全文获取类型
收费全文 | 258篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 166篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 19篇 |
物理学 | 76篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 8篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 11篇 |
2007年 | 15篇 |
2006年 | 20篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 17篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有266条查询结果,搜索用时 31 毫秒
1.
Electron paramagnetic resonance (EPR) spectra of powder and oriented films of montmorillonite, hectorite, and saponite intercalated with [Cu(cyclam)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) exhibit three components: an orientation-dependent component without hyperfine features, an orientation-dependent component with hyperfine features, and an orientation-independent component without hyperfine feature. EPR spectra of [Cu(cyclam)](2+)-saponite, which exhibit only two components and the best resolved hyperfine features, were simulated. The spectra indicate that a large portion of the saponite platelets are inclined to the glass surface, although they tend to align with their basal planes parallel to the glass surface. The orientation-dependent spectra could be simulated by introducing a Gaussian distribution with a standard deviation of 20 degrees for the inclination angle. The standard deviation may be used as a disorder parameter for the microcrystals assembled on glass plates. Spectral simulation also shows that the CuN(4) plane of [Cu(cyclam)](2+) is parallel to the clay layers. EPR spectra of some other partially oriented systems are also discussed. 相似文献
2.
Abstract The Cu(III) oxides were investigated first for the unusual copper oxidation state and then for the high-Tc superconductivity. In the last case this property is observed when a mixed copper valence is stabilized : Cu(I)/Cu(II) or Cu(II)/Cu(III). A new mixed valence Cu(III)/Cu(IV) has been stabilized in the three dimensional lattice of the perovskite-type oxide Lal-xSrxCuO3 (0 ≥ ′ ≥ 0,25). Chemical analysis and XPS study confirm the mixed valence. This compound shows metallic properties with an broadening of the conduction band compared to LaCu03. Such a behaviour can be explained either by the increase of the covalence of the average Cu-0 bond or by the decrease of the structural distortion induced by the substitution of Sr(II) for La(III). No superconducting property has been detected down to 4K. 相似文献
3.
X.G.?TangEmail author J.?Wang Y.W.?Zhang H.L.W.?Chan A.L.?Ding C.L.?Choy 《Applied Physics A: Materials Science & Processing》2004,78(8):1205-1209
Highly (100)-oriented, compositionally graded (Pb,Ca)TiO3 (PCT) thin films with a Ca content from 0 to 24 mol% on Pt/Ti/SiO2/Si substrates were prepared by a sol-gel process. The graded structure of the Au/PCT/Pt film capacitor showed a well-saturated hysteresis loop at an applied field of 500 kV/cm with remanent polarization (Pr), and coercive electric field (Ec) values of 9.35 C/cm2 and 130 kV/cm, respectively. At 100 kHz, the dielectric constant and dielectric loss of the film were 129 and 0.024, respectively. The leakage current density of the graded PCT film was less than 1.0×10-7 A/cm2 over a voltage range from 0 to 4 V. The conduction current depended on the voltage polarity. At low electric field (110 and 180 kV/cm, respectively, for Pt and Au electrodes biased negatively), the Au/PCT and PCT/Pt interfaces form a Schottky barrier. At high electric field (>110 kV/cm), the Au electrode biased negatively shows space-charge-limited current (SCLC) behavior. The temperature dependencies of the pyroelectric coefficients of the graded PCT film were measured by a dynamic technique. From 20 to 82 °C, the pyroelectric coefficients of graded PCT film remain steady in the range 106 to 118 C/m2K. The detectivity figure of merit (FD) of the graded PCT film was 6.7×10-6 Pa-0.5. PACS 77.80.-s; 77.70.+a; 77.22.-d; 51.50.+v; 68.37.-d 相似文献
4.
Well-crystallized and stoichiometric Pb(Zr, Ti)O3 (PZT) films, typically ∼5 μm thick, with pure perovskite-type rhombohedral structures have been successfully prepared via an electrospray assisted vapour deposition (ESAVD) method. Control of the deposition temperature within a narrow range of 300-400 °C resulted in films with the most desirable phases. PZT films with close stoichiometric match with the expected composition ratio and uniform element distribution were obtained by adding the appropriate levels of excess Pb in the precursor solutions. The annealed films were uniform, dense, compact and adherent to the substrates. The dielectric constant, ?r, and loss tangent, tan δ, of the fabricated PZT films measured at 10 kHz were 442 and 0.09, respectively. The ESAVD deposited PZT films showed a remanent polarization, Pr, of 15.3 μC/cm2 and coercive field, Ec, of 86.7 kV/cm. These results demonstrate the clear potential of the ESAVD method as a promising technique for the fabrication of thick PZT films. 相似文献
5.
