全文获取类型
收费全文 | 1375篇 |
免费 | 60篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 43篇 |
综合类 | 155篇 |
化学工业 | 37篇 |
金属工艺 | 277篇 |
机械仪表 | 563篇 |
建筑科学 | 1篇 |
矿业工程 | 79篇 |
能源动力 | 6篇 |
轻工业 | 117篇 |
水利工程 | 2篇 |
石油天然气 | 10篇 |
武器工业 | 1篇 |
无线电 | 23篇 |
一般工业技术 | 66篇 |
冶金工业 | 40篇 |
原子能技术 | 1篇 |
自动化技术 | 36篇 |
出版年
2024年 | 7篇 |
2023年 | 9篇 |
2022年 | 28篇 |
2021年 | 30篇 |
2020年 | 35篇 |
2019年 | 21篇 |
2018年 | 32篇 |
2017年 | 31篇 |
2016年 | 52篇 |
2015年 | 82篇 |
2014年 | 104篇 |
2013年 | 75篇 |
2012年 | 137篇 |
2011年 | 146篇 |
2010年 | 65篇 |
2009年 | 57篇 |
2008年 | 34篇 |
2007年 | 77篇 |
2006年 | 70篇 |
2005年 | 61篇 |
2004年 | 55篇 |
2003年 | 46篇 |
2002年 | 38篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有1457条查询结果,搜索用时 31 毫秒
1.
通过对42CrMo4风机主轴结构尺寸、性能要求、材质特点等方面进行分析,对原有锻后热处理工艺进行优化,制定出既能达到锻后热处理效果又经济节能的工艺参数。 相似文献
2.
基于神经网络和遗传算法的锭子弹性管性能优化 总被引:1,自引:0,他引:1
为得到减振弹性管对下锭胆的支承弹性和锭子高速运动下的稳定性等性能的最优匹配效率,依据减振弹性管的等效抗弯刚度及底部等效刚度系数公式,利用MatLab数值分析软件构建弹性管抗弯刚度和底部挠度数学模型。首先,结合Isight优化软件基于径向基神经网络构建其近似模型,且使精度达到可接受水平,并以模型的关键结构参数弹性模量、螺距、槽宽、壁厚为设计变量,结合遗传算法对弹性管抗弯刚度和底部挠度进行多目标优化设计,得到Pareto最优解集和Pareto前沿图,确定出减振弹性管结构工艺参数的优化方案。通过对优化数据进行分析发现,该方案在保证减振弹性管弹性的同时,其底部振幅明显减弱。 相似文献
3.
4.
5.
High speed machine tools are required to operate in a wide range of spindle rotational speeds with high stiffness and high accuracy. The stiffness of the spindle is largely dependent on the axial preload of the angular contact bearings. A large preload is required at lower range of speeds to provide sufficient stiffness for vibration-free heavy cutting. However, at higher speeds, it results in rapid temperature rise and reduces the life of the bearing. For optimum performance, it is essential that the bearing preload is reduced as the rotational speed increases. In this paper, an automatic variable preload system is proposed that changes the preload on the bearings as a function of rotational speed. This system is based on the use of centrifugal forces and requires little space inside the spindle. The performance of this mechanical system is determined using finite element modeling. A prototype of the system is fabricated and its performance is investigated using a specially devised test stand for direct measurement of the preload. The effectiveness of the proposed system in reducing the preload at higher speeds is demonstrated. 相似文献
6.
为探究锭子弹性管的减振机制,将其开螺旋槽部分作为矩形弹簧模型处理,建立了减振弹性管的抗弯刚度及底部振幅的理论数学模型,并利用MatLab仿真分析了减振弹性管关键结构参教与其抗弯刚度和底部振动特性的耦合关系,同时结合有限元仿真及模态测试得到弹性管各阶固有频率。研究结果表明:随着槽宽和圈数的增大,刚度降低,底部振幅增加;随着壁厚、螺距、螺旋升角、弹性模量的增大,刚度增加,底部振幅降低;弹性管固有频率和锭子系统共振频率区间一致,且工作频率有效避开了共振频率。 相似文献
7.
The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers. This paper focuses on designing a class of 2R1T (R: Rotation; T: Translation) parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension (2D) large rotational angles. In order to construct 2D rotational degrees of freedom (DOFs), a platform with 2D revolute joints is proposed first. Based on the constraint screw theory, the feasible limbs that can be connected in the platform are synthesized. In order to provide constant rotational axis for the platform, a class of redundant limbs are designed. A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion. The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform. The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed. The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers. 相似文献
8.
为研究不同工况下轴承预紧力对电主轴轴承动力学的影响规律,基于外轨道控制理论,建立了一种以旋滚比可优化的轴承预紧力动力学模型。通过分析高速状态下滚动体载荷和特征参数动态变化过程,构建综合考虑滚动体滚动、自旋转、陀螺运动和离心力的轴承动力学分析模型,在此基础上,计算旋滚比动态变化结果;研究Jones发现的阈值与旋滚比之间的动态定量映射关系;以轴承滚动体打滑状态为优化目标,使用MATLAB仿真分析不同工况下轴承最佳预紧力。建模分析表明,轴承旋滚比大小可以反映轴承预紧效果,也可实现轴承预紧力动态定量优化。 相似文献
9.
10.
Making an analysis for vibration modal and frequency response of the lathe spindle, respectively by using finite element method based on ANSYS and experiment of CA6140 type lathe in machining, and the calculation results are compared and analyzed, which verified the accuracy of ANSYS method. Numerical simulation and experimental results show that: Spindle in the first order and fifth order are prone to resonance, but did not reach resonance, the low order natural frequency have more effect than the high order natural frequency of the spindle vibration; by the experiments can conclude that the maximum vibration of the main shaft in the working state is mainly concentrated in the vicinity of its two ends, therefore, the improved bearing is an important way to reduce the vibration of the main shaft and ensure the machining accuracy, and the research results can provide a theoretical reference for the structural optimization design of the lathe. 相似文献