全文获取类型
收费全文 | 3066篇 |
免费 | 525篇 |
国内免费 | 612篇 |
专业分类
化学 | 2540篇 |
晶体学 | 60篇 |
力学 | 169篇 |
综合类 | 14篇 |
数学 | 366篇 |
物理学 | 1054篇 |
出版年
2024年 | 19篇 |
2023年 | 52篇 |
2022年 | 98篇 |
2021年 | 107篇 |
2020年 | 148篇 |
2019年 | 145篇 |
2018年 | 115篇 |
2017年 | 97篇 |
2016年 | 151篇 |
2015年 | 162篇 |
2014年 | 146篇 |
2013年 | 229篇 |
2012年 | 223篇 |
2011年 | 242篇 |
2010年 | 223篇 |
2009年 | 251篇 |
2008年 | 254篇 |
2007年 | 237篇 |
2006年 | 179篇 |
2005年 | 180篇 |
2004年 | 133篇 |
2003年 | 124篇 |
2002年 | 151篇 |
2001年 | 137篇 |
2000年 | 59篇 |
1999年 | 69篇 |
1998年 | 40篇 |
1997年 | 18篇 |
1996年 | 30篇 |
1995年 | 33篇 |
1994年 | 21篇 |
1993年 | 23篇 |
1992年 | 22篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有4203条查询结果,搜索用时 15 毫秒
131.
132.
133.
采用基于密度泛函理论的第一性原理方法计算了存在Ga空位缺陷和掺杂B原子的二维GaAs的能带结构、态密度和光学性质.计算结果表明空位缺陷二维GaAs显示出金属特性,B原子的引入使体系变为间接带隙半导体,禁带宽度为0.35 eV.态密度计算发现体系低能带主要由Ga的s态、p态、d态和As的s态、p态构成;高能带主要由Ga和As的s态、p态构成.掺杂B原子与存在空位缺陷的二维GaAs相比,静态介电常数相对较低,变为8.42,且易于吸收紫外光,在3.90~8.63 eV能量范围具有金属反射特性,反射率达到52%. 相似文献
134.
We present an (n,n) threshold quantum secret sharing scheme of secure direct communication using Greenberger-Horne-Zeilinger state and teleportation.After ensuring the security of the quantum channel,the sender encodes the secret message directly on a sequence of particle states and transmits it to the receivers by teleportation.The receivers can recover the secret message by combining their measurement results with the sender's result.If a perfect quantum channel is used,our scheme is completely secure because the transmitting particle sequence does not carry the secret message.We also show our scheme is secure for noise quantum channel. 相似文献
135.
Effect of electromechanical boundary conditions on the properties of epitaxial ferroelectric thin films 下载免费PDF全文
The effects of internal stresses and depolarization fields on the properties of epitaxial ferroelectric perovskite thin films are discussed by employing the dynamic Ginzburg-Landau equation (DGLE). The numerical solution for BaTiO3 film shows that internal stress and the depolarization field have the most effects on ferroelectric properties such as polarization, Curie temperature and susceptibility. With the increase of the thickness of the film, the polarization of epitaxial ferroelectric thin film is enhanced rapidly under high internal compressively stress. With the thickness exceeding the critical thickness for dislocation formation, the polarization increases slowly and even weakens due to relaxed internal stresses and a weak electrical boundary condition. This indicates that the effects of mechanical and electrical boundary conditions both diminish for ferroelectric thick films. Consequently, our thermodynamic method is a full scale model that can predict the properties of ferroelectric perovskite films in a wide range of film thickness. 相似文献
136.
