全文获取类型
收费全文 | 974篇 |
免费 | 273篇 |
国内免费 | 53篇 |
专业分类
化学 | 62篇 |
晶体学 | 7篇 |
力学 | 178篇 |
综合类 | 53篇 |
数学 | 277篇 |
物理学 | 723篇 |
出版年
2024年 | 15篇 |
2023年 | 44篇 |
2022年 | 60篇 |
2021年 | 60篇 |
2020年 | 31篇 |
2019年 | 51篇 |
2018年 | 15篇 |
2017年 | 66篇 |
2016年 | 40篇 |
2015年 | 57篇 |
2014年 | 83篇 |
2013年 | 52篇 |
2012年 | 59篇 |
2011年 | 56篇 |
2010年 | 33篇 |
2009年 | 53篇 |
2008年 | 74篇 |
2007年 | 73篇 |
2006年 | 58篇 |
2005年 | 45篇 |
2004年 | 49篇 |
2003年 | 40篇 |
2002年 | 26篇 |
2001年 | 31篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 17篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1300条查询结果,搜索用时 15 毫秒
891.
892.
<正>Gain saturation is a significant phenomenon of fiber Raman amplifiers(FRAs).Gain figures versus signal power are well explained.For the small signal,the coupled ordinary differential equations are used,and for the large signal,the Raman gain coefficient is modified.It is shown that the saturation power of FRAs decreases with the pump power,and gain saturation is easier to occur in the forward pump scheme than in the backward pump scheme.These phenomena are well explained by the stimulated Brillouin scattering (SBS) effect.This research provides a guide to the fabrication of practical FRAs. 相似文献
893.
A distributed access scheme using optical add/drop multiplexers (OADMs) for long reach hybrid wavelength division multiplexing and time division multiplexing passive optical networks (WDM-TDM PONs) is proposed and demonstrated. Colorless operations are implemented by using commercially available reflective semiconductor optical amplifiers (RSOAs) at both the center office (CO) and the customer side. Four 1.25-Gb/s channels are successfully transmitted over 80-km single-mode fiber with four OADMs. The dynamic input power range of the RSOA is also investigated. Compared with traditional access schemes, the proposed scheme could cover the area along the feed fiber with no blind zone. The experimental results show that it could be an ideal solution for the next generation access networks. 相似文献
894.
提出一种新颖的时隙环网公平机制——环分布式时隙调度(DTSR), 该机制是分布式的, 适合所有目的节点剥离业务的时隙环网。DTSR通过在单向信道上循环传输的时隙控制头(TCH)内增加一个简单的域, 实现对环上“饿死”节点信息的动态收集, 协调各个节点占用资源的时间, 确保各节点之间的公平性; 在发现环上有“饿死”节点后, DTSR利用时隙环网空间重用的特性, 调度相关节点向不经过“饿死”节点的其他节点发送数据, 充分利用了环网资源; 此外DTSR机制具有良好的算法收敛性, 且接入时延较传统算法更小。最后,对DTSR的性能进行仿真, 并和几个典型的时隙环网的公平机制进行了比较。 相似文献
895.
The electromagnetic wave transmission from the slightly rough surface of three-layered medium is studied, and formulae of the transmission coefficients for different polarizations are derived using the small perturbation method. A Gaussian rough surface is presented for describing rough surface of the layered medium, the influence of permittivity of the layered medium, the mean layer thickness of the intermediate medium, the roughness surface parameters and the incident frequency on the transmission coefficient of HH polarization are obtained and discussed with numerical implementation. 相似文献
896.
For a special coupled mKdV system, which can be derived from a two-layer fluid model, Hirota's bilinear direct method is used to construct and yield the complexiton solutions. The detailed physical properties of complexitons are filrther illustrated graphically. 相似文献
897.
Frequency Response of Near-Wall Coherent Structures to Localized Periodic Blowing and Suction in Turbulent Boundary Layer
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We experimentally investigate the frequency response of near-wall coherent structures to localized periodic blow- ing and suction through a spanwise slot in a turbulent boundary layer by changing the frequency of periodic disturbance at similar velocities of free stream. The effects of blowing and suction disturbance on energy redistri- bution, turbulent intensity U^+ rums over y^+ and waveforms of phase-averaged velocity during sweeping process are respectively discussed under three frequencies of periodic blowing and suction in near-wall region of turbulent boundary layer, compared with those in a standard turbulent boundary layer. The most effective disturbance frequency is figured out in this system. 相似文献
898.
We report a novel single-frequency fibre ring laser using self-injection locking with a distributed-feedback (DFB) fibre laser at 1550nm. The operating wavelength is controlled by a saturable absorber and a DFB fibre laser in the ring cavity, the saturable absorber acts as a narrow band-pass filter. In the primary experiment, the laser output exceeds 100mW with the linewidth less than 2kHz. The laser is stable, and no mode-hopping is observed within eight hours. Compared with other cavity designs using spatial hole-burning, our laser shows high controllability. 相似文献
899.
Improvement of Atomic-Layer-Deposited Al2O3/GaAs Interface Property by Sulfuration and NH3 Thermal Nitridation
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fermi level pinning at the interface between high-h gate dielectric and GaAs induced by unstable native oxides is a major obstacle for high performance GaAs-based metal-oxide-semiconductor (MOS) devices. We demonstrate the improved Al2O3/GaAs interracial characteristics by (NH4)2S immersion and NH3 thermal pretreatment prior to A1203 deposition. X-ray photoelectron spectroscopy (XPS) analysis confirms that sulfuration of GaAs surface by (NH4 )2S solution can effectively reduce As-O bonds while Ga-O bonds and elemental As still exist at Al2O3 /GaAs interface. However, it is found that N incorporation during the further thermal nitridation on sulfurated GaAs can effectively suppress the native oxides and elemental As in the sequent deposition of Al2O3. Atomic force microscopy (AFM) shows that the further thermal nitridation on sulfurated GaAs surface can also improve the surface roughness. 相似文献
900.
We present an impedance-matched reduced version of acoustic cloaking whose mass is in a reasonable range. A layered cloak design with isotropic material is also proposed for the reduced cloak. Numerical calculations from the transfer matrix methods show that the present layered cloak can reduce the scattering of an air cylinder substantially. 相似文献