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961.
962.
This study employs expectancy theory to evaluate some key factors that motivate students to participate in the teaching evaluation process. The results show that engineering students generally consider the improvement of teaching to be the most important outcome of teaching evaluations, followed by the improvement of course content and format. Making the results of evaluations available for students' decisions on course and instructor selection ranked third, while the least important use was influencing a professor's tenure, promotion, and salary raise. Students' motivation to participate in teaching evaluations is also impacted significantly by their expectation that they will be able to provide meaningful feedback. 相似文献
963.
A. Bayram 《Materialwissenschaft und Werkstofftechnik》2004,35(1):29-35
The aim of this study was to investigate the mechanical properties of Al‐Mg‐Si alloys aged to peak hardness with different dispersoid volume fraction. It was found that the tensile strength increases with dispersoid content, for alloys having similar ductility. The effect of an increasingly triaxial stress state on a fracture strain above mentioned alloys were measured using a series of notched tensile specimens whose notch root radius of curvature was changed. The alloy ductility was found to increase with dispersoid content and root radius and to decrease with increased stress triaxiality. The fracture toughness of these alloys was determined as a function of dispersoid content and notch root radius of curvature. It was observed that the fracture toughness increased as the dispersoid content and the notch root radius increased. scanning electron microscope analysis of the fracture surfaces revealed that fracture mechanism was transgranular fracture with dimples formation. It is argued that optimum mechanical properties in these alloys can be achieved at about 0.5 % Mn content. 相似文献
964.
965.
Antonio Rodríguez‐Ferran Josep Sarrate Antonio Huerta 《International journal for numerical methods in engineering》2004,59(4):577-596
Numerical modelling of porous flow in a low‐permeability matrix with high‐permeability inclusions is a challenging task because the large ratio of permeabilities ill‐conditions the finite element system of equations. We propose a coupled model where Darcy flow is used for the porous matrix and potential flow is used for the inclusions. We discuss appropriate interface conditions in detail and show that the head drop in the inclusions can be prescribed in a very simple way. Algorithmic aspects are treated in full detail. Numerical examples show that this coupled approach precludes ill‐conditioning and is more efficient than heterogeneous Darcy flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
966.
Y. X. Zhang K. S. Kim 《International journal for numerical methods in engineering》2004,61(11):1771-1796
Two simple 4‐node 20‐DOF and 4‐node 24‐DOF displacement‐based quadrilateral elements named RDKQ‐L20 and RDKQ‐L24 are developed in this paper based on the first‐order shear deformation theory (FSDT) for linear analysis of thin to moderately thick laminates. The deflection and rotation functions of the element sides are obtained from Timoshenko's laminated composite beam functions. Linear displacement interpolation functions of the standard 4‐node quadrilateral isoparametric plane element and displacement functions of a quadrilateral plane element with drilling degrees of freedom are taken as in‐plane displacements of the proposed elements RDKQ‐L20 and RDKQ‐L24, respectively. Due to the application of Timoshenko's laminated composite beam functions, convergence can be ensured theoretically for very thin laminates. The elements are simple in formulation, and shear‐locking free for extremely thin laminates even with full integration. A hybrid‐enhanced procedure is employed to improve the accuracy of stress analysis, especially for transverse shear stresses. Numerical tests show that the new elements are convergent, not sensitive to mesh distortion, accurate and efficient for analysis of thin to moderately thick laminates. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
967.
968.
Fracture Toughness and Crack Resistance of Steam Pipeline Steel in Initial and Used States 总被引:1,自引:0,他引:1
Premature fracture of steam pipelines from 14MoV6 3 steel designed for 100,000 h service life at 540°C has been studied. Test specimens are manufactured from steel in the initial state and after 117 h of operation. Application of the local approach to fracture and the metallographic analysis, in addition to classical methods (tensile, crack resistance, and fatigue strength tests), provided a more precise evaluation of steel properties degradation due to elevated temperatures and stresses. Urgency of further development of the local approach to predicting material fracture after long-term operation at high temperatures has been substantiated. 相似文献
969.
Jialai Wang 《Engineering Fracture Mechanics》2004,71(2):219-231
A novel beam model of end notched flexure (ENF) specimen for mode-II fracture testing is presented. By applying the principle of superposition, the ENF specimen is modeled as two sub-problems: (1) an un-cracked beam under three-point bending; and (2) a skew symmetric cracked beam under shear traction on the crack surface. Due to skew-symmetry of sub-problem two, only the upper half of the beam is analysed, and based on compatibility of deformation, a shear compliance coefficient is introduced to establish beam deformation equation. Explicit and simple closed form solutions of compliance and strain energy release rate are obtained, and they compare well with existing finite element analyses. Compared to other available analytical methods of the ENF specimen, the present beam model is relatively simple and easy to use; further, it can be applied to other beam fracture specimen analysis (e.g., mixed mode fracture and bi-material interface specimen). 相似文献
970.
Youping Chen 《International Journal of Engineering Science》2004,42(10):987-1000
Polycrystalline solid is composed of randomly distributed grains and grain boundaries. The size of grains is usually in the nano/micro-scale. In this paper, the general micromorphic theory, as well as a specialized micromorphic theory for covalent and ionic crystals, is introduced. A statistical model for polycrystalline material is adopted. Each grain is modeled as crystallized solid by micromorphic theory, while the grain boundaries are modeled as in its amorphous phase by classical continuum theory. Size-dependent material properties of silicon are investigated. Finite element analysis of thermomechanical coupling phenomenon in polycrystalline silicon is performed and numerical results are presented and discussed. 相似文献