全文获取类型
收费全文 | 220篇 |
免费 | 35篇 |
国内免费 | 2篇 |
专业分类
地球物理 | 163篇 |
地质学 | 6篇 |
综合类 | 5篇 |
自然地理 | 83篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 1篇 |
2012年 | 3篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 24篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有257条查询结果,搜索用时 296 毫秒
141.
We analyze temporal variations of seismic velocity along the Karadere-Düzce branch of the north Anatolian fault using seismograms
generated by repeating earthquake clusters in the aftershock zones of the 1999 Mw7.4 İzmit and Mw7.1 Düzce earthquakes. The analysis employs 36 sets of highly repeating earthquakes, each containing 4–18 events. The events
in each cluster are relocated by detailed multi-step analysis and are likely to rupture approximately the same fault patch
at different times. The decay rates of the repeating events in individual clusters are compatible with the Omori's law for
the decay rate of regional aftershocks. A sliding window waveform cross-correlation technique is used to measure travel time
differences and evolving decorrelation in waveforms generated by each set of the repeating events. We find clear step-like
delays in the direct S and early S-coda waves (sharp seismic velocity reduction) immediately after the Düzce main shock, followed by gradual logarithmic-type
recoveries. A gradual increase of seismic velocities is also observed before the Düzce main shock, probably reflecting post-seismic
recovery from the earlier İzmit main shock. The temporal behavior is similar at each station for clusters at various source
locations, indicating that the temporal changes of material properties occur in the top most portion of the crust. The effects
are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones, and generally decrease
with normal distance from the fault. A strong correlation between the co-seismic delays and intensities of the strong ground
motion generated by the Düzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow
material. 相似文献
142.
Yuehua Zeng 《Pure and Applied Geophysics》2006,163(2-3):533-548
One of the many important contributions that Aki has made to seismology pertains to the origin of coda waves (Aki, 1969; Aki
and Chouet, 1975). In this paper, I revisit Aki's original idea of the role of scattered surface waves in the seismic coda.
Based on the radiative transfer theory, I developed a new set of scattered wave energy equations by including scattered surface
waves and body wave to surface wave scattering conversions. The work is an extended study of Zeng et al. (1991), Zeng (1993) and Sato (1994a) on multiple isotropic-scattering, and may shed new insight into the seismic coda wave
interpretation. The scattering equations are solved numerically by first discretizing the model at regular grids and then
solving the linear integral equations iteratively. The results show that scattered wave energy can be well approximated by
body-wave to body wave scattering at earlier arrival times and short distances. At long distances from the source, scattered
surface waves dominate scattered body waves at surface stations. Since surface waves are 2-D propagating waves, their scattered
energies should in theory follow a common decay curve. The observed common decay trends on seismic coda of local earthquake
recordings particular at long lapse times suggest that perhaps later seismic codas are dominated by scattered surface waves.
When efficient body wave to surface wave conversion mechanisms are present in the shallow crustal layers, such as soft sediment
layers, the scattered surface waves dominate the seismic coda at even early arrival times for shallow sources and at later
arrival times for deeper events. 相似文献
143.
We have collected 432 vertical component records from 45 stations of new CENC (China Earthquake Network Center) in Chinese mainland and adjacent regions. These records were used to calculate Q0 (Q at 1Hz) and η values of Lg coda from each station by the stack spectral ratio (SSR) method. Then the tomography method was applied to obtaining lateral variation of Q0 and η values in Chinese mainland and adjacent regions. The result indicates that Q0 value varies between 150 and 600 in the studied areas. Yunnan, southwest Sichuan, and northwest Myanmar show the lowest Q0 value (Q0〈240) and the crust of these regions is characterized by complicated crack and strong hydrothermal activity. The highest Q0 value (Qo〉510) exists in the border of southern Mongolia, Alxa and Ordos block. The η value varies between 0.45 and 0.75 in Chinese mainland and its adjacent regions. 相似文献
144.
