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 15 毫秒
901.
The effects of waterfall-induced turbulence on the dissolved oxygen concentration of the Passaic River (New Jersey) at two mostly natural waterfalls were observed during a five-month period encompassing high to low temperature and flow. A parameter defined by past investigators as the “deficit ratio” was found to be useful for mathematically describing the results. The Great Falls system showed the deficit ratio to be an inverse function of temperature for all events, with good correlation. A relationship was developed for the Little Falls system under low flow showing the deficit ratio to likewise be an inverse function of temperature and a power function of flow.  相似文献   
902.
Wetlands provide a variety of ecological services, but are attractive sites for many development activities. Between the mid-1950's and mid-1970's about 550,000 acres, or about 0.5 percent, of the vegetated wetlands remaining in the conterminous states were converted to other uses each year. About 80 percent of these losses involved draining and clearing of inland wetlands for agricultural purposes. Recent reductions in national wetland conversion rates are due primarily to declining rates of agricultural drainage and secondarily to government programs that regulate wetlands use. Several governmental policies and programs exist that either encourage or discourage wetland conversions. Section 404 of the Clean Water Act is the major tool for Federal involvement in controlling the conversion of wetlands to other uses. The 404 program, in combination with State regulatory programs, is responsible for reducing annual conversions nationwide by about 50 percent of what is applied for, or 50,000 acres of wetlands per year, primarily through project modifications. Coastal wetlands are reasonably well protected. Inland, freshwater wetlands are generally poorly protected. Efforts to protect wetlands, given a set level of resources, could be improved by categorizing wetlands according to their relative importance and focusing existing wetland programs on high value wetlands.  相似文献   
903.
ABSTRACT: Present guidelines for selecting a method to determine instream flow requirements and evaluating the validity of the results from a particular method are insufficient. This paper contributes to the efforts of researchers to develop a guide and critique for instream flow methods. A review of instreani flow methods and recommendations for their application is supplemented by a summary of a comparison of four independent analyses. The four analyses: the Physical Habitat Simulation System approach of the Instream Flow Incremental Methodology by the U.S. Fish and Wildlife Service, the Montana Method by Tennant, and two methods by Orsborn (Maximum Spawning Area Flow and Maximum Spawning Area) represent resource intensive and simplistic data collection and analysis methods. Each analysis was used to independently determine flows to support spawning by chinook salmon (Oncorhynchus tshawytscha) in Willow Creek, Alaska. Results of these analyses indicate that each method can be used independently or collectively to generate instream flow recommendations, if calibrated to the site or area studied. Once adjusted to the species and basin of interest, methods similar to the Montana and two Orsborn methods should be used to determine flow recommendations for areas where competition for water is minimal. The Instream Flow Incremental Methodology or similar methods should be applied when competition for water is keen or when detailed evaluations of the responses of species/life phases to flow variations are required.  相似文献   
904.
ABSTRACT: The impact of urbanization on stream insect communities was determined by sampling 22 sites in northern Virginia representing a range of human population densities. Watershed development had little effect on the total insect numbers (no./m2), but shifted the taxonomic composition markedly. Relative abundance of Diptera (mainly chironomids) increased at more highly urbanized sites, while most other insect orders including Ephemeroptera (mayflies), Coleoptera (bettles), Megaloptera (dobsonflies), and Plecoptera (stone-flies) decreased. Trichoptera (caddisfiles) exhibited a variable response. Genus diversity and richness (number of genera) were significantly higher in less urbanized streams. Two genera of chironomids were positively correlated with increased urbanization, while 14 other genera (scattered through several orders) were negatively related to human population density. Principal components analysis demonstrated a gradient from more urbanized to less urbanized stations based on generic and order level biological data. Results of this study indicate that watershed urbanization has a major impact on benthic insect communities even in the absence of point source discharges.  相似文献   
905.
