全文获取类型
收费全文 | 2356篇 |
免费 | 937篇 |
国内免费 | 310篇 |
专业分类
化学 | 161篇 |
晶体学 | 29篇 |
力学 | 269篇 |
综合类 | 81篇 |
数学 | 651篇 |
物理学 | 2412篇 |
出版年
2024年 | 19篇 |
2023年 | 67篇 |
2022年 | 83篇 |
2021年 | 90篇 |
2020年 | 56篇 |
2019年 | 60篇 |
2018年 | 46篇 |
2017年 | 81篇 |
2016年 | 78篇 |
2015年 | 77篇 |
2014年 | 193篇 |
2013年 | 136篇 |
2012年 | 136篇 |
2011年 | 161篇 |
2010年 | 199篇 |
2009年 | 156篇 |
2008年 | 175篇 |
2007年 | 153篇 |
2006年 | 161篇 |
2005年 | 188篇 |
2004年 | 187篇 |
2003年 | 130篇 |
2002年 | 141篇 |
2001年 | 106篇 |
2000年 | 110篇 |
1999年 | 77篇 |
1998年 | 89篇 |
1997年 | 73篇 |
1996年 | 52篇 |
1995年 | 51篇 |
1994年 | 44篇 |
1993年 | 48篇 |
1992年 | 45篇 |
1991年 | 42篇 |
1990年 | 54篇 |
1989年 | 29篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有3603条查询结果,搜索用时 234 毫秒
961.
High-order harmonic generation spectrum of an excited one-dimensional Coulomb atom in an intense laser field
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Response of the wave packet of a one-dimensional Coulomb atom
to an intense laser field is calculated using the symmetrized
split operator fast Fourier method. The high-order harmonic
generation (HHG) of the initial state separately being the ground and excited states
is presented. When the hardness parameter \alpha in the soft
Coulomb potential V(x)=-1/\sqrt{x^2+\alpha} is chosen to be small
enough, the so-called hard Coulomb potential
V(x)=-1/|x| can be obtained. It is well known that the hard one-dimensional Coulomb atom
has an unstable ground
state with an energy eigenvalue of $\sim0.5$ and it
has no states corresponding to physical states in the true atoms, and
has the first and second excited states being degenerate. The parity effects on the HHG
can be seen from the first and second excited states of the hard
one-dimensional Coulomb atom. The HHG spectra of the excited states
from both the soft and hard Coulomb atom models are shown to have more
complex structures and to be much stronger than the corresponding
HHG spectrum of the ground state of the soft Coulomb model with
$\alpha=2$ in the same laser field. Laser-induced non-resonant
one-photon emission is also observed. 相似文献
962.
A single particle magneto-confined in a one-dimensional (1D) quantum
wire experiences a harmonic potential, and imposing a sharply
focused laser beam on an appropriate site shapes a $\delta$
potential. The theoretical investigation has demonstrated that for a
sufficiently strong $\delta$ pulse the quantum motional stationary
state of the particle is one of the eigenstates of the free harmonic
oscillator, and it is determined by the site of the laser beam
uniquely, namely a quantum state is admissible if and only if the
laser site is one of its nodes. The numerical computation shows that
all the nodes of the lower energy states with quantum numbers $n \le
20$, except the coordinate origin, are mutually different. So we can
manipulate the multiphoton transitions between the quantum states by
adjusting the position of the laser $\delta$ pulse and realize the
transition from an unknown higher excitation state to a required
lower energy state. 相似文献
963.
A new approach to formulizing a new high-order matrix spectral
problem from a normal 2× 2 matrix modified Korteweg--de Vries
(mKdV) spectral problem is presented. It is found that the
isospectral evolution equation hierarchy of this new higher-order
matrix spectral problem turns out to be the well-known mKdV equation
hierarchy. By using the binary nonlinearization method, a new
integrable decomposition of the mKdV equation is obtained in the
sense of Liouville. The proof of the integrability shows that
r-matrix structure is very interesting. 相似文献
964.
