全文获取类型
| 收费全文 | 3045篇 |
| 免费 | 1046篇 |
| 国内免费 | 410篇 |
专业分类
| 测绘学 | 244篇 |
| 大气科学 | 255篇 |
| 地球物理 | 1668篇 |
| 地质学 | 1285篇 |
| 海洋学 | 229篇 |
| 天文学 | 15篇 |
| 综合类 | 267篇 |
| 自然地理 | 538篇 |
出版年
| 2024年 | 8篇 |
| 2023年 | 33篇 |
| 2022年 | 96篇 |
| 2021年 | 134篇 |
| 2020年 | 137篇 |
| 2019年 | 189篇 |
| 2018年 | 129篇 |
| 2017年 | 163篇 |
| 2016年 | 163篇 |
| 2015年 | 195篇 |
| 2014年 | 214篇 |
| 2013年 | 193篇 |
| 2012年 | 193篇 |
| 2011年 | 188篇 |
| 2010年 | 144篇 |
| 2009年 | 177篇 |
| 2008年 | 170篇 |
| 2007年 | 217篇 |
| 2006年 | 178篇 |
| 2005年 | 159篇 |
| 2004年 | 162篇 |
| 2003年 | 143篇 |
| 2002年 | 121篇 |
| 2001年 | 93篇 |
| 2000年 | 83篇 |
| 1999年 | 91篇 |
| 1998年 | 99篇 |
| 1997年 | 95篇 |
| 1996年 | 95篇 |
| 1995年 | 77篇 |
| 1994年 | 57篇 |
| 1993年 | 66篇 |
| 1992年 | 50篇 |
| 1991年 | 42篇 |
| 1990年 | 36篇 |
| 1989年 | 23篇 |
| 1988年 | 29篇 |
| 1987年 | 19篇 |
| 1986年 | 16篇 |
| 1985年 | 4篇 |
| 1982年 | 1篇 |
| 1980年 | 2篇 |
| 1979年 | 4篇 |
| 1974年 | 1篇 |
| 1954年 | 12篇 |
排序方式： 共有4501条查询结果，搜索用时 31 毫秒
11.
Summary. Multiparameter inversions of multimode dispersion data are performed for two large regions: the Pacific Ocean and North America. Anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry. Two fundamental questions are studied in detail: (1) how to make the inverted models consistent when using different sets of parameters, (2) what is the significance of transversely isotropic inversion for the actual Earth's structure? It is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data. The models we have obtained are discussed in the light of these investigations. Considering an olivine-rich upper mantle, we make a tentative interpretation of these models in terms of preferred orientation of the a -axis of the crystals in one fixed horizontal direction. 相似文献
12.
13.
14.
Jorge Luis De Souza 《Pure and Applied Geophysics》1991,136(2-3):245-264
The Rayleigh wave phase and group velocities in the period range of 24–39 sec, obtained from two earthquakes which occurred in northeastern brazil and which were recorded by the Brazilian seismological station RDJ (Rio de Janeiro), have been used to study crustal and upper mantle structures of the Brazilian coastal region. Three crustal and upper mantle models have been tried out to explain crustal and upper mantle structures of the region. The upper crust has not been resolved, due basically to the narrow period range of the phase and group velocities data. The phase velocity inversions have exhibited good resolutions for both lower crust and upper mantle, with shear wave velocities characteristic of these regions. The group velocity data inversions for these models have showed good results only for the lower crust. The shear wave velocities of the lower crust (3.86 and 3.89 km/sec), obtained with phase velocity inversions, are similar to that (=3.89 km/sec) found byHwang (1985) to the eastern South American region, while group velocity inversions have presented shear velocity (=3.75 km/sec) similar to that (=3.78 km/sec) found byLazcano (1972) to the Brazilian shield. It was not possible to define sharply the crust-mantle transition, but an analysis of the phase and group velocity inversions results has indicated that the total thickness of the crust should be between 30 and 39 km. The crustal and upper mantle model, obtained with phase velocity inversion, can be used as a preliminary model for the Brazilian coast. 相似文献
15.
16.
Magnetotelluric investigations have been carried out in the Garhwal Himalayan corridor to delineate the electrical structure
of the crust along a profile extending from Indo-Gangetic Plain to Higher Himalayan region in Uttarakhand, India. The profile
passing through major Himalayan thrusts: Himalayan Frontal Thrust (HFF), Main Boundary Thrust (MBT) and Main Central Thrust
(MCT), is nearly perpendicular to the regional geological strike. Data processing and impedance analysis indicate that out
of 44 stations MT data recorded, only 27 stations data show in general, the validity of 2D assumption. The average geoelectric
strike, N70°W, was estimated for the profile using tensor decomposition. 2D smooth geoelectrical model has been presented,
which provides the electrical image of the shallow and deeper crustal structure. The major features of the model are (i) a low resistivity (<50Ωm), shallow feature interpreted as sediments of Siwalik and Indo-Gangetic Plain, (ii) highly resistive (> 1000Ωm) zone below the sediments at a depth of 6 km, interpreted as the top surface of the Indian plate,
(iii) a low resistivity (< 10Ωm) below the depth of 6 km near MCT zone coincides with the intense micro-seismic activity in the
region. The zone is interpreted as the partial melting or fluid phase at mid crustal depth. Sensitivity test indicates that
the major features of the geoelectrical model are relevant and desired by the MT data. 相似文献
17.
The synoptic analysis of sea fog in western Antarctic sea region is made based on the observation data in the Chinese Antarctic station, Great Wall Station, from December 1994 to November 1995, and the facsimile weather charts issued by Chile. It is found that more than 90% fog in this region is the advection cooling fog. Also, the synoptic mechanism of the fog creation and distinction is discussed by analyzing the pressure field, the temperature field and the upperlevel stratification. Finally, the focus of attention in forecasting fog is pointed out. 相似文献
18.
本文提出了一种地震折射液的虚拟射线理论,根据该理论,只要已知地表层的速度,即可直接由折射波信息提取地震参数,从而可实现折射界面的反演。 文中通过实际介质模型的计算机实验结果,验证了该理论的正确性。 相似文献
19.
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
20.