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991.
The superplastic deformation behavior of quasi-single phase Zn-0.3 wt. %Al was investigated. A series of load relaxation and
tensile tests was conducted at various temperatures ranging from RT (20 °C) to 200 °C. The recently proposed internal variable
theory of structural superplasticity was applied. The flow curves obtained from load relaxation tests were shown to consist
of contributions from interface sliding (IS) and accommodating plastic deformation. In the case of quasi-single phase Zn-0.3
wt.% Al alloy with an average agrain size of 1 μm, the IS behavior could be described as a viscous flow process characterized
by a power index of Mg=0.5. A large elongation of about 1400% was obtained at room temperature and the strain rate sensitivity parameter was about
0.4. Although relatively large-grained (10 μm) single phase alloy showed a high value of strain rate sensitivity comparable
to that of fine-grained alloy at very low strain rate range, IS was not expected from the analysis based on the internal variable
theory of structural superplasticity at room temperature. As the temperature increased above 100 °C, however, the contribution
from IS was observed at a very low strain rate range. A high elongation of ∼400% was obtained in a specimen of 10-μm-grain-size
at 200 °C under a strain rate of 2×10−4/sec.
Jointly appointed at Center for Advanced Aerospace Materials (CAAM) 相似文献
992.
Based on the optimum deposition conditions of ZrN thin film from our previous study, by varying oxygen flow rate ranging from 0 to 8 sccm, nanocrystalline ZrNxOy thin films were deposited on p-type (100) Si substrates using hollow cathode discharge ion-plating (HCD-IP) system. The objective of this study was to investigate the effect of oxygen content on the composition, structure and properties of the ZrNxOy thin films. The oxygen content of the thin film, determined using X-ray photoelectron spectroscopy (XPS), increased with increasing oxygen flow rate. As the oxygen content increased, the color of the ZrNxOy thin film changed from golden yellow to blue and then slate blue, and the microstructure observed by scanning electron microscopy (SEM) varied from columnar structure to finer grains and finally flat and featureless structure. Phase separation of ZrNxOy to ZrN and monoclinic ZrO2 was found from X-ray diffraction (XRD) patterns when the oxygen content was higher than 9.7 at.%. The hardness of the film slightly increased as the oxygen content was less than 9.7% and then decreased to 15.7 GPa, a typical hardness of ZrO2 phase, as the oxygen content further increased. The total residual stress of the film was measured using an optical method, and the residual stresses of ZrN and ZrO2 phases were determined separately using modified XRD sin2ψ method. The total stress was close to the stress in ZrN phase as the ZrO2 fraction was less than 30%, and was close to that in ZrO2 phase as the ZrO2 fraction was over 30%. The electrical resistivity of the film increased significantly with the increase of oxygen content. The film properties showed consistent trend with phase separation. As the fraction of ZrO2 phase was small, the apparent properties of the films were more close to those in ZrN. When ZrO2 fraction was over 30%, the films mainly exhibited the properties of ZrO2. 相似文献
993.
994.
Different metallurgical processing, including the standard heat treatment, heat treatment without β aging, addition of high
amount of Cr, and long-term isothermal exposure, was conducted on superalloy Inconel 783. For these processed materials, the
tensile property and hardness at room temperature and stress relaxation behavior at 650 °C were examined. The testing results
showed that isothermal exposure and heat treatment without β aging slightly enhanced the yield strength of alloy 783 at room
temperature as well as all metallurgical processing in this study produced an identical stress relaxation behavior at 650
°C. The microstructure variation with different processing was analyzed using optical microscope, scanning electron microscopy
(SEM), and transmission electron microscopy (TEM). 相似文献
995.
A dual-phase Fe–Mn–Al–C alloy was oxidized at 750°C in air with 2 initial mg/cm2 NaCl deposits. After 9 hr of exposure a fine-void zone was observed in the middle subscale and a coarse-void layer in the inner subscale. The fine-void zone formed due mainly to the interaction between selective oxidation of manganese and the oxidation of metal chlorides, while the formation of the coarse-void layer was caused by chlorination. The product remaining in the fine-void zone was mostly Al2O3, and the structure of the substrate in this zone is oxidation-induced ferrite, where nitriding of aluminum occurs forming AlN. Fine Fe3O4 particles fill in the coarse voids and the structure of the substrate in this layer is secondary austenite. The mechanism of the formation and growth of the internal oxidation and nitriding in the void zones of the subscale are discussed. 相似文献
996.
997.
Characteristics of graphite felt electrode electrochemically oxidized for vanadium redox battery application 总被引:2,自引:0,他引:2
The graphite felt was oxidized at a positive electrode potential in sulfuric acid solution.The electrochemical performance of the treated graphite felt served as electrode for vanadium redox battery was investigated with FT-IR,SEM,XPS,BET,cyclic voltammetry and testing VRB system,respectively.The results show that the molar ratio of O to C increases from 0.085 to 0.15 due to the increase of—COOH functional groups during electrochemical oxidation treatment,and the GF surface is eroded by electrochemical oxidation,resulting in the surface area increase from 0.33 m2/g to 0.49 m 2/g.The VRB with modified GF electrode exhibits excellent performance under a current density of 30 mA/cm 2 .The average current efficiency reaches 94%and average voltage efficiency reaches 85%.The improvement of electrochemical activity for the electrode is ascribed to the increase of the number of—COOH group and the special surface of GF. 相似文献
998.
Hyung-Jun Chang Heung Nam Han Sang-Hoon Joo Kwang-Hee Lee Kyu Hwan Oh 《International Journal of Machine Tools and Manufacture》2007,47(10):1573-1582
The hot roll pressing of iron powder with several rotating speeds was carried out on a pilot-plant scale. From these experiments, it was confirmed that the surface temperature of roller was increased with increasing its rotating speed. It was also known that the heat transfer coefficient between the iron powder and the roller surface is closely related with the rotating speed of roller. These results were quantitatively described by using a mathematical model which was derived based on the steady-state heat transfer during hot roll pressing. In addition, the densification behavior of iron powder during the hot roll pressing was simulated by a finite element model based on the arbitrary Lagrangian and Eulerian (ALE) method and a yield criterion for metal powder. From these models, the maximum critical rotating speed of roller during the hot roll pressing, in which the roller could hold out against the thermal fracture, could be determined. 相似文献
999.
1000.
本文综述了铸造法(搅拌铸造法、挤压铸造法、离心铸造法)制备SiCp/Al复合材料的研究现状,指出了铸造法中存在的主要问题以及今后的研究方向. 相似文献