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141.
Extraordinary blowing snow transport events in East Antarctica 总被引:1,自引:1,他引:0
Claudio Scarchilli Massimo Frezzotti Paolo Grigioni Lorenzo De Silvestri Lucia Agnoletto Stefano Dolci 《Climate Dynamics》2010,34(7-8):1195-1206
In the convergence slope/coastal areas of Antarctica, a large fraction of snow is continuously eroded and exported by wind to the atmosphere and into the ocean. Snow transport observations from instruments and satellite images were acquired at the wind convergence zone of Terra Nova Bay (East Antarctica) throughout 2006 and 2007. Snow transport features are well-distinguished in satellite images and can extend vertically up to 200 m as first-order quantitatively estimated by driftometer sensor FlowCapt?. Maximum snow transportation occurs in the fall and winter seasons. Snow transportation (drift/blowing) was recorded for ~80% of the time, and 20% of time recorded, the flux is >10?2 kg m?2 s?1 with particle density increasing with height. Cumulative snow transportation is ~4 orders of magnitude higher than snow precipitation at the site. An increase in wind speed and transportation (~30%) was observed in 2007, which is in agreement with a reduction in observed snow accumulation. Extensive presence of ablation surface (blue ice and wind crust) upwind and downwind of the measurement site suggest that the combine processes of blowing snow sublimation and snow transport remove up to 50% of the precipitation in the coastal and slope convergence area. These phenomena represent a major negative effect on the snow accumulation, and they are not sufficiently taken into account in studies of surface mass balance. The observed wind-driven ablation explains the inconsistency between atmospheric model precipitation and measured snow accumulation value. 相似文献
142.
Laura?SandriEmail author Warner?Marzocchi Lucia?Zaccarelli 《Bulletin of Volcanology》2004,66(3):263-275
The complexity of the processes responsible for volcanic eruptions makes a theoretical approach to forecasting the evolution of volcanic unrest rather difficult. A feasible strategy for this purpose appears to be the identification of possible repetitive schemes (patterns) in the pre-eruptive unrest of volcanoes. Nevertheless, the limited availability and the heterogeneity of pre-eruptive data, and the objective difficulty in quantitatively recognizing complex pre-eruptive patterns, make this task very difficult. In this work we address this issue by using a pattern recognition approach applied to the seismicity recorded during 217 volcanic episodes of unrest around the world. In particular, we use two non-parametric algorithms that have proven to give satisfactory results in dealing with a small amount of data, even if not normally distributed and/or characterized by discrete or categorical values. The results show evidence of a longer period of instability in the unrest preceding an eruption, compared to isolated unrest. This might indicate, even if not necessarily, a difference in the energy of processes responsible for the two types of unrest. However, if the unrest is followed by an eruption, it seems that the seismic energy released during the unrest (parameterized by the duration of the swarm and the maximum magnitude recorded) is not indicative of the magnitude of the impending eruption. We also found that, in general, unrest followed by the largest explosive eruptions have a longer repose time than those related to moderate eruptions. This evidence supports the fact that the occurrence of a large eruption needs a sufficient amount of time after the last event in order to re-charge the feeding system and to achieve a closed-conduit regime so that a sufficiently large amount of gas can be accumulated.Editorial responsibility: T. Druitt 相似文献
143.
The water leakage in the urban areas causes a continuous rise in the water table, with harmful effects. An experimental drainage
system, based on horizontal well technology, was designed and implemented in a populated area. Groundwater flow modeling was
used to assess the hydrodynamic efficiency of the system through drain conductance parameter estimation. 相似文献
144.
