全文获取类型
收费全文 | 6087篇 |
免费 | 972篇 |
国内免费 | 287篇 |
专业分类
化学 | 920篇 |
晶体学 | 44篇 |
力学 | 52篇 |
综合类 | 41篇 |
数学 | 108篇 |
物理学 | 6181篇 |
出版年
2024年 | 14篇 |
2023年 | 23篇 |
2022年 | 69篇 |
2021年 | 102篇 |
2020年 | 115篇 |
2019年 | 54篇 |
2018年 | 85篇 |
2017年 | 186篇 |
2016年 | 211篇 |
2015年 | 185篇 |
2014年 | 407篇 |
2013年 | 327篇 |
2012年 | 491篇 |
2011年 | 484篇 |
2010年 | 351篇 |
2009年 | 415篇 |
2008年 | 551篇 |
2007年 | 568篇 |
2006年 | 522篇 |
2005年 | 382篇 |
2004年 | 329篇 |
2003年 | 310篇 |
2002年 | 126篇 |
2001年 | 154篇 |
2000年 | 129篇 |
1999年 | 109篇 |
1998年 | 106篇 |
1997年 | 83篇 |
1996年 | 74篇 |
1995年 | 59篇 |
1994年 | 61篇 |
1993年 | 39篇 |
1992年 | 45篇 |
1991年 | 23篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有7346条查询结果,搜索用时 9 毫秒
21.
Summary Both bottom-up sensory information and top-down influences contribute to the perception processes. We studied the perceptual
alternations of a multistable ambiguous pattern. We observed that it is possible to interfere on the process of the perception
alternance by means of subliminal visual stimuli, which either contrast or second the previous perception. We investigated
also the effect of the top-down volitional factor on the perceptual alternation. By using a combination of such top-down factor
and bottom-up stimulation, we ascertained that a non-linear type of interaction occurs between the two above factors.
Paper presented at the International Workshop ?Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing
and Related Phenomena?, Elba, 5–10 June 1994. 相似文献
22.
Suchada Suntornchashwej Dr. Khanit Suwanborirux Dr. Kazushi Koga Minoru Isobe Prof. Dr. 《化学:亚洲杂志》2007,2(1):114-122
Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties. 相似文献
23.
E. K. Sadykov V. V. Arinin G. I. Petrov A. V. Pyataev F. G. Vagizov O. A. Kocharovskaya 《Hyperfine Interactions》2006,167(1-3):893-896
The role of quantum interference (QI) in spectra of the resonant Mössbauer scattering is investigated. As a mechanism ensuring the QI conditions, the radio-frequency (RF) mixing of the spin sublevels of the excited nuclear state is considered. It is shown that QI leads to a significant intensity redistribution of the elastic and Raman scattering. 相似文献
24.
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
25.
26.
Push-pull dithiafulvenes with reduced bond length alternation (BLA) and high optical nonlinearities have been prepared. The interplay between the proaromaticity of the donor and the structural and optical properties of these merocyanines is discussed. The donor ability of dithiafulvenes can reach that of ferrocene or dialkylaminophenyl groups. 相似文献
27.
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
28.
29.
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
30.
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