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601.
602.
在高斯线源扩散模式的基础上,建立了一个适合高速公路大气污染源扩散特点的模式,并以沈阳环城高速公路环境影响评价中的应用为例,说明该模式的实用性和优越性.在建立该模式的过程中,应用了国外关于公路扩散试验的成果来确定和修正模式中的扩散参数. 相似文献
603.
Raimundo Real A. Márcia Barbosa J. Mario Vargas 《Environmental and Ecological Statistics》2006,13(2):237-245
Logistic regression is a statistical tool widely used for predicting species’ potential distributions starting from presence/absence
data and a set of independent variables. However, logistic regression equations compute probability values based not only
on the values of the predictor variables but also on the relative proportion of presences and absences in the dataset, which
does not adequately describe the environmental favourability for or against species presence. A few strategies have been used
to circumvent this, but they usually imply an alteration of the original data or the discarding of potentially valuable information.
We propose a way to obtain from logistic regression an environmental favourability function whose results are not affected
by an uneven proportion of presences and absences. We tested the method on the distribution of virtual species in an imaginary
territory. The favourability models yielded similar values regardless of the variation in the presence/absence ratio. We also
illustrate with the example of the Pyrenean desman’s (Galemys pyrenaicus) distribution in Spain. The favourability model yielded more realistic potential distribution maps than the logistic regression
model. Favourability values can be regarded as the degree of membership of the fuzzy set of sites whose environmental conditions
are favourable to the species, which enables applying the rules of fuzzy logic to distribution modelling. They also allow
for direct comparisons between models for species with different presence/absence ratios in the study area. This makes them
more useful to estimate the conservation value of areas, to design ecological corridors, or to select appropriate areas for
species reintroductions.
Received: June 2005 / Revised: July 2005 相似文献
604.
Thomas C. Edwards Jr. D. Richard Cutler Niklaus E. Zimmermann Linda Geiser Gretchen G. Moisen 《Ecological modelling》2006
We evaluated the effects of probabilistic (hereafter DESIGN) and non-probabilistic (PURPOSIVE) sample surveys on resultant classification tree models for predicting the presence of four lichen species in the Pacific Northwest, USA. Models derived from both survey forms were assessed using an independent data set (EVALUATION). Measures of accuracy as gauged by resubstitution rates were similar for each lichen species irrespective of the underlying sample survey form. Cross-validation estimates of prediction accuracies were lower than resubstitution accuracies for all species and both design types, and in all cases were closer to the true prediction accuracies based on the EVALUATION data set. We argue that greater emphasis should be placed on calculating and reporting cross-validation accuracy rates rather than simple resubstitution accuracy rates. Evaluation of the DESIGN and PURPOSIVE tree models on the EVALUATION data set shows significantly lower prediction accuracy for the PURPOSIVE tree models relative to the DESIGN models, indicating that non-probabilistic sample surveys may generate models with limited predictive capability. These differences were consistent across all four lichen species, with 11 of the 12 possible species and sample survey type comparisons having significantly lower accuracy rates. Some differences in accuracy were as large as 50%. The classification tree structures also differed considerably both among and within the modelled species, depending on the sample survey form. Overlap in the predictor variables selected by the DESIGN and PURPOSIVE tree models ranged from only 20% to 38%, indicating the classification trees fit the two evaluated survey forms on different sets of predictor variables. The magnitude of these differences in predictor variables throws doubt on ecological interpretation derived from prediction models based on non-probabilistic sample surveys. 相似文献
605.
606.
根据我国颁布的《地面水环境质量标准非离子氨换算方法》,用Foxpro语言编程计算非离子氨浓度,提高监测数据处理率,减少计算误差.通过实例计算,程序运行正常,结果正确. 相似文献
607.
Five regression models (Poisson, negative binomial, quasi-Poisson, the hurdle model and the zero-inflated Poisson) were used to assess the relationship between the abundance of a vulnerable plant species, Leionema ralstonii, and the environment. The methods differed in their capacity to deal with common properties of ecological data. They were assessed theoretically, and their predictive performance was evaluated with correlation, calibration and error statistics calculated within a bootstrap evaluation procedure that simulated performance for independent data. 相似文献
608.
R. Newsham P. S. Balson D. G. Tragheim A. M. Denniss 《Journal of Coastal Conservation》2002,8(1):49-54
The rapidly eroding cliffs and foreshore of the Holderness Coast represent one of the largest sources of sediment discharging
in the southern North Sea. For effective coastal management it is important to understand the sediment sources, transport
pathways and depositional sinks. The sediment budget is regarded as one of the key information needs for sustainable planning
and management. In order to quantify the sediment yield from recession of the Holderness Coast, digital photogrammetry has
been used, together with nearshore bathymetric survey data, to produce a single DTM for a length of over 52 km of coastline.
Other data including geological sections, sediment lithology, recession rates and the location of coastal defences have been
added to the DTM to create a GIS for the Holderness Coast. The GIS has been used to predict the volume and nature of the sediment
yield assuming that historical recession rates continue. The GIS can also be used to predict future yields using assumptions
of accelerated recession or the implications of arrested retreat due to construction of defences. 相似文献
609.
Georgiy Stenchikov Nilesh Lahoti David J. Diner Ralph Kahn Paul J. Lioy Panos G. Georgopoulos 《Environmental Fluid Mechanics》2006,6(5):425-450
The collapse of the world trade center (WTC) produced enhanced levels of airborne contaminants in New York City and nearby areas on September 11, 2001 through December, 2001. This catastrophic event revealed the vulnerability of the urban environment, and the inability of many existing air monitoring systems to operate efficiently in a crisis. The contaminants released circulated within the street canyons, but were also lifted above the urban canopy and transported over large distances, reflecting the fact that pollutant transport affects multiple scales, from single buildings through city blocks to mesoscales. In this study, ground-and space-based observations were combined with numerical weather forecast fields to initialize fine-scale numerical simulations. The effort is aimed at reconstructing pollutant dispersion from the WTC in New York City to surrounding areas, to provide means for eventually evaluating its effect on population and environment. Atmospheric dynamics were calculated with the multi-grid Regional Atmospheric Modeling System (RAMS), covering scales from 250 m to 300 km and contaminant transport was studied using the Hybrid Particle and Concentration Transport (HYPACT) model that accepts RAMS meteorological output. The RAMS/HYPACT results were tested against PM2.5 observations from the roofs of public schools in New York City (NYC), Landsat images, and Multi-angle Imaging SpectroRadiometer (MISR) retrievals. Calculations accurately reproduced locations and timing of PM2.5 peak aerosol concentrations, as well as plume directionality. By comparing calculated and observed concentrations, the effective magnitude of the aerosol source was estimated. The simulated pollutant distributions are being used to characterize levels of human exposure and associated environmental health impacts. 相似文献
610.