全文获取类型
收费全文 | 27993篇 |
免费 | 4988篇 |
国内免费 | 2018篇 |
专业分类
化学 | 6158篇 |
晶体学 | 610篇 |
力学 | 696篇 |
综合类 | 149篇 |
数学 | 349篇 |
物理学 | 18273篇 |
综合类 | 8764篇 |
出版年
2024年 | 99篇 |
2023年 | 248篇 |
2022年 | 644篇 |
2021年 | 679篇 |
2020年 | 649篇 |
2019年 | 566篇 |
2018年 | 614篇 |
2017年 | 948篇 |
2016年 | 1053篇 |
2015年 | 1040篇 |
2014年 | 1723篇 |
2013年 | 2062篇 |
2012年 | 1798篇 |
2011年 | 1905篇 |
2010年 | 1329篇 |
2009年 | 1666篇 |
2008年 | 1881篇 |
2007年 | 1954篇 |
2006年 | 1745篇 |
2005年 | 1618篇 |
2004年 | 1420篇 |
2003年 | 1246篇 |
2002年 | 1159篇 |
2001年 | 1011篇 |
2000年 | 945篇 |
1999年 | 830篇 |
1998年 | 665篇 |
1997年 | 649篇 |
1996年 | 514篇 |
1995年 | 468篇 |
1994年 | 408篇 |
1993年 | 317篇 |
1992年 | 257篇 |
1991年 | 192篇 |
1990年 | 155篇 |
1989年 | 152篇 |
1988年 | 109篇 |
1987年 | 90篇 |
1986年 | 60篇 |
1985年 | 38篇 |
1984年 | 29篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Takeshi Murashige Hideo Fujikake Hiroto Sato Hiroshi Kikuchi Taiichiro Kurita Fumio Sato 《Optical Review》2004,11(6):349-352
We have confirmed light diffraction of aligned polymer fibers obtained by a phase separation of an anisotropic-phase solution of liquid crystal and polymer. He—Ne laser light passing through the polymer fibers was scattered in the axis vertical to the fibers, and had two peaks of light intensity symmetrical to the center of the transmitting laser spot. The two peaks were found to be caused by light diffraction due to the periodic polymer-fiber dispersion because the peaks corresponded to values calculated by intervals between the fibers. The periodical fiber networks are considered to be formed by anisotropic spinodal decomposition. This effect can be used to measure the dispersion order of the polymer fibers. © 2004 The Optical Society of Japan 相似文献
22.
The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution). 相似文献
23.
X. H. Li Y. Z. Meng S. J. Wang A. Varada Rajulu S. C. Tjong 《Journal of Polymer Science.Polymer Physics》2004,42(4):666-675
The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004 相似文献
24.
25.
26.
27.
两段级联掺铒光纤放大器的优化研究 总被引:7,自引:4,他引:3
基于Giles模型,研究了980 nm和1480 nm泵浦的两段级联掺铒光纤放大器(EDFA)的设计,得出了掺铒光纤(EDF)的最佳长度和光隔离器的最佳位置随泵浦功率和信号功率的变化关系.比较980 nm和1480 nm泵浦的两段级联EDFA,可以发现,前者的最佳EDF长度短,而光隔离器最佳位置距EDFA输入端远. 相似文献
28.
首先叙述了光纤传输Nd~(3+): YAG激光的优点,接着分析了不同光纤和其传输Nd~(3+): YAG激光的特点。然后通过对光纤传输系统各部分的分析与设计,结合实际,设计了光纤耦合机构。最后,对来自于工件反射光问题提出了解决方案。 相似文献
29.
An all-optical fiber nonlinear Fabry-Perot resonator is proposed. The steady-state model for describing this resonator is developed. The transmission and refection bistabilities are shown numerically. Our results show that the bistability in this system is similar to that in a normal nonlinear Fabry-Perot etalon, except that the characteristics of the bistability can be changed not only by the cavity length but also by the phase shifts of the fiber loop mirrors. 相似文献
30.