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31.
Andrey A. Gurenko Kaj A. Hoernle Alexander V. Sobolev Folkmar Hauff Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2010,159(5):689-702
The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically
depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject
of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6–90.0 mol.% Fo, 1,722–3,915 ppm
Ni, 1,085–1,552 ppm Mn, 1,222–3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine
basaltic) lavas with their bulk rock Sr–Nd–Pb isotope compositions (87Sr/86Sr = 0.70315–0.70331, 143Nd/144Nd = 0.51288–0.51292, 206Pb/204Pb = 19.55–19.93, 207Pb/204Pb = 15.60–15.63, 208Pb/204Pb = 39.31–39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source.
Using the model (Sobolev et al. in: Science 316:412–417, 2007) in which the reaction of Si-rich melts originated during partial
melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free
reaction pyroxenite, we obtain an end member composition for peridotite with 87Sr/86Sr = 0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61 and 208Pb/204Pb = 39.07 (EM-type end member), and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289, 206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62 and 208Pb/204Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30%
pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive
Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands
(Gurenko et al. EPSL 277:514–524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type
pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic
component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic
component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component
from the asthenosphere or lithosphere above the plume center. 相似文献
32.
Frank Preusser Jürgen M. Reitner Christian Schlüchter 《Swiss Journal of Geoscience》2010,103(3):407-426
Overdeepened valleys and basins are commonly found below the present landscape surface in areas that were affected by Quaternary
glaciations. Overdeepened troughs and their sedimentary fillings are important in applied geology, for example, for geotechnics
of deep foundations and tunnelling, groundwater resource management, and radioactive waste disposal. This publication is an
overview of the areal distribution and the geometry of overdeepened troughs in the Alps and their foreland, and summarises
the present knowledge of the age and potential processes that may have caused deep erosion. It is shown that overdeepened
features within the Alps concur mainly with tectonic structures and/or weak lithologies as well as with Pleistocene ice confluence
and partly also diffluence situations. In the foreland, overdeepening is found as elongated buried valleys, mainly oriented
in the direction of former ice flow, and glacially scoured basins in the ablation area of glaciers. Some buried deeply incised
valleys were generated by fluvial down-cutting during the Messinian crisis but this mechanism of formation applies only for
the southern side of the Alps. Lithostratigraphic records and dating evidence reveal that overdeepened valleys were repeatedly
occupied and excavated by glaciers during past glaciations. However, the age of the original formation of (non-Messinian)
overdeepened structures remains unknown. The mechanisms causing overdeepening also remain unidentified and it can only be
speculated that pressurised meltwater played an important role in this context. 相似文献
33.
U. Schreiber M. Schneider C.H. Rowe G.E. Stedman W. Schlüter 《Surveys in Geophysics》2001,22(5-6):603-611
Ring laser rotation sensors are best known from inertial navigation, wherethey have many advantages over mechanical gyroscopes. They have recentlybeen greatly improved, and show potential as fully independent length-of-daysensors. We discuss some important aspects of current limitations in theirperformance. In particular we demonstrate a novel scheme for thestabilisation of a large ring laser against frequency pulling effectsinduced by backscatter. 相似文献
34.
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36.
N. Tomašić A. Gajović V. Bermanec D. S. Su M. Rajić Linarić T. Ntaflos R. Schlögl 《Physics and Chemistry of Minerals》2006,33(2):145-159
The metamict state and recrystallization of fergusonite in metamict natural samples were studied by thermal methods (TGA-DTA), X-ray powder diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and electron microprobe (EPMA). Two metamict mineral samples of fergusonite were investigated in order to identify the original premetamict crystal structure and to identify recrystallization mechanisms. The TEM data and RS provided evidence on the partial preservation of the original structure in the investigated minerals, which are X-ray amorphous. It was shown that fergusonite could recrystallize from a metamict mineral with original fergusonite structure or from metamictized pyrochlore, which was altered before or after metamictization. Two recrystallization mechanisms were recognized: (a) epitaxial growth occurring at the boundary between preserved premetamict structure fragments and completely metamictized areas, and (b) nucleation-crystal growth mechanism occurring in completely amorphous areas of the minerals, and resulting in recrystallization of the original mineral as well as in the crystallization of a new mineral with a modified chemical composition as compared to the initial matrix. 相似文献
37.
