全文获取类型
收费全文 | 2867篇 |
免费 | 1385篇 |
国内免费 | 934篇 |
专业分类
化学 | 964篇 |
晶体学 | 201篇 |
力学 | 80篇 |
综合类 | 72篇 |
数学 | 512篇 |
物理学 | 3357篇 |
出版年
2024年 | 27篇 |
2023年 | 88篇 |
2022年 | 127篇 |
2021年 | 116篇 |
2020年 | 92篇 |
2019年 | 86篇 |
2018年 | 52篇 |
2017年 | 96篇 |
2016年 | 102篇 |
2015年 | 130篇 |
2014年 | 262篇 |
2013年 | 204篇 |
2012年 | 216篇 |
2011年 | 240篇 |
2010年 | 177篇 |
2009年 | 216篇 |
2008年 | 308篇 |
2007年 | 195篇 |
2006年 | 232篇 |
2005年 | 230篇 |
2004年 | 215篇 |
2003年 | 226篇 |
2002年 | 216篇 |
2001年 | 183篇 |
2000年 | 145篇 |
1999年 | 114篇 |
1998年 | 96篇 |
1997年 | 162篇 |
1996年 | 124篇 |
1995年 | 101篇 |
1994年 | 74篇 |
1993年 | 64篇 |
1992年 | 78篇 |
1991年 | 59篇 |
1990年 | 54篇 |
1989年 | 58篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有5186条查询结果,搜索用时 15 毫秒
161.
以单周期信号为例,数值模拟并讨论了注入频率和注入光场波动强度对主从式半导体激光器同步性能的影响。分别通过直接调制和外部调制两种方式获得单周期信号,并采用改进的参数——相似指数评价系统的同步性能。研究结果表明:当注入强度足够大时,系统实现注入锁定同步,外部调制的相似指数大于内部调制;注入强度恒定时,同步品质几乎不受调制指数的影响,而受调制频率的影响;由于内部、外部调制引起主激光器的输出反相,两种调制方式下同步品质随调制频率的变化趋势也相反。 相似文献
162.
外光反馈下的半导体激光器可视为混沌载波发射机.数值研究发现,外部强光注入可以显著提高混沌载波发射机的带宽,带宽提高的程度在一定范围内与注入光的强度成正比.当外部光注入系数kinj=0.39时,混沌载波的带宽由无光注入时的2.7GHz增大到14.5GHz,提高了5倍多.研究还发现,在相同的注入强度条件下,当注入光的频率比半导体激光器的中心频率高2—4GHz时,可实现最大限度的带宽增强.此外,适当提高半导体激光器的偏置电流也可以在一定程度上提高其产生的混沌载波的带宽.
关键词:
半导体激光器
混沌
带宽 相似文献
163.
Semiconductor-Optical-Amplifier-Based Inverted and Non-Inverted Wavelength Conversion at 40 Gb/s Using a Detuning Optical Bandpass Filter 下载免费PDF全文
We experimentally demonstrate 40Gb/s semiconductor-optical-amplifier-based tunable wavelength conversion (WC) using a detuning optical bandpass filter. Both inverted and non-inverted WCs are obtained by shifting the filter central wavelength with respect to the probe wavelength. When the filter is red shifted by 0.4nm or blue shifted by 0.3nm, the WC is non-inverted. However, when the filter is blue shifted by 0.1 nm, the WC is inverted. It is experimentally demonstrated that the WC has a tunable range covering the C-band. 相似文献
164.
165.
166.
167.
Full potential linearized augmented plane wave (FPLAPW) method calculations are carried out for semiconducting orthorhombic BaSi2. The optical properties and the origin of the different optical transitions are investigated. Our calculated band gap of 1.0918eV is indirect, which is in good agreement with the experimental result. The bonds between Ba and Si are considered to be electrovalent bond. The anlsotropy in the imaginary part ε2(w) and real part εl(w) of the optical dielectric tensor are analysed. The contributions of various transition peaks are explained from the imagnary part of the dielectric function. 相似文献
168.
The anomalous Hall effect of heavy holes in semiconductor quantum
wells is studied in the intrinsic transport regime, where the Berry
curvature governs the Hall current properties. Based on the
first--order perturbation of wave function the expression of the
Hall conductivity the same as that from the semiclassical equation
of motion of the Bloch particles is derived. The dependence of Hall
conductivity on the system parameters is shown. The amplitude of
Hall conductivity is found to be balanced by a competition between
the Zeeman splitting and the spin--orbit splitting. 相似文献
169.
The spin current in a parabolically confined semiconductor
heterojunction quantum wire with Dresselhaus spin--orbit coupling is
theoretically studied by using the perturbation method. The formulae
of the elements for linear and angular spin current densities are
derived by using the recent definition for spin current based on spin
continuity equation. It is found that the spin current in this
Dresselhaus spin--orbit coupling quantum wire is antisymmetrical,
which is different from that in Rashba model due to the difference in
symmetry between these two models. Some numerical examples for the
result are also demonstrated and discussed. 相似文献
170.
Dependences of spin polarization on the control parameters in the spin-polarized injection through the magnetic p-n junction 下载免费PDF全文
Effective spin-polarized injection from magnetic semiconductor (MS)
to nonmagnetic semiconductor (NMS) has been highlighted in recent
years. In this paper we study theoretically the dependence of
nonequilibrium spin polarization (NESP) in NMS during spin-polarized
injection through the magnetic p-n junction. Based on the theory in
semiconductor physics, a model is established and the boundary
conditions are determined in the case of no external spin-polarized
injection and low bias. The control parameters that may influence the
NESP in NMS are indicated by calculating the distribution of spin
polarization. They are the doping concentrations, the equilibrium
spin polarization in MS and the bias. The effective spin-polarized
injection can be realized more easily by optimizing the above
parameters. 相似文献