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81.
Binyam W. Woldemichael Jun-Ichi Kimura Daniel J. Dunkley Kenichiro Tani Hiroto Ohira 《International Journal of Earth Sciences》2010,99(8):1773-1790
The reworked Pre-Neoproterozoic and juvenile Neoproterozoic terrane of the Western Ethiopian Shield (WES) consists of three
N–S trending terranes. These are the western migmatitic gneissic terrane, the central metavolcano sedimentary terrane (CVST)
and the eastern migmatitic gneissic terrane. The eastern part of the CVST mostly consists of suture-related ultramafic-metasedimentary
complexes, whereas metavolcanics predominate in the western part. Gabbroic to granitic intrusions frequently occur in the
CVST and in adjacent areas. New zircon SHRIMP U–Pb ages for two gabbros and three diorites in the Ghimbi-Nedjo region of the
WES indicate magmatic crystallization ages. Two pulses of magmatism, at 860–850 and 795–785 Ma, are documented with the former
for the first time. The tholeiitic Kemashi diorite and Bikilal-Ghimbi gabbros have oceanic affinities and yield U/Pb zircon
ages of 856.3 ± 9.8 and 846.0 ± 7.6 Ma, respectively. The calc-alkaline Gebeya Kemisa pyroxene diorite, and the Senbet Dura
hornblende diorite plus the tholeiitic Wayu Meni gabbro, which collectively have arc-back arc characteristics are indistinguishable
at ages of 794.3 ± 9.4, 787.7 ± 8.8 and 778.1 ± 6.3 Ma, respectively. Positive εNd (4.5–7.0) and low initial 87Sr/86Sr (0.7029 ± 0.0002) and a mean T
DM model age of 0.95 Ga for the Ghimbi-Nedjo region (mean T
DM model age of 0.95 Ga for the WES overall) indicate that the magmas were generated from juvenile Neoproterozoic depleted mantle
sources, with no discernable involvement of pre-Neoproterozoic continental crust. The occurrence of gabbros and diorites with
oceanic tholeiite affinities combined with the new ages suggests that the intrusions were emplaced in the earliest stages
of the rifting of Rodinia. This event in the WES led to the development of a passive margin and associated plume-type magmatism
at ~855 Ma. The two intrusive groups with differing magma chemistry and ages suggest that the earliest magmatism was tholeiitic
and associated with the passive margin system followed by continental breakup to form the Mozambique Ocean. The combination
of tholeiitic and calc-alkaline magmatism was related to arc and back-arc basin formation and later terrane accretion (~830–690 Ma). 相似文献
82.
83.
T. Noguchi M. Kimura T. Hashimoto M. Konno T. Nakamura M. E. Zolensky A. Tsuchiyama T. Matsumoto J. Matsuno R. Okazaki M. Uesugi Y. Karouji T. Yada Y. Ishibashi K. Shirai M. Abe T. Okada 《Meteoritics & planetary science》2014,49(7):1305-1314
We observed cross sectional ultra‐thin sections near the surface of 12 particles recovered from the S‐type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer‐to‐submicrometer‐sized sylvite was identified on the surface of Itokawa particle RA‐QD02‐0034. Separately, micrometer‐sized halite was also identified on the surface of Itokawa particle RA‐QD02‐0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S‐type asteroids than previously thought. 相似文献
84.
Ingrid Mann Melanie Köhler Hiroshi Kimura Andrzej Cechowski Tetsunori Minato 《Astronomy and Astrophysics Review》2006,13(3):159-228
Among the observed circumstellar dust envelopes a certain population, planetary debris disks, is ascribed to systems with
optically thin dust disks and low gas content. These systems contain planetesimals and possibly planets and are believed to
be systems that are most similar to our solar system in an early evolutionary stage. Planetary debris disks have been identified
in large numbers by a brightness excess in the near-infrared, mid-infrared and/or submillimetre range of their stellar spectral
energy distributions. In some cases, spatially resolved observations are possible and reveal complex spatial structures. Acting
forces and physical processes are similar to those in the solar system dust cloud, but the observational approach is obviously
quite different: overall spatial distributions for systems of different ages for the planetary debris disks, as opposed to
detailed local information in the case of the solar system. Comparison with the processes of dust formation and evolution
observed in the solar system therefore helps understand the planetary debris disks. In this paper, we review our present knowledge
of observations, acting forces, and major physical interactions of the dust in the solar system and in similar extra-solar
planetary systems. 相似文献
85.
A new method of producing pyrrhotite grains, which are most commonly found in cometary material and interplanetary dust particles, was developed. Pyrrhotite grains in the monophase having a 7C structure were predominately produced using a solid-solid reaction between iron and sulfur grains at room temperature. The characteristic infrared peaks were observed at 602, 563, and 397 cm−1 (16.6, 17.8, and 25.2 μm). 相似文献
86.
