全文获取类型
收费全文 | 441篇 |
免费 | 68篇 |
国内免费 | 87篇 |
专业分类
安全科学 | 68篇 |
废物处理 | 10篇 |
环保管理 | 116篇 |
综合类 | 239篇 |
基础理论 | 70篇 |
污染及防治 | 20篇 |
评价与监测 | 32篇 |
社会与环境 | 20篇 |
灾害及防治 | 21篇 |
出版年
2024年 | 4篇 |
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 26篇 |
2018年 | 20篇 |
2017年 | 21篇 |
2016年 | 27篇 |
2015年 | 21篇 |
2014年 | 24篇 |
2013年 | 34篇 |
2012年 | 38篇 |
2011年 | 26篇 |
2010年 | 19篇 |
2009年 | 25篇 |
2008年 | 17篇 |
2007年 | 33篇 |
2006年 | 19篇 |
2005年 | 26篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 5篇 |
排序方式: 共有596条查询结果,搜索用时 546 毫秒
281.
Summary The major objective of the design of safe crowded transmitting antenna sites is not only to determine a safe zone around each
individual antenna; rather, to establish safety areas at the antenna site itself, as well as, at the neighboring areas. The
requirement is to ascertain the safety regions by considering the following parameters at each Test Point (TP) (or area segment):
the contribution of N co-located radiating antennas to the total radiation incident at the TP, the radiation pattern of each antenna, the near/far
field region of each antenna, and most importantly, the different Permissible Exposure Limits (PELs) associated with each
operating frequency at the antenna site. Implementation of all the above-mentioned aspects in a suitable computer requires
resources that only expert knowledgeable organizations possess. The graphically aided tool presented in this paper facilitates
the calculation of a “safety zone” for RADHAZ around a crowded antenna site from the knowledge of the “safety ranges” which
correspond to the individual transmitting antennas comprising it. 相似文献
282.
ABSTRACT: Recent developments in multiple objective decision making methods presented in the upcoming sequence of research papers are evaluated and compared with respect to their usefulness in addressing challenging problems in water resources management. Because many of the decision making techniques originated in the field of operational research, the historical evolution of this field is outlined and the current need for developing a wide range of techniques for employment in strategic decision making is pointed out. Informative attributes for classifying decision making techniques are given to allow a practitioner to select decision aids that can best model the key characteristics of the particular problems under study. By systematically applying a wide variety of multiple objective decision making techniques to many different kinds of water resources problems, the authors of the papers clearly demonstrate the effectiveness of utilizing these methods for assisting in making both tactical and strategic decisions in water resources management. 相似文献
283.
ABSTRACT. Society has long sought to maximize the welfare of its members by allocating its limited resources so as to provide maximum satisfaction. As long as all of the values that society gains or loses are measured in the market place in terms of price, the process of maximizing through economic models is relatively straightforward. In fact, however, the total value that society receives from the use of its resources is not completely measured through the private market transactions. There are some values created which are external to the market system. The resulting underinvestment in natural resources by the private sector necessitates the entry of the public sector. The presence of intangible benefits and intangible costs has long been recognized, but completely satisfactory methods for including these in the quantitative analysis of benefit-cost have not been developed. Some progress has been made in including recreational values in project analysis via the expenditures method, the Gross National Product method, consumer surplus method, cost method, market value method, and monopoly and discriminating monopoly methods, but little has been done in the area of aesthetic values. Techniques for including such values in project evaluation need to be further researched. Tradeoff models developed by market researchers, the advertising industry, social psychologists and sociologists may have some applicability. Methodology for including proposed multiple objective functions in project analysis is also a critical need. 相似文献
284.
Nigel Roome 《Journal of Environmental Planning and Management》1984,27(1):12-17
The Countryside Commission's report A Better Future for the Uplands puts forward a new strategy for public intervention in the uplands of England and Wales. The aim of the report is to integrate rural policies and to promote higher environmental priorities in rural areas. This paper considers the degree to which the report is successful in planning to achieve these ends. The paper is specifically concerned with the planning methodology on which the report is based. The paper argues for an approach to rural planning which permits the consideration of more radical solutions to rural problems, along with the application of a more systematic planning methodology, in order to assist in the choice of an appropriate direction for planned change. 相似文献
285.
依据惯性效应理论进行污水好氧处理的强化传质试验及工程实践,对曝气池工艺动力学的基本理论进行深入研究.试验及工程应用表明,提高曝气均匀度和加强多相物系中微涡漩的离心惯性效应,可促进物相接触和相界面更替,为活性污泥(或生物膜)、有机底质与氧气进行生化反应提供良好动力条件,提高反应效率,缩短反应历程;试验工艺及实际工程中氧利用率最高可达48%以上;COD容积负荷8.1-9.0kgCOD/m3·d;较常规工艺可降低曝气池工艺一次性投资,节省运行能耗,出水水质稳定可靠. 相似文献
286.
Chris M. Alaouze 《Journal of the American Water Resources Association》1989,25(6):1163-1168
ABSTRACT: Releases from a reservoir may be allocated to a number of uses, each of which may require a given volume of water at a different reliability. The paper provides a method that can be used to estimate the volume of water associated with a given reliability for each use of water when the proportion of releases allocated to each use is known. These results can be used to evaluate the meeting of specified objectives under a published release policy derived by stationary stochastic dynamic programming. The results can also be used to solve water allocation problems when the probability distribution of available water is known (or can be estimated) and water has multiple uses, each of which has different volume and reliability requirements. 相似文献
287.
S. I. Solomon E. Basso C. Osorio H. Melo de Moraes A. Serrano 《Journal of the American Water Resources Association》1986,22(2):209-217
ABSTRACT: The construction of the Tucurui Hydroelectric Plant on the Tocantins River basin in Brazil requires flood forecasting for ensuring the safety of the cofferdam. The latter has been initially designed for a flood with a return frequency of one in 25 years. Lack of adequate forecasting facilities during the earlier stages of construction has resulted in significant damages and construction delays. Statistical forecasting models were developed by Projeto de Hidrologiay Climatologie da Amazonia (PHCA) for the purpose of preventing further damages at the site. These models are currently in use and are the subject of this paper. The application of these models during the 1980 flood season, when the highest flood on record occurred at the Tucurui site, proved of great assistance in preventing the flooding of the cofferdam. In conjunction with the development of these models a number of data collection platforms using data transmission through the GOES system were installed to provide automatically the data required for forecasting. 相似文献
288.
289.
应用藻类生长潜力试验的方法研究滇池藻类生长的控制因子 总被引:3,自引:1,他引:2
采用滇池不同湖区的湖水进行藻类生长潜力试验(AGP试验),研究了稳定环境下,氮、磷两种可控的水华诱导因素对滇池铜绿微囊藻生长潜力的影响.结果表明,滇池各个湖区藻类生长的主要控制因子并不一致,北部与西部湖区,磷是两湖区藻类生长的主要限制性营养物质;湖心与南部湖区,磷和氮都是蓝藻生长的主要控制因子,但它们单独作用都不能有效促进铜绿微囊藻的生长.实验N/P(质量比)在4~20之间,这一范围内N/P对滇池铜绿微囊藻生长没有显著影响. 相似文献
290.
应用AutoCAD二次开发技术,以AutoCAD作为程序的绘图环境,以Visual Basic.NET作为计算环境,针对线屏障和封闭屏障存在的声环境系统,开发了一套计算机程序,以实现声强分布计算和图形表达过程。采用对数加权的处理方法,计算多线屏障的影响;用"线段首尾连接"的方法来追踪等值点。 相似文献