全文获取类型
收费全文 | 18041篇 |
免费 | 1584篇 |
国内免费 | 753篇 |
专业分类
电工技术 | 321篇 |
综合类 | 1277篇 |
化学工业 | 1376篇 |
金属工艺 | 3227篇 |
机械仪表 | 5560篇 |
建筑科学 | 1148篇 |
矿业工程 | 718篇 |
能源动力 | 438篇 |
轻工业 | 410篇 |
水利工程 | 233篇 |
石油天然气 | 723篇 |
武器工业 | 165篇 |
无线电 | 283篇 |
一般工业技术 | 2566篇 |
冶金工业 | 927篇 |
原子能技术 | 93篇 |
自动化技术 | 913篇 |
出版年
2024年 | 131篇 |
2023年 | 340篇 |
2022年 | 418篇 |
2021年 | 505篇 |
2020年 | 569篇 |
2019年 | 559篇 |
2018年 | 583篇 |
2017年 | 674篇 |
2016年 | 661篇 |
2015年 | 640篇 |
2014年 | 861篇 |
2013年 | 1026篇 |
2012年 | 1083篇 |
2011年 | 1152篇 |
2010年 | 803篇 |
2009年 | 961篇 |
2008年 | 769篇 |
2007年 | 1171篇 |
2006年 | 1150篇 |
2005年 | 927篇 |
2004年 | 940篇 |
2003年 | 675篇 |
2002年 | 556篇 |
2001年 | 482篇 |
2000年 | 457篇 |
1999年 | 393篇 |
1998年 | 341篇 |
1997年 | 287篇 |
1996年 | 256篇 |
1995年 | 221篇 |
1994年 | 146篇 |
1993年 | 117篇 |
1992年 | 102篇 |
1991年 | 90篇 |
1990年 | 69篇 |
1989年 | 47篇 |
1988年 | 67篇 |
1987年 | 34篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The load applied to a machine tool feed drive changes during the machining process as material is removed. This load change alters the Coulomb friction of the feed drive. Because Coulomb friction accounts for a large part of the total friction the friction compensation control accuracy of the feed drives is limited if this nonlinear change in the applied load is not considered. This paper presents a new friction compensation method that estimates the machine tool load in real time and considers its effect on friction characteristics. A friction observer based on a Kalman filter with load estimation is proposed for friction compensation control considering the applied load change. A specially designed feed drive testbed that enables the applied load to be modified easily was constructed for experimental verification. Control performance and friction estimation accuracy are demonstrated experimentally using the testbed. 相似文献
2.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
3.
In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects. 相似文献
4.
A novel dual-rotation bobbin tool friction stir welding (DBT-FSW) was developed, in which the upper shoulder (US) and lower shoulder (LS) have different rotational speeds. This process was tried to weld 3.2 mm thick aluminum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formability. Experimental results show that compared to conventional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process. 相似文献
5.
1 Influence of PAMAon Boundary Fil mFormation and Friction1.1 Experi mental methodsUltra-thin optical interferometry has been used tostudy thinlubricating fil ms for more than a decade and theexperi mental details of this technique have been reportedpreviously[1].The principle of the test setup is shown inFigure1.A polished steel ball is loaded and rolled againstthe flat surface of a glass disc that is coated with a thinsemi-reflecting chromiumlayer and a silica spacer of about500nmthickne… 相似文献
6.
O. A. Lambri J. I. Prez-Landazbal J. A. Cano V. Recarte 《Materials Science and Engineering: A》2004,370(1-2):459-463
Mechanical spectroscopy, neutron diffraction and differential scanning calorimetry (DSC) were performed on commercial Fe–6 wt.% Si alloy after quenching from high temperature. The damping spectrum shows a peak at around 800 K and an associated modulus defect. The modulus shows an increase during the second and subsequent heating runs. In addition, an anomaly in the modulus behavior has been found at around 400 K. Different thermal treatments allows to obtain two different recovery degrees of the quenched-in defects. The influence of the recovery degree on the 800 K internal friction peak and on the anelastic modulus has been evaluated and confirm the validity of the grain boundary mechanism associated to this peak. Experimental results are discussed on the basis of recovery and ordering processes. 相似文献
8.
9.
One of the new physical methods that provides much information about the processes going on in a friction contact zone in real time is acoustic emission (AE). Basic experimental results of AE in friction are presented and analysed. Using AE signals we can get an indication about the state of the friction processes, about the quality of solid and liquid layers on the contacting surfaces in real time, sometimes about intensity of wear, changing of wear and friction regimes and so on. The influence of sliding velocity, load, roughness and some physical and mechanical properties of the body on the parameters of AE are also given. Some attention to the practical implementation of these techniques for control of capability for work of friction pairs in real conditions are given. Modern methods and devices enable condition monitoring of sliding and rolling bearings. 相似文献
10.
A lubrication-flow model for a free film in a corner is presented. The model, written in the hyperbolic coordinate system
ξ = x
2 −y
2, η = 2xy, applies to films that are thin in the η-direction. The lubrication approximation yields two coupled evolution equations
for the film thickness and the velocity field which, to lowest order, describes plug flow in the hyperbolic coordinates. A
free film in a corner evolving under surface tension and gravity is investigated. The rate of thinning of a free film is compared
to that of a film evolving over a solid substrate. Viscous shear and normal stresses are both captured in the model and are
computed for the entire flow domain. It is shown that normal stress dominates over shear stress in the far field, while shear
stress dominates close to the corner.
This revised version was published online in October 2005 with corrected page numbers. 相似文献