全文获取类型
| 收费全文 | 26825篇 |
| 免费 | 515篇 |
| 国内免费 | 330篇 |
专业分类
| 测绘学 | 744篇 |
| 大气科学 | 1924篇 |
| 地球物理 | 5290篇 |
| 地质学 | 9226篇 |
| 海洋学 | 2429篇 |
| 天文学 | 6546篇 |
| 综合类 | 53篇 |
| 自然地理 | 1458篇 |
出版年
| 2021年 | 229篇 |
| 2020年 | 260篇 |
| 2019年 | 322篇 |
| 2018年 | 651篇 |
| 2017年 | 624篇 |
| 2016年 | 787篇 |
| 2015年 | 447篇 |
| 2014年 | 738篇 |
| 2013年 | 1397篇 |
| 2012年 | 859篇 |
| 2011年 | 1127篇 |
| 2010年 | 1015篇 |
| 2009年 | 1342篇 |
| 2008年 | 1210篇 |
| 2007年 | 1218篇 |
| 2006年 | 1189篇 |
| 2005年 | 909篇 |
| 2004年 | 884篇 |
| 2003年 | 805篇 |
| 2002年 | 769篇 |
| 2001年 | 646篇 |
| 2000年 | 671篇 |
| 1999年 | 595篇 |
| 1998年 | 581篇 |
| 1997年 | 542篇 |
| 1996年 | 424篇 |
| 1995年 | 416篇 |
| 1994年 | 430篇 |
| 1993年 | 333篇 |
| 1992年 | 330篇 |
| 1991年 | 272篇 |
| 1990年 | 329篇 |
| 1989年 | 282篇 |
| 1988年 | 265篇 |
| 1987年 | 287篇 |
| 1986年 | 244篇 |
| 1985年 | 332篇 |
| 1984年 | 352篇 |
| 1983年 | 352篇 |
| 1982年 | 328篇 |
| 1981年 | 265篇 |
| 1980年 | 275篇 |
| 1979年 | 229篇 |
| 1978年 | 222篇 |
| 1977年 | 225篇 |
| 1976年 | 181篇 |
| 1975年 | 194篇 |
| 1974年 | 179篇 |
| 1973年 | 172篇 |
| 1972年 | 115篇 |
排序方式： 共有10000条查询结果，搜索用时 62 毫秒
1.
A FORTRAN program, consistent with the commercially available finite element (FE) code ABAQUS, is developed based on a three-dimensional (3D) linear elastic brittle damage constitutive model with two damage criteria. To consider the heterogeneity of rock, the developed FORTRAN program is used to set the stiffness and strength properties of each element of the FE model following a Weibull distribution function. The reliability of the program is assessed against available experimental results for granite cylindrical specimens with a throughgoing, flat and inclined fissure. The calibration procedure of the material parameters is explained in detail, and it is shown that the compressive to tensile strength ratio can have a substantial influence on the failure response of the specimens. Numerical simulations are conducted for models with different levels of heterogeneity. The results show a smaller load bearing capacity for models with less homogeneity, representing gradual coalescence of fully damaged elements forming throughout the models during loading. The maximum load bearing capacity is studied for various combinations of inclination angles of two centrally aligned, throughgoing and flat fissures of equal length embedded in cylindrical models under uniaxial and multiaxial loading conditions. The key role of the compressive to tensile strength ratio is highlighted by repeating certain simulations with a lower compressive to tensile strength ratio. It is proven that the peak loads of the rock models with sufficiently small compressive to tensile strength ratios containing two throughgoing fissures of equal length are similar, provided that the minimum inclination angles of the models are the same. The results are presented and discussed with respect to the existing experimental findings in the literature, suggesting that the numerical model applied in this study can provide useful insight into the failure behaviour of rock-like materials. 相似文献
2.
Dynamic modelling of retrogressive landslides with emphasis on the role of clay sensitivity 
下载免费PDF全文
下载免费PDF全文 This paper presents a detailed numerical study of the retrogressive failure of landslides in sensitive clays. The dynamic modelling of the landslides is carried out using a novel continuum approach, the particle finite element method, complemented with an elastoviscoplastic constitutive model. The multiwedge failure mode in the collapse is captured successfully, and the multiple retrogressive failures that have been widely observed in landslides in sensitive clays are reproduced with the failure mechanism, the kinematics, and the deposition being discussed in detail. Special attention has been paid to the role of the clay sensitivity on each retrogressive failure as well as on the final retrogression distance and the final run‐out distance via parametric studies. Moreover, the effects of the viscosity of sensitive clays on the failure are also investigated for different clay sensitivities. 相似文献
3.
4.
5.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
6.
7.
8.
T.-C. Jim Yeh 《水文研究》1992,6(4):369-395
This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended. 相似文献
9.
Mallory S. E. Roberts Crystal L. Brogan Bryan M. Gaensler Jason W. T. Hessels C.-Y. Ng Roger W. Romani 《Astrophysics and Space Science》2005,297(1-4):93-100
A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be
associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the
pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies
seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM. 相似文献