The ability to access information for use in decision making is a well-recognized need within the context of management sciences. A similar need exists in order to make effective technical decisions pertaining to environmental resource management. Data bases are the principle vehicle by which scientists, engineers, and resource managers store and access environmental information. An integrated data-base mechanism is essential in order for federal agencies to manage programs such as enforcement of the Canadian Environmental Protection Act (CEPA), state of the environment (SOE) reporting, and the environmental assessment and review process (EARP). A data-base structure and data dissemination mechanism under current development within Environment Canada, Conservation and Protection, Atlantic Region, is presented along with some of its operational benefits and constraints.  相似文献   
906.
This study examined the cognitive effects associated with homesickness. Theoretical explanations of the homesick syndrome suggest a major cognitive component in the form of a loss of concentration as a result of intrusive thoughts of home. Two attentional demand models proposed by Fisher (1989, Homesickness, Cognition and Health. London: Lawrence Erlbaum) are assessed: the ‘demand strength model’ which suggests intensity of homesickness will decrease attentional ability, and the ‘competing demand model’ which suggests degree of commitment to a new environment will be positively related to attentional ability. Students that had relocated to attend university were evaluated for evidence of homesickness using the Dundee Relocation Inventory (Fisher, 1989). Homesick students and relocated students that showed evidence of commitment to their new environment were compared on attentional ability and academic performance. Results suggest that homesickness may reduce ability to concentrate, but that this loss of concentration is not sufficient to cause a marked loss of academic ability.  相似文献   
907.
Central governments are facing increasingly stringent demands to lead the clean-up of public resources. Historically, governments have chosen legislation and regulation to address these concerns and achieved mixed results, but another tool of public policy holds significant promise and is gaining ground in the policy debate: 'green' taxes. The potential of a tax system to mitigate environmental externalities is explored. The theory of pollution tax is reviewed and a comparison of two country cases where taxes have been designed explicitly to reduce industrial effluents and improve the quality of fresh water resources is presented. If structures to approximate social costs are federally mandated and regionally implemented, a comprehensive tax system can constitute an integral part of an effective response to private spoliation of the commons.  相似文献   
908.
This study examined the effects of individual responsibility and communication in a simulated resource management problem. Subjects faced the problem of how to harvest resources from a regenerating pool so as to maximize their individual harvests without overexploiting the pool. One behavioral option open to individuals involved the sacrifice of a harvesting opportunity in order to add to the pool, thereby benefiting the rest of the group. A 2 x 2 factorial design was used to test the effect of this kind of heroism by (1) including a volunteer leader in the group and (2) including the possibility of communication. Results showed communication produced a significant increase in heroism and in group harvest, resulting from better management of the pool. The presence of a leader in a group had no overall effect on group performance. The implications of these findings for current resource management crises are discussed.  相似文献   
909.
Because remediation techniques and technologies are themselves generally viewed as contaminant source by hazardous waste laws and regulations, permits are required to use them, even if it is only to contain or remove a site's principal contaminants. Referring to such major environmental laws as the Clean Air Act, the Clean Water Act, RCRA, TSCA, and CERCLA, this article outlines the steps needed to translate cleanup projects into the appropriate permits.  相似文献   
910.
Summary The Commission of the European Communities' directive on environmental impact assessment (EIA) finally came into force in July 1988. The main provisions of the Directive are described, together with the objectives it is intended to achieve and the key areas where member state legislation will need to be effective if the principal requirements of the Directive are to be properly implemented. These include adequate coverage of projects, sufficient information in EIA studies, and effective consultation and public participation. Most European countries have some experience with EIA but, as illustrated by the UK Channel Fixed Link reports, the quality of the studies undertaken is very variable. Recommendations are made for improvements in practice through more effective diffusion of best practice, better provision and use of EIA guidance, more focused EIA research, more effective consultation and closer collaboration between the different parties involved in the EIA process, and both quantitative and qualitative improvements in EIA training. The results of a recent survey of European EIA training activity indicate growing interest, but further progress in improving the provision of EIA training is needed before the Directive can be effectively implemented.Drs Christopher Wood and Norman Lee have both been involved on various Environmental Impact Assessment (EIA) studies for the European Commission and have written widely on EIA and related topics. Both are Senior Lecturers at the University of Manchester and they are co-Directors of its EIA Centre. Christopher Wood teaches mainly in the Department of Town and County Planning, Norman Lee in the Department of Economics.  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