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   3126篇
  免费   215篇
  国内免费   200篇
安全科学   141篇
废物处理   17篇
环保管理   1191篇
综合类   1074篇
基础理论   621篇
环境理论   2篇
污染及防治   64篇
评价与监测   102篇
社会与环境   229篇
灾害及防治   100篇
  2023年   22篇
  2022年   54篇
  2021年   68篇
  2020年   73篇
  2019年   74篇
  2018年   83篇
  2017年   117篇
  2016年   132篇
  2015年   134篇
  2014年   107篇
  2013年   176篇
  2012年   148篇
  2011年   206篇
  2010年   149篇
  2009年   167篇
  2008年   156篇
  2007年   175篇
  2006年   165篇
  2005年   147篇
  2004年   108篇
  2003年   128篇
  2002年   80篇
  2001年   89篇
  2000年   80篇
  1999年   99篇
  1998年   49篇
  1997年   43篇
  1996年   54篇
  1995年   46篇
  1994年   36篇
  1993年   19篇
  1992年   24篇
  1991年   18篇
  1990年   14篇
  1989年   12篇
  1988年   13篇
  1987年   22篇
  1986年   23篇
  1985年   24篇
  1984年   24篇
  1983年   13篇
  1982年   12篇
  1980年   17篇
  1979年   17篇
  1978年   20篇
  1977年   14篇
  1975年   10篇
  1973年   16篇
  1972年   14篇
  1971年   16篇
排序方式: 共有3541条查询结果,搜索用时 15 毫秒
941.
The use of computer-assisted map analysis techniques for prediction of storm runoff from a small urban watershed in the United States is investigated. An automated procedure for calculating input parameters for the US Soil Conservation Service (SCS) method of predicting storm runoff volume and peak timing is presented. Advanced techniques of spatial analysis are used to characterize spatial coincidence, surface configuration and effective hydrologic distance. A limited verification of the automated procedure indicates that the model reasonably characterizes water flow. A sensitivity analysis of basin disaggregation suggests that the SCS method yields increased volume and peak discharge predictions as the watershed is divided into smaller and smaller subunits. As a means to demonstrate the practical application of the automated procedure, a simulation of the effects on surface runoff for a potential residential development is presented.  相似文献   
942.
943.
ABSTRACT: The increasing use of irrigation for urban landscapes is causing new demands for efficient watering systems. Conservation techniques for irrigated agricultural fields cannot be applied to urban landscapes without amendment. This paper attempts to review methods of urban landscape water conservation in the context of the diversity and complexity of urban landscapes and the demands upon them for quality of the urban environment. A development's initial site layout and planting design fundamentally determine how much irrigation water will be required; the complexity and creativity inherent in urban design open a number of specific possibilities for reducing water demand. Irrigation hardware is then designed to deliver the required volume of water to the specified landscape efficiently by implementing a number of physical and operational principles. Maintenance of the finished development involves monitoring results and making adjustments as the plantings grow and develop. The potential for conserving urban irrigation water is large. Effective conservation need not compromise other qualities of the urban environment such as aesthetics, screening, or shade. Urban design can address both the kinds of landscapes people need, and minimal consumption of irrigation water.  相似文献   
944.
The author provides an account of Hungarian regional policy and planning during the last 40 years, describing a socialist state trying to escape from a centrally planned economy. The paper discusses the consequences of the reforms and the problems of conflict resolution which resulted. The author argues that central planning will continue to be necessary in the future, and that there is a need to strengthen the co‐ordinative role of regional plans.  相似文献   
945.
The British Ecological Society has suggested that computer‐based techniques could be used in the coordination of policies across different land uses in upland planning. This paper looks briefly at one such technique — a linear programming model — and describes its use at a regional scale for the Sedburgh area in north‐west England. The paper concludes with consideration of why such models are not in more common use.  相似文献   
946.
The Countryside Commission's report, “A Better Future for the Uplands”, contains recommendations that seek a better balance between conservation and farming and conservation and forestry: recommendations that concern the uplands as landscape. This paper considers the recommendations under three headings — those which seek to reduce conflict, those which seek to reinforce the voluntary approach to conflict resolution, and those which seek to extend control. The paper concludes with a consideration of the likely effectiveness of the measures proposed.  相似文献   
947.
In areas where there is little or no topographic relief and where soils, vegetation, geologic structure and other factors are essentially uniform, identification of drainage basin boundaries is difficult or impossible. In such a homogeneous landscape, however, assumptions may be made that the hydrologic and geomorphic controls over drainage basin development are constant within the area. If this is true, it is suggested, the drainage area of a stream is related solely to the stream length and factors governing the length-area relationship are also constant. A simple formula based on these assumptions and the gravity model is proposed which can be used to estimate drainage divides in a homogeneous landscape.  相似文献   
948.
This study compares the effectiveness of two regional planning agencies in terms of public support for various planning activities. The Adirondack Park Agency and the Temporary State Commission on Tug Hill have fundamentally different approaches to planning. The Adirondack Park Agency has implemented a restrictive regulatory program with little citizen participation by Adirondack residents. The Tug Hill Commission has implemented an advisory and coordinating program with an emphasis on public input. Residents of two towns in each region were surveyed to determine environmental concern and support for regional planning activities. Respondents from both regions favored a planning agency that incorporates citizen input; controls air, water, and toxic waste pollution; and develops recreation areas. They strongly opposed an agency that regulates private land-use. Basic demographic characteristics and levels of environmental concern were similar in all four towns, but receptivity to various planning activities was consistently greater among residents of the Tug Hill Region. Paired comparisons of the four towns demonstrated no differences between towns of the same region and significant differences between towns of different regions. Public support for regional planning is greater in the Tug Hill Region than in the Adirondack Park.  相似文献   
949.
刘建军  吴秀芹 《干旱环境监测》2002,16(4):210-211,222
利用 1 988— 2 0 0 0年新疆塔里木河下游TM影像解译的土地覆盖 (土地利用图 )和景观多样性指数、斑块重要值、破碎度、分维数等景观生态学指标 ,进行了塔里木河下游土地利用格局的空间分布和时间动态分析。  相似文献   
950.
LANDSCAPE DEVELOPMENT INTENSITY INDEX   总被引:12,自引:0,他引:12  
  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