全文获取类型
| 收费全文 | 1483篇 |
| 免费 | 161篇 |
| 国内免费 | 209篇 |
专业分类
| 测绘学 | 129篇 |
| 大气科学 | 47篇 |
| 地球物理 | 378篇 |
| 地质学 | 439篇 |
| 海洋学 | 76篇 |
| 天文学 | 575篇 |
| 综合类 | 81篇 |
| 自然地理 | 128篇 |
出版年
| 2024年 | 6篇 |
| 2023年 | 4篇 |
| 2022年 | 18篇 |
| 2021年 | 23篇 |
| 2020年 | 30篇 |
| 2019年 | 46篇 |
| 2018年 | 25篇 |
| 2017年 | 41篇 |
| 2016年 | 45篇 |
| 2015年 | 43篇 |
| 2014年 | 50篇 |
| 2013年 | 87篇 |
| 2012年 | 46篇 |
| 2011年 | 45篇 |
| 2010年 | 60篇 |
| 2009年 | 91篇 |
| 2008年 | 88篇 |
| 2007年 | 130篇 |
| 2006年 | 109篇 |
| 2005年 | 89篇 |
| 2004年 | 88篇 |
| 2003年 | 82篇 |
| 2002年 | 83篇 |
| 2001年 | 62篇 |
| 2000年 | 78篇 |
| 1999年 | 59篇 |
| 1998年 | 52篇 |
| 1997年 | 51篇 |
| 1996年 | 33篇 |
| 1995年 | 36篇 |
| 1994年 | 29篇 |
| 1993年 | 26篇 |
| 1992年 | 20篇 |
| 1991年 | 14篇 |
| 1990年 | 15篇 |
| 1989年 | 9篇 |
| 1988年 | 18篇 |
| 1987年 | 12篇 |
| 1986年 | 5篇 |
| 1985年 | 3篇 |
| 1982年 | 1篇 |
| 1981年 | 1篇 |
排序方式： 共有1853条查询结果，搜索用时 31 毫秒
101.
This paper focuses on the influence of the initial void ratio on the evolution of the passive earth pressure and the formation
of shear zones in a dry sand body behind a retaining wall. For the numerical simulation a rigid and very rough retaining wall
undergoing a horizontal translation against the backfill is considered. The essential mechanical properties of cohesionless
granular soil are described with a micro-polar hypoplastic model which takes into account stresses and couple stresses, pressure
dependent limit void ratios and the mean grain size as a characteristic length. Numerical investigations are carried out with
an initially medium dense and initially loose sand using a homogeneous and random distribution of the initial void ratio.
The geometry of calculated shear zones is discussed and compared with a corresponding laboratory model test. 相似文献
102.
Few building codes contains provisions fault surface ruptures and accompanying soil deformations which constitutes a great risk to human lives, buildings and infrastructure. A numerical and experimental comparison show a fair agreement of result. Analysis of “real” scale show the how water increases the incompressibility of wet soil causing shear deformations to become larger and conjugate ruptures to appear for reverse faults. Field observations and numerical analysis indicates that horizontal compression of soil surrounding underground structures should be taken into account in design. 相似文献
103.
地球磁场极性在地质历史中发生过相当频繁的倒转。作者将地球内部划分为岩石圈－软流圈－中圈－液圈－固核等5个动力学圈层，认为中圈与固核间可异步旋转；地球偶极磁场由中圈与固核异步旋转时所驱动的液圈中的封闭涡流与系磁场作用产生；该偶极子场极性由地球所通过的银道面上侧或下侧磁场方向及液圈涡流的方向共同决定，二者之一反向，极性发生倒转。 相似文献
104.
J. Höpfner 《Journal of Geodesy》2001,75(2-3):137-150
The annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth–atmosphere system reflect
significant signals. They must be caused by further excitation sources. Since, in particular, the contribution for the wind
term from the atmospheric layer between the 10 and 0.3 hPa levels to the seasonal variations in length of day (LOD) is still
missing, it is necessary to extend the top level into the upper stratosphere up to 0.3 hPa. Under the conservation of the
total angular momentum of the entire Earth, variations in the oceanic angular momentum (OAM) and the hydrological angular
momentum (HAM) are further significant excitation sources at seasonal time scales. Focusing on other contributions to the
Earth's axial angular momentum budget, the following data are used in this study: axial atmospheric angular momentum (AAM)
data derived for the 10–0.3 hPa layer from 1991 to 1997 for computing the missing wind effects; axial OAM functions as generated
by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, available from 1975 to 1994 and
from 1992 to 1994, respectively, for computing the oceanic contributions to LOD changes, and, concerning the HAM variations,
the seasonal estimates of the hydrological contribution as derived by Chao and O'Connor [(1988) Geophys J 94: 263–270]. Using
vector representation, it is shown that the vectors achieve a close balance in the global axial angular momentum budget within
the estimated uncertainties of the momentum quantities on seasonal time scales.
Received: 6 April 2000 / Accepted: 13 December 2000 相似文献
105.
106.
圆钢管混凝土压弯构件荷载一位移滞回性能分析 总被引：6，自引：1，他引：6
在空钢管中填充混凝土可以避免或延缓钢管过早地发生局部屈曲，并有效地提高构件的延性，从而增强构件的抗震性能，本文在对圆钢管混凝土构件弯矩－曲率关系分析的基础上，分析了圆钢管混凝土压弯构件P－△滞回关系曲线，理论计算结果得到国内外大量结果的验证，基于理论分析模型，分析了各参，如构件轴压比，长细比，截面含钢率和材料强度等因素对圆钢管混凝土压变变构件P－△滞回关系曲线的影响，最后，确定了圆钢管混凝土压弯构件P－△恢复力学模型和延性系数的简化计算方法。 相似文献
107.
108.
109.
The polar motion prediction is computed as a least-squares extrapolation of the polar motion data. The least-squares model consists of a Chandler circle with constant or variable amplitude, annual and semiannual ellipses, and a bias. The model with constant amplitude of the Chandler oscillation is fit to the last three years of polar motion data and the model with variable amplitude of the Chandler oscillation is fit to the whole time series ranging from 1973.0 to 2001.1. The variable amplitude of the Chandler oscillation is modeled from the envelope of the Chandler oscillation filtered by the Fourier transform band pass filter from the long-term IERS EOPC01 polar motion series. The accuracy of the polar motion prediction depends mostly on the phase variation of the annual oscillation, which is treated as a constant in the least-squares adjustment. There were two significant changes of the annual oscillation phase of the order of 30° before the two El Niño events in 1982/83 and 1997/98. 相似文献
110.