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   4819篇
  免费   170篇
  国内免费   134篇
安全科学   169篇
废物处理   43篇
环保管理   1326篇
综合类   1991篇
基础理论   356篇
环境理论   19篇
污染及防治   332篇
评价与监测   647篇
社会与环境   215篇
灾害及防治   25篇
  2023年   29篇
  2022年   39篇
  2021年   62篇
  2020年   169篇
  2019年   73篇
  2018年   74篇
  2017年   129篇
  2016年   151篇
  2015年   124篇
  2014年   193篇
  2013年   253篇
  2012年   178篇
  2011年   328篇
  2010年   171篇
  2009年   299篇
  2008年   238篇
  2007年   246篇
  2006年   238篇
  2005年   121篇
  2004年   145篇
  2003年   202篇
  2002年   187篇
  2001年   186篇
  2000年   214篇
  1999年   181篇
  1998年   156篇
  1997年   156篇
  1996年   93篇
  1995年   65篇
  1994年   83篇
  1993年   76篇
  1992年   54篇
  1991年   31篇
  1990年   15篇
  1989年   21篇
  1988年   18篇
  1987年   10篇
  1986年   21篇
  1985年   14篇
  1984年   18篇
  1983年   7篇
  1982年   11篇
  1981年   6篇
  1980年   7篇
  1979年   7篇
  1978年   12篇
  1977年   7篇
  1974年   3篇
  1972年   1篇
  1971年   1篇
排序方式: 共有5123条查询结果,搜索用时 676 毫秒
611.
ABSTRACT: Decisionmaking associated with the Nation's 1.7 billion acres of forest and range land has become increasingly complicated because of the rise in competition for resource use and in the awareness of environmental and social effects. This system analysis approach uses four models to synthesize pertinent masses of information into measures of economic, environmental, and social impacts. The system results can be used to help evaluate alternative national programs. The models are:
612.
Because of the nature of watersheds, the hydrologic and erosional impacts of logging and related road-building activities may move offsite, affecting areas downslope and downstream from the operation. The degree to which this occurs depends on the interaction of many variables, including soils, bedrock geology, vegetation, the timing and size of storm events, logging technology, and operator performance. In parts of northwestern California, these variables combine to produce significant water quality degradation, with resulting damage to anadromous fish habitat.Examination of recent aerial photographs, combined with a review of public records, shows that many timber harvest operations were concentrated in a single 83 km2 watershed in the lower Klamath River Basin within the past decade. The resulting soil disturbance in this case seems likely to result in cumulative off-site water quality degradation in the lower portion of the Basin.In California, both state and federal laws require consideration of possible cumulative effects of multiple timber harvest operations. In spite of recent reforms that have given the state a larger role in regulating forest practices on private land, each timber harvest plan is still evaluated in isolation from other plans in the same watershed. A process of collaborative state-private watershed planning with increased input of geologic information offers the best long-term approach to the problem of assessing cumulative effects of multiple timber harvest operations. Such a reform could ultimately emerge from the ongoing water quality planning process under Section 208 of the amended Federal Water Pollution Control Act.  相似文献   
613.
To document environmental impact predictions for land development, as required by United States government regulatory agencies, vegetation studies are conducted using a variety of methods. Density measurement (stem counts) is one method that is frequently used. However, density measurement of shrub and herbaceous vegetation is time-consuming and costly. As an alternative, the Braun-Blanquet cover-abundance scale was used to analyze vegetation in several ecological studies. Results from one of these studies show that the Braun-Blanquet method requires only one third to one fifth the field time required for the density method. Furthermore, cover-abundance ratings are better suited than density values to elucidate graphically species-environment relationships. For extensive surveys this method provides sufficiently accurate baseline data to allow environmental impact assessment as required by regulatory agencies.  相似文献   
614.
Whenever a short-term or local need in the exploitation of a scarce natural resource must be pitted against its long-term use or the needs of the larger community, the commons dilemma arises. The study of commons dilemmas originated in agricultural economies but has importance in all resource management areas. Psychologists have recently found it to be a useful paradigm in the study of decision-making behavior.This paper reviews the commons dilemma as it has been used in three areas of psychological research: games theory, animal and human territorial behavior, and behavior reinforcement. In the first area, results show how communication within groups operates in cooperation/competition situations. In the second, the effects of social and political ideologies are examined. In the third, the implications of the commons dilemma with regard to breaking out of social traps are discussed. Throughout, the relevance of this basic psychological research to rational resource management is made clear. An extensive bibliography of relevant original research is provided.  相似文献   
615.
