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61.
Dmitri A. Ionov Antoine Bénard Pavel Y. Plechov 《Contributions to Mineralogy and Petrology》2011,162(6):1159-1174
Glass-bearing inclusions hosted by Cr-spinel in harzburgite xenoliths from Avacha are grouped based on homogenization temperatures
and daughter minerals into high-T (1,200°C; opx + cpx), intermediate (900–1,100°C; cpx ± amph), and low-T (900°C; amph) and
are commonly accompanied by larger “melt pockets”. Unlike previous work on unheated inclusions and interstitial glass in xenoliths
from Kamchatka, the homogenized glass compositions in this study are not affected by low-pressure melt fractionation during
transport and cooling or by interaction with host magma. Primary melt compositions constrained for each inclusion type differ
in major and trace element abundances and were formed by different events, but all are silica saturated, Ca-rich, and K-poor,
with enrichments in LREE, Sr, Rb, and Ba and negative Nb anomalies. These melts are inferred to have been formed with participation
of fluids produced by dehydration of slab materials. The high-T inclusions trapped liquids produced by ancient high-degree,
fluid-induced melting in the mantle wedge. The low-T inclusions are related to percolation of low-T melts or hydrous fluids
in arc mantle lithosphere. Melt pockets arise from localized heating and fluid-assisted melting induced by rising magmas shortly
before the entrapment of the xenoliths. The “high-T” melt inclusions in Avacha xenoliths are unique in preserving evidence
of ancient, high-T melting events in arc mantle, whereas the published data appear to characterize pre-eruption enrichment
events. 相似文献
62.
Dmitri A. Uzdensky 《Astrophysics and Space Science》2004,292(1-4):573-585
In this review I consider modern theoretical models of coupled star–disk magnetospheres. I discuss a number of models, both stationary and time-dependent, and examine what physical conditions govern the selection of a preferred model. 相似文献
63.
Marc W. Pound Jave O. Kane Dmitri D. Ryutov Bruce A. Remington Akira Mizuta 《Astrophysics and Space Science》2007,307(1-3):187-190
Sometimes the most beautiful things are the hardest to understand. Pillars like those of the Eagle Nebula form at the boundary
between some of the hottest (10000~K) and coldest (10~K) gas in the Galaxy. Many physical processes come into play in the
birth and growth of such gaseous pillars: hydrodynamic instability, photoionization, ablation, recombination, molecular heating
and cooling, and probably magnetic fields. High-quality astronomical observations, quantitative numerical simulations, and
scaled laser experiments provide a powerful combination for understanding their formation and evolution.
We put our most recent hydrodynamic model to the test, by creating simulated observations from it and comparing them directly
to the actual radioastronomical observations. Successfully reproducing major characteristics of the observations in this manner
is an important step in designing appropriate laser experiments. 相似文献
64.
Stéphane Colombi rew Jaffe Dmitri Novikov Christophe Pichon 《Monthly notices of the Royal Astronomical Society》2009,393(2):511-526
A method to rapidly estimate the Fourier power spectrum of a point distribution is presented. This method relies on a Taylor expansion of the trigonometric functions. It yields the Fourier modes from a number of fast Fourier transforms (FFTs), which is controlled by the order N of the expansion and by the dimension D of the system. In three dimensions, for the practical value N = 3 , the number of FFTs required is 20.
We apply the method to the measurement of the power spectrum of a periodic point distribution that is a local Poisson realization of an underlying stationary field. We derive an explicit analytic expression for the spectrum, which allows us to quantify – and correct for – the biases induced by discreteness and by the truncation of the Taylor expansion, and to bound the unknown effects of aliasing of the power spectrum. We show that these aliasing effects decrease rapidly with the order N . For N = 3 , they are expected to be, respectively, smaller than ∼10−4 and 0.02 at half the Nyquist frequency and at the Nyquist frequency of the grid used to perform the FFTs. The only remaining significant source of errors is reduced to the unavoidable cosmic/sample variance due to the finite size of the sample.
The analytical calculations are successfully checked against a cosmological N -body experiment. We also consider the initial conditions of this simulation, which correspond to a perturbed grid. This allows us to test a case where the local Poisson assumption is incorrect. Even in that extreme situation, the third-order Fourier–Taylor estimator behaves well, with aliasing effects restrained to at most the per cent level at half the Nyquist frequency.
We also show how to reach arbitrarily large dynamic range in Fourier space (i.e. high wavenumber), while keeping statistical errors in control, by appropriately 'folding' the particle distribution. 相似文献
We apply the method to the measurement of the power spectrum of a periodic point distribution that is a local Poisson realization of an underlying stationary field. We derive an explicit analytic expression for the spectrum, which allows us to quantify – and correct for – the biases induced by discreteness and by the truncation of the Taylor expansion, and to bound the unknown effects of aliasing of the power spectrum. We show that these aliasing effects decrease rapidly with the order N . For N = 3 , they are expected to be, respectively, smaller than ∼10
The analytical calculations are successfully checked against a cosmological N -body experiment. We also consider the initial conditions of this simulation, which correspond to a perturbed grid. This allows us to test a case where the local Poisson assumption is incorrect. Even in that extreme situation, the third-order Fourier–Taylor estimator behaves well, with aliasing effects restrained to at most the per cent level at half the Nyquist frequency.
