全文获取类型
收费全文 | 335篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 29篇 |
晶体学 | 95篇 |
物理学 | 227篇 |
出版年
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 1篇 |
2011年 | 4篇 |
2010年 | 8篇 |
2009年 | 58篇 |
2008年 | 73篇 |
2007年 | 53篇 |
2006年 | 47篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 15篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有351条查询结果,搜索用时 31 毫秒
291.
In the present study we report the results of 29Si, 27Al, 31P and 19F magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) of 4.5SiO2-3Al2O3-1.5P2O5-(5−z)CaO-zCaF2 glasses with z = 0-3 to elucidate the effect of fluoride content on the glass structure. The 29Si MAS-NMR spectra gave a chemical shift of about −90 ppm corresponding to Q3(3Al) and Q4(3Al). The 27Al MAS-NMR showed a large broad central peak around 50 ppm, which is assigned to four-coordinated Al linked via oxygen to P. A shoulder around 30 ppm and a small peak at about 0 to −10 ppm appeared in the 27Al MAS-NMR spectra of the glasses on increasing the fluoride content assigned to five-coordinated and six-coordinated Al species, respectively. The 31P MAS-NMR spectra indicated the presence of Al-O-P bonds. The 31P chemical shift decreased with increasing fluoride content as a result of calcium being complexed with fluoride. This resulted in a reduction of the number of available cations to charge balance non bridging oxygens in phosphorus and an increase in the number of Al-O-P bonds being formed, instead. The 19F spectra indicated the presence of Al-F-Ca(n) and F-Ca(n) species in all the glasses containing fluoride as well as an additional Si-F-Ca(n) species in the glasses with higher fluoride content. 相似文献
292.
C. Benjamin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):403-410
Reflectance measurements from p-type GaSb:Zn epitaxial films with different hole concentrations (1017–1018 cm-3) have been investigated over the frequency region of
100–1000 cm-1. A minimum broadening feature corresponding to the hole plasmon was observed in the reflectance spectra. The experimental
infrared spectra were well fitted using a
Lorentz-Drude dispersion model. The real part ε1 of the dielectric function decreases with increasing hole concentration. However, the imaginary part ε2
increases with hole concentration in the far-infrared region.
This indicates that the acoustic- and optic-phonons mainly
participate in the free carrier absorption processes. The hole
mobility obtained from Hall-effect measurements is slightly
larger than that derived from optical measurements and the
average ratio of mobilities is estimated to be 1.33. Owing to
overdamping effects, the upper branch of longitudinal-optical
phonon plasmon (LPP) coupled modes was observed. The upper
LPP+ frequency increases with hole concentration and it
shows a transition from phonon-like to plasmon-like behavior. A
theoretical analysis with solutions in the complex frequency
plane describes these experimental results. 相似文献
293.
V. V. Hoang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(3):291-297
Dynamical heterogeneities (DH) in low density liquid SiO2 have been
investigated by molecular dynamics (MD) method. Simulations were done in the
basic cube under periodic boundary conditions containing 3000 particles with
the pair interatomic potentials, which have a weak electrostatic interaction
and a Morse type short range interaction (PMSI). We have evaluated the
non-Gaussian parameter for the self part of the van Hove correlation
function and we found a clear evidence of the existence of DH in low density
liquid SiO2. Moreover, the atomic displacement distribution (ADD) in a
model has been obtained and it deviates from a Gaussian form. The results
have been compared with those obtained in another liquid SiO2 system
with the Born-Mayer interatomic potentials (BMP) in order to observe the
interatomic potential effects on the DH in the system and indeed, the
effects are strong. Calculations showed that particles of extremely low or
fast mobility have a tendency to form a cluster and mean cluster size of
most mobile and immobile particles in PMSI models increases with decreasing
temperature. In contrast, no systematic changes have been obtained for the
most mobile and immobile particles in BMP models. Calculations show that
there is no relation between local particle environment and particle
mobility in the system. 相似文献
294.
Thin GaAs films were prepared by pulse plating from an aqueous solution containing 0.20 M GaCl3 and 0.15 M As2O3 at a pH of 2 and at room temperature. The current density was kept as 50 mA cm−2 the duty cycle was varied in the range 10-50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm−2 illumination, an open circuit voltage of 0.5 V and a short circuit current density of 5.0 mA cm−2 were observed for the films deposited at a duty cycle of 50%. 相似文献
295.
In this presentation we focus on the synthesis of buried multielemental semiconductor nanoparticles by sequential high dose ion implantation and post-implantation annealing. Nanocluster formation and alloying was studied by Raman-, Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction analysis (XRD) on a materials library of CdSxSe1−x nanoclusters buried in thermally grown SiO2 on silicon. Characteristic peak shifts of the LO-Raman signal and XRD-peaks due to varying S- and Se-fraction indicate that the ion beam synthesized clusters consist of a solid solution of Cd, S and Se. In addition the influence of the implanted dose ratios on the structural evolution of the nanocluster-SiO2 system will be discussed. 相似文献
296.
