全文获取类型
收费全文 | 24396篇 |
免费 | 5536篇 |
国内免费 | 1299篇 |
专业分类
化学 | 2101篇 |
晶体学 | 173篇 |
力学 | 403篇 |
综合类 | 46篇 |
数学 | 71篇 |
物理学 | 13677篇 |
无线电 | 14760篇 |
出版年
2024年 | 49篇 |
2023年 | 137篇 |
2022年 | 270篇 |
2021年 | 461篇 |
2020年 | 464篇 |
2019年 | 322篇 |
2018年 | 367篇 |
2017年 | 637篇 |
2016年 | 734篇 |
2015年 | 840篇 |
2014年 | 1308篇 |
2013年 | 1124篇 |
2012年 | 1669篇 |
2011年 | 1765篇 |
2010年 | 1173篇 |
2009年 | 1234篇 |
2008年 | 1770篇 |
2007年 | 1947篇 |
2006年 | 1747篇 |
2005年 | 1552篇 |
2004年 | 1504篇 |
2003年 | 1243篇 |
2002年 | 1196篇 |
2001年 | 1058篇 |
2000年 | 1010篇 |
1999年 | 917篇 |
1998年 | 739篇 |
1997年 | 694篇 |
1996年 | 634篇 |
1995年 | 521篇 |
1994年 | 486篇 |
1993年 | 394篇 |
1992年 | 374篇 |
1991年 | 314篇 |
1990年 | 190篇 |
1989年 | 96篇 |
1988年 | 71篇 |
1987年 | 58篇 |
1986年 | 31篇 |
1985年 | 19篇 |
1984年 | 31篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
A novel and simple two-frequency Brillouin fiber laser is presented. It is based on a fiber Fabry-Perot cavity with fiber Bragg gratings as reflectors. The model of stimulated Brillouin scattering in fiber grating-based Fabry-Perot resonator is investigated. The laser allows conversion efficiency of close to 100% and suppresses the higher-order Stokes waves. The theoretical prediction is presented and the experimental demonstration is realized. 相似文献
22.
23.
V. S. Gorelik P. P. Sverbil' A. B. Fadyushin V. V. Vasil'ev 《Journal of Russian Laser Research》2004,25(1):54-63
A possibility of application of semiconductor lasers of the visible range as exciting sources for Raman spectroscopy is studied. An experimental set-up for measuring Raman spectra of polycrystalline dielectrics and broad-gap semiconductors excited by a semiconductor laser with a wavelength of 640 nm was created. The conditions under which the spectral width of the lasing line of a semiconductor laser was within 10-3 cm-1 in the continuous mode with a power of 10 mW are realized. The characteristics of various types of exciting sources used in Raman spectroscopy are compared. The results of studies of the characteristic Raman spectra excited with a semiconductor laser in polycrystalline sulfur are presented. 相似文献
24.
A. N. Logunov 《Journal of Russian Laser Research》2004,25(4):331-348
A physical multidimensional local model of the propagation process of a laser pulse in air having no analogy to famous models in laser physics is constructed. It is based on the representations of classical wave mechanics characteristic of the theory of scalar wave fields. 相似文献
25.
26.
从激光推进的要求出发,阐述了用于激光推进的高功率激光器的选择原则,即激光器必须满足:(1)高的平均功率和峰值功率;(2)高的单脉冲能量;(3)高的重复频率;(4)优良的大气传输特性。主要分析了目前YAG固体激光器、自由电子激光器和TEA脉冲CO2激光器的特点,通过上述4个方面性能的比较,认为在目前水平下,TEA脉冲CO2激光器是进行激光推进的首选强激光源,其优点表现在:功率可达10kW量级,单脉冲能量可达0.5~1kJ,重复频率为20~40Hz;激光波长处于大气传输窗口,对大气变化不敏感;工作物质快速流动,不存在热透镜效应和破坏阈值;相关光学元件易于制造;光束质量较好;运行成本低。 相似文献
27.
Until recently, simple and reliable high repetition-rate laser sources with nanosecond pulses much shorter than from conventional A-O Q-switch lasers were not available. However over the past 2 years we have developed such lasers based on proprietary fast E-O switching technology, which allows designs delivering 1 ns pulses and subnanosecond jitter for good synchronisation. The technology provides pulses with multi-kW peak power and repetition-rates to >100 kHz.Most recently, the performance of these short pulse lasers has been developed further by implementing oscillator/amplifier (master oscillator and power amplifier, MOPA) technology which increases the output to >1 W average power. Here we report on a simple model that has been used to predict the performance of the CW pumped Nd:YVO4 amplifier used in the MOPA laser. The model is based on the well-known expressions for the saturated gain applying to laser pulses, but more usually applied to pulse-excited amplifiers. The model is shown to allow a good interpretation of the amplifier behaviour for kHz pulses and to be a useful tool for predicting the performance of the MOPA laser. 相似文献
28.
29.
研究了热传导方程的通解,进而提出激光热源形成的微观机理和热源形成过程的三个理论计算式。对激光热效应的应用具有指导意义。 相似文献
30.