全文获取类型
收费全文 | 1951篇 |
免费 | 223篇 |
国内免费 | 998篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 37篇 |
地球物理 | 422篇 |
地质学 | 1907篇 |
海洋学 | 282篇 |
天文学 | 339篇 |
综合类 | 58篇 |
自然地理 | 86篇 |
出版年
2024年 | 10篇 |
2023年 | 20篇 |
2022年 | 60篇 |
2021年 | 77篇 |
2020年 | 93篇 |
2019年 | 101篇 |
2018年 | 38篇 |
2017年 | 59篇 |
2016年 | 89篇 |
2015年 | 94篇 |
2014年 | 122篇 |
2013年 | 82篇 |
2012年 | 119篇 |
2011年 | 188篇 |
2010年 | 151篇 |
2009年 | 168篇 |
2008年 | 170篇 |
2007年 | 183篇 |
2006年 | 168篇 |
2005年 | 156篇 |
2004年 | 137篇 |
2003年 | 102篇 |
2002年 | 97篇 |
2001年 | 94篇 |
2000年 | 91篇 |
1999年 | 75篇 |
1998年 | 50篇 |
1997年 | 54篇 |
1996年 | 52篇 |
1995年 | 41篇 |
1994年 | 44篇 |
1993年 | 38篇 |
1992年 | 43篇 |
1991年 | 31篇 |
1990年 | 18篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有3172条查询结果,搜索用时 15 毫秒
181.
Fault-controlled dolomitization at Swan Hills Simonette oil field (Devonian), deep basin west-central Alberta, Canada 总被引:6,自引:0,他引:6
The partly dolomitized Swan Hills Formation (Middle‐Upper Devonian) in the Simonette oil field of west‐central Alberta underwent a complex diagenetic history, which occurred in environments ranging from near surface to deep (>2500 m) burial. Five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post‐date stylolites in limestones (depths >500 m). These include early planar varieties and later saddle dolomites. Fluid inclusion data from saddle dolomite cements (Th=137–190 °C) suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data (Tpeak=160 °C). Thus, at least some dolomitizing fluids were ‘hydrothermal’. Fluorescence microscopy identified three populations of primary hydrocarbon‐bearing fluid inclusions and confirms that saddle dolomitization overlapped with Upper Cretaceous oil migration. The source of early dolomitizing fluids probably was Devonian or Mississippian seawater that was mixed with a more 87Sr‐rich fluid. Fabric‐destructive and fabric‐preserving dolostones are over 35 m thick in the Swan Hills buildup and basal platform adjacent to faults, thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults. This ‘plume‐like’ geometry suggests that early and late dolomitization events were fault controlled. Late diagenetic fluids were, in part, derived from the crystalline basement or Palaeozoic siliciclastic aquifers, based on 87Sr/86Sr values up to 0·7370 from saddle dolomite, calcite and sphalerite cements, and 206Pb/204Pb of 22·86 from galena samples. Flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m, both vertically along reactivated faults and laterally in the buildup along units that retained primary and/or secondary porosity. 相似文献
182.
Abstract: Synchrotron X-ray fluorescence analyses on individual hypersaline fluid inclusions were tested to using synchrotron source at Tsukuba (KEK), Japan. The XRF instrumentation at KEK meets the purpose of fluid inclusion analysis, nondestructive, multi–element, ppm detection limits, with micro spatial resolution. In practice, however, the quantitative chemical analysis of fluid inclusion requires further considerable data accumulation. Semi-quantitative distribution of elements (mass number > 25) in single fluid inclusion was obtained. 相似文献
183.
