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   227篇
  免费   15篇
  国内免费   1篇
安全科学   18篇
废物处理   17篇
环保管理   76篇
综合类   29篇
基础理论   54篇
污染及防治   21篇
评价与监测   17篇
社会与环境   8篇
灾害及防治   3篇
  2022年   1篇
  2021年   3篇
  2020年   6篇
  2019年   6篇
  2018年   4篇
  2017年   11篇
  2016年   13篇
  2015年   11篇
  2014年   2篇
  2013年   14篇
  2012年   13篇
  2011年   12篇
  2010年   4篇
  2009年   15篇
  2008年   10篇
  2007年   10篇
  2006年   13篇
  2005年   14篇
  2004年   14篇
  2003年   13篇
  2002年   8篇
  2001年   11篇
  2000年   7篇
  1999年   2篇
  1998年   3篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   4篇
  1988年   1篇
  1987年   4篇
  1984年   3篇
  1983年   1篇
  1979年   1篇
  1973年   1篇
  1963年   1篇
排序方式: 共有243条查询结果,搜索用时 15 毫秒
141.
A Regional Assessment of Windbreak Habitat Suitability   总被引:4,自引:0,他引:4  
The Environmental Monitoring and Assessment Programwas initiated in 1989 by the United StatesEnvironmental Protection Agency to collect, analyze,and report quantitative, statistically unbiasedinformation about the state of the nation'senvironment on a regional basis. During a pilotprogram in Nebraska we measured a habitat suitabilityindex for a probability sample of 40 windbreaks andexpanded the results to estimate the potential valueof windbreaks as wildlife habitat in Nebraska. Theindex estimates the suitability of a windbreak ashabitat for wildlife including breeding birds, smallmammals, and deer. Index values range from zero toone, where a value of one indicates maximal habitatvalue. We estimated that 50% (±13% at 90%confidence) of windbreaks in Nebraska have a habitatsuitability index of 0.25 or less and that nowindbreaks have a suitability index greater than 0.6. Our results indicate that increasing the area ofindividual windbreaks is the most effective way toimprove their value as wildlife habitat. Monitoringwindbreak condition over time would alert wildlifemanagers to changes in the resource that might affectwildlife populations. Because our data were highlyvariable, the power to detect change in habitatcondition between two measurement periods was low. Amuch larger sample would be required to detect smallchanges in habitat condition. Variability may bereduced, and power increased, by carefully andconsistently constructing the sampling frame, keepingdata collection as simple as possible, appropriatelystratifying sample selection, and using a small numberof well-trained data collection teams. However, wesuggest adapting the index for use with aerialphotography in future efforts to evaluate windbreaksas wildlife habitat in extensive areas.  相似文献   
142.
1,2,5,6-Tetrabromocyclooctane (TBCO) is a commercial brominated flame retardant that is employed mainly as an additive in textiles, paints and plastics. Very little is known about its presence or behavior in the environment or its analysis. TBCO can exist as two diastereomers, the stereochemistries of which have not been previously reported. We have named the first eluting isomer, under HPLC conditions, as alpha-TBCO (α-TBCO) and the later eluting isomer as beta-TBCO (β-TBCO) when using an Acquity UPLC BEH C18 column with methanol/acetonitrile/water as the mobile phase. The structural elucidation of these two isomers was accomplished by 1H NMR spectroscopy, GC/MS, LC/MS and X-ray structure determinations. α-TBCO is (1R,2R,5S,6S)-1,2,5,6-tetrabromocyclooctane and β-TBCO is rac-(1R,2R,5R,6R)-1,2,5,6-tetrabromocyclooctane. As with some other brominated cycloaliphatic compounds, TBCO is thermally labile and the isomers easily interconvert. A thermal equilibrium mixture of α- and β-TBCO consists of approximately 15% and 85% of these isomers, respectively. Separation of the two diastereomers, with minimal thermal interconversion between them, is achievable by careful selection of GC-capillary column length and injector temperature. LC/MS analyses of TBCO also presents an analytical challenge due to poor resolution of the isomers on chromatographic stationary phases, and weak intensity of molecular ions (or major fragment ions) when using LC-ESI/MS. Only bromide ions were seen in the mass spectra. APCI and APPI also failed to produce the molecular ion with sufficient intensity for identification.  相似文献   
143.
The fisher (Martes pennanti) has recently recovered from historic extirpations across much of its geographic range. There are at least five explanations for the recovery of the fisher, including changes in the amount of habitat, the suitability of habitat, trapping pressure, societal attitudes toward predators, and climate. We evaluated a recovering fisher population in Ontario to test two conditions we viewed as necessary to support the hypothesis that fisher populations have increased due to an increase in the amount of forested land. First, we tested whether the amount of forested land has increased. Second, we tested whether contemporary fisher abundance (and therefore habitat quality) was related to the amount of forest. Topographic maps showed that the proportion of forested land in the study area had increased by 1.9% per decade since 1934 and 3.3% per decade since 1959, likely as a result of land conversion from agricultural uses. Overall the proportion of the study area that was forested increased from 29% to 40% during 1934 to 1995. Census data from the region indicated that there had been a decline in the amount of land area being farmed during the last 50 years. Recent livetrapping data showed that fisher abundance was positively related to the proportion of landscapes that were forested. Based on our results, we could not reject the hypothesis that an increase in the amount of forested land has contributed to the recovery of fisher populations.  相似文献   
144.
Day-of-week patterns in toxic air contaminants in southern California   总被引:1,自引:0,他引:1  
Day-of-week mean ambient concentrations were computed for six high-cancer-risk toxic air contaminants (TACs): 1,3-butadiene, benzene, acetaldehyde, formaldehyde, carbon tetrachloride (CCl4), and perchloroethylene. Data from six urban sites in southern California, from 1989 through 2001, were analyzed. Graphical displays were used to search for repeated patterns. Benzene and 1,3-butadiene, emitted mainly by mobile sources, exhibit distinctly lower concentrations on Sundays and slightly lower concentrations on Saturdays and Wednesdays. Acetaldehyde and formaldehyde show some trace of a weekly pattern similar to that of benzene and 1,3-butadiene, but the pattern is not strongly marked. Perchloroethylene, used primarily as a dry-cleaning solvent, is also distinctly lower on Sundays. CCl4 does not show a day-of-week pattern.  相似文献   
145.
Governments everywhere are recognising environmental sustainability as a major driver of technological and economic development—with innovative direction being found at the interface of our efforts to become more socially and environmentally sustainable. Rural communities, faced with the pressures of unprecedented change, have an opportunity to embrace the principles of sustainable development, to create a new future at the leading edge of global change—but they need help. They need both knowledge and skills to enable them to self-evaluate and strategically plan, and they need a highly motivated, creative, and coherent community to carry it through. Small Towns: Big Picture is a community development process designed to foster creative, energetic, and collaborative action by five small rural communities in central Victoria—focusing on the development of social, environmental, and economic sustainability indicators. The project bought together artists, researchers and local communities to produce a coherent and shared understanding of the sustainability issues and opportunities. This paper presents Small Towns: Big Picture, focusing specifically on the social dimension and the development of a Community Cohesion indicator through an arts-led community engagement process.  相似文献   
146.
147.
148.
149.
150.
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