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941.
A unified energy approach to a class of micromechanics models for composite materials 总被引:4,自引:0,他引:4
Several micromechanics models for the determination of composite moduli are investigated in this paper, including the dilute
solution, self-consistent method, generalized self-consistent method, and Mori-Tanaka's method. These micromechanical models
have been developed by following quite different approaches and physical interpretations. It is shown that all the micromechanics
models share a common ground, the generalized Budiansky's energy-equivalence framework. The difference among the various models
is shown to be the way in which the average strain of the inclusion phase is evaluated. As a bonus of this theoretical development,
the asymmetry suffered in Mori-Tanaka's method can be circumvented and the applicability of the generalized self-consistent
method can be extended to materials containing microcracks, multiphase inclusions, non-spherical inclusions, or non-cylindrical
inclusions. The relevance to the differential method, double-inclusion model, and Hashin-Shtrikman bounds is also discussed.
The application of these micromechanics models to particulate-reinforced composites and microcracked solids is reviewed and
some new results are presented. 相似文献
942.
Yeon-Pun Chang Bing-Chwen Yang Jiin-Wen Hwang 《Experimental Thermal and Fluid Science》1998,16(4):299-304
The influence of grooves in the U-turn areas for the multi-channel-plate heat exchangers (MCPHEs) is significant due to the friction and flow phenomena in this region. In this study, two types of MCPHE made of acrylic plates were tested: one with grooves in the U-turn area, one without. During this series of experiments, heat transfer rate, overall volumetric heat transfer coefficient, Nusselt number and overall pressure drop (i.e., including the entrance and exit losses) were measured and calculated in order to understand the overall performance of these two different constructions of MCPHE. The experimental results show that the heat exchanger without grooves in the U-turn area possessed higher heat transfer performance and lower overall pressure drop. 相似文献
943.
part(Ⅰ)of this work is on the theory of minimal polynomial matrix and Part(Ⅱ)onthe applications of this theory to linear multivariable systems.In Part(Ⅰ).concepts of annihilating polynomial matrix and the minimal polynomialmatrix of a given linear transformation in a vector group are given and the concepts of thegenerating system and minimal generating system of an invariant subspace for a givenlinear transformation are given as well.After discussing the basic properties of theseconcepts the relations between them and the characteristic matrix corresponding to aninduced operator of a given linear transformation in any of its invariant subspace arestudied in detail.The characteristics of the minimal polynomial matrix for a given vectorgroup and the necessary and sufficient condition for the two generating systems to have thesame generating subspace is given.Using these results we can give the expression for the setof all B’s which makes the system x=Ax Bu a complete controllable system for a givenA. 相似文献
944.
Huanyu Cheng Yihui Zhang Keh-Chih Hwang John A. Rogers Yonggang Huang 《International Journal of Solids and Structures》2014
Controlled buckling can impart stretchable mechanics to brittle materials when integrated as thin films on soft, elastomeric substrates. Typical elastomers are permeable to fluids, however, and therefor unable to provide robust barriers to entry of water, for instance, into devices built with the supported thin films. In addition, the mechanical strength of a system dominated by a soft substrate is often unsatisfactory for realistic applications. We show that introduction of a bi-layer substrate yields a robust, high strength system that maintains stretchable characteristics, with a soft layer on top of a relatively stiff layer in the substrate. As a mechanical protection, a soft encapsulation layer can be used on top of the device and the stretchability of the encapsulated system is smaller than that of the system without encapsulation. A simple, analytic model, validated by numerical analysis and FEA, is established for stiff thin films on a bi-layer substrate, and is useful to the design of stretchable systems. 相似文献
945.
黄黔 《应用数学和力学(英文版)》1982,3(1):99-112
By reducing the boundary value problem in stress analysis of bellows into initial value problem, this paper presents a numerical solution of stress distribution in semi-circular arc type bellows based upon the toroidal shell equation of V. V. Novozelov[8]. Throughout the computation, S. Gill’s method[1O] of extrapolation is used. The stresses and deformations of bellows under axial load and internal pressure are c-alculated, the results of which agree completely with those derived from the general solution of Prof. Chien Wei-zang[1-4]. The extrapolation formula presented in this paper greatly promotes the accuracy of discrete calculation.The computer program in BASIC language of Wang 2200 VS computer is included in the appendix. 相似文献
946.
