全文获取类型
收费全文 | 194篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 7篇 |
地球物理 | 95篇 |
地质学 | 48篇 |
海洋学 | 15篇 |
天文学 | 39篇 |
自然地理 | 4篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 3篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 19篇 |
2012年 | 11篇 |
2011年 | 16篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2005年 | 8篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1983年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有217条查询结果,搜索用时 0 毫秒
31.
Tunnels are believed to be rather “insensitive” to earthquakes. Although a number of case histories seem to favor such an argument, failures and collapses of underground
structures in the earthquakes of Kobe (1995), Düzce–Bolu (1999), and Taiwan (1999) have shown that there are exceptions to
this “rule”. Among them: the case of tunnels crossed by fault rupture. This paper presents the analysis and design of two highway cut-and-cover
tunnels in Greece against large tectonic dislocation from a normal fault. The analysis, conducted with finite elements, places
particular emphasis on realistically modeling the tunnel-soil interface. Soil behavior is modeled thorough an elastoplastic
constitutive model with isotropic strain softening, which has been extensively validated through successful predictions of
centrifuge model tests. A primary conclusion emerging from the paper is that the design of cut-and-cover structures against
large tectonic deformation is quite feasible. It is shown that the rupture path is strongly affected by the presence of the
tunnel, leading to development of beneficial stress-relieving phenomena such as diversion, bifurcation, and diffusion. The
tunnel may be subjected either to hogging deformation when the rupture emerges close to its hanging-wall edge, or to sagging deformation when the rupture is near its footwall edge. Paradoxically, the maximum stressing is not always attained with
the maximum imposed dislocation. Therefore, the design should be performed on the basis of design envelopes of the internal
forces, with respect to the location of the fault rupture and the magnitude of dislocation. Although this study was prompted by the needs of a specific project, the method of analysis,
the design concepts, and many of the conclusions are sufficiently general to merit wider application. 相似文献
32.
Ioannis K. Georgiadis Antonios Koroneos Ananias Tsirambides Michael Stamatakis 《Central European Journal of Geosciences》2012,4(3):465-477
Modern sand samples were collected from the Vertiskos Unit of the Serbomacedonian Massif, northern Greece, and were examined for their texture and mineralogical composition. They were collected from active channels and torrents. The textural study demonstrated that these modern sands are moderately to very-poorly sorted, often polymodal in grain size distribution, texturally and mineralogically immature to submature, and consist of coarse-grained gravelly sands to slightly-gravelly muddy sands. The dominant composition is quartzofeldspathic. All samples contain detrital minerals of metamorphic origin, mainly amphibole and garnet, in addition to minor amounts of pyroxene and detrital calcite. These sediments were deposited rapidly and close to their source, the metamorphic basement of the Vertiskos Unit. The mineral constituents of the samples indicate that the Vertiskos Unit is undergoing rapid physical weathering due to the temperate and seasonal climate. The results of this study suggest that these modern sands constitute one sedimentary petrologic province comprised of primarily of amphibole-garnet. 相似文献
33.
Francesco Marazzi Ioannis Politopoulos Alberto Pavese 《Bulletin of Earthquake Engineering》2011,9(2):623-640
This paper presents a synthesis of the activities carried out in the framework of the European project EFAST (design study
of a European Facility for Advanced Seismic Testing) to determine the general characteristics of a new European world-class
facility for earthquake testing of structures. To this end the demands for the necessary testing to support the modern seismic
engineering research have been investigated and compared to the actual capabilities of European laboratories. The outcome
is the determination of performance objectives and requirements in the gross. On the basis of the needs assessment carried
out during the first phase of the project and taking into account the technological advances in both experimental techniques
and equipment (hardware and software) for seismic testing, a modern facility for experimental seismic research should be composed,
mainly, of a high performance shaking tables array and a large reaction structure where both traditional (pseudo-static/dynamic)
and innovative testing techniques (e.g. real time hybrid testing) can be applied and combined. A tentative layout of the facility
is also proposed and issues related to the best utilization of such a laboratory are discussed. 相似文献
34.
