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941.
942.
943.
944.
945.
The alkaline-earth fluorohalide crystals MFX, where M=Ca, Sr, Ba, Pb and X=Cl, Br, I, form an important class of materials crystallizing in the PbFCl-type tetragonal structure which is also called the matlockite structure. These compounds have long been of interest because of the various defect species which can be detected by spin resonance and associated techniques. The crystals were prepared by slow cooling of the melt of a stoichiometric mixture of BaF 2 and the corresponding chloride or bromide under 0.2 bar of ultrapure argon (5N5), often slightly fluorinated. We have studied the mechanoluminescence (ML) of BaFBr:Sm 2+ and BaFCl:Sm 2+ crystals. It is seen that after the impact of a moving piston, initially the ML intensity increases with time, attains a maximum value and then it decreases with time up to a particular minimum value, and then it increases again, attaining a peak value and finally disappears. The first peak lies in the deformation region and the second peak lies in the post-deformation region. The ML intensity of the BaFCl:Sm 2+ crystal is much higher than the ML intensity of the BaFBr:Sm 2+ crystal. For different impact velocities, the ML intensity increases with velocity; and the total ML intensity attains a saturation value for higher impact velocities. The total ML intensity increases with the increase in the applied load. It is suggested that the moving dislocation produced during deformation of crystals captures holes from hole-trapped centers (like H centers), and the subsequent radiative recombination of the dislocation holes with electron gives rise to ML. Thermoluminescence (TL) of BaFBr:Sm 2+ and BaFCl:Sm 2+ crystals was studied after exposure to ultraviolet rays with the help of a TLD reader. The peak of TL for the BaFBr:Sm 2+ crystal is found at ~247°C and for BaFCl:Sm 2+ crystals at 283°C. The TL intensity initially increases with increase in the UV radiation and then it attains saturation for higher values of UV exposure. The absorption spectrum was recorded with the help of a UV–visible spectrophotometer (Shimadzu). The band found at 275 nm was attributed to H centers. 相似文献
946.
TiO2 thin films were deposited on a glass substrate by the radio frequency magnetron sputtering method, and annealed for 2 h at temperatures of 550°C. Then, 60Co γ rays with different doses were used to irradiate the resulting TiO2 thin films. The surface features of films before and after irradiation were observed by scanning electron microscope (SEM). Simultaneously, the crystal structure and optical properties of films before and after irradiation were studied by X-ray diffraction (XRD), UV–VIS transmission spectrum and Photoluminescence (PL) spectrum, respectively. The SEM analysis shows that the film is smooth with tiny particles on the film surface, and non-crystallization trend was clear after irradiated with γ rays. The XRD results indicated that the structure of the film at the room temperature mainly exists in the form of amorphous and mixed crystal at a sputtering power of 200 W, and non-crystallinity was more obvious after irradiation. Obvious difference can be found for the transmissibility of the irradiated and pre irradiation TiO2 films by the UV-VIS spectra. The color becomes light yellow, and the new absorption edge also appeared at about 430 nm. PL spectra and photocatalysis experiments indicate that the photocatalysis degradation rate of the TiO2 films on methylthionine chloride solution irradiated with the maximum dose can be increased to 90%. 相似文献
947.
The spin-Hamiltonian (SH) parameters (g factors g||, g⊥ and hyperfine structure constants A||, A⊥) and d–d transitions for ZnCdO:Cu2+ are calculated based on the perturbation formulas for a 3d9 ion in tetragonally elongated octahedra. Good agreement between the calculated results (four SH parameters and three optical absorption bands) and the experimental results can be obtained. Since the SH parameters are sensitive to the local structure of a paramagnetic impurity center, the tetragonal distortion (characterized by the relative elongation ratio ρ ≈ 3.5% along the C4 axis) of the impurity center due to the Jahn–Teller effect is also acquired from the calculations. The negative and positive signs of hyperfine structure constants A|| and A⊥ for ZnCdO:Cu2+, respectively, are also suggested in the discussions. 相似文献
948.
This paper describes the effect of ionizing radiation on the interface properties of Al/Ta2O5/Si metal oxide semiconductor (MOS) capacitors using capacitance–voltage (C–V) and current–voltage (I–V) characteristics. The devices were irradiated with X-rays at different doses ranging from 100?rad to 1?Mrad. The leakage behavior, which is an important parameter for memory applications of Al/Ta2O5/Si MOS capacitors, along with interface properties such as effective oxide charges and interface trap density with and without irradiation has been investigated. Lower accumulation capacitance and shift in flat band voltage toward negative value were observed in annealed devices after exposure to radiation. The increase in interfacial oxide layer thickness after irradiation was confirmed by Rutherford Back Scattering measurement. The effect of post-deposition annealing on the electrical behavior of Ta2O5 MOS capacitors was also investigated. Improved electrical and interface properties were obtained for samples deposited in N2 ambient. The density of interface trap states (Dit) at Ta2O5/Si interface sputtered in pure argon ambient was higher compared to samples reactively sputtered in nitrogen-containing plasma. Our results show that reactive sputtering in nitrogen-containing plasma is a promising approach to improve the radiation hardness of Ta2O5/Si MOS devices. 相似文献
949.
The optical absorption spectra (d-d transition bands) and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is Ri?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni2+ center in Ca3Sc2Ge3O12 crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni2+ ion in the octahedral site of Ga3Sc2Ge3O12 is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d8 ions in octahedral lattices. 相似文献
950.
Abstract Measurements of electron paramagnetic resonance, infrared and electrical properties were carried out for the K2SO4—Na2SO4 mixed system before and after γ-irradiation. EPR measurements revealed the presence of a quartet of lines characterized by an isotropic g-value of 2.0034. These lines are mainly attributed to the formation of a SO? 3 center which results from the interaction of γ-rays with the sulfate ion. A decrease in the absorption intensity of the Infrared radiation was observed after γ-irradiation due to radiation damage in the sulfate group. The electrical conductivity, σ, was measured for the K2SO4—Na2SO4 system before and after γ-irradiation in the temperature range from 30 up to 430°C. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after γ-irradiation. The energy of formation of Frenkel defects was estimated to be 2.94eV. The current-voltage characteristics were measured at different temperatures in order to estimate the type of conduction in the samples. Isothermal annealing kinetics was investigated at different temperatures before and after γ-irradiation. The electrical conductivity decreases with increasing time of annealing and the annealing process is dominated by a unique rate process. 相似文献