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121.
The gas permeability of plastic films is important in packaging, containment, and agricultural fumigation. Recently, an approach for estimating the mass transfer coefficient of vapors across a film was presented by Papiernik et al. (2001). The mass transfer coefficient is an intrinsic property of a film-chemical combination, independent of the concentration gradient maintained across the film. Here we describe an apparatus useful for obtaining permeability data; the model of Papiernik et al. (2001) may be fitted to the data to determine mass transfer coefficients. The assembled equipment provides a sealed permeability cell, where a sample of the film to be tested is sandwiched between two static half-cells. Vapor is spiked to one side of the film and the concentrations in the spiked and receiving chamber are monitored until equilibrium. A sealed system is required for this approach; the permeability cells described here were gas-tight for >40 d. This approach produces reproducible measures of mass transfer coefficients that are not dependent on the size of the experimental apparatus. Model parameters were similar when fitted simultaneously as when determined independently from the same data set. 相似文献
122.
Urs Baumann Gustav Peter Ernst Pletscher Marcel Wettstein 《Environmental Sciences Europe》2003,15(4):227-233
Before waste-water-relevant organic materials are to be found in large quantities, their specific behavior in sewage treatment plants must be known. With the aid of the OECD simulation test #303 A, an estimation of their elimination in biological clarification stages can be made. In this work, an economical and continuous testing system is presented, which consists of a polyester flies bound to an activated biosludge with a high inoculum density, allowing one to measure no only the elimination of individual substances, but also the specific degree of mineralization. The toxicity of the activated biosludge and the nitrifying substances can also be examined. With the described testing procedure, it is possible to determine the rate of degradation within only a few hours. Finally, it can also be seen that it is possible to reliably and continuously determine the rate of anaerobic, biological degradability through the use of such a modified testing procedure. 相似文献
123.
H. Hollert M. Ernst T.-B. Seiler J. Wölz T. Braunbeck T. Kosmehl S. Keiter S. Grund W. Ahlf L. Erdinger M. Dürr 《Environmental Sciences Europe》2009,21(2):160-176
Background Being an important determinant in aquatic ecosystems, sediments have gotten more and more into focus of scientific and public discussions. While water quality has been significantly improving during recent years, highly contaminated sediments in many European rivers will still have ongoing impact for several centuries from now. Hence, monitoring and assessment of sediment quality are crucial for national legislation as well as the implementation of the European Water Framework Directive (WFD). Aim On the occasion of the retirement of Prof. Dr. Dr. h.?c. Volker Storch, this article reviews the various concepts of sediment assessment and introduces case studies in sediment toxicology which have been carried out in Heidelberg and surrounding areas. Results and Discussion Initially, the article portrays benefits and drawbacks of chemical analytics and biotest systems. The individual approach has only limited informative value, but combining both perspectives allows for a comprehensive characterization of the state of sediments. As examples of toxicity evaluation based on this strategy, weight-of-evidence studies for tiered investigations and integrated sediment assessment are presented. In addition, a combination of chemical fractionation, bioanalytic investigations and chemical analysis – known as ‘effect-directed analysis’ (EDA) – is discussed. This integrated concept eventually aims at the identification of hazardous substance classes or even of single compounds. Finally, the article raises the issue of sediment mobility as an important parameter for risk analyses of highly contaminated legacy sediments within further WFD implementation. Outlook Using various case studies, the article outlines the potentials of integrated approaches for cause-effect analysis of complex environmental samples within aquatic ecosystems as well as for action programs of management plans dealing with chemically polluted rivers. Effect-directed analysis in particular, but also the combined application of acute and mechanism-specific bioassays together with in-situ investigations, complemented by investigations on sediment mobility, appear promising with regard to comprehensive sediment assessment weight-of-evidence studies. 相似文献
124.
