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   12177篇
  免费   1077篇
  国内免费   1147篇
安全科学   1601篇
废物处理   168篇
环保管理   2890篇
综合类   6490篇
基础理论   1036篇
环境理论   49篇
污染及防治   432篇
评价与监测   755篇
社会与环境   862篇
灾害及防治   118篇
  2024年   35篇
  2023年   141篇
  2022年   198篇
  2021年   317篇
  2020年   368篇
  2019年   331篇
  2018年   297篇
  2017年   543篇
  2016年   555篇
  2015年   603篇
  2014年   572篇
  2013年   825篇
  2012年   836篇
  2011年   874篇
  2010年   702篇
  2009年   646篇
  2008年   460篇
  2007年   756篇
  2006年   765篇
  2005年   681篇
  2004年   601篇
  2003年   553篇
  2002年   435篇
  2001年   437篇
  2000年   442篇
  1999年   293篇
  1998年   218篇
  1997年   196篇
  1996年   136篇
  1995年   155篇
  1994年   89篇
  1993年   101篇
  1992年   53篇
  1991年   31篇
  1990年   26篇
  1989年   18篇
  1988年   10篇
  1987年   8篇
  1986年   10篇
  1984年   6篇
  1982年   7篇
  1981年   7篇
  1980年   6篇
  1979年   9篇
  1978年   6篇
  1977年   9篇
  1976年   5篇
  1975年   6篇
  1973年   5篇
  1972年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
ABSTRACT: In urbanizing areas, the usual increase in flood flows also increases erosional capability of streams. In order to evaluate such tendencies quantitatively, 25 stream reaches were studied, and were classified as to whether erosion of the channel and banks was light, medium, or heavy. Analysis of characteristics indicated that (1) densely developed areas are correlated with greater erosion, (2) wide stream buffers of natural vegetation are correlated with lesser erosion, and (3) there is no definite correlation of erosion to slope or characteristics of soil. Erosional stream instability can be avoided by retention of storm water runoff, creating additional channel roughness or reducing channel slope during floods by drop structures, such as culverts, which restrict flow. Channel straightening and general bank protection should be minimized in such streams. Design of culverts should take such effects into consideration.  相似文献   
972.
ABSTRACT: A method of project planning for systematically assessing and recording impacts of alternative timber harvest startegies for subareas of a sale planning area is presented. This method uses an interdisciplinary team composed of specialists and decisionmaker to develop and analyze treatment alternatives and uses impact prediction matrices with explicit evaluation criteria to illustrate and record ratings of impacts on resource factors. The method is a system for organizing, for discovering appropriate alternatives, for facilitating interaction, and for documenting environmental analysis. It provides for decisionmaker control over the project, for exchange of value perspectives, and for reduction in conflict between specialists. The quality of decisions which result from the method presented depends upon the information available and the effectiveness of interaction between all members of the interdisciplinary team.  相似文献   
973.
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   
974.
ABSTRACT: Faced with the necessity of meeting growing municipal water requirements in areas where available supplies are completely allocated, numerous cities throughout the West are turning to their eminent domain powers to affect a reallocation of water from less preferred uses to municipal uses, thus bringing about a sharp conflict with agricultural interests. As a basis for discussing these eminent domain powers, this paper begins with a brief review of the development of property rights. The existence of both private and public (social) rights in the “bundle of rights” is noted. In recent years the Public Trust Doctrine has been used to limit private rights in property, and to protect and strengthen social rights. A case study which focuses on a conflict between individual and social interests in water rights is discussed. This case involves the City of Thorton, Colorado which initiated municipal condemnation proceedings to acquire the water rights and structures of two nearby irrigation companies. The case represents an attempt to incorporate the spirit of the Public Trust Doctrine into legislation which sets forth procedures for resolution of similar water rights conflicts that will inevitably become more numerous throughout the West in the future.  相似文献   
975.
ABSTRACT: Interbasin water transfer is one of the most controversial water-resources-planning topics. Local communities, particularly those from which the water is to be taken (donor regions), generate enough opposition to doom many projects to failure. The opposition often arises because planners have traditionally considered excess water a free commodity rather than a marketable resource. To make transfer schemes mutually acceptable to donor and recipient regions, visible benefits must be offered. Agreement must be made on an acceptable purchase price and/or on other benefits such as a substantial amount of low flow augmentation or possibly some degree of flood control on the donor source stream. The hydrologic and economic feasibility of water transfer from the East Susquehanna River basin to the Delaware Reservoir System for supplemental supply to the New York City area was investigated. Nine alternative schemes for diversions up to 400 cfs and compensations in the form of low flow augmentation and/or flood control were considered resulting in unit costs to the recipient region between $90 and $380/mg. If only the minimum state-mandated flow is released to the Susquehanna River, the savings to the water recipients would be sufficient to pay a purchase price of about $21/mg, which would be equivalent to a total amount of $420,000/year for an average export of 100 cfs.  相似文献   
976.
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   
977.
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   
978.
遥感在生态与环境监测中的主要应用领域   总被引:4,自引:2,他引:4  
遥感是一种以物理手段、数学方法和地学分析为基础的综合应用技术 ,具有宏观、综合、动态和快速的特点。在解决宏观尺度的环境问题时 ,卫星遥感可重复获取多种空间、不同时相和不同波谱分辨率的地球信息 ,是适宜于调查和研究这些主题的唯一的、最有效的工具。本文通过对遥感在环境与生态监测的主要应用领域进行概要阐述 ,旨在抛砖引玉 ,推动遥感在环境与生态监测中的广泛应用。  相似文献   
979.
根据NO2^-与AY(吖啶黄)的重氮化偶联反应。研究了反应的最佳条件,利用四波长处吸光度加和值与NO2^-浓度在一定范围内呈线性关系。建立四波长测定微量NO2^-含量的新方法。应用于环境样品的监测。获得了满意的效果。符合环境监测的要求。  相似文献   
980.
企业环境监测工作有其自身特点,本文从监测对象、监测项目、监测职能、监测手段、监测信息处理等方面论述了强化企业环境监测的途径和方法。  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