2013年   2419篇
  2012年   843篇
  2011年   1209篇
  2010年   937篇
  2009年   1007篇
  2008年   1207篇
  2007年   1269篇
  2006年   1156篇
  2005年   938篇
  2004年   924篇
  2003年   947篇
  2002年   884篇
  2001年   1124篇
  2000年   826篇
  1999年   497篇
  1998年   384篇
  1997年   404篇
  1996年   424篇
  1995年   477篇
  1994年   458篇
  1993年   424篇
  1992年   419篇
  1991年   426篇
  1990年   447篇
  1989年   431篇
  1988年   385篇
  1987年   366篇
  1986年   342篇
  1985年   332篇
  1984年   380篇
  1983年   352篇
  1982年   397篇
  1981年   353篇
  1980年   308篇
  1979年   314篇
  1978年   303篇
  1977年   260篇
  1976年   246篇
  1975年   232篇
  1974年   278篇
  1973年   264篇
  1972年   249篇
  1971年   221篇
  1970年   196篇
  1967年   196篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
731.
A case of spontaneous abortion after transcervical CVS is presented. Despite no evidence of bacteria in the vagina and cervix prior to sampling and the prophylactic use of Metronidazole, pathological evidence of chorioamnionitis was found. The implications of this are discussed.  相似文献   
732.
733.
Reduction in serum requirement for culture of primary human amniotic fluid cells can be achieved by the addition of 10 growth-promoting factors to the nutrient medium. This supplemented medium preserves cell types normally found in amniotic fluid cell cultures supplemented with 20–30 per cent fetal bovine serum. The volume of amniotic fluid required to initiate culture can be as little as 1 ml. Amniotic fluid samples contaminated with red blood cells with no visible clot also grow well in the low serum medium. Cell-free amniotic fluid combined with equal parts of supplemented medium is useful in initiating cell culture.  相似文献   
734.
The effects of reduced oxygen concentrations in the gas phase over the culture medium on colony formation and cell proliferation were investigated in high and low cell density primary and secondary cultures of amniotic fluid cells. Using two standard culture methods (25 cm2 plastic flasks and Leighton type tubes) a significantly reduced culture time was observed at high cell density for mass cultures by incubation within a low oxygen tension gas phase (2.5 per cent to 7.5 per cent O2) instead of conventional air (18 per cent O2). At low cell density colony formation was significantly enhanced in cultures grown at reduced oxygen tension. Using gas permeable membranes as support, lowering the oxygen tension from 7.5 per cent to 2.5 per cent yielded an increase in plating efficiency of cells from approximately 5 per cent to 25 per cent, whereas plating efficiency was less than 2 per cent for cells grown at ambient 18 per cent O2. It is suggested that low oxygen tension in the gas phase is an effective means of enhancing clonal growth in amniotic fluid cell cultures, thereby reducing both culture time and risk of culture failure.  相似文献   
735.
736.
Prenatal diagnosis of Sandhoff disease (infantile onset) at 16 weeks gestation has been made by detection and analysis of N-acetylglucosaminyl-oligosaccharides in amniotic fluid using high performance liquid chromatography. The elution profile for the branched chain oli-gosaccharides was identical with that obtained with neonatal and infantile Sandhoff urine. The concentration of the oligosaccharides in the fluid was 1/100th that of urine but when calculated relative to creatinine the levels were similar. No oligosaccharides were detected in normal control amniotic fluids (10 patients) at a similar gestational age. Based on the levels of the amniotic fluid oligosaccharides and the sensitivity limits of the assay, prenatal diagnosis of patients with the juvenile onset form of the disease may also be possible with this technique.  相似文献   
737.
738.
Tensile water     
Kuppers JR 《American scientist》1973,61(1):10; author reply 10
  相似文献   
739.
At 10 weeks' gestation, chorionic villus biopsy was obtained from a woman at risk for Sanfilippo type C disease. Acetyl-CoA: α-glucosaminide N-acetyltransferase activity was markedly deficient. The pregnancy was terminated at 12 weeks' gestation and follow-up study on fetal fibroblasts confirmed the diagnosis.  相似文献   
740.
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