全文获取类型
收费全文 | 517篇 |
免费 | 28篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 13篇 |
地球物理 | 184篇 |
地质学 | 179篇 |
海洋学 | 38篇 |
天文学 | 90篇 |
综合类 | 2篇 |
自然地理 | 23篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 25篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 17篇 |
2014年 | 22篇 |
2013年 | 34篇 |
2012年 | 21篇 |
2011年 | 30篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 35篇 |
2007年 | 30篇 |
2006年 | 15篇 |
2005年 | 21篇 |
2004年 | 22篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1985年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1963年 | 3篇 |
1961年 | 1篇 |
1953年 | 1篇 |
1950年 | 1篇 |
1940年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有547条查询结果,搜索用时 15 毫秒
101.
Paola Bordoni John Haines Giuliano Milana Sandro Marcucci Fabrizio Cara Giuseppe Di Giulio 《Bulletin of Earthquake Engineering》2011,9(3):761-781
This is the first part of a study on the seismic response of the L’Aquila city using 2D simulation and experimental data.
We have studied two velocity-depth models with the aim of outlining the behavior of a velocity reversal in the top layer,
which is associated with the stiff Brecce de L’Aquila unit (BrA). In this setting, the SMTH model is topped by a layer with
about 2:1 impedance contrast with the underlying layer while the NORV model has no velocity reversal. We have simulated the
propagation of SH and P-SV wavefields in the range 0–10 Hz for incidence 0°–90°. Earthquake spectral ratios of the horizontal
and vertical components at six sites in L’Aquila downtown are compared to corresponding synthetics spectral ratios. The vertical
component of P-SV synthetics enables us to investigate a remarkable amplification effect seen in the vertical component of
the recorded strong motion. Sites AQ04 and AQ05 are best matched by synthetics from the NORV model while FAQ5 and AQ06 have
a better match with synthetics spectral ratios from the SMTH model. All simulations show this behavior systematically, with
horizontal and near-horizontal incident waves predicting the overall pattern of matches more clearly than vertical and near-vertical
incidence. The model inferences are in agreement with new geological data reporting lateral passages in the top layer from
the stiff BrA to softer sediments. Matches are good in terms of frequency of the first amplification peak and of spectral
amplitude: the horizontal components have spectral ratio peaks predominantly at 0.5 Hz in the simulations and at 0.7 Hz in
the data, both with amplitudes of 4, while the vertical component spectral ratios reach values of 6 at frequencies of about
1 Hz in both data and simulations. The vertical component spectral ratios are very well matched using Rayleigh waves with
incidence at 90°. The NORV model without the velocity reversal predicts spectral ratio peaks for the horizontal components
at frequencies up to 6 Hz. The reversal of velocity acts as a low-pass frequency filter on the horizontal components reducing
the amplification effect of the sediment filled valley. 相似文献
102.
Donatello Cardone Giuseppe Gesualdi Domenico Nigro 《Bulletin of Earthquake Engineering》2011,9(4):1227-1255
The mechanical properties of elastomers can change significantly due to air temperature variations. In particular, prolonged
exposure to subzero temperatures can result in rubber crystallization, with a considerable increase in the shear stiffness
of the material. As a result, the seismic response of structures with elastomeric isolators can be strongly influenced by
air temperature. Current seismic codes, indeed, require an upper and lower bound analysis, using suitable modification factors,
to account for the changes in the cyclic behavior of elastomeric isolators due to air temperature variations. In this study,
the sensitivity of the cyclic behavior of elastomeric isolators to air temperature variations is investigated based on the
experimental results of an extensive test program on six different elastomeric compounds for seismic isolators, characterized
by a shear modulus ranging from 0.5 to 1.2 MPa at 100% shear strain and 20°C. The cyclic tests have been performed on small-size
specimens, subjected to shear strain amplitudes and frequency of loading typical for elastomeric seismic isolators, at seven
different air temperatures, ranging from 40 to −20°C. The effects of rubber crystallization due to prolonged exposure to low-temperatures
have been also investigated. A finite element model for the evaluation of the temperature contour map inside a full-size elastomeric
isolator exposed to low air temperatures has been also developed. In the paper, the experimental outcomes are compared with
the modification factors provided by the current seismic codes to account for the temperature effects on the mechanical properties
of elastomeric isolators. 相似文献
103.
