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   94501篇
  免费   1230篇
  国内免费   1115篇
安全科学   3814篇
废物处理   3404篇
环保管理   14516篇
综合类   21304篇
基础理论   26930篇
环境理论   73篇
污染及防治   16709篇
评价与监测   5638篇
社会与环境   3870篇
灾害及防治   588篇
  2022年   786篇
  2021年   799篇
  2020年   655篇
  2019年   871篇
  2018年   1182篇
  2017年   1224篇
  2016年   2207篇
  2015年   1849篇
  2014年   2593篇
  2013年   9267篇
  2012年   2347篇
  2011年   2767篇
  2010年   3321篇
  2009年   3463篇
  2008年   2363篇
  2007年   2248篇
  2006年   2540篇
  2005年   2464篇
  2004年   2791篇
  2003年   2615篇
  2002年   2199篇
  2001年   2613篇
  2000年   2169篇
  1999年   1581篇
  1998年   1403篇
  1997年   1396篇
  1996年   1522篇
  1995年   1604篇
  1994年   1507篇
  1993年   1349篇
  1992年   1345篇
  1991年   1317篇
  1990年   1259篇
  1989年   1238篇
  1988年   1083篇
  1987年   1002篇
  1986年   1004篇
  1985年   1081篇
  1984年   1171篇
  1983年   1183篇
  1982年   1182篇
  1981年   1104篇
  1980年   951篇
  1979年   937篇
  1978年   833篇
  1977年   730篇
  1976年   658篇
  1974年   630篇
  1973年   656篇
  1972年   671篇
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
271.
272.
This paper examines the relationship between survivor reactions to a downsizing and retention subsequent to a downsizing. We hypothesize that survivors who experience the downsizing as distributively, procedurally, and interactionally just and who see top management as trustworthy will feel more attached to the organization because each reduces the threat inherent in downsizing. In addition, we hypothesize that survivors who feel empowered will also feel more attached to the organization because they feel better able to cope with the downsizing. We further hypothesize that those survivors who feel more attached to the organization following the downsizing will be more likely to remain with the organization in the coming year. The theoretical model is tested on a sample of aerospace employees who survived an organizational downsizing. The trustworthiness of management, distributive justice, procedural justice, and three dimensions of empowerment are found to facilitate more organizational attachment. Higher levels of attachment are found, in turn, to facilitate less voluntary turnover in the year following the downsizing. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
273.
274.
Four microbial isolates, OP2, OP3, OP6, and OP7, of earthworm casts ofPontoscolex corethrurus were found to be acid tolerant actinomycetes and efficient rock phosphate (RP) solubilizers that could grow fast on NH4Cl-enriched or N-free carboxymethyl cellulose or glucose as sole carbon source. CMC (carboxymethyl cellulose) induced production of extracellular cellulase enzyme and the production of reducing sugar in all the isolates. RP solubilizing power was observed to be inversely related to glucose consumption. The most efficient RP solubilizer was found to consume the least glucose. Growth was faster on cellulose than on glucose media. N-free CMC induced greater glucose production than NH4Cl-enriched CMC medium. Both CMC and glucose media were acidified by all the isolates, however, RP solubilizing power decreased with acidification. Solubilization power was greatest with isolate OP7, which also produced the greatest amount of reducing sugar per gram CMC. Both RP solubilizing power and the cellulolytic efficiency varied among isolates. A minimum of 631 μg P/0.1 g RP and a maximum of 951.4 μg P/0.1 g RP was recorded.  相似文献   
275.
276.
277.
278.
Simplicity and efficiency in design and estimation are all important in deciding on sampling strategies. A simple model is given and illustrated for four practical situations to show how a good sampling strategy should be selected.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.  相似文献   
279.
The effectiveness of inorganic alumino-silicate sorbents (alumina and kaolinite) to adsorb airborne lead and cadmium from the effluent stream of a simulated waste incinerator was studied. A 20 kW (68,000 BTU/h) flow reactor was used to achieve the temperature and residence times typical of a waste incinerator. Solutions containing lead or cadmium were introduced yielding airborne metals concentrations between 15 and 150 ppm. Gas samples were drawn into a particle impactor that collected the airborne particles and condensed phase metal aerosols, separating them into ten size ranges from 0.2 μm to greater than 10 μm. Metals to sorbent mass ratios between 0.03 and 1.56 were investigated. Scavenging efficiency increased as the ratio of sorbent to injected metal mass was increased. The scavenging efficiencies were as high as 76% for lead scavenged by kaolinite to as low as 14% for cadmium scavenged by alumina.  相似文献   
280.
This study examines 45 cases of trisomy 13 and 59 cases of trisomy 18 and reports an algorithm to identify pregnancies with a fetus affected by trisomy 13 or 18 by a combination of maternal age fetal nuchal translucency (NT) thickness, and maternal serum free β-hCG and PAPP-A at 11–14 weeks of gestation. In this mixed trisomy group the median MoM NT was increased at 2.819, whilst the median MoMs for free β-hCG and PAPP-A were reduced at 0.375 and 0.201 respectively. We predict that with the use of the combined trisomy 13 and 18 algorithm and a risk cut-off of 1 in 150 will for a 0.3% false positive rate allow 95% of these chromosomal defects to be identified at 11–14 weeks. Such algorithms will enhance existing first trimester screening algorithms for trisomy 21. Copyright © 2002 John Wiley & Sons, Ltd.  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