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221.
John Cairns Jr. 《Environmental management》1990,14(5):517-526
An inadequate basis for precisely predicting the outcome of lotic ecosystem recovery, whether due to unaided natural processes
or management techniques or both, exists because: (1) the field of ecology has not yet matured as a rigorous predictive science;
(2) the precise sequence of events, including climatic occurrences, affecting the recovery process may be unique events and
thus rarely or never repeated; and (3) even when attempts are made to control the recolonization process through introduction
of species, etc., the interaction of these species may not follow deterministic models. Although this symposium focuses on
lotic ecosystems, such systems are influenced strongly by exports from the surrounding land mass and, under certain circumstances,
this may be the overriding influence on the recovery process; therefore, unless the boundary conditions are determined realistically,
the recovery process may not follow desirable pathways. Despite the lack of a robust theoretical support base for lotic ecosystem
recovery, some remarkable and rapid recoveries have occurred to either a close approximation of the original condition or
to a condition ecologically superior to the damaged condition. In some cases, the recovery was due entirely to natural processes
and, in others, often followed relatively straightforward management practices. There is evidence indicating that lotic ecosystem
restoration is both cost effective and likely to produce satisfying results relatively rapidly. It is both fortunate that
this is the case, since society is likely to support such efforts when the results have been extraordinarily successful, and
unfortunate since restoration ecology needs a predictive capability. 相似文献
222.
The prognosis for the remediation of contaminated fractured media is much worse than that for more homogeneous units. Fractures act as conduits for the flow of dense non-aqueous phase liquids (DNAPLs), while diffusion is responsible for the storage of dissolved mass in the surrounding matrix. A numerical model incorporating aqueous phase transport in a variable-aperture fracture and its surrounding matrix is developed and coupled with an existing two-phase flow model. The processes of transient two-phase flow, non-equilibrium dissolution, advective–dispersive transport in the fracture, and three-dimensional matrix diffusion are included in the model. Results from various investigations show that the DNAPL distribution is very sensitive to variations in aperture within a single fracture. Diffusion-controlled mass removal from both the matrix and from the hydraulically inaccessible zones within the fracture itself result in extremely large time frames for significant mass removal from these systems. Success in aqueous phase mass removal from the matrix is very sensitive to the effective fracture spacing. The hydraulic gradient in the fracture only affects the amount of water removed from the system, and does not greatly affect the amount of time required to remove the contaminant mass from the matrix. The ability to remove mass is somewhat sensitive to the porosity and effective matrix diffusion coefficient over the range of expected values. 相似文献
223.
Policymakers today are faced with a difficult task of planning for large scale infrastructure that can cater to the climatic and socio-economic changes that the future will bring. To address the deeply uncertain nature resulting from long-term changes, it is becoming necessary to develop strategies that support flexibility and react more strategically than traditional planning approaches. This paper applies the concept of adaptation tipping points and adaptation pathways to a case study in Singapore for the planning of long-term urban drainage infrastructure. Using conventional grey and sustainable green solutions in isolation and in combination, adaptation pathway maps are developed and compared across outlined climatic and landuse scenarios. To understand and justify if the imparted flexibility is worth its cost, economic assessments are performed. This is a valuable extension of the existing framework, helps to identify the preferred configuration of land use and sub-select adaptation actions that should be implemented at the current time frame. The main finding of this study is that the adaptation pathways map for the sustainable grey landuse scenario economically outperforms those of the other outlined land uses. This provides a valuable insight for policy makers, as it implies that if carefully planned development is undertaken, the requirements of storm water management can be met in a sustainable manner, while simultaneously freeing up land for other purposes. This is especially important in the context of highly dense urban areas such as Singapore, where land is a scare resource. 相似文献
224.
T. Corbire-Nicollier B. Gfeller Laban L. Lundquist Y. Leterrier J. -A. E. Mnson O. Jolliet 《Resources, Conservation and Recycling》2001,33(4):579
This article aims to determine the environmental performance of China reed fibre used as a substitute for glass fibre as reinforcement in plastics and to identify key environmental parameters. A life cycle assessment (LCA) is performed on these two materials for an application to plastic transport pallets. Transport pallets reinforced with China reed fibre prove to be ecologically advantageous if they have a minimal lifetime of 3 years compared with the 5-year lifetime of the conventional pallet. The energy consumption and other environmental impacts are strongly reduced by the use of raw renewable fibres, due to three important factors: (a) the substitution of glass fibre production by the natural fibre production; (b) the indirect reduction in the use of polypropylene linked to the higher proportion of China reed fibre used and (c) the reduced pallet weight, which reduces fuel consumption during transport. Considering the whole life cycle, the polypropylene production process and the transport cause the strongest environmental impacts during the use phase of the life cycle. Since thermoplastic composites are hardly biodegradable, incineration has to be preferred to discharge on landfills at the end of its useful life cycle. The potential advantages of the renewable fibres will be effective only if a purer fibre extraction is obtained to ensure an optimal material stiffness, a topic for further research. China reed biofibres are finally compared with other usages of biomass, biomaterials, in general, can enable a three to ten times more efficient valorisation of biomass than mere heat production or biofuels for transport. 相似文献
225.
