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   264篇
  免费   3篇
  国内免费   4篇
安全科学   7篇
废物处理   11篇
环保管理   43篇
综合类   13篇
基础理论   82篇
环境理论   1篇
污染及防治   88篇
评价与监测   15篇
社会与环境   8篇
灾害及防治   3篇
  2023年   1篇
  2022年   2篇
  2021年   1篇
  2020年   1篇
  2019年   4篇
  2018年   3篇
  2017年   4篇
  2016年   4篇
  2015年   8篇
  2014年   7篇
  2013年   42篇
  2012年   8篇
  2011年   15篇
  2010年   3篇
  2009年   7篇
  2008年   7篇
  2007年   17篇
  2006年   11篇
  2005年   11篇
  2004年   8篇
  2003年   12篇
  2002年   6篇
  2001年   9篇
  2000年   8篇
  1999年   9篇
  1998年   4篇
  1997年   5篇
  1996年   3篇
  1995年   4篇
  1993年   1篇
  1992年   4篇
  1991年   3篇
  1990年   4篇
  1989年   1篇
  1988年   5篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   4篇
  1983年   5篇
  1982年   5篇
  1981年   1篇
  1980年   2篇
  1976年   3篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1970年   1篇
排序方式: 共有271条查询结果,搜索用时 156 毫秒
131.
More cities in developing countries now consider mechanic village (MV) as superior to the city wide auto-workshop practice following the increasing influx of used or waste automobile from industrialized nations. This is because of the numerous advantages of the mechanic village concept as a capacity building, and in poverty alleviation. Nevertheless, mechanic villages are poorly developed with no waste management plan. They are now identified with severe to excessive heavy metal soil pollution, causing ecological and public health hazards. This paper has a wider explanation of what it takes for a mechanic village to be environmentally friendly based on spectroscopic analysis and physical measurements conducted in three MVs. Heavy metal concentrations (mg kg(?-1)) above background levels in the upper 100 cm soil profiles of the Okigwe, the Orji, and the Nekede MVs in the Imo River basin collectively range 748-70,606 for Fe; 99-1,090 for Pb; 186-600 for Mn; 102-1,001 for Cu; 8-23 for Cd; 4-27 for Cr; and 3-10 for Ni. The most abundant metals of environmental concerns are Pb, Mn, and Cu, in the order of Pb > Mn > Cu. Three-phase storm water treatment, emission testing, minimum safe farming distance (350 m), extended producer responsibility for disposal or recycling of used motor oil, phyto-remediation using local plants, groundwater monitoring wells, and continuous education of mechanics are recommended. Exporters of waste automobiles to developing countries and the United Nations may assist developing countries in establishing environmentally friendly MVs.  相似文献   
132.
Abstract: Wetland development within the United States is regulated primarily by size. Decisions concerning wetland destruction or conservation are therefore based in part on three inherent assumptions: (1) small wetlands contain water for short portions of the year; (2) small wetlands support few species; and (3) species found in small wetlands are also found in larger wetlands. We tested these assumptions using data on wetland size, relative hydroperiod (drying scores), and relative species richness of amphibians in depression wetlands of the southeastern United States. We found a significant (p = 0.03) but weak (r2 = 0.05) relationship between hydroperiod and wetland size and no relationship (p = 0.48) between amphibian species richness and wetland size. Furthermore, synthetic models of lentic communities predict that short-hydroperiod wetlands support a unique group of species. Empirical investigations support this prediction. Our results indicate that hydroperiod length should be included as a primary criterion in wetland regulations. We advocate a landscape approach to wetlands regulation, focused in part on conserving a diversity of wetlands that represent the entire hydroperiod gradient.  相似文献   
133.
134.
135.
