全文获取类型
收费全文 | 3677篇 |
免费 | 350篇 |
国内免费 | 154篇 |
专业分类
化学 | 176篇 |
晶体学 | 2篇 |
力学 | 877篇 |
综合类 | 53篇 |
数学 | 2284篇 |
物理学 | 789篇 |
出版年
2024年 | 2篇 |
2023年 | 45篇 |
2022年 | 64篇 |
2021年 | 74篇 |
2020年 | 131篇 |
2019年 | 102篇 |
2018年 | 88篇 |
2017年 | 110篇 |
2016年 | 122篇 |
2015年 | 102篇 |
2014年 | 166篇 |
2013年 | 270篇 |
2012年 | 159篇 |
2011年 | 211篇 |
2010年 | 176篇 |
2009年 | 238篇 |
2008年 | 211篇 |
2007年 | 213篇 |
2006年 | 199篇 |
2005年 | 201篇 |
2004年 | 164篇 |
2003年 | 165篇 |
2002年 | 110篇 |
2001年 | 114篇 |
2000年 | 110篇 |
1999年 | 107篇 |
1998年 | 107篇 |
1997年 | 68篇 |
1996年 | 60篇 |
1995年 | 28篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 36篇 |
1991年 | 36篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有4181条查询结果,搜索用时 0 毫秒
51.
基于欧拉框架下ADER格式,构造一维守恒只有一个时间步的、高精度中心型拉格朗日ADER(LADER)格式.构造r阶LADER格式包括:从欧拉方程出发推导拉格朗日框架下积分形式的方程、采用WENO方法高精度重构节点处守恒量和从1阶到r-1阶的空间导数、求拉氏框架下这些变量的Godunov值,并计算1阶到r-1阶的时间全导数,最后高精度离散积分形式的流通量函数.对光滑流场的模拟表明,LADER格式达到设计的精度;对含强间断的流场模拟表明,数值解在间断附近基本无振荡. 相似文献
52.
Dingfang Li Xiaofeng Wang & Hui Feng 《advances in applied mathematics and mechanics.》2013,5(1):55-77
A fully higher-order compact (HOC) finite difference scheme on the
9-point two-dimensional (2D) stencil is formulated for solving the
steady-state laminar mixed convection flow in a lid-driven inclined
square enclosure filled with water-$Al_2O_3$ nanofluid. Two
cases are considered depending on the direction of temperature
gradient imposed (Case I, top and bottom; Case II, left and right).
The developed equations are given in terms of the stream
function-vorticity formulation and are non-dimensionalized and then
solved numerically by a fourth-order accurate compact finite
difference method. Unlike other compact solution procedure in
literature for this physical configuration, the present method is
fully compact and fully higher-order accurate. The fluid flow, heat
transfer and heat transport characteristics were illustrated by
streamlines, isotherms and averaged Nusselt number. Comparisons with
previously published work are performed and found to be in excellent
agreement. A parametric study is conducted and a set of graphical
results is presented and discussed to elucidate that significant
heat transfer enhancement can be obtained due to the presence of
nanoparticles and that this is accentuated by inclination of the
enclosure at moderate and large Richardson numbers. 相似文献
53.
54.
Near-IR femtosecond lasers have been proposed to produce high-field terahertz radiation in the air via the laser-plasma interaction, but the physical mechanism still needs to be further explored. In this work, we theoretically investigate the effect of the two-color laser wavelength on the terahertz generation in the air based on a transient photocurrent model.We show that the long wavelength laser excitation can greatly enhance the terahertz amplitude for a given total laser intensity. Furthermore, we utilize a local current model to illustrate the enhancement mechanism. Our analysis shows that the terahertz amplitude is determined by the superposition of contributions from individual ionization events, and for the long wavelength laser excitation, the electron production concentrates in a few ionization events and acquires the larger drift velocities, which results in the stronger terahertz radiation generation. These results will be very helpful for understanding the terahertz generation process and optimizing the terahertz output. 相似文献
55.
56.
Simulating high Reynolds number flow in two-dimensional lid-driven cavity by multi-relaxation-time lattice Boltzmann method 总被引:3,自引:0,他引:3 下载免费PDF全文
By coupling the non-equilibrium extrapolation scheme for boundary condition with the
multi-relaxation-time lattice Boltzmann method, this paper finds that the stability
of the multi-relaxation-time model can be improved greatly, especially on
simulating high Reynolds number (Re) flow. As a discovery, the super-stability
analysed by Lallemand and Luo is verified and the complex structure of the cavity
flow is also exhibited in our numerical simulation when Re is high enough. To the
best knowledge of the authors, the maximum of Re which has been investigated by
direct numerical simulation is only around 50,000 in the literature; however,
this paper can readily extend the maximum to 1000,000 with the above combination. 相似文献
57.
在一般的近代物理实验教材中,关于电子衍射实验采用的是晶体表面反射衍射或金属箔透射衍射。本文提出一套基于双缝衍射的、用于研究微观粒子波粒二象性的电子衍射实验方案,并且鉴于在一般的实验中不具备进行电子双缝衍射实验的条件,本实验方案是在电子双缝衍射计算机模拟的仿真环境下进行的。 相似文献
58.
R. Wadsworth I. RagnarssonB.G. Carlsson Hai-Liang Ma P.J. DaviesC. Andreoiu R.A.E. Austin M.P. CarpenterD. Dashdorj S.J. Freeman P.E. Garrett J. GreeneA. Görgen D.G. JenkinsF. Johnston-Theasby P. JoshiA.O. Macchiavelli F. MooreG. Mukherjee W. ReviolD.G. Sarantites D. SeweryniakC.E. Svensson J.J. Valiente-Dobón 《Physics letters. [Part B]》2011,701(3):306-312
Four previously known rotational bands in 76Rb have been extended to moderate spins using the Gammasphere and Microball γ ray and charged particle detector arrays and the 40Ca(40Ca, 3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g9/2 particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape coexisting structures at medium spins. 相似文献
59.
A theoretical investigation is reported of the fine structure levels and the spin-singlet contributions to zero-field-splitting (ZFS) parameters for Cr2+ ion in CdGa2S4 crystals. Firstly, the complete energy matrix including all spin states for a 3d 4 ion in tetrahedral D 2d symmetry is constructed according the double-group chain in the strong-field scheme. Then, by diagonalizing the complete energy of electron–electron interactions, the crystal field and the spin–orbit coupling for the Cr2+ (3d 4) ion in CdGa2S4 crystal, the fine structure levels and the spin-singlet contributions to ZFS parameters a, D and F are calculated. The results show that the spin-singlet contribution to D is negligible, but the contributions to a and F are very important. So, to obtain more accurate ZFS parameters for 3d 4 ions in the tetrahedral crystals, all spin states should be considered. 相似文献
60.
The main difficulty for the numerical calculation of the wave running up a beach is the treatment of its moving water boundary.
In this paper a scheme of turning the free boundary problem into a fixed boundary problem is designed. The calculated run-up
height is consistent with the experiments. Some interesting wave phenomena are also found. 相似文献