A performance-based adaptive methodology for the seismic evaluation of multi-span simply supported deck bridges 总被引:1,自引:1,他引:0
Donatello Cardone Giuseppe Perrone Salvatore Sofia 《Bulletin of Earthquake Engineering》2011,9(5):1463-1498
A performance-based adaptive methodology for the seismic assessment of highway bridges is proposed. The proposed methodology
is based on an Inverse (I), Adaptive (A) application of the Capacity Spectrum Method (CSM), with the capacity curve of the
bridge derived through a Displacement-based Adaptive Pushover (DAP) analysis. For this reason, the acronym IACSM is used to
identify the proposed methodology. A number of Performance Levels (PLs), for which the seismic vulnerability and seismic risk
of the bridge shall be evaluated, are identified. Each PL is associated to a number of Damage States (DSs) of the critical
members of the bridge (piers, abutments, joints and bearing devices). The IACSM provides the earthquake intensity level (PGA)
corresponding to the attainment of the selected DSs, using over-damped elastic response spectra as demand curves. The seismic
vulnerability of the bridge is described by means of fragility curves, derived based on the PGA values associated to each
DS. The seismic risk of the bridge is evaluated as convolution integral of the product between the fragility curves and the
seismic hazard curve of the bridge site. In this paper, the key aspects and basic assumptions of the proposed methodology
are presented first. The IACSM is then applied to nine existing simply supported deck bridges, characterized by different
types of piers and bearing devices. Finally, the IACSM predictions are compared with the results of nonlinear response time-history
analysis, carried out using a set of seven ground motions scaled to the expected PGA values. 相似文献
104.
The present paper proposes a numerical model to determine horizontal and vertical components of the hydrodynamic forces on a slender submarine pipeline lying at the sea bed and exposed to non-linear waves plus a current. The new model is an extension of the Wake II type model, originally proposed for sinusoidal waves (Soedigdo et al., 1999) and for combined sinusoidal waves and currents (Sabag et al., 2000), to the case of periodic or random waves, even with a superimposed current. The Wake II type model takes into account the wake effects on the kinematic field and the time variation of drag and lift hydrodynamic coefficients. The proposed extension is based on an evolutional analysis carried out for each half period of the free stream horizontal velocity at the pipeline. An analytical expression of the wake velocity is developed starting from the Navier–Stokes and the boundary layer equations. The time variation of the drag and lift hydrodynamic coefficients is obtained using a Gaussian integration of the start-up function. A reduced scale laboratory investigation in a large wave flume has been conducted in order to calibrate the empirical parameters involved in the proposed model. Different wave and current conditions have been considered and measurements of free stream horizontal velocities and dynamic pressures on a bottom-mounted pipeline have been conducted. The comparison between experimental and numerical hydrodynamic forces shows the accuracy of the new model in evaluating the time variation of peaks and phase shifts of the horizontal and vertical wave and current induced forces. 相似文献
105.
Giuseppe Palladino 《Basin Research》2011,23(5):591-614
The stratigraphical organization of the Pliocene thrust‐top deposits cropping out at the front of the Southern Apennine thrust‐belt has been debated for a long time taking a great importance in the context of the geodynamics of the Central Mediterranean area. During this time, spreading episodes in the Apennine backarc zone alternate with important phases of overthrusting in the thrust‐belt. As a consequence, the Pliocene succession appears to be arranged in a series of stacked units, recording the poliphase tectonic history that leads to the building of the front of the southern Apennine thrust‐belt. Although there is not yet an accordance on the nature and position of the main unconformities bounding the thrust‐top units, all authors agree that the creation of new accommodation space is mainly ruled by contractional tectonics consequent to the eastward nappe propagation according to the Apennine vergence polarity. A detailed geological survey, carried out along a large portion of southern Apennine thrust‐belt front, running south of the Vulture volcano, allowed the collecting of new data concerning the basinal‐formation mechanisms acting during the sedimentation of Pliocene deposits. From this analysis, it is clear that even if contractional tectonics is the predominant factor controlling the creation or destruction of accommodation space, other mechanisms, as well as wedge uplift‐related extensional tectonics and eustasy, could have also played a significant role in the basin accommodation. In order the considered sector of southern Apennines can provide an useful example about the complex phenomena occurring at mountain belt front where the accommodation space results from a concomitance of eustatic and tectonic factors mainly linked to the accretionary wedge activity. 相似文献
106.
André C. Colonese Giovanni Zanchetta Catherine Perlès Russell N. Drysdale Giuseppe Manganelli Ilaria Baneschi Elissavet Dotsika Hélène Valladas 《Quaternary Research》2013
This paper investigates the stable isotopic composition from late Pleistocene–Holocene (~ 13 to ~ 10.5 cal ka BP) shells of the land snail Helix figulina, from Franchthi Cave (Greece). It explores the palaeoclimatic and palaeoenvironmental implications of the isotope palaeoecology of archaeological shells at the time of human occupation of the cave. Modern shells from around the cave were also analysed and their isotopic signatures compared with those of the archaeological shells. The carbon isotope composition of modern shells depicts the consumption of C3 vegetation. Shell oxygen isotopic values are consistent with other Mediterranean snail shells from coastal areas. Combining empirical linear regression and an evaporative model, the δ18Os suggest that modern snails in the study area are active during periods of higher relative humidity and lower rainfall δ18O, probably at night. Late glacial and early Holocene δ18Os show lower values compared to modern ones. Early Holocene δ18Os values likely track enhanced moisture and isotopic changes in the precipitation source. By contrast, lower late glacial δ18O could reflect lower temperatures and δ18Op, compared to the present day. Shell carbon isotope values indicate the presence of C3 vegetation as main source of carbon to late glacial and early Holocene snails. 相似文献
107.
