全文获取类型
收费全文 | 2499篇 |
免费 | 781篇 |
国内免费 | 320篇 |
专业分类
化学 | 846篇 |
晶体学 | 110篇 |
力学 | 165篇 |
综合类 | 21篇 |
数学 | 146篇 |
物理学 | 2312篇 |
出版年
2024年 | 12篇 |
2023年 | 39篇 |
2022年 | 83篇 |
2021年 | 81篇 |
2020年 | 86篇 |
2019年 | 80篇 |
2018年 | 101篇 |
2017年 | 142篇 |
2016年 | 145篇 |
2015年 | 100篇 |
2014年 | 183篇 |
2013年 | 255篇 |
2012年 | 177篇 |
2011年 | 224篇 |
2010年 | 170篇 |
2009年 | 196篇 |
2008年 | 180篇 |
2007年 | 185篇 |
2006年 | 132篇 |
2005年 | 129篇 |
2004年 | 129篇 |
2003年 | 113篇 |
2002年 | 112篇 |
2001年 | 75篇 |
2000年 | 77篇 |
1999年 | 70篇 |
1998年 | 59篇 |
1997年 | 46篇 |
1996年 | 42篇 |
1995年 | 26篇 |
1994年 | 29篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有3600条查询结果,搜索用时 8 毫秒
11.
A multilayer dielectric cylindrical mirror (MDCM) based on the one-dimensional omnidirectional reflection of a photonic crystal is presented. In this case, the refractive indices of the two materials are 1.6 (polystyrene) and 4.6 (tellurium), and the corresponding optimized thicknesses are 0.75a and 0.25a. A very high reflectance over a wide frequency range is observed. In this case, a is the lattice constant of the photonic crystal. In this band, the MDCM has good reflection and focal properties. Therefore, it is feasible to use the MDCM for integrated waveguide devices. As an example, an etched diffraction grating demultiplexer based on the MDCM is also proposed. Both the operational principle and design of the device are introduced. This provides a method for designing compact integrated waveguide devices. 相似文献
12.
The electronic structure and magnetic properties of the Ti2CoB Heusler compound with a high-ordered CuHg2Ti structure were investigated using the self-consistent full potential linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT). Spin-polarized calculations show that the Ti2CoB compound is half-metallic ferromagnetic with a magnetic moment of 2 μB at the equilibrium lattice constant, a=5.74 Å. The Ti2CoB Heusler compound is ferromagnetic below the equilibrium lattice constant and ferrimagnetic above the equilibrium lattice constant. A large peak in majority-spin DOS and an energy gap in minority-spin DOS are observed at the Fermi level, yielding a spin polarization of 100%. A spin polarization higher than 90% is achieved for a wide range of lattice constants between 5.6 and 6.0 Å. 相似文献
13.
Hailin LiuZhihong Lu ling YueJing Liu Zhanghua GanChang Shu Ting ZhangJing Shi Rui Xiong 《Applied Surface Science》2011,257(22):9355-9361
A series of Ti1−xMoxO2−yNy samples were prepared by using sol-gel method and characterized by X-ray diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. All Ti1−xMoxO2−yNy samples are anatase phase. It is found that Mo, N mono-doping can increase visible light absorption, while (Mo + N) co-doping can greatly enhance absorption in whole visible region. Results of our first-principles band structure calculations reveal that (Mo + N)-doping, especially passivated co-doping can increase the up-limit of dopant concentration and create more impurity bands in the band gap of TiO2, which leads to a greatly increase of its visible-light absorption without a decrease of its redox potential. It reveals that (Mo + N) co-doped TiO2 is promising for a photocatalyst with high photocalystic activity under visible light. 相似文献
14.
A 2+1 version of a rotating perfect fluid spacetime of Gödel type is examined to see whether it has a Finkelstein-Misner kink. It is shown, by three different methods, that the kink number is one. 相似文献
15.
A theoretical investigation of 1D stationary and transient quasi-periodical dielectric structures is presented. A new approach for solving the problem of field interaction with such structures common for both stationary and transient cases, based on integral equations for the fields in transient media, is proposed. Some special cases of quasi-periodical structures with doubled quasi-periodicity are investigated numerically, showing that an additional complexity of the structure allows to obtain good filtering properties with a small number of quasi-periods. Transient structures with the same spatial dependencies, but with a time-dependent permittivity were also investigated. 相似文献
16.
Nonlinear wave propagation is studied theoretically in a one-dimensional photonic band gap structure containing single negative materials. It is found that Kerr nonlinearity is greatly enhanced near the lower edge of a recently explored angular gap for transverse magnetic polarized light. Consequently, optical bistability is achieved at very low values of input intensity in a periodic structure composed of only a few repeating units. The characteristics of optical bistability are affected only slightly with the variation of the incident angle and thickness ratio of the layers. The effect of losses is also found to be relatively insignificant in such a small structure. 相似文献
17.
Fei Zhang GaoShan Huang XiaoFei Nie Xin Cao Zhe Ma Fei Ding ZengFeng Di HongLou Zhen YongFeng Mei 《Physics letters. A》2019,383(24):2938-2942
In this study, we investigate the modulation of energy band in 3D self-assembled nanomembranes containing GaAs/Al0.26Ga0.74As quantum wells (QWs). Photoluminescence (PL) characterizations demonstrate that the self-assembled structures have different optical transition properties and the modulation of the energy band is thus realized. Detailed spectral analyses disclose that the small strain change in structures with different curvatures cannot cause remarkable change in energy bands in Al0.26Ga0.74As layer. On the other hand, the optical transitions of GaAs QW layer is influenced by the strain evolution in term of light emission intensity. We also find the first order Stark effect in rolled-up nanomembrane with diameter of 150 μm, which is closely connected with the coupling effect between the deformation potential and the piezoelectric potential. Our work may pave a way for the fabrication of high performance rolled-QW infrared photo-detectors. 相似文献
18.
The second CH stretching overtone of cyanoacetylene, HC3N, near 9700 cm−1 has been recorded by Fourier Transform Spectroscopy (FTS) and by Intracavity Laser Absorption Spectroscopy (ICLAS) with a Vertical External Cavity Surface Emitting Laser (VECSEL). In total thirteen bands have been identified in the highly congested spectra and rotationally assigned. Their rovibrational spectroscopic parameters have been obtained from a fit of the line centers. 相似文献
19.
The spectral characteristics of mini-optically pumped NH3 cavity laser emission at 67.2μm was studied. It was found that the spectrum of 67.2μm emission was duality. With low power
CO2-9R(30) pumping condition (lp<1MW/cm2), the spectrum appeared to be two wide FIR laser lines (∼4.6GHz for each line), which were the result of competition of multi-Raman
processes. With high power pumping condition (lp>2MW/cm2), the spectrum extended to be a very wide band (∼14GHz), which was the result of the combination of the competition and interaction
enhancement of Raman processes. The wide band spectral characteristics of 67.2 μm would be significant to the tuning of NH3 OPFIRL.
Supported by theNatural Science Foundation of Guangdong Province, P.R. China. 相似文献
20.
Two-level injection-locked opto-electronic oscillator is proposed for low phase noise. Dielectric resonator oscillator (DRO) is used as the first injection source, injection locking a long-fiber loop based opto-electronic oscillator, then its output is injection locking another long-fiber opto-electronic oscillator for getting a lower-phase noise output carrier. After the first injection, the single side band (SSB) phase noise at 10 kHz offset frequency decreases from −123 dBc/Hz to −135 dBc/Hz, then through the second injection the SSB phase noise drops down to −146 dBc/Hz. 相似文献