全文获取类型
收费全文 | 174篇 |
免费 | 7篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 4篇 |
地球物理 | 55篇 |
地质学 | 92篇 |
海洋学 | 5篇 |
综合类 | 2篇 |
自然地理 | 20篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 10篇 |
2012年 | 1篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2009年 | 27篇 |
2008年 | 20篇 |
2007年 | 17篇 |
2006年 | 17篇 |
2005年 | 10篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有191条查询结果,搜索用时 31 毫秒
101.
The aim of this work is to investigate whether it is possible to determine a critical sampling grid density for a given ore body, above which further improvement in the accuracy of the estimated ore reserves would be small or negligible. The methodology employed is based on the theory of information. First, it is proven that the range of influence, when appears in the variogram function, is a measure of the maximum variability frequency observed in the ore body. Then, a simple application of the well-known sampling theorem shows that, under certain assumptions, it is possible to define a critical sampling density as mentioned before. An approximate rule of thumb can then be stated: that critical sampling grid size is half the range of influence observed in the variogram. 相似文献
102.
103.
Jiachun Shi Haizhen Wang Jianming Xu Jianjun Wu Xingmei Liu Haiping Zhu Chunlan Yu 《Environmental Geology》2007,52(1):1-10
Six hundred and sixty-five soil samples were taken from Changxing County in Zhejiang Province, China, to characterize the
spatial variability of Hg Cd, Pb, Cu, As and Cr. The geostatistics and geographic information system (GIS) techniques were
applied, and the ordinary kriging and lognormal kriging were used to map the spatial patterns of the six heavy metals. Hg,
Pb, Cu and As were fitted to the spherical model with a range of 85.75, 82.32, 86.10, and 23.17 km, respectively. Cr was fitted
to the exponential model with a range of 6.27 km, and Cd was fitted to the linear model with a range of 37.66 km. Both Pb
and Cu had strong spatial dependence due to the effects of natural factors including parent material, topography and soil
type. Hg, Cd, Cr and As had, however, moderate spatial dependence, indicating an involvement of human factors. Meanwhile,
based on the comparison between the original data and the guide values of the six metals, the disjunctive kriging technique
was used to quantify their pollution risks. The results showed that only Cd and Hg exhibited pollution risks in the study
area. The pollution source evaluated was closely corresponded with the real discharge of industrial production and the application
of organomercury pesticides. The results of this study provide insight into risk assessment of environmental pollution and
decision making for agricultural production and industrial adjustment of building materials. 相似文献
104.
Xavier Emery 《Mathematical Geology》2007,39(6):607-623
Conditioning realizations of stationary Gaussian random fields to a set of data is traditionally based on simple kriging.
In practice, this approach may be demanding as it does not account for the uncertainty in the spatial average of the random
field. In this paper, an alternative model is presented, in which the Gaussian field is decomposed into a random mean, constant
over space but variable over the realizations, and an independent residual. It is shown that, when the prior variance of the
random mean is infinitely large (reflecting prior ignorance on the actual spatial average), the realizations of the Gaussian
random field are made conditional by substituting ordinary kriging for simple kriging. The proposed approach can be extended
to models with random drifts that are polynomials in the spatial coordinates, by using universal or intrinsic kriging for
conditioning the realizations, and also to multivariate situations by using cokriging instead of kriging. 相似文献
105.
Linda J. Young Carol A. Gotway 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):589-600
A nationwide Environmental Public Health Tracking program is being created to monitor environmental impacts on human health.
This, and many other efforts to relate environmental and health outcomes, depend largely on the synthesis of existing data
sets; little new data are being generated for this purpose. More often than not, the data available for such synthesis have
been collected for different geographic or spatial units, and any set of these units may be different from the one of interest.
In this paper, we compare and contrast two approaches that can be used within a Geographic Information System to link spatial
data from different sources. The first approach works with centroids of areal units and is commonly used in environmental
health analyses. The second approach honors the spatial support (size, shape and orientation) of the data. Using traditional
regression models and a spatially-varying coefficient regression model, we show that different linkage methods can lead to
different inference. We describe key ideas pertaining to the support of spatial data that are often ignored in many analyses
of environmental health data and present a general analytical approach to change-of-support problems. 相似文献
106.
