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   94107篇
  免费   1227篇
  国内免费   1114篇
安全科学   3847篇
废物处理   3515篇
环保管理   14385篇
综合类   21135篇
基础理论   26769篇
环境理论   73篇
污染及防治   16281篇
评价与监测   5706篇
社会与环境   4154篇
灾害及防治   583篇
  2022年   854篇
  2021年   870篇
  2020年   663篇
  2019年   872篇
  2018年   1238篇
  2017年   1271篇
  2016年   2215篇
  2015年   1845篇
  2014年   2576篇
  2013年   9219篇
  2012年   2370篇
  2011年   2830篇
  2010年   3354篇
  2009年   3500篇
  2008年   2425篇
  2007年   2225篇
  2006年   2537篇
  2005年   2496篇
  2004年   2773篇
  2003年   2612篇
  2002年   2164篇
  2001年   2449篇
  2000年   2042篇
  1999年   1555篇
  1998年   1377篇
  1997年   1370篇
  1996年   1504篇
  1995年   1606篇
  1994年   1486篇
  1993年   1339篇
  1992年   1336篇
  1991年   1310篇
  1990年   1253篇
  1989年   1220篇
  1988年   1065篇
  1987年   1000篇
  1986年   998篇
  1985年   1066篇
  1984年   1163篇
  1983年   1170篇
  1982年   1176篇
  1981年   1099篇
  1980年   938篇
  1979年   935篇
  1978年   830篇
  1977年   721篇
  1976年   639篇
  1975年   610篇
  1973年   652篇
  1972年   648篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
252.
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   
253.
254.
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   
255.
256.
257.
258.
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   
259.
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   
260.
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