Using single-crystal X-ray diffraction from a diamond anvil cell, the compressibility of a synthetic fluorapatite was determined up to about 7?GPa. The compression pattern was anisotropic, with greater change along a than c. Unit cell parameters varied linearly with β a =3.32(8)?10?3 and β c =2.40(5)?10?3 GPa?1, giving a ratio β a :β c =1.38:1. Data fitted with a third-order Birch-Murnaghan EOS yielded a bulk modulus of K 0=93(4)?GPa with K′=5.8(1.8). The evolution of the crystal structure of fluorapatite was analysed using data collected at room pressure, at 3.04 and 4.72?GPa. The bulk modulus of phosphate tetrahedron is about three times greater than the bulk modulus of calcium polyhedra. The values were 270(10), 100(4) and 86(3) GPa for P, Ca1 (nine-coordinated) and Ca2 (seven-coordinated) respectively. While the calcium polyhedra became more regular with pressure, the distortion of the phosphate tetrahedron remained unchanged. The size of the channel extending along the [001] direction represented the most compressible direction. The Ca2–Ca2 distance decreased from 3.982 to 3.897?Å on compression from 0.0001 to 4.72?GPa. The anisotropic compressional pattern may be understood in terms of the greater compressibility of the channel size over the polyhedral units. The reduction of the channel volume was measured by the evolution of the trigonal prism, having the Ca2–Ca2–Ca2 triangle as its base and the c lattice parameter as its height. This prism volume changed from 47.3?Å3 at room pressure to 44.78?Å3 at 4.72?GPa. Its relatively high bulk moduli, 86(3) GPa, indicated that the channel did not collapse with pressure and the apatite structure could remain stable at very high pressure. 相似文献
184.
J. M. Léger J. Haines C. Chateau G. Bocquillon M. W. Schmidt S. Hull F. Gorelli A. Lesauze R. Marchand 《Physics and Chemistry of Minerals》2001,28(6):388-398
The structure of the cristobalite-like polymorph of phosphorus oxynitride PON has been refined using neutron powder diffraction
data. It is tetragonal, space group I&4macr;2d, Z=4. The four P–(O,N) distances are equal but the tetrahedron is compressed along c. In AX2 or ABX4 compounds, the tetragonal I&4macr;2d or I&4macr; structure is obtained when the average ratio of the cation to anion radius is below 1.186, whereas the tetragonal P41212 or orthorhombic C2221 structure is obtained at low temperatures for larger ratios. The cell parameters of this PON polymorph have been determined
as a function of hydrostatic pressure by in situ angle dispersive X-ray powder diffraction in a diamond-anvil cell. Under
truly hydrostatic pressure, a strong anisotropic behavior is observed with the c parameter being nearly incompressible. Very slight anisotropic stress strongly modifies the high-pressure behavior. According
to the pressure-temperature conditions of treatment, three phases, cristobalite-, moganite-, and quartz-like, have been obtained
by quenching experiments, and the P–T phase diagram of PON was derived. The high-pressure behavior of the α-quartz, moganite, and cristobalite-like polymorphs
of PON and SiO2 is discussed.
Received: 7 August 2000 / Accepted: 21 January 2001 相似文献
185.
Luo Yan Liu Yongsheng Hu Shenghong Gao Shan Open Laboratory of Constitution Interaction Dynamics of the Crust Mantle System Ministry of National Lands Resources China University of Geosciences Wuhan Lin Shoulin Faculty of Material Sc 《中国地质大学学报(英文版)》2001,12(3)
INTRODUCTIONLaserablationinductivelycoupledplasmamassspectrome tryisanincreasinglydevelopedanalyticaltechniqueforsolidsampleanalysis.LA ICP MSoffersattractivecharacteristicsofhighsensitivity ,lowdetectionlimits,minimalsampleprepara tion ,lessoxidesinterfe… 相似文献
186.
187.
188.
本文提出以粉末样品直接压饼法测定岩石化探样品中的微量U,Th,其方法简便、快速,适用于各类地质样品,尤其是岩石化探样品测量。 相似文献
190.
本文论述用地面伽玛能谱资料估计地层(体)含铀性和资源量方法,并提出富铀富集体、铀源富集体、尤其富铀源富集体是最有利于成矿的结论。 相似文献