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   44874篇
  免费   454篇
  国内免费   566篇
安全科学   1261篇
废物处理   2016篇
环保管理   5587篇
综合类   7207篇
基础理论   12308篇
环境理论   23篇
污染及防治   11143篇
评价与监测   3077篇
社会与环境   3003篇
灾害及防治   269篇
  2022年   410篇
  2021年   393篇
  2020年   318篇
  2019年   361篇
  2018年   974篇
  2017年   996篇
  2016年   1249篇
  2015年   783篇
  2014年   1171篇
  2013年   3310篇
  2012年   1549篇
  2011年   2458篇
  2010年   1846篇
  2009年   1887篇
  2008年   2273篇
  2007年   2504篇
  2006年   1672篇
  2005年   1486篇
  2004年   1339篇
  2003年   1468篇
  2002年   1360篇
  2001年   1659篇
  2000年   1193篇
  1999年   697篇
  1998年   487篇
  1997年   518篇
  1996年   516篇
  1995年   597篇
  1994年   613篇
  1993年   482篇
  1992年   514篇
  1991年   487篇
  1990年   534篇
  1989年   470篇
  1988年   405篇
  1987年   396篇
  1986年   340篇
  1985年   367篇
  1984年   387篇
  1983年   368篇
  1982年   340篇
  1981年   317篇
  1980年   269篇
  1979年   291篇
  1978年   258篇
  1977年   212篇
  1975年   207篇
  1974年   190篇
  1972年   199篇
  1971年   179篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
911.
912.
913.
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   
914.
915.
This paper presents data collected in Europe on 107 prenatal diagnoses of cystic fibrosis (CF) using linked DNA markers. To date, 38 children have been born without CF, as predicted, demonstrating the present rapid move from research to clinical genetic service.  相似文献   
916.
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   
917.
918.
919.
Model oligo esters of terephthalic acid with 1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol have been investigated with regard to their biodegradability in different biological environments. Well-characterized oligomers with weight-average molar masses of from 600 to 2600 g/mol exhibit biodegradation in aqueous systems, soil, and compost at 60°C. SEC investigations showed a fast biological degradation of the oligomer fraction consisting of 1 or 2 repeating units, independent of the diol component used for polycondensation, while polyester oligomers with degrees of polymerization higher than 2 were stable against microbial attack at room temperature in a time frame of 2 months. At 60°C in a compost environment chemical hydrolysis also degrades chains longer than two repeating units, resulting in enhanced degradability of the oligomers. Metabolization of the monomers and the dimers as well by the microorganisms could be confirmed by comparing SEC measurements and carbon balances in a Sturm test experiment. Based on these results degradation characteristics of potential oligomer intermediates resulting from a primary chain scission from copolyesters consisting of aromatic and aliphatic dicarbonic acids can be predicted depending on their composition. These results will have an evident influence on the evaluation of the biodegradability of commercially interesting copolyesters and lead to new ways of tailor-made designing of new biodegradable materials as well.  相似文献   
920.
The biodegradation of aliphatic and aromatic hydrocarbons by natural soil microflora and seven fungi species, including imperfect strains and higher level lignolitic species, is compared in a 90-day laboratory experiment using a natural, not-fertilized soil contaminated with 10% crude oil. The natural microbial soil assemblage isolated from an urban forest area was unable to significantly degrade crude oil, whereas pure fungi cultures effectively reduced the residues by 26-35% in 90 days. Normal alkanes were almost completely degraded in the first 15 days, whereas aromatic compounds (phenanthrene and methylphenanthrenes) exhibited slower kinetics. Aspergillus terreus and Fusarium solani, isolated from oil-polluted areas, produced the more efficient attack of aliphatic and aromatic hydrocarbons, respectively. Overall, imperfect fungi isolated from polluted soils showed a somewhat higher efficiency, but the performance of unadapted, indigenous, lignolitic fungi was comparable, and all three species, Pleurotus ostreatus, Trametes villosus and Coriolopsis rigida, effectively degraded aliphatic and aromatic components. The simultaneous, multivariate analysis of 22 parameters allowed the elucidation of a clear reactivity trend of the oil components during biodegradation: lower molecular weight n-alkanes > phenanthrene > 3-2-methylphenanthrenes > intermediate chain length n-alkanes > longer chain length n-alkanes > isoprenoids approximately 9-1-methylphenanthrenes. Irrespective of the individual degrading capacities, all fungi species tested seem to follow this decomposition sequence.  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