全文获取类型
收费全文 | 1015篇 |
免费 | 271篇 |
国内免费 | 20篇 |
专业分类
化学 | 37篇 |
晶体学 | 2篇 |
力学 | 252篇 |
综合类 | 19篇 |
数学 | 333篇 |
物理学 | 663篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 19篇 |
2018年 | 21篇 |
2017年 | 27篇 |
2016年 | 40篇 |
2015年 | 31篇 |
2014年 | 33篇 |
2013年 | 67篇 |
2012年 | 59篇 |
2011年 | 65篇 |
2010年 | 46篇 |
2009年 | 57篇 |
2008年 | 69篇 |
2007年 | 84篇 |
2006年 | 58篇 |
2005年 | 58篇 |
2004年 | 45篇 |
2003年 | 52篇 |
2002年 | 54篇 |
2001年 | 49篇 |
2000年 | 42篇 |
1999年 | 44篇 |
1998年 | 28篇 |
1997年 | 32篇 |
1996年 | 13篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 27篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有1306条查询结果,搜索用时 250 毫秒
101.
K.I. Petsas A. Gatti L.A. Lugiato C. Fabre 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):501-512
We investigate the spatial behaviour of the quantum-noise-reduction spectrum of the vacuum state emitted by a degenerate optical
parametric oscillator below threshold. In view of possible experimental implementations, we consider a mode-degenerate resonator
and two matching lenses and show that, for the realistic case of a finite-width pump, significant level of squeezing can be
observed in a very small region of the beam.
Received 25 September 2002 Published online 11 February 2003 相似文献
102.
S. Ghosh M.P. Rishi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):223-230
The modulation of an intense electromagnetic beam induced by the acousto-optic (AO) effect has been analysed in a transversely
magnetised semiconductor-plasma medium. The effect of carrier diffusion on the threshold field and gain profile of the modulated
wave has been extremely investigated using coupled mode theory. The origin of the AO interaction is assumed to lie in the
induced nonlinear diffusion current density of the medium. By considering the modulation process as a four wave parametric
interaction an expression for effective third-order AO susceptibility describing the phenomena has been deduced. The modulation
is greatly modified by propagation characteristics such as dispersion and diffraction due to dielectric relaxation of the
acoustic mode. The threshold pump field and the steady state growth rates are estimated from the effective third-order polarisation
in the plasma medium. Analytical estimation reveals that in the presence of enhanced diffusion due to excess charge carriers
the modulated beam can be effectively amplified in a dispersionless acoustic wave regime. The presence of an external dc magnetic
field is found to be favourable for the onset of diffusion induced modulational amplification of the modulated wave in heavily
doped regime.
Received 5 November 2001 相似文献
103.
本文报道了AgGaS_2晶体Ⅱ类非共线相位匹配Q开关Nd:YAG激光泵浦CO_2激光参量上转换研究结果,用迭代法计算了相位失配因子△K=0时的最佳非共线夹角.当泵浦功率密度为6MW/cm~2和晶体长度为4.7mm时,功率转换效率达16.1%,并且首次采用硅雪崩光电二极管接收和频信号. 相似文献
104.
105.
106.
Summary A new high-powered ultraviolet laser system is proposed. The system doubles the infrared light from a Nd-Yag laser mode-locked
at 100 MHz, injects this light into a storage-ring cavity to accumulate a high power in the visible and then doubles this
into the ultraviolet at 2600 ?. The power levels anticipated at this wavelength are much larger than those of commercially
available c.w. lasers. The new system can have a far-reaching impact in basic research and, even more so, in a great many
industrial applications. 相似文献
107.
描述了在BBOⅠ类相位匹配的飞秒光参量放大(OPA)中,利用非共线结构和倾斜抽运光的脉 冲波面来完全补偿三波群速失配的方法.理论计算了三波群速匹配时,非共线角、相位匹配 角、抽运光的脉冲波面倾斜角随信号光波长的变化,并分析了对抽运光光斑尺寸的要求和对 空间走离长度的影响.结果表明,利用该方法不仅能够实现最大的参量带宽,而且能够完全 补偿飞秒OPA中三波的群速失配.此外,选取合适的抽运光光斑尺寸和非线性晶体的长度对提 高参量增益也至关重要.
关键词:
群速匹配
非共线相位匹配
脉冲波面倾斜
飞秒光参量放大 相似文献
108.
R. Fedele H. Schamel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):313-320
An investigation to deepen the connection between the family of nonlinear Schr?dinger equations and the one of Korteweg-de
Vries equations is carried out within the context of the Madelung's fluid picture. In particular, under suitable hypothesis
for the current velocity, it is proven that the cubic nonlinear Schr?dinger equation, whose solution is a complex wave function,
can be put in correspondence with the standard Korteweg-de Vries equation, is such a way that the soliton solutions of the
latter are the squared modulus of the envelope soliton solution of the former. Under suitable physical hypothesis for the
current velocity, this correspondence allows us to find envelope soliton solutions of the cubic nonlinear Schr?dinger equation,
starting from the soliton solutions of the associated Korteweg-de Vries equation. In particular, in the case of constant current
velocities, the solitary waves have the amplitude independent of the envelope velocity (which coincides with the constant
current velocity). They are bright or dark envelope solitons and have a phase linearly depending both on space and on time coordinates. In the case of an arbitrarily
large stationary-profile perturbation of the current velocity, envelope solitons are grey or dark and they relate the velocity u0 with the amplitude; in fact, they exist for a limited range of velocities and have a phase nonlinearly depending on the combined
variable x-u0 s (s being a time-like variable). This novel method in solving the nonlinear Schr?dinger equation starting from the Korteweg-de
Vries equation give new insights and represents an alternative key of reading of the dark/grey envelope solitons based on the fluid language. Moreover, a comparison between the solutions found in the
present paper and the ones already known in literature is also presented.
Received 20 February 2002 and Received in final form 22 April 2002 Published online 6 June 2002 相似文献
109.
Zukang Zheng 《中国科学A辑(英文版)》1997,40(9):932-944
The stability of testing hypotheses is discussed. Differing from the usual tests measured by Neyman-Pearson lemma, the regret
and correction of the tests are considered. After the decision is made based on the observationsX
1,X
2, ⋅⋅⋅,X
n, one more piece of datumX
n+1 is picked and the test is done again in the same way but based onX
1,X
2, ⋅⋅⋅,X
n,X
n+l There are three situations: (i) The previous decision is right but the new decision is wrong; (ii) the previous decision
is wrong but the new decision is right; (iii) both of them are right or both of them are wrong. Of course, it is desired that
the probability of the occurrence of (i) is as small as possible and the probability of the occurrence of (ii) is as large
as possible. Since the sample size is sometimes not chosen very precisely after the type I error and the type II error are
determined in practice, it seems more urgent to consider the above problem. Some optimal plans are also given.
Project supported by the National Natural Science Foundation of China and the Doctoral Programme Foundation. 相似文献
110.
本文应用Normal Form理论和退化向量场的普适开折理论研究了参数激励与强迫激励联合作用下非线性振动系统的余维2退化分叉,用Melnikov方法讨论了全局分叉的存在性. 相似文献