Large volume semi-submersible units may present significant wave induced resonant motions in heave, roll and pitch. Evaluating the slow motions of such systems is important from the initial stages of their designs and therefore requires a model that is both accurate and expedite enough. In the present article, different options for modeling the second-order hydrodynamic forces and induced motions are discussed using as a case-study the PETROBRAS 52 unit—P-52. Computations of the low frequency forces are performed in the frequency domain by means of a commercial Boundary Element Method (BEM) code. Different hydrodynamic approximations are tested and evaluated by directly comparing the predicted responses with those measured in small-scale tests performed in a wave-basin. From the results obtained in theses comparisons, a methodology based on a white-noise approach of the force spectrum is proposed. The validity of such approximation is attributable to the typically low damping levels in heave, roll and pitch motions. Furthermore, results also indicate that the second order forces may be calculated disregarding the free-surface forcing components, an option that helps to reduce the computational burden even more, rendering the procedure suitable for preliminary design calculations. 相似文献
35.
We study the motion of a secondary celestial body under the influence of the logarithmic corrected gravitational force of a primary one. This kind of correction was introduced by Fabris and Campos (Gen. Relativ. Gravit. 41(1):93, 2009). We derive two equations to compute the rate of change of the anomalistic period with respect to the eccentric anomaly and its total variation over one revolution. In a kinematical sense, this influence produces an apsidal motion. We perform numerical estimations for some celestial bodies. We also compare our results to those obtained by considering a Yukawa correction. 相似文献
36.
Behaviour of deep immersed tunnel under combined normal fault rupture deformation and subsequent seismic shaking 总被引:1,自引:0,他引:1
Ioannis Anastasopoulos Nikos Gerolymos Vasileios Drosos Takis Georgarakos Rallis Kourkoulis George Gazetas 《Bulletin of Earthquake Engineering》2008,6(2):213-239
Immersed tunnels are particularly sensitive to tensile and compressive deformations such as those imposed by a normal seismogenic
fault rupturing underneath, and those generated by the dynamic response due to seismic waves. The paper investigates the response
of a future 70 m deep immersed tunnel to the consecutive action of a major normal fault rupturing in an earthquake occurring
in the basement rock underneath the tunnel, and a subsequent strong excitation from a different large-magnitude seismic event
that may occur years later. Non-linear finite elements model the quasi-static fault rupture propagation through the thick
soil deposit overlying the bedrock and the ensuing interaction of the rupture with the immersed tunnel. It is shown that despite
imposed bedrock offset of 2 m, net tension or excessive compression between tunnel segments could be avoided with a suitable
design of the joint gaskets. Then, the already deformed (“injured”) structure is subjected to strong asynchronous seismic
shaking. The thick-walled tunnel is modelled as a 3-D massive flexural beam connected to the soil through properly-calibrated
nonlinear interaction springs and dashpots, the supports of which are subjected to the free-field acceleration time histories.
The latter, obtained with 1-D wave propagation analysis, are then modified to account for wave passage effects. The joints between tunnel segments are modeled with special non-linear hyper-elastic elements, properly accounting
for their 7-bar longitudinal hydrostatic pre-stressing. Sliding is captured with special gap elements. The effect of segment
length and joint properties is explored parametrically. A fascinating conclusion emerges in all analysed cases for the joints
between segments that were differentially deformed after the quasi-static fault rupture: upon subsequent very strong seismic
shaking, overstressed joints de-compress and understressed joints re-compress—a “healing” process that leads to a more uniform
deformation profile along the tunnel. This is particularly beneficial for the precariously de-compressed joint gaskets. Hence,
the safety of the immersed tunnel improves with “subsequent” strong seismic shaking! 相似文献
37.
Ioannis M. Taflampas Constantine C. SpyrakosIoannis A. Koutromanos 《Soil Dynamics and Earthquake Engineering》2009
This study presents a new definition of the strong motion duration combining the alternative bracketed and significant duration definitions. Based on the time integral of the absolute ground velocity, a new index is defined, as cumulative absolute displacement (CAD), and used to estimate the strong motion duration. The proposed bracketed-significant duration tbs is found to be well correlated with the strong motion part of the records, especially in the case of near-source events. The duration tbs and the CAD index are used to assess the anticipated structural behavior of medium–long period structures. 相似文献
38.
