全文获取类型
收费全文 | 1622篇 |
免费 | 198篇 |
国内免费 | 295篇 |
专业分类
安全科学 | 409篇 |
废物处理 | 40篇 |
环保管理 | 390篇 |
综合类 | 751篇 |
基础理论 | 138篇 |
污染及防治 | 160篇 |
评价与监测 | 86篇 |
社会与环境 | 80篇 |
灾害及防治 | 61篇 |
出版年
2024年 | 8篇 |
2023年 | 51篇 |
2022年 | 53篇 |
2021年 | 73篇 |
2020年 | 77篇 |
2019年 | 65篇 |
2018年 | 44篇 |
2017年 | 90篇 |
2016年 | 117篇 |
2015年 | 115篇 |
2014年 | 85篇 |
2013年 | 120篇 |
2012年 | 145篇 |
2011年 | 133篇 |
2010年 | 111篇 |
2009年 | 91篇 |
2008年 | 61篇 |
2007年 | 104篇 |
2006年 | 96篇 |
2005年 | 70篇 |
2004年 | 47篇 |
2003年 | 60篇 |
2002年 | 37篇 |
2001年 | 45篇 |
2000年 | 27篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 13篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 11篇 |
1970年 | 4篇 |
排序方式: 共有2115条查询结果,搜索用时 15 毫秒
901.
Objectives for Multiple-Species Conservation Planning 总被引:2,自引:0,他引:2
Abstract: The first step in conservation planning is to identify objectives. Most stated objectives for conservation, such as to maximize biodiversity outcomes, are too vague to be useful within a decision-making framework. One way to clarify the issue is to define objectives in terms of the risk of extinction for multiple species. Although the assessment of extinction risk for single species is common, few researchers have formulated an objective function that combines the extinction risks of multiple species. We sought to translate the broad goal of maximizing the viability of species into explicit objectives for use in a decision-theoretic approach to conservation planning. We formulated several objective functions based on extinction risk across many species and illustrated the differences between these objectives with simple examples. Each objective function was the mathematical representation of an approach to conservation and emphasized different levels of threat. Our objectives included minimizing the joint probability of one or more extinctions, minimizing the expected number of extinctions, and minimizing the increase in risk of extinction from the best-case scenario. With objective functions based on joint probabilities of extinction across species, any correlations in extinction probabilities had to be known or the resultant decisions were potentially misleading. Additive objectives, such as the expected number of extinctions, did not produce the same anomalies. We demonstrated that the choice of objective function is central to the decision-making process because alternative objective functions can lead to a different ranking of management options. Therefore, decision makers need to think carefully in selecting and defining their conservation goals. 相似文献
902.
从造成重大油污染事件的原因分析及其治理的评估,可以看出信息技术都起着重要作用。随着以互联网、万维网、电子邮件等为特征的现代信息技术的迅速发展,油污染防治也进入了一个新阶段。文中介绍该技术在防治油污染中的应用。 相似文献
903.
为了从控制运行的角度促进简化数学模型的应用,必须借助其它优化手段进一步提高预测精度。本文主要介绍了应用于简化数学模型的扩展卡尔曼滤波、神经网络和误差反馈系统三种优化方法以及优化后的验证结果。从验证结果来看,优化的ROM模型与ASMl模型的定性变化行为相似,基于神经网络的复合模型对PO4^3-和NOx^-的预测结果非常准确,误差反馈的优化系统模拟性能良好。 相似文献
904.
905.
宁东能源化工基地规划产业布局的生态适宜性分析 总被引:3,自引:0,他引:3
基于遥感和地理信息系统技术,在宁东地区土壤侵蚀敏感性评价的基础上,对宁东能源化工基地规划的产业布局进行了生态适宜性分析.结果表明,宁东能源化工基地规划的煤炭、电力和煤化工三大主导产业布 局与该区生态环境不相适宜.在规划的12座煤矿、7个电厂和3个煤化工园区中,有3座煤矿、2个电厂和1个化工园区位于土壤侵蚀的高度敏感区内;有2座煤矿、3个电厂和1个化工园区位于土壤侵蚀的中度敏感区内.为更好的促进区域生态环境与经济社会的协调发展,探索性地提出了宁东能源化工基地产业布局规划的优化调整建议. 相似文献
906.
