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131.
G. Christakos C. T. Miller D. Oliver 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(3):213-239
As is well known, a complete stochastic solution of the stochastic differential equation governing saturated groundwater flow leads to an infinite hierarchy of equations in terms of higher-order moments. Perturbation techniques are commonly used to close this hierarchy, using power-series expansions. These methods are applied by truncating the series after a finite number of terms, and products of random gradients of conductivity and head potential are neglected. Uncertainty regarding the number or terms required to yield a sufficiently accurate result is a significant drawback with the application of power series-based perturbation methods for such problems. Low-order series truncation may be incapable of representing fundamental characteristics of flow and can lead to physically unreasonable and inaccurate solutions of the stochastic flow equation. To support this argument, one-dimensional, steady-state, saturated groundwater flow is examined, for the case of a spatially distributed hydraulic conductivity field. An ordinary power-series perturbation method is used to approximate the mean head, using second-order statistics to characterize the conductivity field. Then an interactive perturbation approach is introduced, which yields improved results compared to low-order, power-series perturbation methods for situations where strong interactions exist between terms in such approximations. The interactive perturbation concept is further developed using Feynman-type diagrams and graph theory, which reduce the original stochastic flow problem to a closed set of equations for the mean and the covariance functions. Both theoretical and practical advantages of diagrammatic solutions are discussed; these include the study of bounded domains and large fluctuations. 相似文献
132.
Viet-Ha Nhu Khabat Khosravi James R. Cooper Mahshid Karimi Ozgur Kisi Binh Thai Pham 《水文科学杂志》2020,65(12):2116-2127
ABSTRACT The predictive capability of a new artificial intelligence method, random subspace (RS), for the prediction of suspended sediment load in rivers was compared with commonly used methods: random forest (RF) and two support vector machine (SVM) models using a radial basis function kernel (SVM-RBF) and a normalized polynomial kernel (SVM-NPK). Using river discharge, rainfall and river stage data from the Haraz River, Iran, the results revealed: (a) the RS model provided a superior predictive accuracy (NSE = 0.83) to SVM-RBF (NSE = 0.80), SVM-NPK (NSE = 0.78) and RF (NSE = 0.68), corresponding to very good, good, satisfactory and unsatisfactory accuracies in load prediction; (b) the RBF kernel outperformed the NPK kernel; (c) the predictive capability was most sensitive to gamma and epsilon in SVM models, maximum depth of a tree and the number of features in RF models, classifier type, number of trees and subspace size in RS models; and (d) suspended sediment loads were most closely correlated with river discharge (PCC = 0.76). Overall, the results show that RS models have great potential in data poor watersheds, such as that studied here, to produce strong predictions of suspended load based on monthly records of river discharge, rainfall depth and river stage alone. 相似文献
133.
134.
岩溶坝区透水参数的随机模型 总被引:1,自引:0,他引:1
岩溶坝区的渗透特性受高应力场的作用,使其固有的非均质各向异性更趋复杂,采用确定性的方法不能准确的描述其本质特性。本文在对岩溶坝区透水性随机场进行分析的基础上,提出了渗透随机性的数学描述。考察岩溶坝区主要的两场作用,即渗流与应力场的耦合。基于Taylor随机有限元建立了渗流应力耦合的随机微分方程格式,并对耦合随机模型反演求解渗透参数提出了思路。 相似文献
135.
综合小波分析与分形方法进行弱磁异常识别 总被引:1,自引:0,他引:1
利用小波分析塔式算法对单一分形模型数据进行处理,结合“随机共振”理论,对高精度弱磁异常中的噪声和误差进行有效的分析评价,依据趋势分析方法获得的剩余磁异常,提出“加窗移动”最小二乘方法对应用非整数阶微积分的布郎运动正态随机行走进行控制,为高精度弱磁异常的有效识别提供有益的指导。 相似文献
136.
137.
LIU ZhiQiang LAI YuanMing ZHANG MingYi & ZHANG XueFu State Key Laboratory of Frozen Soil Engineering Cold Arid Regions Environmental Engineering Research Institute Chi- nese Academy of Sciences Lanzhou China School of Civil Engineering Lanzhou Jiao Tong University Lanzhou China Chongqing Jiao Tong University Chongqing China 《中国科学D辑(英文版)》2007,50(3):404-410
The stochastic finite element equations for random temperature are obtained using the first-order per-turbation technique taking into account the random thermal properties and boundary condition, based on heat transfer variational principle. The local average method for 2-D is used to discretize random fields. Then, the random temperature fields of embankment in cold regions are investigated on condi-tion that the thermal properties and boundary condition are taken as random fields, respectively, by using the program, which is written by the methods. The expected value of temperature field and the standard deviation of the temperature field of embankment in cold regions are obtained and analyzed. 相似文献
138.
This paper presents the development and utilisation of an automated image processing algorithm for detection and analysis
of grains. Using optical polarising microscopy, a set of colored images are collected from an area on a thin section. A filtering
operation, using rotation of a morphological alternating sequence filter (based on a structuring element), is used to remove
twinning features within individual grains. Filtering is followed by the watershed segmentation technique to determine grain
boundaries. The method is used for the identification of calcite grains in marble and the subsequent analysis of morphological
anisotropy. 相似文献
139.
B. G. Hankin K. J. Beven 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(6):397-412
Part 1 of this study assessed the effectiveness of dispersion models based around random particle tracking (RPT) applied
an overbank flow in the Flood Channel Facility at HR Wallingford. Several of the RPT models that were used predicted the mixing
behaviour of the tracer in the complex channel flow to within an acceptable accuracy. If there is no uniqueness in the model
structure which can be used to represent the true system to within the limitations of the available observations, then this
implies an inherent degree of ambiguity in our knowledge of the physically based model structure. This suggests that we should
be less forthright in the optimisation of each individual model structure, and perhaps investigate more of the parameter combinations
for each model which yield feasible simulations of the system. An alternative fuzzy calibration technique is introduced which
avoids the optimisation process and takes account of uncertainties in the model structure, parameter sets and observed data
in prediction. 相似文献
140.
为准确建立线路中小跨径梁桥桥墩的地震易损性模型,采用统计工具得到某山区高速公路桥梁双柱墩的结构、几何和材料特性的概率分布,由拉丁超立方体抽样生成桥墩属性数据集,建立了参数化的有限元模型.通过Pushover分析和基于非弹性需求谱的能力谱方法获取双柱墩的地震需求和抗震性能数据点,提出由随机森林(RF)模型建立桥墩地震易损... 相似文献