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151.
Velio Coviello Lucia Capra Rosario Vázquez Victor H. Márquez-Ramírez 《地球表面变化过程与地形》2018,43(10):2219-2231
We present direct observations and monitoring data of a hyperconcentrated flow that occurred along La Lumbre ravine, one of the most active channels of Volcán de Colima in Mexico. Flow properties were inferred from video images and seismic data recorded by a geophone installed outside the channel. We collected flow samples 400 m upstream from the monitoring station and analyzed the variation of sediment concentration and grain‐size distribution over time. A joint analysis of hydrological (i.e. flow velocity, wetted perimeter) and rheological (i.e. yield stress τy and dynamic viscosity μm ) parameters was performed to characterize the flow. Different flow regimes and sediment transport processes were identified and analyzed in comparison with both the amplitude and spectral features of the seismic signal. We observed differing sediment concentrations at the same discharge, suggesting a decoupling between sediment transport processes and discharge for low‐magnitude flows. A straightforward correlation was found between the amplitude of the seismic signal and the sediment concentration, and a value of 1.8 × 10?3 mm/s was identified that can be used as a threshold to recognize the hyperconcentrated phase of the flow. This information was tested on the complete seismic dataset gathered at La Lumbre ravine during the 2015 rainy season. We identified the transition from streamflow to hyperconcentrated flow (and/or vice versa) in 16 low‐magnitude events and we validated this result using the video recordings. The correlation between seismic amplitude and sediment concentration is valid at La Lumbre ravine but would need to be tested in other locations for the development of automatic flow classification methods. This work contributes to standardized seismic methods for characterizing flow processes in volcanic environments, also for the development of lahar early warning systems. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
152.
Very long baseline interferometry (VLBI) tracking of satellites is a topic of increasing interest for the establishment of space ties. This shall strengthen the connection of the various space geodetic techniques that contribute to the International Terrestrial Reference Frame. The concept of observing near-Earth satellites demands research on possible observing strategies. In this paper, we introduce this concept and discuss its possible benefits for improving future realizations of the International Terrestrial Reference System. Using simulated observations, we develop possible observing strategies that allow the determination of radio telescope positions in the satellite system on Earth with accuracies of a few millimeters up to 1–2 cm for weekly station coordinates. This is shown for satellites with orbital heights between 2,000 and 6,000 km, observed by dense regional as well as by global VLBI-networks. The number of observations, as mainly determined by the satellite orbit and the observation interval, is identified as the most critical parameter that affects the expected accuracies. For observations of global positioning system satellites, we propose the combination with classical VLBI to radio sources or a multi-satellite strategy. Both approaches allow station position repeatabilities of a few millimeters for weekly solutions. 相似文献
153.
154.
Acta Geotechnica - The complete loss of soil strength and stiffness, which occurs during soil liquefaction, marks a change of state of the soil that switches from solid to liquid. In particular,... 相似文献
155.
Dino Bindi Lucia Luzi Francesca Pacor Roberto Paolucci 《Bulletin of Earthquake Engineering》2011,9(6):1921-1939
In this work, we analyze the records of the Italian strong motion database (ITACA,
) with the aim of identifying stations affected by site effects that are not captured by standard seismic classification schemes.
In particular, we consider four different site classifications, two of them based on geological/geophysical characteristics
and two driven by data. For each classification we develop a ground motion prediction equation using a random effect approach
to isolate the between-station and within-station distribution of errors. The site coefficients obtained for the different
classes confirm that site amplification effects are significant for both the horizontal and vertical components. The between-station
error normalized to the standard deviation of the between-station error distribution is then used to identify stations characterized
by large errors, attributable to site effects not accounted for by the classification schemes. The results show that large
errors can affect the predictions when the site effects are not uniquely related to the reduction of the seismic impedance
in the uppermost layers. For example, amplifications of ground motion over the long period range are observed for stations
installed within alluvial closed-shape basins, as consequence of locally generated surface waves. For these stations, classifications
based on the horizontal to vertical response spectra ratio are not reliable, since amplifications are also affecting the vertical
component. Another interesting feature which emerges from the analysis is the significant de-amplification of short period
spectral ordinates that seems to be related to stations typically set in at the foundation level of massive structures. To
increase the usefulness of the data set, the most important distinctive features of the strong motion stations are documented
in the ITACA database reports containing the instrument information and the available geological-geotechnical data. 相似文献
156.
Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka 总被引:1,自引:0,他引:1
Sonia Calvari Stefano Branca Rosa Anna Corsaro Emanuela De Beni Lucia Miraglia Gianluca Norini Jan Wijbrans Enzo Boschi 《Bulletin of Volcanology》2011,73(1):101-112
A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions
on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka
during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases.
Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The
eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a
lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in
a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter
ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved
groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred
during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo.
The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from
the main feeding system of the volcano. 相似文献
157.
Sebastian Fischer Axel Liebscher Marco De Lucia Lutz Hecht 《Environmental Earth Sciences》2013,70(8):3687-3708
To evaluate mineralogical-geochemical changes within the reservoir of the Ketzin pilot CO2 storage site in Brandenburg, Germany, two sets of laboratory experiments on sandstone and siltstone samples from the Stuttgart Formation have been performed. Samples were exposed to synthetic brine and pure CO2 at experimental conditions and run durations of 5.5 MPa/40 °C/40 months for sandstone and 7.5 MPa/40 °C/6 months for siltstone samples, respectively. Mineralogical changes in both sets of experiments are generally minor making it difficult to differentiate natural variability of the whole rock samples from CO2-induced alterations. Results of sandstone experiments suggest dissolution of the anorthite component of plagioclase, anhydrite, K-feldspar, analcime, hematite and chlorite + biotite. Dissolution of the anorthite component of plagioclase, anhydrite and K-feldspars is also observed in siltstone experiments. In an inverse modeling approach, an extensive set of equilibrium simulations was set up in order to reproduce the experimental observations of the sandstone experiments. Simulations generally show fairly good matches with the experimental observations. Best matches with measured brine data are obtained from mineral combinations of albite, analcime, anhydrite, dolomite, hematite, illite, and kaolinite. The major discrepancies during equilibrium modeling, however, are reactions involving Fe2+ and Al3+. The best matching subsets of the equilibrium models were finally run including kinetic rate laws. These simulations reveal that experimentally determined brine data was well matched, but reactions involving K+ and Fe2+ are not fully covered. The modeling results identified key primary minerals as well as key chemical processes, but also showed that the models are not capable of covering all possible contingencies. 相似文献
158.
159.
The many lives of active galactic nuclei: cooling flows, black holes and the luminosities and colours of galaxies 总被引:2,自引:0,他引:2
160.
Milan Gomboš Andrej Tall Jarmila Trpčevská Branislav Kandra Dana Pavelkova Lucia Balejčíková 《Arabian Journal of Geosciences》2018,11(20):635
The aim of the submitted paper is to identify the lower limit of Stokes’ law for calculating the deposition rate of soil microparticles. The authors’ hypothesis on the lower limit of Stokes’ law is based on the idea that with the gradual formation of the colloidal dispersion system, both the particle size and the sedimentation rate decrease. It is assumed that under the lower particle size limit, Stokes’ law does not apply. As a result of the diffusion, the state of the sedimentation equilibrium gradually emerges. The results of the experiment showed that in laboratory conditions, Stokes’ equation ceases to be valid for sedimentation of the particles sized d(90)?<?2 μm. During the experiment, a dynamic sedimentation equilibrium was reached at the particle size d(90)?=?0.27 μm. The scientific contribution of this knowledge is the accuracy of the determination of hydropedological characteristics dependent on the texture of the soil. In this context, the results stated in the paper define the lower limit of the validity for the laboratory procedures determining soil texture on the basis of the sedimentation methods. To identify the textures below this limit, it is necessary to choose the methods based on other principles. Determination of the lower limit is particularly important in clay soils containing a high proportion of clay particles (clay particles <?2 μm). 相似文献