全文获取类型
收费全文 | 11800篇 |
免费 | 1995篇 |
国内免费 | 767篇 |
专业分类
化学 | 2661篇 |
晶体学 | 86篇 |
力学 | 539篇 |
综合类 | 66篇 |
数学 | 231篇 |
物理学 | 10979篇 |
出版年
2024年 | 15篇 |
2023年 | 39篇 |
2022年 | 167篇 |
2021年 | 203篇 |
2020年 | 242篇 |
2019年 | 132篇 |
2018年 | 203篇 |
2017年 | 398篇 |
2016年 | 463篇 |
2015年 | 395篇 |
2014年 | 824篇 |
2013年 | 790篇 |
2012年 | 785篇 |
2011年 | 883篇 |
2010年 | 625篇 |
2009年 | 799篇 |
2008年 | 988篇 |
2007年 | 962篇 |
2006年 | 876篇 |
2005年 | 750篇 |
2004年 | 640篇 |
2003年 | 597篇 |
2002年 | 391篇 |
2001年 | 378篇 |
2000年 | 346篇 |
1999年 | 288篇 |
1998年 | 256篇 |
1997年 | 220篇 |
1996年 | 177篇 |
1995年 | 153篇 |
1994年 | 125篇 |
1993年 | 76篇 |
1992年 | 90篇 |
1991年 | 63篇 |
1990年 | 49篇 |
1989年 | 39篇 |
1988年 | 20篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
非对称三态叠加多模泛函叠加态光场的高次压缩——广义电场分量的不等幂次和压缩效应研究 总被引:2,自引:0,他引:2
多模真空态|{0j}〉q与两个空间强度分布特征不同的多模复共轭泛函相干态|{f(j a)*(x,y,z)}〉q和|{f(j b)*(x,y,z)}〉q的线性叠加组成的三态叠加多模泛函叠加态光场|ψ(f3)〉q,利用多模压缩态理论,研究了态|ψ(f3)〉q中广义电场分量的不等幂次高次和(H)压缩特性.结果表明:在一定的条件下,态|ψ(f3)〉q的广义电场分量可呈现出周期性变化的任意奇数次和任意偶数次的不等幂次高次H压缩效应;光场的经典振幅和经典初始相位的任意非对称空间分布特征对其压缩程度和压缩深度等压缩特性将产生直接的影响. 相似文献
42.
43.
Endoscopic illumination systems conduct light down a built-in fibre-optic bundle to illuminate the object. Many modern endoscopes employ wide-field imaging optical systems and therefore require an illuminating beam of large divergence. This is commonly provided by placing a strong diverging lens at the far end of the fibre bundle, but it results in a poor uniformity of illumination in the object space. This paper describes the design of a telescopic illumination system to overcome this problem. 相似文献
44.
Dieter Petrak 《Particle & Particle Systems Characterization》2002,19(6):391-400
The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity. 相似文献
45.
46.
47.
An acoustic pulse propagating on a two-mode fiber can act as a beam splitter in a scanning interferometer. When this device
is employed in white-light interferometry, the effects of distributed coupling and dispersive interferometer arms need to
be considered. A theory suitable for treating acousto-optic interaction of partially coherent light in a moving interaction
region was developed. It was found that differential optical dispersion should be negligible and the acoustic pulse length
short. Also the coherence time should be short but long compared to the intermodal group delay difference over a pulse length.
Experiments with long acoustic pulses were performed, and fairly good agreement with theory was obtained. 相似文献
48.
The problem of computing light scattering by cylindrical fibers with high aspect ratio in the framework of the Null‐Field method with discrete sources is treated. Numerical experiments for investigating the scattering properties of two fiber geometries are performed using distributed spherical vector wave functions as discrete sources. 相似文献
49.
An intensity-modulated optical fibre sensor system is described which employs a single LED source to provide the measurand and the reference signals with two separate wavelength bands. The allocated wavelength bands are selected to minimize any differential intensity effects that may arise from LED thermal variations. The sensor system, comprising a transceiver unit connected to an optical displacement sensor using a single optical fibre, provides an output fully referenced for all major common-mode variations that are likely to occur. Performance characteristics for the prototype system are reported which show a linear displacement range of over 20 mm. 相似文献
50.
Tomohiro Shirai 《Optical Review》2004,11(5):312-319
Spatial coherence of the field modified by low-order adaptive optics is analyzed to establish a theoretical basis for the recent idea of using adaptive optics as a spatial coherence modifier. In this context low-order adaptive optics has the ability to correct some of the low-order aberrations specified by Zernike polynomials. The initial field to be modified is assumed to be a spatially partially coherent one resulting from phase disturbance. It is demonstrated, as in the previous study, that low-order adaptive optics serves to enhance the spatial coherence of the resultant field and that the effect of the enhancement becomes stronger as the spatial coherence of the initially partially coherent field increases. Potential applications of low-order adaptive optics as a spatial coherence modifier are briefly discussed. 相似文献