全文获取类型
收费全文 | 2379篇 |
免费 | 531篇 |
国内免费 | 203篇 |
专业分类
测绘学 | 642篇 |
大气科学 | 19篇 |
地球物理 | 1267篇 |
地质学 | 485篇 |
海洋学 | 186篇 |
天文学 | 10篇 |
综合类 | 111篇 |
自然地理 | 393篇 |
出版年
2024年 | 12篇 |
2023年 | 42篇 |
2022年 | 59篇 |
2021年 | 93篇 |
2020年 | 95篇 |
2019年 | 111篇 |
2018年 | 106篇 |
2017年 | 128篇 |
2016年 | 121篇 |
2015年 | 121篇 |
2014年 | 142篇 |
2013年 | 151篇 |
2012年 | 127篇 |
2011年 | 111篇 |
2010年 | 120篇 |
2009年 | 134篇 |
2008年 | 155篇 |
2007年 | 182篇 |
2006年 | 160篇 |
2005年 | 121篇 |
2004年 | 113篇 |
2003年 | 110篇 |
2002年 | 108篇 |
2001年 | 69篇 |
2000年 | 63篇 |
1999年 | 59篇 |
1998年 | 44篇 |
1997年 | 49篇 |
1996年 | 40篇 |
1995年 | 29篇 |
1994年 | 21篇 |
1993年 | 34篇 |
1992年 | 17篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1979年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有3113条查询结果,搜索用时 15 毫秒
41.
The S-velocity structure of the East Asian mantle from inversion of shear and surface waveforms 总被引:15,自引:0,他引:15
Wolfgang Friederich 《Geophysical Journal International》2003,153(1):88-102
42.
43.
44.
45.
46.
Seismic evidence for deep low-velocity anomalies in the transition zone beneath West Antarctica 总被引:1,自引:0,他引:1
Anne Sieminski Eric Debayle Jean-Jacques Lévêque 《Earth and Planetary Science Letters》2003,216(4):645-661
We present a three-dimensional (3D) SV-wave velocity model of the upper mantle beneath the Antarctic plate constrained by fundamental and higher mode Rayleigh waves recorded at regional distances. The good agreement between our results and previous surface wave studies in the uppermost 200 km of the mantle confirms that despite strong differences in data processing, modern surface wave tomographic techniques allow to produce consistent velocity models, even at regional scale. At greater depths the higher mode information present in our data set allows us to improve the resolution compared to previous regional surface wave studies in Antarctica that were all restricted to the analysis of the fundamental mode. This paper is therefore mostly devoted to the discussion of the deeper part of the model. Our seismic model displays broad domains of anomalously low seismic velocities in the asthenosphere. Moreover, we show that some of these broad, low-velocity regions can be more deeply rooted. The most remarkable new features of our model are vertical low-velocity structures extending from the asthenosphere down to the transition zone beneath the volcanic region of Marie Byrd Land, West Antarctica and a portion of the Pacific-Antarctic Ridge close to the Balleny Islands hotspot. A deep low-velocity anomaly may also exist beneath the Ross Sea hotspot. These vertical structures cannot be explained by vertical smearing of shallow seismic anomalies and synthetic tests show that they are compatible with a structure narrower than 200 km which would have been horizontally smoothed by the tomographic inversion. These deep low-velocity anomalies may favor the existence of several distinct mantle plumes, instead of a large single one, as the origin of volcanism in and around West Antarctica. These hypothetical deep plumes could feed large regions of low seismic velocities in the asthenosphere. 相似文献
47.
