全文获取类型
收费全文 | 121篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 6篇 |
地球物理 | 20篇 |
地质学 | 60篇 |
海洋学 | 4篇 |
天文学 | 33篇 |
自然地理 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2021年 | 5篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 5篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 5篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有132条查询结果,搜索用时 250 毫秒
51.
The amino acid and hydrocarbon contents of the Paris meteorite: Insights into the most primitive CM chondrite 下载免费PDF全文
Zita Martins Paola Modica Brigitte Zanda Louis Le Sergeant d'Hendecourt 《Meteoritics & planetary science》2015,50(5):926-943
The Paris meteorite is one of the most primitive carbonaceous chondrites. It is reported to be the least aqueously altered CM chondrite, and to have experienced only weak thermal metamorphism. We have analyzed for the first time the amino acid and hydrocarbon contents of this pristine meteorite by gas chromatography–mass spectrometry (GC–MS). When plotting the relative amino acids abundances of several CM chondrites according to the increasing hydrothermal scale (petrologic subtypes), from the CM2.7/2.8 Paris to the CM2.0 MET 01070, Paris has the lowest relative abundance of β‐alanine/glycine (0.15), which fits with the relative abundances of β‐alanine/glycine increasing with increasing aqueous alteration for CM chondrites. These results confirm the influence of aqueous alteration on the amino acid abundances and distribution. The amino acid analysis shows that the isovaline detected in this meteorite is racemic (d /l = 0.99 ± 0.08; l ‐enantiomer excess = 0.35 ± 0.5%; corrected d /l = 1.03; corrected l ‐enantiomer excess = ?1.4 ± 2.6%). The identified hydrocarbons show that Paris has n‐alkanes ranging from C16 to C25 and 3‐ to 5‐ring nonalkylated polycyclic aromatic hydrocarbons (PAHs). The lack of alkylated PAHs in Paris seems to be also related to this low degree of aqueous alteration on its parent body. The extraterrestrial hydrocarbon content, suggested by the absence of any biomarker, may well have a presolar origin. The chemistry of the Paris meteorite may thus be closely related to the early stages of the solar nebula with a contribution from interstellar (molecular cloud) precursors. 相似文献
52.
53.
54.
55.
We propose a multicomponent analysis of starburst galaxies, based on a model that takes into account the young and evolved stellar components and the gas emission, with their respective extinction, in the frame of a coherent dust distribution pattern. Near-IR signatures are preferentially investigated, in order to penetrate as deep as possible into the dusty starburst cores. We computed the 1.4-2.5 μm spectra of synthetic stellar populations evolving through strong, short timescale bursts of star formation (continuum and lines, R ? 500). The evolution model is specifically sensitive to cool stellar populations (AGB and red supergiant stars). It takes advantage of the stellar library of Lançon & Rocca-Volmerange (1992) [A&ASS, 96, 593], observed with the same instrument (FTS/CFHT) as the analysed galaxy sample, so that the instrumental effects are minimised. The main near-IR observable constraints are the molecular signatures of CO and H2O and the slope of the continuum, observed over a range exceptionally broad for spectroscopic data. The H - K colour determined from the spectra measures the intrinsic stellar energy distribution but also differential extinction, which is further constrained by optical emission line ratios. Other observational constraints are the near-IR emission lines (Brγ, He I 2.06 μm, [Fe II] 1.64 μm, H2 2.12 μm) and the far-IR luminosity. The coherence of the results relies on the interpretation in terms of stellar populations from which all observable properties are derived, so that the link between the various wavelength ranges is secured. The luminosity LK is used for the absolute calibration.We apply this approach to the typical spectrum of the core of NGC 1614. Consistent solutions for the starburst characteristics (star-formation rate, IMF, burst age, morphology) are found and the role of each observational constraint in deriving satisfactory models is extensively discussed. The acceptable contamination of the K band light by the underlying population amounts ≥ 15% even through a 5 arcsec aperture. The model leads to a limit on the direct absorption of Lyman continuum photons by dust situated inside the ionised areas, which in turn, with standard gas-to-dust ratios, translates into small characteristic sizes for the individual coexisting H II regions of the massive starburst area (clusters containing ∼ 102 ionising stars). We show that room is left for IMFs extending to 120 M⊙, rather than truncated at ∼ 60 M⊙ as most conservative studies conclude. High internal velocity dispersions (≥ 20 km s−1) are then needed for the H II regions. An original feature of this work is to base the analysis of near-infrared spectral galaxy observations on a large wavelength range, using models constructed with spectral stellar data observed with the same instrument. However a broader use of this spectral evolution model on other spectral or photometric data samples is possible if the spectral resolution of the model is adapted to observations or if colours are derived from the energy distributions.Catherine J. Cesarsky 相似文献
56.
