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821.
Optical anisotropy and the direction of polarization of exciton emissions in a semiconductor quantum dot:Effect of heavy-and light-hole mixing
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The dependence of the directions of polarization of exciton emissions, fine structure splittings(FSS), and polarization anisotropy on the light-and heavy-hole(LH–HH) mixing in semiconductor quantum dots(QDs) is investigated using a mesoscopic model. In general, all QDs have a four-fold exciton ground state. Two exciton states have directions of polarization in the growth-plane, while the other two are along the growth direction of the QD. The LH–HH mixing does affect the FSS and polarization anisotropy of bright exciton states in the growth-plane in the low symmetry QDs(e.g., C_(2V),C_S, C_1), while it has no effect on the FSS and polarization anisotropy in high symmetry QDs(e.g., C_(3V), D_(2d)). When the hole ground state is pure HH or LH, the bright exciton states in the growth-plane are normal to each other. The LH–HH mixing affects the relative intensities and directions of bright exciton states in the growth-plane of the QD. The polarization anisotropy of exciton emissions in the growth-plane of the QD is independent of the phase angle of LH–HH mixing but strongly depends on the magnitude of LH–HH mixing in low symmetry QDs. 相似文献
822.
Optical properties of Cd1−xZnxTe thin films fabricated through sputtering of compound semiconductors
Cd1−xZnxTe thin film fabrication is necessary for its photovoltaic and imaging applications in large scale. Thermally annealed and thereby interdiffused r.f. sputtered multilayers comprising of CdTe and ZnTe have been utilized here for the fabrication of Cd1−xZnxTe thin films. Photoluminescence and change of resistance of the multilayer under illumination were studied using different annealing temperatures and varying number of repetitions. It was found that three number of repetitions annealed at 300 °C exhibited the best results. 相似文献
823.
Rajiv Srivastava Rajat Kumar Singh Yatindra Nath Singh 《Optical and Quantum Electronics》2009,41(6):463-480
This paper presents optical packet switch architecture with large buffering capacity for the contention resolution of the
packets. The main feature of the architecture is no requirement of Demux/Mux and splitter/combiner which are used in most
of the other loop buffer based switch architectures. Therefore physical loss of the architecture is very less, and switch
performance is not limited by the physical degradation of the signal. In the buffer, TWCs/SOAs are replaced by Tunable Fiber
Bragg Gratings (TFBGs). The use of TFBGs inside the buffer is a novel approach towards buffering structure. The architecture
presented here can be modeled as output queue buffer scheme. This paper investigates the advantages of the proposed architecture
over the earlier architecture. The performance of the architecture in terms of physical layer parameters (loss analysis, power
analysis and noise analysis), packaging volume and optical cost is done. 相似文献
824.
The addition of polymethyl methacrylate (PMMA) having different molecular weights to electrolytes containing ammonium trifluoromethanesulfonate
(NH4CF3SO3) in diethyl carbonate (DEC) has been found to result in conductivity enhancement and to yield gel electrolytes with conductivity
higher than the corresponding liquid electrolytes. The increase in conductivity has been found to be due to the dissociation
of undissociated NH4CF3SO3 and ion aggregates present in the electrolytes, and this has been supported by Fourier transform infrared spectroscopy results,
which suggests active interaction of PMMA and NH4CF3SO3 in these gel electrolytes. The increase in conductivity also depends upon the molecular weight of the polymer used and is
relatively more for PMMA having lower molecular weight. The increase in viscosity with PMMA addition also depends upon the
molecular weight of the polymer and is closely related to the conductivity behavior of these electrolytes. Polymer gel electrolytes
have been found to be thermally stable up to a temperature of 125 °C. 相似文献
825.
The observer-based procedure, used in research applications to measure the hearing sensitivity of young infants, is analyzed within the framework of a two-stage (infant-judge) detection model involving a minimum number of assumptions. The model is taken to develop convergence theorems useful for estimating the number of judges and/or trials required to achieve a desired level of accuracy using the procedure. The model is also used to consider ways in which bias in estimates, known to be associated with the procedure, might be evaluated and reduced. Finally, a method is proposed by which the results of the analysis and different procedural variations designed to improve estimates can be evaluated empirically. 相似文献
826.
We use ultrafast electron crystallography to study structural changes induced in graphite by a femtosecond laser pulse. At moderate fluences of < or =21 mJ/cm2, lattice vibrations are observed to thermalize on a time scale of approximately 8 ps. At higher fluences approaching the damage threshold, lattice vibration amplitudes saturate. Following a marked initial contraction, graphite is driven nonthermally into a transient state with sp3-like character, forming interlayer bonds. Using ab initio density functional calculations, we trace the governing mechanism back to electronic structure changes following the photoexcitation. 相似文献
827.
828.
829.
Taribagil R Arunagirinathan MA Manohar C Bellare JR 《Journal of colloid and interface science》2005,289(1):242-248
When some poorly water-soluble solid surfactants are contacted with water, several microstructures are observed as part of the dissolution process of the surfactants in water. One such microstructure called "myelin," which is observed when a surfactant like phosphatidylcholine is contacted with water, is the subject of this paper. In this study we have used video microscopy to investigate myelin growth over a wide time range, namely 0.25-700 s, and found that existing models do not correctly express myelin growth over extended time ranges. When studied over a wide time range, the myelin growth was found to evolve over three distinct regimes, namely ballistic, diffusional, and subdiffusional regimes. The underlying growth models are physically explained and mathematically expressed. A relationship is derived between the width of myelin and the growth rate at long times. The estimated width of myelin is consistent with experiments. 相似文献
830.
Non-linear natural vibration characteristics and the dynamic response of hingeless and fully articulated rotors of rectangular cross-section are studied by using the finite element method. In the formulation of response problems, the global variables are augmented with appropriate additional variables, facilitating direct determination of sub-harmonic response. Numerical results are given showing the effect of the geometric non-linearity on the first three natural frequencies. Response analysis of typical rotors indicates a possibility of substantial sub-harmonic response especially in the fully articulated rotors widely adopted in helicopters. 相似文献