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排序方式: 共有626条查询结果,搜索用时 15 毫秒
611.
Francesco Panzera Sebastiano D’Amico Giuseppe Lombardo Emanuela Longo 《Journal of Seismology》2016,20(3):1001-1019
The Siracusa area, located in the southeastern coast of Sicily (Italy), is mainly characterized by the outcropping of a limestone formation. This lithotype, which is overlain by soft sediments such as sandy clays and detritus, can be considered as the local bedrock. Records of ambient noise, processed through spectral ratio techniques, were used to assess the dynamic properties of a sample survey of both reinforced concrete and masonry buildings. The results show that experimental periods of existing buildings are always lower than those proposed by the European seismic code. This disagreement could be related to the role played by stiff masonry infills, as well as the influence of adjacent buildings, especially in downtown Siracusa. Numerical modeling was also used to study the effect of local geology on the seismic site response of the Siracusa area. Seismic urban scenarios were simulated considering a moderate magnitude earthquake (December 13th, 1990) to assess the shaking level of the different outcropping formations. Spectral acceleration at different periods, peak ground acceleration, and velocity were obtained through a stochastic approach adopting an extended source model code. Seismic ground motion scenario highlighted that amplification mainly occurs in the sedimentary deposits that are widespread to the south of the study area as well as on some spot areas where coarse detritus and sandy clay outcrop. On the other hand, the level of shaking appears moderate in all zones with outcropping limestone and volcanics. 相似文献
612.
613.
Lorenza Evangelista Luigi Landolfi Anna d’Onofrio Francesco Silvestri 《Bulletin of Earthquake Engineering》2016,14(12):3363-3387
During the Abruzzo earthquake (6.IV.2009, MW = 6.3), the village of Castelnuovo, lying on an elliptical hill about 60 m high, underwent an intensive damage (IMCS = 9–10), that could be partly ascribed to the topographic amplification and to the presence of an underground cavity network. To verify these hypotheses, the seismic response of the hill was carefully investigated adopting both 2D and 3D finite difference numerical models. Analyses were carried out using a detailed geotechnical model, defined on the basis of a comprehensive field investigation (boreholes, DH, HVSR, ERT) and accurate laboratory tests (RC-TS). The reference input motion was reproduced considering the time history of the mainshock recorded at an accelerometric station close to the epicenter, conveniently deconvoluted to the bedrock and scaled in amplitude to the site of Castelnuovo. The results of the numerical analyses, expressed in terms of distribution of the amplification factor of peak acceleration and Housner intensity, proved that the topographic effects significantly influenced the ground motion at surface, whereas the role of cavities seemed to be negligible. 相似文献
614.
Enzo Martinelli Francesco Perri Carmen Sguazzo Ciro Faella 《Bulletin of Earthquake Engineering》2016,14(6):1695-1720
This work reports the results of an experimental programme aimed at investigating the in-plane behaviour of clay-brick masonry walls externally strengthened by carbon fiber reinforced polymer (CFRP) strips. Particularly, four different geometrical layouts were considered for the CFRP strips, though keeping unchanged the quantity of composites employed in each wall. Firstly, a preliminary experimental work was carried out on samples of the constitutive materials for quantifying their key mechanical properties and evaluating the bond behaviour of FRP strips on the masonry substrates. Then, eleven cyclic shear-compression tests were performed to observe the response of strengthened walls and the influence of the strengthening layouts under investigation. The proposed experimental report is intended as a contribution to the current state of knowledge about the behaviour of FRP-strengthened masonry walls: it is available to assess the accuracy and possibly improve the predictive capacity of design-oriented capacity models. Finally, the comparison of the reported experimental results with the predictions obtained by applying the analytical relationships proposed by a recently issued guideline for FRP strengthening of masonry structures is proposed. 相似文献
615.
A Revised Earthquake Catalogue for South Iceland 总被引:1,自引:0,他引:1
616.
