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931.
方形钝体受限绕流的三维数值模拟 总被引:4,自引:2,他引:2
采用一种具有二阶精度的分裂步有限元方法作为大涡模拟的空间离散格式,经过标准算例的验证后,对Re=1.0×104条件下的方形钝体三维受限湍流绕流流场进行了数值模拟.计算中,为消除初始效应,略去初始段的计算结果.数值分析表明在均匀来流条件下,该湍流场沿槽道轴面对称,并呈现出一定的拟周期特性.在流场特性分析的基础上,进行了湍流能耗场的分析,结果表明,方形钝体受限绕流的能耗主要集中在大涡丰富的流动区段内.计算过程反映出,采用该空间离散格式的大涡模拟方法,能够捕捉到非常丰富的涡系及涡动的时变过程,适用于方形钝体受限绕流的数值模拟. 相似文献
932.
V. G. Savchenko 《International Applied Mechanics》2008,44(9):975-981
The paper proposes a method to allow for the stress mode in analyzing the thermoelastoplastic stress-strain state of compound
bodies of revolution under asymmetric loading and heating. Use is made of a semianalytic finite-element method and the method
of successive approximations. Some numerical results are presented
Translated from Prikladnaya Mekhanika, Vol. 44, No. 9, pp. 26–35, September 2008. 相似文献
933.
Propagation of two-dimensional nonstationary vibrations in an electrically excited piezoceramic prismatic body 总被引:1,自引:1,他引:0
The paper outlines a numerical method to solve a plane problem for a piezoceramic prismatic body having rectangular cross-section
and undergoing mechanically excited nonstationary vibrations. The features of the onset and propagation of vibrations are
studied. The dynamic state of bodies with different widths is analyzed. The thickness and transverse displacements versus
time are plotted
Translated from Prikladnaya Mekhanika, Vol. 44, No. 11, pp. 71–78, November 2008. 相似文献
934.
A crack is represented as a continuous set of linear dislocations. Simple analytical expressions are obtained for the potential
and kinetic energies of the environment of moving cracks and the attached mass of cracks for an arbitrary form of the stress
applied to the crack P(x). It is shown that the indicated analytical expressions are bilinear integrals of the functions P(x)
and ∂P(x)/∂x. These integrals are calculated in explicit form for a constant stress over the entire crack length and the stress
due to the action of molecular adhesion forces in a narrow region near the crack openings. It is shown that the calculation
results does not depend on the form of molecular adhesion forces. The proposed approach to describing cracks and calculations
based on it has made it possible for the first time to obtain a complete analytical expression for the limiting crack propagation
velocity in elastic materials as a function of the main mechanical characteristics of such materials.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 158–166, July–August, 2009. 相似文献
935.
This paper concerns the non-smooth dynamics of planar mechanical systems with isolated contact in the presence of Coulomb friction. Following Stronge [Impact Mechanics, Cambridge University Press, Cambridge, 2000], a set of closed-form analytic formulae is derived for a rigid-body impact law based on an energetic coefficient of restitution and a resolution of the impact phase into distinct segments of relative slip and stick. Thus, the impact behavior is consistent both with the assumption of Coulomb friction and with the dissipative nature of impacts. The analysis highlights the presence of boundaries between open regions of initial conditions and parameter values corresponding to distinct forms of the impact law and investigates the smoothness properties of the impact law across these boundaries. It is shown how discontinuities in the impact law are associated with discontinuity-induced bifurcations of periodic trajectories, including non-smooth folds and persistence scenarios. Numerical analysis of an example mechanical model is used to illustrate and validate the conclusions. 相似文献
936.
The present work is aimed to study mixed convection heat transfer characteristics for a lid-driven air flow within a square enclosure having a circular body. Flows are driven by the left lid, which slides in its own plane constant velocity. This wall is isothermal and it moves up or down in y direction while the other walls remain stationary. The horizontal walls are adiabatic. The cavity is differentially heated and the left wall is maintained at a higher temperature than the right wall. Three different temperature boundary conditions were applied for the inner cylinder as adiabatic, isothermal or conductive. The computation is carried out for wide ranges of Richardson numbers, diameter of inner cylinder and center and location of the inner cylinder. It was found that the most effective parameter on flow field and temperature distribution is the orientation of the moving lid. The circular body can be a control parameter for heat and fluid flow. An interesting obtained result that the thermal conductivity becomes insignificant for small values of diameter of the circular body. 相似文献
937.
A set of four quaternion matrices is used to represent the equations of finite rotation theory and to describe the kinematics
and nonlinear dynamics of an asymmetric rigid body in space. The results obtained are tested in setting up direction-cosine
matrices, calculating three-index symbols, establishing the relationship between the components of angular velocity in body-fixed
and space-fixed frames of reference, and using a set of three independent rotations. Euler–Lagrange equations and a set of
four quaternion matrices are used to construct a block-matrix model describing the nonlinear dynamics of a free asymmetric
rigid body in three-dimensional space. The model gives the matrix Euler’s equations of motion and other special cases. Algorithms
adapted to use in a numerical experiment are developed
Translated from Prikladnaya Mekhanika, Vol. 45, No. 2, pp. 133–143, February 2009. 相似文献
938.
939.
Jakub Kedzierski Peiqi Xuan Vivek Subramanian Jeffrey Bokor Tsu-Jae King Chenming Hu Erik Anderson 《Superlattices and Microstructures》2000,28(5-6)
As the scaling of CMOS transistors extends to the sub-20 nm regime, the most challenging aspect of device design is the control of the off-state current. The traditional methods for controlling leakage current via the substrate doping profile will be difficult to implement at these dimensions. A promising method for controlling leakage in sub-20 nm transistors is the reduction in source-to-drain leakage paths through the use of a body region which is significantly thinner then the gate length, with either a single or a double gate. In this paper we present ultra-thin body PMOS transistors with gate lengths down to 20 nm fabricated using a low-barrier silicide as the source and drain. Calixarene-based electron-beam lithography was used to define critical device dimensions. These transistors show 260 μ A μ m − 1on-current and on/off current ratios of 106, for a conservative oxide thickness of 40 Å and | Vg − Vt| = 1.2 V. Excellent short-channel effect, with only 0.2 V reduction in | Vt| is obtained in devices with gate lengths ranging from 100 to 20 nm. 相似文献
940.
用多体微扰理论和原子体系图示法,研究和讨论了钠原子双激发 [2p,3s]→[4p,kl(kp+kf)]并计算了钠原子的光电离激发截面,计算结果与实验结 果相符。 相似文献