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71.
Heat flow and geodynamics in the Tyrrhenian Sea 总被引:1,自引:0,他引:1
The present heat flow in the southern Tyrrhenian Sea appears as a transient thermal wave that has migrated eastward in time. The higher heat flow in the south‐eastern side of the basin confirms the suggestion of an eastward‐migrating rift. Punctuation of the Tyrrhenian backarc extension in lithospheric boudins is accompanied by a concentrated increase in heat flow generated by asthenospheric intrusions and related magmatism progressively moving eastward. The migration of the asthenosphere in the same direction could explain these phenomena. 相似文献
72.
Watershed management and headwater reconstruction programs require a reliable knowledge of sediment dynamics. Geographical Information Systems (GIS) provide the framework for the implementation of different complex techniques for the assessment of shallow landsliding and erosion processes in mountain basins. This paper presents some morphometric indicators aimed at erosion and sediment delivery analysis. The proposed indicators can be easily derived from medium to fine resolution Digital Elevation Models (DEM). Applications conducted in Eastern Italian Alps have shown the adequateness of the proposed approach to address erosion and sediment-related problems. The analysis considered the classification of sediment source areas with regard to their activity, the comparison between drainage basins having different morphological characteristics and the topographic control on sediment transport capacity, with a particular attention to the identification of channel reaches characterised by a low sediment transport capacity. 相似文献
73.
A pseudotachylite vein network crosscutting late Hercynian foliated tonalites can be observed along the Copanello cliffs (Calabria, Southern Italy). Pseudotachylites formed during the Oligocene–Miocene at intermediate crustal levels (ca. 10 km). They show variable thickness ranging from few mm up to 10 cm, as observed in injection veins branching from the fault plane. Microscopic observations indicate that pseudotachylite matrix mainly consists of plagioclase (An46–An58) and biotite microlites. Rounded clasts of quartz, plagioclase or of plagioclase–quartz lithic fragments are disseminated in the matrix. Intergranular, flow and spherulitic textures are commonly observed. Microstructural features are consistent with rapid crystallisation from melt. EDS analyses of rare and tiny glass veins indicated a trachyandesite or An50 plagioclase melt composition.The conditions for pseudotachylite formation were reproduced by an analytical model taking into account the heat released by friction along a horizontal fault plane during a seismic event. The model is based on a three-stage rupture history that includes nucleation, propagation and stopping. In addition, by means of a numerical approach, the model reproduces cooling that follows the stopping stage.According to previous studies, the thermal perturbation induced by fault displacement is very intense. In fact, temperatures exceeding the tonalite and even An50 plagioclase liquidus (1470 °C) are reproduced by small amount of slip (≤ 6 cm) in suprahydrostatic regime. On the other hand, the thermal perturbation is strongly localised and of short duration. Peak temperatures abruptly decrease at a short distance from the fault plane (typically in few millimetres). In these conditions a thin film of melt can be produced. Therefore, the presence of cm-scale pseudotachylite veins can be only explained assuming an efficient and fast melt migration towards dilatant sites, such as pull-apart structures and injections veins. Results of the model may be useful to predict the thermal disturbance produced by earthquakes of low intensity. 相似文献
74.
The estimation of debris‐?ow magnitude is an essential step in the assessment of debris‐?ow hazard. Although different methods have been developed for the assessment of debris‐?ow magnitude, this is still a dif?cult task because of the complexity of ?ow processes and the lack of data to test estimation procedures in many mountainous regions. Data on debris‐?ow magnitude from 127 basins in the Eastern Italian Alps have been collected from scienti?c and technical journals, technical reports, historical documents gathered from local archives, and ?eld surveys. These data were used to develop and test different predictive approaches, encompassing regression equations, geomorphological surveys and probabilistic analysis of time series. Regression techniques were used to correlate debris‐?ow magnitude to morphometric parameters and geological characteristics of the basins. Values of the channel debris yield rate (contribution per unit length of channel), proposed in the literature, were compared with data from the study area for identifying reference values for channel stretches of different morphological characteristics. Although limited to the few basins in which suf?cient data were available, the probabilistic analysis of time series of debris‐?ow magnitude provides indications about the relations between magnitude and frequency of debris ?ows. Some observations about the capability and drawbacks of considered methods are presented and the combined use of different approaches for the estimation of debris‐?ow magnitude is suggested. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
75.
F. Cella S. de Lorenzo M. Fedi M. Loddo F. Mongelli A. Rapolla G. Zito 《Tectonophysics》2006,412(1-2):27-47
The gravity anomaly field of the Tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the Oligocene–Miocene. They can resume in lithospheric thinning and asthenospheric rising beneath the Tyrrhenian Basin, coexisting with the roll-back subduction of the African plate margin westward sinking beneath the Calabrian Arc. The geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects.A model of the litho-asthenospheric structure of this region is suggested, showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro-physical features of the mantle. The first phase of this study consisted of the computation of the isotherms in the crust–mantle system beneath the Tyrrhenian Basin and, afterwards, of the density distribution within the partially melted upwelling asthenosphere. The second phase consisted of a temperature/density modelling of the slab subducting beneath the Calabrian Arc. Finally, a 21 / 2 interpretation of gravity data was carried out by including as constraints the results previously obtained. Thus, the final result depicts a model matching both gravity, thermal and petrographic data. They provide (a) a better definition of the thermal regime of the passive mantle rise beneath the Tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and (b) a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works. 相似文献
76.