The systematic analysis of seismograms recorded on the Romanian territory using Vrancea intermediate-depth earthquakes shows a strong asymmetric pattern relative to the epicentral area: on one side, in the Transylvanian Basin and the Eastern Carpathians (approximately along the inner volcanic chain), the amplitudes are reduced by a factor of 20 on average and the high frequencies are attenuated, in contrast with the other side, in the foreland platform. This pattern is explained by a significant attenuation increase caused by a strong lateral variation of the structure in the upper mantle, immediately towards NW of the Vrancea seismic active volume. This region corresponds to the most recent volcanic activity in the Persani Mountains and with the low-velocity body adjacent toward NW to the high-velocity body subducted beneath Vrancea area as indicated by seismic tomography and heat flow results. The CALIXTO'99 tomography experiment, deployed for 6 months in 1999, provides the largest number of observations for Vrancea earthquakes ever recorded on the Romanian territory. We select data from 8 earthquakes generated in this time interval in the Vrancea nest, which were recorded with signal / noise ratio greater than 5 by at least 25 stations. All of them are small- to moderate-magnitude events (3.6 ≤ Mw ≤ 4.2). The attenuation is much more important in the high-frequency range (> 1 Hz), than at low frequencies. Since the large Vrancea earthquakes can radiate significant energy in the low-frequency range (< 1 Hz), our results show that the seismic hazard level is much more uniform all over the Romanian territory in the low-frequency range than in the high-frequency range. 相似文献
145.
Lucia Capra 《Natural Hazards》2007,43(1):45-61
Volcanic activity can enhance several secondary effects, including the formation of one or more natural dams. A common example
is from volcanic collapse, where huge mass volumes are rapidly emplaced, obstructing the drainage around a volcano. Their
duration depends on the volume of the obstructing mass, inflow rate, and on its textural characteristics. A block facies of
a debris avalanche produces durable and permeable dams that consist of decimeter to meter-sized blocks without matrix, whereas
a mixed facies is easily eroded after overflowing. Analysis of the sedimentological characteristics of different volcaniclastic
deposits that formed natural dams indicate that a mean grain size (Md) equal to −1 phi divides the field of debris avalanche
dams (Md < −1 phi) from that formed from other types of volcanic deposits. In addition, the matrix proportion of dams formed
by debris avalanches are less than the 50% and the percentage of mud fraction is highly variable, up to 30%. Combining the
granulometric textures with duration time of the dam shows no clear relation. Dam durability is probably more dependent on
the volume of the lake and the inflow rate. Only in some cases, as mud fraction increases is the blockage also less durable
because the lower permeability favors rapid infilling. The texture of the dam also determines the types of secondary flows
that originate by their breakdown. These vary from cohesive debris flow to hyperconcentrated flow, representing different
hazards due to their magnitude and their different behavior downstream. 相似文献
146.
After the major 1991–1993 eruption, Mt. Etna resumed flank activity in July 2001 through a complex system of eruptive fissures
cutting the NE and the S flanks of the volcano and feeding effusive activity, fire fountains, Strombolian and minor phreatomagmatic
explosions. Throughout the eruption, magmas with different petrography and composition were erupted. The vents higher than
2,600 m a.s.l. (hereafter Upper vents, UV) erupted porphyritic, plagioclase-rich trachybasalt, typical of present-day summit
and flank activity. Differently, the vents located at 2,550 and 2,100 m a.s.l. (hereafter Lower vents, LV) produced slightly
more primitive trachybasalt dominated by large clinopyroxene, olivine and uncommon minerals for Etna such as amphibole, apatite
and orthopyroxene and containing siliceous and cognate xenoliths. Petrologic investigations carried out on samples collected
throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity, namely the coeval
occurrence of distinct magmas. We interpret this evidence as the result of a complex plumbing system. It consists in two separate
magma storage systems: a shallow one feeding the activity of the UV and a deeper and more complex storage related to the activity
of LV. In this deep storage zone, which is thermally and compositionally zoned, the favourable conditions allow the crystallization
of amphibole and the occurrence of cognate xenoliths representing wall cumulates. Throughout 2001 eruption, UV and LV magmas
remain clearly distinct and ascended following different paths, ruling out the occurrence of mixing processes between them.
Furthermore, integrating the 2001 eruption in the framework of summit activity occurring since 1995, we propose that the 2001
magma feeding the vents lower than 2,600 m a.s.l. is a precursor of a refilling event, which reached its peak during the 2002–2003
Etna flank eruption. 相似文献
147.
