全文获取类型
收费全文 | 7864篇 |
免费 | 2024篇 |
国内免费 | 2272篇 |
专业分类
测绘学 | 307篇 |
大气科学 | 2094篇 |
地球物理 | 3068篇 |
地质学 | 4195篇 |
海洋学 | 1235篇 |
天文学 | 158篇 |
综合类 | 492篇 |
自然地理 | 611篇 |
出版年
2024年 | 31篇 |
2023年 | 81篇 |
2022年 | 229篇 |
2021年 | 286篇 |
2020年 | 297篇 |
2019年 | 429篇 |
2018年 | 339篇 |
2017年 | 348篇 |
2016年 | 346篇 |
2015年 | 391篇 |
2014年 | 539篇 |
2013年 | 505篇 |
2012年 | 483篇 |
2011年 | 488篇 |
2010年 | 455篇 |
2009年 | 610篇 |
2008年 | 572篇 |
2007年 | 695篇 |
2006年 | 583篇 |
2005年 | 538篇 |
2004年 | 514篇 |
2003年 | 424篇 |
2002年 | 414篇 |
2001年 | 283篇 |
2000年 | 296篇 |
1999年 | 287篇 |
1998年 | 266篇 |
1997年 | 231篇 |
1996年 | 214篇 |
1995年 | 145篇 |
1994年 | 162篇 |
1993年 | 149篇 |
1992年 | 116篇 |
1991年 | 106篇 |
1990年 | 74篇 |
1989年 | 46篇 |
1988年 | 54篇 |
1987年 | 44篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1971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
171.
The effect of scattering in surface wave tomography 总被引:6,自引:1,他引:6
Jesper Spetzler Jeannot Trampert Roel Snieder 《Geophysical Journal International》2002,149(3):755-767
172.
173.
The Precambrian massif of Ourika is crosscut by two systems of basic dykes, striking N40°E and N90–120°E. Using incompatible trace elements, the two systems form two distinct chemical groups, displaying a continental tholeiitic affinity. The composition variations between the two defined groups can be due to heterogeneities of mantle sources and to contamination, during the magma ascent, by the continental crust. The emplacement of these basic dykes, before the late-PIII formations, can be related to the Neoproterozoic distension generalised to the Anti-Atlas chain. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 827–833. 相似文献
174.
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
175.
176.
玄武岩的多角度偏振反射光谱研究 总被引:7,自引:0,他引:7
该文研究玄武岩在2π空间的多角度反射光谱、偏振反射光谱特征。实验测定了玄武岩在2π空间上反射光谱、偏振反射光谱与光线入射角、探测角、方位角、波段、偏振性等因子之间的关系。结果表明:1)光线入射角对玄武岩的反射光谱、偏振反射光谱影响很大;2)空间水平方位角对光谱具有偏振(极化)特征。空间竖直探测角的影响是随着光线入射角的不同而显著影响着玄武岩的波形曲线特征;3)波段的不同,影响着玄武岩反射光谱、偏振反射光谱吸收能量的大小,但不显著影响玄武岩的空间波形曲线特征。 相似文献
177.
178.
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
179.
180.
根据体波层析成像技术,利用大量走时数据,做出0°~180°E,30°S~90°S范围内0~2889km深的三维速度分布图像,得到欧亚地区局部区域岩石圈及地幔的高分辨率速度结构,并从地球动力学角度出发对这些成像结果做进一步解释。 相似文献