ABSTRACT: Most of California's precipitation falls at the wrong place in the wrong season in relation to the water needs. Redistribution and regulation are essential. Aquifer systems – groundwater basins – can provide a share of the future cyclic storage regulation. There are some differences in management concepts in using a full basin in comparison with a partially dewatered basin. Legal, water quality, and physical impacts on aquifer systems, including subsidence, are concerns. Storage may be for the benefit of overlying water users or for distant areas. Extraction during dry periods or recharge methods will require careful planning. Existing rights and uses and equitable treatment of all parties must be assured. Financial compensation may be involved. Changes in methods of operation or degree of self-determination by affected water agencies will require committed watermanship to resolve. Legislation or amendments to organic acts may be needed but much can be accomplished within existing statutes. Environmental impacts which can be avoided by not using large surface storage sites are important. Energy for pumping will be a key consideration. About 40 percent of California is underlain by aquifer systems. This resource offers major potential in overcoming the maldistribution of natural water resources.  相似文献   
616.
New concepts and insights concerning human and natural systems in the coastal zone are emerging from recent energy analysis and synthesis studies. By using new concepts for measuring the quality of energy, one can express the work of ecosystems and human economies in equivalent terms. From energy models and new energy quality evaluations, one can learn what kinds of coastal systems maximize power, are competitive, economically vital, and likely to have a survival advantage.Energy analysis and synthesis is aided by energy circuit diagrams. Models of the coastal zone that emphasize the change in external driving functions related to world energy sources provide insights and some predictive abilities that are not found in economic studies, since money flows alone do not evaluate external driving energies.This paper suggests four procedures for coastal planning: 1) calculation of investment ratio in units of equal quality to determine which projects are economic in a broad sense, 2) development of energy signatures for coastal ecosystems, 3) determination of which interface ecosystems develop the best energy flows, and 4) development of regional models that include the main features of human and natural ecosystems.  相似文献   
617.
Irreversible environmental changes are occurring along the Colorado River in the Grand Canyon as a result of regulation of the river flow by the Glen Canyon Dam. The questions of primary importance in managing this great natural resource are 1) in what manner and how rapidly are the physical and ecological adjustments taking place, and 2) is the increased use of the river for recreational boating contributing to the degradation? Human use along the Colorado River is limited, for the most part, to the relic, pre-dam fluvial deposits colloquially called “beaches.” With the new river regime these deposits are positioned well above the present high-water stage, 27,000 cubic feet/second (cfs), or 765 cubic meters/second (cms), so they are not replenished periodically as they were prior to construction of the dam in 1963. The dominant natural processes now are aeolian sand transport and mass wasting. The float-trip passengers use the river beaches for hiking, camping, and. lunch stops. At the most desirable sites thirty to forty people camp on the beaches each night over a four to five month season. Human impact includes incorporation of campsite litter, burial of chemically treated waste, and the direct stress associated with people walking on the vegetation and unstable sedimentary deposits. Results of our investigations indicate that the rate of degradation at the most heavily used sites exceeds the capacity of aeolian processes to reestablish natural landscapes. Therefore, careful management of float trjps is needed if these environments are to be maintained in a natural state rather than a “sand-box” state.  相似文献   
618.
ABSTRACT: The environmental effects of flood control channel modifications such as clearing and snagging, straightening, enlargement, and/or paving can be quite severe in some cases. Information review reveals that several environmental features have been incorporated into the design, construction, operation, or maintenance of recent flood control channel projects to avoid adverse environmental impacts and enhance environmental quality. Typically, these features have been proposed by conservation agencies and designed with minimal quantitative analysis. Environmental features for channel projects include selective clearing and snagging techniques, channel designs with nonuniform geometry such as single bank modification and floodways, restoration and enhancement of aquatic habitat, improved techniques for placement of excavated material, and revegetation.  相似文献   
619.
ABSTRACT: The major objectives are (1) to identify the problems involved in measuring the environmental impacts of public projects from selected perspectives, and (2) to elaborate a sociological approach used in an empirical investigation in that respect. The construct of environmental impact of a planned action is generally operationalized from different perspectives and with different methodological emphases in the various disciplines. Even the term environment does not elicit agreement among users as to its exact meaning. Although there has been a steady increase in the number of studies from a sociological perspective concerning environmental problems, there is lack of sociological counsel in writing environmental impact statements. Overall, we lack sociological methodology and operational procedures for that purpose. In an attempt to bring some empirical focus to this field, attitudinal measures employed to discover how residents of a river basin perceived negative and positive environmental impacts of a proposed watershed development project are reviewed. These come from a study of creation of the Cooper Reservoir and Dam in Texas. Data on 343 heads of households m the selected areas were collected through structured questionnaires with items on personal information, a vested interest scale, a knowledge of the project scale, and an environmental impact scale. Data show that perception of impacts by residents is influenced significantly by degree of their vested interests involved. Variables for inclusion in a sociological model of environmental impact are suggested.  相似文献   
620.
应用多目标决策中的TOPSIS法(即逼近于理想解的排序方法)对湖南长沙等十城市的大气环境质量进行评价,并与欧几里德贴近度法和上海指数法相比较,认为该评价方法对比较多个城市(或多个监测点,下同)的大气环境质量的优劣,比欧几里德贴近度法和上海指数法均优越.  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