全文获取类型
收费全文 | 5613篇 |
免费 | 1293篇 |
国内免费 | 496篇 |
专业分类
化学 | 1469篇 |
晶体学 | 66篇 |
力学 | 750篇 |
综合类 | 94篇 |
数学 | 449篇 |
物理学 | 4574篇 |
出版年
2024年 | 16篇 |
2023年 | 81篇 |
2022年 | 120篇 |
2021年 | 147篇 |
2020年 | 165篇 |
2019年 | 149篇 |
2018年 | 151篇 |
2017年 | 200篇 |
2016年 | 238篇 |
2015年 | 241篇 |
2014年 | 418篇 |
2013年 | 358篇 |
2012年 | 334篇 |
2011年 | 400篇 |
2010年 | 319篇 |
2009年 | 353篇 |
2008年 | 333篇 |
2007年 | 401篇 |
2006年 | 423篇 |
2005年 | 314篇 |
2004年 | 274篇 |
2003年 | 271篇 |
2002年 | 201篇 |
2001年 | 234篇 |
2000年 | 183篇 |
1999年 | 147篇 |
1998年 | 150篇 |
1997年 | 136篇 |
1996年 | 135篇 |
1995年 | 97篇 |
1994年 | 63篇 |
1993年 | 37篇 |
1992年 | 48篇 |
1991年 | 53篇 |
1990年 | 30篇 |
1989年 | 23篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 18篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有7402条查询结果,搜索用时 15 毫秒
61.
62.
Qingfeng Zhang Shanjia Xu 《International Journal of Infrared and Millimeter Waves》2006,27(11):1539-1552
A novel uniplanar 2-D composite right/left-handed transmission line (CRLH-TL) structure is proposed based on a general transmission
line theory and the way to increase the relative operating bandwidth in the left-handed (LH) region and lower the LH operating
frequency is illustrated. In addition, a new method to extract parameters and calculate the Bloch impedance of the structure
is presented. Numerical results of the dispersion as well as the extracted parameters are given, which are calculated based
on full-wave simulation. The present 2-D uniplanar CRLH-TL structure is applicable to 2-D left-handed materials in lower and
wider LH frequency range.
Supported by the National Natural Science Foundation of China (No. 60371010) (No. 60471037) (No. 63531020) 相似文献
63.
M.Yu. Tretyakov V.V. Parshin M.A. Koshelev A.P. Shkaev A.F. Krupnov 《Journal of Molecular Spectroscopy》2006,238(1):91-97
Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′ka′, kc′-Jka, kc = 51,5-42,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 31,3-22,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given. 相似文献
64.
光谱色散匀滑技术与衍射光学器件联用性能的空间频谱分析 总被引:1,自引:0,他引:1
基于空间频谱分析方法,建立了光谱色散匀滑技术(SSD: Smoothing by Spectral Dispersion)与衍射光学器件(DOE: Diffractive Optical Element)联用性能的简化分析模型,为SSD与DOE联用时,SSD参量的优化提供了理论依据.数值模拟了SSD各参量,包括脉冲时间、调制频率、位相调制系数、光栅线色散系数等对束匀滑性能的影响.模拟结果表明,SSD参量经过优化选取,且波前畸变随时间快速变化时,能获得良好的束匀滑性能. 相似文献
65.
66.
J. Fang 《Optics & Laser Technology》1991,23(6):349-352
A rotational mismatch of gratings is used to generate a fringe carrier of an in-plane moiré pattern so that specimen deformation shows itself in the form of modulation of the carrier frequency. As both the unmodulated and modulated carriers are the patterns without fringe-loop or fringe-connection, they are automatically numbered with monotonical increasing orders by a digital image processing system without any ambiguity. The orders at every pixel of the image are determined by interpolation of the orders of the tracked fringes to establish two grey image files, from the difference of which, the orders of the in-plane displacement moiré are displayed with grey-level variation. 相似文献
67.
68.
We present a design technique of retarders suitable for nonlinear optical systems. A thin sample of LiNbO3 crystal is utilized as a retarder for wide-ranging applications. Analysis shows that the same crystal can be used for single-wave or two-wave retardations, changing the orientation of the crystal only. As an application, the retarder is used to polarize two waves orthogonal, as necessary for difference frequency mixing in an AgGaSe2 crystal. 相似文献
69.
研究了充有不同温度退火Fe基纳米晶粉芯LC回路的磁致频移特性(MFS),发现充有不同温度退火Fe基纳米晶粉芯LC回路的磁致频移不同,充有经600℃退火Fe基纳米晶粉芯LC回路的磁致频移最灵敏。 相似文献
70.
A compact high-resolution optical heterodyne interferometer combining a two-frequency light module and a minute optical system
is described. The light module, which generates two independent frequencies of light, is fabricated by proton exchange method
on LiNbO3 substrate. We report an experiment evaluating measurement accuracy using a micro-displacement measurement system which incorporates
this interferometer. Results of the experiment with a standard thickness sample show high thermal stability with maximum measurement
error of 1.8 nm at a temperature from 19°C to 33°C. The system was used to measure the hysteresis of a piezoelectric element
for displacements of several nm, thereby making it possible to analyze the system quantitatively in practice. 相似文献