An integrated approach for investigating geomorphic response to extreme events: methodological framework and application to the October 2011 flood in the Magra River catchment,Italy 下载免费PDF全文
Massimo Rinaldi William Amponsah Marco Benvenuti Marco Borga Francesco Comiti Ana Lucía Lorenzo Marchi Laura Nardi Margherita Righini Nicola Surian 《地球表面变化过程与地形》2016,41(6):835-846
A high‐magnitude flash flood, which took place on 25 October 2011 in the Magra River catchment (1717 km2), central‐northern Italy, is used to illustrate some aspects of the geomorphic response to the flood. An overall methodological framework is described for using interlinked observations and analyses of the geomorphic impacts of an extreme event. The following methods and analyses were carried out: (i) hydrological and hydraulic analysis of the event; (ii) sediment delivery by event landslide mapping; (iii) identification and estimation of wood recruitment, deposition, and budgeting; (iv) interpretation of morphological processes by analysing fluvial deposits; (v) remote sensing and geographic information system (GIS) analysis of channel width changes. In response to the high‐magnitude hydrological event, a large number of landslides occurred, consisting of earth flows, soil slips, and translational slides, and a large quantity of wood was recruited, in most part deriving from floodplain erosion caused by bank retreat and channel widening. The most important impact of the flood event within the valley floor was an impressive widening of the overall channel bed and the reactivation of wide portions of the pre‐event floodplain. Along the investigated (unconfined or partly confined) streams (total investigated length of 93.5 km), the channel width after the flood was up to about 20 times the channel width before the event. The study has shown that a synergic use of different methods and types of evidence provides fundamental information for characterizing and understanding the geomorphic effects of intense flood events. The prediction of geomorphic response to a flood event is still challenging and many limitations exist; however a robust geomorphological analysis can contribute to the identification of the most critical reaches. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
617.
Francesco G. Carollo Costanza Di Stefano Vito Ferro Vincenzo Pampalone Francesco Sanzone 《地球表面变化过程与地形》2016,41(7):867-874
In order to measure soil loss in equipped plots the estimate of the weight of solid material intercepted at their lower end is required. At the experimental area of Sparacia, Sicily, the runoff produced by an erosive event is collected within storage tanks with a capacity of about 1 m3. In this paper, the use of a new sampler is proposed to measure easily the weight of solid material eroded from an experimental plot and collected into a storage tank. The sampler is a cylinder having a closing valve at the bottom. Two different series of runs were carried out both to test the reliability of the sampler and to establish a sampling procedure, respectively. An analysis of various sampling configurations usable in the field differentiated by the number and location of sampling verticals in the tank cross‐section was finally carried out. The results of the present investigation are that the concentration measurement by the sampler was more accurate than that obtained by other methods involving a collection tank, agitation and sampling of the suspension. This sampler is cheap and usable in combination with a quick field sampling procedure which is particularly advisable when the number of plots equipped at an experimental area is large. The sampler was tested using a clay soil contained within cylinders and a cubic tank, but it appeared also to be usable with coarser sediment than clay and in combination with tanks having a different shape. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
618.
Curvature analysis as a tool for subsidence-related risk zones identification in the city of Tuzla (BiH) 总被引:1,自引:0,他引:1
Shallow Miocene salt deposits located below the city of Tuzla (BiH) have been exploited during the last 60 years by means of wells extracting salt-saturated groundwater brines. The massive extraction activities have led to severe subsidence accommodated by collapse and strain localization. Surface topography and geomorphology have been influenced and modified by several faults and fractures.A series of sequential topographical survey data collected during the last 50 years have been used to obtain the total subsidence envelope surface. In order to analyze the salt dissolution-related morphological development of the Tuzla topography and to identify the location of faults and fractures in the deformed area, we applied curvature analysis to the subsidence surface by means of two different analytical methods: the directional, two-dimensional curvature and the analytic Gaussian curvature. The comparison of the curvature maps with those of surface fractures visible in the area shows a good spatial agreement between the directional curvature and fracture intensity, whereas the subsurface normal faults are more evident in the Gaussian curvature maps. 相似文献
619.
