全文获取类型
收费全文 | 512487篇 |
免费 | 61140篇 |
国内免费 | 43354篇 |
专业分类
电工技术 | 47325篇 |
技术理论 | 1篇 |
综合类 | 57960篇 |
化学工业 | 61757篇 |
金属工艺 | 36488篇 |
机械仪表 | 37478篇 |
建筑科学 | 39908篇 |
矿业工程 | 22913篇 |
能源动力 | 13261篇 |
轻工业 | 55478篇 |
水利工程 | 18183篇 |
石油天然气 | 17848篇 |
武器工业 | 8771篇 |
无线电 | 53340篇 |
一般工业技术 | 40618篇 |
冶金工业 | 19756篇 |
原子能技术 | 8518篇 |
自动化技术 | 77378篇 |
出版年
2024年 | 2510篇 |
2023年 | 7870篇 |
2022年 | 20232篇 |
2021年 | 25847篇 |
2020年 | 18473篇 |
2019年 | 12690篇 |
2018年 | 13532篇 |
2017年 | 15457篇 |
2016年 | 13852篇 |
2015年 | 22735篇 |
2014年 | 28982篇 |
2013年 | 33793篇 |
2012年 | 43690篇 |
2011年 | 45520篇 |
2010年 | 43742篇 |
2009年 | 41492篇 |
2008年 | 43115篇 |
2007年 | 42187篇 |
2006年 | 35786篇 |
2005年 | 29153篇 |
2004年 | 20966篇 |
2003年 | 13557篇 |
2002年 | 12631篇 |
2001年 | 11578篇 |
2000年 | 9044篇 |
1999年 | 3246篇 |
1998年 | 872篇 |
1997年 | 661篇 |
1996年 | 507篇 |
1995年 | 446篇 |
1994年 | 311篇 |
1993年 | 347篇 |
1992年 | 303篇 |
1991年 | 180篇 |
1990年 | 199篇 |
1989年 | 235篇 |
1988年 | 150篇 |
1987年 | 95篇 |
1986年 | 96篇 |
1985年 | 52篇 |
1984年 | 67篇 |
1983年 | 58篇 |
1982年 | 47篇 |
1981年 | 88篇 |
1980年 | 167篇 |
1979年 | 109篇 |
1965年 | 16篇 |
1964年 | 10篇 |
1959年 | 107篇 |
1951年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
901.
The microstructure development of Pd77.5Au6Si16.5 alloy droplet solidified in a drop tube process was studied. It was found that two distinct microstructures, i.e. (Pd,Au)3Si primary phase and Pd+(Pd,Au)3Si eutectic can be obtained when the droplet diameter is within the range between 2.3~0.4 mm. The morpologies of the (Pd,Au)3Si developed from dendrite trunk-like with single branching only into dendrite cluster-like with ternary branching with the decrease of the droplet diameter. When the droplet diameter is about 0.25 mm, the primary phase (Pd,Au)3Si almost disappears and the microstructure mainly shows Pd+(Pd,Au)3Si eutectic. The morphology of the eutectic transforms from fiber-like to plate-like with the decrease of the droplet diameter in the range between 2.3-0.25 mm. When the droplet diameter is about 0.19 mm, the microstructure is only the single phase of Pd solid solution 相似文献
902.
本文介绍了一个用Turbo C语言在AST-286机器上实现的计算机辅助数据库设计系统CAD^2B。该系统提供了人机交互的环境,供设计者进行概念模型设计,并自动完成从概念模型逻辑模型的映射,创建满足规范化要求的关系表。该系统采用的概念模型是引入了事件和时间的扩展了的实体关系模型。该模型既能充分反映应用环境的静态和动态语义,又是向关系模式转化的基础。 相似文献
903.
Fracture of Aramid Fiber/Epoxy Resin Micro Composites 总被引:6,自引:0,他引:6
Kevlar-49 fiber was modified through cold air plasma treatment and plasma grafting with acrylic monomers. Fracture of aramid fiber/epoxy resin micro composites has been studied by means of single fiber pull-out test. Tow types of pull-out curves are correlated with the different failure modes. A polyacrylic acid-co-ethyl acrylate graft layer can improve the adhesion and protect the fiber from damage caused by interfacial stresses. 相似文献
904.
905.
Ductile Phase Toughened Brittle Materials 总被引:6,自引:0,他引:6
Xudong SUNJ.A. Yeomans 《材料科学技术学报》1996,12(2):124-134
Toughening of brittle materials by the inclusion of ductile phases is governed by several important factors which include ceramic-ductile phase interfacial bond strength, physical and chemical compatibility between ceramic and ductile phase, geometry and mechanical properties of ductile phase. The present understanding of the effect of these factors on toughening is reviewed and clarified. Continuous ductile phases (network, fibre or plate) are found to be more efficient for the toughening of brittle materials than discrete ductile particles. However, ductile particle toughened brittle materials have the advantages of material homogeneity isotropy and particularly better high temperature properties. It has been demonstrated that the influence of interfacial bond strength is determined by the geometry of the ductile phase in the composites. For the comparatively continuous ductile phase, such as ductile network, fibre or plate, comparatively weak inteffocial bond strength can promote partial debonding of the brittle matrix-ductile phase intedece during crack propagation and is beneficial for toughening. For discrete particulate ductile phase toughened brittle materials, the small gauge length of the ductile phase often results in the ductile phase pull-out during crack propagation which is the main limitation to toughening.Thus strong bond strength is required to ensure the bridging of the crack by the ductile phase.The coefficient of thermal expansion (CTE) mismatch between matrix and ductile phase has also been correlated with the geometry of the ductile phase. In most of the ceramic/metal systems,the CTE of the ductile metal phase is greater than that of the ceramic matrix. In the case of ductile network, fibre or plate, the residual stress created by the CTE mismatch can contribute to toughening through its influence on the initial crack opening stress while the bridging of the crack by the ductile phase is still ensured. However, for discrete ductile particles, the residual stress created by CTE mismatch is liable to cause cracks to by-pass the spherical particles, limiting the efficient use of the inherent toughness of the ductile phase. Low-modulus ductile inclusions are beneficial for the bridging of cracks by the ductile phase. Softer, more ductile inclusions are more effective for the toughening of brittle materials by particulate ductile phase 相似文献
906.
高强IF钢析出物的析出特征 总被引:3,自引:0,他引:3
高强IF钢是汽车用深冲钢板中深冲性能最好的高强度钢板。目前,国际上对该钢种的研究十分活跃。本文在实验条件下,通过对高强IF钢析出物的观察研究了高强IF钢析出物的析出特征,发现了新的析出相TiFeP,并对磷对深冲性能影响的作用机制,进行了探讨。 相似文献
907.
析出物对IF钢性能的影响 总被引:3,自引:0,他引:3
一种阻性的晶闸管控制制动器被用于阻尼向串联补偿传输供电的热电发电机中的瞬态扭。重点放在开发适用的控制算,并通过多种不同的运行方式验证算法。作为一种制动器最优控制的可能方法,本文研究了离散等级一般化预先控制(GPC),讨论了系统上GPC执行过程中存在一些问题。用Prong分析来辩识系统传递函数,此传递函数与控制方案的考虑及强度特性有关。 相似文献
908.
909.
910.