全文获取类型
| 收费全文 | 2260篇 |
| 免费 | 370篇 |
| 国内免费 | 391篇 |
专业分类
| 测绘学 | 7篇 |
| 大气科学 | 7篇 |
| 地球物理 | 1321篇 |
| 地质学 | 1193篇 |
| 海洋学 | 67篇 |
| 天文学 | 4篇 |
| 综合类 | 49篇 |
| 自然地理 | 373篇 |
出版年
| 2024年 | 6篇 |
| 2023年 | 31篇 |
| 2022年 | 63篇 |
| 2021年 | 92篇 |
| 2020年 | 72篇 |
| 2019年 | 79篇 |
| 2018年 | 85篇 |
| 2017年 | 90篇 |
| 2016年 | 67篇 |
| 2015年 | 82篇 |
| 2014年 | 85篇 |
| 2013年 | 107篇 |
| 2012年 | 106篇 |
| 2011年 | 89篇 |
| 2010年 | 93篇 |
| 2009年 | 118篇 |
| 2008年 | 114篇 |
| 2007年 | 156篇 |
| 2006年 | 153篇 |
| 2005年 | 118篇 |
| 2004年 | 148篇 |
| 2003年 | 120篇 |
| 2002年 | 103篇 |
| 2001年 | 81篇 |
| 2000年 | 82篇 |
| 1999年 | 75篇 |
| 1998年 | 65篇 |
| 1997年 | 67篇 |
| 1996年 | 83篇 |
| 1995年 | 58篇 |
| 1994年 | 67篇 |
| 1993年 | 59篇 |
| 1992年 | 58篇 |
| 1991年 | 34篇 |
| 1990年 | 31篇 |
| 1989年 | 19篇 |
| 1988年 | 25篇 |
| 1987年 | 6篇 |
| 1986年 | 14篇 |
| 1985年 | 6篇 |
| 1984年 | 1篇 |
| 1983年 | 2篇 |
| 1981年 | 1篇 |
| 1980年 | 1篇 |
| 1979年 | 3篇 |
| 1978年 | 1篇 |
| 1977年 | 4篇 |
| 1954年 | 1篇 |
排序方式： 共有3021条查询结果，搜索用时 296 毫秒
71.
There have been several claims that seismic shear waves respond to changes in stress before earthquakes. The companion paper develops a stress-sensitive model (APE) for the behaviour of low-porosity low-permeability crystalline rocks containing pervasive distributions of fluid-filled intergranular microcracks, and this paper uses APE to model the behaviour before earthquakes. Modelling with APE shows that the microgeometry and statistics of distributions of such fluid-filled microcracks respond almost immediately to changes in stress, and that the behaviour can be monitored by analysing seismic shear-wave splitting. The physical reasons for the coupling between shear-wave splitting and differential stress are discussed.
In this paper, we extend the model by using percolation theory to show that large crack densities are limited at the grain-scale level by the percolation threshold at which interacting crack clusters lead to pronounced increases in rock-matrix permeability. In the simplest formulation, the modelling is dimensionless and almost entirely constrained without free parameters. Nevertheless, APE modelling of the evolution of fluid-saturated rocks under stress reproduces the observed fracture criticality and the narrow range of shear-wave azimuthal anisotropy in crustal rocks. It also reproduces the behaviour of temporal variations in shear-wave splitting observed before and after the 1986, M = 6, North Palm Springs earthquake, Southern California, and several other smaller earthquakes.
The agreement of APE modelling with a wide range of observations confirms that fluid-saturated crystalline rocks are stress-sensitive and respond to changes in stress by critical fluid-rock interactions at the microscale level. This means that the effects of changes in stress and other parameters can be numerically modelled and monitored by appropriate observations of seismic shear waves. 相似文献
In this paper, we extend the model by using percolation theory to show that large crack densities are limited at the grain-scale level by the percolation threshold at which interacting crack clusters lead to pronounced increases in rock-matrix permeability. In the simplest formulation, the modelling is dimensionless and almost entirely constrained without free parameters. Nevertheless, APE modelling of the evolution of fluid-saturated rocks under stress reproduces the observed fracture criticality and the narrow range of shear-wave azimuthal anisotropy in crustal rocks. It also reproduces the behaviour of temporal variations in shear-wave splitting observed before and after the 1986, M = 6, North Palm Springs earthquake, Southern California, and several other smaller earthquakes.
The agreement of APE modelling with a wide range of observations confirms that fluid-saturated crystalline rocks are stress-sensitive and respond to changes in stress by critical fluid-rock interactions at the microscale level. This means that the effects of changes in stress and other parameters can be numerically modelled and monitored by appropriate observations of seismic shear waves. 相似文献
72.
M. Cocco J. Pacheco S. K. Singh F. Courboulex 《Geophysical Journal International》1997,131(1):135-145
An analysis of the Zihuatanejo, Mexico, earthquake of 1994 December 10 ( M = 6.6), based on teleseismic and near-source data, shows that it was a normal-faulting, intermediate-depth ( H = 50 ± 5 km) event. It was located about 30 km inland, within the subducted Cocos plate. The preferred fault plane has an azimuth of 130°, a dip of 79° and a rake of −86°. The rupture consisted of two subevents which were separated in time by about 2 s, with the second subevent occurring downdip of the first. The measured stress drop was relatively high, requiring a Δσ of about a kilobar to explain the high-frequency level of the near-source spectra. A rough estimate of the thickness of the seismogenic part of the oceanic lithosphere below Zihuatanejo, based on the depth and the rupture extent of this event, is 40 km.
This event and the Oaxaca earthquake of 1931 January 15 ( M = 7.8) are the two significant normal-faulting, intermediate-depth shocks whose epicentres are closest to the coast. Both of these earthquakes were preceded by several large to great shallow, low-angle thrust earthquakes, occurring updip. The observations in other subduction zones show just the opposite: normal-faulting events precede, not succeed, updip, thrust shocks. Indeed, the thrust events, soon after their occurrence, are expected to cause compression in the slab, thus inhibiting the occurrence of normal-faulting events. To explain the occurrence of the Zihuatanejo earthquake, we note that the Cocos plate, after an initial shallow-angle subduction, unbends and becomes subhorizontal. In the region of the unbending, the bottom of the slab is in horizontal extension. We speculate that the large updip seismic slip during shallow, low-angle thrust events increases the buckling of the slab, resulting in an incremental tensional stress at the bottom of the slab and causing normal-faulting earthquakes. This explanation may also hold for the 1931 Oaxaca event. 相似文献
This event and the Oaxaca earthquake of 1931 January 15 ( M = 7.8) are the two significant normal-faulting, intermediate-depth shocks whose epicentres are closest to the coast. Both of these earthquakes were preceded by several large to great shallow, low-angle thrust earthquakes, occurring updip. The observations in other subduction zones show just the opposite: normal-faulting events precede, not succeed, updip, thrust shocks. Indeed, the thrust events, soon after their occurrence, are expected to cause compression in the slab, thus inhibiting the occurrence of normal-faulting events. To explain the occurrence of the Zihuatanejo earthquake, we note that the Cocos plate, after an initial shallow-angle subduction, unbends and becomes subhorizontal. In the region of the unbending, the bottom of the slab is in horizontal extension. We speculate that the large updip seismic slip during shallow, low-angle thrust events increases the buckling of the slab, resulting in an incremental tensional stress at the bottom of the slab and causing normal-faulting earthquakes. This explanation may also hold for the 1931 Oaxaca event. 相似文献
73.
74.
Deformation of subducted oceanic lithosphere 总被引：2，自引：0，他引：2
75.
76.
77.
78.
79.
80.