全文获取类型
收费全文 | 3211篇 |
免费 | 317篇 |
国内免费 | 231篇 |
专业分类
化学 | 249篇 |
晶体学 | 25篇 |
力学 | 2027篇 |
综合类 | 24篇 |
数学 | 302篇 |
物理学 | 1132篇 |
出版年
2024年 | 12篇 |
2023年 | 40篇 |
2022年 | 92篇 |
2021年 | 68篇 |
2020年 | 120篇 |
2019年 | 88篇 |
2018年 | 75篇 |
2017年 | 132篇 |
2016年 | 136篇 |
2015年 | 107篇 |
2014年 | 155篇 |
2013年 | 158篇 |
2012年 | 143篇 |
2011年 | 187篇 |
2010年 | 130篇 |
2009年 | 134篇 |
2008年 | 134篇 |
2007年 | 174篇 |
2006年 | 167篇 |
2005年 | 157篇 |
2004年 | 176篇 |
2003年 | 160篇 |
2002年 | 111篇 |
2001年 | 113篇 |
2000年 | 91篇 |
1999年 | 96篇 |
1998年 | 110篇 |
1997年 | 63篇 |
1996年 | 58篇 |
1995年 | 43篇 |
1994年 | 51篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 46篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 21篇 |
1987年 | 7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3759条查询结果,搜索用时 0 毫秒
971.
应用波的相干原理分析了相控阵雷达的工作原理.以波的形成、波的发射和回波的接收等三个环节为主线,简要地介绍了由固态技术、光电子技术、计算机技术和信号处理技术所形成的相控阵雷达关键技术的背景、现状,并展望了相控阵雷达关键技术的未来. 相似文献
972.
讨论圆截面弹性细杆在黏性介质中的平面振动. 基于Kirchhoff理论,以杆中心线的Frenet坐标系为参考系,建立其动力学方程,杆中心线为任意平面曲线时,其扭转振动与弯曲振动解耦. 讨论两端固定条件下任意形状杆的平面扭转振动,以及无扭转的轴向受压直杆和圆环杆的平面弯曲振动,导出其自由振动频率和阻尼系数. 证明空间域内压杆的Lyapunov稳定性和欧拉稳定性条件为时域内渐近稳定性的充分必要条件,或无阻尼压杆的稳定性必要条件. 圆环杆平衡恒满足渐近稳定性条件.
关键词:
弹性细杆
黏性介质
扭转振动
弯曲振动 相似文献
973.
974.
Shigeo Hara Katsuhiro Yamamoto Shigetaka Shimada Hajime Nishi 《Journal of Polymer Science.Polymer Physics》2004,42(8):1539-1547
Temperature‐dependent electron spin resonance spectra of main‐chain free radicals, ? CF2(β)? C · F(α)? CF2(β)? , in poly(tetrafluoroethylene) (PTFE) were analyzed by the change in the hyperfine splitting due to β‐fluorines, which was a decreasing function of the observation temperature. The results were interpreted in terms of the rotational vibration around the Cα? Cβ bond. The amplitude of the vibration was estimated on the assumption of its harmonic oscillation. The vibration of the PTFE chain was found to have a large amplitude in comparison with that of a polyethylene chain in single crystals. The vibration of the large amplitude was caused by a weak interchain interaction in the PTFE matrices. The amplitude of the vibration in crosslinked PTFE was much larger than that in noncrosslinked PTFE. This result indicated that the free radicals in crosslinked PTFE were trapped in the amorphous region, which had the disordered sites of crosslinking, whereas the free radicals in noncrosslinked PTFE were mainly trapped in the paracrystalline region. The decay reaction of the free radicals in the PTFE matrices was also related to the heterogeneity in the structure and the rotational vibration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1539–1547, 2004 相似文献
975.
Procedures developed recently to extend the quasi-conservativeaveraging method to the case of non-white broad-band excitations arefurther extended and presented in a unified framework. The excitationscan be stationary or nonstationary with known evolutionary spectra, andthey can be additive, or multiplicative, or both. Relative merits ofthese procedures are compared, and their accuracies are substantiated byMonte Carlo simulations. 相似文献
976.
977.
978.
We present a comprehensive, functional analysis of clinical voice data derived from both high-speed digital imaging (HSDI) of the larynx and simultaneously acquired acoustic recordings. The goals of this study are to: (1) correlate dynamic characteristics of the vocal folds derived from direct laryngeal imaging with indirectly acquired acoustic measurements; (2) define the advantages of using a combined imaging/acoustic approach for the analysis of voice condition; and (3) identify new quantitative measures to evaluate the regularity of the vocal fold vibration and the complexity of the vocal output -- these measures will be key to successful diagnosis of vocal abnormalities. Image- and acoustic-based analyses are performed using an analytic phase plot approach previously introduced by our group (referred to as 'Nyquist' plot). Fast Fourier Transform (FFT) spectral analyses are performed on the same data for a comparison. Clinical HSDI and acoustic recordings from subjects having normal and specific voice pathologies, including muscular tension dysphonia (MTD) and recurrent respiratory papillomatosis (RRP) were analyzed using the Nyquist plot approach. The results of these analyses show that a combined imaging/acoustic analysis approach provides better characterization of the vibratory behavior of the vocal folds as it correlates with vocal output and pathology. 相似文献
979.
980.
Performance of ultra-low frequency passive vertical vibration isolation system with reverse pendulum
A novel long period passive vertical vibration isolator constructed by mounting reverse pendulums on two pairs of torsion
springs is presented. By theoretical analysis and numerical calculation, it is shown that the isolator can achieve much longer
resonant period due to gravitational positive feedback and is smaller in size than the current torsion spring isolators with
the same geometric parameters.
Project supported by the Post-doctoral Foundation of Huazhong University of Science and Technology. 相似文献