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991.
The widespread use of sliding bearings for the seismic isolation of structures
requires detailed knowledge of their behavior and improved modeling capability under seismic conditions. The paper summarizes the results of a large experimental investigation on steel–PTFE interfaces, aimed at evaluating the effects of sliding velocity, contact pressure, air temperature and state of lubrication on the mechanical behavior of steel-PTFE sliding bearings. Based on the experimental outcomes, two different mathematical models have been calibrated, which are capable of accounting for the investigated parameters in the evaluation of the sliding friction coefficient. The first model is basically an extension of the model proposed by Constantinou et al. (1990)Journal of Earthquake Engineering, 116(2), 455–472, while the second model is derived from the one proposed by Changet al. (1990)Journal of Engineering Mechanics, 116, 2749–2763. Expressions of the model parameters as a function of bearing pressure and air temperature are presented for lubricated and non-lubricated sliding surfaces. Predicted and experimental results are finally compared. 相似文献
992.
Earthquakes are recognized as resulting from a stick–slip frictional instability along faults. Based on the node‐to‐point contact element strategy (an arbitrarily shaped contact element strategy applied with the static‐explicit algorithm for modelling non‐linear frictional contact problems proposed by authors), a finite element code for modelling the 3‐D non‐linear friction contact between deformable bodies has been developed and extended here to analyse the non‐linear stick–slip frictional instability between deformable rocks with a rate‐ and state‐dependent friction law. A typical fault bend model is taken as an application example to be analysed here. The variations of the normal contact force, the frictional force, the transition of stick–slip instable state and the related relative slip velocity along the fault between the deformable rocks and the stress evolution in the total bodies during the different stages are investigated, respectively. The calculated results demonstrate the usefulness of this code for simulating the non‐linear frictional instability between deformable rocks. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
993.
A new type of energy‐dissipated structural system for existing buildings with story‐increased frames is presented and investigated in this paper. In this system the sliding‐friction layer between the lowest increased floor of the outer frame structure and the roof of the original building is applied, and energy‐dissipated dampers are used for the connections between the columns of the outer frame and each floor of the original building. A shaking table test is performed on the model of the system and the simplified structural model of this system is given. The theory of the non‐classical damping approach is introduced to the calculation analyses and compared with test results. The results show that friction and energy‐dissipated devices are very effective in reducing the seismic response and dissipating the input energy of the model structure. Finally, the design scheme and dynamic time‐history analyses of an existing engineering project are investigated to illustrate the application and advantages of the given method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
994.
The Time-Dependent Reduction of Sliding Cohesion due to Rock Bridges Along Discontinuities: A Fracture Mechanics Approach 总被引:1,自引:3,他引:1
J. Kemeny 《Rock Mechanics and Rock Engineering》2003,36(1):27-38
Summary
In this paper, a fracture mechanics model is developed to illustrate the importance of time-dependence for brittle fractured
rock. In particular a model is developed for the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion
is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics
model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function
of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found
to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value
that results in slope instability. A second example is given where variations in some of the material parameters are assumed.
A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability
of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples
show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for
relatively short-term rock structures.
Received November 5, 2001; accepted July 24, 2002; Published online November 19, 2002 相似文献
995.
西北地区沙尘暴预报方法的初步研究 总被引:12,自引:6,他引:12
沙尘暴是我国西北地区春季常发生的一种灾害性天气现象,也是气象业务预报工作中的一个难点。作者首先建立一个沙尘暴产生的天气学概念模型;据此模型,设计了用摩擦速度和大气边界层稳定度状况来对沙尘暴进行预报的数值方法;用PSU/NCAR的非静力中尺度模式MM5对该天气学模型的检验结果表明了该模型的合理性。最后给出了运用天气学原理和数值预报方法相结合来对沙尘暴进行预报的流程图。 相似文献
996.
Cause-Effect Models of Large Landslides 总被引:2,自引:0,他引:2
Within the scope of the International Decade ofNatural Disaster Reduction (IDNDR), cause-effectmodels of large landslides are being developed toestimate hazard. This work is based on a structuralexploration of the landslide areas mainly by seismicmethods. Information about the status of deformationis obtained by comparison of the actual topographywith a reconstruction of the original topography, byGPS, and by SAR interferometry. Geologic andgeomorphological evidence, as well as relevantinformation from other geo-scientific disciplines, isconsidered. The Finite Element Method is used to modelthe initial phase of a mass movement. Later on thismodeling will be extended to the quasi-stationarycreep phase and the transition from creeping to rapidsliding.Four large landslides within the crystalline rocks ofthe Eastern Alps have been investigated since 1997.Two of them are evaluated so far, and are presented inthis paper. The largest one is the Köfelslandslide with a total volume of 3.9 km3 and apotential energy release of 5 × 1016 Joule.Refraction and reflection multi-component seismictechniques were used to resolve structure and elasticparameters of the landslide masses. For the modelingof the initial phase of the landslides by the FiniteElement Method a strain softening behavior of the rockmass has been assumed. The development of softened orfractured zones was successfully simulated, inagreement with the structures obtained by the seismicmeasurements. 相似文献
997.
998.
999.
用载荷试验及钢筋计测试联合确定一定深度上的桩基承载力 总被引:1,自引:0,他引:1
结合北京大使公寓工程桩基的测试,采用载荷试验和钢筋计的测试联合确定一定深度以下的桩基承载力的方法,对3根试验桩进行了测试。试验平面位于自然地表以下6 5m处,要求提供基础埋深-13 4m以下的有效桩长所具有的极限承载力。测试时,在桩体内主钢筋上预装了钢筋计,并测定了-6 5~-13 4m深度范围的桩侧摩阻力。从载荷试验中测定的-6 5m处桩基所具有的极限承载力中扣除上述桩侧摩阻力,可得到工程所要求的桩基极限承载力。实践证明,这是一种有效的测试方法。 相似文献
1000.