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911.
912.
913.
A spatial array of wave gauges installed on an observatoion platform has been designed and arranged to measure the lo-cal features of winter monsoon directional waves off Taishi coast of Taiwan. A new method, named the Bayesian Parameter Estimation Method(BPEM) , is developed and adopted to determine the main direction and the directional spreading parame-ter of directional spectra. The BPEM could be considered as a regression analysis to find the maximum joint probability of parameters, which best approximates the observed data from the Bayesian viewpoint. The result of the analysis of field wave data demonstrates the highly dependency of the characteristics of normalized directional spreading on the wave age. The Mit-suyasu type empirical formula of directional spectrum is therefore modified to be representative of monsoon wave field. More-over, it is suggested that Smax could be expressed as a function of wave steepness. The values of Smax decrease with increas-ing steepness. Finally, a local directi 相似文献
914.
Development and Implementation of a Bayesian-based Aquifer Vulnerability Assessment in Florida 总被引:4,自引:1,他引:4
Jonathan D. Arthur H. Alex R. Wood Alan E. Baker James R. Cichon Gary L. Raines 《Natural Resources Research》2007,16(2):93-107
The Florida Aquifer Vulnerability Assessment (FAVA) was designed to provide a tool for environmental, regulatory, resource
management, and planning professionals to facilitate protection of groundwater resources from surface sources of contamination.
The FAVA project implements weights-of-evidence (WofE), a data-driven, Bayesian-probabilistic model to generate a series of
maps reflecting relative aquifer vulnerability of Florida’s principal aquifer systems. The vulnerability assessment process,
from project design to map implementation is described herein in reference to the Floridan aquifer system (FAS). The WofE
model calculates weighted relationships between hydrogeologic data layers that influence aquifer vulnerability and ambient
groundwater parameters in wells that reflect relative degrees of vulnerability. Statewide model input data layers (evidential
themes) include soil hydraulic conductivity, density of karst features, thickness of aquifer confinement, and hydraulic head
difference between the FAS and the watertable. Wells with median dissolved nitrogen concentrations exceeding statistically
established thresholds serve as training points in the WofE model. The resulting vulnerability map (response theme) reflects
classified posterior probabilities based on spatial relationships between the evidential themes and training points. The response
theme is subjected to extensive sensitivity and validation testing. Among the model validation techniques is calculation of
a response theme based on a different water-quality indicator of relative recharge or vulnerability: dissolved oxygen. Successful
implementation of the FAVA maps was facilitated by the overall project design, which included a needs assessment and iterative
technical advisory committee input and review. Ongoing programs to protect Florida’s springsheds have led to development of
larger-scale WofE-based vulnerability assessments. Additional applications of the maps include land-use planning amendments
and prioritization of land purchases to protect groundwater resources. 相似文献
915.
Earthquakes are conspicuous manifestations of tectonic stress, but the non-linear relationships between the stresses acting on a fault plane, its frictional slip, and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress. Moreover, observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations. However, by assuming that each earthquake in a small volume of the crust represents a single, uniform state of stress, the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated. Here, we outline a probabilistic (Bayesian) technique for estimating tectonic stress directions from primary seismological observations. The Bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation. We show our Bayesian formulation to be equivalent to a well-known analytical solution for a single, errorless focal mechanism observation. The new approach has the distinct advantage, however, of including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors and (4) any prior knowledge of the stress field. Our approach, while computationally demanding in some cases, is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, such as seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations. 相似文献
916.
Nicolas Gillet rew Jackson Christopher C. Finlay 《Geophysical Journal International》2007,171(3):1005-1016
We incorporate a maximum entropy image reconstruction technique into the process of modelling the time-dependent geomagnetic field at the core–mantle boundary (CMB). In order to deal with unconstrained small lengthscales in the process of inverting the data, some core field models are regularized using a priori quadratic norms in both space and time. This artificial damping leads to the underestimation of power at large wavenumbers, and to a loss of contrast in the reconstructed picture of the field at the CMB. The entropy norm, recently introduced to regularize magnetic field maps, provides models with better contrast, and involves a minimum of a priori information about the field structure. However, this technique was developed to build only snapshots of the magnetic field. Previously described in the spatial domain, we show here how to implement this technique in the spherical harmonic domain, and we extend it to the time-dependent problem where both spatial and temporal regularizations are required. We apply our method to model the field over the interval 1840–1990 from a compilation of historical observations. Applying the maximum entropy method in space—for a fit to the data similar to that obtained with a quadratic regularization—effectively reorganizes the magnetic field lines in order to have a map with better contrast. This is associated with a less rapidly decaying spectrum at large wavenumbers. Applying the maximum entropy method in time permits us to model sharper temporal changes, associated with larger spatial gradients in the secular variation, without producing spurious fluctuations on short timescales. This method avoids the smearing back in time of field features that are not constrained by the data. Perspectives concerning future applications of the method are also discussed. 相似文献
917.
介绍了Bayesian Networks(简称BNs)产生“Tuned”模板新方法的基本原理以及BNs法与蚁群行为仿真技术和单纯形法组合的方法。通过实际航空影像的实验结果表明,新方法对纹理影像的识别率是令人满意的,同时还将新方法与遗传算法的结果作了对比,结果表明新方法是很有应用前景的。 相似文献
918.
可视化交互空间数据挖掘原型系统设计与实现 总被引:1,自引:0,他引:1
基于VC^++ 6.0和MapObject2.0组件技术设计,开发了一个可视化交互空间数据挖掘的原型系统VGC(visual geo—classify),并用实例数据对系统性能和算法、规则有效性进行了验证。结果表明,该原型系统是一个适用的、可扩展的可视化交互空间数据挖掘工具。 相似文献
919.
Autoregressive (AR) extrapolation of travel-time data is tested using several synthetic tomography examples using a cross-borehole
geometry. Earlier studies have shown crossborehole tomography using travel-times can have reduced resolution because of the
limitations on ray coverage. We apply AR extrapolation to partial travel-time data and then compare the tomographic inversions
using the full data and the extrapolated data. Both the overall patterns of the extended data and the tomographic reconstructions
with the extended data show that AR extrapolation can effectively extend the synthetic crossborehole tomographic data to a
broader coverage and can improve the cross-hole reconstruction images. 相似文献
920.
抗差Tikhonov正则化方法及其应用 总被引:4,自引:0,他引:4
提出了抗差Tikhonov正则化方法,并给出了3种常用的计算正则化参数的抗差估计方法,即抗差L-曲线法、抗差广义交叉检核法和抗差广义不符原理。计算结果表明,抗差Tikhonov正则化方法不仅能克服方程病态,而且能有效地控制观测异常影响。 相似文献