Brigitte Schmieder Nicole Mein Yuanyong Deng Cristiana Dumitrache Jean-Marie Malherbe Joachim Staiger E. E. Deluca 《Solar physics》2004,223(1):119-141
This paper is focused on the formation of two filaments in a complex center of decaying active regions (AR 8329 and AR 8326), located in the northern hemisphere. The observations were obtained in Hα by the Multi-channel Subtractive Double Pass spectrograph (MSDP mounted on the German telescope VTT in Tenerife) and EUV lines with TRACE (Transition Region And Corona Explorer). High Doppler shifts are found to be related to the ends of filament segments where canceling magnetic fields are also located (as seen on magnetograms from Big Bear Solar Observatory). At these locations, velocities along the line of sight, derived by using a cloud model method reach −20 km s−1, the segments of filaments merge and frequently a time-related sub-flare is observed by TRACE. The chirality of the filament segments has been determined by different methods: the segments of dextral chirality join together and form a long dextral filament, and a single filament of sinistral chirality forms end to end with the dextral filament but does not merge with it. Assuming a model of twisted flux tube for filament material, we suggest that the dextral filament has negative helicity and a relationship between its formation and the close by sunspot with the same sign of helicity. 相似文献
57.
Jérôme Gattacceca Roger H. Hewins Jean‐Pierre Lorand Pierre Rochette France Lagroix Cécile Cournède Minoru Uehara Sylvain Pont Violaine Sautter Rosa. B. Scorzelli Chrystel Hombourger Pablo Munayco Brigitte Zanda Hasnaa Chennaoui Ludovic Ferrière 《Meteoritics & planetary science》2013,48(10):1919-1936
58.
Abstract– Chondrule compositions suggest either ferroan precursors and evaporation, or magnesian precursors and condensation. Type I chondrule precursors include granoblastic olivine aggregates (planetary or nebular) and fine‐grained (dustball) precursors. In carbonaceous chondrites, type I chondrule precursors were S‐free, while type II chondrules have higher Fe/Mn than in ordinary chondrites. Many type II chondrules contain diverse forsteritic relicts, consistent with polymict dustball precursors. The relationship between finer and coarser grained type I chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules. Fe metal in type I, and Na and S in type II chondrules indicate high partial pressures in ambient gas, as they are rapidly evaporated at canonical conditions. The occurrence of metal, sulfide, or low‐Ca pyroxene on chondrule rims suggests (re)condensation. In Semarkona type II chondrules, Na‐rich olivine cores, Na‐poor melt inclusions, and Na‐rich mesostases suggest evaporation followed by recondensation. Type II chondrules have correlated FeO and MnO, consistent with condensation onto forsteritic precursors, but with different ratios in carbonaceous chondrites and ordinary chondrites, indicating different redox history. The high partial pressures of lithophile elements require large dense clouds, either clumps in the protoplanetary disk, impact plumes, or bow shocks around protoplanets. In ordinary chondrites, clusters of type I and type II chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together. In carbonaceous chondrites, the much less abundant type II chondrules were probably added late to batches of type I chondrules from different O isotopic reservoirs. 相似文献
59.
Hervé Guillou Brigitte Van Vliet-Lanoë Agust Guðmundsson Sébastien Nomade 《Quaternary Geochronology》2010,5(1):10-19
Indisputable geochronology of Icelandic volcanism may contribute to improving the use of volcanic proxies for paleoenvironmental studies. Accurate and reliable ages may also provide some useful constraints in studying the possible relationship between volcanism and deglaciation in Iceland. Given the difficulty of dating accurately young and low potassic volcanic samples from Iceland, the relationship between deglaciation and increasing levels of volcanism has been shown only for the last deglaciation. The purpose of this study is to evaluate the potential of the unspiked K–Ar dating method for dating Quaternary Icelandic volcanic rocks, because we consider that reliable K–Ar ages of interglacial and sub-glacial volcanic products may generate useful data sets for paleoclimatic reconstructions, so enabling the link between glaciation and volcanic activity to be better established. Given the ages and precisions obtained, this study demonstrates that the unspiked K–Ar method is a promising tool for reconstructing the recent volcanic activity in Iceland during glacial and interglacial intervals. 相似文献
60.