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The paper presents a beam finite element for the long-term analysis of steel–concrete composite decks taking into account the shear lag in the slab and the partial shear interaction at the slab–girder interface. Using the displacement approach, beam kinematics is developed from the Newmark model for composite beams with partial shear connection; warping of the slab cross section is caught with the product of an established function which describes the warping shape, and an intensity function that measures the warping magnitude along the beam axis. Time-dependent behaviour is considered through an integral-type viscoelastic creep law for the concrete. The numerical solution is obtained by means of the finite element method and a step-by-step procedure for evolution in time. A refined, locking free, 13-dof beam finite element is derived considering second and third order hermitian polynomials in order to ensure consistent interpolation of the displacements. The convergence test results and comparisons with the experimental results of composite beams subjected to sustained loads demonstrate the precision of the proposed method. Further applications to realistic cases show the accuracy of the proposed element and its ability to describe the elastic and the time-dependent behaviour of bridge composite decks.  相似文献   
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Friction accounts for a large amount of energy lost in mechanical systems and applications. Nanofluids, with particles less than 100 nm, added to a base fluid have been proven to be effective in reducing friction and wear. Diamond has superior mechanical, thermal, optical, electrical, and chemical properties. Therefore, nanodiamond holds a lot of promise for use in nanofluids. The tribological properties of oil-based nanofluids with spherical nanodiamond particles with the size of 3–10 nm in diameter were investigated using a ball-on-disk friction test by varying nanodiamond concentration, sliding velocity, normal load, and disk roughness. The friction testing was performed using a UMT-2 Micro Tribometer. Wear analysis was performed and chemical composition of the disk surface was examined using a WYKO 3D surface profiler and X-ray photoelectron spectroscopy. In general, the addition of nanodiamonds to oil leads to a reduction in the coefficient of friction but an increase in wear of the disk.  相似文献   
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Time-Dependent Analysis of Shear-Lag Effect in Composite Beams   总被引:1,自引:0,他引:1  
Taking into account the long-term behavior of the concrete, a model for analyzing the shear-lag effect in composite beams with flexible shear connection is proposed. By assuming the slab loss of planarity described by a fixed warping function, the linear kinematics of the composite beam is expressed by means of four unknown functions: the vertical displacement of the whole cross section; the axial displacements of the concrete slab and of the steel beam; and the intensity of the warping (shear-lag function). A variational balance condition is imposed by the virtual work theorem for three-dimensional bodies, from which the local formulation of the problem, which involves four equilibrium equations with the relevant boundary conditions, is achieved. The assumptions of linear elastic behavior for the steel beam and the shear connection and of linear viscoelastic behavior for the concrete slab lead to an integral-differential type system, which is numerically integrated. The numerical procedure, based on the step-by-step general method and the finite-difference method, is illustrated and applied to an example of practical interest.  相似文献   
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In previous studies, nanoparticles and ionic liquids (ILs) have been used separately as oil additives and have been shown to reduce friction and wear. In this study, the stability and tribological performance of ionic nanoliquids (INLs), which combine nanoparticles and miscible ionic liquids together as oil additives, were investigated. Zinc oxide nanoparticles were dispersed in a mixture of polyalphaolefin (PAO) oil and ionic liquid (tetradecyltrihexylphosphonium bis (2,4,4-trimethylpentyl phosphinate)) using an ultrasonic homogenizer. The coefficient of friction was studied using a tribometer with a ball-on-disk configuration. The wear track was measured using a Bruker Contour GT-K Optical Profiler and the wear volume was calculated. The effects of concentration and load on the coefficient of friction and wear were investigated. The effects of ultrasonic mixing time and nanoparticle concentration on the stability of the solutions were also studied.  相似文献   
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This paper presents an analytical formulation for the analysis of two-layered composite beams with longitudinal and vertical partial interaction. The particularity of this model is its ability to incorporate an interface connection deforming both longitudinally, i.e., along the beam length, and vertically, i.e., transverse to the connection interface, which is modelled by means of a uniformly distributed spring. The novel formulation is based on the principle of virtual work expressed in terms of the displacement field consisting of the vertical and axial displacements of the two layers; for completeness, the proposed model is presented in both its weak and strong forms. The partial interaction problem is then solved by means of the finite element method. A parametric study is presented to investigate the effects of different combinations of longitudinal and transverse connection rigidities on the overall structural response. For the purpose of these simulations, a bi-linear constitutive model has been specified for the transverse interface connection to reflect the more realistic case in which two different responses are observed in the transverse interaction, one in which one layer is bearing against the other one, one when the two layers are separating. An iterative procedure has been proposed to obtain the convergence to the final solution.  相似文献   
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The aim of this paper was to design and assess a comprehensive model for managing the e-learning process and to define the relationship between systematic implementation of the model, outcomes of certain e-learning aspects and subject of e-learning. The validation of the model was performed by using two questionnaires sent via e-mail to teachers and field experts from the chosen sample of 14 European schools participating in an EU-funded project. Research results imply the existence of a clear link between planning and controlling of the e-learning process and its learning outcomes. On the other hand, no empirical relationship between the e-learning outcomes and the subject of learning has been established. It is believed that the model and its practical implications can be used by institutions engaged in e-learning, or as a process model for introducing e-learning related activities.  相似文献   
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