全文获取类型
收费全文 | 264篇 |
免费 | 5篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 23篇 |
地球物理 | 35篇 |
地质学 | 69篇 |
海洋学 | 31篇 |
天文学 | 100篇 |
综合类 | 1篇 |
自然地理 | 10篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 20篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 8篇 |
2009年 | 11篇 |
2008年 | 7篇 |
2007年 | 17篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 13篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有273条查询结果,搜索用时 15 毫秒
21.
Using the correspondence principle of viscoelasticity the Displacement Discontinuity Method has been extended to model the rate-dependent behaviour of a jointed rock mass. The intact rock is assumed to behave as a linear viscoelastic material while, in general, a non-linear rate-dependent behaviour of the rock joints can be accounted for. A number of numerical examples are presented which illustrate the accuracy and potential of the method for analysing complex engineering problems. 相似文献
22.
G. V. Gibbs D. F. Cox T. D. Crawford M. B. Boisen Jr M. Lim 《Physics and Chemistry of Minerals》2002,29(5):307-318
The electron localization function, η, evaluated for first-principles geometry optimized model structures generated for quartz and coesite, reveals that the oxide anions are coordinated by two hemispherically shaped η-isosurfaces located along each of the SiO bond vectors comprising the SiOSi angles. With one exception, they are also coordinated by larger banana-shaped isosurfaces oriented perpendicular to the plane centered in the vicinity of the apex of each angle. The hemispherical isosurfaces, ascribed to domains of localized bond-pair electrons, are centered ~0.70 Å along the bond vectors from the oxide anions and the banana-shaped isosurfaces, ascribed to domains of localized nonbonding lone-pair electrons, are centered ~0.60 Å from the apex of the angle. The oxide anion comprising the straight SiOSi angle in coesite is the one exception in that the banana-shaped isosurface is missing; however, it is coordinated by two hemispherically shaped isosurfaces that lie along the bond vectors. In the case of a first-principles model structure generated for stishovite, the oxide anion is coordinated by five hemispherically shaped η-isosurfaces, one located along each of the three SiO bond vectors (ascribed to domains of bonding-electron pairs) that are linked to the anion with the remaining two (ascribed to domains of nonbonding-electron pairs) located on opposite sides of the plane defined by three vectors, each isosurface at a distance of ~0.5 Å from the anion. The distribution of the five isosurfaces is in a one-to-one correspondence with the distribution of the maxima displayed by experimental Δρ and theoretical ??2ρ maps. Isosurface η maps calculated for quartz and the (HO) 3 SiOSi(OH) 3 molecule also exhibit maxima that correspond with the (3,?3) maxima displayed by distributions of ??2ρ. Deformation maps observed for the SiOSi bridges for the silica polymorphs and a number of silicates are similar to that calculated for the molecule but, for the majority, the maxima ascribed to lone-pair features are absent. The domains of localized nonbonding-electron pair coordinating the oxide anions of quartz and coesite provide a basis for explaining the flexibility and the wide range of the SiOSi angles exhibited by the silica polymorphs with four-coordinate Si. They also provide a basis for explaining why the SiO bond length in coesite decreases with increasing angle. As found in studies of the interactions of solute molecules with a solvent, a mapping of η-isosurfaces for geometry-optimized silicates is expected to become a powerful tool for deducing potential sites of electrophilic attack and reactivity for Earth materials. The positions of the features ascribed to the lone pairs in coesite correspond with the positions of the H atoms recently reported for an H-doped coesite crystal. 相似文献
23.
Andrew Ball and Ian Crawford report on NASA's planning for a return to the Moon, with some thoughts on opportunities open to the UK. 相似文献
24.
25.
26.
27.
Anthony J. Crawford 《Contributions to Mineralogy and Petrology》1981,75(4):353-367
The Howqua Olivine Pyroxenite of eastern Victoria, Australia, intrudes a metamorphosed sequence of Cambrian high-Mg lavas. It crystallized an unusual mineral assemblage: Cr-rich magnesiochromite, olivine (Fo94), and protoenstatite (now inverted to polysynthetically-twinned clinoenstatite). Residual liquid crystallized strongly-zoned interstitial pyroxenes followed by pargasite. Pargasite, often showing quench habit, crystallized in interstitial glass which is now altered to serpentine.The extremely refractory nature of the cumulus phases indicates a very high temperature of crystallization for liquidus olivine and chromite from a high-MgO, low-Al2O3 parent liquid similar in some respects to Archaean peridotitic komatiites. The suggested origin by hydrous melting of depleted mantle peridotite, plus other compositional and mineralogical similarities (especially the olivine-liquid reaction producing protoenstatite) indicate that the parent magma of the Howqua Olivine Pyroxenite had many features in common with the high-SiO2, high-MgO clinoenstatite-bearing boninitic lavas of the Western Pacific. It is interpreted as a more extreme melt with affinities to boninite and it demonstrates that ultramafic magmas existed in the Cambrian. 相似文献
28.
29.
30.
An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples
下载免费PDF全文
![点击此处可从《Meteoritics & planetary science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Louise Alexander Joshua F. Snape Katherine H. Joy Hilary Downes Ian A. Crawford 《Meteoritics & planetary science》2016,51(9):1654-1677
Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine‐grained (grain size <0.3 mm), a “paired samples t‐test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance. 相似文献