X. Zhao J. Wang H.L.W. Chan C.L. Choy H. Luo 《Applied Physics A: Materials Science & Processing》2005,80(3):653-658
Microdomain-macrodomain transformations and phase transitions in 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 111, 011 and 001 directions) and dc bias field. The crystals have a microdomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 001 or 011 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range. PACS 77.80.-e; 77.22.-d; 81.40.-z 相似文献
6.
J.-M. Liu N. Chong H.L.W. Chan K.H. Wong C.L. Choy 《Applied Physics A: Materials Science & Processing》2003,76(1):93-96
Epitaxial (001) aluminum nitride (AlN) thin films on (111) Si substrates are prepared using pulsed-laser deposition. The epitaxial
structure of the as-prepared thin films is characterized by checking the X-ray-diffraction θ-2 θ scan and pole-figure, using
scanning electron microscopy, infrared radiation (IR) spectroscopy and Raman spectroscopy. The surface acoustic-wave resonance
at 345 MHz for a 1.5 μm thick AlN film on a (111) Si substrate is observed using an inter-digital electrode.
Received: 18 September 2001 / Accepted: 29 January 2002 / Published online: 3 June 2002
RID="*"
ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: liujm@nju.edu.cn 相似文献
7.
Stephen T. L. Choy 《Analysis Mathematica》1981,7(4):235-237
S — E, F — . C(S, E) S E. : C(S, E) F C(S) . , C(S, E) C(S). 相似文献
8.
S.T. Lau K.H. Lam H.L.W. Chan C.L. Choy H.S. Luo Q.R. Yin Z.W. Yin 《Applied Physics A: Materials Science & Processing》2005,80(1):105-110
A newly developed ceramic fibre hydrophone with an active element as small as 0.25 mm in diameter is described in this work. Lead magnesium niobate-lead titanate (PMN-PT) ceramic fibre with a nominal composition of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 was fabricated by an extrusion method. PMN-PT single crystals were ground to a powder form and then mixed with poly(acrylic) acid to form a homogenous slurry. The fibre was extruded by pressing the slurry through a spinneret and then sintering at 1250 °C for crystallization. The electrical characteristics of the PMN-PT fibre were evaluated by measuring the relative permittivity and the impedance spectrum. A piezoelectric PMN-PT fibre hydrophone was fabricated and its sensitivity, angular response, and spatial resolution were evaluated. The fibre hydrophone provides good spatial resolution, angular response and receiving sensitivity. PACS 43.58.+z; 77.84.Dy 相似文献
9.
C.H. Song J. Ma Y.Y. Yao X.M. Lu Y.N. Wang C.L. Choy 《Solid State Communications》2004,129(12):775-780
Bi4Ti3O12 (BiT), Bi3.25La0.75Ti3O12 (BLT), Bi4−x/3Ti3−xNbxO12 (BTN) and Bi3.25−x/3La0.75Ti3−xNbxO12 (BLTN) thin films have been prepared by pulsed laser deposition. BTN and BLTN films exhibit a maximum in the remanent polarization Pr at a Nb content x=0.018. At this Nb content, the BLTN film has a Pr value (25 μC/cm2) that is much higher than that of BiT and a coercive field similar to that of BiT. The polarization of this BLTN film is fatigue-free up to 109 switching cycles. The high fatigue resistance is mainly due to the substitution of Bi3+ ions by La3+ ions at the A site and the enhanced Pr arises largely from the replacement of Ti4+ ions by Nb5+ ions at the B site. The mechanisms behind the effects of the substitution at the two sites are discussed. 相似文献
10.
Single-element, planar transducers have been fabricated using electron-irradiated poly(vinylidene fluoride-trifluoroethylene) 80/20 mol% copolymers with different electron dosage. Electrical field-induced strain response of copolymer film with 100 Mrad dosage has been studied at 5 kHz and the electrostrictive coefficient was calculated. The transmitting response of the air-backing and epoxy-backing transducers was evaluated with the application of high DC bias voltages. Clear ultrasonic amplitudes and high frequency spectrum (>20 MHz) were observed when driven from a standard ultrasonic voltage source through a decoupling circuit. It has also showed that larger generation of ultrasonic waves will be induced under high DC bias field, which is due to the increase of induced d(33) piezoelectric coefficient. Two different polar bias voltages, positive and negative, were applied to the transducers and inverse waveforms were received, which was coincident with the theoretical analysis of the strain response of electrostrictive film. 相似文献