Effects of walk-off on cross-phase modulation induced modulation instability in an optical fibre with high-order dispersion 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper investigates the effects of walk-off among optical pulses
on cross-phase modulation induced modulation instability in the
normal dispersion region of an optical fibre with high-order
dispersion. The results indicate that, in the case of high-order
dispersion, the walk-off effect takes on new characteristics and will
influence considerably the shape, position and especially the number
of the spectral regions of the gain spectra of modulation
instability.
Not only the group-velocity mismatch, but also the difference
of the third-order dispersion of two optical waves will alter the gain
spectra of modulation instability but in different ways. Depending on the
values of the walk-off parameters, the number of the spectral regions may
increase from two to at most four, and the spectral shape and position may
change too. 相似文献
965.
会切磁场中大回旋电子束产生的研究 总被引:1,自引:0,他引:1
研究了会切磁场产生的机理。通过对Moster-Molnar 模型的探讨, 建立了会切磁场的物理模型。在会切磁场理论分析和数值模拟基础上, 探讨了影响会切磁场设计的因数; 利用拉格朗日公式求解了会切磁场中电子运动轨迹。探讨了会切磁场与大回旋空心会切电子枪的关系, 得到了改进会切电子枪性能的一些一般性结论。 相似文献
966.
A critical pattern of crossflow around a slender 总被引:1,自引:0,他引:1
IntroductionModernhigh_performancefightersoftenrequiretobeoperatedunderafairlylargeangleofattacksoastoachieveexcellentmaneuverabilityandagility .Atsuchlargeangleofattack ,asymmetricallee_sidevortexflowwillformatthefrontpartofthefuselage .Sothatsuchagreats… 相似文献
967.
三阶WNND格式的构造及在复杂流动中的应用 总被引:5,自引:0,他引:5
引入Liu的加权(weight)思想,在NND格式的二阶模板基础上,构造了空间三阶精度的WNND格式.通过对线性波动方程、一维Euler方程和三维Navier-Stokes方程的数值模拟表明:WNND格式在不增加模板插值点的前提下,在对各种间断的分辨率和收敛特性等方面均优于NND格式.采用WNND格式对升力体外形高超声速流场数值模拟表明:升力体外形三维流场结构十分复杂,攻角从0°~50°变化时,背风面表面极限流线依次由不分离、开式分离向起始于鞍、结点组合的高阶奇点的分离方式转化,翼面横向分离亦随攻角增大而增大;垂直于体轴的横截面流动拓扑结构与张涵信给出的理论分析一致,大于20°攻角后,在部分横截面背风对称线上出现结构不稳定的鞍点相连现象. 相似文献
968.
金属纳米粒子在聚合物中的磁致排列──实验及分子动力学模拟 总被引:4,自引:0,他引:4
用磁场控制碳包镍纳米颗粒在环氧树脂中的排列,制备了具有优异电学性能的一维有序的纳米复合材料.在添加质量分数为3%-10%的镍纳米颗粒时,导电率提高了3个数量级,介电常数增大了2-3倍.对纳米颗粒的磁致排列进行了分子模拟,结果表明,偶极强相互作用是导致纳米粒子排列的主要原因,排列过程经历了聚合、成链和粗化等阶段,成链的时间尺度在秒数量级.模拟结构与实验观察结果基本一致. 相似文献
969.
Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of a two-dimensional hydrogen negative ion H^{-} in a magnetic field. The results show that the ground and low-excited states of H^{-} in low-dimensional space are more stable than those in three-dimensional space and there may exist more bound states. 相似文献
970.
非线性时滞差分方程的持续生存和渐近性质 总被引:2,自引:0,他引:2
研究了一类非线性时滞差分方程解的渐近性质,得到了方程持续生存和全局吸引的充分条件.这些结果可应用于一类非线性时滞差分方程和时滞离散Logistic模型,并包含了一些已知的结果. 相似文献