全文获取类型
收费全文 | 14450篇 |
免费 | 3510篇 |
国内免费 | 1842篇 |
专业分类
测绘学 | 203篇 |
大气科学 | 20篇 |
地球物理 | 11481篇 |
地质学 | 6090篇 |
海洋学 | 261篇 |
天文学 | 16篇 |
综合类 | 1195篇 |
自然地理 | 536篇 |
出版年
2024年 | 35篇 |
2023年 | 139篇 |
2022年 | 379篇 |
2021年 | 554篇 |
2020年 | 476篇 |
2019年 | 599篇 |
2018年 | 559篇 |
2017年 | 559篇 |
2016年 | 458篇 |
2015年 | 662篇 |
2014年 | 808篇 |
2013年 | 769篇 |
2012年 | 837篇 |
2011年 | 856篇 |
2010年 | 758篇 |
2009年 | 1020篇 |
2008年 | 780篇 |
2007年 | 871篇 |
2006年 | 877篇 |
2005年 | 821篇 |
2004年 | 784篇 |
2003年 | 757篇 |
2002年 | 611篇 |
2001年 | 606篇 |
2000年 | 597篇 |
1999年 | 500篇 |
1998年 | 504篇 |
1997年 | 446篇 |
1996年 | 447篇 |
1995年 | 400篇 |
1994年 | 345篇 |
1993年 | 286篇 |
1992年 | 226篇 |
1991年 | 135篇 |
1990年 | 101篇 |
1989年 | 80篇 |
1988年 | 54篇 |
1987年 | 36篇 |
1986年 | 25篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1979年 | 20篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 271 毫秒
921.
In marine strata from Sinian to Middle Triassic in South China, there develop four sets of regional and six sets of local
source rocks, and ten sets of reservoir rocks. The occurrence of four main formation periods in association with five main
reconstruction periods, results in a secondary origin for the most marine gas pools in South China. To improve the understanding
of marine gas pools in South China with severely deformed geological background, the dominant control factors are discussed
in this paper. The fluid sources, including the gas cracked from crude oil, the gas dissolved in water, the gas of inorganic
origin, hydrocarbons generated during the second phase, and the mixed pool fluid source, were the most significant control
factors of the types and the development stage of pools. The period of the pool formation and the reconstruction controlled
the pool evolution and the distribution on a regional scale. Owing to the multiple periods of the pool formation and the reconstruction,
the distribution of marine gas pools was complex both in space and in time, and the gas in the pools is heterogeneous. Pool
elements, such as preservation conditions, traps and migration paths, and reservoir rocks and facies, also served as important
control factors to marine gas pools in South China. Especially, the preservation conditions played a key role in maintaining
marine oil and gas accumulations on a regional or local scale. According to several dominant control factors of a pool, the
pool-controlling model can be constructed. As an example, the pool-controlling model of Sinian gas pool in Weiyuan gas field
in Sichuan basin was summed up. 相似文献
922.
923.
924.
Confidence intervals for earthquake source parameters 总被引:2,自引:0,他引:2
G. A. Prieto D. J. Thomson F. L. Vernon P. M. Shearer R. L. Parker 《Geophysical Journal International》2007,168(3):1227-1234
925.
Far-field simulation of the 1946 Aleutian tsunami 总被引:1,自引:0,他引:1
We present hydrodynamic far-field simulations of the Aleutian tsunami of 1946 April 1, using both a dislocation source representing a slow earthquake and a dipolar one modelling a large landslide. The earthquake source is derived from the recent seismological study by López and Okal, while the landslide source was previously used to explain the exceptional run-up at Scotch Cap in the near field. The simulations are compared to a field data set previously compiled from testimonies of elderly witnesses at 27 far-field locations principally in the Austral and Marquesas Islands, with additional sites at Pitcairn, Easter and Juan Fernández. We find that the data set is modelled satisfactorily by the dislocation source, while the landslide fails to match the measured amplitudes, and to give a proper rendition of the physical interaction of the wavefield with the shore, in particular at Nuku Hiva, Marquesas. The emerging picture is that the event involved both a very slow earthquake, responsible for the far-field tsunami, and a major landslide explaining the near-field run-up, but with a negligible contribution in the far field. 相似文献
926.
927.
928.
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
929.
930.