A review of the techniques and applications of multichannel ellipsometry in the dual-rotating-compensator configuration is given. This ellipsometric approach has been established as the ultimate in real-time, single-spot optical measurement, as it determines the entire 16-element Mueller matrix of a sample over a wide spectral range (up to 1.7-5.3 eV) from raw data collected over a single optical period of 0.25 s. The sequence of optical elements for this ellipsometer is denoted PC1rSC2rA, where P, S, and A represent the polarizer, sample, and analyzer. C1r and C2r represent two MgF2 rotating compensators, either biplates or monoplates that rotate synchronously at frequencies of ω1 = 5ω and ω2 = 3ω, where π/ω is the fundamental optical period. Previous high-speed Mueller matrix measurements with this instrument have been performed on uniform, weakly anisotropic samples such as (110) Si, in which case one can extract the bulk isotropic and near-surface anisotropic optical responses simultaneously. In such an application, the instrument is operated at its precision/accuracy limits. Here, ex situ results on a strongly anisotropic, locally biaxial film are presented that demonstrate instrument capabilities for real-time analysis of such films during fabrication or modification. In addition, the use of the instrument as a real-time probe to extract surface roughness evolution on three different in-plane scales for an isotropic film surface is demonstrated for the first time. 相似文献
297.
Recently, we have discovered a new type of first order phase transition around 120 K for (n-C3H7)4N[FeIIFeIII(dto)3] (dto=C2O2S2), where the charge transfer transition between FeII and FeIII occurs reversibly. In order to elucidate the origin of this peculiar first order phase transition. Detailed information about the crystal structure is indispensable. We have synthesized the single crystal of (n-C3H7)4N[CoIIFeIII(dto)3] whose crystal structure is isomorphous to that of (n-C3H7)4N[FeIIFeIII(dto)3], and determined its detailed crystal structure. Crystal data: space group P63, a=b=10.044(2) Å, c=15.960(6) Å, α=β=90°, γ=120°, Z=2 (C18H28NS6O6FeCo). In this complex, we found a ferromagnetic transition at Tc=3.5 K. Moreover, on the basis of the crystal data of (n-C3H7)4N[CoIIFeIII(dto)3], we determined the crystal structure of (n-C3H7)4N[FeIIFeIII(dto)3] by simulation of powder X-ray diffraction results. 相似文献
298.
Raman investigations were carried out for various compositions of chalcogenide glasses in the GeS2-Ga2S3-CdS system. Addition of Ga2S3 into GeS2 results in the formation of metal-metal bonds and edge-shared GaS4/2 tetrahedra. Ge2+ ions may surround [GaS4/2]1− tetrahedra acting as charge compensators. Upon the addition of CdS into the GeS2-Ga2S3 system, the number of the metal-metal bonds and edge-shared GaS4/2 tetrahedra decreases, resulting in the formation of corner-shared tetrahedra with non-bridging sulfurs (NBS). Cd2+ ions can be dissolved into the glass network as charge compensators for these NBS and exited few [GaS4/2]1− tetrahedra. The high solubility of CdS is ascribed to the dissociation of metal-metal bonds and edge-shared tetrahedra in these Ga-containing glasses. 相似文献
299.
Thermal analysis of Ge20Te80−xPbx (2≤x≤8) glasses has been undertaken using modulated differential scanning calorimetry (MDSC). The compositional dependence of thermal parameters is investigated. The crystallization temperatures (Tc) estimated from the total heat flow show detectable changes at compositions x=4, 6.5 and 7.5. Further, the heat capacity change at the glass transition temperature, measured from the reversible heat flow curve (ΔCpR), is found to exhibit a maximum and an inflexion at compositions x=4 and 6.5 and minimum at x=7.5, respectively. Also, the relaxation enthalpy, estimated from the area under the non-reversing heat flow curve (ΔHNR), exhibits similar features at the said compositions. From the observed MDSC results, it has been proposed that the compositions x=4 and x=6.5 denote to the onset and completion of rigidity percolation and x=7.5 corresponds to the chemical threshold of the system. 相似文献
300.
Lithium cesium mixed alkali borate glasses of the composition 67B2O3·xLi2O·(32−x)Cs2O (where x=8, 12, 16, 20 and 24) containing 1 mol% Nd2O3 were prepared by melt quenching. The absorption spectra of Nd3+ were studied from the experimental oscillator strengths and the Judd-Ofelt intensity parameters were obtained. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) (AT), branching ratios (β) and integrated absorption cross-sections (Σ) of the Nd3+ transitions from the excited state J manifolds to the lower lying J′ manifolds. Radiative lifetimes (τR) are estimated for certain excited states of Nd3+ in these mixed alkali borate glasses. Luminescence spectra were measured and the emission cross-sections (σp) were evaluated for the three emission transitions. The variation of luminescence intensity with x was recorded for the three transitions at different excitation power to see the effect of mixed alkalies in these borate glasses. 相似文献