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141.
Guido Garay Kate J. Brooks Diego Mardones Ray Norris 《Astrophysics and Space Science》2004,292(1-4):517-523
We report multi-wavelength observations towards IRAS 16547–4247, a luminous infrared source with a bolometric luminosity of 6.2 × 104 L ⊙. Dust continuum observations at 1.2-mm indicate that this object is associated with a dust cloud with a size of about 0.4 pc in diameter and a mass of about 1.3 × 103 M ⊙. Radio continuum observations show the presence of a triple radio source consisting of a compact central object and two outer lobes, separated by about 0.3 pc, symmetrically located from the central source. Molecular hydrogen line observations show a chain of knots that trace a collimated flow extending over 1.5 pc. We suggest that IRAS 16547–4247 corresponds to a dense massive core which hosts near its central region a high-mass star in an early stage of evolution. This massive YSO is undergoing the ejection of a collimated stellar wind which drives the H2 flow. The radio emission from the lobes arises in shocks resulting from the interaction of the collimated wind with the surrounding medium. We conclude that the thermal jets found in the formation of low-mass stars are also produced in high-mass stars. 相似文献
142.
Output generated by hydrologic simulation models is traditionally calibrated and validated using split‐samples of observed time series of total water flow, measured at the drainage outlet of the river basin. Although this approach might yield an optimal set of model parameters, capable of reproducing the total flow, it has been observed that the flow components making up the total flow are often poorly reproduced. Previous research suggests that notwithstanding the underlying physical processes are often poorly mimicked through calibration of a set of parameters hydrologic models most of the time acceptably estimates the total flow. The objective of this study was to calibrate and validate a computer‐based hydrologic model with respect to the total and slow flow. The quick flow component used in this study was taken as the difference between the total and slow flow. Model calibrations were pursued on the basis of comparing the simulated output with the observed total and slow flow using qualitative (graphical) assessments and quantitative (statistical) indicators. The study was conducted using the Soil and Water Assessment Tool (SWAT) model and a 10‐year historical record (1986–1995) of the daily flow components of the Grote Nete River basin (Belgium). The data of the period 1986–1989 were used for model calibration and data of the period 1990–1995 for model validation. The predicted daily average total flow matched the observed values with a Nash–Sutcliff coefficient of 0·67 during calibration and 0·66 during validation. The Nash–Sutcliff coefficient for slow flow was 0·72 during calibration and 0·61 during validation. Analysis of high and low flows indicated that the model is unbiased. A sensitivity analysis revealed that for the modelling of the daily total flow, accurate estimation of all 10 calibration parameters in the SWAT model is justified, while for the slow flow processes only 4 out of the set of 10 parameters were identified as most sensitive. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
143.
The massive unit of a lava flow from Porri volcano (Salina, Aeolian Islands) displays many unusual structures related to
the physical interaction between two different magmas. The magma A represents approximately 80% of the exposed lava surface;
it has a crystal content of 51 vol.% and a dacitic glass composition (SiO2=63–64 wt.%). The magma B has a basaltic-andesite glass composition (SiO2=54–55 wt.%) and a crystal content of approximately 18 vol.%. It occurs as pillow-like enclaves, banding, boudin-like and
rolling structures which are hosted in magma A. Structural analysis suggests that banding and boudin-like structures are the
result of the deformation of enclaves at different shear strain. The linear correlation between strain and stratigraphic height
of the measured elements indicates a single mode of deformation. We deduce that the component B deformed according to a simple
shear model. Glass analyses of the A–B boundary indicate that A and B liquids mix together at high shear strain, whereas only
mingling occurs at low shear strain. This suggests that the amount of deformation (i.e. forced convection) plays an important
role in the formation of hybrid magmas. High shear strain may induce stretching, shearing and rolling of fluids which promote
both forced convection and dynamical diffusion processes. These processes allow mixing of magmas with large differences in
their physical properties.
Received: 15 July 1995 / Accepted: 30 May 1996 相似文献
144.
145.
We present direct observations of Mars zonal wind velocities around northern spring equinox (LS = 336°, LS = 355°, LS = 42°) during martian year 27 and 29. Data was acquired by means of infrared heterodyne spectroscopy of CO2 features at 959.3917 cm?1 (10.4232 μm) and 957.8005 cm?1 (10.4405 μm) using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) at the McMath–Pierce telescope of the National Solar Observatory on Kitt Peak in Arizona and the NASA Infrared Telescope Facility on Mauna Kea, Hawaii between 2005 and 2008. Winds were measured on the dayside of Mars with an unprecedented spatial resolution allowing sampling of up to nine independent latitudes over the martian disk. Retrieved wind velocities depend strongly on latitude and season with values ranging from 180 m/s prograde to ?94 m/s retrograde. A comparison of the observational results to predicted values from the Mars Climate Database yield a reasonable agreement between modeling and observation. 相似文献
146.
Kelly E. Fast Theodor Kostiuk Franck Lefèvre Timothy A. Livengood Juan D. Delgado John Annen Guido Sonnabend 《Icarus》2009,203(1):20-27
Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center’s Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 μm-atm), as were measurements made close in time (ranging from <1 to >8 μm-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC’s Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2-4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity. 相似文献
147.