Atmospheric back radiation in the tropical pacific: Intercomparison of in-situ measurements, simulations and satellite retrievals 总被引:1,自引:0,他引:1
Summary The back radiation has been measured with an Eppley pyrgeometer on board the R/V Vickers in the tropical Pacific Ocean during the field campaigns COARE (Coupled Ocean Atmosphere Response Experiment) and CEPEX (Central Equatorial Pacific Experiment) in February and March 1993, respectively. As part of these compaigns radiosondes have been launched from the Vickers several times per day and cloud cover was observed frequently. The radiosonde and cloud observations are used together with a radiative transfer model to calculate the back radiation for a subsequent intercomparison with the pyrgeometer measurements. Another means of comparison is derived from space-borne SSM/I (Special Sensor Microwave/Imager) measurements. The mean difference between pyrgeometer measurements and simulated downwelling irradiance at the sea surface is less than 2 W/m2, at a mean of 425 W/m2 in the warm pool, with a standard deviation of 8 W/m2. The comparison of satellite measurements with pyrgeometer readings shows a mean difference of-3 W/m2 and a standard deviation of 14 W/m2. The mean difference between satellite-derived back radiation and simulated one is 3 W/m2 with a standard deviation of 14 W/m2. Comparisons with results obtained from bulk formulae applied to surface meteorological observations show a good performance of the bulk parameterisations in the cloud-free case but a general overestimation of the back radiation in cloudy situations.With 5 Figures 相似文献
38.
Josef Kallrath Johannes P. Schlöder Hans Georg Bock 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):353-371
A recent least squares algorithm, which is designed to adapt implicit models to given sets of data, especially models given by differential equations or dynamical systems, is reviewed and used to fit the Hénon-Heiles differential equations to chaotic data sets.This numerical approach for estimating parameters in differential equation models, called theboundary value problem approach, is based on discretizing the differential equations like a boundary value problem,e.g. by a multiple shooting or collocation method, and solving the resulting constrained least squares problem with a structure exploiting generalized Gauss-Newton-Method (Bock, 1981).Dynamical systems like the Hénon-Heiles system which can have initial values and parameters that lead to positive Lyapunov exponents or phase space filling Poincaré maps give rise to chaotic time series. Various scenarios representing ideal and noisy data generated from the Hénon-Heiles system in the chaotic region are analyzedw.r.t. initial conditions, parameters and Lyapunov exponents. The original initial conditions and parameters are recovered with a given accuracy. The Lyapunov spectrum is then computed directly from the identified differential equations and compared to the spectrum of the true dynamics.presently at IWR, Universität Heidelberg, Im Neuenheimer Feld 368, D-6900 Heidelberg, Germany 相似文献
39.
Armin Freundt Wilfried Strauch Steffen Kutterolf Hans-Ulrich Schmincke 《Pure and Applied Geophysics》2007,164(2-3):527-545
This paper emphasizes the fact that tsunamis can occur in continental lakes and focuses on tsunami triggering by processes
related to volcanic eruptions and instability of volcanic edifices. The two large lakes of Nicaragua, Lake Managua and Lake
Nicaragua, host a section of the Central American Volcanic Arc including several active volcanoes. One case of a tsunami in
Lake Managua triggered by an explosive volcanic eruption is documented in the geologic record. However, a number of events
occurred in the past at both lakes which were probably tsunamigenic. These include massive intrusion of pyroclastic flows
from Apoyo volcano as well as of flank-collapse avalanches from Mombacho volcano into Lake Nicaragua. Maar-forming phreatomagmatic
eruptions, which repeatedly occurred in Lake Managua, are highly explosive phenomena able to create hugh water waves as was
observed elsewhere. The shallow water depth of the Nicaraguan lakes is discussed as the major limiting factor of tsunami amplitude
and propagation speed. The very low-profile shores facilitate substantial in-land flooding even of relatively small waves.
Implications for conceiving a possible warning system are also discussed. 相似文献
40.