全文获取类型
收费全文 | 3344篇 |
免费 | 411篇 |
国内免费 | 241篇 |
专业分类
化学 | 293篇 |
晶体学 | 31篇 |
力学 | 1980篇 |
综合类 | 31篇 |
数学 | 303篇 |
物理学 | 1358篇 |
出版年
2024年 | 8篇 |
2023年 | 33篇 |
2022年 | 93篇 |
2021年 | 67篇 |
2020年 | 120篇 |
2019年 | 85篇 |
2018年 | 76篇 |
2017年 | 135篇 |
2016年 | 150篇 |
2015年 | 112篇 |
2014年 | 187篇 |
2013年 | 179篇 |
2012年 | 174篇 |
2011年 | 210篇 |
2010年 | 141篇 |
2009年 | 149篇 |
2008年 | 143篇 |
2007年 | 178篇 |
2006年 | 177篇 |
2005年 | 178篇 |
2004年 | 177篇 |
2003年 | 167篇 |
2002年 | 119篇 |
2001年 | 122篇 |
2000年 | 98篇 |
1999年 | 99篇 |
1998年 | 116篇 |
1997年 | 64篇 |
1996年 | 62篇 |
1995年 | 43篇 |
1994年 | 50篇 |
1993年 | 41篇 |
1992年 | 40篇 |
1991年 | 46篇 |
1990年 | 34篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1971年 | 3篇 |
1957年 | 8篇 |
排序方式: 共有3996条查询结果,搜索用时 281 毫秒
31.
振动系统的模态分析实验设计 总被引:8,自引:0,他引:8
利用模态分析原理和简单试验仪器,得到了直观的悬臂梁和圆盘前4阶模态振型,使学生熟悉了模态分析原理和测试方法,有利于学生对振动规律的理解. 相似文献
32.
In order to study cross flow induced vibration of heat exchanger tube bundles, a new fluid–structure interaction model based on surface vorticity method is proposed. With this model, the vibration of a flexible cylinder is simulated at Re=2.67 × 104, the computational results of the cylinder response, the fluid force, the vibration frequency, and the vorticity map are presented. The numerical results reproduce the amplitude‐limiting and non‐linear (lock‐in) characteristics of flow‐induced vibration. The maximum vibration amplitude as well as its corresponding lock‐in frequency is in good agreement with experimental results. The amplitude of vibration can be as high as 0.88D for the case investigated. As vibration amplitude increases, the amplitude of the lift force also increases. With enhancement of vibration amplitude, the vortex pattern in the near wake changes significantly. This fluid–structure interaction model is further applied to simulate flow‐induced vibration of two tandem cylinders and two side‐by‐side cylinders at similar Reynolds number. Promising and reasonable results and predictions are obtained. It is hopeful that with this relatively simple and computer time saving method, flow induced vibration of a large number of flexible tube bundles can be successfully simulated. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
33.
34.
Condition monitoring and life prediction of the vehicle engine is an important and urgent problem during the vehicle development process. The vibration signals that are closely associated with the engine running condition and its development trend are complex and nonlinear. The chaos theory is used to treat the nonlinear dynamical system recently. A novel chaos method in conjunction with SVD (singular value decomposition)denoising skill are used to predict the vibration time series. Two types of time series and their prediction errors are provided to illustrate the practical utility of the method. 相似文献
35.
36.
Probabilistic characteristics of a sliding structure is investigated by using new versions of stochastic linearization technique. The structure is composed of base part and upper part, which are connected to each other in a spring-damping system. Coulomb friction between the base structure and earth ground is considered. Two alternative versions of stochastic linearization approach, suggested by X. Zhang and I. Elishakoff, respectively, are applied to such a sliding structure to evaluate its statistical properties. Compared with the results of Monte Carlo simulation, the two new approaches are performing much better than the conventional one in their applications to the sliding structure. Moreover, numerical results indicate that the criterion proposed by Elishakoff turns out to be superior to all other versions in the problem under study. Numerical results also suggest that the entire structure may be replaced by the rigid body in the sliding problem as long as the difference of velocity responses are considered less important than those of displacement responses. 相似文献
37.
The intensity dynamics of the double-clad Yb fibre laser have been characterised. Stabilisation of the fibre laser intensity by using uniform bi-directional pumping is demonstrated. For the single-end-pumped Yb fibre laser, the output becomes more stable for the shorter fibre length due to the higher threshold of stimulated Brillouin scattering, SBS, and Kerr effects and the reduction of saturated absorber effects caused by any unpumped fibre section. By additional pumping in a double-end-pumped configuration, the output power can be scaled higher before detecting high intensity pulses initiated by SBS in the Yb fibre laser due to the reduction of saturable absorption effect. It is confirmed that uniform pumping enhances the stability of the laser output. 相似文献
38.
39.
A diode-end-pumped Nd:YAG laser is passively Q-switched by using Cr4+:YAG as saturable absorber. When CW pumped with a laser diode which the maximum power is 550 mW, the laser produces pulses of 24 ns duration at 1064 nm, with an energy of 26 μJ. 相似文献
40.
硅杂环丁烷在有机硅化学中是一类非常重要的小分子环系化合物。由于硅杂环丁烷和环丁烷的环张力相似,因而显示出较高的反应活性。例如能与某些试剂作用,生成开环产物;在光解或热解条件下,产生具有Si=C结构的高活性中间体,可用以合成多种有机硅化合物。 相似文献