Velocity structure of uppermost mantle beneath North China from Pn tomography and its implications 总被引:1,自引:0,他引:1
20301 Pn arrival time data are collected from the seismological bulletins of both national and regional seismic networks. Pn travel time residuals are tomographically inverted for the Pn velocity structure of uppermost mantle beneath North China. The result indicates that the average Pn velocity in North China is 7.92 km/s, and the velocity varies laterally from ?0.21 to +0.29 km/s around the average. The approximately NNE trending high and low velocity regions arrange alternatively west-eastward. From west to east we can see high velocity in the middle Ordos region, the Shanxi graben low, the Jizhong depression high, the west Shandong uplift and Bohai Sea low, and the high velocity region to the east of the Tanlu fault. In the southern boundary zone of the North China block, except for the high velocity in the Qingling Mountains region, the velocity is generally lower than the average. Obvious velocity anisotropy is seen in the Datong Cenozoic volcanic region, with the fast velocity direction in NNE-SSW. Notable velocity anisotropy is also seen around the Bay of Bohai Sea, and the fast velocity directions seem to show a rotation pattern, possibly indicating a flow-like deformation in the uppermost mantle there. The Pn velocity variations show a reversed correlation with the Earth's heat flow. The low Pn velocity regions generally show high heat flow, e.g., the Shanxi graben and Bohai Sea region. While the high Pn velocity regions usually manifest low heat flow, e.g., the region of Jizhong depression. This indicates that the Pn velocity variation in the study region is mainly aroused by the regional temperature difference in the uppermost mantle. Strong earthquakes in the crust tend to occur in the region with the abnormal low Pn velocity, or in the transition zone between high and low Pn velocity regions. The earthquakes in the low velocity region are shallower, while that in the transition zone are deeper. 相似文献
48.
J. Escuder Viruete R. Carbonell D. Martí M. J. Jurado A. Prez-Estaún 《Tectonophysics》2003,361(1-2):97-120
The 3-D seismic tomographic data are used together with field, core and well log structural information to determine the detailed 3-D architecture of fault zones in a granitic massif of volume 500×575×168 m at Mina Ratones area in the Albalá Granitic Pluton. To facilitate the integration of the different data, geostatistical simulation algorithms are applied to interpolate the relatively sparse structural (hard) control data conditioned to abundant but indirect 3-D (soft) seismic tomographic data. To effectively integrate geologic and tomographic data, 3-D migration of the velocity model from the time domain into the depth domain was essential. The resulting 3-D model constitutes an image of the fault zone architecture within the granitic massif that honours hard and soft data and provides an evaluation of the spatial variability of structural heterogeneities based on the computation of 3-D experimental variograms of Fracture Index (fault intensity) data. This probabilistic quantitative 3-D model of spatially heterogeneous fault zones is suitable for subsequent fluid flow simulations. The modeled image of the 3-D fault distribution is consistent with the fault architecture in the Mina Ratones area, which basically consists of two families of subvertical structures with NNE–SSW and ENE–WSW trends that displaces the surfaces of low-angle faults (North Fault) and follows their seismically detected staircase geometry. These brittle structures cut two subvertical dykes (27 and 27′ Dykes) with a NNE–SSW to N–S trend. The faults present high FI (FI>12) adjacent bands of irregular geometry in detail that intersect in space delimiting rhombohedral blocks of relatively less fractured granite (FI<6). Both structural domains likely correspond with the protolith and the damaged zone/fault core in the widely accepted model for fault zone architecture. Therefore, the construction of 3-D grids of the FI in granitic areas affected by brittle tectonics permits the quantitative structural characterization of the rock massif. 相似文献
49.
在多相流动电磁波成像测井研究中,测量敏感场是设计测量仪器和研究图像重建算法的前提工作. 本文用数值方法计算多相流动电磁波成像测井测量敏感场. 根据测量探头电极阵列的对称性,将三维敏感场问题划分为轴向和横向两个平面问题,然后应用有限元算法求解两个平面电势分布问题,对于不同介质模型,计算各种测量条件下测量区域内电势分布,进而根据电势分布计算测量敏感场. 结果表明测量敏感区域为发射电极到测量电极的弧形区域,在发射电极到测量电极的电势梯度线上,测量敏感函数近似于一个指数函数. 相似文献
50.