We recover the gross space–time characteristics of high-frequency (HF) radiator of the great Sumatra-Andaman islands earthquake of 2004 December 26 ( M w = 9.1–9.3) using the time histories of the power of radiated HF P waves. To determine these time histories we process teleseismic P waves at 36 BB stations, using, in sequence: (1) bandpass filtering (four bands: 0.4–1.2, 1.2–2, 2–3 and 3–4 Hz); (2) squaring wave amplitudes, making 'power signals' for each band and (3) stripping the propagation-related distortion ( P coda, etc.) from the power signal and thus recovering source time function for HF power. In step (3) we employ an inverse filter constructed from an empirical Green's function, which is estimated as the power signal from an aftershock. For each ray we thus obtain signals with relatively well-defined end and no coda. From these signals we extract: total duration (joint estimate for all four bands) and temporal centroid of signal power for each band. Through linear inversion, the set of duration values for a set of rays delivers estimates of the rupture stopping point and stopping time. Similarly, the set of temporal centroids can be inverted to obtain the position of the space–time centroid of HF energy radiator. The quality of inversion for centroid is acceptable for lower-frequency bands but deteriorates for higher-frequency bands where only a fraction of stations provide useful data. For the source length and duration the following joint estimates were obtained: 1241 ± 224 km, 550 ± 10 s. The estimated stopping point position corresponds to the northern extremity of the aftershock zone. Spatial HF radiation centroids are located at distances 350–700 km from the epicentre, in a systematic way: the higher is the frequency, the farther is the centroid from the epicentre. Average rupture propagation velocity is estimated as 2.25 km s–1 . 相似文献
145.
146.
江西九江-瑞昌震区的尾波衰减特征初探 总被引:2,自引:1,他引:1
根据单次散射模型,利用数字地震记录资料研究和讨论了江西省九江-瑞昌震区的尾波衰减特征,获得了可信的结果。经过计算,震中距30 km内的5个地震台站得到Q0值在75~79内波动。η值大体可以分为两类:九江台和范镇台η值为0.86~0.88;丁家山、狮子洞和武皎台η值为0.94~0.97,这种差别可能与台站方位有一定的关系。考虑到此次地震的破裂尺度不会太大,可采用后3个台的计算结果,拟合得到九江-瑞昌震区尾波Qc值随频率的变化关系为Qc(f)=(77.5±15.6)f0.96±0.09。九江-瑞昌震区的Q0值为77.5,η值为0.96,与云南武定、施甸地区接近,这种类似现象是构造运动活跃地区的特征体现还是反映了中强地震破裂区局部介质性质的一种共性,有待于进一步深入研究。本研究参与计算的5个台站最大尾波流逝时间为40~44 s,得到的平均采样体深度约为53 km,相对江西地区地壳平均厚度33 km而言,结果反映的是九江-瑞昌震区地壳和上地幔顶部的介质性质。 相似文献
147.
148.
149.
Based on the formulation of a multiple non-isotropic scattering process, a characteristic source time is introduced to define the initial impulse width of energy density at the source. An analytical expression of the initial intensity spectral density of a seismic wave is incorporated into the integral equation of seismic wave energy density. And, a recursive formula of Green’s function is derived to obtain the higher order Green’s function, which is included to describe the stronger non-isotropic scattering process. Then, the effect of the scattering pattern on the energy density envelope is investigated by the modified scattering theory. Significant differences are found in the decay of the energy density envelopes with distances using different scattering patterns. The envelope synthesized by the forward dominated scattering pattern is larger than the results obtained by the isotropic and backward dominated scattering pattern. Different scattering patterns are also used to fit the observation data from the aftershocks of the 2008 Wenchuan earthquake. It is concluded that the envelopes synthesized by the forward scattering pattern can match the data better than the isotropic and backward dominated scattering cases, and a new interpretation of the coda wave is given. Finally, using the forward dominated scattering pattern, the envelope broadening of the observed data is reproduced. 相似文献
150.
Fault zone monitoring with passive image interferometry 总被引:4,自引:0,他引:4