全文获取类型
收费全文 | 742篇 |
免费 | 135篇 |
国内免费 | 136篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 26篇 |
地球物理 | 254篇 |
地质学 | 309篇 |
海洋学 | 81篇 |
天文学 | 110篇 |
综合类 | 21篇 |
自然地理 | 181篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 30篇 |
2018年 | 22篇 |
2017年 | 18篇 |
2016年 | 31篇 |
2015年 | 30篇 |
2014年 | 33篇 |
2013年 | 34篇 |
2012年 | 30篇 |
2011年 | 39篇 |
2010年 | 24篇 |
2009年 | 40篇 |
2008年 | 39篇 |
2007年 | 43篇 |
2006年 | 58篇 |
2005年 | 41篇 |
2004年 | 29篇 |
2003年 | 37篇 |
2002年 | 51篇 |
2001年 | 35篇 |
2000年 | 37篇 |
1999年 | 35篇 |
1998年 | 42篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 24篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1013条查询结果,搜索用时 468 毫秒
61.
The strain‐dependent spatial evolution of garnet in a high‐P ductile shear zone from the Western Gneiss Region (Norway): a synchrotron X‐ray microtomography study 下载免费PDF全文
Reaction and deformation microfabrics provide key information to understand the thermodynamic and kinetic controls of tectono‐metamorphic processes, however, they are usually analysed in two dimensions, omitting important information regarding the third spatial dimension. We applied synchrotron‐based X‐ray microtomography to document the evolution of a pristine olivine gabbro into a deformed omphacite–garnet eclogite in four dimensions, where the 4th dimension is represented by the degree of strain. In the investigated samples, which cover a strain gradient into a shear zone from the Western Gneiss Region (Norway), we focused on the spatial transformation of garnet coronas into elongated garnet clusters with increasing strain. The microtomographic data allowed quantification of garnet volume, shape and spatial arrangement evolution with increasing strain. The microtomographic observations were combined with light microscope and backscatter electron images as well as electron microprobe (EMPA) and electron backscatter diffraction (EBSD) analysis to correlate mineral composition and orientation data with the X‐ray absorption signal of the same mineral grains. With increasing deformation, the garnet volume almost triples. In the low‐strain domain, garnet grains form a well interconnected large garnet aggregate that develops throughout the entire sample. We also observed that garnet coronas in the gabbros never completely encapsulate olivine grains. In the most highly deformed eclogites, the oblate shapes of garnet clusters reflect a deformational origin of the microfabrics. We interpret the aligned garnet aggregates to direct synkinematic fluid flow, and consequently influence the transport of dissolved chemical components. EBSD analyses reveal that garnet shows a near‐random crystal preferred orientation that testifies no evidence for crystal plasticity. There is, however evidence for minor fracturing, neo‐nucleation and overgrowth. Microprobe chemical analysis revealed that garnet compositions progressively equilibrate to eclogite facies, becoming more almandine‐rich. We interpret these observations as pointing to a mechanical disintegration of the garnet coronas during strain localization, and their rearrangement into individual garnet clusters through a combination of garnet coalescence and overgrowth while the rock was deforming. 相似文献
62.
F. Rezanezhad W. L. Quinton J. S. Price T. R. Elliot D. Elrick K. R. Shook 《水文研究》2010,24(21):2983-2994
In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air‐filled pores control the unsaturated hydraulic conductivity of peat soils using high‐resolution (45 µm) three‐dimensional (3D) X‐ray computed tomography (CT) and digital image processing of four peat sub‐samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross‐sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air‐filled pore hydraulic radius, tortuosity, air‐filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air‐filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
63.
64.
65.
66.
67.
68.
Beverley J. Moore 《Geophysical Journal International》1993,115(3):1137-1142
The total Green's function for two-point boundary-value problems can be related to the propagator for initial-value problems. A very simple expression for the Green's function is obtained when the unperturbed medium may be described by material with a constant gradient in quadratic slowness. The derivation requires a correct understanding of assumptions made in the propagator solution. Expressions are also obtained for Green's function in multilayered media. 相似文献
69.
赵荣国 《地震地磁观测与研究》1994,15(1):21-37
本文是1993年大震速报培训班讲课的一部分。主要讨论了仅用某一地震台的地震图分析远震和极远震震相方法问题。包括地震波和震相的异同、地震图的复杂性、震相特征和分析方法。讲座的第一、二章刊登在本刊1993年第6期上。此处为接续。 相似文献
70.
Three dimensional velocity structure beneath the Kunming Telemetered Seismic Network(王椿镛)(王溪莉)(颜其中)Threedimensionalvelocityst... 相似文献