全文获取类型
收费全文 | 12494篇 |
免费 | 2590篇 |
国内免费 | 2045篇 |
学科分类
地球科学 | 17129篇 |
出版年
2024年 | 52篇 |
2023年 | 166篇 |
2022年 | 316篇 |
2021年 | 394篇 |
2020年 | 493篇 |
2019年 | 571篇 |
2018年 | 466篇 |
2017年 | 448篇 |
2016年 | 455篇 |
2015年 | 519篇 |
2014年 | 635篇 |
2013年 | 704篇 |
2012年 | 712篇 |
2011年 | 773篇 |
2010年 | 674篇 |
2009年 | 766篇 |
2008年 | 775篇 |
2007年 | 912篇 |
2006年 | 958篇 |
2005年 | 814篇 |
2004年 | 783篇 |
2003年 | 682篇 |
2002年 | 570篇 |
2001年 | 420篇 |
2000年 | 432篇 |
1999年 | 368篇 |
1998年 | 346篇 |
1997年 | 292篇 |
1996年 | 321篇 |
1995年 | 259篇 |
1994年 | 251篇 |
1993年 | 226篇 |
1992年 | 148篇 |
1991年 | 103篇 |
1990年 | 71篇 |
1989年 | 65篇 |
1988年 | 55篇 |
1987年 | 43篇 |
1986年 | 29篇 |
1985年 | 12篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 16篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Majid T. Manzari 《国际地质力学数值与分析法杂志》2004,28(10):1011-1032
A micropolar elastoplastic model for soils is formulated and a series of finite element analyses are employed to demonstrate the use of a micropolar continuum in overcoming the numerical difficulties encountered in application of finite element method in standard Cauchy–Boltzmann continuum. Three examples of failure analysis involving a deep excavation, shallow foundation, and a retaining wall are presented. In all these cases, it is observed that the length scale introduced in the polar continuum regularizes the incremental boundary value problem and allows the numerical simulation to be continued until a clear collapse mechanism is achieved. The issue of grain size effect is also discussed. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
It is well known that the Babuska–Brezzi stability criterion or the Zienkiewicz–Taylor patch test precludes the use of the finite elements with the same low order of interpolation for displacement and pore pressure in the nearly incompressible and undrained cases, unless some stabilization techniques are introduced for dynamic analysis of saturated porous medium where coupling occurs between the displacement of solid skeleton and pore pressure. The numerical manifold method (NMM), where the interpolation of displacement and pressure can be determined independently in an element for the solution of u–p formulation, is derived based on triangular mesh for the requirement of high accurate calculations from practical applications in the dynamic analysis of saturated porous materials. The matrices of equilibrium equations for the second‐order displacement and the first‐order pressure manifold method are given in detail for program coding. By close comparison with widely used finite element method, the NMM presents good stability for the coupling problems, particularly in the nearly incompressible and undrained cases. Numerical examples are given to illustrate the validity and stability of the manifold element developed. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
3.
The study of the chemical stability of vitreous material in aqueous media is well‐established. There has to date been little consideration of the implications of variations in the chemical durability of tephra in Quaternary tephrochronology. Chemical alteration can take the form of cationic leaching from the matrix, or complete destruction of the silica network, either of which could constrain the ability to chemically identify distal tephra. Here we apply established models of vitreous durability to the published chemical analyses of a large number of Icelandic tephras in order to predict their relative durabilities under equivalent conditions. This suggests that some important tephras have relatively poor chemical stability, and that rhyolitic tephras are, in general, more stable than basaltic. We conclude that tephras should be expected to show predictable differential chemical stability in the post‐depositional environment. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
4.
Abdul Ahmad 《Celestial Mechanics and Dynamical Astronomy》1995,61(2):181-196
The periodic solutions of the restricted three-body problem representing analytic continuations of Keplerian rectilinear periodic motions are well known (Kurcheeva, 1973). Here the stability of these solutions are examined by applying Poncaré's characteristic equation for periodic solutions. It is found that the isoperiodic solutions are stable and all other solutions are unstable. 相似文献
5.
6.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
7.
8.
9.
The paper provides a new stereo‐analytical method, which is a combination of the stereographic method and analytical methods, to separate finite removable blocks from the infinite and tapered blocks in discontinuous rock masses. The methodology has applicability to both convex and concave blocks. Application of the methodology is illustrated through examples. Addition of this method to the existing block theory procedures available in the literature improves the capability of block theory in solving practical problems in rock engineering. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献