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   20639篇
  免费   267篇
  国内免费   213篇
安全科学   643篇
废物处理   848篇
环保管理   3450篇
综合类   2938篇
基础理论   5442篇
环境理论   9篇
污染及防治   5329篇
评价与监测   1297篇
社会与环境   1013篇
灾害及防治   150篇
  2022年   133篇
  2021年   175篇
  2020年   136篇
  2019年   197篇
  2018年   297篇
  2017年   305篇
  2016年   461篇
  2015年   344篇
  2014年   456篇
  2013年   1751篇
  2012年   602篇
  2011年   861篇
  2010年   716篇
  2009年   698篇
  2008年   924篇
  2007年   911篇
  2006年   854篇
  2005年   650篇
  2004年   748篇
  2003年   688篇
  2002年   631篇
  2001年   779篇
  2000年   566篇
  1999年   371篇
  1998年   307篇
  1997年   278篇
  1996年   292篇
  1995年   316篇
  1994年   332篇
  1993年   280篇
  1992年   312篇
  1991年   265篇
  1990年   302篇
  1989年   281篇
  1988年   224篇
  1987年   210篇
  1986年   195篇
  1985年   203篇
  1984年   232篇
  1983年   224篇
  1982年   215篇
  1981年   230篇
  1980年   181篇
  1979年   171篇
  1978年   154篇
  1977年   133篇
  1975年   130篇
  1974年   120篇
  1973年   119篇
  1972年   138篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
42.
43.
44.
45.
The occurrence and impact of psychological contract violations were studied among graduate management alumni (N = 128) who were surveyed twice, once at graduation (immediately following recruitment) and then two years later. Psychological contracts, reciprocal obligations in employment developed during and after recruitment, were reported by a majority of respondents (54.8 per cent) as having been violated by their employers. The impact of violations are examined using both quantitative and qualitative data. Occurrence of violations correlated positively with turnover and negatively with trust, satisfaction and intentions to remain.  相似文献   
46.
20世纪70和80年代,"酸雨"成为一个主要公共政策问题.在加拿大和北欧的斯堪的纳维亚半岛的酸化水体中,生物群落及生境遭到频繁破坏,诸如土著鲑鱼和鳟鱼种群受损乃至灭绝的现象屡见不鲜.  相似文献   
47.
An active capping demonstration project in Washington, D.C., is testing the ability to place sequestering agents on contaminated sediments using conventional equipment and evaluating their subsequent effectiveness relative to conventional passive sand sediment caps. Selected active capping materials include: (1) AquaBlokTM, a clay material for permeability control; (2) apatite, a phosphate mineral for metals control; (3) coke, an organic sequestration agent; and (4) sand material for a control cap. All of the materials, except coke, were placed in 8,000‐ft test plots by a conventional clamshell method during March and April 2004. Coke was placed as a 1.25‐cm layer in a laminated mat due to concerns related to settling of the material. Postcap sampling and analysis were conducted during the first, sixth, and eighteenth months after placement. Although postcap sampling is expected to continue for at least an additional 24 months, this article summarizes the results of the demonstration project and postcap sampling efforts up to 18 months. Conventional clamshell placement was found to be effective for placing relatively thin (six‐inch) layers of active material. The viability of placing high‐value or difficult‐to‐place material in a controlled manner was successfully demonstrated with the laminated mat. Postcap monitoring indicates that all cap materials effectively isolated contaminants, but it is not yet possible to differentiate between conventional sand and active cap layer performance. Monitoring of the permeability control layer indicated effective reductions in groundwater seepage rates through the cap, but also showed the potential for gas accumulation and irregular release. All of the cap materials show deposition of new contaminated sediment onto the surface of the caps, illustrating the importance of source control in maintaining sediment quality. © 2006 Wiley Periodicals, Inc.  相似文献   
48.
49.
Whereas past research has treated co-management of common pool resources as if villagers and project implementing authorities were the only relevant actors, numerous external factors beyond the control of these two partners create barriers to successful co-management. This paper draws on discussions with Forest Department officials to examine the influence of these forces on the outcomes of Joint Forest Management (JFM) in Tamil Nadu, India. An empirical inquiry into the operational aspects of JFM indicates the important roles of political parties, powerful people, and other state institutions and functionaries as well as the flow of foreign funding. Further, the strong demand by local people for socio-economic development interventions as opposed to improvement of degraded forests belittles the role of the Forest Department relative to other departments. Numerous other conditioning factors and relationships are explored. The authors call for reforms in public governance to allow better participation of all the actors involved for this participatory management approach to succeed and sustain.  相似文献   
50.
Childhood-onset spinal muscular atrophy (SMA) is one of the most common neurodegenerative genetic disorders. SMN1 is the SMA-determining gene deleted or mutated in the majority of SMA cases. There is no effective cure or treatment for this disease yet. Thus, the availability of prenatal testing is important. Here we report prenatal prediction for 68 fetuses in 63 Turkish SMA families using direct deletion analysis of the SMN1 gene by restriction digestion. The genotype of the index case was known in 40 families (Group A) but unknown in the remaining 23 families (Group B). A total of ten fetuses were predicted to be affected. Eight of these fetuses were derived from Group A and two of these fetuses were from Group B families. Two fetuses from the same family in Group A had the SMNhyb1 gene in addition to homozygous deletion of the NAIP gene. One fetus from Group A was homozygously deleted for only exon 8 of the SMN2 gene, and further analysis showed the presence of both the SMN1 and SMNhyb1 genes but not the SMN2 gene. In addition, one carrier with a homozygous deletion of only exon 8 of the SMN1 gene was detected to have a SMNhyb2 gene, which was also found in the fetus. To our knowledge, these are the first prenatal cases with SMNhyb genes. Follow-up studies demonstrated that the prenatal predictions and the phenotype of the fetuses correlated well in 33 type I pregnancies demonstrating that a careful molecular analysis of the SMN genes is very useful in predicting the phenotype of the fetus in families at risk for SMA. 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