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521.
Shin-ichiro Gozu Kouichi Akahane Naokatsu Yamamoto Akio Ueta Naoki Ohtani 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):230
InGaAs/AlAsSb systems lattice matched to InP have two distinguishable features: a high conduction band offset and type-II band configuration. Although, the former results in a large intersubband transition (ISBT) at conduction band, the latter makes it difficult to use the effective interband transition (IBT). To overcome this latter problem, the effect of the Sb was investigated because Sb would act as a band modulator from type-II to type-I. In0.57Ga0.43As1-xSbx/AlAs0.48Sb0.52 single quantum well (SQW) samples with various Sb compositions x, were grown on GaAs substrates via AlAs0.48Sb0.52 buffer layer. Their photoluminescence (PL) properties were examined to identify their band configurations. When the excitation laser power was increased, the PL property of In0.57Ga0.43As SQW sample, showed a larger blue shift than that of ones. This indicates that the band configuration modulates from type-II to type-I when the antimonide composition is larger than 0.13. These findings indicate that new functional devices can be fabricated using a combination of IBT and ISBT. 相似文献
522.
V. Hannstein G. C. Hegerfeldt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):415-422
A simplified scheme for the investigation of cooperative effects in
the quantum jump statistics of small numbers of fluorescing atoms
and ions in a trap is
presented. It allows the analytic treatment of three
dipole-dipole interacting four-level systems which model the
relevant level scheme of Ba+ ions. For the latter, a huge rate of
double and triple jumps was reported in a former experiment and the
huge rate was attributed to the dipole-dipole interaction. Our theoretical
results show that the effect of the dipole-dipole interaction on these rates
is at most 5% and that for
the parameter values of the experiment there is practically no
effect. Consequently it seems that the
dipole-dipole interaction can be ruled out as a possible explanation for
the huge rates reported in the experiment. 相似文献
523.
以功能性核磁共振造影初探10Hz调制激光针灸刺激所引发人类大脑皮质的活化现象(英文) 总被引:1,自引:0,他引:1
使用10 Hz调制的低功率激光针灸刺激探究大脑皮质反应.以功能性核磁共振造影技术探讨当激光针灸刺激左脚涌泉穴(K1)时,大脑可能产生的反应机制.研究发现调制激光针灸所引发显著的大脑活化反应,包括右额叶中央前回、右额叶上回、左额叶中央前回、左顶叶中央后回、左侧下部顶叶、左小脑舌前叶、左海马旁回和左小脑山顶等区域.安慰剂组实验并没有发现在脑部有任何活化反应,大多数反应区域所涉及功能与记忆、注意力及自我意识等有关联.结果显示出调制激光针灸的大脑血液动力学反应,并隐含此反应机制不只是依据传入感觉信息处理,而且还有着随外部刺激的变化而有所改变的血液动力学性质. 相似文献
524.
研究了枪弹头痕迹自动比对方法,用最优化的方法消除测量误差,通过中值滤波去除随机噪声,并根据数据的相似性度量理论确定了以横向相关性为基础的比对方案. 相似文献
525.
A. Balzarotti 《Il Nuovo Cimento D》1993,15(2-3):459-466
Summary Using a scanning tunnelling microscope, the tunnelling currentvs. voltage is measured between a gold tip and the chemically etched (001) surface of YBa2Cu3O
x
crystals at room temperature. The tunnelling barrier height and thickness are derived by modelling the system in the normal
state as a conventional N-I-N junction. TheI(V) andG(V) curves are computed for the same junction in the superconducting state (N-I-S junction). The predicted gap structure for
a single BCS-Dynes-like gap is simple and has low zero-bias conductance. The complexG(V) spectra measured belowT
c
on the etched junctions with ∼ 50% zero-bias conductance suggest a possible multilayer contribution in the unit cell.
In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching. 相似文献
526.
Summary We present luminescence spectra of gallium selenide at 2 K in which a slow and continuous evolution from excitonic recombination
to an electron-hole plasma emission is observed when the excitation intensity is increased. We find a small red-shift and
a broadening of the direct exciton emission line which is followed by its disappearing. We explain these results with a model
which takes into account the electron-hole correlation.
Part of this work was carried out during a stage at the Institut de Physique Appliquée of the Ecole Polytechnique Fédérale
de Lausanne (Switzerland). 相似文献
527.
