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   38740篇
  免费   422篇
  国内免费   303篇
安全科学   1116篇
废物处理   1315篇
环保管理   5439篇
综合类   7245篇
基础理论   10630篇
环境理论   27篇
污染及防治   9871篇
评价与监测   2113篇
社会与环境   1465篇
灾害及防治   244篇
  2021年   229篇
  2019年   272篇
  2018年   474篇
  2017年   470篇
  2016年   690篇
  2015年   595篇
  2014年   801篇
  2013年   2843篇
  2012年   1052篇
  2011年   1566篇
  2010年   1249篇
  2009年   1315篇
  2008年   1558篇
  2007年   1631篇
  2006年   1476篇
  2005年   1213篇
  2004年   1213篇
  2003年   1179篇
  2002年   1142篇
  2001年   1520篇
  2000年   1053篇
  1999年   699篇
  1998年   528篇
  1997年   528篇
  1996年   577篇
  1995年   589篇
  1994年   568篇
  1993年   512篇
  1992年   536篇
  1991年   499篇
  1990年   517篇
  1989年   538篇
  1988年   460篇
  1987年   416篇
  1986年   387篇
  1985年   422篇
  1984年   395篇
  1983年   430篇
  1982年   435篇
  1981年   390篇
  1980年   354篇
  1979年   375篇
  1978年   337篇
  1977年   285篇
  1976年   299篇
  1975年   262篇
  1974年   283篇
  1973年   269篇
  1972年   289篇
  1970年   223篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
311.
312.
Part of the work was supported by the Bundesministerium für Forschung und Technologie, the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and from the Carl Zeiss, Hoechst, and Ernst Leitz companies. Special thanks are due to Dr. K. Wahn, Department of Virology, University of Giessen, for conducting the electron microscope and phase-contrast investigations, to Prof. G. Sauer, German Cancer Research Center, Heidelberg, and Dr. W. R. Willems, Department of Medical Virology, University of Giessen, for supplying the different cell lines.  相似文献   
313.
The distribution of actinomycetes in oil contaminated sandy loam ultisols of the Niger Delta region of Nigeria was studied to aid in understanding the effect of hydrocarbons on indigenous microbial population in tropical soils. The average total counts of actinomycetes in all the oil samples analysed was 103 cfu/g. Higher counts of actinomycetes were observed during the dry season than during the wet season. The counts of hydrocarbonoclastic actinomycetes correlated positively with the total count of actinomycetes.The actinomycetes were generally restricted to the top soil(0-10 cm soil depth) although a seemingly deeper(down to 40 cm soil depth) distribution was noticed in the dry season. The isolates included oil degrading species of Actinoplanes, Norcadia,Streptomyces and Streptosporangium. Their high oil utilization ability indicates their positive potential and role in the bioremediation of oil-spilled soils.  相似文献   
314.
The biological activity of the Matsucoccus spp. sex pheromones and diene modified analogs has been tested in forests of Israel and Portugal in order to explore the structure-activity relationship of the pine bast scale pheromone/kairomone system. The response of the adult predatory bugs, Elatophilus hebraicus and E. crassicornis and of the brown lacewing, Hemerobius stigma is more selective than that of the conspecific Matsucoccus males. The removal of the terminal methyl group from the diene terminus of both pheromones 1 and 2 eliminates all kairomonal activity but retains moderate pheromonal activity. Addition of a methyl group to the diene terminus of pheromones 1 and 2 sustains full pheromonal and kairomonal activities of the Elatophilus spp. but eliminates entirely the kairomonal activity of H. stigma. Subtle designed alterations in the structure of the diene group, typical of all Matsucoccus pheromones, change the mode of the kairomonal activity markedly.  相似文献   
315.
316.
317.
318.
Rabenau  A.  Schulz  Heinz  Stoeger  W. 《Die Naturwissenschaften》1976,63(5):245-245
The Science of Nature -  相似文献   
319.
320.
This study uses an integrative approach to study the water-quality impacts of future global climate and land-use changes. In this study, changing land-use types was used as a mitigation strategy to reduce the adverse impacts of global climate change on water resources. The climate scenarios were based on projections made by the Intergovernmental Panel on Climate Change (IPCC) and the United Kingdom Hadley Centre's climate model (HadCM2). The Thornthwaite water-balance model was coupled with a land-use model (L-THIA) to investigate the hydrologic effects of future climate and land-use changes in the Ohio River Basin. The land-use model is based on the Soil Conservation Service's curve-number method. It uses the curve number, an index of land use and soil type, to calculate runoff volume and depth. The ArcView programming language, Avenue, was used to integrate the two models into a geographic information system (GIS). An output of the water-balance model, daily precipitation values adjusted for potential evapotranspiration, served as one of the inputs into the land-use model. Two watersheds were used in the present study: one containing the city of Cincinnati on the main stem of the Ohio River, and one containing the city of Columbus on a tributary of the Ohio River. These cities represent two major metropolitan areas in the Ohio River Basin with different land uses experiencing different rates of population growth. The projected hypothetical land-use changes were based on linear extrapolations of current population data. Results of the analyses indicate that conversion from agricultural land use to low-density residential land use may decrease the amount of surface runoff. The land-use practices which generate the least amount of runoff are forest, low-density residential, and agriculture; whereas high-density residential and commercial land-use types produce the highest runoff. The hydrologic soil type present was also an important factor in determining the amount of runoff and non-point-source pollution. A runoff-depth matrix and total nitrogen matrix were created for Cincinnati and Columbus to describe possible land-use mitigation measures in response to global climate change. The differences in Cincinnati and Columbus were due to differences in geographic location, air temperature, and total runoff. The results of this study may be useful to planners and policy makers for defining the possible impacts of future global climate and land-use changes on water resources.  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