全文获取类型
收费全文 | 5863篇 |
免费 | 601篇 |
国内免费 | 2879篇 |
专业分类
安全科学 | 322篇 |
废物处理 | 301篇 |
环保管理 | 1241篇 |
综合类 | 4730篇 |
基础理论 | 1167篇 |
污染及防治 | 993篇 |
评价与监测 | 422篇 |
社会与环境 | 126篇 |
灾害及防治 | 41篇 |
出版年
2024年 | 26篇 |
2023年 | 141篇 |
2022年 | 262篇 |
2021年 | 286篇 |
2020年 | 296篇 |
2019年 | 282篇 |
2018年 | 281篇 |
2017年 | 253篇 |
2016年 | 347篇 |
2015年 | 302篇 |
2014年 | 331篇 |
2013年 | 641篇 |
2012年 | 457篇 |
2011年 | 498篇 |
2010年 | 366篇 |
2009年 | 350篇 |
2008年 | 347篇 |
2007年 | 364篇 |
2006年 | 345篇 |
2005年 | 263篇 |
2004年 | 236篇 |
2003年 | 329篇 |
2002年 | 336篇 |
2001年 | 296篇 |
2000年 | 290篇 |
1999年 | 242篇 |
1998年 | 183篇 |
1997年 | 157篇 |
1996年 | 281篇 |
1995年 | 125篇 |
1994年 | 77篇 |
1993年 | 58篇 |
1992年 | 33篇 |
1991年 | 40篇 |
1990年 | 11篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 24篇 |
1984年 | 42篇 |
1983年 | 39篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1972年 | 1篇 |
1971年 | 14篇 |
1967年 | 1篇 |
排序方式: 共有9343条查询结果,搜索用时 586 毫秒
941.
/ A methodology to estimate the number of pump-out facilities and dump stations required to service human waste disposal for recreational power boating activities in Pennsylvania during the 1994 boating season is described. Study results suggest that a total of 39 additional pump-out stations and 13 dump stations may be required on seven major waterbodies: The Three Rivers Area, Lake Erie/Presque Isle Bay, Raystown Lake, the Susquehanna River, the Delaware River, Lake Wallenpaupack, and the Kinzua Reservoir. Suggestions for improving the methodology are provided. KEY WORDS: Human waste; Recreation; Power boating; Waste facilities; Waste disposal; Pennsylvania 相似文献
942.
Joseph N. Lekakis 《Environmental management》1998,22(1):1-8
/ Collaboration of countries with an aim to share fresh surface water resources promises to generate potential joint benefits. Unfortunately, existing agreements lack the perspective and capacity to produce any real action in efficient cross-border water allocation. When that problem is encountered by any two adjacent countries claiming riparian rights to the same watercourse, this paper suggests that apossible solution to be examined is a water market. This market requires the relevant countries to engage in a bargaining process as described in the theory of bilateral monopoly. The bargaining process should determine both the water quantity to be transferred and the price to be paid. However, there has to be a fair allocation of the joint benefits resulting from the transfer for a sustainable price solution. As an empirical illustration, the paper examines the case of river Nestos shared by Bulgaria and Greece in the southern Balkans. A net revenue function quadratic in water is specified and estimated using scarce data on three agricultural crops in Greece. Sensitivity analysis on the size and distribution of the net benefits is also performed.KEY WORDS: Bilateral agreements; Water markets; Efficient allocation 相似文献
943.
/ Tidal marshes have been actively restored in Connecticut for nearly 20 years, but evaluations of these projects are typically based solely on observations of vegetation change. A formerly impounded valley marsh at the Barn Island Wildlife Management Area is a notable exception; previous research at this site has also included assessments of primary productivity, macroinvertebrates, and use by fishes. To determine the effects of marsh restoration on higher trophic levels, we monitored bird use at five sites within the Barn Island complex, including both restoration and reference marshes. Use by summer bird populations within fixed plots was monitored over two years at all sites. Our principal focus was Impoundment One, a previously impounded valley marsh reopened to full tidal exchange in 1982. This restoration site supported a greater abundance of wetland birds than our other sites, indicating that it is at least equivalent to reference marshes within the same system for this ecological function. Moreover, the species richness of birds and their frequency of occurrence at Impoundment One was greater than at 11 other estuarine marshes in southeastern Connecticut surveyed in a related investigation. A second marsh, under restoration for approximately ten years, appears to be developing in a similar fashion. These results complement previous studies on vegetation, macroinvertebrates, and fish use in this system to show that, over time, the reintroduction of tidal flooding can effectively restore important ecological functions to previously impounded tidal marshes.KEY WORDS: Estuarine; Tidal marsh; Wetland birds; Restoration 相似文献
944.