Zhan Wang Chongyang Shen Yichun Du Yulong Zhang Baoguo Li 《Frontiers of Environmental Science & Engineering》2019,13(5):79
226.
环境雌激素(Environmental Estrogens, EEs)种类繁多、来源多样且分布广泛,大量工业添加剂、食品添加剂和农药类物质已被证实具有雌激素活性。EEs对人体生殖、神经、免疫等系统生物毒性,已经引起了公众的普遍关注。近年来的研究表明,EEs不仅可以结合雌激素核受体(nuclear Estrogen Receptor, nER)干扰正常的雌激素基因组信号通路,还能活化雌激素膜受体(membrane Estrogen Receptor, mER)引发快速的雌激素非基因组信号转导途径。本文总结了EEs通过nER、mER介导的多种雌激素基因组和非基因组信号途径及其产生的生物学效应,综述了在其毒理学作用机理基础上发展的环境样品的雌激素活性评估和EEs混合物的联合作用研究,以期为该类污染物的筛查、风险评估和进一步的机制研究提供参考。 相似文献
227.
228.
Ecological network and emergy analysis of urban metabolic systems: Model development,and a case study of four Chinese cities 总被引:2,自引:0,他引:2
Analysis of the structure and function of urban metabolic systems is an important goal of urban research. We used network pathways and network utility analysis to analyze the basic network structure of the urban metabolic system and the complex ecological relationships within the system, providing a new way to perform such research. Using four Chinese cities as examples, we developed an ecological network model of the urban metabolic system. By using network pathway analysis, we studied the changing relationships between metabolic length and the number of metabolic pathways, and between metabolic length and reachability. Based on the distribution of the number of metabolic pathways, we describe the basic structure and intercompartment relationships of the system. By using the sign distribution in the network utility matrix, we determined the ecological relationships and degree of mutualism between the compartments of the system. The basic components of the system consisted of the internal environment, the external environment, and the agricultural, industrial, and domestic sectors. With increasing metabolic length, the ecological relationships among the components of the system became more diverse, and the numbers of metabolic paths and their reachability improved. Although the basic network structure of the four cities was identical, the mutualism index differed. Beijing's mutualism index was superior to that of Shanghai, and much higher than those of Tianjin and Chongqing. By analyzing the structure and function of the urban metabolic system, we provide suggestions for optimizing the structure and adjusting the relationships, and propose methods for the application of ecological network analysis in future urban system research. 相似文献
229.
230.
为了在核污染事故处理时提供精细化预警,以辽宁省某核电站周边部分重要目标(大衣屯、大周屯、红沿河镇、驼山乡、西杨乡、复大线应急撤离线路)为研究对象,将环境保护指挥自动化系统C4ISRE(Command,Control,Communications,Computer,Intelligence,Surveillance,Reconnaissance,Environmental Impact Assessment)与HYSPLIT 4.9模型相耦合,采用NCEP(美国国家环境预报中心)的FNL全球气象数据对核污染扩散轨迹进行仿真研究.结果表明:自模拟初始时间2014-04-01T00:00:00.00开始,进、出大衣屯边界时间分别为00:06:16.560、00:06:49.000,历时31.340 s;由西向东横穿过大周屯,进、出时间分别为于00:06:16.56到达大衣屯北部边界,于00:06:46.90扩散出大衣屯边界,经过大衣屯区域耗时共计29.00 s;核污染气团于00:15:30.85到达大周屯上空500 m处,由西向东横穿过大周屯,于00:15:46.05离开大周屯上空,过程耗时15.20 s;核污染气团于00:32:14.25经过重要应急撤离线路2(复大线),全程耗时32 min 14.25 s.核污染气团与从2014-04-01T00:00:00.000进入红沿河镇上空500 m区域,于00:24:27.00扩散出,全程历时24 min 27.00 s;进、出驼山乡上空500 m区域的时间分别为00:24:28、00:51:00,历时26 min 32.00 s;进、出西杨乡上空的时间分别为00:51:01、01:05:4.70,历时14 min 37.00 s;重点区域大衣屯和大周屯行政区的预警时间分别为376.56、930.85 s,重点撤离线路2区域预警时间为1934.25 s. 相似文献