Summary For photon energies below the absorption edge in CdS, CdSe and other II–VI crystals the polariton dispersion curves forE⊥c andE‖c (c-axis in a wurtzite crystal) corss at some points called isotropic points (IP). The occurrence of isotropic points provides
the possibility of mode coupling between ordinary and extraordinary waves. Since the consequences of mode coupling on the
optical properties for photon energies near the lowest IP lying much below the first excitonic state were widely discussed
in recent years, more attention is now paid to isotropic points lying near the band gap and related to then=2,3, … excitonic states (?higher isotropic points?). Making use of Stahl's real density matrix approach we derive the polariton
dispersion relationsk
⊥ (ω), andk
‖ (ω), for CdS and CdSe bulk crystals and determine the positions of IP's due to the crossing of theB-polariton with higherA-excitonic resonances. By the method of multiple internal reflection we calculate the transmission spectra for various crystal
thicknesses (between 3 μm and 0.5 mm) and coupling mechanisms. The calculated transmission shows sharply peaked structures
centred at the isotropic points. 相似文献
528.
INFLUENCE OF SAMPLE THICKNESS ON ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYMERS IN A CONFINED VOLUME 总被引:2,自引:0,他引:2
Hui Sun Zhi-ying Zhang Shi-zhen Wu Bin Yu Chang-fa Xiao 《高分子科学》2005,(6):657-663
Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method. The influence of sample thickness on some kinetic parameters of crystallization was quantitatively evaluated. It was found that there was a critical thickness value. Influence of thickness on the crystallization behavior was only found for samples of thickness near and less than the critical value. For thick samples the Avrami plot showed straight lines with a turning point at the late stage of crystallization due to the secondary crystallization. When the thickness was near or less than the critical value a primary turning point appeared in the Avrami plot at the very beginning of the crystallization process. A model was proposed to explain the mechanism of this phenomenon. According to this model the critical thickness value is related to the nucleation density or the average distance between adjacent nuclei, and the primary turning point is an indication of a transformation of crystal growth geometry from a three-dimensional mode to a two-dimensional one. Analysis of experimental results of PEO isothermally crystallized at 53.5℃ was consistent with the proposed model. 相似文献
529.
A novel ternary borate, sodium strontium pentaborate, NaSrB5O9, has been prepared by solid-state reaction below 800 ℃. The single-crystal X-ray structural analysis showed that NaSrB5O9 crystallizes in monoclinic, space group P21/c with a = 6.499(2), b = 13.979(3), c = 8.045(2) , β = 106.92(2)°, V = 699.2(3) 3, Z = 4, Mr = 308.66, Dc = 2.932 g/cm3, μ = 7.804 mm-1, F(000) = 584, R = 0.0264 and wR = 0.0621 for 2426 observed reflections and 146 variables. NaSrB5O9 is a layered compound containing double ring B5O11 building units composed of two BO4 tetrahedra and three BO3 triangles. Each B5O11 unit is connected to four other equivalent units through exocyclic oxygen atoms to form a two-dimensional ∞2 [B5O9]3- layer. Symmetry-center related layers are stacked along the b axis and held together by Na+ and Sr2+ cations via electrostatic interactions. 相似文献
530.
Summary A simple and sensitive method for the determination of trace amounts of bisphenol-A (BPA), bisphenol-A diglycidyl dimethacrylate
(bis-GMA), bisphenol-A dimethacrylate (bis-DMA) and triethyleneglycol dimethacrylate (TEGDMA) in human saliva is proposed.
These materials are used in dental restorations, as composites and sealants, and are sometimes detected in human saliva after
dental treatment. The proposed method involves protein precipitation using acetonitrile followed by acidification, evaporation
of the solvent and dissolution with dichloromethane prior to injection into a GC-MS.
Thermal derivatization in the injection system was used for the identification and quantification of bis-GMA. Clean-up is
not necessary using SIM mode. Bisphenol-F (BPF) was used as internal standard. The linear range was 15 to 1000 μg·L−1 for BPA, 50 to 10 000 μg·L−1 for bis-GMA, 50 to 1000 μg·L−1 for bis-DMA and 1 to 100 μg·L−1 for TEGDMA.
The detection limits were 3,15,10 and 0.3 μg·L−1 for BPA, bis-GMA, bis-DMA and TEGD-MA, respectively. Validation of the proposed method was carried out by using the standard
addition methodology.
Samples of 10 mL of human saliva collected 1 h after dental treatment were analysed in order to assess the applicability of
the method to detect and quantify such compounds originated from methacrylic resins used in odontological treatment. 相似文献