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   33697篇
  免费   316篇
  国内免费   242篇
安全科学   747篇
废物处理   1346篇
环保管理   4433篇
综合类   6528篇
基础理论   8708篇
环境理论   15篇
污染及防治   7748篇
评价与监测   2164篇
社会与环境   2399篇
灾害及防治   167篇
  2022年   210篇
  2021年   226篇
  2019年   220篇
  2018年   841篇
  2017年   823篇
  2016年   961篇
  2015年   530篇
  2014年   674篇
  2013年   2253篇
  2012年   989篇
  2011年   1761篇
  2010年   1238篇
  2009年   1383篇
  2008年   1671篇
  2007年   1927篇
  2006年   1116篇
  2005年   983篇
  2004年   952篇
  2003年   1012篇
  2002年   946篇
  2001年   1075篇
  2000年   764篇
  1999年   502篇
  1998年   379篇
  1997年   376篇
  1996年   403篇
  1995年   417篇
  1994年   415篇
  1993年   391篇
  1992年   376篇
  1991年   374篇
  1990年   365篇
  1989年   320篇
  1988年   298篇
  1987年   268篇
  1986年   289篇
  1985年   284篇
  1984年   319篇
  1983年   314篇
  1982年   305篇
  1981年   290篇
  1980年   263篇
  1979年   248篇
  1978年   219篇
  1977年   212篇
  1974年   203篇
  1973年   170篇
  1972年   181篇
  1971年   174篇
  1967年   169篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
251.
Summary The labelling of ecofriendly products has been introduced in a number of developed countries to assist in the protection of the environment. Recently, developing countries like India, have introduced the scheme. This paper examines the steps involved in establishing the Indian Ecomark. For the successful implementation of the scheme the effective coordination of a number of agencies is necessary. Consumers, as well as manufacturers, have to be educated in the longterm benefits of the scheme. Initiatives necessary for the successful implementation of Ecomark have been highlighted.Mr S. S. Arvind is a member of faculty at the Centre for Energy, Environment and Technology, at the Administrative Staff College of India. He is currently on secondment to the Centre for Technology Development, Clark University, 950, Main Street, Worcester MA 01610-1477, USA. Mr E.V. Muley is a scientist working for the Ministry of Environment and Forests, Government of India, Paryavaran Bhavan, CGO Complex, Lodi Road, New Delhi 110003, India.  相似文献   
252.
Sequential extraction of metals from solid media is a common analytical tool used in environmental and exploration geochemistry. A number of procedures exist, but without harmonization and standardization, meaningful comparisons are tenuous without baseline data. A newly developed, standardized sequential extraction procedure (optimized BCR) was applied to two contaminated certified reference soils from Montana, US (SRM 2710 and SRM 2711) for Cu, Pb and Zn. Four operationally defined fractions were isolated, acid extractable, reducible, oxidizable, and residual (by aqua regia). Fraction-specific concentrations, percentages and recoveries for Cu, Pb and Zn were used to explore differences between the optimized BCR procedure and three other sequential extraction schemes with published data for SRM 2710 and 2711 (i.e. Tessier scheme, Geological Survey of Canada scheme and the original BCR scheme). Results indicate significant differences between the four schemes, even for schemes that are closely associated (i.e. the original and optimized BCR schemes). Order-of-magnitude fraction-specific concentration differences were observed, especially for Pb in the reducible fraction. Differences between schemes are worrisome because trends varied between metals, between fractions and between reference soils. These data reinforce the need for increased adoption of standardized sequential extraction procedures and further examination of different solid media.  相似文献   
253.
Becker  E. W.  Bier  W.  Ehrfeld  W.  Schubert  K.  Schütte  R.  Seidel  D. 《Die Naturwissenschaften》1976,63(9):407-411
The Science of Nature - The development of reliable manufacturing methods for commercial separation elements, the successful operation of separative stages, and extensive tests performed on plant...  相似文献   
254.
255.
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   
256.
257.
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   
258.
259.
260.
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