全文获取类型
收费全文 | 3528篇 |
免费 | 320篇 |
国内免费 | 398篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 288篇 |
地球物理 | 1124篇 |
地质学 | 312篇 |
海洋学 | 1076篇 |
天文学 | 694篇 |
综合类 | 64篇 |
自然地理 | 663篇 |
出版年
2024年 | 13篇 |
2023年 | 38篇 |
2022年 | 41篇 |
2021年 | 40篇 |
2020年 | 61篇 |
2019年 | 89篇 |
2018年 | 62篇 |
2017年 | 75篇 |
2016年 | 71篇 |
2015年 | 80篇 |
2014年 | 105篇 |
2013年 | 189篇 |
2012年 | 50篇 |
2011年 | 116篇 |
2010年 | 111篇 |
2009年 | 215篇 |
2008年 | 263篇 |
2007年 | 305篇 |
2006年 | 227篇 |
2005年 | 176篇 |
2004年 | 188篇 |
2003年 | 207篇 |
2002年 | 178篇 |
2001年 | 123篇 |
2000年 | 149篇 |
1999年 | 163篇 |
1998年 | 153篇 |
1997年 | 75篇 |
1996年 | 103篇 |
1995年 | 78篇 |
1994年 | 77篇 |
1993年 | 71篇 |
1992年 | 61篇 |
1991年 | 55篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 29篇 |
1987年 | 27篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 19篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1954年 | 4篇 |
排序方式: 共有4246条查询结果,搜索用时 0 毫秒
21.
The S-velocity structure of the East Asian mantle from inversion of shear and surface waveforms 总被引:15,自引:0,他引:15
Wolfgang Friederich 《Geophysical Journal International》2003,153(1):88-102
22.
Shear wave statics using receiver functions 总被引:1,自引:0,他引:1
23.
24.
Practical VTI approximations: a systematic anatomy 总被引:3,自引:0,他引:3
Transverse isotropy (TI) with a vertical symmetry axis (VTI) often provides an appropriate earth model for prestack imaging of steep-dip reflection seismic data. Exact P-wave and SV-wave phase velocities in VTI media are described by complicated equations requiring four independent parameters. Estimating appropriate multiparameter earth models can be difficult and time-consuming, so it is often useful to replace the exact VTI equations with simpler approximations requiring fewer parameters. The accuracy limits of different previously published VTI approximations are not always clear, nor is it always obvious how these different approximations relate to each other. Here I present a systematic framework for deriving a variety of useful VTI approximations. I develop first a sequence of well-defined approximations to the exact P-wave and SV-wave phase velocities. In doing so, I show how the useful but physically questionable heuristic of setting shear velocities identically to zero can be replaced with a more precise and quantifiable approximation. The key here to deriving accurate approximations is to replace the stiffness a13 with an appropriate factorization in terms of velocity parameters. Two different specific parameter choices lead to the P-wave approximations of Alkhalifah (Geophysics 63 (1998) 623) and Schoenberg and de Hoop (Geophysics 65 (2000) 919), but there are actually an infinite number of reasonable parametrizations possible. Further approximations then lead to a variety of other useful phase velocity expressions, including those of Thomsen (Geophysics 51 (1986) 1954), Dellinger et al. (Journal of Seismic Exploration 2 (1993) 23), Harlan (Stanford Exploration Project Report 89 (1995) 145), and Stopin (Stopin, A., 2001. Comparison of v(θ) equations in TI medium. 9th International Workshop on Seismic Anisotropy). Each P-wave phase velocity approximation derived this way can be paired naturally with a corresponding SV-wave approximation. Each P-wave or SV-wave phase velocity approximation can then be converted into an equivalent dispersion relation in terms of horizontal and vertical slownesses. A simple heuristic substitution also allows each phase velocity approximation to be converted into an explicit group velocity approximation. From these, in turn, travel time or moveout approximations can also be derived. The group velocity and travel time approximations derived this way include ones previously used by Byun et al. (Geophysics 54 (1989) 1564), Dellinger et al. (Journal of Seismic Exploration 2 (1993) 23), Tsvankin and Thomsen (Geophysics 59 (1994) 1290), Harlan (89 (1995) 145), and Zhang and Uren (Zhang, F. and Uren, N., 2001. Approximate explicit ray velocity functions and travel times for P-waves in TI media. 71st Annual International Meeting, Society of Exploration Geophysicists, Expanded Abstracts, 106–109). 相似文献
25.
The attenuation of P- and S-waves in Southeastern Sicily was estimated by applying two different methods in time and frequency domains. We analyzed waveforms from about 290 local events (0.6≤ML≤4.6) recorded at a three-component digital network.By applying the pulse broadening method to the first P-wave pulse, we found an average Qp value of ca. 140. The application of the frequency decay method provided a Qp value of ca. 120, in the low-frequency band (3-9 Hz). Conversely, in the high frequency range (16-27 Hz) the average Qp is significantly larger (ca. 640). The frequency decay method was also applied to S-waves spectra. In the low frequency range (2-5 Hz) the estimated average Qs is ca. 190. As for Qp, also Qs, in the high frequency range (16-27 Hz), is larger (ca. 700). These results evidenced a frequency dependence of both the quality factors Qp and Qs, as commonly observed in tectonically active zones characterized by high degree of heterogeneity. 相似文献
26.
27.
28.
29.
30.