全文获取类型
收费全文 | 1141篇 |
免费 | 32篇 |
国内免费 | 28篇 |
专业分类
化学 | 343篇 |
晶体学 | 22篇 |
力学 | 26篇 |
综合类 | 2篇 |
数学 | 379篇 |
物理学 | 429篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 31篇 |
2019年 | 50篇 |
2018年 | 52篇 |
2017年 | 40篇 |
2016年 | 41篇 |
2015年 | 8篇 |
2013年 | 55篇 |
2012年 | 16篇 |
2011年 | 3篇 |
2010年 | 13篇 |
2009年 | 47篇 |
2008年 | 50篇 |
2007年 | 60篇 |
2006年 | 54篇 |
2005年 | 54篇 |
2004年 | 77篇 |
2003年 | 65篇 |
2002年 | 46篇 |
2001年 | 44篇 |
2000年 | 34篇 |
1999年 | 29篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 30篇 |
1995年 | 29篇 |
1994年 | 25篇 |
1993年 | 20篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有1201条查询结果,搜索用时 15 毫秒
111.
We present a magnetic study of vanadium oxide nanotubes (VOx-NTs) with polyaniline (PAni). Transmission electron microscopy (TEM) shows the tubular shape and the multi-wall structure of the nanotubes. The static magnetic susceptibility measured at different magnetic fields shows a Curie behavior, while the magnetization versus magnetic field presents a non-linear dependence at low temperatures. Both experiments can be explained by the presence of paramagnetic ions with S = 1/2. Using Electron Paramagnetic Resonance technique, we identified as V4+(3d1) the paramagnetic ions present in the nanostructures. All the experimental results can be explained by a fraction between 14% and 18% of V4+ with respect to the total V atoms in the system. 相似文献
112.
The dynamic single-mode and modulation performance of λ/4 phase-shifted distributed feedback laser diode with chirped grating (QWS-CG-DFB) are analyzed theoretically. The numerical simulation shows that, in contrast to purely QWS-DFB laser, the enhanced dynamic single-mode suppression ratio (SMSR) can be reached by QWS-CG-DFB laser. Under the smaller biasing current, the modulation band-width in presence of chirped grating is narrower, this difference shrinks for larger biasing current. For large signal modulation, the chirped grating is helpful to increase the output extinction ratio, but worsens the frequency chirping. The good dynamic characteristic can be obtained by selecting system parameters reasonably. 相似文献
113.
Transmission Frequency Properties of Elastic Waves along a Hetero-Phononic Crystal Waveguide 下载免费PDF全文
We investigate the propagation properties of hetero-phononic crystal waveguides by the improved eigen-mode matching theory, which can be used at same time to calculate both the transmission (reflection) coefficient and band structure. The numerical results show that the transmission frequency range is the same as the common range for two uniform waveguides composing the hereto-system, and the gap of any composite waveguide is also the gap of the hetero-phononic crystals waveguide. 相似文献
114.
Using two different 25-mer oligonucleotide probes covalently grafted on a silicon substrate, we demonstrate how efficient atomic force microscopy (AFM) can be for monitoring each step of DNA chip preparation: from probe immobilization to hybridization on the molecular scale. We observed the probe-molecule organization on the chip after immobilization, and the target molecules, which hybridized with probes could be individually identified. This article presents a method of straightforwardly identifying not only single and double DNA strands, but also, and more significantly, the hybridized part on them. 相似文献
115.
Igor I. Smolyaninov 《Physics letters. A》2008,372(47):7043-7045
Photoluminescence from a gold nanotip, which is induced by surface plasmons propagating over a curved tapered nanotip surface is considered in a co-moving accelerated reference frame. Similar to the surface-enhanced Raman scattering (SERS) effect, nonlinear optical mixing of the surface plasmons with the Unruh quanta is supposed to be enhanced by many orders of magnitude. 相似文献
116.
117.
不同化学环境对Er^3+离子的配位场能级结构的影响 总被引:1,自引:0,他引:1
首次在C3v点群对称汤中,运用双层点电荷配位场(DSCPCF)模型计算了CS3Y2I9晶体中Er^3 离子的59个配位场能级,与实验得到的能级比较,其均方根偏差为24.89cm^-1,而用点电荷配位场(PCF)模型计算的均方根偏差为29.08cm^-1,这说明双层点电荷配位场模型能更好地符合实验结果。同时,详细地分析CsLu2,Cs3Lu2Br9,Cs3Y2I9晶体中Er^3 离子能级结构的变化,由于Er^3 -X^-键共价性的增强,使Er^3 离子的能级重心发生红移,Cl→Br→I的配位场能级的分裂程序减小。 相似文献
118.
The roles of aliovalent CaII-for-YIII substitution and high-pressure-oxygen annealing in the process of ‘superconducterizing’ the Co-based layered copper oxide, CoSr2(Y1−xCax)Cu2O7+δ (Co-1212), were investigated. The as-air-synthesized samples up to x=0.4 were found essentially oxygen stoichiometric (−0.03≤δ≤0.00). These samples, however, were not superconducting, suggesting that the holes created by the divalent-for-trivalent cation substitution are trapped on Co in the charge reservoir. Ultra-high-pressure heat treatment carried out at 5 GPa and 500 °C for 30 min in the presence of Ag2O2 as an excess oxygen source induced bulk superconductivity in these samples. The highest Tc was obtained for the high-oxygen-pressure treated x=0.3 sample at ∼40 K. 相似文献
119.
H. Tajima S. IkedaM. Matsuda N. HanasakiJi-Won Oh H. Akiyama 《Solid State Communications》2003,126(10):579-581
We have fabricated a light-emitting diode from horse-heart cytochrome c and measured the electro-luminescence (EL) spectra. The spectra exhibit broad peaks around 530 and 690 nm, and a weak shoulder around 410 nm. The EL spectra are completely different from the photo-luminescence spectra previously reported. The appearance of the 690 nm emission band suggests the charge-transfer between the iron and the axial methionine ligand plays a crucial role in the electrical conduction in the cytochrome c film. 相似文献
120.
Xin-Gui Tang Jie Wang Xiao-Xing Wang Helen Lai-Wah Chan 《Solid State Communications》2004,130(6):373-377
Antiferroelectric PbZrO3 thin films were grown on Pt/Ti/SiO2/Si substrates with predominant (111) orientation using a sol-gel process. The Pt/PbZrO3/Pt film capacitor showed well-saturated hysteresis loops at an applied voltage of 5 V with remanent polarisation (Pr) and coercive electric field (Ec) values of 8.97 μC/cm2 and 162 kV/cm, respectively. The leakage current density of the highly (111)-oriented PbZrO3 film was less than 1.0×10−7 A/cm2 over electric field ranges from 0 to 105 kV/cm. The conduction current depended on the voltage polarity. The PbZrO3/Pt interface forms a Schottky barrier at electric fields from 20 to 160 kV/cm. The dielectric relaxation current behaviour of Pt/PbZrO3/Pt capacitor obeys the well-known Curie-Von Schweidler law at electric field of 20-80 kV/cm, the currents have contributions of both dielectric relaxation current and leakage current. 相似文献