Continental climate in the East Siberian Arctic during the last interglacial: Implications from palaeobotanical records 总被引:1,自引:0,他引:1
Frank Kienast Pavel Tarasov Lutz Schirrmeister Guido Grosse Andrei A. Andreev 《Global and Planetary Change》2008,60(3-4):535-562
To evaluate the consequences of possible future climate changes and to identify the main climate drivers in high latitudes, the vegetation and climate in the East Siberian Arctic during the last interglacial are reconstructed and compared with Holocene conditions. Plant macrofossils from permafrost deposits on Bol'shoy Lyakhovsky Island, New Siberian Archipelago, in the Russian Arctic revealed the existence of a shrubland dominated by Duschekia fruticosa, Betula nana and Ledum palustre and interspersed with lakes and grasslands during the last interglacial. The reconstructed vegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles an open variant of subarctic shrub tundra as occurring near the tree line about 350 km southwest of the study site. Such difference in the plant cover implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today. Our pollen-based climatic reconstruction suggests a mean temperature of the warmest month (MTWA) range of 9–14.5 °C during the warmest interval of the last interglacial. The reconstruction from plant macrofossils, representing more local environments, reached MTWA values above 12.5 °C in contrast to today's 2.8 °C. We explain this contrast in summer temperature and soil moisture with a combination of summer insolation higher than present and climatic continentality in arctic Yakutia stronger than present as result of a considerably less inundated Laptev Shelf during the last interglacial. 相似文献
148.
Löwen Kersten Meinhold Guido Güngör Talip Berndt Jasper 《International Journal of Earth Sciences》2017,106(8):2771-2796
International Journal of Earth Sciences - Detrital zircon U–Pb geochronology of 15 Late Palaeozoic to Early Mesozoic siliciclastic sandstones from the Karaburun Peninsula in western Turkey... 相似文献
149.
Guido Meinhold Dimitrios Kostopoulos Dirk Frei Felix Himmerkus Thomas Reischmann 《International Journal of Earth Sciences》2010,99(4):813-832
The Pirgadikia Terrane in northern Greece forms tectonic inliers within the Vardar suture zone bordering the Serbo-Macedonian
Massif to the southwest. It comprises Cadomian basement rocks of volcanic-arc origin and very mature quartz-rich metasedimentary
rocks. U–Pb laser ablation sector-field inductively-coupled plasma mass spectrometry analyses of detrital zircons from the
latter reveal a marked input from a Cadomian–Pan-African source with minor contribution from Mesoproterozoic, Palaeoproterozoic
and Archaean sources. The metasedimentary rocks are correlated with Ordovician overlap sequences at the northern margin of
Gondwana on the basis of their maturity and zircon age spectra. The Pirgadikia Terrane can be best interpreted as a peri-Gondwana
terrane of Avalonian origin, which was situated close to the Cadomian terranes in the Late Neoproterozoic–Early Palaeozoic,
very much like the Istanbul Terrane. The second unit investigated is the Vertiskos Terrane, which constitutes the major part
of the Serbo-Macedonian Massif in Greece. It comprises predominantly igneous rocks of Silurian age and minor metasedimentary
rocks of unknown age and provenance. U–Pb analyses of detrital zircons from a garnetiferous mica schist of the Vertiskos Terrane
indicate derivation from 550 to 1,150 Ma-old source rocks with a major Cadomian peak. This, combined with minor input of >1,950 Ma-old
zircons and the absence of ages between ca. 1.2 and 1.7 Ga suggests a NW Africa source. The protolith age of the garnetiferous
mica schist is presumably Early Ordovician. One sample of garnet-bearing biotite gneiss, interpreted as meta-igneous rock,
comprises predominantly subhedral zircons of igneous origin with late Middle Ordovician to Silurian ages. We suggest that
the rock association of the Vertiskos Terrane is part of an ancient active-margin succession of the Hun superterrane, comparable
to successions of the Austro- and Intra-Alpine Terranes. The new data of this study provide evidence of occurrences of Avalonia-
and Armorica-derived terranes in the Eastern Mediterranean and moreover help to clarify palaeogeographic reconstructions for
the peri-Gondwana realm in the Early Palaeozoic. 相似文献
150.
Uncertainty quantification in the calibration of a dynamic viscoplastic model of slow slope movements 总被引:3,自引:2,他引:1
Most landslides occurring in Italy consist of shallow-translational movements, which involve fine, essentially clayey material.
They are usually characterized by low velocities, typically of few centimeters per year. The main triggering factor is hydrologic,
since movements are usually strictly connected to groundwater level fluctuations. This slow and periodical trend can be interpreted
by a viscous soil response, and in order to catch the actual kinematics of the soil mass behavior, a dynamic analysis should
be adopted. This paper discusses the case of the Alverà mudslide, located in the Northern Alps (Italy), for which a very detailed
and almost 9-year-long monitoring database, including displacements and groundwater levels records, is available. A well-defined
dynamic viscoplastic model, capable of returning a displacement prediction and a mobilized shear strength angle estimate from
a groundwater level input, was considered. A first deterministic calibration proved the ability of the model to reproduce
the mudslide overall displacements trend if a suitable reduction of the mobilized angle _0\varphi ^{\prime }_{0} is allowed. Then, an uncertainty quantification analysis was performed by measuring the model parameters variability, and
all parameters could be represented using a probability density function and a correlation structure. As a consequence, it
was possible to define a degree of uncertainty for model predictions, so that an assessment of the model reliability was obtained.
The final outcome is believed to represent an important advancement in relation to hazard assessment and for future landslide
risk management. 相似文献