全文获取类型
| 收费全文 | 4920篇 |
| 免费 | 610篇 |
| 国内免费 | 229篇 |
专业分类
| 化学 | 431篇 |
| 晶体学 | 49篇 |
| 力学 | 499篇 |
| 综合类 | 68篇 |
| 数学 | 2353篇 |
| 物理学 | 1066篇 |
| 无线电 | 1293篇 |
出版年
| 2025年 | 23篇 |
| 2024年 | 94篇 |
| 2023年 | 98篇 |
| 2022年 | 102篇 |
| 2021年 | 161篇 |
| 2020年 | 172篇 |
| 2019年 | 167篇 |
| 2018年 | 155篇 |
| 2017年 | 210篇 |
| 2016年 | 167篇 |
| 2015年 | 186篇 |
| 2014年 | 247篇 |
| 2013年 | 419篇 |
| 2012年 | 242篇 |
| 2011年 | 224篇 |
| 2010年 | 209篇 |
| 2009年 | 233篇 |
| 2008年 | 229篇 |
| 2007年 | 271篇 |
| 2006年 | 260篇 |
| 2005年 | 246篇 |
| 2004年 | 199篇 |
| 2003年 | 175篇 |
| 2002年 | 205篇 |
| 2001年 | 171篇 |
| 2000年 | 146篇 |
| 1999年 | 120篇 |
| 1998年 | 114篇 |
| 1997年 | 107篇 |
| 1996年 | 70篇 |
| 1995年 | 55篇 |
| 1994年 | 50篇 |
| 1993年 | 31篇 |
| 1992年 | 27篇 |
| 1991年 | 25篇 |
| 1990年 | 20篇 |
| 1989年 | 14篇 |
| 1988年 | 13篇 |
| 1987年 | 8篇 |
| 1986年 | 12篇 |
| 1985年 | 16篇 |
| 1984年 | 11篇 |
| 1983年 | 6篇 |
| 1982年 | 10篇 |
| 1981年 | 6篇 |
| 1980年 | 7篇 |
| 1979年 | 5篇 |
| 1978年 | 7篇 |
| 1971年 | 3篇 |
| 1936年 | 2篇 |
排序方式： 共有5759条查询结果，搜索用时 15 毫秒
61.
Hiroshi Negishi Saiko Negishi Minoru Sasaki Masasi Inoue Shigeo Ohara 《Molecular Crystals and Liquid Crystals》2013,570(2):63-68
Abstract EXAFS and XANES spectra of Ti K-edge have been measured for 3d transition metal intercalation compounds M x TiS2 (M = Mn, Fe, Co and Ni; x ≤ 0.33). We have found that the interatomic distance between Ti and the first nearest neighbor S atoms, R(Ti-S), increases with the guest concentration x. The variation in XANES spectra with x reveals the reduction of the valence state of Ti atoms upon intercalation of M. From these results as well as the M K-edge EXAFS data studied previously, we have proposed a simple model on the local structure of M x TiS2 to reproduce the observed values of R(Ti-S) by averaging local shift of S atoms caused by intercalation. 相似文献
62.
In this paper, the locally conservative Galerkin (LCG) method (Numer. Heat Transfer B Fundam. 2004; 46 :357–370; Int. J. Numer. Methods Eng. 2007) has been extended to solve the incompressible Navier–Stokes equations. A new correction term is also incorporated to make the formulation to give identical results to that of the continuous Galerkin (CG) method. In addition to ensuring element‐by‐element conservation, the method also allows solution of the governing equations over individual elements, independent of the neighbouring elements. This is achieved within the CG framework by breaking the domain into elemental sub‐domains. Although this allows discontinuous trial function field, we have carried out the formulation using the continuous trial function space as the basis. Thus, the changes in the existing CFD codes are kept to a minimum. The edge fluxes, establishing the continuity between neighbouring elements, are calculated via a post‐processing step during the time‐stepping operation. Therefore, the employed formulation needs to be carried out using either a time‐stepping or an equivalent iterative scheme that allows post‐processing of fluxes. The time‐stepping algorithm employed in this paper is based on the characteristic‐based split (CBS) scheme. Both steady‐ and unsteady‐state examples presented show that the element‐by‐element formulation employed is accurate and robust. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
63.
64.
Ezequiel J. López Norberto M. Nigro Sofía S. Sarraf Santiago Márquez Damián 《国际流体数值方法杂志》2012,69(1):124-145
65.
