全文获取类型
收费全文 | 15452篇 |
免费 | 1499篇 |
国内免费 | 1572篇 |
专业分类
化学 | 3568篇 |
晶体学 | 228篇 |
力学 | 1961篇 |
综合类 | 257篇 |
数学 | 9989篇 |
物理学 | 2520篇 |
出版年
2024年 | 25篇 |
2023年 | 145篇 |
2022年 | 154篇 |
2021年 | 247篇 |
2020年 | 385篇 |
2019年 | 358篇 |
2018年 | 337篇 |
2017年 | 427篇 |
2016年 | 450篇 |
2015年 | 337篇 |
2014年 | 635篇 |
2013年 | 1076篇 |
2012年 | 778篇 |
2011年 | 917篇 |
2010年 | 891篇 |
2009年 | 983篇 |
2008年 | 1059篇 |
2007年 | 1131篇 |
2006年 | 930篇 |
2005年 | 870篇 |
2004年 | 766篇 |
2003年 | 816篇 |
2002年 | 692篇 |
2001年 | 549篇 |
2000年 | 509篇 |
1999年 | 464篇 |
1998年 | 411篇 |
1997年 | 334篇 |
1996年 | 270篇 |
1995年 | 252篇 |
1994年 | 204篇 |
1993年 | 150篇 |
1992年 | 141篇 |
1991年 | 110篇 |
1990年 | 96篇 |
1989年 | 70篇 |
1988年 | 70篇 |
1987年 | 55篇 |
1986年 | 60篇 |
1985年 | 64篇 |
1984年 | 49篇 |
1983年 | 25篇 |
1982年 | 60篇 |
1981年 | 45篇 |
1980年 | 33篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry
Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a 13C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10?2 weight‐average molecular weight (Mw)0.815 (mL g?1) in the Mw region from 3.2 × 104 to 12.9 × 104. The persistence length (q), molar mass per unit contour length (ML), and characteristic ratio (C∞) of cellulose in the dilute solution were 6.0 nm, 350 nm?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004 相似文献
62.
对于超细长弹性杆静力学的Kirchhoff方程,用动力学的概念和方法研究其常值特解 和稳定性问题.计算了Kirchhoff方程相对固定坐标系、截面主轴坐标系以及中心线Frenet 坐标系的常值特解,进行了Kirchhoff动力学比拟,用一次近似理论分别讨论了它们的Lyapu nov稳定性,导出了若干稳定性判据,并在参数平面上绘出了稳定域.
关键词:
超细长弹性杆
Kirchhoff方程
常值特解
Lyapunov稳定性 相似文献
63.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
64.
Wolfgang Knirsch 《Mathematische Nachrichten》2004,265(1):15-23
On weighted spaces with strictly plurisubharmonic weightfunctions the canonical solution operator of and the ‐Neumann operator are bounded. In this paper we find a class of strictly plurisubharmonic weightfunctions with certain growth conditions, so that they are Hilbert‐Schmidt operators between weighted spaces with different weightfunctions, if they are restricted to forms with holomorphic coefficients. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
65.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
66.
In this article we prove the existence of the solution to the mixed problem for Euler–Bernoulli beam equation with memory term. The existence is proved by means of the Faedo–Galerkin method and the exponential decay is obtained by making use of the multiplier technique combined with integral inequalities due to Komornik. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
67.
We study the complex Ginzburg–Landau equation with zero Neumann boundary conditions on a finite interval and establish that this boundary problem (with suitably chosen parameters) has countably many stable two-dimensional self-similar tori. The case of periodic boundary conditions is also investigated. 相似文献
68.
本文通过研究匹配问题的实例空间,匈牙利算法和解空间三者之间的关系,指出S实例空间的数目与问题复杂度之间的关系既不是充分也不是必要的,而如何对问题的解空间进行合理的分解才能是问题的关键。 相似文献
69.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
70.
Norikazu Yamaguchi 《Mathematical Methods in the Applied Sciences》2005,28(13):1507-1526
In this paper we are concerned with the initial boundary value problem of the micropolar fluid system in a three dimensional bounded domain. We study the resolvent problem of the linearized equations and prove the generation of analytic semigroup and its time decay estimates. In particular, Lp–Lq type estimates are obtained. By use of the Lp–Lq estimates for the semigroup, we prove the existence theorem of global in time solution to the original nonlinear problem for small initial data. Furthermore, we study the magneto‐micropolar fluid system in the final section. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献