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71.
Seonpil Kim 《Journal of Mechanical Science and Technology》1998,12(4):624-641
This paper represents a three-dimensional motion analysis of the human knee joint under given conditions of loading and constraint.
As the knee is extended by a known force applied to the quadriceps tendon, relative displacements of the femur, tibia, and
patella are measured using a video motion analysis system. The most prominent motion of the tibia is external rotation and
anterior displacement relative to the femur during knee extension. The patellar flexion angle decreases from 70° to 0°. The
moment arm of the knee extensor mechanism exhibits a characteristic bell shape which peaks somewhere in the 40°–60° region
of flexion. In general, the quadriceps force results primarily from an increase in the torque exerted by the weight of the
lower leg. In the range of 20°–60°, the quardricep force needed to extend the leg remains relatively constant. As the knee
approaches full extension, the moment arm decreases due to the fact that the posterior capsule and the ACL begin to tighten
in this region. Consequently, the quadriceps force increases rapidly. 相似文献
72.
Aspheric optics has been widely employed in some high-tech industries for its superiority. In order to achieve the ultra-precision machining of these aspheric surfaces, the large optical ultra-precision grinding machine becomes crucial because it determines the efficiency of the whole process. As the key functional unit in ultra-precision machine tool, the hydrostatic guideways are commonly adopted for the excellent performance. However, the motion errors of hydrostatic guideways have a direct influence on the accuracy of the machined workpiece, and some analysis approaches have been reported correspondingly. Although the existed analysis models do work, their imperfections also can be easily captured. Accordingly, a novel analysis model with less imperfection is deserved to be developed. In this paper, the kinematic theory is utilized to establish the quasi-static analysis model for motion errors in closed hydrostatic guideways. Through the large ultra-precision grinding machine designed by our research group, the consistently good agreement between the predicted results and the measured experimental data are obtained. Furthermore, it is found that the motion accuracy is more sensitive to the profile error of the guide rail bearing the external load rather than that of the other guide rail in the closed hydrostatic guideway. The presented research is supposed to be valuable to the peer designers. 相似文献
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75.
The trajectory planning of redundant robots through the pseudoinverse control leads to undesirable drift in the joint space. This paper presents a new technique to solve the inverse kinematics problem of redundant manipulators, which uses a fractional differential of order α to control the joint positions. Two performance measures are defined to examine the strength and weakness of the proposed method. The positional error index measures the precision of the manipulator's end-effector at the target position. The repeatability performance index is adopted to evaluate if the joint positions are repetitive when the manipulator execute repetitive trajectories in the operational workspace. Redundant and hyper-redundant planar manipulators reveal that it is possible to choose in a large range of possible values of α in order to get repetitive trajectories in the joint space. 相似文献
76.
We consider the problem of moving a line segment (a “rod” or “ladder”) in the plane between two given placements when subject
to the constraint that no point on the line segment may exceed a given velocity bound. Specifically, we consider those trajectories
which minimize the total time between given initial and goal placements, and provide a complete characterization of all solution,
together with explicit constructions for each of the various cases encountered.
This research was supported by the National Science Foundation under Grant CCR-9207422, and by a grant from the James H. Zumberge
Research Innovation Fund. This problem was initially posed in an open problem session of the Second DIMACS Workshop in Computational
Geometry, held at Princeton University in October, 1989. A preliminary version of this paper was presented at the 9th Annual
ACM Symposium on Computational Geometry [8]. 相似文献
77.
Input-output kinematics of a novel, exoskeletal manipulator mechanism has been analysed. The abstract model is two equilateral tetrahedral wire frames which move relatively so that their edges remain in intersecting, parallel or coincident pairs. A mechanical, rigid body model was constructed and a computer animation was performed. 相似文献
78.
79.
为解决基于并联机构中运动副存在间隙而使得激振台在高频激振的情况下运动无法传递的问题,提出了运用柔性万向节代替普通万向节的并联机构激振台。在ADMAS中建立柔性关节激振平台的虚拟样机模型,通过仿真验证并联机构柔性激振台的可行性。并对普通万向节测试其运动输出。 相似文献
80.
This paper presents two methods of forming profile holes, previously drilled in rotational and casing blanks. The methods can be implemented on lathes, milling, drilling and centering machines, etc. Kinematic synthesis of the methods is shown based on the kinematics of a body rotating around coplanar axes. The rational field of application of the methods has been found. Principal diagrams of the devices and tools enabling implementation of the method are shown. 相似文献