全文获取类型
收费全文 | 1155篇 |
免费 | 318篇 |
国内免费 | 107篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 24篇 |
地球物理 | 628篇 |
地质学 | 552篇 |
海洋学 | 48篇 |
天文学 | 4篇 |
综合类 | 36篇 |
自然地理 | 249篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 20篇 |
2021年 | 17篇 |
2020年 | 26篇 |
2019年 | 48篇 |
2018年 | 57篇 |
2017年 | 49篇 |
2016年 | 51篇 |
2015年 | 47篇 |
2014年 | 73篇 |
2013年 | 72篇 |
2012年 | 56篇 |
2011年 | 81篇 |
2010年 | 71篇 |
2009年 | 75篇 |
2008年 | 80篇 |
2007年 | 76篇 |
2006年 | 94篇 |
2005年 | 67篇 |
2004年 | 65篇 |
2003年 | 58篇 |
2002年 | 40篇 |
2001年 | 41篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 25篇 |
1997年 | 29篇 |
1996年 | 42篇 |
1995年 | 34篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 3篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有1580条查询结果,搜索用时 15 毫秒
121.
We present a generic, semi-automated algorithm for generating non-uniform coarse grids for modeling subsurface flow. The method is applicable to arbitrary grids and does not impose smoothness constraints on the coarse grid. One therefore avoids conventional smoothing procedures that are commonly used to ensure that the grids obtained with standard coarsening procedures are not too rough. The coarsening algorithm is very simple and essentially involves only two parameters that specify the level of coarsening. Consequently the algorithm allows the user to specify the simulation grid dynamically to fit available computer resources, and, e.g., use the original geomodel as input for flow simulations. This is of great importance since coarse grid-generation is normally the most time-consuming part of an upscaling phase, and therefore the main obstacle that has prevented simulation workflows with user-defined resolution. We apply the coarsening algorithm to a series of two-phase flow problems on both structured (Cartesian) and unstructured grids. The numerical results demonstrate that one consistently obtains significantly more accurate results using the proposed non-uniform coarsening strategy than with corresponding uniform coarse grids with roughly the same number of cells. 相似文献
122.
Rayleigh’s method of approximation is employed to find out the reflection and transmission coefficients due to an incident
plane SH wave at a corrugated interface between a laterally and vertically inhomogeneous anisotropic elastic solid half-space
and a laterally and vertically inhomogeneous isotropic visco-elastic solid half-space. The lateral and vertical inhomogeneities
are described by the exponential variations of elastic parameters. The formulae of reflection and transmission coefficients
are derived in closed form for the first-order approximation of the corrugation. The effects of the corrugation of the interface,
the inhomogeneity, the anisotropy, the visco-elasticity and the frequency of the incident wave on these coefficients are studied
analytically and numerically for a specific model containing a periodic interface. The results of earlier workers have been
reduced as particular cases from the present formulation. 相似文献
123.
124.
横向各向同性介质中的弹性波方程逆时偏移及其成像条件 总被引:1,自引:3,他引:1
作者在本文中导出了在横向各向同性介质情况下,二维弹性波逆时传播的高阶差分格式,实现了弹性波在数值空间中的逆时延拓,从snell定量出发,采用插值法求取网格空间中各点的直达波旅行时,以此作为弹性波逆时偏移的成像条件,实现多波多分量资料的逆时偏移,数值试验表明,逆时偏移能够使地表接收到的波场准确归位,提高资料处理的精度。 相似文献
125.
126.
127.
128.
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
129.
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
130.