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741.
742.
This article points out some particular features conditioning seismic hazard assessments (SHA) in Spain, a region with low–moderate
seismicity. Although sized earthquakes occurred in the past, as evidenced by historical documents and neotectonic studies,
no large events occurred during the last decades. The absence of strong motion records corresponding to earthquakes with magnitude
larger than 5.5 is an important obstacle for the development of ground motion models constrained by local data, with the consequent
difficulty in SHA studies. In this paper, some recent developments aiming at providing solutions to these difficulties are
presented. Specifically, a strong motion databank containing a massive collection of accelerograms and response spectra from
different configurations source-path-site corresponding to earthquakes all over the world is introduced, together with software
utilities for its management. A first application of this databank is the development of specific ground motion models for
Spain and for the Mediterranean region that predict peak ground accelerations as a function of several definitions of magnitude,
distance and soil class. The predictive power of these ground motion models is tested by contrasting their estimates with
recently recorded ground motions. The comparison between our ground-motion models with others proposed in the literature for
other areas reveals a regular overestimation of the expected ground motions at Spanish sites by the non-local models. Consequently,
SHA studies based in external models may overestimate the predicted hazard at the Iberian sites. In the last part of the paper
a method for checking whether the response spectra proposed in the Spanish Building Code (NCSE-02) are consistent with actual
accelerometric data from recent low magnitude earthquakes is applied. The spectral shapes of the Spanish Building Code NCSE-02
are compared with the response spectral shapes deduced from the available accelerograms by normalising the response spectra
with the recorded PGA. It is appreciated that the NCSE-02 spectral shapes are exceeded by a large number of actual spectral
shapes for short periods (around 0.2 s), a result to be taken into account in further revisions of the NCSE-02 code. The issues
tackled in this work constitute not only an improvement for ground-motion characterisation in Spain, but also provide guidelines
of general interest for potential applications in other regions with similar seismicity. 相似文献
743.
本文将常规双平方根(DSR)单程波动方程从深度域变换到双程垂直走时(τ)域,由此推导出可从数学上实现“沉降观测”的单程波DSR传播算子. 其递归波场延拓算法包含波数域针对常速背景的相移处理和空间域针对横向速度扰动的相位校正,可以应对上覆地层速度横向变化对构造成像的影响. 结合零炮检距、零时间成像条件,提出了在τ域进行波场延拓与成像的DSR方程叠前偏移新方法. 为了克服其全三维偏移算法在实际应用中可能面临的困难,本文采用稳相近似,在crossline常炮检距偏移理论基础上推导了实用的共方位角叠前τ偏移方法. 数值试验表明,DSR方程叠前τ偏移在强横向非均匀介质中的成像精度与分辨率优于传统的时间域成像技术. 相似文献
744.
We consider the advantages of a formalism based on concept of the asymmetric continuum and we present some equivalence theorems
relating it to the asymmetric elasticity and to micropolar and micromorphic theories as founded by Nowacki, Cosserats and
Eringen.
We consider the basic processes in an asymmetric continuum which could be reduced to the point basic motions/deformations.
The co-action of spin and shear motions is assumed to play the main role in fracturing process, while the constitutive relation
between the antisymmetric stresses and rotations replaces the friction constitutive law. 相似文献
745.
The Khanaser Valley was geoelectrically thoroughly surveyed through a grid which consisted of twelve VES profiles. The tectonically-oriented
Pichgin and Habibullaev method was enhanced to be applicable in areas of rugged relief and topography. The enhanced profiles
were tectonically interpreted and subsurface structures within the Khanaser Valley were delineated. Accordingly, a tectonic
evolutional scenario of the valley was established and its hydrogeological characteristics were derived. An approach for groundwater
exploration in areas of prominent relief and topography in dry areas such as the Khanaser Valley was established and its validity
was estimated. 相似文献
746.
John Douglas 《Bulletin of Earthquake Engineering》2007,5(3):363-376
Accurate estimates of the ground motions that occurred during damaging earthquakes are a vital part of many aspects of earthquake
engineering, such as the study of the size and cause of the uncertainties within earthquake risk assessments. This article
compares a number of methods to estimate the ground shaking that occurred on Guadeloupe (French Antilles) during the 21st
November 2004 (M
w
6.3) Les Saintes earthquake, with the aim of providing more accurate shaking estimates for the investigation of the sources
of uncertainties within loss evaluations, based on damage data from this event. The various techniques make differing use
of the available ground-motion recordings of this earthquake and by consequence the estimates obtained by the different approaches
are associated with differing uncertainties. Ground motions on the French Antilles are affected by strong local site effects,
which have been extensively investigated in previous studies. In this article, use is made of these studies in order to improve
the shaking estimates. It is shown that the simple methods neglecting the spatial correlation of earthquake shaking lead to
uncertainties similar to those predicted by empirical ground-motion models and that these are uniform across the whole of
Guadeloupe. In contrast, methods (such as the ShakeMap approach) that take account of the spatial correlation in motions demonstrate
that shaking within roughly 10 km of a recording station (covering a significant portion of the investigated area) can be
defined with reasonable accuracy but that motions at more distant points are not well constrained. 相似文献
747.
