全文获取类型
收费全文 | 638049篇 |
免费 | 8744篇 |
国内免费 | 1909篇 |
专业分类
电工技术 | 11538篇 |
综合类 | 491篇 |
化学工业 | 98052篇 |
金属工艺 | 23768篇 |
机械仪表 | 18563篇 |
建筑科学 | 16880篇 |
矿业工程 | 2599篇 |
能源动力 | 16280篇 |
轻工业 | 61482篇 |
水利工程 | 5956篇 |
石油天然气 | 8703篇 |
武器工业 | 29篇 |
无线电 | 77514篇 |
一般工业技术 | 121120篇 |
冶金工业 | 118024篇 |
原子能技术 | 11894篇 |
自动化技术 | 55809篇 |
出版年
2021年 | 4399篇 |
2019年 | 4072篇 |
2018年 | 6907篇 |
2017年 | 6962篇 |
2016年 | 7441篇 |
2015年 | 5473篇 |
2014年 | 9071篇 |
2013年 | 28621篇 |
2012年 | 15391篇 |
2011年 | 21752篇 |
2010年 | 17115篇 |
2009年 | 19534篇 |
2008年 | 20597篇 |
2007年 | 20746篇 |
2006年 | 18558篇 |
2005年 | 17280篇 |
2004年 | 16547篇 |
2003年 | 16141篇 |
2002年 | 15805篇 |
2001年 | 15820篇 |
2000年 | 14797篇 |
1999年 | 15339篇 |
1998年 | 35534篇 |
1997年 | 26136篇 |
1996年 | 20505篇 |
1995年 | 15915篇 |
1994年 | 14253篇 |
1993年 | 13808篇 |
1992年 | 10488篇 |
1991年 | 10176篇 |
1990年 | 9705篇 |
1989年 | 9485篇 |
1988年 | 9182篇 |
1987年 | 7777篇 |
1986年 | 7739篇 |
1985年 | 9218篇 |
1984年 | 8779篇 |
1983年 | 7778篇 |
1982年 | 7316篇 |
1981年 | 7395篇 |
1980年 | 7031篇 |
1979年 | 6870篇 |
1978年 | 6663篇 |
1977年 | 7881篇 |
1976年 | 10393篇 |
1975年 | 5801篇 |
1974年 | 5546篇 |
1973年 | 5461篇 |
1972年 | 4633篇 |
1971年 | 4167篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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
82.
83.
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
84.
85.
86.
87.
Senthilkumar M. Vasundhara M. G. Kalavathi G. K. 《International Journal of Mechanics and Materials in Design》2019,15(3):611-627
International Journal of Mechanics and Materials in Design - The resonant frequency of electromechanical energy harvester should be tuned to ambient frequency so as to maximize the harvester power.... 相似文献
88.
Radiochemistry - Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH,... 相似文献
89.
90.
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