全文获取类型
收费全文 | 2100篇 |
免费 | 379篇 |
国内免费 | 588篇 |
专业分类
测绘学 | 10篇 |
地球物理 | 633篇 |
地质学 | 1792篇 |
海洋学 | 67篇 |
天文学 | 8篇 |
综合类 | 61篇 |
自然地理 | 496篇 |
出版年
2024年 | 7篇 |
2023年 | 24篇 |
2022年 | 43篇 |
2021年 | 50篇 |
2020年 | 54篇 |
2019年 | 51篇 |
2018年 | 41篇 |
2017年 | 44篇 |
2016年 | 50篇 |
2015年 | 58篇 |
2014年 | 57篇 |
2013年 | 81篇 |
2012年 | 127篇 |
2011年 | 92篇 |
2010年 | 68篇 |
2009年 | 96篇 |
2008年 | 132篇 |
2007年 | 194篇 |
2006年 | 188篇 |
2005年 | 163篇 |
2004年 | 171篇 |
2003年 | 134篇 |
2002年 | 126篇 |
2001年 | 115篇 |
2000年 | 106篇 |
1999年 | 116篇 |
1998年 | 109篇 |
1997年 | 92篇 |
1996年 | 85篇 |
1995年 | 63篇 |
1994年 | 56篇 |
1993年 | 68篇 |
1992年 | 33篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 20篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 16篇 |
1985年 | 6篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有3067条查询结果,搜索用时 922 毫秒
341.
342.
343.
344.
345.
Are Arc Basalts Dry, Wet, or Both? Evidence from the Sumisu Caldera Volcano, Izu-Bonin Arc, Japan 总被引:2,自引:0,他引:2
TAMURA Y.; TANI K.; ISHIZUKA O.; CHANG Q.; SHUKUNO H.; FISKE R. S. 《Journal of Petrology》2005,46(9):1769-1803
Basaltbasaltic andesite (<55 wt % SiO2) and daciterhyolite(6674 wt % SiO2) are the predominant eruptive productsin the Sumisu caldera volcano, IzuBonin arc, Japan. Themost magnesian basalt (8·5% MgO), as well as some ofthe other basalts, has a low Zr content (2025 ppm), andcannot yield basalts with higher Zr contents (2940 ppm)through fractionation and/or assimilation. The high- and low-Zrbasalts have different phenocryst assemblages, olivine, plagioclaseand pyroxene phenocryst chemistries, REE (rare earth element)patterns, and fluid-mobile element/immobile element ratios.Estimated primary olivine compositions are more magnesian (>Fo91)in the low-Zr basalts compared with those in high-Zr basalts(<Fo89). The low-Zr basalts contain up to 11 vol. % augite,but many high-Zr basalts are free of augite, which appears onlyin their more differentiated products. The low-Zr basalts areconsidered to be hydrous magmas in which olivine crystallizesfirst followed by augite and plagioclase, whereas the high-Zrbasalts are dry. The low-Zr basalts have higher U/Th ratiosthan the high-Zr basalts. We suggest that both dry and wet primarybasalts existed in the Sumisu magmatic system, each having differenttrace element concentrations, mineral assemblages and mineralchemistry. The lower contents of Zr and light REE and magnesianprimary olivines in the wet basalts could have resulted froma higher degree of partial melting (20%) of a hydrous sourcemantle compared with 10% melting of a dry source mantle. TheSr, Nd and Pb isotope compositions of the wet and dry basaltsare similar and are limited in range. These lines of evidenceindicate that a mantle diapir model might be applicable to satisfythe configuration of such a mantle source region beneath a singlevolcanic system such as Sumisu. KEY WORDS: degree of melting; hot fingers; isotopes; mantle diapir; mantle wedge 相似文献
346.