F. Lorenzo A. Alonso M. J. Pellicer J. L. Pagés M. Pérez-Arlucea 《Environmental Geology》2007,52(4):789-802
This research focuses on the development of metal pollution in sediment cores from three estuaries in Northwest Spain: Viveiro,
Ortigueira and Barqueiro. Pb, Cu, Co, Cr, Cd and Zn and total organic carbon were assessed using principal component analysis
(PCA) in order to obtain background values, measure pollution levels and identify pollution sources. Results were interpreted
by considering the local industrial history, grain size and C/N relationship. The pollution levels obtained bear a strong
resemblance to those documented for of a moderately industrialised area. PCA identifies factors that reflect mainly temporal
associations with metals. Sedimentation rates between 0.9 and 1.1 cm/year were determined. In Viveiro core levels of Cr pollution
are associated with tanneries. In Ortigueira, high core levels of Cu and Co are linked to mining, and Cr levels to adjacent
ultramafic rocks. Erosion of Holocene sediment causes high values of Co and Cr in the Barqueiro core. Cu increase in the three
estuaries is related to fungicide use since 1910. Sea level rise appears to be affecting the marine characteristics of the
sediments in Barqueiro. In Viveiro, the nature of the sediment reflects engineering work and land reclamation. 相似文献
77.
The post-Newtonian mean anomaly advance as further post-Keplerian parameter in pulsar binary systems
Lorenzo Iorio 《Astrophysics and Space Science》2007,312(3-4):331-335
The post-Newtonian gravitoelectric secular rate of the mean anomaly ℳ is worked out for a two-body system in the framework
of the General Theory of Relativity. The possibility of using such an effect, which is different from the well known decrease
of the orbital period due to gravitational wave emission, as a further post-Keplerian parameter in binary systems including
at least one pulsar is examined. The resulting effect is almost three times larger than the periastron advance
. E.g., for the recently discovered double pulsar system PSR J0737-3039 A+B it would amount to −47.79 deg yr−1. This implies that it could be extracted from the linear part of a quadratic fit of the orbital phase because the uncertainties
both in the linear drift due to the mean motion and in the quadratic shift due to the gravitational wave are smaller. The
availability of such additional post-Keplerian parameter would be helpful in further constraining the General Theory of Relativity,
especially for such systems in which some of the other post-Keplerian parameters can be measured with limited accuracy. Moreover,
also certain pulsar-white dwarf binary systems, characterized by circular orbits like PSR B1855+09 and a limited number of
measured post-Keplerian parameters, could be used for constraining competing theories of gravity. 相似文献
78.
79.
80.
Dr. Lorenzo Casertano 《Pure and Applied Geophysics》1955,30(1):170-178
Riassunto E'stato calcolato il valore medio dello spessore ottico dell'atmosfera () in funzione degli elementi meteorologici al suolo, riconoscendo che esso può ritenersi praticamente indipendente da questi. Poichè i valori delle intensità delle radiazioni diffuse dall'atmosfera, ricavati dalla teoria delChandrasekhar, sono, per una data altezza del sole e per ogni direzione della visuale, funzioni soltanto di e dell'albedo, si deduce che queste intensità risultano indipendenti dalle condizioni meteorologiche. Il che porta a concludere che: 1o) o effettivamente le intensità della luce diffusa dalle molecole d'aria non dipendono dai fattori meteorologici; 2o) oppure la teoria delChandrasekhar, completa per quel che riguarda le diffusioni multiple, non risponde in pieno alle condizioni reali. — Il confronto delle curve teoriche della polarizzazione della luce-diffusa dalla volta celeste con quelle ottenute in base ad osservazioni eseguite all'Osservatorio Vesuviano, non dà un accordo accettabile. Pur non escludendo che il mancato accordo sia da attribuire, almeno in parte, alla diffusione non molecolare, si è portati verso la seconda alternativa.
Summary The average optical atmospheric thickness () as a function of the meteorologic ground elements has been calculated, obtaining a result which shows its inependence from those elements. The intensity of the radiations scattered by the atmosphere, as deduced fromChandrasekhar's theory for a given hight of the suns and for every direction, being a function only of and of the albedo, it follows that these intensities are independent from the meteorologic conditions. Then it can be concluded that: 1st) either the intensity of the light scattered by the air molecules does not depend from the meteorologic factors, 2nd) orChandrasekhar's theory, adequate for the computation of the effect of multiple scattering, does not entirely represents the real phenomenon. — Comparing the theoretic patterns for the polarization of sky scattered light with the experimental data obtained in the Vesuvian Observatory, an acceptable agreement has not be found. Although taking into account the scattering of other than molecular origin, the second hypothesis seems more probable.相似文献