全文获取类型
收费全文 | 1376篇 |
免费 | 47篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 88篇 |
地球物理 | 343篇 |
地质学 | 501篇 |
海洋学 | 114篇 |
天文学 | 264篇 |
综合类 | 8篇 |
自然地理 | 89篇 |
出版年
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 32篇 |
2017年 | 12篇 |
2016年 | 39篇 |
2015年 | 17篇 |
2014年 | 40篇 |
2013年 | 54篇 |
2012年 | 42篇 |
2011年 | 47篇 |
2010年 | 58篇 |
2009年 | 66篇 |
2008年 | 58篇 |
2007年 | 58篇 |
2006年 | 65篇 |
2005年 | 41篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 28篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 17篇 |
1998年 | 19篇 |
1997年 | 12篇 |
1996年 | 31篇 |
1995年 | 16篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 31篇 |
1984年 | 22篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 17篇 |
1976年 | 21篇 |
1975年 | 18篇 |
1974年 | 24篇 |
1973年 | 27篇 |
排序方式: 共有1427条查询结果,搜索用时 15 毫秒
911.
The visible to near-infrared spectral reflectance properties of intimate and areal pyroxene?+?palagonitic material mixtures as well as pure mafic silicates (low-calcium pyroxene, high-calcium pyroxene, pigeonite, olivine) and mixtures of these minerals were analyzed at high spectral resolution (5 nm) as well as with non-contiguous band passes equivalent to recent HST observations and the Pathfinder IMP in order to determine the quality and quantity of mineralogical information (end member compositions, abundances, and grain sizes) derivable in the presence of palagonitic material. In the case of pyroxene?+?palagonitic material mixtures, pyroxene is detectable at abundances as low as 10 wt%, and its composition can be constrained because (a) its diagnostic absorption feature (located near 1000 nm) persists even for high palagonitic material abundances, and (b) palagonitic material does not appreciably alter the wavelength position of this band (<4 nm variation). For broad band data (such as Pathfinder IMP band passes), different mafic silicates can be discriminated and palagonitic material abundances constrained using a variety of reflectance ratios and three-point “absorption band depths.” However, other properties of mafic silicate?±?palagonitic material assemblages, such as mafic silicate major element compositions, grain sizes, and end member abundances, generally cannot be rigorously quantified. The use of multiple reflectance ratios can, however, be used to identify relative changes in these properties, as most changes in mafic silicate?±?palagonitic material assemblage properties are characterized by a unique corresponding set of reflectance ratio variations. The observed spectral-assemblage property trends are consistent with those expected from the known spectral properties of the end members. 相似文献
912.
Modal abundances of pyroxene,olivine, and mesostasis in nakhlites: Heterogeneity,variation, and implications for nakhlite emplacement 下载免费PDF全文
Catherine M. Corrigan Michael A. Velbel Edward P. Vicenzi 《Meteoritics & planetary science》2015,50(9):1497-1511
Nakhlites, clinopyroxenite meteorites from Mars, share common crystallization and ejection ages, suggesting that they might have been ejected from the same place on Mars by the same ejection event (impact) and are different samples of the same thick volcanic flow unit or shallow sill. Mean modal abundances and abundance ranges of pyroxene, olivine, and mesostasis vary widely among different thin‐sections of an individual nakhlite. Lithologic heterogeneity is the main factor contributing to the observed modal‐abundance variations measured in thin‐sections prepared from different fragments of the same stone. Two groups of nakhlites are distinguished from one another by which major constituent varies the least and the abundance of that constituent. The group consisting of Nakhla, Lafayette, Governador Valadares, and the Yamato nakhlite pairing group is characterized by low modal mesostasis and pyroxene‐olivine covariance, whereas the group consisting of the Miller Range nakhlite pairing group and Northwest Africa 5790 is characterized by low modal olivine and pyroxene‐mesostasis covariance. These two groups sample the slowest‐cooled interior portion and the chilled margin, respectively, of the nakhlite emplacement body as presently understood, and appear to be also related to recently proposed nakhlite groups independently established using compositional rather than petrographic observations. Phenocryst modal abundances vary with inferred depth in the nakhlite igneous body in a manner consistent with solidification of the nakhlite stack from dynamically sorted phenocryst‐rich magmatic crystal‐liquid mush. 相似文献
913.
Rosalind Hopwood Trevor Fulton Edward T. Polehampton Ivan Valtchanov Dominique Benielli Peter Imhof Tanya Lim Nanyao Lu Nicola Marchili Chris P. Pearson Bruce M. Swinyard 《Experimental Astronomy》2014,37(2):195-205
Emission from the Herschel telescope is the dominant source of radiation for the majority of SPIRE Fourier transform spectrometer (FTS) observations, despite the exceptionally low emissivity of the primary and secondary mirrors. Accurate modelling and removal of the telescope contribution is, therefore, an important and challenging aspect of FTS calibration and data reduction pipeline. A dust-contaminated telescope model with time invariant mirror emissivity was adopted before the Herschel launch. However, measured FTS spectra show a clear evolution of the telescope contribution over the mission and strong need for a correction to the standard telescope model in order to reduce residual background (of up to 7 Jy) in the final data products. Systematic changes in observations of dark sky, taken over the course of the mission, provide a measure of the evolution between observed telescope emission and the telescope model. These dark sky observations have been used to derive a time dependent correction to the telescope emissivity that reduces the systematic error in the continuum of the final FTS spectra to ~0.35 Jy. 相似文献
914.
