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   14389篇
  免费   101篇
  国内免费   154篇
安全科学   348篇
废物处理   597篇
环保管理   1572篇
综合类   3239篇
基础理论   3348篇
环境理论   6篇
污染及防治   3597篇
评价与监测   1106篇
社会与环境   761篇
灾害及防治   70篇
  2022年   126篇
  2021年   108篇
  2019年   101篇
  2018年   194篇
  2017年   207篇
  2016年   304篇
  2015年   227篇
  2014年   400篇
  2013年   1038篇
  2012年   450篇
  2011年   586篇
  2010年   470篇
  2009年   526篇
  2008年   566篇
  2007年   578篇
  2006年   540篇
  2005年   494篇
  2004年   454篇
  2003年   458篇
  2002年   433篇
  2001年   595篇
  2000年   372篇
  1999年   261篇
  1998年   147篇
  1997年   165篇
  1996年   171篇
  1995年   190篇
  1994年   180篇
  1993年   130篇
  1992年   164篇
  1991年   173篇
  1990年   168篇
  1989年   141篇
  1988年   156篇
  1987年   96篇
  1986年   128篇
  1985年   127篇
  1984年   122篇
  1983年   114篇
  1982年   120篇
  1981年   120篇
  1980年   87篇
  1979年   99篇
  1978年   101篇
  1976年   92篇
  1974年   104篇
  1972年   87篇
  1971年   85篇
  1967年   100篇
  1964年   92篇
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
911.
ABSTRACT: A study was performed to identify sources of solute loading to the Dirty Devil River and its major tributaries, in southeastern Utah. A primary goal was to determine the contribution of gypsum dissolution to total dissolved solids concentration, and its potential increase in the future if salinity control measures are instituted. Synoptic field data were collected during the low flow period in October 1983. Data were analyzed using the geochemistry models WATEQF and BALANCE to postulate mineral reactions leading to solute loading. Three known sources of solute loading, involving two different geochemical mechanisms, were clearly discernable. Two additional areas of possible gypsum dissolution were located.  相似文献   
912.
ABSTRACT: An index of residential water efficiency - a “W-Index” - can serve as a measure of effectiveness of water conservation features in the home. The index provides a calculated numerical value for each dwelling unit, derived from the number and kind of water-saving features present, including indoor and outdoor water savers and water harvesting or recycling systems. A W-Index worksheet, devised for on-site evaluation of single-family residences in the Tucson, Arizona, region shows that a nonconserving residence with all the water-using features would use 151,000 gallons per year or 148 gallons per capita per day (gpcpd), while the fully conserving model would use 35,300 gallons per year or 35 gpcpd and with water harvesting and graywater recycling systems would have a maximum W-Index of W-160. A Tucson water conservation demonstration home, Casa del Agua, received a rating of W-139, and field tests of about 30 homes in new Tucson subdivisions show values ranging from W-75 to W-100, indicating the incorporation of some water conservation in current new models. By adjustment of some climatic or water-use parameters, the W-Index format can be applied to various types of dwelling units or to other urban areas. The W-Index can be used by individual homeowners or builders to evaluate water efficiency of residential units, or by water providers or water management agencies as a device for promoting and achieving water conservation goals.  相似文献   
913.
A pedestrian safety education film titled And Keep on Looking and aimed at children ages 9 to 12 was evaluated in several cities. The results showed an increase in safe street crossing knowledge among 9- to 12-year-old Connecticut children who viewed the film, and some improvement in safe street crossing behavior among 9- to 12-year-old Seattle, Washington, children. Crash reduction was assessed in a 2-year, citywide field test conducted in Milwaukee. The field test indicated a crash reduction of more than 20% for 9- to 12-year-old children in Milwaukee compared with children in areas surrounding Milwaukee and children in comparison cities.  相似文献   
914.
