全文获取类型
收费全文 | 1595篇 |
免费 | 551篇 |
国内免费 | 46篇 |
专业分类
化学 | 164篇 |
晶体学 | 13篇 |
力学 | 34篇 |
综合类 | 12篇 |
数学 | 57篇 |
物理学 | 1912篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 18篇 |
2020年 | 21篇 |
2019年 | 16篇 |
2018年 | 25篇 |
2017年 | 52篇 |
2016年 | 61篇 |
2015年 | 41篇 |
2014年 | 138篇 |
2013年 | 125篇 |
2012年 | 115篇 |
2011年 | 123篇 |
2010年 | 94篇 |
2009年 | 99篇 |
2008年 | 115篇 |
2007年 | 128篇 |
2006年 | 112篇 |
2005年 | 117篇 |
2004年 | 83篇 |
2003年 | 97篇 |
2002年 | 77篇 |
2001年 | 58篇 |
2000年 | 59篇 |
1999年 | 54篇 |
1998年 | 38篇 |
1997年 | 70篇 |
1996年 | 34篇 |
1995年 | 38篇 |
1994年 | 36篇 |
1993年 | 13篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 1篇 |
排序方式: 共有2192条查询结果,搜索用时 15 毫秒
71.
Huizhou Wu Xiangbo Yang Yan Tang Xiaopeng Tang Dongmei Deng Hongzhan Liu Zhongchao Wei 《Annalen der Physik》2019,531(9)
A PT‐symmetric periodic structure with two‐material waveguide networks is constructed. In this study, how changing the number of cells affects the transmission properties is investigated. The results show that the PT‐unbroken (broken) region of the system is only determined by the cell structure, regardless of the number of unit cells. This means that any system has the same exceptional points (EPs), regardless of the number of cells and as long as the cell structure is consistent. In addition, it is confirmed that the coherent perfect absorbers and lasers (CPA lasers) occur in our model. The transfer matrix method is used to derive a sufficient condition for achieving the CPA laser point. A simple, effective formula for predicting the CPA laser state in an N unit cell system is derived. 相似文献
72.
73.
Mukesh Kumar Alaria A. K. Sinha A. Bera V. Srivastava 《International Journal of Infrared and Millimeter Waves》2008,29(12):1083-1090
The main objective of the paper is to make an efficient design of the input and output coaxial coupler for a helix TWTs. An
approach has been developed for the efficient design and analysis of the coaxial couplers in the practical situation. Normally
multi-section impedance transformer approach is used for any wide band coupler. For a space helix TWT, coupler should be wide
bandwidth and small size. In this case coupler is matched with helix slow wave structure and the standard 50-ohm connectors.
The simulated return loss (dB) profile for different type of couplers is obtained by using Ansoft HFSS, CST microwave studio
and compares those with experimental results. The tip loss design at sever ends for the input and the output section has been
also optimized. 相似文献
74.
Dan Zhang Hongting Jia Kiyotoshi Yasumoto 《International Journal of Infrared and Millimeter Waves》2008,29(9):823-831
A problem of coupling between conventional dielectric waveguides and a two-dimensional photonic crystal waveguide is analyzed,
using the Fourier series expansion method combined with the absorbing boundary condition of a perfectly matched layer (PML).
A novel structure for the input and output ends of the photonic crystal waveguide is proposed to increase the coupling efficiency.
Numerical examples are demonstrated and discussed to validate the effectiveness of the proposed structure. 相似文献
75.
金属异质波导阵列中的表面等离激元传播特性 总被引:3,自引:2,他引:1
提出了一种新的一维金属异质波导阵列的设计方案,即波导芯区周期调制的金属波导阵列.数值模拟的结果表明,金属波导芯区的周期调制引起波导中传播的表面等离激元有效折射率的周期调制,从而可在特定的波段打开一个表面等离激元带隙(如1550nm附近).通过引入合适的缺陷波导单元,可获得特定波长的高品质因子(Q=556)的表面电磁模共振.这一结果可用于设计亚波长的布拉格反射器、光发射器、滤波器等,有可能被用于未来的集成光路. 相似文献
76.
77.
Yu-jun Quan Pei-de Han Qi-jiang Ran Fan-ping Zeng Li-peng Gao Chun-hua Zhao 《Optics Communications》2008,281(11):3105-3110
A photonic wire-based directional coupler based on SOI was fabricated by e-beam lithography (EBL) and the inductively coupled plasma (ICP) etching method. The size of the sub-micron waveguide is 0.34 μm × 0.34 μm, and the length in the coupling region and the separation between the two parallel waveguides are 410 and 0.8 μm, respectively. The measurement results are in good agreement with the results simulated by 3D finite-difference time-domain method. The transmission power from two output ports changed reciprocally with about 23 nm wavelength spacing between the coupled and direct ports. The extinction ratio of the device was between 5 and 10 dB, and the insertion loss of the device in the wavelength range 1520-1610 nm was between 22 and 24 dB, which included an about 18.4 ± 0.4 dB coupling loss between the taper fibers and the polished sides of the device. 相似文献
78.
Crossed waveguide is widely used in optical devices, whose excess loss has a strong impact on multi-turn optical waveguide ring resonator and resonator integrated optic gyro. The resonance curve of the ring resonator is sharply dependent on the loss within the resonator. This paper presents how to get excess loss of the crossed waveguides nondestructively through the comparison of the resonance characteristics between one-turn and multi-turn optical waveguide ring resonators. 相似文献
79.
In the present work, four-layer polymeric waveguides have been fabricated and characterized by interchanging the film layer. Using polyvinyl alcohol (PVA) and styrene acrylonitrile (SAN) polymer it has been shown that polymers do not loose their own property in multilayer structure and better efficiency can be achieved in the form of low propagation losses and mode filtration. Due to high contrast of PVA and SAN films, a broad spectrum of refractive index in four-layer structure has been achieved. 相似文献
80.
Plasmonic waveguides and conventional dielectric waveguides have favorable characteristics in photonic integrated circuits. Typically, plasmonic waveguides can provide subwavelength mode confinement, as shown by their small mode area, whereas conventional dielectric waveguides guide light with low loss, as shown by their long propagation length. However, the simultaneous achievement of subwavelength mode confinement and low-loss propagation remains limited. In this paper, we propose a novel design of an alldielectric bowtie waveguide, which simultaneously exhibits both subwavelength mode confinement and theoretically lossless propagation. Contrary to traditional dielectric waveguides, where the guidance of light is based on total internal reflection, the principle of the all-dielectric bowtie waveguide is based on the combined use of the conservation of the normal component of the electric displacement and the tangential component of the electric field, such that it can achieve a mode area comparable to its plasmonic counterparts. The mode distribution in the all-dielectric bowtie waveguide can be precisely controlled by manipulating the geometric design. Our work shows that it is possible to achieve extreme light confinement by using dielectric instead of lossy metals. 相似文献