Klemm O Schemenauer RS Lummerich A Cereceda P Marzol V Corell D van Heerden J Reinhard D Gherezghiher T Olivier J Osses P Sarsour J Frost E Estrela MJ Valiente JA Fessehaye GM 《Ambio》2012,41(3):221-234
The collection of fog water is a simple and sustainable technology to obtain fresh water for afforestation, gardening, and as a drinking water source for human and animal consumption. In regions where fresh water is sparse and fog frequently occurs, it is feasible to set up a passive mesh system for fog water collection. The mesh is directly exposed to the atmosphere, and the foggy air is pushed through the mesh by the wind. Fog droplets are deposited on the mesh, combine to form larger droplets, and run down passing into a storage tank. Fog water collection rates vary dramatically from site to site but yearly averages from 3 to 10 l m−2 of mesh per day are typical of operational projects. The scope of this article is to review fog collection projects worldwide, to analyze factors of success, and to evaluate the prospects of this technology. 相似文献
125.
Time series of polychlorinated dioxins and furans (PCDD/F) and polychlorinated biphenyls (PCB) in ambient air of a large conurbation in North-Western Germany are presented and analyzed. The trend of PCDD/F concentrations, starting from as early as 1988, shows a pronounced decrease by at least one order of magnitude, demonstrating that the emission reductions were effective. The PCDD/F depositions also have decreased by a factor of 5 since 1992. However, both trends have leveled out since 2005. Time series of PCB concentrations and depositions starting in 1994 show only slight decreases for the concentrations and almost no decrease for the depositions. From the decay rates following first order kinetics, half-lives in the order of 5-15 years for the PCDD/F and 15-31 years for the sum of the six indicator PCB could be calculated, which are much longer than the half-lives estimated from their reactivity towards the OH radical. Apparently, small fresh emissions (PCDD/F), considerable secondary emissions and evaporation from contaminated soils slow down their decay in the atmosphere of big conurbations. Analyzing the decay rates of individual PCB congeners shows that the lower chlorinated and more volatile ones are removed faster than the higher chlorinated congeners, probably via gas phase reactions with the OH radical. It can be concluded from the present study that the input of PCDD/F and PCB into the food chain via the air path will continue for another one or two decades in big conurbations. 相似文献
126.
Life-cycle phases of a zinc- and cadmium-resistant ecotype of Silene vulgaris in risk assessment of polymetallic mine soils 总被引:5,自引:0,他引:5
Short-term exposure of plants to heavy metals is often used for risk assessment of metal-enriched soils (OECD guideline 208) without considering the reliability of the assessment for long-term exposure, i.e. for the completion of a plant's life-cycle. In the present study with 15 orogenic soils three phases of the life-cycle of a Zn-Cd-resistant ecotype of Silene vulgaris were studied to improve risk assessment of metal-enriched soils. The first phase, i.e. emergence of seedlings was not related to the water-soluble or total metal concentration of the soils. Seedling mortality was low as long as the water-soluble metal concentration did not surpass 0.15 micromol Zn and 0.04 micromol Cu g(-1) dry soil. Curtailment of the life-cycle prior to flowering, i.e. the vegetative growth as second phase, occurred on those soils where roots and shoots were heavily enriched by Zn already in the seedling phase. In the third phase, i.e. the generative phase, time to flowering and yield differences between orogenic soils were substantial, but soil metal concentrations could not be directly related to timing of reproduction or biomass. Ranking of data showed a high inconsistency of the responses to metal exposure during the first phases of the life-cycle. It is concluded that total plant mass and seed mass are the only realistic endpoints of life-cycle bioassays in risk assessment as long as ranks are inconsistent between two successive early phases of the life-cycle. 相似文献
127.
128.
Summary The conventional economic accounting systems have not played an enlightening role in statistically revealing the actual damage to the environment. They can, however, be methodologically improved; and they must be complemented by assessments of the ecological costs of the production process.In this article statistical evidence is provided on the level and structure of environmental damage and protection expenditures in the Federal Republic of Germany,i.e. on the environmental damage itself and on the environmental protection investments by industry and government, the capital stock for environmental protection, the total costs of and expenditures for environmental protection.Dr Christian Leipert and Prof. Udo Simonis are both regular contributors toThe Environmentalist (see 1989, pp.171–183; 1990, pp.25–38). Prof. Simonis is Director of the International Institute for Environment and Society (Wissenschaftszentrum) and Dr Leipert a member of its research staff. 相似文献
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130.