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31.
Christiane Helling R. Giles Harrison Farideh Honary Declan A. Diver Karen Aplin Ian Dobbs-Dixon Ute Ebert Shu-ichiro Inutsuka Francisco J. Gordillo-Vazquez Stuart Littlefair 《Surveys in Geophysics》2016,37(4):705-756
Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) brown dwarfs which are amongst the oldest objects in the Universe. Despite this diversity, solar system planets, extrasolar planets and brown dwarfs have broadly similar global temperatures between 300 and 2500 K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emissions. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emissions that potentially originate from accelerated electrons on brown dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation. 相似文献
32.
The mechanism of cation and oxygen isotope exchange in alkali feldspars under hydrothermal conditions 总被引:3,自引:1,他引:2
Dominik R. D. Niedermeier Andrew Putnis Thorsten Geisler Ute Golla-Schindler Christine V. Putnis 《Contributions to Mineralogy and Petrology》2009,157(1):65-76
The mechanism of re-equilibration of albite in a hydrothermal fluid has been investigated experimentally using natural albite
crystals in an aqueous KCl solution enriched in 18O at 600°C and 2 kbars pressure. The reaction is pseudomorphic and produces a rim of K-feldspar with a sharp interface on
a nanoscale which moves into the parent albite with increasing reaction time. Transmission electron microscopy (TEM) diffraction
contrast and X-ray powder diffraction (XRD) show that the K-feldspar has a very high defect concentration and a disordered
Al, Si distribution, compared to the parent albite. Raman spectroscopy shows a frequency shift of the Si-O-Si bending vibration
from ~476 cm−1 in K-feldspar formed in normal 16O aqueous solution to ~457 cm−1 in the K-feldspar formed in 18O-enriched solution, reflecting a mass-related frequency shift due to a high enrichment of 18O in the K-feldspar silicate framework. Raman mapping of the spatial distribution of the frequency shift, and hence 18O content, compared with major element distribution maps, show a 1:1 correspondence between the reaction rim formed by the
replacement of albite by K-feldspar, and the oxygen isotope re-equilibration. The textural and chemical characteristics as
well as the kinetics of the replacement of albite by K-feldspar are consistent with an interface-coupled dissolution-reprecipitation
mechanism. 相似文献
33.
Ute C. Herzfeld 《Mathematical Geosciences》2008,40(5):587-618
The topic of this paper is the retrieval of hidden or secondary information on complex spatial variables from geophysical
data. Typical situations of obscured geological or geophysical information are the following: (1) Noise may disturb the signal
for a variable for which measurements have been collected. (2) The variable of interest may be obscured by other geophysical
processes. (3) The information of interest may formally be captured in a secondary variable, whereas data may have been collected
for a primary variable only, that is related to the geophysical process of interest. Examples discussed here include mapping
of marine-geologic provinces from bathymetric data, identification of sea-ice properties from snow-depth data, analysis of
snow surface data in an Alpine environment and association of deformation types in fast-moving glaciers from airborne video
material or satellite imagery. Data types include geophysical profile or trackline data, image data, grid or matrix-type data,
and more generally, any two-dimensional or three-dimensional discrete or discretizable data sets.
The framework for a solution is geostatistical characterization and classification, which typically involves the following
steps: (1) calculation of vario functions (which may be of higher order or residual type, or combinations of both), (2) derivation
of classification parameters from vario functions, and (3) characterization, classification or segmentation, depending on
the applied problem. In some situations, spatial surface roughness is utilized as an auxiliary variable, for instance, roughness
of the seafloor may be derived from bathymetric data and be indicative of geological provinces.
The objective of this paper is to present components of the geostatistical classification method in a summarizing and synoptical
manner, motivated by applied examples and integrating principal and generalized concepts, such as hyperparameters and parameters
that relate to the same physical processes and work for data in oversampled and undersampled situations, parameters that facilitate
comparison among different data types, data sets and across scales, variograms and vario functions of higher order, and deterministic
and connectionist classification algorithms. 相似文献
34.
Ute Christina Herzfeld 《Mathematical Geology》1993,25(7):901-924
Seafloor classification is aimed at quantitatively characterizing seafloor properties such as roughness and anisotropy, and at using such spatial characteristics to distinguish geological provinces automatically. From geostatistical principals, a variogram method is developed for seafloor classification and it is demonstrated for data from the western flank of the Mid-Atlantic Ridge at 25°45N to 26°40N. This study uses HYDROSWEEP bathymetric data which have been ping-edited to flag erroneous data records, and navigation corrected. The classification method can handle the resultant data gaps inside the survey swaths as well as interpret data from several swaths. For a suite of test areas representative of different geological provinces, directional variograms are calculated, and characteristic parameters are extracted for the classification. Examples include a sediment pond, abyssal hill terrain in several segments and of variable spacing, inside and outside corners of ridge discontinuities, and mixed morphological forms. The dependency of the results on random or regular subsampling and on the size of the test area is investigated. 相似文献
35.
Pierre Cervenka Ute Christina Herzfeld Christian De Moustier 《Marine Geophysical Researches》1994,16(6):407-425
When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350, U.S.A. 相似文献
36.
37.