Traditional bioremediation approaches have been used to treat petroleum source contamination in readily accessible soils and sludges. Contamination under existing structures is a greater challenge. Options to deal with this problem have usually been in the extreme (i.e., to dismantle the facility and excavate to an acceptable regulated residual, or to pump and treat for an inordinately long period of time). The excavated material must be further remediated and cleanfill must be added to close the excavation. If site assessments were too conservative or incomplete, new contamination adulterating fill soils may result in additional excavation at some later date. Innovative, cost-efficient technologies must be developed to remove preexisting wastes under structures and to reduce future remediation episodes. An innovative soil bioremediation treatment method was developed and evaluated in petroleum hydrocarbon contaminated (PHC) soils at compressor stations of a natural gas pipeline running through Louisiana. The in-situ protocol was developed for remediating significant acreage subjected to contamination by petroleum-based lubricants and other PHC products resulting from a chronic leakage of lubricating oil used to maintain the pipeline itself. Initial total petroleum hydrocarbon (TPH) measurements revealed values of up to 12,000 mg/kg soil dry weight. The aim of the remediation project was to reduce TPH concentration in the contaminated soils to a level of <200 mg/kg soil dry weight, a level negotiated to be acceptable to state and federal regulators. After monitoring the system for 122 days, all sites showed greater than 99-percent reduction in TPH concentration.  相似文献   
915.
Campaigns to increase seat belt use have been effective in controlled environments, in small geographic areas, in primary enforcement states, and when conducted in conjunction with the enactment of seat belt legislation. The Thumbs Up project was undertaken to determine if belt use could be facilitated in less advantageous conditions. A 3-month campaign to increase seat belt use was conducted in two sites, each consisting of two Florida counties. At its conclusion, the Thumbs Up project did not yield an overall increase in seat belt use across the two sites. However, observed seat belt use and the number of seat belt citations issued increased significantly in one site. The results are discussed in terms of the two components necessary for a successful campaign: public information and education, and enforcement. Further, recommendations for conducting successful community-based seat belt interventions are offered.  相似文献   
916.
Amid growing concern about the conservation of renewable natural resources, the process, extent and symptoms of their degradation are examined with specific reference to the Upper Pokhara Valley. Based on a household survey, field observations, informal deliberations and land use analysis, the results of this study reveal that forests and grazing land have been subject to increasing degradation caused by demographic, socioeconomic and institutional factors. The intensity of degradation varies by watershed. In particular, rainfed pakho land on steep slopes is under the severe threat of accelerating soil erosion, despite the construction of terraces. This calls for the formulation of a comprehensive natural resource conservation strategy which should be based on a framework comprising an integrated population control programme, planned land use changes and institutional reforms .  相似文献   
917.
Material efficiency improvement saves energy and reduces the consumption of primary resources and reduces the volume of waste. In this article an approach for analysing the potential for material efficiency improvement is proposed and discussed. In this approach the product functions performed by the materials and various improvement measures are taken into account. The potential for material saving and associated energy saving is assessed and evaluated economically. In this paper the approach is tested in an analysis of the potential for material efficiency improvement with respect to plastic packaging in the Netherlands. The technical reduction potential is found to be 34 ± 7% (157 ± 30 ktonne virgin plastics). Realization of this potential would improve the energy efficiency of the lifecycle of plastic packaging by 31% (10 PJ in 1988). From our study we conclude that our approach can indeed be used to investigate the potential for material efficiency improvement. However, a reliable technical and particularly an economical assessment of reduction measures cannot be made until more detailed data become available.  相似文献   
918.
919.
920.
ABSTRACT: Because of its importance and the perceived inability of private sector sources to meet water demands, many countries have depended on the public sector to provide water services for their populations. Yet this has resulted in many inefficient public water projects and in inadequate supplies of good quality and reliable water. Decentralization of water management, including the use of water markets, cannot solve all of these water problems, but it can improve the efficiency of water allocation. When given adequate responsibility and authority, water user associations have effectively taken over water management activities at a savings to tax payers. Moreover, water markets add the potential benefit of improving water efficiency within a sector as well as providing a mechanism for reallocating water among sectors. The key question involves developing innovative mechanisms for reducing the transaction costs of organizing water users and of making water trades. Water rights need to be established which are recorded, tradable, enforceable, and separate from land if markets are to operate effectively. Also, institutions are needed that effectively resolve conflicts over water rights, including third party impacts and water quality concerns.  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