全文获取类型
收费全文 | 7868篇 |
免费 | 1759篇 |
国内免费 | 2370篇 |
专业分类
测绘学 | 139篇 |
大气科学 | 321篇 |
地球物理 | 4899篇 |
地质学 | 4176篇 |
海洋学 | 1264篇 |
天文学 | 16篇 |
综合类 | 449篇 |
自然地理 | 733篇 |
出版年
2024年 | 22篇 |
2023年 | 102篇 |
2022年 | 249篇 |
2021年 | 274篇 |
2020年 | 371篇 |
2019年 | 448篇 |
2018年 | 394篇 |
2017年 | 388篇 |
2016年 | 417篇 |
2015年 | 457篇 |
2014年 | 539篇 |
2013年 | 570篇 |
2012年 | 505篇 |
2011年 | 585篇 |
2010年 | 520篇 |
2009年 | 572篇 |
2008年 | 538篇 |
2007年 | 599篇 |
2006年 | 560篇 |
2005年 | 473篇 |
2004年 | 450篇 |
2003年 | 393篇 |
2002年 | 340篇 |
2001年 | 253篇 |
2000年 | 293篇 |
1999年 | 269篇 |
1998年 | 236篇 |
1997年 | 218篇 |
1996年 | 210篇 |
1995年 | 144篇 |
1994年 | 133篇 |
1993年 | 106篇 |
1992年 | 101篇 |
1991年 | 56篇 |
1990年 | 57篇 |
1989年 | 39篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 8篇 |
1977年 | 8篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Crack damage stress as a composite function of porosity and elastic matrix stiffness in dolomites and limestones 总被引:4,自引:0,他引:4
Twenty-five uniaxial compression tests were performed to determine stress at onset of dilation, referred to herein as “the crack damage stress,” in heterogeneous dolomites and limestones. A simplified model for crack damage stress (σcd) is developed here using porosity, elastic modulus, Poisson's ratio and three empirical coefficients. The model shows that when porosity decreases and elastic modulus increases, σcd rapidly increases and approaches its maximum value. On the other hand, when porosity increases and elastic modulus decreases, σcd rapidly decreases and approaches its minimum value. The proposed model is validated for six heterogeneous limestone and dolomite formations which are widely distributed in Israel. 相似文献
152.
153.
154.
半无限空间中圆形孔洞周围SH波的散射 总被引:14,自引:5,他引:14
建立了求解在含有圆形孔洞的弹性半空间中SH波散射与圆形孔洞附近动应力集中问题的解析方法。利用SH波散射的对称性和多极坐标的方法,构造了一个可以预先满足半空间自由表面上应力自由边界条件的圆形孔洞对SH波散射的波函数。利用这一波函数,则可将该问题转化成对一个圆形孔洞散射的求解问题。该问题的解答最终又可归结为对一组无究代数方程组的求解问题,并可利用截断有限项的方法对其进行计算,最后给出了有关圆形也洞附近动应力集中问题的算例和数值结果,并讨论了波数与圆孔至自由边界距离变化对动应力集中的影响。 相似文献
155.
昆仑山口西8.1级地震前青海省形变及地温前兆特征分析 总被引:6,自引:0,他引:6
通过对青海省地倾斜、地应力、深井地温3种前兆手段在昆仑山口西8.1级地震前异常的分析与研究,得出了强地震远场前兆的一些初步特征,并与近场前兆异常特征做了比较,这对该省今后强震短期预报将是有益的。 相似文献
156.
157.
Introduction It is found that there are some relationships between the thermal structures of subduction zones and the deep seismicity, while the mechanism relates the thermal structure and the deep seismicity is still unsure (Helffrich, Brodholt, 1991; Furukawa, 1994; Kirby, et al, 1996). From 1980s, geoscientists have constituted a series of numerical simulations on the stress states of subduction slabs. Based on the kinetic computation of Sung and Burns (1976a, b), Goto, et al (1983, 1987… 相似文献
158.
Introduction The stress status of the earths crust is closely related to global structure, the direction of plate movement, the drive mechanism of plate, earthquake cause, etc. Therefore the researches of the stress status of the earths crust and the process of dynamic evolution are paid a great attention to by many people around the world (Zoback, Zoback, 1980; Zoback, et al, 1989; Zoback, 1989; Spence, 1997; Fuchs, 1997; Plenefish, Bonjer, 1997; Muller, et al, 1997; XU, et al, 1989; WAN… 相似文献
159.
160.
This paper is the first in a two-part series that discusses the principal axes of M-DOF structures subjected to static and dynamic loads. The primary purpose of this series is to understand the magnitude of the dynamic response of structures to enable better design of structures and control modification devices/systems. Under idealized design conditions, the structural responses are obtained by using single direction input ground motions in the direction of the intended control devices/systems,and by assuming that the responses of the structure is decoupleable in three mutually perpendicular directions. This standard practice has been applied to both new and retrofitted structures using various seismic protective systems. Very limited information is available on the effects of neglecting the impact of directional couplings (cross effects - of which torsion is a component) of the dynamic response of structures. In order to quantify such effects, it is necessary to examine the principal axes of structures under both static and dynamic loading.This first paper deals with quantitative definitions of principal axes and "cross effects" of three-dimensional structures under static load by using linear algebra. It shows theoretically that, for three-dimensional structures, such principal axes rarely exist. Under static loading conditions, the cross effect is typically small and negligible from the viewpoint of engineering applications. However, it provides the theoretical base for subsequent quantification of the response couplings under dynamic loads, which is reported in part Ⅱ of this series. 相似文献