全文获取类型
收费全文 | 3952篇 |
免费 | 402篇 |
国内免费 | 456篇 |
专业分类
化学 | 817篇 |
晶体学 | 23篇 |
力学 | 551篇 |
综合类 | 77篇 |
数学 | 2506篇 |
物理学 | 836篇 |
出版年
2024年 | 12篇 |
2023年 | 56篇 |
2022年 | 74篇 |
2021年 | 117篇 |
2020年 | 122篇 |
2019年 | 110篇 |
2018年 | 120篇 |
2017年 | 120篇 |
2016年 | 132篇 |
2015年 | 137篇 |
2014年 | 177篇 |
2013年 | 281篇 |
2012年 | 149篇 |
2011年 | 213篇 |
2010年 | 197篇 |
2009年 | 227篇 |
2008年 | 263篇 |
2007年 | 227篇 |
2006年 | 237篇 |
2005年 | 238篇 |
2004年 | 183篇 |
2003年 | 194篇 |
2002年 | 153篇 |
2001年 | 143篇 |
2000年 | 165篇 |
1999年 | 132篇 |
1998年 | 113篇 |
1997年 | 108篇 |
1996年 | 85篇 |
1995年 | 42篇 |
1994年 | 37篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1974年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有4810条查询结果,搜索用时 78 毫秒
1.
2.
3.
4.
固体力学有限元体系的结构拓扑变化理论 总被引:2,自引:1,他引:1
本文是文[1]的继续.文[1]提出了杆件系统的结构拓扑变化理论和拓扑变化法本文将这一理论和方法推进到连续体有限元体系;且在此基础上揭示出有限元体系的一个新性质,称为基本位移之梯度的正交性定理,从而给出一套设计敏度的显式表达式,可直接用于计算. 相似文献
5.
Shougo Higashi 《Surface science》2006,600(3):591-597
We have studied the individual adsorption of Mn and Bi, and their coadsorption on Cu(0 0 1) by low-energy electron diffraction (LEED). For Mn, we have determined the c(2 × 2) structure formed at 300 K, whose structure had been determined by several methods. We reconfirmed by a tensor LEED analysis that it is a substitutional structure and that a previously reported large corrugation (0.30 Å) between substitutional Mn and remaining surface Cu atoms coincides perfectly with the present value. In the individual adsorption of Bi, we have found a c(4 × 2) structure, which is formed by cooling below ∼250 K a surface prepared by Bi deposition of ∼0.25 ML coverage at 300 K where streaky half-order LEED spots appear. The c(4 × 2) structure has been determined by the tensor LEED analysis at 130 K and it is a substitutional structure. In the coadsorption, we found a c(6 × 4) structure, which has been determined by the tensor LEED analysis. It is very similar to the previously determined structure of the c(6 × 4) formed by coadsorption of Mg and Bi, and embedded MnBi4 clusters are arranged in the top Cu layer instead of MgBi4. Large lateral displacements of Bi atoms in the c(6 × 4)-(Mn + Bi) suggest that the Mn atoms undergo the size-enhancement caused by their large magnetic moment. 相似文献
6.
We inquire into the time evolution of quantum systems associated with pseudo-or quasi-Hermitian Hamiltonians. We obtain, in
the pseudo-Hermitian case, a generalized Liouville-von Neumann equation for closed systems. We show that quantum systems with
quasi-Hermitian Hamiltonians admit the proper interpretation in terms of open quantum system and derive a generalized Lindblad-Kossakowski
equation. Finally, we extend such formalism to the study of decaying systems.
Partially supported by PRIN “Sintesi”. 相似文献
7.
设 $\varphi$ 是单位园盘 $D$ 到自身的解析映射, $X$ 是 $D$ 上解析函数的 Banach 空间, 对 $f\in X$, 定义复合算子$C_\varphi $ : $C_\varphi (f)=f\circ \varphi$. 我们利用从 ${\cal B}^0$到 $E(p,q)$ 和 $E_0(p,q)$ 空间的复合算子研究了空间 $E(p,q)$ 和 $E_0(p,q)$, 给出了一个新的特征. 相似文献
8.
本文应用上、下解方法和 Leray-Schauder不动点定理 ,证明了一类拟线性椭圆方程边值问题弱解的存在性 ,并且给出了一个应用实例 相似文献
9.
We give necessary and sufficient conditions for an operator on a separable Hilbert space to satisfy the hypercyclicity criterion.
This paper is a part of the second author’s Doctoral thesis, written at Shiraz University under the direction of the first
author. 相似文献
10.
The turbulent flow in a compound meandering channel with a rectangular cross section is one of the most complicated turbulent flows, because the flow behaviour is influenced by several kinds of forces, including centrifugal forces, pressure‐driven forces and shear stresses generated by momentum transfer between the main channel and the flood plain. Numerical analysis has been performed for the fully developed turbulent flow in a compound meandering open‐channel flow using an algebraic Reynolds stress model. The boundary‐fitted coordinate system is introduced as a method for coordinate transformation in order to set the boundary conditions along the complicated shape of the meandering open channel. The turbulence model consists of transport equations for turbulent energy and dissipation, in conjunction with an algebraic stress model based on the Reynolds stress transport equations. With reference to the pressure–strain term, we have made use of a modified pressure–strain term. The boundary condition of the fluctuating vertical velocity is set to zero not only for the free surface, but also for computational grid points next to the free surface, because experimental results have shown that the fluctuating vertical velocity approaches zero near the free surface. In order to examine the validity of the present numerical method and the turbulent model, the calculated results are compared with experimental data measured by laser Doppler anemometer. In addition, the compound meandering open channel is clarified somewhat based on the calculated results. As a result of the analysis, the present algebraic Reynolds stress model is shown to be able to reasonably predict the turbulent flow in a compound meandering open channel. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献