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   33396篇
  免费   360篇
  国内免费   303篇
安全科学   1086篇
废物处理   1569篇
环保管理   4443篇
综合类   5350篇
基础理论   8517篇
环境理论   13篇
污染及防治   8265篇
评价与监测   2359篇
社会与环境   2264篇
灾害及防治   193篇
  2023年   159篇
  2022年   299篇
  2021年   368篇
  2020年   218篇
  2019年   281篇
  2018年   498篇
  2017年   516篇
  2016年   798篇
  2015年   576篇
  2014年   960篇
  2013年   2801篇
  2012年   1125篇
  2011年   1494篇
  2010年   1209篇
  2009年   1296篇
  2008年   1541篇
  2007年   1480篇
  2006年   1360篇
  2005年   1192篇
  2004年   1123篇
  2003年   1102篇
  2002年   1035篇
  2001年   1192篇
  2000年   851篇
  1999年   530篇
  1998年   391篇
  1997年   422篇
  1996年   419篇
  1995年   510篇
  1994年   427篇
  1993年   377篇
  1992年   412篇
  1991年   395篇
  1990年   369篇
  1989年   356篇
  1988年   318篇
  1987年   268篇
  1986年   270篇
  1985年   274篇
  1984年   280篇
  1983年   294篇
  1982年   289篇
  1981年   261篇
  1980年   193篇
  1979年   213篇
  1978年   183篇
  1977年   161篇
  1975年   164篇
  1973年   187篇
  1972年   169篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
811.
Classification and distribution of mangrove vegetation are vital information for the proper development of a mangrove management plan. In this study, classification for the mangroves of the district of Kemaman were done using both 1 : 5000 aerial photographs and Landsat TM imageries. The coverage by aerial photographs is limited to the coastal and estuarine areas only. Thus, for areas further upstream of the aerial photo coverage, Landsat TM imageries were used. Analysis of aerial photographs and remote sensing images revealed that the mangroves of Kemaman could be classified into 14 different classes of vegetation. All the 14 classes were identified from areas covered by the aerial photographs. For areas covered by the Landsat images only 7 classes of vegetation were identified. The accuracy for aerial photograph and Landsat images are 91.2% and 87.8%, respectively. It can be concluded that although both techniques are useful in determining the mangrove vegetation classes, the large 1 : 5000 aerial photographs are more accurate and provided more detailed information comparatively.  相似文献   
812.
While many studies and reviews into the practices conducted by industry and academia to recycle and remanufacture carbon fibre-reinforced plastic (CFRP) exist, to date no investigation exists which regards the correctness of the use of the terms recycling and remanufacturing. As such, this paper seeks to analyse the CFRP reuse industry’s attempt to recycle and remanufacture manufacturing waste CFRP and end-of-life (EOL) CFRP with an emphasis on the terminology used to describe these practices. Firstly, this paper presents a justification of the importance of using EOL terminology correctly; outlining the benefits and problems associated with using the correct and incorrect terminology. This paper finds that in the case of CFRP remanufacturing, terminology is being applied incorrectly and in the case of CFRP recycling, particular care should be taken when applying the term recycled to CFRP or stating that CFRP has been recycled. Further, this paper proposes new terminology (in keeping with EU directives) which could be adopted by industry and academia working in this area. This paper also finds that in the case of remanufacture, CFRP is incapable of being remanufactured.  相似文献   
813.
Russian Journal of Ecology - Climate change entails shifts in the ranges of woody plants along both latitudinal and altitudinal gradients in the boreal forest biome. In this study,...  相似文献   
814.
Public perception of flood hazard in two Nigerian cities   总被引:1,自引:0,他引:1  
  相似文献   
815.
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   
816.
817.
818.
819.
820.
Spatial and temporal patterns of predation on seeds of the seagrass Phyllospadix torreyi S. Watson were quantified at four sites near Santa Barbara, California, USA. Over a period of four flowering seasons during 1995 to 1998, monthly patterns of seed fall and intensity of seed predation were similar among sites, but were temporally quite variable. Abundance of dispersed seeds varied greatly both among seasons and years. Within any one year, seeds were present in the environment every month, but they peaked in abundance during the fall months following the annual flowering period. Seeds were more abundant during the earlier years of the study. The intensity of predation steadily increased throughout the study period, from a low of ≤10% seeds consumed during 1995 to ∼50% consumption by 1997, and it was not correlated with abundance of seeds in the environment. Pre-dispersal seed loss also was estimated in two flowering seasons by counting the numbers of seeds consumed prior to release from the plant, and was relatively low (<15%). No differences were detected among the four study sites in patterns of pre-dispersal loss. Field surveys were done at two sites to identify potential seed predators. Three of the most abundant species identified in these surveys were tested in the laboratory to determine size-specific patterns of feeding activity and to assess which early life stages of P. torreyi (fruits within spadices, dehisced fruits, seedlings) were most vulnerable to predation. All three of the early life stages were consumed. The crabs Pugettiaproducta (Randall) and Pachygrapsus crassipes Randall were much more voracious predators than the isopod Idotea resecata Stimpson. Received: 8 June 1999 / Accepted: 2 February 2000  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