全文获取类型
收费全文 | 12207篇 |
免费 | 2345篇 |
国内免费 | 1174篇 |
专业分类
化学 | 3269篇 |
晶体学 | 223篇 |
力学 | 3174篇 |
综合类 | 153篇 |
数学 | 1381篇 |
物理学 | 7526篇 |
出版年
2024年 | 34篇 |
2023年 | 124篇 |
2022年 | 389篇 |
2021年 | 394篇 |
2020年 | 375篇 |
2019年 | 336篇 |
2018年 | 339篇 |
2017年 | 454篇 |
2016年 | 571篇 |
2015年 | 503篇 |
2014年 | 707篇 |
2013年 | 1101篇 |
2012年 | 785篇 |
2011年 | 897篇 |
2010年 | 752篇 |
2009年 | 799篇 |
2008年 | 828篇 |
2007年 | 879篇 |
2006年 | 768篇 |
2005年 | 675篇 |
2004年 | 545篇 |
2003年 | 532篇 |
2002年 | 442篇 |
2001年 | 385篇 |
2000年 | 362篇 |
1999年 | 294篇 |
1998年 | 325篇 |
1997年 | 202篇 |
1996年 | 157篇 |
1995年 | 119篇 |
1994年 | 125篇 |
1993年 | 104篇 |
1992年 | 72篇 |
1991年 | 67篇 |
1990年 | 54篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 35篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1959年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
151.
The Morse–Witten theory provides a formulation for the inter-bubble forces and corresponding deformations in a liquid foam, accurate in the limit of high liquid fraction. Here we show how the theory may be applied in practice, including allowing for polydispersity in the bubble sizes. The resulting equilibrated 2D structures are consistent with direct calculations, within the limitations of the theory. The path to developing a 3D model is outlined for future work. 相似文献
152.
A new framework is introduced for kinetic simulation of laser–plasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell’s equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell’s equations are solved using an Ohm’s law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere’s law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies. 相似文献
153.
Various methods achieving importance sampling in ensembles of nonequilibrium trajectories enable one to estimate free energy differences and, by maximum-likelihood post-processing, to reconstruct free energy landscapes. Here, based on Bayes theorem, we propose a more direct method in which a posterior likelihood function is used both to construct the steered dynamics and to infer the contribution to equilibrium of all the sampled states. The method is implemented with two steering schedules. First, using non-autonomous steering, we calculate the migration barrier of the vacancy in Fe-α. Second, using an autonomous scheduling related to metadynamics and equivalent to temperature-accelerated molecular dynamics, we accurately reconstruct the two-dimensional free energy landscape of the 38-atom Lennard-Jones cluster as a function of an orientational bond-order parameter and energy, down to the solid–solid structural transition temperature of the cluster and without maximum-likelihood post-processing. 相似文献
154.
P. Thum T. Clees G. Weyns G. Nelissen J. Deconinck 《Journal of computational physics》2010,229(19):7260-7276
The article discusses components and performance of an algebraic multigrid (AMG) preconditioner for the fully coupled multi-ion transport and reaction model (MITReM) with nonlinear boundary conditions, important for electrochemical modeling. The governing partial differential equations (PDEs) are discretized in space by a combined finite element and residual distribution method. Solution of the discrete system is obtained by means of a Newton-based nonlinear solver, and an AMG-preconditioned BICGSTAB Krylov linear solver. The presented AMG preconditioner is based on so-called point-based classical AMG. The linear solver is compared to a standard direct and several one-level iterative solvers for a range of geometries and chemical systems with scientific and industrial relevance. The results indicate that point-based AMG methods, carefully designed, are an attractive alternative to more commonly employed numerical methods for the simulation of complex electrochemical processes. 相似文献
155.
