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   33659篇
  免费   404篇
  国内免费   315篇
安全科学   1185篇
废物处理   1589篇
环保管理   5055篇
综合类   4820篇
基础理论   8618篇
环境理论   12篇
污染及防治   8278篇
评价与监测   2396篇
社会与环境   2197篇
灾害及防治   228篇
  2023年   150篇
  2022年   279篇
  2021年   358篇
  2020年   223篇
  2019年   293篇
  2018年   488篇
  2017年   535篇
  2016年   805篇
  2015年   617篇
  2014年   934篇
  2013年   2915篇
  2012年   1164篇
  2011年   1545篇
  2010年   1256篇
  2009年   1295篇
  2008年   1611篇
  2007年   1541篇
  2006年   1388篇
  2005年   1215篇
  2004年   1180篇
  2003年   1138篇
  2002年   1070篇
  2001年   1158篇
  2000年   867篇
  1999年   568篇
  1998年   432篇
  1997年   438篇
  1996年   454篇
  1995年   526篇
  1994年   449篇
  1993年   402篇
  1992年   437篇
  1991年   391篇
  1990年   365篇
  1989年   360篇
  1988年   320篇
  1987年   274篇
  1986年   287篇
  1985年   284篇
  1984年   306篇
  1983年   302篇
  1982年   301篇
  1981年   273篇
  1980年   208篇
  1979年   203篇
  1978年   185篇
  1977年   147篇
  1975年   150篇
  1973年   177篇
  1972年   148篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
681.
We examine the contexts and patterns of signature whistle production by wild bottlenose dolphin mother-infant pairs (Tursiops spp.) to gain insight into the functional significance of whistles. Results are based on focal observations and simultaneous recordings of underwater vocalizations. Whistles occur primarily when mother-infant pairs are separated, and the probability of whistles increases with distance of separation. The timing of whistles during separations varies, but whistles tend to be produced in repetitive series and are generally concentrated toward the later stages of the separation, i.e., during the process of reunion. Although we focused on infants, mothers do not appear to whistle during separations as frequently as infants. Infant whistles may function to facilitate reunions by conveying information to the mother concerning the infant's motivation to reunite and/or its location. Infant whistles could induce a cooperative response from the mother including approach, slowing to allow the infant to catch up or whistling. Highly individualized signature whistles may be particularly useful in a fission-fusion society in which individuals (mothers and infants as well as adults) join and leave temporary parties in a fluid manner, yet maintain consistent, long-term associations with particular individuals. Correspondence to: R.A. Smolker  相似文献   
682.
This paper focuses on community-wide emergencies caused by war-related events in Lebanon at the beginning of June 1982. Mobilization for the "Peace for Galilee" campaign began on Friday, 4th June. Overnight, families were disrupted, husbands and sons were in danger, and within 24 hours there were notifications of casualities and deaths. Families in crisis became a widespread phenomenon. In Herzlia, as in many other communities, a new service - the Emergency Center - emerged under the auspices of the Ministry of Labor and Social Affairs and the Municipality. The authors describe this process of getting organized, the populations served, how the Center was staffed, the role of citizen volunteers, and the types of interventions used to help vulnerable families as well as soldiers home on leave. Stress is placed on the unique type of short-term co-operation achieved between social workers of the local Department of Social Welfare, the staff of the Department of Community Services (especially its Volunteer Bureau), the local liason officer of the Israel Defence Force, the municipal government, and public-spirited volunteers. Mention is made of conditions which made possible the activation of such a service within hours, of the Center's capacity to serve all segments of the population, and of how it was deactivated within a few weeks when the emergency ended. On the basis of lessons learned from this experience, the paper ends with a number of specific recommendations. The authors hope that such innovative forms of crisis-intervention will become part of the helping technology widely available at the community level in future years.  相似文献   
683.
684.
This paper examines the effects of congestion on recreational behavior within a household production model of consumer behavior. We assume that congestion affects the household's ability to produce constant quality recreational service flows and derive a reduced-form model for participation decisions in remote and developed camping. Empirical estimates of the effects of a congestion measure on the conditional probability of participation as well as on the level of participation are estimated for each activity by the type of trip using information from the 1972 National Recreation Survey. The findings suggest that congestion was most likely to affect the decision to participate and not the level once that decision had been made. While differences in these effects were observed across the activities studied, it is not clear how they should be interpreted since our congestion measure was a proxy variable likely to perform better for remote camping than developed camping.  相似文献   
685.
This article discusses the problems facing refinery operations in developing countries and possible solutions to them. The topics covered include security of crude oil supply to the developing countries; difficulties encountered in development of indigenous expertise in refinery operation; refinery capacity and the special problems of maintenance and repair facing refinery operators in the developing parts of the world; and the potential for improved refinery operation through increased international co-operation.  相似文献   
686.
687.
Epidemiological procedures can be organised under disaster conditions by means of a simple surveillance system and with few personnel.
In the aftermath of the 4 February 1976 earthquake in Guatemala, an information system was organized by which the requisite information for decision-making was obtained with adequate speed and promptness.
The initial epidemiologic informution was based on reports collected during the early days on symptoms observed at hospitals and health centers and in localities and villages in the stricken area.
At a second, post-emergency stage a more elaborate surveillance system was instituted to provide guidance in the investigntwn of outbreaks, evaluate the health activities and establish basic criteria for preventive and control measures.  相似文献   
688.
689.
690.
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