The VRANCEA99 and VRANCEA2001 seismic refraction experiments are part of a multidisciplinary project to study the Eastern Carpathians in Romania. The objectives of these studies are intended to disclose a more detailed picture of the crustal and upper mantle structures above the seismically active Vrancea region. In this paper we provide additional constraints for the upper crustal structures of the area. The 1999 campaign consisted of a 320-km-long N–S profile and a 70-km-long E–W profile. The intersecting 2001 profile extended in E–W direction from the Hungarian border to the Black Sea. In order to enhance the model resolution, first arrival data from local crustal earthquakes were also included.This configuration allowed for the first time to derive a 3-D velocity model for the upper crust of the Romanian Carpathian Orogen, within a 115×235 km wide region, centred over the Vrancea seismic zone. The 3-D model reveals lateral velocity variations, which were not visible on the in-line interpretations. It allows us to distinguish between foreland platform areas, foreland basins and the Carpathian Orogen. Clear velocity differences between the foreland basins south and southeast of the Eastern Carpathians and the Focsani Basin further north indicate different pre-Miocene sedimentary compositions and geological evolutions of these foreland platforms. The involved Moesian and Scythian platforms are separated by the Trotus Fault system, which is observed as a velocity discontinuity. An upper crustal high-velocity zone, above the northern Vrancea seismic zone, could also be identified. This high-velocity zone is explained by a Middle Pliocene to Pleistocene E–W oriented out-of-sequence thrust of the crystalline basement, below the decollement of the flysch nappes. 相似文献
148.
Lucia Civetta Luigi La Volpe Lucio Lirer 《Journal of Volcanology and Geothermal Research》1978,4(3-4)
The temporal evolution of the Yemen Trap series is examined in the light of K-Ar radiometric data.Rifting and volcanic activity characterize the Yemen plateau between 30 and 20 m.y. confirming a fairly common history of the Afro-Arabian plate on both sides of the Red Sea. 相似文献
149.
Maurizio Gaetani Lucia Angiolini Alda Nicora Dario Sciunnach Patrick Le Fort Seifnullah Tanoli Asif Khan 《International Journal of Earth Sciences》1996,85(4):683-704
During the summer of 1992 a geological expedition crossed the northern Karakorum range in northern Pakistan, from the Chitral
to Karambar valleys, from the villages of Mastuj to Imit. Some of the areas visited were geologically unknown. A number of
structural units were crossed, belonging to the Karakorum block or to other crustal blocks north of it. They are: (a) the
axial batholith, in which three plutonic bodies have been identified, and (b) the northern sedimentary belt (NSB), in which
three major tectonostratigraphic units form thrust stacks dipping to the north. Their internal stratigraphy and structural
style are partly different. The most complete contains a crystalline basement, transgressed by a marine succession during
the Early Ordovician. The youngest strata are represented by the Reshun conglomerate, of inferred Cretaceous age. The northernmost
unit of the NSB is tightly folded, whereas the central one forms a monocline. Vertical faults, mainly strike-slip, dissect
the thrusted slabs. Metamorphic deformation is absent or reaches only the anchizone in the studied sector of the Karakorum
NSB. To the north of the Karakorum proper there are several other tectonic units, separated by vertical faults. They are,
from south to north: (a) the Taš Kupruk zone, with metavolcanics of basaltic to latibasaltic composition; (b) the Atark unit,
mostly consisting of massive carbonate rocks of Mesozoic age; and (c) the Wakhan slates which consist of a thick widespread
succession of dark slates, metasiltites and sandstones. The fine-grained elastic rocks are supposed to be Palaeozoic to Early
Triassic in age. The Wakhan slates are intruded by plutons belonging to the East Hindu Kush batholith, from which a single
K/Ar age on muscovite gave a Jurassic age. 相似文献
150.
S. J. Gibowicz Carlo Denis Manfred Koch Chen Yong Michael Manga Tapan Mukerji Gary Mavko W. Bielski Maria Jeleńska Frazer Tabeart Lucia Lovison-Golob Peter Ketelaar Douglas J. Galpin Carlo Denis M. Ghil C. L. Keppenne Tracey K. Tromp Louis François Zbigniew Sorbjan 《Pure and Applied Geophysics》1995,145(2):363-398