Translocations are an important tool for wildlife conservation, although progress in the field of reintroduction biology has been hindered by the ad hoc and opportunistic nature of many translocations. We used an experimental translocation to elucidate the role of raccoon roundworm (Baylisascaris procyonis) and inbreeding depression in the decline of the Allegheny woodrat (Neotoma magister), an endangered species. We translocated woodrats from genetically diverse populations in the core of the species range to 4 previously occupied sites (reintroductions) and 2 sites supporting genetically depauperate populations (reinforcements) in Indiana (U.S.A.). In 2 reintroduction sites and 1 reinforcement site, we distributed anthelmintic baits to passively deworm raccoons and reduce the risk of woodrat exposure to roundworms. The remaining sites served as controls. We used raccoon latrine surveys and fecal flotation to monitor temporal variability in roundworm prevalence and effect of treatment. We used live trapping and microsatellite genotyping to monitor the demographic and genetic response of translocated populations over the following 54 months. At the conclusion of the study, 4 of 6 translocations were successfully maintaining abundance through local recruitment. The distribution of anthelmintic baits reduced levels of roundworm contamination, but levels of contamination were also low in 2 of 3 control sites. Reintroductions failed at control sites, one of which was due to high roundworm exposure. The other failed control reintroduction was likely attributable to demographic stochasticity and limited reproductive potential following initial mortality within the first 4 months. In both control and treatment reinforcements, increases in both allelic richness and heterozygosity were accompanied by increases in abundance, which is suggestive of genetic rescue. Our results demonstrate that mitigation of roundworm exposure through the distribution of anthelmintic baits can facilitate woodrat recovery and that diversity within genetically depauperate populations can be restored through the introduction of a limited number of individuals. El Uso de Reubicaciones Experimentales de Neotoma magister para Descifrar Agentes Causales de Disminución  相似文献   
136.
Despite the plethora of peacebuilding and conflict management institutions operating in Kenya, peace is often elusive in the northern drylands. With a lack of strong conflict management and peacebuilding processes in place from government, despite an active framework for such processes, non-state actors have filled this conflict management space. In this article, we draw on the institutional bricolage and sustainable peace literatures to understand peacebuilding through the frame of legitimacy. Using Laikipia County, Kenya as a case study, we draw on empirical findings which show that different institutions are attributed legitimacy differently. We find that while the Laikipia Professional Peace Caravan was seen as legitimate to pastoralists in conflict areas, its legitimacy was challenged by other practitioners. Similarly, while pastoralists viewed homeguards as legitimate, practitioners did not. The analysis links to discussions of the “business of peace” within the literature to consider why long-term peace has been elusive in Kenya’s northern drylands.  相似文献   
137.
138.
139.
The interest in the identification of volatile organic compounds in the workplace has been a major focus of many National Institute for Occupational Safety and Health (NIOSH) field studies. A primary technique for sampling and analysis of these compounds is summarized by NIOSH Manual of Analytical Methods (NMAM) 2549. This is a screening method that uses a multi-bed sorbent to trap a wide variety of compounds and compound classes. Thermal desorption techniques are used as a first attempt to characterize potential contaminants in a workplace and to determine what future sampling and analyses must be performed. Field examples are provided to show the versatility of thermal desorption methods and techniques. Due to their sensitivity, thermal desorption tube methods are sometimes required in order to measure the workplace concentrations of unusual compounds. In other situations, the exposures are too high or varied to make thermal desorption tubes practical. In these cases, the identification of contaminants with thermal desorption tubes leads to new method developments for the quantification of specific compounds using more conventional solid sorbent-solvent desorption based methods.  相似文献   
140.
The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N2O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N2O emissions 1) elevated NH3 deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO? 3 and NH+ 4 aerosol. Flux measurements of NO and N2O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N2O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH3 concentrations measured by passive diffusion and inference from measurements of the 210Pb inventory of soils under tree canopies compared with open grassland. NO and N2O emissions and KCl-extractable soil NH+ 4 and NO? 3 concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH3 downwind of intensive livestock farms or wet-deposited NH+ 4and NO? 3 in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N2O from these soils increased with both N deposition and KCl extractable NH+ 4, but the relationship between NH+ 4 and N deposition (ln NH+ 4 = 0.62 ln Ndeposition+0.21, r 2 = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N2O fluxes.  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