Stefan Langer 《国际流体数值方法杂志》2012,69(2):332-352
We derive and investigate point implicit Runge–Kutta methods to significantly improve the convergence rate to approximate steady‐state solutions of inviscid flows. It turns out that the point implicit Runge–Kutta can be interpreted as a preconditioned explicit Runge–Kutta method, where the preconditioner arises naturally as local derivative of the residual function. Moreover, many preconditioners suggested in the literature so far are identified as special case of our general ansatz. Conditions will be formulated such that explicit Runge–Kutta methods with local time stepping are equivalent to point implicit methods. In numerical examples, we will demonstrate the improved convergence rates. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
66.
A. Carpinteri A. Sapora 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2010,90(3):203-210
In this paper, a fractional approach to describe the diffusion process in fractal media is put forward. After introducing anomalous diffusion quantities, the continuity and constitutive equations are derived by means of local fractional calculus, and the problem is formulated both in the steady‐state regime and in the transient regime. Eventually, a simple heat conduction problem in the steady‐state regime is solved analytically. 相似文献
67.
G. Wu B. Zhang 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2010,90(6):489-501
Making use of the Fourier localization method, we prove the local‐in‐time existence and uniqueness of solutions to the viscous rotating shallow water equations with a term of capillarity under both the low regularity assumption on the initial data and the assumption that the initial height is bounded away from zero. 相似文献
68.
In this paper, the local radial point interpolation meshless method (LRPIM) is used for the analysis of two‐dimensional potential flows, based on a local‐weighted residual method with the Heaviside step function as the weighting function over a local subdomain. Trial functions are constructed using radial basis functions. The present method is a truly meshless method based only on a number of randomly located nodes. Integration over the subdomains requires only a simple integration cell to obtain the solution. No element matrix assembly is required and no special treatment is needed to impose the essential boundary conditions. The novelty of the paper is the use of a local Heaviside weight function in the LRPIM, which does not need local domain integration and integrations only on the boundary of the local domains are needed. Effects of the sizes of local subdomain and interpolation domain on the performance of the present method are investigated. The behavior of shape parameters of multiquadrics has been systematically studied. Two numerical tests in groundwater and fluid flows are presented and compared with closed‐form solutions and finite element method. The results show that the use of a local Heaviside weight function in the LRPIM is highly accurate and possesses no numerical difficulties. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
69.
In recent years, a practice of tidal prediction based on a deterministic model or by a time series forecasting model has been established. A deterministic model can predict tidal movement and capture the dynamics of the flow pattern over the entire domain. However, due to the simplification of model settings and near shore effects, the accuracy of the numerical model can diminish. Time series forecasting is capable of capturing the underlying mechanism that may not be revealed in the deterministic model simulation. However, such data‐driven forecast fails to maintain accuracy with the progress of forecast horizon. In this paper, a scheme that combines the advantages of these two methods is introduced. The model errors are forecasted to different time horizons using a data‐driven approach, and are then superimposed on the simulation results in order to correct the model output. Based on the proposed method, it is found that the accuracy is significantly improved with more than 50% of the errors removed on the average. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
70.
Almost all evaluations of convection schemes reported in the literature are conducted using simple problems on uniform orthogonal grids; thus, having limited contribution when solving industrial computational fluid dynamics (CFD), where the grids are usually non‐orthogonal with distortions. Herein, several convection schemes are assessed in uniform and distorted non‐orthogonal grids with emphasis on industrial applications. Linear and nonlinear (TVD) convection schemes are assessed on analytical benchmarks in both uniform and distorted grids. To evaluate the performance of the schemes, four error metrics are used: dissipation, phase and L1 errors, and the schemes' effective order of accuracy. Qualitative and quantitative deterioration of these error metrics as a function of the grid distortion metrics are investigated, and rigorous verifications are performed. Recommendations for effective use of the convection schemes based on the range of grid aspect ratio (AR), expansion ratio (ER) and skewness (Q) are included. A ship hydrodynamics case is studied, involving a Reynolds averaged Navier–Stokes simulation of a bare‐hull KVLCC2 tanker using linear and nonlinear convection schemes coupled with isotropic and anisotropic Reynolds‐stress (ARS) turbulence models using CFDShip‐Iowa v4. Predictions of local velocities and turbulent quantities from the midships to the nominal wake plane are compared with experimental fluid dynamics (EFD), and rigorous verification and validation analyses for integral forces and moments are performed for 0° and 12° drift angles. Best predictions are observed when coupling a second‐order TVD scheme with the anisotropic turbulence model. Further improvements are observed in terms of prediction of the vortical structures for 30° drift when using TVD2S‐ARS coupled with DES. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献