全文获取类型
收费全文 | 76篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
地球物理 | 54篇 |
地质学 | 22篇 |
海洋学 | 1篇 |
天文学 | 3篇 |
自然地理 | 4篇 |
出版年
2020年 | 1篇 |
2018年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有84条查询结果,搜索用时 15 毫秒
11.
Michael A. H. Hedlin Peter M. Shearer 《Physics of the Earth and Planetary Interiors》2002,130(3-4):195-208
We investigate the utility of PKP coda waves for studying weak scattering from small-scale heterogeneity in the mid-mantle. Coda waves are potentially a useful probe of heterogeneity in the mid-mantle because they are not preferentially scattered near the CMB, as PKP precursors are, but are sensitive to scattering at all depths. PKP coda waves have not been used for this purpose historically because of interference with other late-arriving energy due to near-surface resonance and scattering. Any study of deep mantle scattering using coda waves requires the removal of near-surface effects from the data. We have analyzed 3624 recordings of PKP precursors and coda made by stations in the Incorporated Research Institutions for Seismology (IRIS) Global Seismographic Network (GSN). To study the range and time dependence of the scattered waves, we binned and stacked envelopes of the recordings. We have considered precursors that arrive within a 20 s window before PKP and coda waves in a 60 s window after PKP. The PKP scattered waves increase in amplitude rapidly with range as predicted by scattering theory. At ranges below 125°, we predict and observe essentially no scattered energy preceding PKP. Coda amplitudes at these ranges are independent of range and provide an estimate of energy due to near-surface effects that we can expect at all ranges. We use the average coda amplitude at ranges from 120 to 125° to correct coda amplitudes at other ranges. PKP coda waves show a strong dependence on time and range and are clearly influenced by scattering in the lower mantle. PKP coda waves, however, do not provide a tighter constraint on the vertical distribution of mantle heterogeneity than is provided by precursors. This is due, in part, to relatively large scatter in coda amplitudes as revealed by a resampling analysis. Modeling using Rayleigh–Born scattering theory and an exponential autocorrelation function shows that PKP coda amplitudes are not highly sensitive to the vertical distribution of heterogeneity in the mantle. To illustrate this we consider single-scattering in two extreme models of mantle heterogeneity. One allows heterogeneity just at the CMB; the other includes heterogeneity throughout the mantle. The amplitudes of precursors are tightly constrained by our stack and support our earlier conclusion that small-scale heterogeneity is uniformly distributed throughout the lower mantle. The best-fit model includes 8 km scale length heterogeneity with an rms velocity contrast throughout the mantle of 1%. 相似文献
12.
根据作者参加大会收集到的资料和考察体会,介绍了在会上交流的地震地质类成果,对某些前缘研究领域的新进展作了重点介绍。 相似文献
13.
Martin Knapmeyer 《Planetary and Space Science》2011,59(10):1062-1068
A key parameter for understanding the geodynamics of a terrestrial planet is the size of its core. Numerical evaluation of 28 different interior structure models of Mercury, Venus, Earth, the Moon, and Mars suggests that there is an almost linear relationship between the core radius and the extent of the seismic P-wave core shadow. A scaling law is derived from a simple mantle density and velocity model that permits the interpretation of respective seismic measurements on terrestrial planetary bodies. 相似文献
14.
选取1970年以来中国大陆东南地区5.0级以上、 华北地区5.5级以上、 西部地区7.0级以上地震作为研究对象, 并选择了8种物理意义明确、 独立性较强的地震学指标进行全时空的异常扫描, 通过改变采样时间域尺度、 空间域滑移及强度区间等样本条件, 分析对地震学指标时间进程计算结果的影响, 并讨论了空间扫描滑移方向相对于区域主应力方向的变化对参数扫描结果的影响。 结果表明, 空间参数的改变对扫描结果的影响最大, 并给出了不同震级地震学指标在扫描中影响最小的空间范围和时空扫描的最佳条件参数。 相似文献
15.
16.