Fred J. Molz Tomasz J. Kozubowski Krzysztof Podgórski James W. Castle 《Hydrogeology Journal》2007,15(4):809-816
In order to generalize the fractal/facies concept, a new stochastic fractal model for ln(K) increment probability density functions (PDFs) is presented that produces non-Gaussian behavior at smaller lags and converges to Gaussian at larger lags. The model is based on the classical Laplace PDF. The new stochastic fractal family is called fractional Laplace motion (fLam) having stationary increments called fractional Laplace noise (fLan). This fractal is different from other fractals because the character of the underlying increment PDFs changes dramatically with lag size, which leads to lack of self-similarity. Data also appear to display this characteristic. In the larger lag size ranges, approximate self-affinity does hold. The basic field procedure for further testing of the fractional Laplace theory is to measure ln(K) increment distributions along transects, calculate frequency distributions from the data, and compare results to appropriate fLan family members. The variances of the frequency distributions should also change with lag size (scale) in a prescribed manner. There are mathematical reasons such as the geometric central limit theorem, for surmising that fLam/fLan may be more fundamental than other approaches that have been proposed for modeling ln(K) frequency distributions. 相似文献
107.
This study is concerned with the spatial variability of some wet atmospheric precipitation parameters such as; pH, conductivity (EC). The study also depicts the spatial variability of some ions (cations and anions) of atmospheric precipitation in Jordan such as, Ca2+, Mg2+, Na+ and K+, HCO3−, Cl−, NO3− and SO42−. The basis of the work is to establish a relationship through the cumulative semivariogram technique between the distance ratios and the spatial dependence structure of the chemical composition of atmospheric precipitation. All semivariogram models are constructed in this study in order to understand the behavior of the spatial distribution. The spatial distributions of rainwater parameters show differences from station to station which is expressed in terms of angle, where the larger the angle the weaker the correlation. The semivariogram (SV) models are constructed to show the variation of the rainfall chemistry in Jordan. The SV models show weak correlation between mountain and leeside mountain stations, i.e. mountain and desert stations. On the other hand, good correlations are observed when transferring from south to north of the country. The larger is the found angle, the weaker is the correlation. For most of the SV model the correlation is found to be very weak between desert and mountainous locality. The Standard Regional Dependence Factor (SRDF) is used for prediction of the distribution of rain fall parameters. It shows the relative error between observed and predicted values of rainwater parameters. The overall regional relative error between the observed and estimated concentrations remains less than 15%. 相似文献
108.
When groundwater pollution occurs,to come up with an efficient remediation plan,it is particularly important to collect information of contaminant source(location and source strength)and hydraulic conductivity field of the site accurately and quickly.However,the information can not be obtained by direct observation,and can only be derived from limited measurement data.Data assimilation of observations such as head and concentration is often used to estimate parameters of contaminant source.As for hydraulic conductivity field,especially for complex non-Gaussian field,it can be directly estimated by geostatistics method based on limited hard data,while the accuracy is often not high.Better estimation of hydraulic conductivity can be achieved by solving inverse groundwater problem.Therefore,in this study,the multi-point geostatistics method Quick Sampling(QS)is proposed and introduced for the first time and combined with the iterative local updating ensemble smoother(ILUES)to develop a new data assimilation framework QS-ILUES.It helps to solve the contaminant source parameters and non-Gaussian hydraulic conductivity field simultaneously by assimilating hydraulic head and pollutant concentration data.While the pilot points are utilized to reduce the dimension of hydraulic conductivity field,the influence of pilot points’layout and the ensemble size of ILUES algorithm on the inverse simulation results are further explored. 相似文献
109.
The application of regionalized variables requires the estimation of the variogram function and the evaluation of its integral. By representing the variogram by a general polygonal function the requisite integrals may be easily computed by a closed form representation of simple integrals. This paper provides the integration formulas for two-dimensional variogram functions whose domain is represented as a finite collection of rectangles. The integration formulas essential for a fully developed polygonal approach to an extensive statistical evaluation of geostatistical quantities are presented. 相似文献
110.
In this paper, we have basically attempted to solve two problems: (i) the restricted kriging problem as stated by Matheron, and (ii) the defining of Matheron's kriging problem within the framework of fuzzy logic in order to interpret the Lagrange multiplier, which is a function of kriging variance and is a dual variable with respect to which the generalized Lagrange function F(X, ) is minimized.on leave from Department of Geology, Indian Institute of Technology, Kharagphur 721302, West Bengal, India. 相似文献