全文获取类型
收费全文 | 7589篇 |
免费 | 1777篇 |
国内免费 | 1484篇 |
专业分类
测绘学 | 330篇 |
大气科学 | 669篇 |
地球物理 | 3973篇 |
地质学 | 2859篇 |
海洋学 | 1818篇 |
天文学 | 123篇 |
综合类 | 435篇 |
自然地理 | 643篇 |
出版年
2024年 | 31篇 |
2023年 | 113篇 |
2022年 | 204篇 |
2021年 | 298篇 |
2020年 | 309篇 |
2019年 | 436篇 |
2018年 | 337篇 |
2017年 | 352篇 |
2016年 | 353篇 |
2015年 | 405篇 |
2014年 | 446篇 |
2013年 | 448篇 |
2012年 | 393篇 |
2011年 | 516篇 |
2010年 | 413篇 |
2009年 | 520篇 |
2008年 | 560篇 |
2007年 | 608篇 |
2006年 | 533篇 |
2005年 | 394篇 |
2004年 | 402篇 |
2003年 | 369篇 |
2002年 | 340篇 |
2001年 | 243篇 |
2000年 | 256篇 |
1999年 | 227篇 |
1998年 | 182篇 |
1997年 | 191篇 |
1996年 | 165篇 |
1995年 | 132篇 |
1994年 | 133篇 |
1993年 | 116篇 |
1992年 | 95篇 |
1991年 | 81篇 |
1990年 | 55篇 |
1989年 | 39篇 |
1988年 | 41篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Masao Komazawa Hitoshi Morikawa Kajuro Nakamura Junpei Akamatsu Keiichi Nishimura Sumio Sawada Ayfer Erken Akin Onalp 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):829-836
The 1999 Kocaeli earthquake brought serious damage to downtown of Adapazari. To study why strong motions were generated at the town, a bedrock structure was investigated on the basis of Bouguer gravity anomaly, and SPAC and H/V analyses of microseisms. It was revealed that, the basin consists of three narrow depressions of bedrock with very steep edges, extending in E–W or NE–SW directions along the North Anatolia faults, and the depth to bedrock reaches 1000 m or more. Downtown of Adapazari is located 1–2 km apart from the basin-edge. It is considered that, the specific configuration of bedrock amplifies ground motions at the downtown area by focusing of seismic waves and/or interference between incident S-waves and surface-waves secondarily generated at the basin-edge. Studying 3D bedrock structure is an urgent issue for microzoning an urban area in a sedimentary basin. 相似文献
92.
南京地区新近沉积土的动剪切模量和阻尼比的初步研究 总被引:9,自引:1,他引:9
本文通过对南京地区两个工程场地漫滩相成因的砂土和淤泥质粉粘土与粉砂互层土的自振动柱试验结果进行分析,探讨了围压对剪切模量G及阻力比λ的影响,通过与Seed和Idriss建议的砂土G/Gmax-γ和λ-γ曲线变化范围的对比,认为不能简单地把淤泥质粉质粘土与粉砂层土当作砂土或粉质粘土对待。 相似文献
93.
The experimental studies on electrical con-ductivities and P-wave velocities of anortho-site at high pressure and high temperature 总被引:1,自引:0,他引:1
Introduction The measurements of the compressional wave velocity and electrical conductivity of minerals and rocks are of fundamental importance to look into the earths interior, including composition, geotherm, generation and distribution of fluids and melts. Hydrous minerals formed by metamatu-siom are abundant within the earth. Previous studies have been carried out on the dehydration effect on the electrical conductivity and wave velocity of rocks such as serpentine, amphibole, most of whi… 相似文献
94.
G. Lefeuve-Mesgouez A. T. Peplow D. Le Houdec 《Soil Dynamics and Earthquake Engineering》2002,22(6):692
The transmission of vibrations over the surface of the ground, due to high-speed moving, vertical harmonic rectangular loads, is investigated theoretically. The problem is three-dimensional and the interior of the ground is modelled as an elastic half-space or a multilayered ground. The transformed solutions are obtained using the Fourier transform on the space variable. A new damping model in the spatial wavenumber domain, presented in Lefeuve-Mesgouez et al. [J. Sound. Vibr. 231 (2000) 1289] is used. Numerical results for the displacements on the surface are presented for loads moving with speeds up to and beyond the Rayleigh wave speed of the half-space. 相似文献
95.
96.
Active tectonics of the South Caspian Basin 总被引:15,自引:0,他引:15
James Jackson Keith Priestley Mark Allen Manuel Berberian 《Geophysical Journal International》2002,148(2):214-245
97.
98.
Velocity profile of a sand cloud blowing over a gravel surface 总被引:2,自引:0,他引:2
Particle dynamic analyzer (PDA) measurement technology was used to study the turbulent characteristics and the variation with height of the mean horizontal (in the downwind direction) and vertical (in the upward direction) particle velocity of a sand cloud blowing over a gravel surface. The results show that the mean horizontal particle velocity of the cloud increases with height, while the mean vertical velocity decreases with height. The variation of the mean horizontal velocity with height is, to some extent, similar to the wind profile that increases logarithmically with height in the turbulent boundary layer. The variation of the mean vertical velocity with height is much more complex than that of the mean horizontal velocity. The increase of the resultant mean velocity with height can be expressed by a modified power function. Particle turbulence in the downwind direction decreases with height, while that in the vertical direction is complex. For fine sands (0.2–0.3 mm and 0.3–0.4 mm), there is a tendency for the particle turbulence to increase with height. In the very near-surface layer (<4 mm), the movement of blown sand particles is very complex due to the rebound of particles on the bed and the interparticle collisions in the air. Wind starts to accelerate particle movement about 4 mm from the surface. The initial rebound on the bed and the interparticle collisions in the air have a profound effect on particle movement below that height, where particle concentration is very high and wind velocity is very low. 相似文献
99.
Wind velocity and sand transport on a barchan dune 总被引:2,自引:0,他引:2
G. Sauermann J. S. Andrade Jr. L. P. Maia U. M. S. Costa A. D. Araújo H. J. Herrmann 《Geomorphology》2003,54(3-4):245-255
We present measurements of wind velocity and sand flux performed on the windward side of a large barchan dune in Jericoacoara, northeastern Brazil. From the measured profile, we calculate the air shear stress using an analytical approximation and treat the problem of flow separation by an heuristic model. We find that the results from this approach agree well with our field data. Moreover, using the calculated shear velocity, we predict the sand flux according to well-known equilibrium relations and with a phenomenological continuum saltation model that includes saturation transients and thus allows for nonequilibrium conditions. Based on the field data and theoretical predicted results, we indicate the principal differences between saturated and nonsaturated sand flux models. Finally, we show that the measured dune moves with invariant shape and predict its velocity from our data and calculations. 相似文献
100.