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   107716篇
  免费   1733篇
  国内免费   6753篇
安全科学   4649篇
废物处理   4369篇
环保管理   15453篇
综合类   29121篇
基础理论   29111篇
环境理论   75篇
污染及防治   21744篇
评价与监测   6153篇
社会与环境   4336篇
灾害及防治   1191篇
  2023年   656篇
  2022年   1452篇
  2021年   1324篇
  2020年   1042篇
  2019年   1260篇
  2018年   1641篇
  2017年   1833篇
  2016年   2952篇
  2015年   2795篇
  2014年   3690篇
  2013年   10747篇
  2012年   3567篇
  2011年   4002篇
  2010年   4239篇
  2009年   4368篇
  2008年   3271篇
  2007年   3054篇
  2006年   3320篇
  2005年   3016篇
  2004年   3111篇
  2003年   3097篇
  2002年   2590篇
  2001年   2903篇
  2000年   2558篇
  1999年   2013篇
  1998年   1782篇
  1997年   1715篇
  1996年   1823篇
  1995年   1887篇
  1994年   1713篇
  1993年   1532篇
  1992年   1484篇
  1991年   1392篇
  1990年   1339篇
  1989年   1301篇
  1988年   1120篇
  1987年   1035篇
  1986年   1018篇
  1985年   1091篇
  1984年   1183篇
  1983年   1191篇
  1982年   1191篇
  1981年   1117篇
  1980年   947篇
  1979年   942篇
  1978年   830篇
  1977年   722篇
  1976年   657篇
  1973年   665篇
  1972年   665篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
53.
54.
55.
56.
Early non-invasive fetal sexing is widely available over the Internet, leading to concerns about its possible use for sex selection. The aim of this review is to summarise the results of surveys describing lay attitudes towards sex selection for non-medical reasons to help address or inform such concerns. A search of electronic databases and key journals was supplemented by an Internet search and citation-tracking. Twenty-one quantitative studies were identified. Most were conducted in the US, with five recent studies in the UK and Germany. Most studies found that, overall, people were not in favour of sex selection. However, this varied from 94 to 18%. People may hold more negative attitudes when the method of sex selection is specified, particularly if this involves termination of pregnancy (TOP). Attitudes towards the general availability of sex selection are less negative than those towards personal use. Attitudes were consistently negative in German surveys. Little is known of such attitudes outside the US, the UK and Germany, and how such attitudes may change as new sex selection technologies become available. Studies of use of early non-invasive fetal sexing for sex selection for non-medical reasons are needed to assess the extent to which concerns about usage are justified and to assist in debates on how these might be most appropriately addressed. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
57.
58.
59.
Critical loads offer a unique way of evaluating impacts of acid deposition by quantifying environmental sensitivity. The critical loads of acidity for UK peat soils have been based upon an arbitrary reduction in pH of 0.2 units. This chemical shift needs to be better related to adverse effects on sensitive biological receptors. It is known that effective precipitation pH equates closely to soil solution pH, and the latter is directly linkable to biotic effects of pH change. On continuation of a long-term experiment assessing impacts of simulated acid rain on peat microcosms in a realistic outdoor environment, Calluna vulgaris continued to flourish at acid deposition loads well above the existing critical load. Calluna plants were harvested and analysed, and acid deposition treatments to the microcosms continued to allow natural vegetation to regenerate. A diverse mixture of moorland plants and bryophytes established at acidity treatments well above the existing critical load, and only a very high acid load resulted in no natural regeneration. A critical effective rain pH value of 3.6 is suggested as a basis for setting critical loads. At this pH, Calluna grows well, and a healthy diverse vegetation community re-establishes when harvested. It is suggested that the peat critical load should be set at the acid load that, at any specific site, would result in a mean effective precipitation pH of 3.6.  相似文献   
60.
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