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41.
Kathryn G. GARDNER‐VANDY Dolores H. HILL Dante S. LAURETTA Yulia S. GOREVA Kenneth J. DOMANIK Richard C. GREENWOOD Ian A. FRANCHI Marvin KILLGORE 《Meteoritics & planetary science》2011,46(7):1052-1070
Abstract– Analysis of the mineralogy, isotopic, and bulk compositions of the eucrite meteorites is imperative for understanding their origin on the asteroid 4 Vesta, the proposed parent body of the HED meteorites. We present here the petrology, mineral compositions, and bulk chemistry of several lithic components of the new brecciated basaltic eucrite Northwest Africa (NWA) 3368 to determine if all the lithologies reflect formation from one rock type or many rock types. The meteorite has three main lithologies: coarse‐ and fine‐grained clasts surrounded by a fine‐grained recrystallized silicate matrix. Silicate compositions are homogeneous, and the average rare earth element pattern for NWA 3368 is approximately 10× CI chondrites with a slight negative Eu anomaly. Major and trace element data place NWA 3368 with the Main Group‐Nuevo Laredo trend. High‐Ti chromites with ilmenite exsolution lamellae provide evidence of NWA 3368’s history of intense metamorphism. We suggest that this meteorite underwent several episodes of brecciation and metamorphism, similar to that proposed by Metzler et al. (1995) . We conclude that NWA 3368 is a monomict basaltic eucrite breccia related to known eucrites in texture and in mineral, bulk, and oxygen isotopic composition. 相似文献
42.
Morphological analyses of high resolution spectral recordings of Jovian decametric radiation show a regime of phenomena not seen at lower resolutions. Observed emissions range from narrowband (50 kHz) simple quasiperiodic bursts to wideband emissions (extending over a 500 kHz passband) exhibiting complex structural detail. Assuming gyroemission from electrons in a dipole field for which the magnetic moment is 10 Gauss RJ3, drift rate measurements of the bursts indicate that the source size is of the order of 600 km and its location is near R = 1.3 RJ at a colatitude of 27.3°. The measurements suggest that the emitting electrons belong to a population having a very specific equatorial pitch angle near 3.5°. This study concludes that it may be possible to verify gyroemission as the mechanism responsible for the decametric radiation. 相似文献
43.
Andrea Patzer Dolores H. Hill William V. Boynton Luitgard Franke Ludolf Schultz A. J. Timothy Jull Lanny R. McHargue Ian A. Franchi 《Meteoritics & planetary science》2002,37(6):823-833
Abstract— We report noble gas, oxygen isotope, 14C and 10Be data of Itqiy as well as noble gas, 14C and 10Be results for Zak?odzie. Both samples have been recently classified as anomalous enstatite meteorites and have been compared in terms of their mineralogy and chemical composition. The composition of enstatite and kamacite and the occurrence of specific sulfide phases in Itqiy indicate it formed under similar reducing conditions to those postulated for enstatite chondrites. The new results now seem to point at a direct spatial link. The noble gas record of Itqiy exhibits the presence of a trapped subsolar component, which is diagnostic for petrologic types 4–6 among enstatite chondrites. The concentration of radiogenic 4He is very low in Itqiy and indicates a recent thermal event. Its 21Ne cosmic‐ray exposure age is 30.1 ± 3.0 Ma and matches the most common age range of enstatite chondrites (mostly EL6 chondrites) but not that of Zak?odzie. Itqiy's isotopic composition of oxygen is in good agreement with that observed in Zak?odzie as well as those found in enstatite meteorites suggesting an origin from a common oxygen pool. The noble gas results, on the other hand, give reason to believe that the origin and evolution of Itqiy and Zak?odzie are not directly connected. Itqiy's terrestrial age of 5800 ± 500 years sheds crucial light on the uncertain circumstances of its recovery and proves that Itqiy is not a modern fall, whereas the 14C results from Zak?odzie suggest it hit Earth only recently. 相似文献
44.
Juan C. Surís-Regueiro Manuel M. Varela-Lafuente M. Dolores Garza-Gil 《Ocean & Coastal Management》2011,54(8):593-600
In 2011, the European Commission will make its legislative proposal for the reform of the Common Fisheries Policy public. The purpose of this paper is to analyse the direction the possible reforms to be implemented in the Fisheries Structural Policy will take. In order to do so, we will look at the recent results of the policy and its current situation, and study its trends. The main conclusion we can draw is that the future EU fisheries policy will not undergo major changes, neither in its fundamental principles nor with regard to its main goals or priority action axes. Eventual progress and any adjustments made to such reforms will take place within the ambit of the policy’s specific action measures via the European Fisheries Fund. 相似文献
45.
