全文获取类型
收费全文 | 23364篇 |
免费 | 3873篇 |
国内免费 | 979篇 |
专业分类
电工技术 | 872篇 |
技术理论 | 1篇 |
综合类 | 1534篇 |
化学工业 | 1564篇 |
金属工艺 | 10791篇 |
机械仪表 | 2501篇 |
建筑科学 | 1104篇 |
矿业工程 | 563篇 |
能源动力 | 328篇 |
轻工业 | 337篇 |
水利工程 | 167篇 |
石油天然气 | 1443篇 |
武器工业 | 213篇 |
无线电 | 1184篇 |
一般工业技术 | 2894篇 |
冶金工业 | 1476篇 |
原子能技术 | 102篇 |
自动化技术 | 1142篇 |
出版年
2024年 | 46篇 |
2023年 | 225篇 |
2022年 | 428篇 |
2021年 | 455篇 |
2020年 | 562篇 |
2019年 | 594篇 |
2018年 | 640篇 |
2017年 | 975篇 |
2016年 | 1020篇 |
2015年 | 929篇 |
2014年 | 1471篇 |
2013年 | 1779篇 |
2012年 | 1665篇 |
2011年 | 1744篇 |
2010年 | 1345篇 |
2009年 | 1274篇 |
2008年 | 1151篇 |
2007年 | 1659篇 |
2006年 | 1675篇 |
2005年 | 1301篇 |
2004年 | 1249篇 |
2003年 | 1067篇 |
2002年 | 893篇 |
2001年 | 765篇 |
2000年 | 623篇 |
1999年 | 508篇 |
1998年 | 414篇 |
1997年 | 371篇 |
1996年 | 308篇 |
1995年 | 247篇 |
1994年 | 186篇 |
1993年 | 114篇 |
1992年 | 108篇 |
1991年 | 94篇 |
1990年 | 74篇 |
1989年 | 70篇 |
1988年 | 42篇 |
1987年 | 25篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1979年 | 5篇 |
1964年 | 3篇 |
1963年 | 4篇 |
1959年 | 2篇 |
1956年 | 3篇 |
1955年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
11.
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
12.
Xuezhi Wang Xue Sun Zhelun Ma Tianbiao Yu Wanshan Wang 《Ceramics International》2018,44(18):22301-22307
Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field. 相似文献
13.
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
14.
Reports an error in "Tradeoffs and Theory: The Double-Mediation Model" by Marc Scholten and Steven J. Sherman (Journal of Experimental Psychology: General, 2006 May, Vol 135[2], 237-261). This article was inadvertently printed with the incorrect title. The original title was "Tradeoffs and Conflict: The Double-Mediation Model." This title highlights the relation between tradeoffs and conflict as investigated by the authors and accounted for by their model. However, readers are asked to refer to the article by the title with which it was printed to facilitate its retrieval.. (The following abstract of the original article appeared in record 2006-06642-006.) Most theories of decision making suggest that, when options imply tradeoffs between their attributes, conflict increases as tradeoff size increases, because greater sacrifices are to be incurred in choosing one option instead of another. An alternative view is that conflict decreases as tradeoff size increases, because stronger arguments can be made for any decision. The authors propose a unified model, the double-mediation model, which combines the mediating effects of sacrifice and argumentation. Our model generally predicts an inverse U-shaped relation between tradeoff size and conflict. Results support this prediction. Also, when the decision situation increases the mediating effect of sacrifice relative to that of argumentation, the relation between tradeoff size and conflict changes in an upward direction; conversely, when the decision situation increases the mediating effect of argumentation relative to that of sacrifice, the relation changes in a downward direction. Results support these predictions as well. Commonalities and differences between our model and other formulations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
15.
于立兴 《兵器材料科学与工程》2003,26(1):55-57
板厚为 5 5mm的 16Mn钢采用CO2 半自动气保焊建造大型转炉炉体的可能性和可靠性如何 ?目前尚缺少足够的试验数据。为了给转炉工程的施工焊接提供可靠数据 ,确保焊接质量 ,对板厚 5 5mm16Mn钢CO2 半自动的焊接性能进行了一系列的试验研究 相似文献
16.
对Incoloy825材料的焊接和抗腐蚀性能,以及在加氢裂化装置高压空冷器上的应用中应注意的问题进行了探讨.对此种空冷器在制造中如何解决异种钢焊接的难题,在清洗和水压试验中如何避免腐蚀等提出了建议. 相似文献
17.
中压蒸汽管道作为工厂的公用管网的组成部分,在生产中起着非常重要的作用,其主要用于压缩机蒸汽透平等关键工艺单元,除了对材料有特殊要求外,还要求运行可靠、管内高度洁净,因此对焊接质量提出了更高要求。结合齐鲁石化公司煤代油技术改造工程的中压蒸汽管道的施工,就焊接质量用统计分析的方法,对焊接产生的气孔、夹渣、未焊透等缺陷产生的原因及采取的控制措施进行了分析,并就今后的焊接质量控制提出建议。 相似文献
18.
采用SEM 和 Magiscan-2A 图像分析系统研究了晶须取向对SiCw/6061Al复合材料在300℃压缩变形行为的影响.结果表明:晶须取向影响着晶须折断程度和转动角度; 随着晶须取向角的增加,晶须转动和折断行为所导致的软化效果下降.同时晶须取向也影响复合材料的热压缩应力-应变曲线的形状.在热压缩变形过程中,晶须取向角为0°和30°的复合材料表现出明显应变软化现象, 晶须取向角为45°的复合材料无明显软化现象.晶须取向角为90℃的复合材料表现出应变硬化现象. 相似文献
19.
20.
分析了韩国、日本及国内运营商手机游戏业务的发展状况.探讨了手机游戏业务的模式.论述了该业务的战略定位和市场前景。从地区提供给移动通信市场对外部环境、产业链的准备是否充分以及运营商内部的资源和运营状况等三个方面阐明了手机游戏业务发展的关键因素。 相似文献