全文获取类型
收费全文 | 1536篇 |
免费 | 477篇 |
国内免费 | 129篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 11篇 |
地球物理 | 1184篇 |
地质学 | 421篇 |
海洋学 | 52篇 |
天文学 | 11篇 |
综合类 | 54篇 |
自然地理 | 366篇 |
出版年
2024年 | 12篇 |
2023年 | 31篇 |
2022年 | 40篇 |
2021年 | 65篇 |
2020年 | 68篇 |
2019年 | 67篇 |
2018年 | 76篇 |
2017年 | 75篇 |
2016年 | 75篇 |
2015年 | 73篇 |
2014年 | 96篇 |
2013年 | 76篇 |
2012年 | 68篇 |
2011年 | 63篇 |
2010年 | 69篇 |
2009年 | 80篇 |
2008年 | 98篇 |
2007年 | 117篇 |
2006年 | 127篇 |
2005年 | 87篇 |
2004年 | 77篇 |
2003年 | 88篇 |
2002年 | 76篇 |
2001年 | 56篇 |
2000年 | 47篇 |
1999年 | 46篇 |
1998年 | 38篇 |
1997年 | 40篇 |
1996年 | 40篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 34篇 |
1992年 | 16篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 15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2142条查询结果,搜索用时 8 毫秒
1.
2.
David M. Hirsch 《Contributions to Mineralogy and Petrology》2008,155(4):401-415
Garnet-bearing schists from the Waterville Formation of south-central Maine provide an opportunity to examine the factors
governing porphyroblast size over a range of metamorphic grade. Three-dimensional sizes and locations for all garnet porphyroblasts
were determined for three samples along the metamorphic field gradient spanning lowest garnet through sillimanite grade, using
high-resolution X-ray computed tomography. Comparison of crystal size distributions to previous data sets obtained by stereological
methods for the same samples reveals significant differences in mode, mean, and shape of the distributions. Quantitative textural
analysis shows that the garnets in each rock crystallized in a diffusion-controlled nucleation and growth regime. In contrast
to the typical observation of a correlation between porphyroblast size and position along a metamorphic field gradient, porphyroblast
size of the lowest-grade specimen is intermediate between the high- and middle-grade specimens’ sizes. Mean porphyroblast
size does not correlate with peak temperatures from garnet-biotite Fe-Mg exchange thermometry, nor is post-crystallization
annealing (Ostwald Ripening) required to produce the observed textures, as was previously proposed for these rocks. Robust
pseudosection calculations fail to reproduce the observed garnet core compositions for two specimens, suggesting that these
calc-pelites experienced metasomatism. For each of these two specimens, Monte Carlo calculations suggest potential pre-metasomatism
bulk compositions that replicate garnet core compositions. Pseudosection analyses allow the estimation of the critical temperatures
for garnet growth: ∼481, ∼477, and ∼485°C for the lowest-garnet-zone, middle-garnet-zone, and sillimanite-zone specimens,
respectively. Porphyroblast size appears to be determined in this case by a combination of the heating rate during garnet
crystallization, the critical temperature for the garnet-forming reaction and the kinetics of nucleation. Numerical simulations
of thermally accelerated, diffusion-controlled nucleation, and growth for the three samples closely match measured crystal
size distributions. These observations and simulations suggest that previous hypotheses linking the garnet size primarily
to the temperature at the onset of porphyroblast nucleation can only partially explain the observed textures. Also important
in determining porphyroblast size are the heating rate and the distribution of favorable nucleation sites. 相似文献
3.
Crustal structure of the Eastern Alps along the TRANSALP profile from wide-angle seismic tomography 总被引:1,自引:1,他引:1
The objective of the TRANSALP project is an investigation of the Eastern Alps with regard to their deep structure and dynamic evolution. The core of the project is a 340-km-long seismic profile at 12°E between Munich and Venice. This paper deals with the P-wave velocity distribution as derived from active source travel time tomography. Our database consists of Vibroseis and explosion seismic travel times recorded at up to 100 seismological stations distributed in a 30-km-wide corridor along the profile. In order to derive a velocity and reflector model, we simultaneously inverted refractions and reflections using a derivative of a damped least squares approach for local earthquake tomography. 8000 travel time picks from dense Vibroseis recordings provide the basis for high resolution in the upper crust. Explosion seismic wide-angle reflection travel times constrain both deeper crustal velocities and structure of the crust–mantle boundary with low resolution. In the resulting model, the Adriatic crust shows significantly higher P-wave velocities than the European crust. The European Moho is dipping south at an angle of 7°. The Adriatic Moho dips north with a gentle inclination at shallower depths. This geometry suggests S-directed subduction. Azimuthal variations of the first-break velocities as well as observations of shear wave splitting reveal strong anisotropy in the Tauern Window. We explain this finding by foliations and laminations generated by lateral extrusion. Based on the P-wave model we also localized almost 100 local earthquakes recorded during the 2-month acquisition campaign in 1999. Seismicity patterns in the North seem related to the Inn valley shear zone, and to thrusting of Austroalpine units over European basement. The alignment of deep seismicity in the Trento-Vicenza region with the top of the Adriatic lower crust corroborates the suggestion of a deep thrust fault in the Southern Alps. 相似文献
4.
5.
6.
7.
8.
9.
10.