Geomechanical Evaluation of Derinkuyu Antique Underground City and its Implications in Geoengineering 总被引:2,自引:2,他引:0
Derinkuyu Underground City, located in the Cappadocia Region of Turkey, is an important structure not only for its antique and archaeological characteristics, but also as a structure in terms of the long-term stability of underground rock structures excavated by mankind. The authors carried out some observational, experimental and theoretical rock mechanics studies in the region from 1996 in the context of a research project supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan for the assessment of the long-term behaviour of Derinkuyu Underground City, and these studies are still continuing. In addition to the monitoring of the environmental conditions such as temperature, moisture and air pressure, they also installed acoustic emission (AE) and electrical potential (EP) measurement systems to monitor the behaviour and response of the surrounding rock at the fifth and seventh floors of the underground city. In this article, the geology, seismicity and state of stress of the Cappadocia Region, climatic conditions in the underground city and its vicinity, short- and long-term behaviours of the surrounding rock, its index and mechanical properties, and effects of water content and freezing–thawing processes were investigated. The stability of Derinkuyu Underground City was also evaluated using theoretical and numerical methods, and the results were presented. Furthermore, its implications in modern geoengineering are also discussed. 相似文献
108.
Ernst-Jan Buis Marco Beijersbergen Giuseppe Vacanti Marcos Bavdaz David Lumb 《Experimental Astronomy》2005,20(1-3):105-113
If sensitive enough, future missions for nuclear astrophysics will be a great help in understanding supernovae explosions. In contrast to coded-mask instruments, both crystal diffraction lenses and grazing angle mirrors offer a possibility to construct a sensitive instrument to detect γ-ray lines in supernovae. We report on possible implementations of grazing angle mirrors and simulations carried out to determine their performance. 相似文献
109.
Giuseppe Nunnari Giuseppe Puglisi Alessandro Spata 《Pure and Applied Geophysics》2008,165(8):1619-1641
In this paper we describe a warning system based on statistical analysis for the purpose of monitoring ground deformation
at the Sciara del Fuoco (Stromboli Volcano, Sicily). After a statistical analysis of ground deformation time-series measured
at Stromboli by the monitoring system known as THEODOROS (THEOdolite and Distancemeter Robot Observatory of Stromboli), the
paper describes the solution adopted for implementing the warning system. A robust statistical index has been defined in order
to evaluate the movements of the area. A fuzzy approach has been proposed to evaluate an AI (Alarm Intensity) index which
indicates the level of hazard of the Sciara del Fuoco sliding. 相似文献
110.
Fabio Scarciglia Rosanna De Rosa Giuseppe Vecchio Carmine Apollaro Gaetano Robustelli Filippo Terrasi 《Journal of Volcanology and Geothermal Research》2008
This paper focuses on the main morphological, physical, chemical and mineralogical features of an andic-like soil, widely outcropping in the Sila upland plateau of Calabria (southern Italy), and its potential role in tephrostratigraphy. A multidisciplinary and multiscale approach allowed identification of this soil as a “masked” distal archive of volcanic products, developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis. The study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence, limited extent or poor preservation of primary eruptive products. The soil has an Andisol-like appearance, despite laboratory data that do not match the entire suite of diagnostic criteria for the Andisol taxonomic order. Geomorphological, stratigraphic and pedologic results, coupled with tephrostratigraphic and radiometric data, concur to suggest a Late Pleistocene(?) to Holocene age of the Andisol-like soil. In particular, the rhyolitic chemical composition of small-sized glass fragments (identified by SEM–EDS analyses) indicates soil genesis contributed by volcanic ash, probably sourced from Aeolian Arc explosive activity spanning the last 30 ka. Accordingly, the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties (in turn related to the neoformation of clay minerals from the weathering of volcanic glass) are consistent with a climatic shift from a seasonally-contrasted to a constantly humid pedoenvironment. This change can be ascribed to the Lateglacial(?) or Early–Middle Holocene to Late Holocene transition. Calibrated AMS 14C dates performed on charcoal fragments sampled from three representative soil profiles, provide Late Holocene ages (3136 ± 19, 343 ± 16 and 92 ± 24 yr BP), in accord with archaeological finds. On the basis of the consistent stratigraphic position, lateral continuity and wide extent, the soil can be considered a good pedostratigraphic marker in the Sila highlands and is informally defined as the “Cecita Lake geosol”. It supplies valuable time constraints for the underlying (occasionally overlying) deposits and/or soils. Moreover, it allows regional-scale morphostratigraphic correlations and detailed reconstruction of Late Pleistocene–Holocene geomorphic events in Calabria, a very suitable region for distal tephra deposition in the central Mediterranean peri-volcanic area. The effects of high-energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals. 相似文献