Bradford R. Crain 《Environmental management》1998,22(3):471-481
L and width 2w, then by a selection of viewing window is meant a choice of w, with the intent being to search for optimal viewing windows, with the goal in mind of improving variances of estimators
of population density, reducing sampling effort, while maintaining the property of unbiasedness. The notions of increasing
window sensitivity (IWS) and decreasing window sensitivity (DWS) are introduced, and a method of deriving confidence intervals
is discussed. 相似文献
945.
Fish Community Structure as a Measure of Degradation and Rehabilitation of Riparian Systems in an Agricultural Drainage Basin 总被引:7,自引:0,他引:7
/ Assessing the health of ecological components of agroecosystems may be accomplished by examining changes in the drainage basin, which serves as an integrator of the agroecosystem landscape. In this study we examined fish communities in terms of an array of indicators of structure and related these to changes in riparian vegetation and agricultural practice. Evidence suggests management practices designed to foster healthier environments by, for example, reestablishing riparian vegetation were associated with positive impacts on the integrity of the fish community. At the same time, continued intensification of agricultural practices in parts of the drainage basin in recent years likely has had an off-setting influence in overall improvements in agroecosystem health. Assessments of changes in the structure of the fish associations provide the balance sheet by which the counteracting influences can be aggregated and assessed.KEY WORDS: Fish community structure; Riparian system; Agricultural drainage basin 相似文献
946.
Marc Hockings 《Environmental management》1998,22(3):337-345
/ An approach to evaluating the effectiveness of management of protected areas is proposed. This approach has been used in developing an evaluation strategy for the Fraser Island World Heritage Area in Australia. The main component of the strategy is built upon the desired outcomes specified in the management plan for the area and thus provides a basis for assessing the extent to which the plan's objectives are being achieved. A series of monitoring programs have been proposed to enable this assessment. Examples of monitoring programs developed as part of the evaluation strategy are presented. A second component of the strategy monitors the implementation of the management plan. A management information system has been developed to record and report on the extent to which the specific actions specified in the management plan have been implemented. The strategy is discussed in relation to seven objectives set for the evaluation program in its design phase.KEY WORDS: Planning; Evaluation; Monitoring; Management; Protected areas 相似文献
947.
/ Public contact is a vital component of any program to manage natural resources. A well-planned public contact program uses a variety of strategies to create a sympathetic and environmentally aware public and to meet specific management-related objectives. A methodology is proposed that can be applied to planning public contact at any level, from media design for a specific project to corporate strategies for communication. The methodology integrates management-driven, client-driven and resource-driven planning to provide the connections essential to effective communication.KEY WORDS: Planning; Public contact; Interpretation; Conservation; Management 相似文献
948.
James Fielding Smith 《Environmental management》1998,22(2):263-276
/ Questionnaires from 39 state National Pollutant Discharge Elimination System (NPDES) agencies were analyzed using principal component analysis and multiple regression. Decentralized programs scored better in a fundamental indicator of efficiency (lower percentage of expired permits) and in the key effectiveness measure of unit-cost compliance achieved. In no case did centralized states score significantly better than decentralized ones. These results indicated support for the theory that superior local knowledge is the key mechanism. Case studies of five states suggested internal program adjustments may cause outcomes to converge towards efficiency and effectiveness, perhaps explaining the large number of variables showing no difference between centralized programs and decentralized ones.KEY WORDS: NPDES; Compliance; Decentralization; Outcome; Efficiency; Unit-cost analysis 相似文献
949.
950.