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51.
52.
The controllability for switched linear system with time-delay in controls was first investigated. The whole work contains
three parts. This is the first part, including problem formulation and some preliminaries. Firstly, the mathematical model
of switched linear systems with time-delay in control functions was presented. Secondly, the concept of column space, cyclic
invariant subspace and generalized cyclic invariant subspace were introduced. And some basic properties, such as separation
lemma, were presented. Finally, a basic lemma was given to reveal the relation between the solution set of a centain integral
equations and the generalized cyclic invariant subspace. This lemma will play an important role in the determination of controllability.
All these definitions and lemmas are necessary research tools for controllability analysis.
Contributed by YE Qing-kai
Foundation items: the National Natural Science Foundation of China (69925307, 60274001); the National Key Basic Reasearch and Development
Program (2002CB312200); the Postdoctoral Program Foundation of China
Biography: XIE Guang-ming (1972∼), Doctor (E-mail: xiegming@mech.pku.edu.cn) 相似文献
53.
探讨了一种能够揭示三维复合型断裂现象并能记录这些现象的三维复合型断裂研究的实验方法,用此方法完成了LC4-CS航空结构铝合金不同厚度紧凑拉伸试样的I+Ⅱ复合型断裂试验。结果表明:此方法能够简便地确定出复合型裂纹的起裂载荷、破坏载荷、裂尖张开位移、滑移位移和起裂角,基本解决三维复合型断裂研究所需实验数据问题。同时发现此种材料试样的承载能力和超裂方向的确具有明显的厚度效应。 相似文献
54.
This paper proposes a formulation for modelling mechanisms witha cam/follower type of contact using a multibody approach in relativecoordinates. The proposed approach is inspired from the wheel/railcontact model developed by Fisette and Samin but, in the present case,possible intermittent contact between the cam and the follower isconsidered, for generality purposes.Loop kinematicconstraints are introduced to satisfy tangent and punctual contact aslong as the bodies lean against each other. The effective presence (ornot) of the contact is governed by the sign of the normal constraintforce which can be computed thanks to the Lagrange multiplierstechnique.The above-mentioned option to kinematicallyconstraint the bodies in their contact phase unavoidably leads to ashift from one model to another when a contact disappears (or,conversely, reappears). Indeed, this increases (or decreases) the numberof degrees of freedom of the current system. The control of the variablepartitioning is thus absolutely necessary and is all the more complex sothat practical applications can contain several pairs of bodies inintermittent contact.Illustrative examples are proposed: acomparison with another multibody formalism, an experimental validationand the modelling of universal wheels of mobile robots which representsa quite original application of the proposed formulation. 相似文献
55.
G. V. Galatenko 《International Applied Mechanics》2007,43(7):745-753
The generalized Dugdale crack model is used to formulate two-parameter failure criteria for the cases of quasibrittle state
and developed plastic zones at a mode I crack tip. The failure criteria relate the fracture strength characteristics and the
stress mode at the crack tip through the plastic constraint factor. The critical state of bodies with cracks under uni-and
biaxial loading is analyzed in the cases of plane stress and plane strain using the Tresca and von Mises yield criteria. A
small-scale yield criterion, which is an analytic relation between the critical stress intensity factor and T-stresses, is established
__________
Translated from Prikladnaya Mekhanika, Vol. 43, No. 7, pp. 47–57, July 2007. 相似文献
56.
Optimal Control of Deployment of a Tethered Subsatellite 总被引:6,自引:0,他引:6
One of the most important operations during a tethered satellite system mission is the deployment of a subsatellite from a space ship. We restrict tothe simple but practically important case that the system ismoving on a circular orbit around the Earth. The main problem duringdeployment due to gravity gradient is that the two satellites do not move along the straight radial relative equilibrium position which is stable for a tether of constant length. Instead, deploymentleads to an unstable motion with respect to the radial relativeequilibrium configuration. Therefore we introduce an optimal control strategy using theMaximum Principle to achieve a force controlled deployment of the tethered subsatellite from the radial relative equilibrium position close to the space ship to the radial relative equilibrium position far away from the space ship. 相似文献
57.
Efficient Evaluation of the Elastic Forces and the Jacobian in the Absolute Nodal Coordinate Formulation 总被引:1,自引:0,他引:1
This paper develops a new procedure for evaluating the elastic forces, the elastic energy and the jacobian of the elastic
forces in the absolute nodal coordinate formulation. For this procedure, it is fundamental to use some invariant sparse matrices
that are integrated in advance and have the property of transforming the evaluation of the elastic forces in a matrix multiplication
process. The use of the invariant matrices avoids the integration over the volume of the element for every evaluation of the
elastic forces. Great advantages can be achieved from these invariant matrices when evaluating the elastic energy and calculating
the jacobian of the elastic forces as well. The exact expression of the jacobian of the differential system of equations of
motion is obtained, and some advantages of using the absolute nodal coordinate formulation are pointed out. Numerical results
show that there is important time saving as a result of the use of the invariant matrices. 相似文献
58.
Non-linear systems are here tackled in a manner directly inherited from linear ones, that is, by using proper normal modes of motion. These are defined in terms of invariant manifolds in the system's phase space, on which the uncoupled system dynamics can be studied. Two different methodologies which were previously developed to derive the non-linear normal modes of continuous systems — one based on a purely continuous approach, and one based on a discretized approach to which the theory developed for discrete systems can be applied-are simultaneously applied to the same study case-an Euler-Bernoulli beam constrained by a non-linear spring-and compared as regards accuracy and reliability. Numerical simulations of pure non-linear modal motions are performed using these approaches, and compared to simulations of equations obtained by a classical projection onto the linear modes. The invariance properties of the non-linear normal modes are demonstrated, and it is also found that, for a pure non-linear modal motion, the invariant manifold approach achieves the same accuracy as that obtained using several linear normal modes, but with significantly reduced computational cost. This is mainly due to the possibility of obtaining high-order accuracy in the dynamics by solving only one non-linear ordinary differential equation. 相似文献
59.
研究了具有非线性homologous变形约束条件的桁架结构形态分析问题。在已有的线性homologous变形约束桁架形态分析的基础上,将结构的节点分成三类:homologous变形约束节点,形状可变节点和边界点。运用Moore-Penrose广义逆矩阵性质,将基础方程组解的存在条件表示为包含形状可变节点未知坐标的非线性方程组,为采用Newton-Raphson方法求解非线性方程组,对AA (A为任意矩阵,A 为A的Moore-Penrose广义逆矩阵)求偏导数,找到了满足保型要求的形态,给出的桁架算例说明了本文方法的有效性。 相似文献
60.
David J. Wagg 《Nonlinear dynamics》2006,43(1-2):137-148
The behaviour of a multi-degree-of-freedom vibro-impact system is studied using a 2 degree-of-freedom impact oscillator as
a motivating example. A multi-modal model is used to simulate the behaviour of the system, and examine the complex dynamics
which occurs when both degrees of freedom are subjected to a motion limiting constraint. In particular, the chattering and
sticking behaviour which occurs for low forcing frequencies is discussed. In this region, a variety of non-smooth events can
occur, including newly studied phenomena such as sliding bifurcations. In this paper, the multiple non-smooth events which
can occur in the 2 degree-of-freedom system are categorised, and demonstrated using numerical simulations. 相似文献