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71.
72.
D. A. Drabold 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):1-21
In this Colloquium, I describe some current frontiers in the physics of semiconducting amorphous materials and glasses, including
a short, but self-contained discussion of techniques for creating computer models, among them the quench from the melt method,
the Activation-Relaxation Technique, the decorate and relax method, and the experimentally constrained molecular relaxation
scheme. A representative study of an interesting and important glass (amorphous GeSe3:Ag) is provided. This material is a fast-ion conductor and a serious candidate to replace current FLASH memory. Next, I discuss
the effects of topological disorder on electronic states. By computing the decay of the density matrix in real space, and
also computing well-localized Wannier functions, we close with a quantitative discussion of Kohn’s Principle of Nearsightedness in amorphous silicon. 相似文献
73.
Larisa P. Demyanova 《Journal of fluorine chemistry》2009,130(9):799-805
The effect of fluorination on silicate and alumino-silicate minerals has been investigated, in particular on the lepidolite [K(Li,Al)3 [Si3AlO10] (F,OH)2] of the mica-type. The fluorination techniques included direct F2-gas and cold radio-frequency-plasma involving c-C4F8 or O2/CF4 mixtures. The modifications of the surface properties have been followed mostly by XPS. Depending of the fluorination route used, either a reactive etching process involving M-F bonding occurs (direct F2-gas; O2-CF4 rf-plasma), or a carbon fluoride deposition takes place (c-C4F8 rf-plasma). 相似文献
74.
Martin Palou Eva Kuzielová Martin Vitkovič Maha S. M. Noaman 《Central European Journal of Chemistry》2009,7(2):228-233
Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics
of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller
particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle
sizes. Inclusion of FA in the LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism
is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize
is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like
phases after soaking in SBF.
相似文献
75.
L.C. Costa 《Journal of Non》2011,357(10):2178-2181
In this work we study the effect of introducing europium oxide in lead borate glasses, in concentrations up to x = 0.20, using the impedance spectroscopy in a large frequency range (0.1 Hz to 9 GHz). Two relaxation processes can be identified. The low frequency process deviates considerably from the Debye type and is modelled by the Cole-Davidson expression. The high frequency relaxation is also a non-Debye type and is fitted by the Cole-Cole expression. These results imply some distribution of relaxation times, due to the interaction between the dipoles.The behaviour of the dielectric strength is similar in the low and high frequency regions, indicating a cluster formation at a critical concentration of europium oxide (x = 0.03). 相似文献
76.
The diffusivity of sulphur in nominal 10 Na2O-16 CaO-74 SiO2 (NCS) and 26 Na2O-74 SiO2 (NS3) melts was investigated in the temperature range 1273-1473 K using the 35S radioactive isotope in a sandwich setup. Samples were sealed in platinum capsules and run with vertical alignment at 100 MPa confining pressure in an internally heated gas pressure vessel. Using the lowest diffusion coefficient D (m2 s− 1) for each temperature the Arrhenian relations logD = −(4.6 ± 0.3) − (216 ± 7) kJ mol− 1/RT for NCS and logD = −(6.3 ± 0.6) − (167 ± 17) kJ mol− 1/RT for NS3 were determined. Viscosity of the melts was used to test the applicability of the Stokes-Einstein (SE) and the Eyring (EY) equations to sulphur diffusion. The SE equation yields unrealistically low radii of the diffusing particles, a consequent of the non-molecular structure of the silicate melts. On the other hand, the Eyring relation yields reasonable jump distances of 550 pm (NCS) and 750 pm (NS3) by fitting the diffusion data to the EY equation. These large values imply that sulphate ions (ionic diameter = 290 pm) migrate as large entities through the silicate network. 相似文献
77.
Ultrasonic slurry sampling electrothermal vaporisation inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) was applied to the elemental analysis of silicate based minerals, such as talc or quartz, without any pre-treatment except the grinding of the sample. The electrothermal vaporisation device consists of a tungsten coil connected to a home-made power supply. The voltage program, carrier gas flow rate and sonication time were optimised in order to obtain the best sensitivity for elements determined. The relationship between the amount of sample in the slurry and the signal intensity was also evaluated. Unfortunately, in all cases, quantification had to be carried out by the standard additions method owing to the strong matrix interferences. The global precision of the proposed method was always better than 12%. The limits of detection, calculated as three times the standard deviation of the blank value divided by the slope of the calibration curve, were between 0.5 ng/g for As and 3.5 ng/g for Ba. The method was validated by comparing the concentrations found for Cu, Mn, Cr, V, Li, Pb, Sn, Mg, U, Ba, Sr, Zn, Sb, Rb and Ce using the proposed methodology with those obtained by conventional nebulisation ICP-MS after acid digestion of the samples in a microwave oven. The concentration range in the solid samples was between 0.2 μg/g for Cr and 60 μg/g for Ba. All results were statistically in agreement with those found by conventional nebulisation. 相似文献
78.
Ion dynamics of AgI-doped Ag2O–TeO2 glasses and Ag2S doped glass nanocomposites have been studied using impedance spectroscopy and correlated with their structures investigated using Fourier transform infrared spectroscopy. The composition dependences of the dc conductivity and the activation energy of these glasses and nanocomposites have been compared with those of AgI-doped silver phosphate and borate glasses. We have studied the ion dynamics in the framework of the power-law and the electric modulus formalisms. We have established a correlation between the crossover rate of the mobile silver ions and the rearrangement of the structural units of glassy networks. The scaling of the conductivity spectra has been used to interpret the temperature and composition dependence of the relaxation dynamics. Analysis of the dielectric relaxation in the framework of modulus formalism indicates an increase in ion–ion cooperation in the glass compositions with increasing AgI content. 相似文献
79.
The surface plasmon (SP) excited infrared-to-visible upconversion luminescence has been studied in the oxyfluoride glass ceramics containing Er3+-doped fluoride nano-crystals. Upconversion luminescence was observed at glass ceramics. Quantum yield of upconversion luminescence increased with increasing heat-treatment temperature. The transparent glass ceramics heat-treated at 700 °C was covered with a 50 nm gold film, and then attached to an SF10 prism with index-matching oil to make an attenuated total reflection (ATR) illumination. The intense upconversion luminescence bands at 540 and 660 nm were observed at the SP resonance angle by using p-polarized laser beam. The apparent dependences of the upconversion efficiency on laser polarization and on incident angle demonstrated the SP excited upconversion of Er3+. 相似文献
80.
Luminescent glasses activated with Sm3+ ions are of current interest given their potential for a wide range of photonic applications. In this work, Sm3+-containing P2O5:BaO glasses are prepared by a simple melt-quench method, and the influence of CuO and SnO co-doping on Sm3+ photoluminescence (PL) is investigated. Optical absorption, solid-state 31P nuclear magnetic resonance spectroscopy, and PL spectroscopy are employed in the assessment of material optical and structural properties. The data indicates that monovalent copper ions and twofold-coordinated Sn centers are successfully stabilized in the matrix and both species can enhance the orange–red emission of Sm3+ ions. The optical properties of the material after heat treatment have been also assessed. Results indicate the chemical reduction of ionic copper via Sn2+ ultimately producing Cu nanoparticles as evidenced by the surface plasmon resonance. As a result, Sm3+ PL diminishes consistent with an excitation energy transfer to plasmonic Cu particles, i.e. the “plasmonic diluent” effect prevails. 相似文献