Ute V. Möstl Nikolay V. Erkaev Michael Zellinger Helmut Lammer Hannes Gröller Helfried K. Biernat Daniil Korovinskiy 《Icarus》2011,216(2):476-484
The Kelvin–Helmholtz instability gained scientific attention after observations at Venus by the spacecraft Pioneer Venus Orbiter gave rise to speculations that the instability contributes to the loss of planetary ions through the formation of plasma clouds. Since then, a handful of studies were devoted to the Kelvin–Helmholtz instability at the ionopause and its implications for Venus. The aim of this study is to investigate the stability of the two instability-relevant boundary layers around Venus: the induced magnetopause and the ionopause. We solve the 2D magnetohydrodynamic equations with the total variation diminishing Lax–Friedrichs algorithm and perform simulation runs with different initial conditions representing the situation at the boundary layers around Venus. Our results show that the Kelvin–Helmholtz instability does not seem to be able to reach its nonlinear vortex phase at the ionopause due to the very effective stabilizing effect of a large density jump across this boundary layer. This seems also to be true for the induced magnetopause for low solar activity. During high solar activity, however, there could occur conditions at the induced magnetopause which are in favour of the nonlinear evolution of the instability. For this situation, we estimated roughly a growth rate for planetary oxygen ions of about 7.6 × 1025 s−1, which should be regarded as an upper limit for loss due to the Kelvin–Helmholtz instability. 相似文献
38.
Isabel Seifert Annegret H. Thieken Mirjam Merz Dietmar Borst Ute Werner 《Natural Hazards》2010,52(2):453-479
For risk analyses not only knowledge about the impact of different types of hazards, but also information about the elements
and values at risk is necessary. This article introduces a methodology for a countrywide estimation of asset values for commercial
and industrial properties using Germany as an example. It consists of a financial appraisal of asset values on the municipal
level and a further disaggregation by means of land use data. Novelties are the distinction of 60 economic activities, the
consideration of production site sizes and the application of a dasymetric mapping technique for a sector-specific estimation
and disaggregation of asset values. A validation with empirical data confirms the feasibility of the calculation. The resulting
maps can be used for loss estimations e.g. in the framework of cost–benefit analyses that aim to evaluate hazard mitigation
measures or for portfolio analyses by banks and insurance companies. The approach can be used for other countries if the necessary
data is available (mainly in industrialized countries). In any case, it reveals the critical points when estimating commercial
and industrial asset values. 相似文献
39.
Ian Parsons John D. Fitz Gerald James K. W. Lee Tim Ivanic Ute Golla-Schindler 《Contributions to Mineralogy and Petrology》2010,160(2):155-180
Microtextural changes brought about by heating alkali feldspar crystals from the Shap granite, northern England, at atmospheric
pressure, have been studied using transmission and scanning electron microscopy. A typical unheated phenocryst from Shap is
composed of about 70 vol% of tweed orthoclase with strain-controlled coherent or semicoherent micro- and crypto-perthitic
albite lamellae, with maximum lamellar thicknesses <1 μm. Semicoherent lamellae are encircled by nanotunnel loops in two orientations
and cut by pull-apart cracks. The average bulk composition of this microtexture is Ab27.6Or71.8An0.6. The remaining 30 vol% is deuterically coarsened, microporous patch and vein perthite composed of incoherent subgrains of
oligoclase, albite and irregular microcline. The largest subgrains are ~3 μm in diameter. Heating times in the laboratory
were 12 to 6,792 h and T from 300°C into the melting interval at 1,100°C. Most samples were annealed at constant T but two were heated to simulate an 40Ar/39Ar step-heating schedule. Homogenisation of strain-controlled lamellae by Na↔K inter-diffusion was rapid, so that in all run
products at >700°C, and after >48 h at 700°C, all such regions were essentially compositionally homogeneous, as indicated
by X-ray analyses at fine scale in the transmission electron microscope. Changes in lamellar thickness with time at different
T point to an activation energy of ~350 kJmol−1. A lamella which homogenised after 6,800 h at 600°C, therefore, would have required only 0.6 s to do so in the melting interval
at 1,100°C. Subgrains in patch perthite homogenised more slowly than coherent lamellae and chemical gradients in patches persisted
for >5,000 h at 700°C. Homogenisation T is in agreement with experimentally determined solvi for coherent ordered intergrowths, when a 50–100°C increase in T for An1 is applied. Homogenisation of lamellae appears to proceed in an unexpected manner: two smooth interfaces, microstructurally
sharp, advance from the original interfaces toward the mid-line of each twinned, semicoherent lamella. In places, the homogenisation
interfaces have shapes reflecting the local arrangements of nanotunnels or pull-aparts. Analyses confirm that the change in
alkali composition is also relatively sharp at these interfaces. Si–Al disordering is far slower than alkali homogenisation
so that tweed texture in orthoclase, tartan twinning in irregular microcline, and Albite twins in albite lamellae and patches
persisted in all our experiments, including 5,478 h at 700°C, 148 h at 1,000°C and 5 h at 1,100°C, even though the ensemble
in each case was chemically homogeneous. Nanotunnels and pull-aparts were modified after only 50 min at 500°C following the
simulated 40Ar/39Ar step-heating schedule. New features called ‘slots’ developed away from albite lamellae, often with planar traces linking
slots to the closest lamella. Slot arrays were often aligned along ghost-like regions of diffraction contrast which may mark
the original edges of lamellae. We suggest that the slot arrays result from healing of pull-aparts containing fluid. At 700°C
and above, the dominant defects were subspherical ‘bubbles’, which evolved from slots or from regions of deuteric coarsening.
The small degree of partial melting observed after 5 h at 1,100°C was often in the vicinity of bubbles. Larger micropores,
which formed at subgrain boundaries in patch perthite during deuteric coarsening, retain their shape up to the melting point,
as do the subgrain boundaries themselves. It is clear that modification of defects providing potential fast pathways for diffusion
in granitic alkali feldspars begins below 500°C and that defect character progressively changes up to, and beyond, the onset
of melting. 相似文献
40.