全文获取类型
收费全文 | 58034篇 |
免费 | 4798篇 |
国内免费 | 2583篇 |
学科分类
工业技术 | 65415篇 |
出版年
2024年 | 194篇 |
2023年 | 1015篇 |
2022年 | 1589篇 |
2021年 | 2366篇 |
2020年 | 1918篇 |
2019年 | 1547篇 |
2018年 | 1713篇 |
2017年 | 1896篇 |
2016年 | 1653篇 |
2015年 | 2305篇 |
2014年 | 2969篇 |
2013年 | 3313篇 |
2012年 | 3635篇 |
2011年 | 4112篇 |
2010年 | 3562篇 |
2009年 | 3340篇 |
2008年 | 3246篇 |
2007年 | 3032篇 |
2006年 | 3113篇 |
2005年 | 2598篇 |
2004年 | 1867篇 |
2003年 | 1658篇 |
2002年 | 1636篇 |
2001年 | 1403篇 |
2000年 | 1306篇 |
1999年 | 1549篇 |
1998年 | 1288篇 |
1997年 | 1120篇 |
1996年 | 1002篇 |
1995年 | 832篇 |
1994年 | 664篇 |
1993年 | 482篇 |
1992年 | 416篇 |
1991年 | 260篇 |
1990年 | 210篇 |
1989年 | 164篇 |
1988年 | 121篇 |
1987年 | 77篇 |
1986年 | 61篇 |
1985年 | 41篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 6篇 |
1940年 | 3篇 |
1933年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
981.
982.
983.
ZHANGWei LIJiuqing WUYinshun ZHANGPei HEJianping 《稀有金属(英文版)》2004,23(1):48-52
Cerium contained conversion films were deposited on LC4 aluminum alloy using square wave pulse (SWP) in aCeCl3 solution with KMnO4 as the oxidant. Energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) were adopted to study the composition and the morphology of the film. It is found that the film is composed of Al, Zn, Cu,and small amount of cerium. The polarization curves of the specimens treated with SWP technique measured in 3.5% (mass fraction) NaCl solution reveal that the film thus formed inhibits both the anodic and cathodic process of the corrosion of the specimen. The immersion tests of treated specimens in 3.5% NaCl solution indicate that the corrosion resistance of the SWP treated specimen is better than that of the untreated and is equivalent to or even better than that of the traditionally electro-chemically treated specimens. 相似文献
984.
冲压自动化的若干基本问题 总被引:1,自引:1,他引:1
本文分析讨论了冲压自动化领域中的若干基本问题,包括模具结构,工件上下料,毛坯开垛上料,工件码垛,安全问题等,文章介绍了一条先进的冲压自动化生产线,可供实际生产参考。 相似文献
985.
986.
987.
通过对企业信息化认识问题和核心内容的探讨 ,并结合株洲硬质合金集团公司钻石工业园的发展和产品结构 ,提出了建立信息化刀具制造CALS框架模型 ,以提高企业的竞争力。 相似文献
988.
The analysis of the microstructural characterization and phase composition of electron beam welded joint zones of Ti- 43Al-9V-O. 3Y alloy has been done in this study. The welded seam is mainly composed of B2 phase, the partial γ + α2 twophase lamellar structure and granular γm phase. And the lanthanon Y existed as YAl2 phase and served as grain refined. The impact of different cooling rates on joint microstructure, fracture characteristic and tensile strength were investigated. The high cooling rate restrained the structural transformation and resulted in the ordering structure. The fracture of the joint was brittle cleavage fracture because the ordering structure went against restraining the crack propagation. With the decrease of cooling rate, the transformation amounts of lamellar structure increased, and the fracture presented the layered and crosslayered characteristic. 相似文献
989.
On the mechanical performance of closed cell Al alloy foams 总被引:8,自引:0,他引:8
Y. Sugimura J. Meyer M.Y. He H. Bart-Smith J. Grenstedt A.G. Evans 《Acta Materialia》1997,45(12):5245-5259
The mechanical properties of three different commercially available closed cell Al alloys all made by foam casting are examined. The objective is to assess the roles of cell morphology and of imperfections in governing the basic properties: stiffness, yield strength and fracture resistance. This assessment provides goals for manufacturing strategies that enable attainment of good mechanical performance with affordable process technologies. A prevalent role of curves and wiggles in the cell walls on stiffness and strength (anticipated by models) is affirmed by the present measurements. Systematically larger stiffnesses and yield strengths found in tension than in compression are consistent with a prominent role exerted by such imperfections. Moreover, foam casting is apparently capable of cell morphologies that impart properties approaching the best achievable values for an isotropic closed cell solid, devoid of imperfections. There are associated implications for performance and affordability. Fracture measurements indicate crack growth occurring along the cell walls by a mechanism analogous to the plastic tearing of thin sheets. The crack growth resistances are in the range of 1 kJm−2. This mechanism infers a toughness that scales with the cell wall thickness and its yield strength. 相似文献
990.