Tian Yu Tang Sheng Qiang Ren Yuan Liu Jing Quan Zhang Cai Liu Li Li Wu Wen Wu Wang Wei Li Liang Huan Feng 《Russian Journal of Physical Chemistry B, Focus on Physics》2018,12(3):503-509
Zn2SnO4 (ZTO) is a stable semiconductor in ZnO–SnO2 system and important transparent conducting oxide (TCO) predominantly used in optoelectronic devices. ZTO thin films were prepared by RF magnetron sputtering using Zn2SnO4 ceramic target in this paper. The effects of annealing temperatures and oxygen contents on characterization of ZTO thin films were studied. The results show that ZTO thin films prepared by RF magnetron sputtering are amorphous with an optical band gap of 3.22 eV. After annealing at 650°C in Ar atmosphere for 40 min, ZTO films possess a spinel structure with an optical band gap of 3.62 eV. The atomic force microscope (AFM) data of morphology reveals that the surface roughness of films is about 2 nm. The results of energy dispersive spectrometer (EDS) show that the concentration ratio of Zn to Sn is in the range from 1.44 to 1.57. The results of Hall-effect-measurement system reveal that the resistivity of films varies from 102 to 10–1 Ωcm, carrier concentration is about 1017 cm–3, and mobility ranges from 100 to 101 cm2 v–1 s–1. 相似文献
137.
本文利用磁控溅射的方法制备了L1_0-CoPt薄膜,研究了不同退火条件对薄膜结构、磁性以及表面形貌的影响.通过优化退火温度、保温时间以及升温速率,制备出了具有大矫顽力、高矩形比、粗糙度小的垂直各向异性L1_0-CoPt薄膜.实验发现,较高的退火温度有利于克服CoPt薄膜有序化转变所需要的能量,同时适当延长退火时间可以提高CoPt薄膜的扩散系数,从而促使无序相fcc转化为L1_0有序相fct结构.此外,退火过程中减缓升温速率可以有效减小薄膜粗糙度,从而形成平整连续膜. 相似文献
138.
Ying Jie Shen Rui Jun Lan Yin Chang Zhao Chuan Peng Qian Tong Yu Dai Bao Quan Yao 《Journal of Russian Laser Research》2017,38(6):559-563
We design a continuous-wave Tm:YLF laser with a composite slab crystal end-pumped by two fiber-coupled laser diodes at room temperature. We achieve a maximum continuous wave output power of 105 W for the bonded slab Tm:YLF laser; the corresponding slope efficiency is 47.7% and the optical-to-optical conversion efficiency is 42.0% with respect to the incident pump power. The laser operated at 1,907.5 nm with a beam quality factor of M2 ~3.2 at the highest output power. 相似文献
139.
Strategy of improving the stability and detonation performance for energetic material by introducing the boron atoms 下载免费PDF全文
Wen‐Jie Wu Wei‐Jie Chi Quan‐Song Li Jian‐Nan Ji Ze‐Sheng Li 《Journal of Physical Organic Chemistry》2017,30(12)
A novel stable energetic compound (E)‐1,2‐diamino‐1,2‐dinitrodiboron (DANB) was theoretically designed based on the structure of 1,1‐diamino‐2,2‐dinitroethene (FOX‐7). Atomization method in combination with Hess' law was used to predict the heat of formation. The detonation velocity (D) and detonation pressure (P) of DANB were approximatively estimated by using Kamlet–Jacobs equations. As a result, DANB has huge heat of formation (2013.5 kJ/mol) and specific enthalpy of combustion (?26.4 kJ/g). Furthermore, DANB possesses high crystal density (1.85 g/cm3) and heat of detonation (5476.0 cal/g), which lead to surprising detonation performance (D = 10.72 km/s, P = 51.9 GPa) that is greater than those of FOX‐7 (D = 8.63 km/s, P = 34.0 GPa) and CL‐20 (D = 9.62 km/s, P = 44.1 GPa). More importantly, DANB is very stable because its bond dissociation energy of the weakest bond (BDE = 357.8 kJ/mol) is larger than those of the most common explosives, such as FOX‐7 (BDE = 200.4 kJ/mol), CL‐20(BDE = 209.2 kJ/mol), HMX(BDE = 165.7 kJ/mol), and RDX (BDE = 161.4 kJ/mol). Therefore, our results show that DANB is a promising candidate for stable and powerful energetic material. 相似文献
140.