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91.
Palaeomagnetic studis on oriented samples from two sequences of olivine basalt lava flows on the island of Réunion together record the Réunion normal polarity event within the Matuyama reversed polarity epoch. Detailed K?Ar dating of the lavas indicates that the Réunion event has a mean age 2.02±0.02 my with a duration estimated to lie within the range 10,000 to 50,000 yr. This could explain the rarity of detection of the event in deep sea sedimentary cores. 相似文献
92.
We have compared solutions obtained from the general 13-moment system of transport equations with those obtained from the standard collision-dominated transport equations for conditions corresponding to low speed thermal proton flow in the topside ionosphere in the vicinity of the plasmapause. In general, the solutions obtained from the 13-moment system of equations, which allows for different species temperatures parallel and perpendicular to the geomagnetic field and non-classical heat flows, are different from those obtained from the standard transport equations, which account for isotropic temperatures and classical collision-dominated heat flows. Within the plasmasphere, where the electron density is high, the differences between the 13-moment and standard solutions are typically small. However, outside the plasmasphere where the electron density is lower and in the ionosphere above SAR-arcs, where substantial electron and proton heat flows occur, there can be significant differences between the 13-moment and standard solutions. Generally, the differences are much larger for the protons than for the electrons. Our 13-moment solutions indicate that the proton and electron distributions are anisotropic with the difference between parallel and perpendicular temperatures approaching 4000 K for the protons and 2500 K for the electrons in the ionosphere above SAR-arcs. Also, above SAR-arcs the 13-moment heat flow equations yield proton heat flows as much as a factor of 10 lower and electron heat flows as much as a factor of 2 lower than those predicted by the classical collision-dominated heat flow expressions for the same boundary conditions. 相似文献
93.
J. M. Watkins J. D. Clemens P. J. Treloar 《Contributions to Mineralogy and Petrology》2007,154(1):91-110
Two natural, low K2O/Na2O, TTG tonalitic gneisses (one hornblende-bearing and the other biotite-bearing) were partially melted at 0.8–1.2 GPa (fluid-absent).
The chief melting reactions involve the breakdown of the biotite and hornblende. The hornblende tonalite is slightly less
fertile than the biotite tonalite, but melt volumes reach around 30% at 1,000°C. This contrasts with results of most previous
work on more potassic TTGs, which generally showed much lower fertility, though commonly producing more potassic melts. Garnet
is formed in biotite-bearing tonalitic protoliths at P > 0.8 GPa and at > 1.0 GPa in hornblende-bearing tonalitic protoliths. All fluid-absent experiments produced peraluminous
granitic to granodioritic melts, typically with SiO2 > 70 wt.%. For the biotite tonalite, increasing T formed progressively more melt with progressively lower K2O/Na2O. However, the compositions of melts from the hornblende tonalite do not vary significantly with T. With increasing P, melts from the biotite tonalite become less potassic, due to the increasing thermal stability of biotite. For the hornblende
tonalite, again there is no consistent trend. Fluid-absent melting of sodic TTGs produces melts with insufficient K2O to model the magmas that formed the voluminous, late, potassic granites that are common in Archaean terranes. Reconnaissance
fluid-present experiments at 0.6 GPa imply that H2O-saturated partial melting of TTGs is also not a viable process for producing magmas that formed these granites. The protoliths
for these must have been more potassic and less silicic. Nevertheless, at granulite-facies conditions, sodic TTGs will produce
significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths. Upward abstraction
of this melt would result in some LILE depletion of the terrane. Younger K-rich magmatism is unlikely to represent recycling
of TTG crust on its own, and it seems most likely that evolved crustal rocks and/or highly enriched mantle must be involved.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
94.
95.
The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al2O2 contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements 相似文献
96.
97.
Experimental batch and miscible-flow cultures were studied in order to determine the mechanistic pathways of microbial Fe(III)
respiration in ferruginous smectite clay, NAu-1. The primary purpose was to resolve if alteration of smectite and release
of Fe precedes microbial respiration. Alteration of NAu-1, represented by the morphological and mineralogical changes, occurred
regardless of the extent of microbial Fe(III) reduction in all of our experimental systems, including those that contained
heat-killed bacteria and those in which O2, rather than Fe(III), was the primary terminal electron acceptor. The solid alteration products observed under transmission
electron microscopy included poorly crystalline smectite with diffuse electron diffraction signals, discrete grains of Fe-free
amorphous aluminosilicate with increased Al/Si ratio, Fe-rich grains, and amorphous Si globules in the immediate vicinity
of bacterial cells and extracellular polymeric substances. In reducing systems, Fe was also found as siderite. The small amount
of Fe partitioned to the aqueous phase was primarily in the form of dissolved Fe(III) species even in the systems in which
Fe(III) was the primary terminal electron acceptor for microbial respiration. From these observations, we conclude that microbial
respiration of Fe(III) in our laboratory systems proceeded through the following: (1) alteration of NAu-1 and concurrent release
of Fe(III) from the octahedral sheets of NAu-1; and (2) subsequent microbial respiration of Fe(III). 相似文献
98.
99.
100.
Natural Hazards - The objective of this research is to establish a model that characterizes integrated humanitarian operations management in response to flood disasters, during which an optimal... 相似文献