Andrew J. L. Harris Massimiliano Favalli Francesco Mazzarini Christopher W. Hamilton 《Bulletin of Volcanology》2009,71(4):459-474
We use a kinematic GPS and laser range finder survey of a 200 m-long section of the Muliwai a Pele lava channel (Mauna Ulu,
Kilauea) to examine the construction processes and flow dynamics responsible for the channel–levee structure. The levees comprise
three packages. The basal package comprises an 80–150 m wide ′a′a flow in which a ∼2 m deep and ∼11 m wide channel became
centred. This is capped by a second package of thin (<45 cm thick) sheets of pahoehoe extending no more than 50 m from the
channel. The upper-most package comprises localised ′a′a overflows. The channel itself contains two blockages located 130 m
apart and composed of levee chunks veneered with overflow lava. The channel was emplaced over 50 h, spanning 30 May–2 June,
1974, with the flow front arriving at our section (4.4 km from the vent) 8 h after the eruption began. The basal ′a′a flow
thickness yields effusion rates of 35 m3 s−1 for the opening phase, with the initial flow advancing across the mapped section at ∼10 m/min. Short-lived overflows of fluid
pahoehoe then built the levee cap, increasing the apparent channel depth to 4.8 m. There were at least six pulses at 90–420 m3 s−1, causing overflow of limited extent lasting no more than 5 min. Brim-full flow conditions were thus extremely short-lived.
During a dominant period of below-bank flow, flow depth was ∼2 m with an effusion rate of ∼35 m3 s−1, consistent with the mean output rate (obtained from the total flow bulk volume) of 23–54 m3 s−1. During pulses, levee chunks were plucked and floated down channel to form blockages. In a final low effusion rate phase,
lava ponded behind the lower blockage to form a syn-channel pond that fed ′a′a overflow. After the end of the eruption the
roofed-over pond continued to drain through the lower blockage, causing the roof to founder. Drainage emplaced inflated flows
on the channel floor below the lower blockage for a further ∼10 h. The complex processes involved in levee–channel construction
of this short-lived case show that care must be taken when using channel dimensions to infer flow dynamics. In our case, the
full channel depth is not exposed. Instead the channel floor morphology reflects late stage pond filling and drainage rather
than true channel-contained flow. Components of the compound levee relate to different flow regimes operating at different
times during the eruption and associated with different effusion rates, flow dynamics and time scales. For example, although
high effusion rate, brim-full flow was maintained for a small fraction of the channel lifetime, it emplaced a pile of pahoehoe
overflow units that account for 60% of the total levee height. We show how time-varying volume flux is an important parameter
in controlling channel construction dynamics. Because the complex history of lava delivery to a channel system is recorded
by the final channel morphology, time-varying flow dynamics can be determined from the channel morphology. Developing methods
for quantifying detailed flux histories for effusive events from the evidence in outcrop is therefore highly valuable. We
here achieve this by using high-resolution spatial data for a channel system at Kilauea. This study not only indicates those
physical and dynamic characteristics that are typical for basaltic lava flows on Hawaiian volcanoes, but also a methodology
that can be widely applied to effusive basaltic eruptions. 相似文献
620.
Morpho-structural setting of Stromboli volcano revealed by high-resolution bathymetry and backscatter data of its submarine portions 总被引:1,自引:0,他引:1
Alessandro Bosman Francesco L. Chiocci Claudia Romagnoli 《Bulletin of Volcanology》2009,71(9):1007-1019
The first high-resolution bathymetric and backscatter maps of offshore Stromboli Island are presented, together with an interpretation
of its volcanic, structural and sedimentary features. The volcanic edifice is characterized by a sub-conical shape with a
quasi-bilateral symmetry with respect to a NE-SW axis. The dimensions of the Strombolicchio volcanic centre, to the NE of
Stromboli, have been restored by redrawing its morphology before wave action that eroded it in Late Quaternary time. On the
NE submarine flank of Strombolicchio, a N64°E structural trend controls the shape of Strombolicchio Canyon. On the southern
side of Stromboli, the submarine flank has a radial structural trend, possibly reflecting a volcanic stress regime. Landslide
scars at various scales are ubiquitous on the submarine slopes of Stromboli. Repeated large-scale lateral collapses have affected
both the northwestern and southeastern unbuttressed flanks of the volcano, producing large debris avalanche deposits. 相似文献