全文获取类型
收费全文 | 382篇 |
免费 | 27篇 |
国内免费 | 18篇 |
专业分类
安全科学 | 46篇 |
废物处理 | 6篇 |
环保管理 | 180篇 |
综合类 | 81篇 |
基础理论 | 43篇 |
污染及防治 | 3篇 |
评价与监测 | 28篇 |
社会与环境 | 24篇 |
灾害及防治 | 16篇 |
出版年
2023年 | 4篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 10篇 |
2014年 | 12篇 |
2013年 | 13篇 |
2012年 | 5篇 |
2011年 | 23篇 |
2010年 | 14篇 |
2009年 | 18篇 |
2008年 | 26篇 |
2007年 | 26篇 |
2006年 | 16篇 |
2005年 | 18篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1971年 | 9篇 |
1970年 | 3篇 |
排序方式: 共有427条查询结果,搜索用时 31 毫秒
31.
Across the globe, continued policy debates regarding the management of old-growth forests center around the difficult task of balancing economic and ecological considerations. Though the forests of the Pacific Northwest United States are among the most studied old-growth ecosystems, ecological and economic analyses have yielded public land management directives that remain controversial. Specifically, the recently adopted Northwest Forest Plan lacks explicit goals for maintaining intergenerational equity for the use of forest resources and the diversity of old-growth ecosystems. Unlike previous studies which rely on monetary quantification of costs and benefits, this study develops and applies a conceptual framework for evaluating socially optimal Pacific Northwest old-growth forest utilization strategies. Conditions for the optimal management of old-growth forests are derived using dynamic programming. The objective function synthesizes relevant biological and economic attributes of the old-growth allocation problem. Results in the form of extraction paths are compared given social pressure for consumptive and non-consumptive benefits, as well as different planning horizons, rates of social time preference, and environmental variance. Lengthening the planning horizon results in a vast divergence of optimal policies in the absence of discounting. Extraction rates appear to approach zero as the planning horizon approaches infinity. While higher rates of social time preference increase the rate of extraction, forest stocks remaining at the terminal time period equal levels remaining with a lower discount rate. Increasing environmental variance results in a higher level of stock remaining at the terminal time period. This analysis, while specific to the old-growth controversy of the Pacific Northwest, does provide general guidelines for addressing similar problems of multiple uses of natural areas, particularly where such uses are mutually incompatible, or where one use may be irreversibly destructive to another. 相似文献
32.
Bernard Roy Roman Slowiski Wiktor Treichel 《Journal of the American Water Resources Association》1992,28(1):13-31
ABSTRACT: The aim of this paper is to present a multicriteria methodology for decision aid at the stage of programming a water supply system (WSS) for a rural area. The programming stage is an intermediate one between planning and designing water supply facilities, and can be decomposed into two problems: (a) setting up a priority order of water users, taking into account socio-economic criteria; and (b) choosing the best technical variant of the WSS. Among the criteria considered for the latter problem, there is a criterion of distance between the socio-economic priorities of users and the precedence orders of users according to the technical programming, which plays a coordinating role between problems (a) and (b). All steps of the presented methodology are illustrated by a real case study. 相似文献
33.
Seok-Ku Ko Darrell G. Fontane John W. Labadie 《Journal of the American Water Resources Association》1992,28(1):111-127
ABSTRACT: Development of optimal operational policies for large-scale reservoir systems is often complicated by a multiplicity of conflicting project uses and purposes. A wide range of multiobjective optimization methods are available for appraising tradeoffs between conificting objectives. The purpose of this study is to provide guidance as to those methods which are best suited to dealing with the challenging large-scale, nonlinear, dynamic, and stochastic characteristics of multireservoir system operations. As a case study, the selected methodologies are applied to the Han River Reservoir System in Korea for four principal project objectives: water supply and low flow augmentation; annual hydropower production, reliable energy generation, and minimization of risk of violating firm water supply requirements. Additional objectives such as flood control are also considered, but are imposed as fixed constraints. 相似文献
34.
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
35.