以1975年以来中国大陆6.0级以上地震震例作为研究对象,在一定的扫描时段和扫描半径等条件的约束下,选择了10种物理意义明确、独立性较强的测震学指标,对大陆西南、华北、西北3个研究区进行了强震前震源区附近地震学参数中期震兆标志研究,结果发现,西南研究区15个震例异常的平均对应率为0.8,华北研究区10个震例的异常的平均对应率为0.7,西北研究区18个震例异常的平均对应率为0.7。提取了中国大陆强震测震学指标分区预测标志,西南研究区为0.8,华北研究区为0.7,西北研究区为0.7。 相似文献
17.
在作者以往工作的基础上,增加了中国地震年报(1997~1998年)、朝鲜以及我国各区域地震台网的数据,使Pn到时数据增加到近14万条,从中选取符合反演条件的8043次地震在581个地震台站上记录到的Pn射线99440条,重新作了中国大陆Pn波速层析成像,空间分辨率达到3°×3°. 文中将Pn波速度横向变化与活动地块的划分进行了对比,结果表明: Pn波速度横向变化与Ⅰ级活动地块区之间关系密切,大致以105°E为界,西部地区速度以正异常为主,其中西域地块区速度正异常最大,其次是青藏地块区,而滇缅地块区为负异常区;东部地区速度以负异常为主,华北地块区速度负异常最大,其次是东北亚地块区. 西部的地块区上地幔顶部Pn波速度各向异性的平均快波速度方向大体为NWW—SEE向;东部的地块区大体为NNW—SSE向,大致与相应的张应力优势方向一致. Pn波速度横向变化与强震活动间的关系也较明显,所有MS≥7.0的强震大部分发生在上地幔顶部Pn波速度的低速异常区上面的地壳内,少数发生在高、低速区域的过渡地带或两个高速区之间的相对低速部分. 相似文献
18.
19.
George Helffrich 《Tectonophysics》2006,416(1-4):23
Small-scale seismic heterogeneity exists at different levels in the lower mantle, and is detected by methods that analyze scattered–not direct–energy from natural and artificial sources. Its vertical distribution, association with subduction, and its ≤ 10-km characteristic scale length strongly suggest that it is chemical/petrological in nature and originally created by melting and differentiation during mid-ocean ridge formation. What is of interest is that the scale lengths of both upper and lower mantle seismic heterogeneity are similar, which supports the view of a common origin explored here. Unlike the lower mantle however, which is broadly homogeneous in structure, the upper mantle contains things that trap and impede the dispersal and re-mixing of heterogeneity: continental crust, lithosphere and cratonic roots. These probably control the depths, the longevity and the age of heterogeneities at shallow mantle levels, and suggest that heterogeneities observed in continental mantle lithosphere are probably old, trapped by the process that grows continental roots. Alternatively, if crustal heterogeneity is controlled by the details of a magmatic process, it must either be somehow continually renewed, for which there is no recognizable surface expression, or it must be depleted over time and the present is a time when, by luck, we may still witness it. 相似文献
20.
A growing body of evidence suggests that fluids are intimately linked to a variety of faulting processes. Yet, the particular mechanisms through which fluids and associated parameters influence the stress regime and thus the seismicity of a particular area are not well understood.We carry out a study of the spatio-temporal behavior of earthquakes, fluid-related parameters (groundwater levels) and meteorological observables (precipitation) in the swarm earthquake area of Bad Reichenhall, southeastern Germany. The small volume in which the earthquakes take place, almost yearly occurring earthquake swarms and a permanent, seismo-meteorological monitoring network, provide nearly controlled experimental conditions to study the physics of earthquake swarms and to infer characteristic properties of the seismogenic crust.In this paper we (1) describe this fairly unique study area in terms of geology, seismicity and atmospheric conditions; (2) present two cases of earthquake swarms that seem to follow above-average rainfall events; and (3) examine the observed migration of hypocenters with a simple pore pressure diffusion model.We find significant correlation of seismicity with rainfall and groundwater level increase, and estimate an average hydraulic diffusivity of D = 0.75 ± 0.35 m2/s for Mt. Hochstaufen in 2002. 相似文献