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71.
A method of combining moiré interferometry and the finite-element method to effect localized stress analysis is presented.
The displacement data from local regions of interest in the optical experiment are used as boundary conditions for the finite-element
stress analysis.
The stability of the method is examined with data from simple numerical models one of which corresponded to the stress analysis
of a pin-loaded plate with friction. These studies show that the method requires the sensivity of moiré interferometry for
successful implementation, i.e., displacement data accuracy within 0.1 μm or 4 μin.
This localized hybrid method of stress analysis provides a powerful and efficient method for the reduction of experimental
data. 相似文献
72.
We formulate integral statements of force balance, energy balance, and entropy imbalance for an interface between a body and
its environment. These statements account for interfacial energy, entropy, and stress but neglect the inertia of the interface.
Our final results consist of boundary conditions describing thermomechanical interactions between the body and its environment.
In their most general forms, these results are partial differential equations that account for dissipation and encompass as
special cases Navier’s slip law, Newton’s law of cooling, and Kirchhoff’s law of radiation. When dissipation is neglected,
our results reduce to the well-known zero-slip, free-surface, zero-shear, prescribed temperature, and flux-free conditions.
Dedicated to James K. Knowles: teacher, colleague, friend 相似文献
73.
Gurtin recently proposed a strain-gradient theory for crystal plasticity in which the gradient effect originates from a defect energy that characterizes energy storage due to the presence of a net Burgers vector. Here we consider a number of different possibilities for this energy: specifically, working within a simple two-dimensional framework, we compare predictions of the theory with results of discrete-dislocation simulations of stress relaxation in thin films. Our objective is to investigate which specific defect energies are capable of capturing the size-dependent response of such systems for different crystal orientations. 相似文献
74.
A series of experiments has been conducted to determine the effect of loading variables such as cyclic frequency, load ratio, and material on acoustic emission from fatigue-crack propagation. It is shown that the applied-stress intensity range (ΔK) is the controlling parameter for all materials studied while the other parameters have lesser effects. Two potential methods for engineering application of acoustic emission during fatigue loading are described. 相似文献
75.
A theory of strain-gradient plasticity for isotropic, plastically irrotational materials. Part I: Small deformations 总被引:1,自引:0,他引:1
This study develops a small-deformation theory of strain-gradient plasticity for isotropic materials in the absence of plastic rotation. The theory is based on a system of microstresses consistent with a microforce balance; a mechanical version of the second law that includes, via microstresses, work performed during viscoplastic flow; a constitutive theory that allows:
- •
- the microstresses to depend on , the gradient of the plastic strain-rate, and
- •
- the free energy ψ to depend on the Burgers tensor .
76.
Morton E. Gurtin 《Journal of the mechanics and physics of solids》2004,52(11):2545-2568
This study develops a gradient theory of small-deformation viscoplasticity based on: a system of microforces consistent with its peculiar balance; a mechanical version of the second law that includes, via the microforces, work performed during viscoplastic flow; a constitutive theory that accounts for the Burgers vector through a free energy dependent on , with Hp the plastic part of the elastic-plastic decomposition of the displacement gradient. The microforce balance and the constitutive equations, restricted by the second law, are shown to be together equivalent to a nonlocal flow rule in the form of a coupled pair of second-order partial differential equations. The first of these is an equation for the plastic strain-rate in which the stress T plays a basic role; the second, which is independent of T, is an equation for the plastic spin. A consequence of this second equation is that the plastic spin vanishes identically when the free energy is independent of, but not generally otherwise. A formal discussion based on experience with other gradient theories suggests that sufficiently far from boundaries solutions should not differ appreciably from classical solutions, but close to microscopically hard boundaries, boundary layers characterized by a large Burgers vector and large plastic spin should form.Because of the nonlocal nature of the flow rule, the classical macroscopic boundary conditions need be supplemented by nonstandard boundary conditions associated with viscoplastic flow. As an aid to solution, a variational formulation of the flow rule is derived.Finally, we sketch a generalization of the theory that allows for isotropic hardening resulting from dissipative constitutive dependences on . 相似文献
77.
As nanoparticle syntheses in aqueous and organic systems have their own merits and drawbacks, specific applications may call for the transfer of newly formed nanoparticles from a polar to a non-polar environment (or vice versa) after synthesis. This critical review focuses on the application of phase transfer in nanoparticle synthesis, and features core-shell structures in bimetallic nanoparticles, replacement reactions in organic media, and catalytic properties of various nanostructures. It also describes the reversible organic and aqueous phase transfer of semiconductor and metallic nanoparticles for biological applications, and the use of phase transfer in depositing noble metals on semiconductor nanoparticles (258 references). 相似文献
78.
In this paper we present a new framework for identifying preferred solutions to multi-objective binary optimisation problems.
We develop the necessary theory which leads to new formulations that integrate the decision space with the space of criterion
weights. The advantage of this is that it allows for incorporating preferences directly within a unique binary optimisation
problem which identifies efficient solutions and associated weights simultaneously. We discuss how preferences can be incorporated
within the formulations and also describe how to accommodate the selection of weights when the identification of a unique
solution is required. Our results can be used for designing interactive procedures for the solution of multi-objective binary
optimisation problems. We describe one such procedure for the multi-objective multi-dimensional binary knapsack formulation
of the portfolio selection problem. 相似文献
79.
The identification of phosphocholine and phosphoethanolamine lipids by MALDI TOF/TOF, including characterisation of the headgroup and delineation of the acyl chain at each position of the glycerol backbone, has been explored using lipids representative of each type. The relative intensities of fragments involving the neutral loss of one or other of the acyl chains from ion adducts of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) were compared. For POPC and POPE, a statistical preference for the loss of the chain from the sn-1 position was observed in the presence of lithium. For OPPC this selectivity was reversed for one of the fragments. In the absence of lithium, fragmentation was favoured at the sn-2 position for all lipids. In all cases, spectra obtained in the presence of lithium yielded more intense product ion peaks. Although Collision Induced Dissociation (CID) could be used for complete lipid characterisation, LIFT? was found to be a better method due to the presence of a greater number of distinguishing product ion peaks and a better shot-to-shot reproducibility of peak intensities. 相似文献
80.
Zhang Y Tan M Li H Zheng Y Gao S Zhang H Ying JY 《Chemical communications (Cambridge, England)》2011,47(26):7365-7367
Novel mesoscopic organic nanosheets were developed by functionalizing bulk 2D organic covalent framework polymers with small molecules. The water-soluble fluorescent nanosheets are promising as nanocarriers for biological applications. 相似文献