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71.
J. Siva Kumar U. V. Subba Rao K. V. Satyanarayana Rao K. Narasimha Reddy 《Crystal Research and Technology》1991,26(1):103-108
Thin films of various thicknesses in the MIM structure have been prepared from the the powders of SnO2, Sb2O3 and (SnO2 + Sb2O3) of high purity by the thermal evaporation technique in a vacuum of 10−5 Torr. Dielectric properties of SnO2, Sb2O3, and their mixed thin films have been studied with ac and dc electric fields and frequency. Capacitance and loss tangent are almost independent on dc voltage upto 1.0 V for SnO2, 10.0 V for Sb2O3 and 2.5 V for mixed films. These capacitors become unstable at 1.0 V for SnO2 films and 2.5 V for mixed films. For higher film thicknesses the decay in these films starts at higher voltages. Capacitance and loss tangent increases with applied ac voltage in SnO2, Sb2O3, and their mixed films. A comparison of the capacitance values of SnO2, Sb2O3, and their mixed films showed that the capacitance values are less in Sb2O3 as compared to SnO2 films. In mixed films the capacitance is greater than the constituent films. These studies have shown that Sb2O3 films are found to be more stable compared to SnO2 and their mixed films for ac and dc voltages. The results thus obtained on SnO2, Sb2O3, and their films are presented and discussed. 相似文献
72.
ABSTRACT The present work describes a phenomenological approach to explain the instantaneous behaviour of tungsten heavy alloys (WHAs) in heat-treated and swaged conditions. The strengths and elongation values of heat-treated materials are lower and higher than those of the swaged samples respectively. The heat-treated materials exhibit two slopes in true stress–true plastic strain curves and follow the Ludwigson constitutive equation. On the other hand, swaged materials display a single slope and adhere to typical Swift constitutive equation. The latter reflect the presence of pre-strain in the materials due to swaging deformation. The fracture surfaces in heat-treated materials consist of W-W decohesion along with matrix rupture and W-cleavage, while swaged samples consist of mainly W-cleavage. Both the materials display three typical stages (I, II and III) of work hardening. The second derivatives of true stress–true plastic strain curves of these alloys exhibit a perfect parabola although the nature of true stress–true strain as well as true stress–true plastic strain curves is quite different in heat-treated and swaged materials. This has been observed for the first time in WHAs consisting of matrix and W-grains. The shape of the parabola is simple and easy to fit. The fitting parameters of parabolas have been successfully employed to explain the flow behaviour of a large number of tungsten heavy alloys having two-phase microstructure in different processing conditions. 相似文献
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76.
Microhardness of KBr crystals doped with various concentration of Ba2+ have been investigated in the asgrown state and after quenching from various elevated temperatures. It is observed that hardness increases with increase in impurity concentration and at high concentration the hardness starts decreasing. Microstructural investigations have showed the formation of visible precipitates at high concentrations. The heat treatment studies showed that in crystals quenched from elevated temperatures the visible precipitates dissociate and hardness increases. 相似文献
77.
78.
N. Pandaraiah K. Narasimha Reddy U. V. Subba Rao B. M. Wanklyan 《Crystal Research and Technology》1984,19(4):571-576
Thermoluminescence (TL) studies of cobalt-doped Al2O3 crystals irradiated with X-rays have shown that the TL glow curve consists of three peaks at 105, 195 and 260°C. Bleaching, annealing and quanching studies have been performed in order to understand the nature of colour centers responsible for the formation of the three peaks. The values of the fundamental parameters like trap depth and frequency factor are estimated from TL data and the results obtained are discussed. 相似文献
79.
Elevated irradiation temperature studies with NaYF4 samples reveal that the intensity of the two glow peaks observed around 120 and 180°C enhances. The effect of temperature of irradiation (Tirr) on the sensitisation of the both peaks are studied. The half lives of these glow peaks were calculated and concluded that the half lives of these peaks decreases with the increase in irradiation temperatures. 相似文献
80.
Structural, morphological and optical properties of rare earth ions (RE3+=Sm3+ or Dy3+) activated Ca3Ga2Si3O12 (CaGaSi) phosphors synthesized by the sol-gel method are reported. XRD results confirmed the cubic phase structure of RE3+:CaGaSi phosphors. From the SEM images of RE3+:CaGaSi phosphors, it is observed that the particles are agglomerated. Photoluminescence spectra of Sm3+:CaGaSi phosphors have shown bright orange red emission at 598 nm (4G5/2→6H7/2) with an excitation wavelength of λexci=401 nm. In the case of Dy3+:CaGaSi phosphors bright yellow emission has been observed at 574 nm (4F9/2→ 6H13/2) with λexci=451 nm. From the PL spectral results, the rare earth ion concentration of CaGaSi phosphors is optimized. 相似文献