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1.
The paper's focus is the calculation of unsteady incompressible 2D flows past airfoils. In the framework of the primitive variable Navier–Stokes equations, the initial and boundary conditions must be assigned so as to be compatible, to assure the correct prediction of the flow evolution. This requirement, typical of all incompressible flows, viscous or inviscid, is often violated when modelling the flow past immersed bodies impulsively started from rest. Its fulfillment can however be restored by means of a procedure enforcing compatibility, consisting in a pre‐processing of the initial velocity field, here described in detail. Numerical solutions for an impulsively started multiple airfoil have been obtained using a finite element incremental projection method. The spatial discretization chosen for the velocity and pressure are of different order to satisfy the inf–sup condition and obtain a smooth pressure field. Results are provided to illustrate the effect of employing or not the compatibility procedure, and are found in good agreement with those obtained with a non‐primitive variable solver. In addition, we introduce a post‐processing procedure to evaluate an alternative pressure field which is found to be more accurate than the one resulting from the projection method. This is achieved by considering an appropriate ‘unsplit’ version of the momentum equation, where the velocity solution of the projection method is substituted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
Time‐resolved coherent anti‐Stokes Raman scattering (CARS) impulsively excited by a supercontinuum (SC) is investigated. We show that it is critical to optimize the temporal overlapping of the constituent solitons of a SC in order to impulsively excite vibrational modes over a broad frequency range. The cross‐correlation frequency‐resolved optical gating technique is utilized to retrieve the optical response function of molecules under SC impulsive excitation, and background‐free CARS with spectral resolution significantly better than the bandwidth of the probe pulses is achieved. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
4.
An impulsive delayed feedback control strategy to control period-doubling bifurcations and chaos is proposed. The control method is then applied to a discrete small-world network model. Qualitative analyses and simulations show that under a generic condition, the bifurcations and the chaos can be delayed or eliminated completely. In addition, the periodic orbits embedded in the chaotic attractor can be stabilized. 相似文献
5.
The problem of finite-time stabilizing control design for state-dependent impulsive dynamical linear systems (SD-IDLS) is tackled in this paper. Such systems are characterized by continuous-time, linear, possibly time-varying, dynamics coupled with discrete-time, linear, possibly time-varying, dynamics. The continuous-time part determines the system evolution in any time interval between two consecutive resetting events, while the discrete-time part governs its instantaneous state jump whenever the system trajectory intersects a resetting set, i.e. a region of the state space assumed to be time-independent. By making use of a quadratic control Lyapunov function, the finite-time stabilization of SD-IDLS through a static output feedback control design is specifically discussed in this paper. A sufficient and constructive result is provided based on the conical hulls of the resetting set subregions and on some cone copositivity properties of the chosen control Lyapunov function. Such a result is based on the solution of a feasibility problem that involves a set of coupled Difference/Differential Linear Matrix Inequalities (D/DLMI), which is shown to be less conservative and more numerically amenable with respect to other results available in the literature. An example illustrates the effectiveness of the proposed approach. 相似文献
6.
This paper studies the stability problem of two-time-scale system via event-triggered impulsive control and self-triggered impulsive control. The overall system is modeled with the hybrid formalism. Two Chang transformations are introduced to completely decouple the hybrid system states into flow set and jump set. A composite impulsive controller based on slow and fast system states is proposed, under which the slow and fast subsystems are simultaneously triggered by event-triggered and self-triggered mechanism, respectively. As a result, the stability conditions are derived for the system under event-triggered and self-triggered impulsive control, respectively. Furthermore, the theoretical result of self-triggered impulsive control is applied to the consensus of the interconnected two-time-scale systems. Finally, simulation examples and comparison study show the effectiveness of the proposed control strategies. 相似文献
7.
B. A. van Tiggelen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(2):261-269
In this work we apply field regularization techniques to formulate a number of new phenomena related to momentum induced by
electromagnetic zero-point fluctuations. We discuss the zero-point momentum associated with magneto-electric media, with moving
media, and with
magneto-chiral media. 相似文献
8.
F.E. van Dorsselaer G. Nienhuis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(2):175-180
We present a scheme for stochastic quantum-state diffusion (QSD) with adaptive noise to calculate the time evolution of an
arbitrary observable of an open system. The method is based on the fact that the observable is much less sensitive to adaptive
noise than to noise with a random phase. Hence, the individual realisations of the expectation value of the observable stay
closer to the average evolution and fewer realisations are required to obtain the ensemble average. This is illustrated by
applying QSD to a driven two-level system using both randomly phased and adaptive noise. Applying QSD with adaptive noise
to an undriven two-level system enables us to derive a deterministic Schr?dinger equation that produces the exact evolution
of an arbitrary observable.
Received: 31 July 1997 / Received in final form: 12 February 1998 / Accepted: 13 March 1998 相似文献
9.
H. Eleuch 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(3):391-395
Our work presents a theoretical study on the behavior of the fluctuation statistics of the field emitted from a semiconductor
microcavity containing a quantum well. We derive an analytical expression of the noise spectra in non-resonant pumping. Dynamical
behaviors of the noise spectra depending on the thermal bath and the detuning between exciton and cavity frequencies are discussed. 相似文献
10.
This paper uses the method of linear approximation for impulsive systems and gets a theorem which guarantees a fishery modei to be asymptotically stable at its equilibrium point and gives the ecological explanation. 相似文献