全文获取类型
收费全文 | 1729篇 |
免费 | 263篇 |
国内免费 | 275篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 44篇 |
地球物理 | 503篇 |
地质学 | 618篇 |
海洋学 | 526篇 |
天文学 | 135篇 |
综合类 | 64篇 |
自然地理 | 288篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 26篇 |
2019年 | 68篇 |
2018年 | 50篇 |
2017年 | 42篇 |
2016年 | 43篇 |
2015年 | 68篇 |
2014年 | 79篇 |
2013年 | 87篇 |
2012年 | 64篇 |
2011年 | 65篇 |
2010年 | 53篇 |
2009年 | 91篇 |
2008年 | 101篇 |
2007年 | 118篇 |
2006年 | 132篇 |
2005年 | 116篇 |
2004年 | 113篇 |
2003年 | 96篇 |
2002年 | 82篇 |
2001年 | 70篇 |
2000年 | 69篇 |
1999年 | 76篇 |
1998年 | 88篇 |
1997年 | 58篇 |
1996年 | 67篇 |
1995年 | 40篇 |
1994年 | 38篇 |
1993年 | 37篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2267条查询结果,搜索用时 5 毫秒
11.
12.
13.
14.
15.
A seismic refraction study on old (110 Myr) lithosphere in the northwest Pacific Basin has placed constraints on crustal and uppermantle seismic structure of old oceanic lithosphere, and lithospheric aging processes. No significant lateral variation in structure other than azimuthally anisotropic mantle velocities was found, allowing the application of powerful amplitude modeling techniques. The anisotropy observed is in an opposite sense to that expected, suggesting the tectonic setting of the area may be more complex than originally thought. Upper crustal velocities are generally larger than for younger crust, supporting current theories of decreased porosity with crustal aging. However, there is no evidence for significant thickening of the oceanic crust with age, nor is there any evidence of a lower crustal layer of high or low velocity relative to the velocity of the rest of Layer 3. The compressional and shear wave velocities rule out a large component of serpentinization of mantle materials. The only evidence for a basal crustal layer of olivine gabbro cumulates is a 1.5 km thick Moho transition zone. In the slow direction of anisotropy, upper mantle velocities increase from 8.0 km s-1 to 8.35 km s-1 in the upper 15 km below the Moho. This increase is inconsistent with an homogeneous upper mantle and suggests that compositinal or phase changes occur near the Moho. 相似文献
16.
从射线声学和简正波声学的角度,概述了海洋声层析的基本理论,包括射线走时反演、简正波走时反演、简正波相位反演和简正波水平折射层析。海洋声层析以反演海水温度和流速为基础。还总结了声层析在海洋学研究中的应用。 相似文献
17.
Kern E. Kenyon 《Journal of Oceanography》1997,53(1):89-92
The effects of the gravity torques acting on the angular momentum of surface gravity waves are calculated theoretically. For
short crested waves the gravity torque is caused by the force of gravity on the orbiting fluid particles acting down the slopes
of the crests and troughs and in the direction parallel to the crests and troughs. The gravity torque tries to rotate the
angular momentum vectors, and thus the waves themselves, counterclockwise in the horizontal plane, as viewed from above, in
both hemispheres. The amount of rotation per unit time is computed to be significant assuming reasonable values for the along-crest
and trough slopes for waves in a storm area. The gravity torque has a frequency which is double the frequency of the waves.
For long crested waves the gravity torque acts in the vertical plane of the orbit and tries to decelerate the particles when
they rise and accelerate them when they fall. By disrupting the horizontal cyclostrophic balance of forces on the fluid particles
(centrifugal force versus pressure force) the gravity torque accounts qualitatively for the three characteristics of breaking
waves: that they break at the surface, that they break at the crest, and that the crest breaks in the direction of wave propagation. 相似文献
18.
19.
20.
This chapter describes two separate but complementary research echosounder systems originally developed by Krupp Atlas Elektronik GmbH for the new German oceanographic research vessel Meteor.The Hydrosweep is a Hydrographic wide-swathe sweep survey echosounder for both shallow and deep water applications providing accurate bathymetric surveys and terrain-following navigation capabilities.The Parasound system is a hull-mounted dual channel parametric narrow-beam deep sea survey and sub-bottom profiling echosounder enabling particularly high vertical and horizontal resolution of seabed features. 相似文献