Trevor Fulton Rosalind Hopwood Jean-Paul Baluteau Dominique Benielli Peter Imhof Tanya Lim Nanyao Lu Nicola Marchili David Naylor Edward Polehampton Bruce Swinyard Ivan Valtchanov 《Experimental Astronomy》2014,37(2):381-395
Herschel/SPIRE Fourier transform spectrometer (FTS) observations contain emission from both the Herschel Telescope and the SPIRE Instrument itself, both of which are typically orders of magnitude greater than the emission from the astronomical source, and must be removed in order to recover the source spectrum. The effects of the Herschel Telescope and the SPIRE Instrument are removed during data reduction using relative spectral response calibration curves and emission models. We present the evolution of the methods used to derive the relative spectral response calibration curves for the SPIRE FTS. The relationship between the calibration curves and the ultimate sensitivity of calibrated SPIRE FTS data is discussed and the results from the derivation methods are compared. These comparisons show that the latest derivation methods result in calibration curves that impart a factor of between 2 and 100 less noise to the overall error budget, which results in calibrated spectra for individual observations whose noise is reduced by a factor of 2–3, with a gain in the overall spectral sensitivity of 23 % and 21 % for the two detector bands, respectively. 相似文献
915.
Guneshwar Thangjam Andreas Nathues Kurt Mengel Martin Hoffmann Michael Schäfer Vishnu Reddy Edward A. Cloutis Ulrich Christensen Holger Sierks Lucille Le Corre Jean‐Baptiste Vincent Christopher T. Russell 《Meteoritics & planetary science》2014,49(10):1831-1850
We present an analysis of olivine‐rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine‐rich materials at these localities as described by Ammannito et al. ( 2013a ) using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various howardite–eucrite–diogenite meteorites, high‐Ca pyroxenes, olivines, and olivine‐orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine‐rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine‐rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivine‐rich exposures are in accordance with both the magma ocean and the serial magmatism model (e.g., Righter and Drake 1997 ; Yamaguchi et al. 1997 ). However, it remains unsolved why the olivine‐rich materials are mainly concentrated in the northern hemisphere (approximately 36–42°N, 46–74°E) and are almost absent in the Rheasilvia basin. 相似文献
916.
917.
Jon Y. Landvik Edward J. Brook Lyn Gualtieri Henriette Linge Grant Raisbeck Otto Salvigsen Françoise Yiou 《Boreas: An International Journal of Quaternary Research》2013,42(1):43-56
The Late Weichselian ice sheet of western Svalbard was characterized by ice streams and inter‐ice‐stream areas. To reconstruct its geometry and dynamics we investigated the glacial geology of two areas on the island of Prins Karls Forland and the Mitrahalvøya peninsula. Cosmogenic 10Be surface exposure dating of glacial erratics and bedrock was used to constrain past ice thickness, providing minimum estimates in both areas. Contrary to previous studies, we found that Prins Karls Forland experienced a westward ice flux from Spitsbergen. Ice thickness reached >470 m a.s.l., and warm‐based conditions occurred periodically. Local deglaciation took place between 16 and 13 ka. At Mitrahalvøya, glacier ice draining the Krossfjorden basin reached >300 m a.s.l., and local deglaciation occurred at c. 13 ka. We propose the following succession of events for the last deglaciation. After the maximum glacier extent, ice streams in the cross‐shelf troughs and fjords retreated, tributary ice streams formed in Forlandsundet and Krossfjorden, and, finally, local ice caps were isolated over both Prins Karls Forland and Mitrahalvøya and their adjacent shelves. 相似文献
918.
Vivienne Wild John A. Peacock Ofer Lahav Edward Conway Steve Maddox Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ian Lewis Stuart Lumsden Darren Madgwick Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,356(1):247-269
919.
Edward P. F. Rose 《Geology Today》2004,20(1):24-29
Several geologists accompanied the army of Napoleon Bonaparte that landed in Egypt in 1798 – indicating that perception of the military value of geology is almost as old as Earth science itself. 相似文献
920.
Karri Muinonen Jenni Virtanen Edward Bowell 《Celestial Mechanics and Dynamical Astronomy》2001,81(1-2):93-101
We introduce new techniques for the computation of the collision probability for Earth-crossing asteroids in the case of short observational arcs and/or small numbers of observations. The techniques rely on the orbital element probability density computed using statistical orbital ranging. We apply the techniques to the Earth-crossing asteroid 1998 OX4with non-vanishing collision probability in numerous close approaches after the year 2012 (inclusive). We study the invariance of the collision probability in transformations between different orbital element sets, and develop a Spearman rank correlation measure for the validity of the linear approximation. We introduce an optimized, fast version of the statistical ranging method. 相似文献