Yamato 792947, 793408 and 82038: The most primitive H chondrites,with abundant refractory inclusions
M. Kimura H. Hiyagon H. Palme B. Spettel D. Wolf R. N. Clayton T. K. Mayeda T. Sato A. Suzuki H. Kojima 《Meteoritics & planetary science》2002,37(10):1417-1434
Abstract— In this paper we report petrological and chemical data of the unusual chondritic meteorites Yamato (Y)‐792947, Y‐93408 and Y‐82038. The three meteorites are very similar in texture and chemical composition, suggesting that they are pieces of a single fall. The whole‐rock oxygen isotopes and the chemical compositions are indicative of H chondrites. In addition, the mineralogy, and the abundances of chondrule types, opaque minerals and matrices suggest that these meteorites are H3 chondrites. They were hardly affected by thermal and shock metamorphism. The degree of weathering is very low. We conclude that these are the most primitive H chondrites, H3.2–3.4 (S1), known to date. On the other hand, these chondrites contain extraordinarily high amounts of refractory inclusions, intermediate between those of ordinary and carbonaceous chondrites. The distribution of the inclusions may have been highly heterogeneous in the primitive solar nebula. The mineralogy, chemistry and oxygen isotopic compositions of inclusions studied here are similar to those in CO and E chondrites. 相似文献
87.
88.
In the standard Friedmann cosmology the black-body radiation spectrum is usually taken (without explicit proof as far as we know) to have the same familiarT
4-form that it has in a flat space. With explicit use of the equation of motion of a quantized massless field propagating in a curved background Robertson-Walker metric we show (for the readily tractable scalar field case) that the assumption is in fact true for an open Universe. For a closed Universe, we find that there is an in principle modification to theT
4-law. Unfortunately, the correction turns out to be too small to be experimentally detectable. In passing, we also obtain a simple derivation for the cosmological red shift of frequencies. 相似文献
89.
Arnold Gucsik Taro Endo Hirotsugu Nishido Kiyotaka Ninagawa Masahiro Kayama Szaniszló Bérczi Szabolcs Nagy Péter Ábrahám Yuki Kimura Hitoshi Miura Ildikó Gyollai Irakli Simonia Péter Rózsa József Posta Dániel Apai Krisztián Mihályi Mihály Nagy Ulrich Ott 《Meteoritics & planetary science》2013,48(12):2577-2596
Highly forsteritic olivine (Fo: 99.2–99.7) in the Kaba meteorite emits bright cathodoluminescence (CL). CL spectra of red luminescent forsterite grains have two broad emission bands at approximately 630 nm (impurity center of divalent Mn ions) in the red region and above 700 nm (trivalent Cr ions) in the red–IR region. The cores of the grains show CL blue luminescence giving a characteristic broad band emission at 400 nm, also associated with minor red emissions related to Mn and Cr ions. CL color variation of Kaba forsterite is attributed to structural defects. Electron probe microanalyzer (EPMA) analysis shows concentrations of Ca, Al, and Ti in the center of the forsterite grain. The migration of diffusible ions of Mn, Cr, and Fe to the rim of the Kaba meteoritic forsterite was controlled by the hydrothermal alteration at relatively low temperature (estimated at about 250 °C), while Ca and Al ions might still lie in the core. A very unusual phase of FeO (wüstite) was also observed, which may be a terrestrial alteration product of FeNi‐metal. 相似文献
90.
Alexey Y. Martynov Jun-Ichi Kimura Yuri A. Martynov Alexsander V. Rybin 《Island Arc》2010,19(1):86-104
Middle Miocene to Quaternary lavas on Kunashir Island in the southern zone of the Kurile Arc were examined for major, trace, and Sr–Nd–Pb isotope compositions. The lavas range from basalt through to rhyolite and the mafic lavas show typical oceanic island arc signatures without significant crustal or sub-continental lithosphere contamination. The lavas exhibit across-arc variation, with increasingly greater fluid-immobile incompatible element contents from the volcanic front to the rear-arc; this pattern, however, does not apply to some other incompatible elements such as B, Sb, and halogens. All Sr–Nd–Pb isotope compositions reflect a depleted source with Indian Ocean mantle domain characteristics. The Nd and Pb isotope ratios are radiogenic in the volcanic front, whereas Sr isotope ratios are less radiogenic. These Nd isotope ratios covary with incompatible element ratios such as Th/Nd and Nb/Zr, indicating involvement of a slab-derived sediment component by addition of melt or supercritical fluid capable of mobilizing these high field-strength elements and rare earth elements from the slab. Fluid mobile elements, such as Ba, are also elevated in all basalt suites, suggesting involvement of slab fluid derived from altered oceanic crust. The Kurile Arc lavas are thus affected both by slab sediment and altered basaltic crust components. This magma plumbing system has been continuously active from the Middle Miocene to the present. 相似文献