A series resonance circuit under sinuousoidal driving is investigated experimentally. The inductance consists of an air coil. The capacitance is made up of a ferroelectric material that introduces its nonlinear dielectric properties into the circuit. The dynamical system linear coil-nonlinear capacaitor shows an interesting behaviour. The phase portrait differs in general from the ellipse of the harmonic oscillator. For appropriate external conditions period doubling sequences, chaos and therein enclosed periodic windows might occur. Starting from a cubic nonlinearity of the dielectric properties a Duffing equation is proposed as a model for periodic behaviour of the series resonance circuit. Simulations of experimentally recorded phase portraits yield good agreement between experiment and model. 相似文献
156.
157.
The angular distribution of atoms sputtered from germanium under 1–20 keV Ar+ ion bombardment (normal incidence) has been studied experimentally and using computer simulations. A collector technique combined with Rutherford backscattering to analyze the distribution of collected material was used. In addition, the surface topography was under control. It was found that the experimental angular distribution of sputtered atoms (E 0=3–10 keV) could be approximated by the function cos n θ with n≈ 1.65. Such a high value of n is connected with the surface scattering of ejected atoms and a noticeable contribution of backscattered ions to the formation of the sputter flux (the mass effect). The target surface was found to be practically flat even at ion fluencies ~1018 ions/cm2. The results obtained are compared with data from the literature, including our recent data on Si sputtering. 相似文献
158.
Abstract The on- or off-axis behavior and the vibrational properties of the F A (Li+) center are investigated in several alkali halides by means of polarized resonant Raman scattering. The observed Raman modes are interpreted and classified according to their nature and frequency. A comparison between on- and off-axis systems and between the vibrational modes of the isolated Li+ and the F A (Li+) center reveals a displacement of the Li+ equilibrium position parallel to the F A (Li+) defect axis and, due to the small impurity size, away from the adjacent F center. 相似文献
159.
Tariq Talha 《Journal of Turbulence》2013,14(11):1091-1113
The unsteady turbulent channel flow subject to the temporal acceleration is considered in this study. Large-eddy simulations were performed to study the response of the turbulent flow to the temporal acceleration. The simulations were started with the fully developed turbulent channel flow at an initial Reynolds number of Re0 = 3500 (based on the channel half-height and the bulk-mean velocity), and then a constant temporal acceleration was applied. During the acceleration, the Reynolds number of the channel flow increased linearly from the initial Reynolds number to the final Reynolds number of Re1 = 22,600. The effect of grid resolution, domain size, time step size on the simulation results was assessed in a preliminary study using simulations of the accelerating turbulent flow as well as simulations of the steady turbulent channel flow at various Reynolds numbers. Simulation parameters were carefully chosen from the preliminary study to ascertain the accuracy of the simulation. From the accelerating turbulent flow simulations, the delays in the response of various flow properties to the temporal acceleration were measured. The distinctive features of the delays responsible for turbulence production, energy redistribution, and radial propagation were identified. Detailed turbulence statistics including the wall shear stress response during the acceleration were examined. The results reveal the changes in the near-wall structures during the acceleration. A self-sustaining mechanism of turbulence is proposed to explain the response of the turbulent flow to the temporal acceleration. Although the overall flow characteristics are similar between the channel and pipe flows, some differences were observed between the two flows. 相似文献
160.
Robert Prosser 《Combustion Theory and Modelling》2017,21(5):954-975
The accurate resolution of flame structure is critically important to the direct numerical simulation of reacting flows. While grid-resolution estimates are readily available for cold flows, premixed flames appear to have received relatively little attention. In this paper, a premixed flame characterised by single-step chemistry at moderate-to-high Zel'dovitch numbers (β) is analysed, and its structure is used to provide estimates for sufficient grid resolution. It is found that the critical region of the flame exhibits a weak inverse Zel'dovitch number dependence, and that heuristic methods of resolution estimation based on flame thickness grow relatively less meaningful as β → ∞. Resolution estimates for second- and fourth-order finite-difference schemes are provided. 相似文献