全文获取类型
收费全文 | 866篇 |
免费 | 50篇 |
国内免费 | 25篇 |
专业分类
化学 | 71篇 |
晶体学 | 11篇 |
力学 | 17篇 |
数学 | 31篇 |
物理学 | 677篇 |
综合类 | 134篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 27篇 |
2009年 | 105篇 |
2008年 | 117篇 |
2007年 | 91篇 |
2006年 | 97篇 |
2005年 | 62篇 |
2004年 | 44篇 |
2003年 | 59篇 |
2002年 | 51篇 |
2001年 | 33篇 |
2000年 | 36篇 |
1999年 | 26篇 |
1998年 | 19篇 |
1997年 | 3篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有941条查询结果,搜索用时 171 毫秒
841.
ZHANG Yejin CHEN Weiyou LIU Caixia LIU Shiyong 《Chinese Journal of Lasers》2001,10(3):171-173
1 Introduction Itiswellknownthattherearetwomainmaterialsystemsforlong wavelengthsemiconductorlasers.TheIn1 -xGaxAs1 -yPy systemhasbeenresearchedextensively[1 ,2 ] ,buttheIn1 -x-yGayAlxAssystemonlyrecentlybegantoyieldhighqualityresults[3,4] .FortheIn1 -x-yGayAlxAssys… 相似文献
842.
This article reports the effects of porosity on the enhancement of the Schottky barrier height (SBH) and reduction of the leakage current of Pt Schottky diode based on n-type GaN. The porous GaN layer in this work was generated by electroless chemical etching under UV illumination. For comparative study, two additional samples, i.e. one as-grown sample and one thermally treated sample, were also prepared. The structural studies showed that the porous GaN sample has a relatively rough surface morphology with slightly broader X-ray diffraction peak of the (0 0 0 2) plane. The current-voltage (I-V) measurements revealed that the electrical characteristics of the Pt Schottky diode were improved significantly by the presence of the porous layer, in which SBH was observed to be enhanced by 27%. 相似文献
843.
Rectification properties of Au Schottky diodes were investigated in high‐temperature operation. These diodes were fabricated on a p‐type diamond single crystal using the vacuum‐ultraviolet light/ozone treatment. The ideality factor n of the Schottky diodes decreased monotonically with increasing measurement temperature whereas the Schottky barrier height ?b increased, and ?b reached 2.6 eV at 550 K with n of 1.1. Through high temperature heating at 870 K, the mean value of ?b at 300 K changed permanently from 2.2 eV to 1.1 eV. Decrease of ?b might originate from a dissolution of oxygen termination at the Au/diamond interface. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
844.
通过施加直流电压于P型SiOxNy薄膜,使热电子注入到薄膜而引起薄膜电学参数的改变。测试了薄膜在电子注入前后电学参数的变化,以研究薄膜的电子注入特性,探求薄膜的抗电子注入能力与制备工艺之间的关系。结合俄歇电子能谱和红外光谱分析膜的微机结构,对薄膜的电子注入特性进行了理论分析与讨论。 相似文献
845.
Gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates using RF magnetron co-sputtering, followed by H2 ambient annealing at 623 K to explore a possibility of steady and low-cost process for fabricating transparent electrodes. While it was observed that the ZnO:Ga thin films were densely packed c-axis oriented self-textured structures, in the as-deposited state, the films contained Ga2O3 and ZnGa2O4 which had adverse effect on the electrical properties. On the other hand, post-annealing in H2 ambient improved the electrical properties significantly via reduction of Ga2O3 and ZnGa2O4 to release elemental Ga which subsequently acted as substitutional dopant increasing the carrier concentration by two orders of magnitude. Transmittance of the ZnO:Ga thin films were all over 90% that of glass while the optical band gap varied in accordance with the carrier concentrations due to changes in Fermi level. Experimental observation in this study suggests that transparent conductive oxide (TCO) films based on Ga doped ZnO with good electrical and optical properties can be realized via simple low-cost process. 相似文献
846.
The contact properties of TiN on p- and n-type Si (1 0 0) obtained by magnetron reactive sputtering were investigated. Schottky diode characteristics were observed on p-type Si (1 0 0) as determined by forward current-voltage (I-V) measurements, but on n-type Si (1 0 0) the reverse I-V relation has shown a nonsymmetrical character. The zero-bias barrier heights evaluated by I-V on both type diodes were in the range of ∼0.60-0.64 V within the range of a few mVs, not more than ∼±(10-30) mV from each other. Incorporation of the effect of the series resistance in the I-V analysis resulted in a significant reduction in the magnitude of the ideality factor of the TiN/p-type specimen. Almost no change has occurred in the barrier height values. The contradictory reports on the TiN/n-type Si (1 0 0) diode characteristics in earlier works have been explained in terms of surface passivation of Si by the HF cleaning solution. It was stated in these reports that following annealing at 673 K the diodes have shown rectifying behavior. It has been speculated, that the nonsymmetrical nature of the TiN/n-Si (1 0 0) showing an intermediate behavior between Ohmic and rectifying behavior is a result of the specimen being exposed to a temperature lower than 673 K during sputtering where no complete depassivation took place. In order to obtain a rectifying behavior of TiN on both n-type and p-type Si surface passivation has to be eliminated. 相似文献
847.