Volcanism in the Vitim Volcanic Field, Siberia: Geochemical Evidence for a Mantle Plume Beneath the Baikal Rift Zone 总被引:6,自引:1,他引:5
JOHNSON J. S.; GIBSON S. A.; THOMPSON R. N.; NOWELL G. M. 《Journal of Petrology》2005,46(7):1309-1344
The Baikal Rift is a zone of active lithospheric extension adjacentto the Siberian Craton. The 616 Myr old Vitim VolcanicField (VVF) lies approximately 200 km east of the rift axisand consists of 5000 km3 of melanephelinites, basanites, alkaliand tholeiitic basalts, and minor nephelinites. In the volcanicpile, 142 drill core samples were used to study temporal andspatial variations. Variations in major element abundances (e.g.MgO = 3·314·6 wt %) reflect polybaric fractionalcrystallization of olivine, clinopyroxene and plagioclase. 87Sr/86Sri(0·70390·7049), 143Nd/144Ndi (0·51270·5129)and 176Hf/177Hfi (0·28290·2830) ratiosare similar to those for ocean island basalts and suggest thatthe magmas have not assimilated significant amounts of continentalcrust. Variable degrees of partial melting appear to be responsiblefor differences in Na2O, P2O5, K2O and incompatible trace elementabundances in the most primitive (high-MgO) magmas. Fractionatedheavy rare earth element (HREE) ratios (e.g. [Gd/Lu]n > 2·5)indicate that the parental magmas of the Vitim lavas were predominantlygenerated within the garnet stability field. Forward major elementand REE inversion models suggest that the tholeiitic and alkalibasalts were generated by decompression melting of a fertileperidotite source within the convecting mantle beneath Vitim.Ba/Sr ratios and negative K anomalies in normalized multi-elementplots suggest that phlogopite was a residual mantle phase duringthe genesis of the nephelinites and basanites. Relatively highlight REE (LREE) abundances in the silica-undersaturated meltsrequire a metasomatically enriched lithospheric mantle source.Results of forward major element modelling suggest that meltingof phlogopite-bearing pyroxenite veins could explain the majorelement composition of these melts. In support of this, pyroxenitexenoliths have been found in the VVF. High Cenozoic mantle potentialtemperatures (1450°C) predicted from geochemical modellingsuggest the presence of a mantle plume beneath the Baikal RiftZone. KEY WORDS: Baikal Rift; mafic magmatism; mantle plume; metasomatism; partial melting 相似文献
347.
348.
Lithospheric thermal structure in the Baltic shield 总被引:1,自引:0,他引:1
349.
ZHAO Wenjin ZHAO Xun SHI Danian LIU Kui JIANG Wan WU Zhenhan XIONG Jiayu ZHENG Yukun Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》2004,78(4):931-939
This paper introduces 8 major discoveries and new understandings with regard to the deep structure and tectonics of the Himalayas and Tibetan Plateau obtained in Project INDEPTH, They are mainly as follows. (1) The upper crust, lower crust and mantle lithosphere beneath the blocks of the plateau form a "sandwich" structure with a relatively rigid-brittle upper crust, a visco-plastic lower crust and a relatively rigid-ductile mantle lithosphere. This structure is completely different from that of monotonous, cold and more rigid oceanic plates. (2) In the process of north-directed collision-compression of the Indian subcontinent, the upper crust was attached to the foreland in the form of a gigantic foreland accretionary wedge. The interior of the accretionary wedge thickened in such tectonic manners as large-scale thrusting, backthrusting and folding, and magmatic masses and partially molten masses participated in the crustal thickening. Between the upper crust and lower crust lies a large detachment (e.g 相似文献
350.
Using a Love number formalism, the elastic deformations of the mantle and the mass redistribution gravitational potential within the Earth induced by the fluid pressure acting at the core–mantle boundary (CMB) are computed. This pressure field changes at a decadal time scale and may be estimated from observations of the surface magnetic field and its secular variation. First, using a spherical harmonic expansion, the poloidal and toroidal part of the fluid velocity field at the CMB for the last 40 years is computed, under the hypothesis of tangential geostrophy. Then the associated geostrophic pressure, whose order of magnitude is about 1000 Pa, is computed. The surface topography induced by this pressure field is computed using Love numbers, and is a few millimetres. The mass redistribution gravitational potential induced by these deformations and, in particular, the zonal components of the related surface gravitational potential perturbation (J2, J3 and J4 coefficients), are calculated. Overall perturbations for the J2 coefficient of about 10–10, for J3 of about 10–11 and for J4 are found of about 0.3×10–11. Finally, these theoretical results are compared with recent observations of the decadal variation of J2 from satellite laser ranging. Results concerning J2 can be described as follows: first, they are one order of magnitude too small to explain the observed decadal variation of J2 and, second, they show a significant linear trend over the last 40 years, whose rate of decrease amounts to 7% of the observed value. 相似文献