Ioannis F. Moschonas Andreas J. Kappos Panagiotis Panetsos Vissarion Papadopoulos Triantafyllos Makarios Pavlos Thanopoulos 《Bulletin of Earthquake Engineering》2009,7(2):439-468
This study focusses on the estimation of seismic fragility curves for all common bridge types found in modern greek motorways.
At first a classification scheme is developed in order to classify the existing bridges into a sufficient number of classes.
A total of 11 representative bridge classes resulted, based on the type of piers, deck, and pier-to-deck connection. Then
an analytical methodology for deriving fragility curves is proposed and applied to the representative bridge models. This
procedure is based on pushover analysis of the entire bridge and definition of damage states in terms of parameters of the
bridge pushover curves. The procedure differentiates the way of defining damage according to the seismic energy dissipation
mechanism in each bridge, i.e. bridges with yielding piers of the column type and bridges with bearings (with or without seismic
links) and non-yielding piers of the wall type. The activation of the abutment-backfill system due to closure of the gap between
the deck and the abutments is also taken into account. The derived fragility curves are subjected to a first calibration against
empirical curves based on damage data from the US and Japan. 相似文献
39.
Ioannis Rigopoulos Basilios Tsikouras Panagiotis Pomonis Konstantin Hatzipanagiotou 《Rock Mechanics and Rock Engineering》2013,46(5):1061-1072
This paper investigates the influence of the petrographic characteristics of mafic ophiolitic rocks on the initiation and propagation of microcracks during uniaxial compression. The microcrack patterns of a troctolite and a diorite, collected from the Pindos and Othrys ophiolites (Greece), respectively, were analysed. Thorough observation and quantification of microcracks before and after the uniaxial compression test were conducted. Combined fluorescent and polarised microscopy of polished thin sections, together with digital image analysis, indicated that the intragranular microcracks are the dominating crack type in both loaded and unloaded specimens, only in terms of their total number and length. On the other hand, the intergranular and transgranular cracks seem to grow more readily compared to the intragranular cracks, implying that the longer microcracks grow more extensively under stress. The orientation of most of the newly formed intragranular and transgranular microcracks is nearly parallel to the loading direction; however, some of the randomly oriented transgranular cracks have probably been formed during the propagation of intergranular cracks. In the troctolite, the frequency of the intragranular microcracks decreases in the olivine crystals after the uniaxial compression test due to their partial serpentinisation, which increases their resistance to brittle deformation. In the plagioclase crystals of the troctolite, microcracks are often oriented parallel to the cleavage planes, implying that such crystallographic orientations act as planes of weakness. On the contrary, the plagioclase crystals of the diorite are mainly crossed by randomly oriented microcracks, presumably due to their high degree of alteration. In the diorite, the evolution of microcracks is substantially controlled by the two perfect cleavages of amphibole. The failure of a rock occurs as a result of the growth, interaction and coalescence of a great number of pre-existing and newly formed intragranular and transgranular microcracks. The petrographic and microcrack analysis may assist in the selection of the most suitable rock type for various construction applications. 相似文献
40.
Self‐localization is the process of identifying one's current position on a map, and it is a crucial part of any wayfinding process. During self‐localization the wayfinder matches visually perceptible features of the environment, such as landmarks, with map symbols to constrain potential locations on the map. The success of this visual matching process constitutes an important factor for the success of self‐localization. In this research we aim at observing the visual matching process between environment and map during self‐localization with real‐world mobile eye tracking. We report on one orientation and one self‐localization experiment, both in an outdoor urban environment. The gaze data collected during the experiments show that successful participants put significantly more visual attention to those symbols on the map that were helpful in the given situation than unsuccessful participants. A sequence analysis revealed that they also had significantly more switches of visual attention between map symbols and their corresponding landmarks in the environment, which suggests they were following a more effective self‐localization strategy. 相似文献