46.
Andrea Patzer Dolores H. Hill William V. Boynton 《Meteoritics & planetary science》2001,36(11):1495-1505
Abstract— Itqiy is a unique coarse‐grained, metal‐rich enstatite meteorite that was found in the Western Sahara and consists of two rocks together weighing 4.72 kg, which are both completely coated with fusion crust. We report results from our electron microprobe and instrumental neutron activation analysis techniques. Itqiy consists of subhedral, equigranular, millimeter‐sized enstatite, ?25 vol% of millimeter‐sized kamacite and a few tiny intergrowths of sulfides and kamacite. Relic chondrules are absent. Pyroxene (Fs0.2) is chemically similar to enstatite in EL chondrites, but the metal is closer in composition to that in EH chondrites. Sulfides resemble those in E chondrites but their compositions are distinct from those in both EL and EH chondrites. Itqiy clearly formed under very reducing conditions, but it does not appear to have formed from EH or EL chondrites. Two thermal events can be distinguished. Silicate compositions including rare earth element abundances indicate loss of partial melt and slow cooling. Heterogeneous sulfides indicate a subsequent reheating and quenching event, which may have been due to shock as many enstatite grains show shock stage S3 features. 相似文献
47.
Andrea PATZER Jochen SCHLÜTER Ludolf SCHULTZ Mahmud TARKIAN Dolores H. HILL William V. BOYNTON 《Meteoritics & planetary science》2004,39(9):1555-1575
Abstract— We report new petrographic and chemical data for the equilibrated EL chondrite Grein 002, including the occurrence of osbornite, metallic copper, abundant taenite, and abundant diopside. As inferred from low Si concentrations in kamacite, the presence of ferroan alabandite, textural deformation, chemical equilibration of mafic silicates, and a subsolar noble gas component, we concur with Grein 002's previous classification as an EL4‐5 chondrite. Furthermore, the existence of pockets consisting of relatively coarse, euhedral enstatite crystals protruding large patches of Fe‐Ni alloys suggests to us that this EL4‐5 chondrite has been locally melted. We suspect impact induced shock to have triggered the formation of the melt pockets. Mineralogical evidence indicates that the localized melting of metal and adjacent enstatite must have happened relatively late in the meteorite's history. The deformation of chondrules, equilibration of mafic silicates, and generation of normal zoning in Fe, Zn‐sulfides took place during thermal alteration before the melting event. Following parent body metamorphism, daubreelite was exsolved from troilite in response to a period of slow cooling at subsolidus temperatures. Exsolution of schreibersite from the coarse metal patches probably occurred during a similar period of slow cooling subsequent to the event that induced the formation of the melt pockets. Overall shock features other than localized melting correspond to stage S2 and were likely established by the final impact that excavated the Grein 002 meteoroid. 相似文献
48.
Dolores Perez-Ramirez Johan H. Knapen Seppo Laine 《Astrophysics and Space Science》2001,276(2-4):625-631
In this paper we present first results from an observational study of the connection between the global parameters of barred
galaxies and the appearance of structures, such as dust lanes and star-forming rings in their circumnuclear regions. We combine
near-infrared imaging of the central small-scale core structure with optical imaging of the large-scale discs of these barred
galaxies. We present more detailed studies of two of our sample galaxies, NGC1530 and NGC 3504, for which we relate the presence
and morphology of dust lanes (with different curvature radii) to the strength of the bar. A relation where strong bars lead
to straight dust lanes and ovals or weak bars to curved dust lanes is expected theoretically and is borne out by our preliminary
imaging results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
49.
Behaviour of boron in the generation of an anatectic complex: The Pen˜a Negra complex, central Spain
The Pe˜na Negra anatectic complex (central Spain) was formed from a pelitic protolith low in boron (3–80 ppm), by dehydration reactions, melting and fluid loss, which expelled much of the boron; residual B is present in sillimanite and muscovite. Migmatite melanosomes and restites (sillimanite + biotite + ilmenite) are relatively richer in B (mean 29 ppm), while the leucosomes are poorer (13 ppm). Late shears, fractures and zones of retrograde alteration have permitted some reintroduction of B. Experiments demonstrated that B cannot be removed from these rocks by heating or by leaching, indicating that very little is present in superficial adsorption and that the element occurs in mineral structures. 相似文献
50.