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581.
582.
The analysis of large data sets concerning fires in various forested areas of the world has pointed out that burned areas can often be described by different power-law distributions for small, medium and large fires and that a scaling law for the time intervals separating successive fires is fulfilled. The attempts of deriving such statistical laws from purely theoretical arguments have not been fully successful so far, most likely because important physical and/or biological factors controlling forest fires were not taken into account. By contrast, the two-layer spatially extended forest model we propose in this paper encapsulates the main characteristics of vegetational growth and fire ignition and propagation, and supports the empirically discovered statistical laws. Since the model is fully deterministic and spatially homogeneous, the emergence of the power and scaling laws does not seem to necessarily require meteorological randomness and geophysical heterogeneity, although these factors certainly amplify the chaoticity of the fires. Moreover, the analysis suggests that the existence of different power-laws for fires of various scale might be due to the two-layer structure of the forest which allows the formation of different kinds of fires, i.e. surface, crown, and mixed fires. 相似文献
583.
Judy L. Meyer Michael J. Sale Patrick J. Mulholland N. LeRoy Poff 《Journal of the American Water Resources Association》1999,35(6):1373-1386
ABSTRACT: We review published analyses of the effects of climate change on goods and services provided by freshwater ecosystems in the United States. Climate-induced changes must be assessed in the context of massive anthropogenic changes in water quantity and quality resulting from altered patterns of land use, water withdrawal, and species invasions; these may dwarf or exacerbate climate-induced changes. Water to meet instream needs is competing with other uses of water, and that competition is likely to be increased by climate change. We review recent predictions of the impacts of climate change on aquatic ecosystems in eight regions of North America. Impacts include warmer temperatures that alter lake mixing regimes and availability of fish habitat; changed magnitude and seasonality of runoff regimes that alter nutrient loading and limit habitat availability at low flow; and loss of prairie pothole wetlands that reduces waterfowl populations. Many of the predicted changes in aquatic ecosystems are a consequence of climatic effects on terrestrial ecosystems; shifts in riparian vegetation and hydrology are particularly critical. We review models that could be used to explore potential effects of climate change on freshwater ecosystems; these include models of instream flow, bioenergetics models, nutrient spiraling models, and models relating riverine food webs to hydrologic regime. We discuss potential ecological risks, benefits, and costs of climate change and identify information needs and model improvements that are required to improve our ability to predict and identify climate change impacts and to evaluate management options. 相似文献
584.
河长制从地方性实验到获得全国推广并正式写入法律,不过短短十年时间。河长制的成功之处在于解决了河湖管理保护"多龙治水"的困局,并调动了地方政府治水的积极性。但河长制也面临着高度依赖河长个人与考核制度的隐忧,其发展过程始终伴随着人治与法治之争、应急机制与长效机制之辩,以及重奖励轻惩罚、强化权力集中弱化公众参与的评价。提升与完善河长制可以从制度内与制度外两个方面着手:制度内的提升是指河长制内部机制的改良,包括考核制度的完善、公众参与水平的提高;制度外的提升是指与河长制配套的制度环境建设,包括环保行政队伍与行政执法力度的加强,以及与水环境治理相关的市场工具、政策工具与法律工具的综合 运用。 相似文献
585.
大气污染:危害人类健康的“无形杀手” 总被引:1,自引:1,他引:0
环境保护是事关人类生存发展的战略性、全球性、世纪性的大课题,而大气污染则城市环境问题的首要问题,作者站在创建“生态环境医学”的制高点上,引证了大量翔实的例症,剖析了大气污染给人类生态环境身健康所带来的种种危害和机理,并从多角度提示了标本兼治大气污染的应急措施,从而疾呼“地球人”要确立科学的发展,坚定地走经济发展、环境保护、生态文明的可持续发展之路,这才是“依法治气”的根本之策。 相似文献
586.
农业生态环境保护的法制建设 总被引:2,自引:0,他引:2
概要地介绍了农业生态环境保护法制建设的必要性,提出了加强和完善农业环境保护法律,法规的具体思路,提出了农业生态环境保护法制建设中应注意的问题和解决办法。 相似文献
587.
Emma C. Hardison Michael A. O’Driscoll John P. DeLoatch Robert J. Howard Mark M. Brinson 《Journal of the American Water Resources Association》2009,45(4):1032-1046
Abstract: This study evaluates the effects of urban land use on stream channels and riparian ground‐water levels along low‐order Inner Coastal Plain streams in North Carolina. Six sites with stream catchments of similar size (1.19‐3.46 km2) within the Tar River Basin were selected across an urban land use gradient, as quantified by a range of catchment total impervious area (TIA; 3.8‐36.7%). Stream stage and ground‐water levels within three floodplain monitoring wells were measured manually and using pressure transducers from May 2006‐June 2007. Channel incision ratio (CIR), the ratio of bank height to bankfull height, was also measured at each monitoring site and along stream reaches within the study area (12 urban and 12 rural sites). Riparian ground‐water levels were inversely related to catchment TIA (%). As TIA (%) and stormwater runoff increased, the degree of stream channel incision increased and riparian ground‐water tables declined. In urban floodplains (>15% TIA), the median ground‐water level was 0.84 m deeper than for the rural settings (<15% TIA). This has resulted in a shift to drier conditions in the urban riparian zones, particularly during the summer months. CIR was found to be a reliable surface indicator of “riparian hydrologic drought” in these settings. 相似文献
588.
瓦斯煤尘爆炸特性及传播规律研究进展 总被引:5,自引:3,他引:2
概要介绍国内外的瓦斯爆炸和瓦斯煤尘混合物爆炸特性及传播规律研究进展,瓦斯爆炸研究主要集中在瓦斯爆炸压力、火焰、温度等特征参数、不同障碍物对瓦斯爆炸压力、火焰传播的影响以及分岔、拐弯等不同形状管道内的传播规律,而瓦斯煤尘混合物爆炸研究主要集中在瓦斯对煤尘爆炸的最小点火能、爆炸下限、最大爆炸压力等爆炸特性及传播规律的影响。对不同研究人员采用的主要研究指标、手段、方法和研究结论进行综合评述,同时也对爆炸事故人员伤害模型在国内外的研究状况进行讨论,最后指出目前存在的主要问题和下一步的研究方向。 相似文献
589.
Kuheli Dutt 《Environment, Development and Sustainability》2009,11(4):705-723
This paper examines the environment-income relationship in the context of the Environmental Kuznets Curve (EKC), and explores
the possible role that factors like governance, political institutions, socioeconomic conditions, and education play in influencing
this relationship. The results suggest that the EKC exists for carbon dioxide emissions for cross-country data over the period
1984–2002. However, there is nothing automatic about this relationship; policies designed to protect the environment may be
responsible for this phenomenon. Two other significant findings are: one, countries with better quality of governance, stronger
political institutions, better socioeconomic conditions and greater investment in education have lower emissions; and two,
only around 15% of the countries in the dataset have reached income levels high enough to be associated with an unambiguous
decline in emissions. The implications of these results are discussed within the context of the international environmental
policy arena and the Kyoto Protocol. One of the main objectives of this paper is to bridge the gap between studies conducted
on the EKC and developments in the international environmental policy arena. As a final note this paper emphasizes that one
needs to connect the body of knowledge on the EKC hypothesis to the international environmental policy arena, despite the
apparent difficulty of doing so. One hopes that future studies will further build on this line of thought.
相似文献
Kuheli DuttEmail: |
590.