Fermi Level Unpinning and Schottky Barrier Modification by Ti, Sc and V Incorporation at NiSi2/Si Interface 下载免费PDF全文
A new method is proposed to modify the Schottky barrier height (SBH) for nickel silicide/Si contact. Chemical and electrical properties for NiSi2/Si interface with titanium, scandium and vanadium incorporation are investigated by first-principles calculations. The metal/semiconductor interface states within the gap region are greatly decreased, which is related to the diminutions of junction leakage when Ti-cap is experimentally used in nickel silicide/Si contact process. It leads to an unpinning metal/semiconductor interface. The SBH obeys the Schottky-Mort theory. Compared to Ti substitution, the SBH for electrons is reduced for scandium and increases for vanadium. 相似文献
848.
Igor Dubenko Mahmud Khan Arjun Kumar Pathak Bhoj Raj Gautam Shane Stadler Naushad Ali 《Journal of magnetism and magnetic materials》2009,321(7):754-757
The Mn-based Heusler alloys encompass a rich collection of useful materials from highly spin-polarized systems to shape memory alloys to magnetocaloric materials. In this work we have summarized our studies of magnetostructural transitions from paramagnetic austenite to ferromagnetic martesite phases at TMC in Ni2MnGa-based alloys (Ni2Mn0.75Cu0.25-xCoxGa, Ni2Mn0.70Cu0.30Ga0.95Ge0.05, Ni2Mn1-xCuxGa, Ni2+xMn1-xGa, and Ni2Mn0.75-xCuxGa), and martensitic transitions from the ferromagnetic austenite to the martesite state in off-stoichiometric Ni-Mn-(In/Sb) Heusler alloys. The phase transition temperatures and respective magnetic entropy changes (ΔS) depend on composition in these systems and have been determined from magnetization measurements in the temperature interval 5-400 K, and in magnetic fields up to 5 T. It is shown that, depending on the composition and doping scheme the “giant” ΔS=40-60 J/(kgK) (for a field change of 5 T) can be observed in the temperature range (300-360 K) for the Ga-based alloys. The interplay between or coupling of the various transitions in Ni2Mn(Mn,X) systems with X=Sb and In leads to exchange bias effects, giant magnetoresistance, and both inverse and “normal” magnetocaloric effects. 相似文献
849.
K.V. Shah P. Manfrinetti A. Provino S.K. Dhar 《Journal of magnetism and magnetic materials》2009,321(19):3164-3170
We report the effect of replacing Cu by Pd in RCu5 (R=Pr, Nd, Sm and Eu). The parent RCu5 compounds crystallize in the hexagonal CaCu5-type structure. The hexagonal symmetry is retained in PrCu4Pd and EuCu5−xPdx (x=1 and 2) but the crystal structure changes to cubic AuBe5-type in PrCu3Pd2, NdCu5−xPdx (x=1 and 2) and SmCu4Pd. Substitution with Pd leads to lattice expansion and modifies the magnetic behavior. While PrCu5 is known to be a van-Vleck paramagnet with a singlet ground state, PrCu4Pd and PrCu3Pd2 show ferromagnetic-like behavior at low temperatures. SmCu4Pd orders ferromagnetically near 28 K in contrast to the antiferromagnetic nature of the parent SmCu5. The divalent nature of the Eu ions in EuCu5 is retained in the ternary alloys, but the Curie temperature is reduced from 57 to 24.5 and 14.5 K in EuCu4Pd and EuCu3Pd2, respectively, inferred from the location of peak in the heat capacity of these two compounds. The magnetic hyperfine field at the Eu nucleus measured with 151Eu Mössbauer spectroscopy in the ternary Eu-alloys is comparable to that in EuCu5. The magnetic behavior of NdCu4Pd is similar to that reported in NdCu5. The zero-field-cooled, low-field magnetization of NdCu3Pd2 shows a region of diamagnetic behavior roughly between 21 and 4 K, but the field-cooled response is positive. 相似文献
850.
A. P. Zhou W. D. Sheng 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(2):233-236
Electron and hole effective masses in self-assembled InAs/GaAs quantum dots are determined by fitting the energy levels calculated
by a single-band model to those obtained by a more sophisticated tight-binding method. For the dots of various shapes and
dimensions, the electron effective-mass is found to be much larger than that in the bulk and become anisotropic in the dots
of large aspect ratio while the hole effective-mass becomes almost isotropic in the dots of small aspect ratio. For flat InAs/GaAs
quantum dots, the most appropriate value for the electron and hole effective-mass is believed to be the electron effective-mass
in bulk GaAs and the vertical heavy-hole effective-mass in bulk InAs, respectively. 相似文献