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41.
The Khaluta carbonatite complex comprizes fenites, alkaline syenites and shonkinites, and calcite and dolomite carbonatites. Textural and compositional criteria, melt inclusions, geochemical and isotopic data, and comparisons with relevant experimental systems show that the complex formed by liquid immiscibility of a carbonate-saturated parental silicate melt. Mineral and stable isotope geothermometers and melt inclusion measurements for the silicate rocks and carbonatite all give temperatures of crystallization of 915–1,000°C and 890–470°C, respectively. Melt inclusions containing sulphate minerals, and sulphate-rich minerals, most notably apatite and monazite, occur in all of the lithologies in the Khaluta complex. All lithologies, from fenites through shonkinites and syenites to calcite and dolomite carbonatites, and to hydrothermal mineralisation are further characterized by high Ba and Sr activity, as well as that of SO3 with formation of the sulphate minerals baryte, celestine and baryte-celestine. Thus, the characteristic features of the Khaluta parental melt were elevated concentrations of SO3, Ba and Sr. In addition to the presence of SO3, calculated fO2 for magnetites indicate a high oxygen fugacity and that Fe+3>Fe+2 in the Khaluta parental melt. Our findings suggest that the mantle source for Khaluta carbonatite and associated rocks, as well as for other carbonatites of the West Transbaikalia carbonatite province, were SO3-rich and characterized by high oxygen fugacity. 相似文献
42.
The possibility of the formation of galaxies both during the galactic clustering of small structural units originated earlier and at fragmentation of larger formations is considered. A selfsimilar spectrum of long-wave perturbations is obtained. The results of numerical calculations and conclusions of Press and Schechter's (1974) work are discussed.Translated by Miss Eva Vokálová, Astronomical Institute of Charles University, Prague. 相似文献
43.
G. S. Ripp N. S. Karmanov A. G. Doroshkevich M. V. Badmatsyrenov I. A. Izbrodin 《Geochemistry International》2006,44(4):395-402
This paper presents the results of a study of the Vesely carbonatite occurrence in a new carbonatite-bearing area of northern Transbaikalia. The REE patterns, oxygen and carbon isotope compositions of carbonates and magnetites, and strontium isotope composition of dolomite allow us to classify the rocks as carbonatites. This study focused on minerals from xenoliths that were identified as mantle-derived on the basis of structure and mineral composition. The compositions of Cr-bearing chlorite, phengite, magnetite, rutile, ilmenite, and titanite are reported. Aggregates of closely intergrown magnetite and rutile occurring in the xenoliths resemble exsolution structures. A possible origin of these aggregates is discussed. 相似文献
44.
A. G. Doroshkevich F. Wall G. S. Ripp 《Contributions to Mineralogy and Petrology》2007,153(3):339-353
A recently discovered dolomite carbonatite at Pogranichnoe, North Transbaikalia, Russia, dated at 624 ± 3 Ma, contains xenoliths
of calcite-bearing dolomite carbonatite with graphite spherulites. Apatite and aegirine are the other rock-forming minerals.
Chemically the carbonatites are ferrocarbonatite and ferruginous calciocarbonatite. The graphite forms <1 mm up to 1.5 mm
diameter spherulites, with Raman spectra similar to published spectra of microcrystalline, amorphous carbon and disordered
graphite, with G and D bands at 1,580−1,600 cm−1 and at around 1,350 cm−1. Alteration has formed Fe-bearing calcite to Ca-bearing siderite compositions not previously reported in nature around the
graphite along cracks and fractures. Mineral and stable isotope geothermometers and melt inclusion measurements for the carbonatite
all give temperatures of 700°–900°. It is concluded that the graphite precipitated from the ferrocarbonatite magma. There
are three candidates to control the precipitation of graphite (a) a redox reaction with FeII in the magma, (b) potential presence of organics in the magma (c) seeding of, or dissolution in, the magma of graphite/diamond
from the mantle, and further work is required to identify the most important mechanism(s). Graphite in carbonatite is rare,
with no substantial published accounts since the 1960s but graphite at other localities seems also to have precipitated from
carbonatite magma. The precipitation of reduced carbon from carbonatite provides further evidence that diamond formation in
carbonate melts at high mantle pressures is feasible. 相似文献
45.
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47.
This paper reports the results of isotopic investigations of the rocks of the Khalyuta carbonatite complex (carbonatites,
comagmatic silicate rocks, fenites, and hydrothermal rocks) and host limestones and granites. Pyroxene, amphibole, magnetite,
potassium feldspar, apatite, phlogopite, calcite, dolomite, strontianite, celestite, and barite were investigated. The isotopic
compositions of C, O, Sr, and S were analyzed. The character of the distribution of oxygen isotopic composition in minerals
(carbonates, silicates, phosphates, and oxides) suggests their equilibrium formation. It was supposed that the evolutionary
trend of C and O isotopic compositions is mainly related to the processes of differentiation in the melt-fluid system and
indicates the absence of significant contamination by carbon and oxygen from a crustal source during rock formation from the
magmatic stage to the hydrothermal stage. The isotopic compositions of S and Sr did not change. 相似文献
48.
We consider possibilities for presently operating and planned infrared, submillimeter, and millimeter telescopes for observations
of the epoch of reionization in the Universe, i.e., of the sources of ultraviolet radiation that have caused the reionization
(galaxies, quasars, etc.) and the ionized intergalactic medium. Along with direct observations of such sources in the optical
and infrared, we analyze the feasibility of observations of the intergalactic gas, as well as fluctuations of the temperature
and polarization of the cosmic microwave background due to inhomogeneities in the reionization process. 相似文献
49.
We show that both the mass and composition of dark matter (DM) particles strongly influence the formation of low mass DM halos. Comparison of theoretical predictions with observations allows us to select the more promising DM models. More details can be found in our paper arXiv:1404.3362. 相似文献
50.
Astronomy Letters - We propose a method of analyzing the absorption spectra of quasars that allows the physical parameters of absorbing clouds, absorbers, to be roughly estimated: their masses,... 相似文献