A constitutive relation to describe pseudo-elastic deformation in shape memory alloys is presented in this paper. It is capable
of describing deformation behaviour of polycrystalline materials under triaxial stress state as well as of monocrystalline
materials under one-dimensional condition. Total strain rate is supposed to be composed of elastic strain rate and transformation
strain rate. Deformation behaviour of Cu−Zn−Sn alloy and Ti−ni alloy is simulated by use of the proposed constitutive relation.
it is shown that simulated results are in a good agreement with experimental data.
The project supported by National Natural Science Foundation of China. 相似文献
947.
Coherent gradient sensing (CGS) method, a real time, full-field optical technique, is insensitive to vibrations and able to provide slope and curvature maps and surface topographies, to investigate non-uniform deformations. In this paper, we analyze the thermal effects on the optical path in CGS due to air convection, and the influence of grating thickness and refractive index on the measurement accuracy. A modified governing equation is derived considering the grating thickness, which is demonstrated by testing a standard sample. Finally, we apply CGS method to measure the full-field deformation of a specimen at high temperature. 相似文献
948.
Carbon nanomaterials, including herringbone graphite carbon nanofibers (GNFH), multiwalled carbon nanotubes (MWCNT), and carbon black, were surface-modified by a new poly(vinylpyrrolidone) (PVP) grafting process as well as by the conventional acid-oxidation (AO) process, and characterized by FTIR, TGA, Raman, HRTEM, XRD, and XPS measurements. Pt nanoparticles of 1.8 nm were evenly deposited on all PVP-grafted carbon nanomaterials. The effects of the two surface modification processes on the dispersion, average Pt nanoparticle sizes, the electrocatalytic performance, and electrical conductivities of Pt-carbon nanocomposites in direct methanol oxidation were systematically studied and compared. It was found that the PVP-grafted carbon nanomaterials have much less loss in the electric conductivity and thus better electrocatalytic performance, 17-463% higher, than their corresponding acid oxidation-treated nanocomposites. The electrocatalytic performance of the Pt-carbon nanocomposites decreases in the following order: Pt-PVP-GNFH > Pt-PVP-MWCNTarc > Pt-AO-MWCNTarc > Pt-PVP-MWCNTCVD > Pt-AO-MWCNTCVD > Pt-XC-72R > Pt-AO-GNFH, with the Pt-PVP-GNFH nanocomposite having approximately 270% higher performance than that of the Pt-Vulcan XC-72R nanocomposite. In addition, PtRu-PVP-GNFH shows even better (50% higher) electrocatalytic activity than the Pt-PVP-GNFH nanocomposite at a 0.6 V applied voltage. 相似文献
949.
The coordinating properties of N-o-chlorobenzamido-meso-tetraphenylporphyrin (N-NHCO(o-Cl)C6H4-Htpp; 11) have been investigated for the Zn2+ ion. Insertion of Zn results in the formation of the zinc complex Zn(N-NCO(o-Cl)C6H4-tpp)(MeOH) · MeOH (12 · MeOH). The diamagnetic 12 · MeOH can be transformed into the diamagnetic Zn(N-NHCO(o-Cl)C6H4-tpp)Cl · CH2Cl2 (13 · CH2Cl2) in a reaction with aqueous hydrogen chloride (2%). X-ray structures for 12 · MeOH and 13 · CH2Cl2 have been determined. The coordination sphere around the Zn2+ ion in 12 · MeOH is a distorted trigonal bipyramid with N(2), N(4) and O(2) lying in the equatorial plane, whereas for the Zn2+ ion in 13 · CH2Cl2, it is a square-based pyramid in which the apical site is occupied by the Cl(1) atom. 相似文献
950.
Hyperthermia effects (39-44°C) induced by pulsed high-intensity focused ultrasound (HIFU) have been regarded as a promising therapeutic tool for boosting immune responses or enhancing drug delivery into a solid tumor. However, previous studies also reported that the cell death occurs when cells are maintained at 43°C for more than 20 minutes. The aim of this study is to investigate thermal responses inside in vivo rabbit auricular veins exposed to pulsed HIFU (1.17 MHz, 5300 W/cm2 , with relatively low-duty ratios (0.2%-4.3%). The results show that: (1) with constant pulse repetition frequency (PRF) (e.g., 1 Hz), the thermal responses inside the vessel will increase with the increasing duty ratio; (2) a temperature elevation to 43°C can be identified at the duty ratio of 4.3%; (3) with constant duty ratios, the change of PRF will not significantly affect the temperature measurement in the vessel; (4) as the duty ratios lower than 4.3%, the presence of microbubbles will not significantly enhance the thermal responses in the vessel, but will facilitate HIFU-induced inertial cavitation events. 相似文献