Patrick A. Mower J. Philip J. O'Kane Jerry D.F. Sherrif Tim Wyatt J. David Barrett 《Journal of the American Water Resources Association》1971,7(4):831-843
ABSTRACT .Operating rule procedures are developed for the optimal use of desalination in conjunction with surface water impoundments. Results obtained from the use of hill-climbing and dynamic programming methods are compared. Benefits to be obtained from the integrated use of desalination are demonstrated through a case study for the Barcelona area of Spain. 相似文献
36.
Neil L. Drobny 《Journal of the American Water Resources Association》1971,7(6):1180-1193
Applications of linear programming to water quality and water quantity problems are discussed, and a fairly comprehensive sample of recent literature in these areas is reviewed. Basic elements of linear programming are also discussed. Emphasis is placed on the elements of linear programming that make it a useful tool for analyzing water resource problems and the basic features of various water resource problems that render them amenable to meaningful analysis by linear programming. 相似文献
37.
Edvardsson K 《Environmental management》2004,34(2):170-180
In Sweden, environmental policy is essentially carried out through a system of environmental objectives adopted by Parliament in the late 1990s. This system contains principles, objectives, interim targets, strategies, and follow-up mechanisms, which together provide a solid ground for increased efficiency and improved prioritization in environmental policies. Despite the ambitious approach of the Swedish Parliament, the system of environmental objectives suffers from certain shortcomings. Some of the objectives are imprecise and difficult to evaluate, and there are no rules or principles that may be used to solve goal conflicts and to prioritize between different objectives. As a consequence, the environmental objectives tend to differ in their degrees of operationalizability, and the priority-setting between different objectives is often unclear.*Rskr. denotes a written communication (from the Swedish Parliament to the Swedish Government) of a Parliamentary decision.
Note: This version was published online in June 2005 with the cover date of August 2004. 相似文献
38.
A safety self-management intervention for mining operations 总被引:4,自引:0,他引:4
PROBLEM: This quasi-experimental field study examined the efficacy of a safety self-management process to increase safety-related work practices in mining operations. METHODS: After a 7-week baseline, 15 miners participated in a safety self-management training and education presentation. The participants in a prebehavior condition (n=8) recorded their intentions to engage in specific percentages of safety-related work behaviors before starting their shift for the day. In contrast, participants in a postbehavior condition (n=7) recorded their percentages of safety-related work behaviors after their shift for the day. RESULTS: During withdrawal (4 weeks), the miners did not complete any self-monitoring forms. Based on 10,905 behavioral observations, safety self-management was effective at increasing the frequency of safety-related behavior (p<.05). For the prebehavior condition, the mean percent safe score across three target behaviors increased 34.8% during intervention. Similarly, in the postbehavior condition, the mean percent safe score across three target behaviors increased 40.1% during intervention. IMPACT ON INDUSTRY: The results suggest that employees who work in relative isolation or have little oversight, compared to traditional industrial workers, may benefit from a process by which they can systematically observe themselves. 相似文献
39.
40.
Manoliadis OG 《Environmental management》2001,28(4):497-504
Irrigation management calls for objective criteria capable of representing the economy, reliability, and productivity of irrigation
systems. These criteria must be compatible with long-term sustainability and conservation goals. The criteria representing
the above goals are the economic effect of management on yield reduction, economic effect, and reliability referring to plant
growth and operation of the network. In this study environmental indices are introduced to express the above criteria in quantitative
terms. The inclusion of these indices at the farm and network level create a multicriteria framework for decision-making based
on composite programming. An experimental study was conducted during the irrigation periods of 1989 and 1990 in Chania, Greece,
concerning water delivered to 40 experimental plots, soil moisture content at the rootzone, and irrigation system operational
failures. The data collected in real time were used for the calculation of the corresponding environmental indices. The variation
in time and space is high and resulted in up to 62% of yield loss and low system performance (up to 7% of system temporal
reliability). The study indicated that environmental indices could be incorporated to select alternatives and also to develop
policies on water delivery. The final decision involves a trade-off analysis between cost of application and desired system
performance. Measures of both primary objectives can be obtained using environmental indices that represent system operation
aggregation at its basic levels (on farm and network). 相似文献