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   859篇
  免费   33篇
  国内免费   11篇
安全科学   45篇
废物处理   28篇
环保管理   181篇
综合类   159篇
基础理论   244篇
环境理论   3篇
污染及防治   150篇
评价与监测   47篇
社会与环境   35篇
灾害及防治   11篇
  2023年   14篇
  2022年   10篇
  2021年   26篇
  2020年   32篇
  2019年   31篇
  2018年   32篇
  2017年   40篇
  2016年   49篇
  2015年   45篇
  2014年   30篇
  2013年   71篇
  2012年   50篇
  2011年   73篇
  2010年   46篇
  2009年   31篇
  2008年   42篇
  2007年   46篇
  2006年   43篇
  2005年   28篇
  2004年   15篇
  2003年   24篇
  2002年   16篇
  2001年   12篇
  2000年   6篇
  1999年   11篇
  1998年   10篇
  1997年   9篇
  1996年   5篇
  1995年   14篇
  1994年   11篇
  1993年   7篇
  1992年   5篇
  1991年   2篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1979年   2篇
  1977年   1篇
  1974年   1篇
  1958年   1篇
排序方式: 共有903条查询结果,搜索用时 31 毫秒
901.
Fractionation and spectroscopic properties of fulvic acid and its extract   总被引:1,自引:0,他引:1  
Ma X  Green SA 《Chemosphere》2008,72(10):1425-1434
Novel results were obtained when a fulvic acid was isolated from Acros humic acid and fractionated by traditional preparative thin-layer chromatography. Eight colorful bands were directly viewed and analyzed showing very different fluorescence and absorption properties. The fluorescence quantum yield of the bands ranged from 2% to 9.4%, significantly higher than that of natural humic substances. An aqueous fulvic acid solution was also extracted with methylene chloride (CH(2)Cl(2)) by continuous liquid-liquid extraction. The CH(2)Cl(2) extract was further fractionated by thin-layer chromatography. Eleven highly fluorescent colorful bands and six weakly fluorescent bands were observed and examined. UV-vis absorption and fluorescence (including 3D matrix) spectra and fluorescence quantum yields revealed that each band still represented a mixture of compounds. Moreover, substantial differences in optical properties were observed among bands. A single band possessed the highest fluorescence quantum yield (6%) and highest specific fluorescence (fluorescence/mass), and accounted for 21% of the total fluorescence of the extract. The mass of individual bands varied from 1.6% to 14.1% of the total materials recovered. Components of all fractions were grouped into 11 fluorophore families according to their maxima on 3D matrix fluorescence spectra. No component is dominant in the whole fulvic acid or extracted portion in terms of optical properties. Over 40 natural products are proposed for model chromophores.  相似文献   
902.
Biodiversity loss is driven by human behavior, but there is uncertainty about the effectiveness of behavior-change programs in delivering benefits to biodiversity. To demonstrate their value, the biodiversity benefits and cost-effectiveness of behavior changes that directly or indirectly affect biodiversity need to be quantified. We adapted a structured decision-making prioritization tool to determine the potential biodiversity benefits of behavior changes. As a case study, we examined two hypothetical behavior-change programs––wildlife gardening and cat containment––by asking experts to consider the behaviors associated with these programs that directly and indirectly affect biodiversity. We assessed benefits to southern brown bandicoot (Isoodon obesulus) and superb fairy-wren (Malurus cyaneus) by eliciting from experts estimates of the probability of each species persisting in the landscape given a range of behavior-change scenarios in which uptake of the behaviors varied. We then compared these estimates to a business-as-usual scenario to determine the relative biodiversity benefit and cost-effectiveness of each scenario. Experts projected that the behavior-change programs would benefit biodiversity and that benefits would rise with increasing uptake of the target behaviors. Biodiversity benefits were also predicted to accrue through indirect behaviors, although experts disagreed about the magnitude of additional benefit provided. Scenarios that combined the two behavior-change programs were estimated to provide the greatest benefits to species and be most cost-effective. Our method could be used in other contexts and potentially at different scales and advances the use of prioritization tools to guide conservation behavior-change programs.  相似文献   
903.
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