全文获取类型
收费全文 | 1187篇 |
免费 | 313篇 |
国内免费 | 123篇 |
专业分类
测绘学 | 40篇 |
大气科学 | 35篇 |
地球物理 | 621篇 |
地质学 | 571篇 |
海洋学 | 49篇 |
天文学 | 9篇 |
综合类 | 40篇 |
自然地理 | 258篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 21篇 |
2021年 | 17篇 |
2020年 | 25篇 |
2019年 | 47篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 49篇 |
2015年 | 45篇 |
2014年 | 69篇 |
2013年 | 73篇 |
2012年 | 57篇 |
2011年 | 79篇 |
2010年 | 74篇 |
2009年 | 77篇 |
2008年 | 79篇 |
2007年 | 81篇 |
2006年 | 100篇 |
2005年 | 76篇 |
2004年 | 70篇 |
2003年 | 62篇 |
2002年 | 44篇 |
2001年 | 46篇 |
2000年 | 45篇 |
1999年 | 46篇 |
1998年 | 28篇 |
1997年 | 31篇 |
1996年 | 42篇 |
1995年 | 34篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1623条查询结果,搜索用时 15 毫秒
111.
112.
The mechanical model for plane strain, time-harmonic seismic wave propagation problems in cracked, multi-layered geological regions with surface topography and non-parallel interfaces was described in the first part of this work. Here, this model is used to investigate the response of such a region to the presence of traveling elastic waves generated by a seismic source. The computational methodology that was developed in the first part is based on a combination of both the regular (displacement-based) and the hypersingular (traction-based) Boundary Integral Equation Method (BIEM). First, the accuracy and convergence characteristics of this hybrid BIEM are studied. Then, a series of problems involving four different configurations of a reference geological deposit with both interface and internal cracks are solved, for a loading that is due to a seismically-induced pressure wave propagating upwards from the underlying rigid half-plane. The purpose of the numerical study is to investigate the influence of various key parameters of the problem, such as frequency and incidence angle of the incoming wave, size of the surface relief, location and size of the buried cracks, interaction effects between cracks and finally the presence of layers, on both the scattered displacement field and the stress concentration field. 相似文献
113.
Nenad Gucunski 《Soil Dynamics and Earthquake Engineering》1996,15(8):485-497
The analysis of the response of a flexible circular foundation on layered media due to an arbitrarily distributed vertical loading is presented. The analysis is based on the ‘ring method’ approach, i.e. discretization of the foundation in a set of concentric rings. The arbitrarily distributed loading is expanded in the circumferential direction in a Fourier series. The influence coefficient matrix of soil for each element of the series is evaluated utilizing the stiffness matrix approach. The stiffness matrix of the foundation is obtained from the finite difference energy method approach. Numerical examples illustrate the influence of several soil-foundation parameters on the rocking response of a foundation. Results are presented in terms of displacement and soil reaction distributions and impedance functions point to significantly different responses of flexible and rigid foundations. 相似文献
114.
115.
PresentsituationoftheresearchandapplicationofengineeringmultiwaveseismicprospectinginChinaXIAO-PINGWU(吴小平),HONG-RUZHAO(赵鸿儒)(D... 相似文献
116.
TheMTinversionforconductivityanisotropyandEDAprecursor,stresfieldanddefor┐mationbandintheEarthsdeepcrustCHANG-YOULIN(林长佑),C... 相似文献
117.
This work examines the propagation of time harmonic, horizontally polarized shear waves through a naturally occurring heterogeneous medium that exhibits viscous behaviour as well as random fluctuations of its elastic modulus about a mean value. As a first step, the governing equation, which is a heterogeneous Helmholtz equation, is solved using algebraic transformations and the relevant Green's function is obtained for two sets of boundary conditions, one corresponding to a finite depth layer and the other to an infinite layer. Viscous material behaviour is introduced by considering the depth-dependent elastic modulus to be a complex quantity. Subsequently, material stochasticity in the medium is handled through the perturbation approach by assuming that the elastic modulus has a small random fluctuation about its mean value. The final results are closed-form expressions for the mean value and covariance matrix of both the wave speed profile in the medium and the corresponding Green's function. In Part II, (Soil Dynam. Earth. Engng, 1996,15, 129-39), two examples concerning seismic wave propagation in soft topsoil and in sandstone serve to illustrate the methodology and comparisons are made with Monte Carlo simulations. 相似文献
118.
119.
Spatial averaging of hydraulic conductivity in three-dimensional heterogeneous porous media 总被引:4,自引:0,他引:4
A. J. Desbarats 《Mathematical Geology》1992,24(3):249-267
Numerical models of groundwater flow require the assignment of hydraulic conductivities to large grid blocks discretizing the flow domain; however, conductivity data is usually available only at the much smaller scale of core samples. This paper describes a geostatistical model for hydraulic conductivity at both the core or point scale and that of grid blocks. Conductivity at the block scale is obtained empirically as a spatial power-average of point scale values. Assuming a multivariate Gaussian model for point log-conductivity, expressions are derived for the ensemble mean and variance of block conductivity. The expression for the ensemble mean of block scale conductivity is found to be similar to an expression for the ensemble effective conductivity of an infinite field derived analytically by earlier authors. Here, block conductivities obtained by power averaging are compared with effective conductivities obtained from a numerical flow model and are found to be in excellent agreement for a suitably chosen averaging exponent. This agreement deteriorates gradually as the log variance of conductivity increases beyond 2. For arbitrary flow field geometry and anisotropic conductivity covariances, the averaging exponent can be calibrated by recourse to numerical flow experiments. For cubic fields and an isotropic spatial covariance, the averaging exponent is found to be 1/3. In this particular case, it was found that flow field discretization at the block scale through local averaging of point conductivities gave similar results to those obtained directly using a point scale discretization of the flow field. 相似文献
120.
Deep borehole log evidence for fractal distribution of fractures in crystalline rock 总被引:7,自引:0,他引:7
Peter Leary 《Geophysical Journal International》1991,107(3):615-627