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   26146篇
  免费   293篇
  国内免费   219篇
安全科学   760篇
废物处理   973篇
环保管理   3643篇
综合类   4851篇
基础理论   6723篇
环境理论   17篇
污染及防治   6424篇
评价与监测   1611篇
社会与环境   1459篇
灾害及防治   197篇
  2022年   214篇
  2021年   216篇
  2020年   171篇
  2019年   220篇
  2018年   343篇
  2017年   375篇
  2016年   521篇
  2015年   445篇
  2014年   606篇
  2013年   2108篇
  2012年   791篇
  2011年   1062篇
  2010年   865篇
  2009年   993篇
  2008年   1092篇
  2007年   1100篇
  2006年   1006篇
  2005年   858篇
  2004年   782篇
  2003年   816篇
  2002年   748篇
  2001年   957篇
  2000年   714篇
  1999年   428篇
  1998年   308篇
  1997年   322篇
  1996年   351篇
  1995年   377篇
  1994年   373篇
  1993年   347篇
  1992年   327篇
  1991年   351篇
  1990年   338篇
  1989年   309篇
  1988年   257篇
  1987年   228篇
  1986年   256篇
  1985年   240篇
  1984年   251篇
  1983年   261篇
  1982年   260篇
  1981年   251篇
  1980年   232篇
  1979年   243篇
  1978年   168篇
  1977年   183篇
  1975年   136篇
  1974年   161篇
  1973年   152篇
  1972年   159篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
211.
The paper focuses upon the organization of a federal state-funded pollution prevention project in the Styrian industry. The project includes 13 companies from the textile, pulp and paper, machine building, wood working and printed circuit board manufacturing industries, covering most of the sectors and sizes in the Styrian industry. It started in January 1994 and will last for one year. It will demonstrate the possibilities of pollution prevention and the need for further research work. This project will make use of the methods and tools that were refined in the Austrian Prepare project. As a first step, a systematic balance of all the inputs and outputs of a company is made, after which the weak points and inefficiencies of material and energy use are identified and the options for improvements, both economical and ecological, are defined. Consequently, modifications in products and production lead to a situation with less waste and emissions. The preliminary lessons from these projects are presented: as a rule, the utilities (consumption of process materials and water, cleaning, energy, preparatory and finishing steps) are treated as black boxes and usually represent a considerable optimization potential. In these areas especially there is usually a lack of information and coordination as well as a need for a systematic and comprehensive approach. Leadership in the company and creative consultants are needed for starting lasting successful pollution prevention projects.  相似文献   
212.
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   
213.
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   
214.
215.
Forchhammer  K.  Böck  A. 《Die Naturwissenschaften》1991,78(11):497-504
The importance of selenium as an essential trace element has progressively emerged during the last years due to the analysis of selenium deficiency diseases and to the identification and characterization of a number of selenoenzymes. Selenium is incorporated in the catalytic site of the enzymes as an integral selenocysteine residue. The pathway of selenocysteine biosynthesis and incorporation has been elucidated recently for Escherichia coli. This article presents an overview on these subjects and describes the mechanisms which confer selenocysteine specificity in the framework of protein biosynthesis. In addition, some considerations concerning the phylogeny of selenocysteine incorporation are presented and a model for the evolution of the selenocysteine pathway is proposed.  相似文献   
216.
217.
218.
219.
220.
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