全文获取类型
收费全文 | 11991篇 |
免费 | 1135篇 |
国内免费 | 524篇 |
专业分类
化学 | 758篇 |
晶体学 | 36篇 |
力学 | 1526篇 |
综合类 | 111篇 |
数学 | 416篇 |
物理学 | 2829篇 |
综合类 | 7974篇 |
出版年
2024年 | 64篇 |
2023年 | 162篇 |
2022年 | 317篇 |
2021年 | 335篇 |
2020年 | 380篇 |
2019年 | 275篇 |
2018年 | 280篇 |
2017年 | 394篇 |
2016年 | 397篇 |
2015年 | 454篇 |
2014年 | 750篇 |
2013年 | 726篇 |
2012年 | 763篇 |
2011年 | 818篇 |
2010年 | 548篇 |
2009年 | 586篇 |
2008年 | 666篇 |
2007年 | 669篇 |
2006年 | 554篇 |
2005年 | 551篇 |
2004年 | 489篇 |
2003年 | 459篇 |
2002年 | 386篇 |
2001年 | 332篇 |
2000年 | 299篇 |
1999年 | 298篇 |
1998年 | 202篇 |
1997年 | 228篇 |
1996年 | 203篇 |
1995年 | 159篇 |
1994年 | 145篇 |
1993年 | 152篇 |
1992年 | 110篇 |
1991年 | 130篇 |
1990年 | 89篇 |
1989年 | 68篇 |
1988年 | 57篇 |
1987年 | 45篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1957年 | 5篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 176 毫秒
961.
962.
Mahendra K. Verma 《Pramana》2003,61(3):577-594
Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated
by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimensiond = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy
fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field,
and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately
equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤r
A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies asd
1/3. For the normalized cross helicity σc →1, the cascade rates are proportional to (1 − σc)/(1 + σc , and the Kolmogorov’s constants vary significantly with σcc. 相似文献
963.
Does three-dimensional incompressible Euler flow with smooth initial conditions develop a singularity with infinite vorticity after a finite time? This blowup problem is still open. After briefly reviewing what is known and pointing out some of the difficulties, we propose to tackle this issue for the class of flows having analytic initial data for which hypothetical real singularities are preceded by singularities at complex locations. We present some results concerning the nature of complex space singularities in two dimensions and propose a new strategy for the numerical investigation of blowup. 相似文献
964.
965.
煤粉浓淡分离装置的特性研究 总被引:2,自引:0,他引:2
通过冷态模化试验 ,对煤粉浓淡分离器两相流的分离特性和阻力特性进行研究 ,了解它们的特性 ,以便更好地改进装置的性能 ,提高装置的利用率 ,同时对类似装置的研究提供借鉴 相似文献
966.
This first segment of the two‐part paper systematically examines several turbulence models in the context of three flows, namely a simple flat‐plate turbulent boundary layer, an axisymmetric separating flow, and a swirling flow. The test cases are chosen on the basis of availability of high‐quality and detailed experimental data. The tested turbulence models are integrated to solid surfaces and consist of: Rodi's two‐layer k–ε model, Chien's low‐Reynolds number k–ε model, Wilcox's k–ω model, Menter's two‐equation shear‐stress‐transport model, and the one‐equation model of Spalart and Allmaras. The objective of the study is to establish the prediction accuracy of these turbulence models with respect to axisymmetric separating flows, and flows of high streamline curvature. At the same time, the study establishes the minimum spatial resolution requirements for each of these turbulence closures, and identifies the proper low‐Mach‐number preconditioning and artificial diffusion settings of a Reynolds‐averaged Navier–Stokes algorithm for optimum rate of convergence and minimum adverse impact on prediction accuracy. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
967.
This second segment of the two‐part paper systematically examines several turbulence models in the context of two flows, namely a vortex flow created by an inclined jet in crossflow, and the flow field in a diffusing S‐shaped duct. The test cases are chosen on the basis of availability of high‐quality and detailed experimental data. The tested turbulence models are integrated to solid surfaces and consist of: Rodi's two‐layer k–ε model, Wilcox's k–ω model, Menter's two‐equation shear–stress‐transport model, and the one‐equation model of Spalart and Allmaras. The objective of the study is to establish the prediction accuracy of these turbulence models with respect to three‐dimensional separated flows with streamline curvature. At the same time, the study establishes the minimum spatial resolution requirements for each of these turbulence closures, and identifies the proper low‐Mach‐number preconditioning and artificial diffusion settings of a Reynolds‐averaged Navier–Stokes algorithm for optimum rate of convergence and minimum adverse impact on prediction accuracy. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
968.
The incompressible flow around bluff bodies (a square cylinder and a cube) is investigated numerically using turbulence models. A non‐linear k–ε model, which can take into account the anisotropy of turbulence with less CPU time and computer memory then RSM or LES, is adopted as a turbulence model. In tuning of the model coefficients of the non‐linear terms are adjusted through the examination of previous experimental studies in simple shear flows. For the tuning of the coefficient in the eddy viscosity (=Cμ), the realizability constraints are derived in three types of basic 2D flow patterns, namely, a simple shear flow, flow around a saddle and a focal point. Cμ is then determined as a function of the strain and rotation parameters to satisfy the realizability. The turbulence model is first applied to a 2D flow around a square cylinder and the model performance for unsteady flows is examined focussing on the period and the amplitude of the flow oscillation induced by Karman vortex shedding. The applicability of the model to 3D flows is examined through the computation of the flow around a surface‐mounted cubic obstacle. The numerical results show that the present model performs satisfactorily to reproduce complex turbulent flows around bluff bodies. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
969.
Yong Zhang Yuanlong Mo Xiaolan Zhou 《International Journal of Infrared and Millimeter Waves》2003,24(4):525-535
Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). Although TM
01 mode is it's main mode, the asymmetry mode may be excited by slight asymmetry of the structure, misalignment of the beam, or the asymmetry associated with the input or output structure. So research about asymmetry mode of disk-loaded waveguide is necessary. The general dispersion equation and interaction impedance expression of disk-loaded waveguide is obtained with accurate field theory for the first time. Based on these results, a broadband and a narrowband disk-loaded waveguides are designed which can be used in the Ka band HPTWT. Moreover, the theoretical calculated results are compared with the simulated results from the HFSS (High Frequency Structure Simulator) code using finite element method. It is found that frequency domain overlapped by these two modes of the narrowband structure is very narrow, so the HEM
11 mode may be ignored when calculating Beam-wave interaction. In the other hand, the interaction impedance of HEM
11 mode is very low generally. 相似文献
970.