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291.
Proposal of a method to define areas of landslide hazard and application to an area of the Dolomites, Italy 总被引:1,自引:0,他引:1
A numerical–cartographical method has been developed to create landslide hazard maps. This method allows the assigning of a rating to the various parameters which contribute to landslides. The parameters considered are: (1) erodibility and degradability of the rocks and Quaternary deposits; (2) permeability of the ground to identify areas prone to hydraulic overpressure; (3) the geometric ratio between discontinuities and slope, and thickness of Quaternary deposits; (4) angle of the slopes; and (5) land use. A thematic map is constructed for each factor considered which defines different areas through ratings, after which all the thematic maps are overlaid and the ratings added up (or multiplied). The map which is thus obtained is reclassified in order to create the final map of landslide hazard. This method, which has already been tested in various areas, has produced excellent results in this case too, allowing a map to be constructed which corresponds to the actual instability problems. 相似文献
292.
The Influence of Strong-Motion Duration on the Seismic Response of Masonry Structures 总被引:2,自引:3,他引:2
Julian J. Bommer Guido Magenes Jonathan Hancock Paola Penazzo 《Bulletin of Earthquake Engineering》2004,2(1):1-26
The influence of strong-motion duration on the response of saturated soils is clearly recognised and accounted for in the
assessment of liquefaction potential. The degree to which duration of shaking influences damage to structures, however, remains
a topic of debate, with resolution of the issue complicated by the variety of definitions of duration and the variety of structural
behaviours, as well as the difficulty of decoupling the specific effect of duration from other features of the ground motion.
A suite of seven structural models with strength and stiffness degrading characteristics, designed to reflect the seismic
behaviour of masonry structures commonly encountered in many parts of Europe, are analysed using a suite of almost 500 strong-motion
accelerograms. Correlations are explored between the damage, measured in terms of the strength degradation, and a range of
strong-motion parameters, demonstrating that Arias intensity and spectral acceleration at the fundamental initial period of
the structure are both reasonably good damage indicators for such structures. A significantly improved correlation is obtained
by using the elastic spectral accelerations averaged over a period range from the initial period of the structure to a value
approximately three times greater, reflecting the stiffness degradation as the shaking progresses. The scatter in the correlation
is shown to be partially explained by differences in duration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
293.
The aim of this paper is to provide some constrains on the time behavior of earthquake generation mechanism, through the usage of a non-parametric statistics that leads up to the empirical estimation of the hazard function. The results indicate that the most characterizing temporal feature for large (M 7.0+) worldwide shallow earthquake occurrence is a clustering lasting few years, indicating that the probability of earthquake occurrence is higher immediately after the occurrence of an event. After that, the process becomes almost time independent, as in a Poisson process. Remarkably, this time clustering is very similar to what previously found for different spatio-magnitude windows, and it does not seem to depend on the tectonic style of the region. This may support the hypothesis of an universal law for earthquake occurrence. 相似文献
294.
295.
296.
Beat Schmid John M. Livingston Philip B. Russell Philip A. Durkee Haflidi H. Jonsson Donald R. Collins Richard C. Flagan John H. Seinfeld Santiago Gassó Dean A. Hegg Elisabeth Öström Kevin J. Noone Ellsworth J. Welton Kenneth J. Voss Howard R. Gordon Paola Formenti Meinrat O. Andreae 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):568-593
We report on clear‐sky column closure experiments (CLEARCOLUMN) performed in the Canary Islands during the second Aerosol Characterization Experiment (ACE‐2) in June/July 1997. We present CLEARCOLUMN results obtained by combining airborne sunphotometer and in‐situ (optical particle counter, nephelometer, and absorption photometer) measurements taken aboard the Pelican aircraft, space‐borne NOAA/AVHRR data and ground‐based lidar and sunphotometer measurements. During both days discussed here, vertical profiles flown in cloud‐free air masses revealed 3 distinctly different layers: a marine boundary layer (MBL) with varying pollution levels, an elevated dust layer, and a very clean layer between the MBL and the dust layer. A key result of this study is the achievement of closure between extinction or layer aerosol optical depth (AOD) computed from continuous in‐situ aerosol size‐distributions and composition and those measured with the airborne sunphotometer. In the dust, the agreement in layer AOD (λ=380–1060 nm) is 3–8%. In the MBL there is a tendency for the in‐situ results to be slightly lower than the sunphotometer measurements (10–17% at λ=525 nm), but these differences are within the combined error bars of the measurements and computations. 相似文献
297.
