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The increasing availability of digital photographic materials has fueled efforts by agencies and organizations to generate land cover maps for states, regions, and the United States as a whole. Regardless of the information sources and classification methods used, land cover maps are subject to numerous sources of error. In order to understand the quality of the information contained in these maps, it is desirable to generate statistically valid estimates of accuracy rates describing misclassification errors. We explored a full sample survey framework for creating accuracy assessment study designs that balance statistical and operational considerations in relation to study objectives for a regional assessment of GAP land cover maps. We focused not only on appropriate sample designs and estimation approaches, but on aspects of the data collection process, such as gaining cooperation of land owners and using pixel clusters as an observation unit. The approach was tested in a pilot study to assess the accuracy of Iowa GAP land cover maps. A stratified two-stage cluster sampling design addressed sample size requirements for land covers and the need for geographic spread while minimizing operational effort. Recruitment methods used for private land owners yielded high response rates, minimizing a source of nonresponse error. Collecting data for a 9-pixel cluster centered on the sampled pixel was simple to implement, and provided better information on rarer vegetation classes as well as substantial gains in precision relative to observing data at a single-pixel. 相似文献
74.
Yunyu Pan Gerwin F. Koopmans Luc T. C. Bonten Jing Song Yongming Luo Erwin J. M. Temminghoff Rob N. J. Comans 《Environmental geochemistry and health》2016,38(6):1355-1372
Alternating flooding and drainage conditions have a strong influence on redox chemistry and the solubility of trace metals in paddy soils. However, current knowledge of how the effects of water management on trace metal solubility are linked to trace metal uptake by rice plants over time is still limited. Here, a field-contaminated paddy soil was subjected to two flooding and drainage cycles in a pot experiment with two rice plant cultivars, exhibiting either high or low Cd accumulation characteristics. Flooding led to a strong vertical gradient in the redox potential (Eh). The pH and Mn, Fe, and dissolved organic carbon concentrations increased with decreasing Eh and vice versa. During flooding, trace metal solubility decreased markedly, probably due to sulfide mineral precipitation. Despite its low solubility, the Cd content in rice grains exceeded the food quality standards for both cultivars. Trace metal contents in different rice plant tissues (roots, stem, and leaves) increased at a constant rate during the first flooding and drainage cycle but decreased after reaching a maximum during the second cycle. As such, the high temporal variability in trace metal solubility was not reflected in trace metal uptake by rice plants over time. This might be due to the presence of aerobic conditions and a consequent higher trace metal solubility near the root surface, even during flooding. Trace metal solubility in the rhizosphere should be considered when linking water management to trace metal uptake by rice over time. 相似文献
75.
R. Michael Erwin David F. Brinker Bryan D. Watts Gary R. Costanzo David D. Morton 《Journal of Coastal Conservation》2011,15(1):51-60
Like many resources in the Chesapeake Bay region of the U.S., many waterbird nesting populations have suffered over the past
three to four decades. In this study, historic information for the entire Bay and recent results from the Tangier Sound region
were evaluated to illustrate patterns of island erosion and habitat loss for 19 breeding species of waterbirds. Aerial imagery
and field data collected in the nesting season were the primary sources of data. From 1993/1994 to 2007/2008, a group of 15
islands in Tangier Sound, Virginia were reduced by 21% in area, as most of their small dunes and associated vegetation and
forest cover were lost to increased washovers. Concurrently, nesting American black ducks (Anas rubripes) declined by 66% , wading birds (herons-egrets) by 51%, gulls by 72%, common terns (Sterna hirundo) by 96% and black skimmers (Rynchops niger) by about 70% in this complex. The declines noted at the larger Bay-wide scale suggest that this study area maybe symptomatic
of a systemic limitation of nesting habitat for these species. The island losses noted in the Chesapeake have also been noted
in other Atlantic U.S. coastal states. Stabilization and/or restoration of at least some of the rapidly eroding islands at
key coastal areas are critical to help sustain waterbird communities. 相似文献
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Pascal de Decker Erwin Lammens Paul van der Sluys Leopold van der Vliet Peter J. Van Severen 《Journal of Environmental Planning and Management》1987,30(2):91-98
This article deals with Flanders’ urbanity. At the moment Flanders, a part of Belgium, is responsible for its own town and country planning. Nevertheless, today's picture of urbanity is, for the greatest part, the result of Belgian policy. The results are nothing to be proud of. In fact Flanders has no urbanity anymore, nor a real rurality. Everywhere in the countryside there are houses and other constructions; on the other hand and consequently the centres of cities and villages are in decay. The following text tries to draw, very briefly, the problems and the development of the problems in urban and rural Flanders. The roots have to be searched in the 19th century, especially in the constitution of Belgium, which is one of the most liberal on earth. The first part of the article is dealing with the history of urbanisation, whilst the second part deals with some recent evolutions in housing and housing policy, in employment and employment policy, in transport and transport policy. Finally, the third part is concerned with the town and country planning which has to structure the developments in spatial use for housing, industrial building and so on, but which has failed. 相似文献
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79.
Poggio L Vrscaj B Schulin R Hepperle E Ajmone Marsan F 《Environmental pollution (Barking, Essex : 1987)》2009,157(2):680-689
Polluted soils can present a significant health risk especially in an urban environment. Most current legislation and health risk frameworks are based on pseudototal metal content. However, only a fraction of these concentrations is available for plant and human uptake. The aim of this work was to study the diffuse metal contamination in the soils of a municipality in Northern Italy in terms of: (i) metal availability, and (ii) metal accessibility to the human body and its relationship to soil properties, considering lead, copper, zinc, nickel, and chromium. Soil metal content was measured simulating availability conditions. Human bioaccessibility was derived from a modified physiologically-based extraction test. The human bioaccessible content was then estimated taking into account the relationships between pseudototal content and selected soil parameters. For the case study, the prediction of human bioaccessibility based on pseudototal content, organic matter and soil texture produced statistically significant models, with r2 = 0.60 for Cu, r2 = 0.53 for Pb and r2 = 0.42 for Zn. 相似文献
80.
William D. Holland Akira Hasegawa James R. Taylor Erwin K. Kauper 《Journal of the Air & Waste Management Association (1995)》2013,63(2):147-174
The simple ATDL urban dispersion model Is based on the formula Xo(g/m3) = CO(g/m2s)/U(m/s). The diurnal variation of the stability factor C, which can be thought of as the width of the urban area divided by the vertical dispersion of the pollution cloud, has not before been satisfactorily estimated. Using observed diurnal variations of CO concentrations and traffic frequencies reported by DeMarrais of the EPA for many stations in the states of Maryland, New Jersey, and Colorado, and using wind data from these states, hourly values of C - XoU/Q were calculated. The ratio of C to the daily average C is found to equal about 2.5 at 4 a.m., drops to about 0.5 by 8 a.m., and remains at 0.5 until about 6 p.m.., when it starts to climb slowly again. Application of this new stability factor to independent CO data from Los Angeles yields correlations between measured and predicted concentrations of about 0.7. 相似文献