全文获取类型
收费全文 | 13749篇 |
免费 | 141篇 |
国内免费 | 101篇 |
专业分类
安全科学 | 345篇 |
废物处理 | 611篇 |
环保管理 | 1424篇 |
综合类 | 2632篇 |
基础理论 | 3477篇 |
环境理论 | 10篇 |
污染及防治 | 3738篇 |
评价与监测 | 882篇 |
社会与环境 | 819篇 |
灾害及防治 | 53篇 |
出版年
2022年 | 125篇 |
2021年 | 94篇 |
2020年 | 86篇 |
2019年 | 111篇 |
2018年 | 221篇 |
2017年 | 225篇 |
2016年 | 322篇 |
2015年 | 251篇 |
2014年 | 336篇 |
2013年 | 916篇 |
2012年 | 396篇 |
2011年 | 615篇 |
2010年 | 477篇 |
2009年 | 503篇 |
2008年 | 663篇 |
2007年 | 626篇 |
2006年 | 557篇 |
2005年 | 479篇 |
2004年 | 428篇 |
2003年 | 467篇 |
2002年 | 447篇 |
2001年 | 579篇 |
2000年 | 400篇 |
1999年 | 236篇 |
1998年 | 177篇 |
1997年 | 171篇 |
1996年 | 180篇 |
1995年 | 206篇 |
1994年 | 172篇 |
1993年 | 132篇 |
1992年 | 162篇 |
1991年 | 156篇 |
1990年 | 162篇 |
1989年 | 159篇 |
1988年 | 115篇 |
1987年 | 109篇 |
1986年 | 89篇 |
1985年 | 113篇 |
1984年 | 114篇 |
1983年 | 104篇 |
1982年 | 105篇 |
1981年 | 100篇 |
1980年 | 80篇 |
1979年 | 84篇 |
1977年 | 80篇 |
1976年 | 77篇 |
1975年 | 72篇 |
1974年 | 74篇 |
1973年 | 80篇 |
1971年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
S. H. Lin L. T. Fan C. L. Hwang 《Journal of the American Water Resources Association》1973,9(4):689-702
A modified transient version of the Streeter-Phelps model along with the energy balance equation is employed to analyze the effects of waste heat discharge from power plants on stream water quality. Analysis is also made to examine the effects of the upstream water quality and stream velocity on the downstream DO concentration level. The resulting coupled nonlinear hyperbolic partial differential equations representing the energy, BOD and DO concentrations are solved by the method of characteristics and simulated on a digital computer. Final numerical results indicate that the allowable quantity of thermal discharge does heavily depend on the upstream quality. 相似文献
992.
S. H. Lin L. T. Fan C. L. Hwang 《Journal of the American Water Resources Association》1973,9(5):874-883
ABSTRACT: The purpose of this work is to study the installation of artificial aerators for water quality control of a stream which receives thermal and organic waste discharges. The location and numer of diffuser type aerators to be installed along the stream are determined so as to maintain the stream DO content above a certain minimum requirement (4 mg/l or 5 mg/l) for normal aquatic life. Effects of the stream velocity, upstream BOD concentration and rates of thermal and organic waste discharges to the stream are examined. 相似文献
993.
Gerald T. Westbrook 《The Environmentalist》1981,1(3):197-205
Summary An earlier version of this paper was originally presented at The American Association of University Women, Michigan, State Division, USA. The paper deals with two main issues: In the first place that there is no single energy source that will solve the energy problem. The solution will come through what has been called An Energy Family Approach. Secondly, that government regulations, which were primarily written in the days when America was viewed as a country with no limits, must be relaxed.Gerald T. Westbrook works for Dow's Hydrocarbons Department as Energy Project Manager. Prior to this current assignment he had been Project Manager in Dow's Functional Products and Systems Department for Business Development concentrating on water purification technologies for the energy industries. He has had over twenty years experience in various technical and functional areas with Dow Chemical in the United States and Imperial Oil Ltd. in Canada. Experience in the energy field has included petroleum refinery design and operations analysis; electric power plant planning, and water systems development; new advanced battery development; and energy economics and forecasting. 相似文献
994.
C. T. K. Ching 《Journal of the American Water Resources Association》1981,17(3):454-457
A significant research problem is the assessment of impacts associated with growth and/or decline in a regional economy. A relevant method for analyzing such problems is the Leontief input/output model. Associated with these models are economic multipliers measuring total changes in sales, income, and employment. In this paper, the author contends resource multipliers are equally relevant. The specific form of these multipliers are defined. Water multipliers for a two-county region in central Nevada are presented and their uses described. 相似文献
995.
D. T. O'Laoghaire 《Journal of the American Water Resources Association》1978,14(4):809-826
ABSTRACT: This paper describes a mathematical model, an algorithm and a computer program that were specially developed to study the problem of a water quality management system undergoing a rapidly increasing environmental stress. The model output will determine the locations, sizes and the timing of construction of new treatment plants plus an overall treatment plant operating policy so that environmental standards are maintained at a minimum cost. The model, as formulated, is a 0-1 mixed integer programming problem which is solved by decomposing it into a capital budgeting problem (solved by Little's branch and bound algorithm) and an operational policy problem (solved by linear programming). The coded algorithm (in FORTRAN 10) has been tested with a semi-realistic example. 相似文献
996.
997.
998.
Edwin T. Engmun 《Journal of the American Water Resources Association》1974,10(3):512-521
ABSTRACT: According to a concept known as partial area hydrology, watershed areas are separated into hydrologically active and passive subareas. The literature relating to the development of the partial area concept is reviewed briefly and the relationship of partial area hydrology to geology, soils, and micrometeorology is illustrated. The potential application of partial area hydrology is discussed with respect to present hydrologic techniques, future hydrologic models, urban hydrology, water quality, and water management. Suggestions for identifying and delineating the contributing areas are discussed. 相似文献
999.
1000.
E T. Foster T. C. Chen J. P. Newton E. O. Isu 《Journal of the American Water Resources Association》1972,8(5):863-870
ABSTRACT. Theoretical and practical results are summarized for a study to determine optimal water resource allocation in a proposed water conservancy district. The area of this district, which covers several river basins, contains a large number of existing and proposed facilities such as reservoirs and diversions. The operation of all of these facilities was to be determined along with the sizing of the proposed facilities in order to optimize given objective functions. Related efforts in optimal river basin utilization were surveyed, and linear programming was selected as an expedient optimization technique. The problem is formulated by identifying time stages which together constitute a repetitive cycle such as a year. With these stages, it is possible to associate operational and capacity variables with network components, which are branches and nodes. Objective functions are assembled for the component variables. Constraint equations are written in terms of the variables to reflect network nodal continuity, capacity restrictions, and adjudications such as water rights. A numerical example is considered in which the existing and proposed facilities are aggregated to produce a small, tractable number of facilities. This paper examines the example results and suggests future improvements for models of this type. 相似文献