The purpose of this study is to quantify the dispersivity in the longitudinal direction by upscaling pore scale mixing over a network domain and to verify the dispersivity with that obtained through the more rigorous upscaling technique, the Brownian particle tracking model (BPTM). We model a porous medium with a network of pore-units that are comprised of pore bodies and bonds of finite volume. Such a pore-unit is assumed to be a mixing cell with the steady state flow condition for a single fluid. Dispersivity can be obtained by solving the mixing cell model (MCM) for the concentration in each pore-unit and by averaging the concentrations for a large number of pore units (as a function of time and space). A minimal size of network that ascertains an asymptotic value of dispersivity was determined and verified with large size pore networks. This numerically computed dispersivity is compared with the results from the BPTM for the same porous medium and flow conditions. We show that the dispersivity obtained from the MCM is equally reliable for the heterogeneous pore-networks and can be estimated as a function of pore size heterogeneity. For homogeneous networks with the MCM, the iteration time step plays an important role. On the other hand, for networks with the BPTM, the assumption of intra-bond velocity profile affects the results. 相似文献
748.
This paper presents a new way of selecting real input ground motions for seismic design and analysis of structures based on a comprehensive method for estimating the damage potential of ground motions, which takes into consideration of various ground motion parameters and structural seismic damage criteria in terms of strength, deformation, hysteretic energy and dual damage of Park & Ang damage index. The proposed comprehensive method fully involves the effects of the intensity, frequency content and duration of ground motions and the dynamic characteristics of structures. Then, the concept of the most unfavourable real seismic design ground motion is introduced. Based on the concept, the most unfavourable real seismic design ground motions for rock, stiff soil, medium soil and soft soil site conditions are selected in terms of three typical period ranges of structures. The selected real strong motion records are suitable for seismic analysis of important structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake, as they can cause the greatest damage to structures and thereby result in the highest damage potential from an extended real ground motion database for a given site. In addition, this paper also presents the real input design ground motions with medium damage potential, which can be used for the seismic analysis of structures located at the area with low and moderate seismicity. The most unfavourable real seismic design ground motions are verified by analysing the seismic response of structures. It is concluded that the most unfavourable real seismic design ground motion approach can select the real ground motions that can result in the highest damage potential for a given structure and site condition, and the real ground motions can be mainly used for structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
749.
Analysis of the weightiness of site effects on reinforced concrete (RC) building seismic behaviour: The Adra town example (SE Spain) 总被引:1,自引:0,他引:1
Manuel Navarro Francisco Vidal Takahisa Enomoto Francisco J. Alcalá Antonio García‐Jerez Francisco J. Sánchez Norio Abeki 《地震工程与结构动力学》2007,36(10):1363-1383
The damage distribution in Adra town (south‐eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south‐east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short‐period microtremor observations were performed in 160 sites on a 100m × 100m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1–0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N, where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1‐D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
750.
Real‐time pseudodynamic (PSD) testing is an experimental technique for evaluating the dynamic behaviour of a complex structure. During the test, when the targeted command displacements are not achieved by the test structure, or a delay in the measured restoring forces from the test structure exists, the reliability of the testing method is impaired. The stability and accuracy of real‐time PSD testing in the presence of amplitude error and a time delay in the restoring force is presented. Systems consisting of an elastic single degree of freedom (SDOF) structure with load‐rate independent and dependent restoring forces are considered. Bode plots are used to assess the effects of amplitude error and a time delay on the steady‐state accuracy of the system. A method called the pseudodelay technique is used to derive the exact solution to the delay differential equation for the critical time delay that causes instability of the system. The solution is expressed in terms of the test structure parameters (mass, damping, stiffness). An error in the restoring force amplitude is shown to degrade the accuracy of a real‐time PSD test but not destabilize the system, while a time delay can lead to instability. Example calculations are performed for determining the critical time delay, and numerical simulations with both a constant delay and variable delay in the restoring force are shown to agree well with the stability limit for the system based on the critical time delay solution. The simulation models are also used to investigate the effects of a time delay in the PSD test of an inelastic SDOF system. The effect of energy dissipation in an inelastic structure increases the limit for the critical time delay, due to the energy removed from the system by the energy dissipation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献