The SITES reserve selection system: A critical review 总被引:1,自引:0,他引:1
Douglas?T.?FischerEmail author Richard?L.?Church 《Environmental Modeling and Assessment》2005,10(3):215-228
Numerous models have been put forth to help with the growing demand for the establishment of biodiversity reserves. One site
selection model that has been used in several recent studies is SITES [S.J. Andelman, I. Ball, F.W. Davis and D.M. Stoms,
SITES V 1.0: an analytical toolbox for designing ecoregional conservation portfolios, Unpublished manual prepared for the
nature conservancy, 1999, 1–43. (available at )]. SITES includes two heuristic solvers: based on Greedy and Simulated Annealing. We discuss the formulation of the SITES
model, present a new formulation for that problem, and solve a number of test problems optimally using off-the-shelf software.
We compared our optimal results with the SITES Simulated Annealing heuristic and found that SITES frequently returns significantly
suboptimal solutions. Our results add further support to the argument, started by Underhill [L.G. Underhill, Optimal and suboptimal
reserve selection algorithms, Biol. Conserv. 70 (1994) 85–87], continuing through Rodrigues and Gaston [A.S.L. Rodrigues and
K.J. Gaston, Optimization in reserve selection procedures – why not?, Biol. Conserv. 107 (2002) 123–129], for greater integration
of optimal methods in the reserve design/selection literature. 相似文献
907.
Using Insurance to Enhance Nitrogen Fertilizer Application to Reduce Nitrogen Losses to the Environment 总被引:2,自引:0,他引:2
The advantage of using insurance to help a farmer adopt a best nitrogen management plan (BNMP) that reduces the impact of agricultural production on the environment is analytically and empirically demonstrated. Using an expected value analysis, it is shown that an insurance program can be structured soas to reduce a farmer's cost of bearing the adoption risk associated with changing production practices and, thus, to improve the farmer's certainty equivalent net return thereby promoting the adoption of a BNMP. Using the adoption of growing-season only N fertilizer application in Iowa as a case study, it is illustrated how insurance may be used to promote the adoption of this practice to reduce N fertilizeruse. It is shown that it is possible for a farmer and an insurance company both to have an incentive to develop an insurance adoption program that will benefit both the farmer and the insurance company, increasing net social welfare and improving environmental quality in Iowa. 相似文献
908.
909.
The increasing growth of the economy in each country necessitates a great amount of investment in infrastructure. The belief that projects involve various uncertainties, such as technical skills, management quality, and the like, indicates that most projects fail to achieve their aims, interests, costs, as well as their timeframes and space requirements. As the environment can pose significant uncertainty to any project, environmental risks should be deeply studied by project management departments. This study intends to analyze as a case the environmental risk management system within a consulting firm. From this analysis, each aspect of a project's environmental risk management is ranked using a fuzzy analytical network process (ANP), a neural network algorithm, and a decision‐making trial and evaluation laboratory (DEMATEL) methodology. From the organizational aspect, budget risk is the most significant. From the technical aspect, the risk of regulations is the most important one. Finally, the risk of project failure from poor communication is another identified main risk in this research. By studying high‐ranking items in this hierarchy, it can be understood that these criteria exist in different aspects; therefore, all aspects of the risk should be taken into account to cover and assess risk. A neural network algorithm for validating and reassessment of ranking is employed. Results of this application showed that, based on Spearman's rank correlation method, two different approaches resulted in similar rankings. Finally, some practical implications for responding to the most highly ranked risks are proposed. 相似文献
910.
Social consequences associated with the use of various optimization methods in the protection of air quality 总被引:1,自引:0,他引:1
Jacek Żeliński Jolanta Telenga-Kopyczyńska 《Journal of Environmental Planning and Management》2019,62(6):960-978
The fundamental tactics employed by the EU against air contamination, which are intended to maintain concentrations at a level that does not exceed the permissible values, usually entail considerable expense. To reduce this to a minimum, the procedure of economic optimization of air quality can be applied. When performed for a heavily polluted industrial city, it shows that it is possible to maintain concentrations below the threshold of air quality standards with relatively moderate expenditure. These evaluations also reveal that variations in population density distribution call into question the conventional wisdom that uniform air quality standards provide the best protection against air contamination for a whole region. On the contrary, an optimization that forces a drop in concentration to be evenly spread over the population, without reference to air quality standards, may lead to more efficient protection of human health and make no difference to overall expenditure. 相似文献