全文获取类型
收费全文 | 7142篇 |
免费 | 851篇 |
国内免费 | 1213篇 |
专业分类
化学 | 6295篇 |
晶体学 | 133篇 |
力学 | 444篇 |
综合类 | 71篇 |
数学 | 1542篇 |
物理学 | 721篇 |
出版年
2024年 | 10篇 |
2023年 | 54篇 |
2022年 | 110篇 |
2021年 | 223篇 |
2020年 | 309篇 |
2019年 | 256篇 |
2018年 | 230篇 |
2017年 | 271篇 |
2016年 | 334篇 |
2015年 | 302篇 |
2014年 | 413篇 |
2013年 | 604篇 |
2012年 | 651篇 |
2011年 | 446篇 |
2010年 | 370篇 |
2009年 | 423篇 |
2008年 | 420篇 |
2007年 | 450篇 |
2006年 | 383篇 |
2005年 | 358篇 |
2004年 | 409篇 |
2003年 | 321篇 |
2002年 | 238篇 |
2001年 | 181篇 |
2000年 | 183篇 |
1999年 | 206篇 |
1998年 | 154篇 |
1997年 | 154篇 |
1996年 | 98篇 |
1995年 | 93篇 |
1994年 | 84篇 |
1993年 | 62篇 |
1992年 | 67篇 |
1991年 | 50篇 |
1990年 | 44篇 |
1989年 | 21篇 |
1988年 | 38篇 |
1987年 | 24篇 |
1986年 | 32篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有9206条查询结果,搜索用时 31 毫秒
11.
We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential compressible fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written as a second-order, nonlinear equation of mixed elliptic-hyperbolic type for the velocity potential. The transonic shock problem can be formulated into the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.
12.
We consider a useful modification of the inexact implicit method with a variable parameter in Wang et al. J Optim Theory 111:
431–443 (2001) for generalized mixed monotone variational inequalities. One of the contributions of the proposed method in
this paper is that the restrictions imposed on the variable parameter are weaker than the ones in Wang et al. J Optim Theory
111: 431–443 (2001). Another contribution is that we establish a sufficient and necessary condition for the convergence of
the proposed method to a solution of the general mixed monotone variational inequality. 相似文献
13.
M. Akbari A. Behzadmehr F. Shahraki 《International Journal of Heat and Fluid Flow》2008,29(2):545-556
Fully developed laminar mixed convection of a nanofluid consists of water and Al2O3 in horizontal and inclined tubes has been studied numerically. Three-dimensional elliptic governing equations have been solved to investigate the flow behaviors over a wide range of the Grashof and Reynolds numbers. Comparisons with previously published experimental and numerical works on mixed convection in a horizontal and inclined tube are performed and good agreements between the results are observed. Effects of nanoparticles concentration and tube inclinations on the hydrodynamics and thermal parameters are presented and discussed. It is shown that the nanoparticles concentration does not have significant effects on the hydrodynamics parameters. Heat transfer coefficient increases by 15% at 4 Vol.% Al2O3. Skin friction coefficient continually increases with the tube inclination, but the heat transfer coefficient reaches a maximum at the inclination angle of 45°. 相似文献
14.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
15.
研究了Banach空间中非线性混合型微分-积分方程初值问题u′=f(t,u,Tu,Su),u(0)=x0的整体解,完全没有要求f的任何增性,利用Mnch不动点定理和比较结果得到了初值问题整体解的存在性和唯一解,并且给出了一致收敛于唯一解的迭代序列,改进推广和统一了已有的许多结果. 相似文献
16.
FengSHI HongYangLI XiaoJunPENG RongZHANG XiaoQiangCHEN JiangLiFAN LiChengSUN 《中国化学快报》2004,15(12):1407-1410
As photosensitizer for solar cell, a new ruthenium (Ⅱ) complex with four ester groups had been synthesized, in which a phenol substituted by {[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)amino]methyl} is covalently linked to ruthenium (Ⅱ) tris-bipyridine. The structures of the new compounds were confirmed by NMR and ESI-MS spectra. The electrochemical and photochemical properties were also studied. 相似文献
17.
18.
19.
本文用变换群理论对运动水平平板混合对流边界层流动的动量、能量和浓度扩散方程进行了分析,得到了与X4/(7-5n)成正比的壁面温度分布和浓度分布,同时壁面运动速度正比于X(3-n)/(7-5n)时存在相似性解.导出了相似性解方程,用四阶Runge-Kutta方法进行了计算,给出了Pr=0.72 和Sc,K1,K2,K3参数下的速度、温度和浓度分布,得出了各参数对流场、温度场的影响。 相似文献
20.
Tatsien Li 《Mathematical Methods in the Applied Sciences》2006,29(13):1543-1553
By means of a direct and constructive method based on the theory of semi‐global C2 solution, the local exact boundary observability and an implicit duality between the exact boundary controllability and the exact boundary observability are shown for 1‐D quasilinear wave equations with various boundary conditions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献