全文获取类型
收费全文 | 12108篇 |
免费 | 2453篇 |
国内免费 | 1034篇 |
专业分类
测绘学 | 46篇 |
大气科学 | 286篇 |
地球物理 | 8181篇 |
地质学 | 3051篇 |
海洋学 | 1459篇 |
天文学 | 700篇 |
综合类 | 463篇 |
自然地理 | 1409篇 |
出版年
2024年 | 21篇 |
2023年 | 86篇 |
2022年 | 243篇 |
2021年 | 297篇 |
2020年 | 377篇 |
2019年 | 477篇 |
2018年 | 370篇 |
2017年 | 357篇 |
2016年 | 323篇 |
2015年 | 406篇 |
2014年 | 514篇 |
2013年 | 629篇 |
2012年 | 551篇 |
2011年 | 647篇 |
2010年 | 544篇 |
2009年 | 701篇 |
2008年 | 769篇 |
2007年 | 918篇 |
2006年 | 880篇 |
2005年 | 707篇 |
2004年 | 737篇 |
2003年 | 674篇 |
2002年 | 561篇 |
2001年 | 410篇 |
2000年 | 464篇 |
1999年 | 415篇 |
1998年 | 413篇 |
1997年 | 292篇 |
1996年 | 343篇 |
1995年 | 266篇 |
1994年 | 251篇 |
1993年 | 237篇 |
1992年 | 161篇 |
1991年 | 114篇 |
1990年 | 89篇 |
1989年 | 88篇 |
1988年 | 64篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
Tadashi Kito reas Rietbrock Christine Thomas 《Geophysical Journal International》2007,169(3):1201-1209
We have developed a new array method combining conventional migration with a slowness-backazimuth deviation weighting scheme. All seismic traces are shifted based on the theoretical traveltime of the scattered wave from specific gridpoints in a 3-D volume. Observed slowness and backazimuth are calculated for each raypath and compared with theoretical values in order to estimate slowness and backazimuth deviations. Subsequently, stacked energy calculated by a conventional migration method is weighted by the slowness and backazimuth deviations to suppress any arrival energy whose slowness and backazimuth are inconsistent with the expected theoretical values. This new method was applied to two P- wave data sets which comprise (1) underside reflections at the 410 and 660 km mantle discontinuities and (2) D" reflections as well as their corresponding synthetic data sets. The results show that the weighting scheme dramatically increases the resolution of the migrated images and enables us to obtain well-constrained, focused images, making upper-mantle discontinuities and D" reflections more distinct by reducing their surrounding energy. 相似文献
954.
Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels 总被引:1,自引:0,他引:1
Nozomu Takeuchi 《Geophysical Journal International》2007,169(3):1153-1163
A whole mantle SH velocity model is obtained by using a unique data set and techniques. Body and surface waveforms including major and multi-orbit phases are used as a data set and are inverted by using 3-D Born kernels. The resultant model, SH18CE, reveals the different natures of the two major upwelling systems: the strong low velocity anomalies beneath Africa extend for more than 1000 km from the core–mantle boundary (CMB), whereas those beneath the Pacific are restricted to 300–400 km from the CMB. The results also show the variable natures of stagnant slabs on the 670 discontinuity around Japan: the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region, which is consistent with the detailed delay time tomography model in this area. 相似文献
955.
U. Kastrup N. Deichmann A. Fröhlich D. Giardini 《Geophysical Journal International》2007,169(3):1273-1288
956.
957.
We present observations of ground accelerations recorded at a small array close to the fault during the Düzce earthquake and its early aftershocks. The records show the strong spatial variability of ground acceleration over distances of only a few hundred metres. During the main shock, the peak horizontal acceleration values ranged from 0.3 to about 1.0 g at stations distant of 1.5 km only. We attribute this spatial variability to a fault zone site effect as peak ground acceleration steadily increases as the distance to the fault trace decreases. The spectral ratio between the ground motion recorded near the fault and the one outside the fault zone shows a shift of the spectral peak to lower frequencies with increasing peak accelerations. Such an observation suggests a non-linear behaviour of the fault zone due to the strong ground shaking. As much as a 45 per cent reduction in the shear wave velocity is necessary for the observed shifts. The opening of pre-existing cracks throughout the fault zone is the proposed mechanism to account for the observed shear wave reductions. The observation that elastic fault zone properties are soon recovered following episodes of large strains shows that cracks and fissures close rapidly after the strong shaking is over. 相似文献
958.
Yih-Min Wu Hiroo Kanamori Richard M. Allen Egill Hauksson 《Geophysical Journal International》2007,170(2):711-717
We explore a practical approach to earthquake early warning in southern California by determining a ground-motion period parameter τ c and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms recorded at the Southern California Seismic Network stations for earthquakes with M > 4.0. At a given site, we estimate the magnitude of an event from τ c and the peak ground-motion velocity ( PGV ) from Pd . The incoming three-component signals are recursively converted to ground acceleration, velocity and displacement. The displacements are recursively filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz, and a P -wave trigger is constantly monitored. When a trigger occurs, τ c and Pd are computed. We found the relationship between τ c and magnitude ( M ) for southern California, and between Pd and PGV for both southern California and Taiwan. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the P wave. When the station density is high, the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach. In an ideal situation, such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds. 相似文献
959.
P. A. Bedrosian N. Maercklin U. Weckmann Y. Bartov T. Ryberg O. Ritter 《Geophysical Journal International》2007,170(2):737-748
Magnetotelluric and seismic methods provide complementary information about the resistivity and velocity structure of the subsurface on similar scales and resolutions. No global relation, however, exists between these parameters, and correlations are often valid for only a limited target area. Independently derived inverse models from these methods can be combined using a classification approach to map geologic structure. The method employed is based solely on the statistical correlation of physical properties in a joint parameter space and is independent of theoretical or empirical relations linking electrical and seismic parameters. Regions of high correlation (classes) between resistivity and velocity can in turn be mapped back and re-examined in depth section. The spatial distribution of these classes, and the boundaries between them, provide structural information not evident in the individual models. This method is applied to a 10 km long profile crossing the Dead Sea Transform in Jordan. Several prominent classes are identified with specific lithologies in accordance with local geology. An abrupt change in lithology across the fault, together with vertical uplift of the basement suggest the fault is sub-vertical within the upper crust. 相似文献
960.
V. Cannelli D. Melini P. De Michelis A. Piersanti F. Florindo 《Geophysical Journal International》2007,170(2):718-724
The deformation at the core–mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core–mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field ( J 2 ) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 1018 Pa s, the postseismic J 2 variation in the next years is expected to leave a detectable signal in geodetic observations. 相似文献