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   1232篇
  免费   42篇
  国内免费   24篇
安全科学   58篇
废物处理   67篇
环保管理   301篇
综合类   154篇
基础理论   326篇
环境理论   4篇
污染及防治   249篇
评价与监测   77篇
社会与环境   53篇
灾害及防治   9篇
  2023年   14篇
  2022年   14篇
  2021年   17篇
  2020年   24篇
  2019年   16篇
  2018年   44篇
  2017年   45篇
  2016年   67篇
  2015年   49篇
  2014年   48篇
  2013年   92篇
  2012年   68篇
  2011年   98篇
  2010年   57篇
  2009年   69篇
  2008年   63篇
  2007年   69篇
  2006年   52篇
  2005年   33篇
  2004年   45篇
  2003年   37篇
  2002年   38篇
  2001年   18篇
  2000年   21篇
  1999年   18篇
  1998年   19篇
  1997年   20篇
  1996年   15篇
  1995年   9篇
  1994年   3篇
  1993年   15篇
  1992年   9篇
  1991年   8篇
  1990年   4篇
  1989年   3篇
  1988年   4篇
  1987年   8篇
  1986年   6篇
  1985年   5篇
  1984年   4篇
  1983年   3篇
  1982年   3篇
  1980年   6篇
  1958年   3篇
  1955年   3篇
  1954年   2篇
  1950年   2篇
  1941年   2篇
  1939年   2篇
  1937年   2篇
排序方式: 共有1298条查询结果,搜索用时 171 毫秒
921.
Carbon dioxide emissions from 1990 to 2100 AD are decomposed into the product of four factors: population size, affluence (measured here as GDP per capita), energy intensity (energy use per unit GDP) and carbon intensity (carbon dioxide emissions per unit energy). These emissions factors are further subdivided into three regions: more developed countries (MDCs), China, and the remaining less developed countries (LDCs). Departures from a baseline scenario (based on IPCC, 1992a — the so-called ‘business-as-usual’ scenario) are calculated for a variety of alternative assumptions concerning the four emissions factors in the three regions. Although the IPCC scenario is called a ‘non-intervention’ scenario, it is shown, for example, that large decreases in energy intensity in China or carbon intensity in MDCs are built into the ‘business as usual’ case — and such large changes vary considerably from region to region. We show what CO2 emissions would look like if each of these four emissions factors projected in the baseline case somehow remained constant at 1990 levels. Certain factors like energy intensity improvements and long-term population growth in LDCs, or GDP growth and carbon intensity improvements in MDCs, are shown to have a big contribution to cumulative global emissions to 2100 AD, and consequently, changes in these projected factors will lead to significant deviations from baseline emissions. None of the scenarios examined in this analysis seems to indicate that any one global factor is clearly dominant, but cultural, economic, and political costs or opportunities of altering each factor may differ greatly from country to country.  相似文献   
922.
923.
924.
本文研究了有关坦桑尼亚珊瑚礁环境不同方面的类珊瑚虫(刺胞动物门,珊瑚虫纲)的分布和丰度.通过设线截距横切和点取标技术,调查了受到人类不同骚扰程度的5种礁.  相似文献   
925.
 Wild rabbits of the two sexes have separate linear rank orders, which are established and maintained by intensive fights. The social rank of individuals strongly influence their fitness: males and females that gain a high social rank, at least at the outset of their second breeding season, have a much higher lifetime fitness than subordinate individuals. This is because of two separate factors: a much higher fecundity and annual reproductive success and a 50% longer reproductive life span. These results are in contrast to the view in evolutionary biology that current reproduction can be increased only at the expense of future survival and/or fecundity. These concepts entail higher physiological costs in high-ranking mammals, which is not supported by our data: In wild rabbits the physiological costs of social positions are caused predominantly by differential psychosocial stress responses that are much lower in high-ranking than in low-ranking individuals. Received: 23 February 1999 / Accepted: 17 March 1999  相似文献   
926.
IntroductionThefrequencyofaccidentaloilspills,andtheassociatedaquaticpollution,aregrowingconcerns.Thereisaneedformodelsystemth?..  相似文献   
927.
928.
929.
Ammonium is an important nutrient in primary production; however, high ammonium loads can cause eutrophication of natural waterways, contributing to undesirable changes in water quality and ecosystem structure. While ammonium pollution comes from diffuse agricultural sources, making control difficult, industrial or municipal point sources such as wastewater treatment plants also contribute significantly to overall ammonium pollution. These latter sources can be targeted more readily to control ammonium release into water systems. To assist policy makers and researchers in understanding the diversity of treatment options and the best option for their circumstance, this paper produces a comprehensive review of existing treatment options for ammonium removal with a particular focus on those technologies which offer the highest rates of removal and cost-effectiveness. Ion exchange and adsorption material methods are simple to apply, cost-effective, environmentally friendly technologies which are quite efficient at removing ammonium from treated water. The review presents a list of adsorbents from the literature, their adsorption capacities and other parameters needed for ammonium removal. Further, the preparation of adsorbents with high ammonium removal capacities and new adsorbents is discussed in the context of their relative cost, removal efficiencies, and limitations. Efficient, cost-effective, and environmental friendly adsorbents for the removal of ammonium on a large scale for commercial or water treatment plants are provided. In addition, future perspectives on removing ammonium using adsorbents are presented.  相似文献   
930.
ABSTRACT: This paper presents an analysis of the effects of different institutional arrangements and economic environments on water markets. Characteristics of water rights transfers in the South Platte Basin of Colorado and transfers of shares of the Northern Colorado Water Conservancy District (NCWCD) are compared to show how different institutional arrangements can affect the types and size distributions of transfers. The characteristics of water rights transfers in the prosperous South Platte are then compared with water rights transfer characteristics in the economically marginal Arkansas River basin of Colorado to identify the effects of different economic environments. Finally, the economic losses from reductions in irrigated acreage resulting from water transfers are estimated for the South Platte and Arkansas and compared with purchase prices by municipalities. Transfers in the South Platte were to new uses in the same basin, while more recent transfers in the Arkansas were to out of basin users. Transfers of South Platte rights and especially NCWCD shares were small and continuous over time, while transfers in the Arkansas were dominated by a few very large transfers. The negative impacts are judged to be more severe in the Arkansas basin than in the South Platte. Purchase prices paid by municipalities substantially exceeded capitalized transitional losses in the selling areas. In the South Platte, gains and losses were in the same basin, while the Arkansas absorbed the losses, with the benefits going to the purchasing basin.  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