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   251922篇
  免费   16118篇
  国内免费   35972篇
安全科学   23587篇
废物处理   11623篇
环保管理   29081篇
综合类   102867篇
基础理论   47638篇
环境理论   211篇
污染及防治   50493篇
评价与监测   16528篇
社会与环境   15005篇
灾害及防治   6979篇
  2024年   626篇
  2023年   3283篇
  2022年   8992篇
  2021年   9049篇
  2020年   8653篇
  2019年   6789篇
  2018年   7929篇
  2017年   9242篇
  2016年   9220篇
  2015年   9091篇
  2014年   11365篇
  2013年   20929篇
  2012年   16095篇
  2011年   18033篇
  2010年   15779篇
  2009年   15579篇
  2008年   15973篇
  2007年   15671篇
  2006年   14583篇
  2005年   11284篇
  2004年   8707篇
  2003年   7662篇
  2002年   6805篇
  2001年   6212篇
  2000年   5266篇
  1999年   3608篇
  1998年   2432篇
  1997年   2202篇
  1996年   2237篇
  1995年   2311篇
  1994年   2029篇
  1993年   1501篇
  1992年   1511篇
  1991年   1365篇
  1990年   1254篇
  1989年   1146篇
  1988年   1016篇
  1987年   907篇
  1986年   861篇
  1985年   870篇
  1984年   895篇
  1983年   824篇
  1982年   920篇
  1981年   819篇
  1980年   628篇
  1979年   686篇
  1978年   585篇
  1977年   513篇
  1975年   467篇
  1974年   461篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
In vitro investigations of the influence of lindane and its metabolites were performed on microsomal and mitochondrial ATPases from liver, kidney and brain of rat and mouse. The microsomal Na+-K+-ATPases in rat liver were inhibited by the tested substances. An increase of activity was observed only with 2.5 X 10(-5) M gamma-HCH. Effects on the microsomal Na+-K+-ATPase from kidney and brain of rat were also indicated. The mitochondrial enzyme in rat liver was stimulated by all the compounds tested at concentrations of 10(-4) M - 10(-2) M. The effects on mitochondrial enzymes from kidney and brain varied in dependence on the tested substances. In the microsomes and mitochondria of mouse an influence on the Na+-K+-ATPases similar to the effects on the preparations from organs of rat was evident.  相似文献   
252.
The purpose of this paper is to analyse the recent behaviour of the US zinc processing industry and the impact of US government policies on it. The first section of the paper is a discussion on the basic structure and conditions of the US zinc processing industry since 1950 and how they have changed. The discussion contains a general presentation of the US zinc market, a detailed look at the behaviour of individual primary zinc processing plants in the USA, Canada, Japan and Western Europe and an analysis of US government policies and their impacts on the US zinc industry. The second section of the paper is a discussion of the factors that have contributed to the decline in US zinc processing capacity and the type of government policy that should be followed in response.  相似文献   
253.
A new, simple method for directly measuring activated sludge density was developed and applied, and the effects of biomass density on activated sludge settling in full-scale systems were evaluated. The driving force of sedimentation is the physical weight of the biological solids, but the role of biomass density in sedimentation has been largely ignored. Biomass density varied amongst treatment systems and this variability was correlated with settleability. Floc densities were approximately normally distributed within individual samples. Nonsoluble phosphorus content was a major contributor to density, and plants with enhanced biological phosphorus removal (EBPR) configurations generally had higher densities and better settleability than non-EBPR plants with similar filament contents. These results suggest that future work may benefit from consideration of density as a factor affecting activated sludge settling.  相似文献   
254.
255.
In the high technology industry, small and medium sized technology enterprises (SMSTEs) play a pivotal role in advancing the whole industry. To achieve sustainable development, they need to extend their scope of business activities beyond a national view and exploit international market actively to meet international competitions that increase quickly in the form of allocating resources within the scope of the world. However, the SMSTEs are also facing risks associated with themselves during the process of exploiting international market owing to their own restrictions, so what they should do is to consider risk evaluations in exploiting the international market.  相似文献   
256.
257.
258.
Abstract:  We surveyed shallow, rocky reefs in southwestern Apulia (Mediterranean Sea) to assess the effects on coastal fish assemblages of the date mussel (  Lithophaga lithophaga ) fishery, an illegal practice that strips the rocky reef bare. We visually sampled fish four times over 15 months at three locations, one affected by date-mussel fishery and two controls. The fish assemblage at the affected location differed significantly from those at the control locations over all sampling times. Herbivorous fishes, sparids, and labrids (genus Symphodus ) contributed most to the differences between the affected location and controls. Lower densities of Symphodus spp. were observed at the affected location, whereas detritivorous fishes were recorded exclusively at control sites. Small serranids and sparids showed temporal trends that differed between the affected location and the control locations. Our results suggest that the date-mussel fishery affects fish assemblages chiefly through reduction of arborescent macroalgae (contributing to habitat complexity and primary production) and emphasize the need for more effective policing against this destructive practice.  相似文献   
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