We also show how to reach arbitrarily large dynamic range in Fourier space (i.e. high wavenumber), while keeping statistical errors in control, by appropriately 'folding' the particle distribution. 相似文献
65.
A new model for the evolution of substellar objects is proposed, which enables computation of their internal structure and evolution in an adiabatic approximation without allowance for axial rotation, magnetic fields, and nuclear reactions. The basic set of differential equations in the model contains a new equation for the gradient of the electron degeneracy parameter and adiabatic coefficients of the new type. The results of numerical simulations of evolutionary sequences of hydrogen (X = 1), helium (Y = 1), and hydrogen-helium (X = 0.75, Y = 0.25) substellar objects with masses M < 0.08 M ⊙ during the evolutionary stage 106 yr < t < 1010 yr are reported. Luminosity-effective temperature, mass-radius, radius-time, central temperature-central density, and central temperature-age relations are analyzed for the indicated chemical composition. 相似文献
66.
Origin of Fe-rich lherzolites and wehrlites from Tok,SE Siberia by reactive melt percolation in refractory mantle peridotites 总被引:2,自引:2,他引:0
Dmitri?A.?IonovEmail author Ingrid?Chanefo Jean-Louis?Bodinier 《Contributions to Mineralogy and Petrology》2005,150(3):335-353
Lherzolite–wehrlite (LW) series xenoliths from the quaternary Tok volcanic field in the southeastern Siberian craton are distinguished
from the more common lherzolite–harzburgite (LH) series by (a) low Mg numbers (0.84–0.89) at high modal olivine (66–84%) and
(b) widespread replacement of orthopyroxene (0–12%) and spinel by clinopyroxene (7–22%). The LW series peridotites are typically
enriched in Ca, Fe, Mn and Ti, and depleted in Si, Ni and Cr relative to refractory LH series rocks (Mg number ≥0.89), which
are metasomatised partial melting residues. Numerical modelling of Fe–Mg solid/liquid exchange during melt percolation demonstrates
that LW series rocks can form by reaction of host refractory peridotites with evolved (Mg numbers 0.6–0.7), silica-undersaturated
silicate melts at high melt/rock ratios, which replace orthopyroxene with clinopyroxene and decrease Mg numbers. This process
is most likely related to underplating and fractionation of basaltic magma in the shallow mantle, which also produced olivine–clinopyroxene
cumulates found among the Tok xenoliths. 相似文献
67.
V. Demyanov S. Soltani M. Kanevski S. Canu M. Maignan E. Savelieva V. Timonin V. Pisarenko 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(1):18-32
This paper deals with the problem of spatial data mapping. A new method based on wavelet interpolation and geostatistical
prediction (kriging) is proposed. The method – wavelet analysis residual kriging (WARK) – is developed in order to assess
the problems rising for highly variable data in presence of spatial trends. In these cases stationary prediction models have
very limited application. Wavelet analysis is used to model large-scale structures and kriging of the remaining residuals
focuses on small-scale peculiarities. WARK is able to model spatial pattern which features multiscale structure. In the present
work WARK is applied to the rainfall data and the results of validation are compared with the ones obtained from neural network
residual kriging (NNRK). NNRK is also a residual-based method, which uses artificial neural network to model large-scale non-linear
trends. The comparison of the results demonstrates the high quality performance of WARK in predicting hot spots, reproducing
global statistical characteristics of the distribution and spatial correlation structure. 相似文献
68.
—?The maximum possible (regional) magnitude Mmax and other seismic hazard parameters like β which is the slope of Gutenberg-Richter law, and λ which is the intensity (rate) of seismic activity are estimated in eight seismic regions of the west side of the circum-Pacific belt. The Bayesian approach, as described by (Pisarenko et?al., 1996; Pisarenko and Lyubushin, 1997, 1999) is a straightforward technique of estimating the seismic hazard. The main assumptions for the method applied are a Poissonian character of seismic events flow, a frequency-magnitude law of Gutenberg-Richter's type with cutoff maximum value for the estimated parameter and a seismic catalog, which have a rather sizeable number of events. We also estimated the quantiles of the probabilistic distribution of the “apparent” Mmax for future given time-length intervals. 相似文献
69.
Statistically treated data of long-term observational series (>30 years) for 66 rivers are used to study the character of distribution of water flow maximums during rain-induced floods in Maritime Territory, Russia. Two probability models are discussed: generalized Pareto distribution (for the domain of very large values) and generalized distribution of extremums (for the rest of the range). The issue of optimal conjunction point of these distributions is discussed. The problem of increasing the accuracy of distribution parameter estimates through data grouping is considered. 相似文献
70.