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101.
102.
中国土壤表层钙元素背景值的地域最佳估值研究 总被引:2,自引:0,他引:2
应用地统计学方法研究了中国土壤表层钙元素背景值的空间变异结构,并藉此进行了钙元素背景值的地域估值.结果表明,这种估值方法突出反映了钙元素在中国的宏观变化规律.与趋势面方法相比,具有明显优势. 相似文献
103.
Spatial statistical models that use flow and stream distance 总被引:6,自引:1,他引:6
Jay M. Ver Hoef Erin Peterson David Theobald 《Environmental and Ecological Statistics》2006,13(4):449-464
We develop spatial statistical models for stream networks that can estimate relationships between a response variable and
other covariates, make predictions at unsampled locations, and predict an average or total for a stream or a stream segment.
There have been very few attempts to develop valid spatial covariance models that incorporate flow, stream distance, or both.
The application of typical spatial autocovariance functions based on Euclidean distance, such as the spherical covariance
model, are not valid when using stream distance. In this paper we develop a large class of valid models that incorporate flow
and stream distance by using spatial moving averages. These methods integrate a moving average function, or kernel, against
a white noise process. By running the moving average function upstream from a location, we develop models that use flow, and
by construction they are valid models based on stream distance. We show that with proper weighting, many of the usual spatial
models based on Euclidean distance have a counterpart for stream networks. Using sulfate concentrations from an example data
set, the Maryland Biological Stream Survey (MBSS), we show that models using flow may be more appropriate than models that
only use stream distance. For the MBSS data set, we use restricted maximum likelihood to fit a valid covariance matrix that
uses flow and stream distance, and then we use this covariance matrix to estimate fixed effects and make kriging and block
kriging predictions.
Received: July 2005 / Revised: March 2006 相似文献
104.
HIROTAKA?SAITOEmail author SEAN?A.?MCKENNA PIERRE?GOOVAERTS 《Environmental and Ecological Statistics》2005,12(1):7-25
Efficient and reliable unexploded ordnance (UXO) site characterization is needed for decisions regarding future land use. There are several types of data available at UXO sites and geophysical signal maps are one of the most valuable sources of information. Incorporation of such information into site characterization requires a flexible and reliable methodology. Geostatistics allows one to account for exhaustive secondary information (i.e.,, known at every location within the field) in many different ways. Kriging and logistic regression were combined to map the probability of occurrence of at least one geophysical anomaly of interest, such as UXO, from a limited number of indicator data. Logistic regression is used to derive the trend from a geophysical signal map, and kriged residuals are added to the trend to estimate the probabilities of the presence of UXO at unsampled locations (simple kriging with varying local means or SKlm). Each location is identified for further remedial action if the estimated probability is greater than a given threshold. The technique is illustrated using a hypothetical UXO site generated by a UXO simulator, and a corresponding geophysical signal map. Indicator data are collected along two transects located within the site. Classification performances are then assessed by computing proportions of correct classification, false positive, false negative, and Kappa statistics. Two common approaches, one of which does not take any secondary information into account (ordinary indicator kriging) and a variant of common cokriging (collocated cokriging), were used for comparison purposes. Results indicate that accounting for exhaustive secondary information improves the overall characterization of UXO sites if an appropriate methodology, SKlm in this case, is used. 相似文献
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为研究广东省某矿区开展生态修复多年后下游农田土壤的金属污染状况,选取该矿区下游某村周边农田土壤及灌溉水渠作为研究对象,对该区域采集了40个土壤表层样本和8个水体样本,利用Arcgis软件对农田土壤样品中As、Cu、Cd、Pb、Zn、Mn和Fe2O3的质量分数进行克里金空间插值,解析该区域农田土壤金属的空间分布特征;采用综合污染指数法和潜在生态风险指数法对该区域耕作层土壤中As、Cu、Cd、Pb、Zn和Mn进行风险评价。结果表明,40个土壤样品中As、Cd、Cu、Zn和Pb的超标率分别为77.5%、70%、87.5%、27.5%和67.5%,说明调查区域农田土壤污染属于多金属复合污染,且对农作物的生产和安全产生巨大的威胁。部分土壤样品中As、Pb和Cd含量超过了中国农用地土壤污染风险管制值,需采取严格管控措施。通过分析土壤金属的空间分布,发现土壤金属含量超标点位主要位于灌溉口与受污染河流周边,且含量与离灌溉口距离成反比。结合目前灌溉水样中的金属均未超标的情况,得出该区域农田土壤污染是由该矿区生态环境修复前所产生的含金属灌溉水导致土壤中金属的积累... 相似文献
109.
Chengfu Zhang John A. Trofymow Fan-Rui Meng Charles P.-A. Bourque 《Ecological modelling》2010,221(16):1944-1244
The forest litter decomposition model (FLDM) described in this paper provides an important basis for assessing the impacts of forest management on seasonal stream water quality and export of dissolved organic carbon (DOC). By definition, models with annual time steps are unable to capture seasonal, within-year variation. In order to simulate seasonal variation in litter decomposition and DOC production and export, we have modified an existing annual FLDM to account for monthly dynamics of decomposition and residual mass in experimental litterbags placed in 21 different forests across Canada.The original annual FLDM was formulated with three main litter pools (fast, slow, and very slow decomposing litter) to address the fact that forest litter is naturally composed of a mixture of organic compounds that decompose at different rates. The annual FLDM was shown to provide better simulations than more complex models like CENTURY and SOMM.The revised monthly model retains the original structure of the annual FLDM, but separates litter decomposition from nitrogen (N) mineralization. In the model, monthly soil temperature, soil moisture, and mean January soil temperature are shown to be the most important controlling variables of within-year variation in decomposition. Use of the three variables in a process-based definition of litter decomposition is a significant departure from the empirical definition in the annual model. The revised model is shown to give similar calculations of residual mass and N concentration as the annual model (r2 = 0.91, 0.78), despite producing very different timeseries of decomposition over six years. It is shown from a modelling perspective that (i) forest litter decomposition is independent of N mineralization, whereas N mineralization is dependent on litter decomposition, and (ii) mean January soil temperature defines litter decomposition in the summer because of winter-temperatures’ role in modifying forest-floor microorganism community composition and functioning in the following summer. 相似文献
110.
Many authors have proposed mechanisms to induce regulated polluting firms to truthfully reveal their private information. This paper proposes an alternative scheme in which the regulator offers each firm a menu of linear price-quantity contracts; faced with this menu, each firm′s dominant strategy is to truthfully report its private information and self-select the contract that is ex post efficient. The proposed menu schedule that is more elastic than the firm′s residual marginal damage function engenders a positive quantity effect, thereby counterbalancing the firm′s incentive to misreport prompted by the linearity of price. Due to its built-in price quantity structure, the scheme performs as designed regardless of the elasticities of marginal damage and demand functions. 相似文献