全文获取类型
收费全文 | 5130篇 |
免费 | 613篇 |
国内免费 | 465篇 |
学科分类
数理化 | 6208篇 |
出版年
2024年 | 13篇 |
2023年 | 42篇 |
2022年 | 116篇 |
2021年 | 119篇 |
2020年 | 172篇 |
2019年 | 141篇 |
2018年 | 104篇 |
2017年 | 216篇 |
2016年 | 247篇 |
2015年 | 162篇 |
2014年 | 267篇 |
2013年 | 299篇 |
2012年 | 268篇 |
2011年 | 309篇 |
2010年 | 215篇 |
2009年 | 263篇 |
2008年 | 253篇 |
2007年 | 294篇 |
2006年 | 285篇 |
2005年 | 263篇 |
2004年 | 264篇 |
2003年 | 245篇 |
2002年 | 194篇 |
2001年 | 167篇 |
2000年 | 169篇 |
1999年 | 155篇 |
1998年 | 153篇 |
1997年 | 93篇 |
1996年 | 109篇 |
1995年 | 81篇 |
1994年 | 88篇 |
1993年 | 72篇 |
1992年 | 57篇 |
1991年 | 65篇 |
1990年 | 56篇 |
1989年 | 46篇 |
1988年 | 37篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1977年 | 3篇 |
1971年 | 6篇 |
1967年 | 1篇 |
1957年 | 13篇 |
排序方式: 共有6208条查询结果,搜索用时 593 毫秒
1.
离子阱中热库诱导退相干的控制 总被引:1,自引:1,他引:0
王中结 《原子与分子物理学报》2006,23(4):757-761
对单个囚禁离子在热库作用下的退相干的控制问题进行了研究.本文提出的控制方法是基于消除自由哈密顿技术和脉冲重聚技术的结合.前者是利用一个经典大失谐激光场作用于囚禁离子来实现的,而后者是利用一系列的激光π脉冲来实现的.解析与数值表明,应用这种控制方法可以有效消除量子退相干且比纯粹应用脉冲重聚技术要好. 相似文献
2.
3.
In this study, the nonlinear dynamic responses of a string are simulated using the Cellular Automata method based on the reflection rule. In the case of nonlinear systems, the velocity of wave propagation is not constant and depends on the amplitude. A new treatment of the dynamic time step is proposed for the Cellular Automata method considering the effect of the propagation velocity. As numerical examples, first, the dynamic responses of a string with linear characteristic are simulated using the Cellular Automata method. A typical resonance curve can be obtained. Second, the dynamic responses of a string with nonlinear characteristic are simulated using the proposed method. Some characteristic types of vibration can be obtained. It is concluded that the linear and nonlinear dynamic responses of a string may be obtained by simulation using the Cellular Automata method. 相似文献
4.
For more than 25 yearsJΨ production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood
while others are still unclear. The current status of the theory ofJΨ production will be sketched, paying special attention to the issues of formation time andJΨ re-interaction in a nuclear medium. 相似文献
5.
6.
乐毅 《宁波大学学报(理工版)》2004,17(4):437-440
从正交各向异性三维弹性动力学的控制方程出发,在求得四边简支矩形板自由振动频率和位移振型的基础上,构造了受迫振动的位移函数;利用自由振动位移振型的正交性,将控制方程的空间变量和时间变量分离,得到了广义质量、广义力和频率表示的关于时间的2阶常微分方程,从而得到了正交各向异性弹性矩形板在受迫振动下的位移场和应力场.给出了本文方法与薄板理论的算例. 相似文献
7.
The process of single liquid drop impact on thin liquid surface is numerically simulated with moving particle semi‐implicit method. The mathematical model involves gravity, viscosity and surface tension. The model is validated by the simulation of the experimental cases. It is found that the dynamic processes after impact are sensitive to the liquid pool depth and the initial drop velocity. In the cases that the initial drop velocity is low, the drop will be merged with the liquid pool and no big splash is seen. If the initial drop velocity is high enough, the dynamic process depends on the liquid depth. If the liquid film is very thin, a bowl‐shaped thin crown is formed immediately after the impact. The total crown subsequently expands outward and breaks into many tiny droplets. When the thickness of the liquid film increases, the direction of the liquid crown becomes normal to the surface and the crown propagates outward. It is also found that the radius of the crown is described by a square function of time: rC = [c(t ? t0)]0.5. When the liquid film is thick enough, a crown and a deep cavity inside it are formed shortly after the impact. The bottom of the cavity is initially oblate and then the base grows downward to form a sharp corner and subsequently the corner moves downward. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
8.
Santwana Mukhopadhyay 《Mechanics Research Communications》2004,31(1):81-89
The present work is concerned with the thermally induced vibration in a homogeneous and isotropic unbounded body with a spherical cavity. The Green and Nagdhi model of thermoelasticity without energy dissipation is employed. The closed form solutions for distributions of displacement, temperature and stresses are obtained. The solutions valid in the case of small frequency are deduced and the results are compared with the corresponding results obtained in other generalized thermoelasticity theories. Numerical results applicable to a copper-like material are also presented graphically and the nature of variations of the physical quantities with radial coordinate and with frequency of vibration is analyzed. 相似文献
9.
光纤传感振动检测系统及其实验研究 总被引:3,自引:0,他引:3
实际工程结构中的振动检测是十分重要的,也是十分复杂的,常用的结构振动检测传感器易受工程现场恶劣环境的影响.而光纤传感器具有小巧、抗电磁干扰、灵敏度高、适合长期监测等优点。本文建立了基于马赫—曾德(Mech-Zehnder)干涉原理的光纤传感振动检测系统.研制了运用先进的数字信号处理技术采集和处理数据的专用软件,并在典型结构件——钢制悬臂梁结构上进行了外加信号作用下的强迫振动检测和冲击载荷作用下的自由衰减振动检测,测量了该结构件的频率及振幅,其结果与同时进行的成熟的电测结果相近,说明光纤传感器用于结构件的振动测量是可靠的。本文为光纤传感器应用于实际工程的振动检测提供了新的技术装置,具有工程应用前景。 相似文献
10.