298.
Roberto Santacroce Raffaello Cioni Paola Marianelli Alessandro Sbrana Roberto Sulpizio Giovanni Zanchetta Douglas J. Donahue Jean Louis Joron 《Journal of Volcanology and Geothermal Research》2008
A review of compositional data of the major explosive eruptions of Vesuvius is presented, comparing compositions (major elements) of whole rock with glass shards from the proximal deposits, hopefully useful for long-distance correlation. A critical review of published and new geochronological data is also provided. All available 14C ages are calibrated to give calendar ages useful for the reconstruction of the volcanological evolution of the volcanic complex. The pyroclastic deposits of the four major Plinian eruptions (22,000 yr cal BP “Pomici di Base”, 8900 yr cal BP “Mercato Pumice”, 4300 yr cal BP “Avellino Pumice”, and A.D. 79 “Pompeii Pumice”) are widely dispersed and allow a four-folded, Plinian to Plinian, stratigraphic division: 1. B–M (between Pomici di Base and Mercato); 2. M–A (between Mercato and Avellino); 3. A–P (between Avellino and Pompeii); 4. P–XX (from the Pompeii Pumice to the last erupted products of the XXth century). Within each interval, the age, lithologic and compositional features of pyroclastic deposits of major eruptions, potentially useful for tephrostratigraphic purposes on distal areas, are briefly discussed. The Vesuvius rocks are mostly high Potassic products, widely variable in terms of their silica saturation. They form three groups, different for both composition and age: 1. slightly undersaturated, older than Mercato eruption; 2. mildly undersaturated, from Mercato to Pompeii eruptions; 3. highly undersaturated, younger than Pompeii eruption. For whole rock analyses, the peculiar variations in contents of some major and trace elements as well as different trends in element/element ratios, allow a clear, unequivocal, easy diagnosis of the group they belong. Glass analyses show large compositional overlap between different groups, but selected element vs. element plots are distinctive for the three groups. The comparative analysis of glass and whole rock major element compositions provides reliable geochemical criteria helping in the recognition, frequently not obvious, of distal products from the different single eruptions. 相似文献
299.
Paola Cusano Simona Petrosino Gilberto Saccorotti 《Journal of Volcanology and Geothermal Research》2008
We present a detailed analysis of the source properties of Long-Period (LP) signals recorded at Campi Flegrei Caldera (Italy) during the last (2005–2006) mini-uplift episode. Moment Tensor inversion via full-waveform modelling of broad-band seismograms indicates a crack-like source with a significant volumetric component. From auto-regressive modelling of the signal's tail we evaluate the dominant frequency and the attenuation factor of the oscillating source. Considering the acoustic properties of a fluid-filled crack, these values are consistent with the resonant oscillations of a crack filled by a water–gas mixture at variable gas–volume fraction. For these fluids, the crack size would be on the order of 40–420 m, a size range which is consistent with the spatial spreading of LP hypocenters. Analysis of temporally-correlated time series of seismological and geochemical data indicates that climaxing of LP activity was preceded by swarms of volcano-tectonic (VT) events and rapidly followed by a consistent increase of both thermal emissions and gas fluxes recorded at the surface (1 month — 2/3 days, respectively). Following these observations, we propose a conceptual model where VT activity increases permeability of the medium, thus favouring fluid mobility. As a consequence, the hydrothermal system experiences pressure perturbations able to trigger its resonant, LP oscillations. 相似文献