全文获取类型
收费全文 | 57990篇 |
免费 | 5093篇 |
国内免费 | 3403篇 |
专业分类
电工技术 | 3848篇 |
技术理论 | 2篇 |
综合类 | 5645篇 |
化学工业 | 3710篇 |
金属工艺 | 4014篇 |
机械仪表 | 4783篇 |
建筑科学 | 8411篇 |
矿业工程 | 2107篇 |
能源动力 | 1278篇 |
轻工业 | 1876篇 |
水利工程 | 2171篇 |
石油天然气 | 2173篇 |
武器工业 | 1036篇 |
无线电 | 6189篇 |
一般工业技术 | 7268篇 |
冶金工业 | 2554篇 |
原子能技术 | 456篇 |
自动化技术 | 8965篇 |
出版年
2024年 | 180篇 |
2023年 | 513篇 |
2022年 | 968篇 |
2021年 | 1099篇 |
2020年 | 1262篇 |
2019年 | 1084篇 |
2018年 | 1030篇 |
2017年 | 1388篇 |
2016年 | 1511篇 |
2015年 | 1744篇 |
2014年 | 2892篇 |
2013年 | 2654篇 |
2012年 | 3668篇 |
2011年 | 4121篇 |
2010年 | 3330篇 |
2009年 | 3647篇 |
2008年 | 3921篇 |
2007年 | 4972篇 |
2006年 | 4334篇 |
2005年 | 3964篇 |
2004年 | 3255篇 |
2003年 | 2812篇 |
2002年 | 2339篇 |
2001年 | 2030篇 |
2000年 | 1609篇 |
1999年 | 1183篇 |
1998年 | 933篇 |
1997年 | 802篇 |
1996年 | 636篇 |
1995年 | 544篇 |
1994年 | 423篇 |
1993年 | 310篇 |
1992年 | 280篇 |
1991年 | 212篇 |
1990年 | 195篇 |
1989年 | 164篇 |
1988年 | 114篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 35篇 |
1984年 | 37篇 |
1983年 | 38篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1966年 | 6篇 |
1957年 | 8篇 |
1956年 | 4篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
本文以云杉八齿小蠹Ips typographus Linnaeus为例,经标本选取,观察虫体整体形态,绘制整体结构草图,电子显微镜观察局部、得到局部数字图像,分别建立虫体每一部分的高精度细节。把模型每部分拼装在一起组成整体模型,构建出了云杉八齿小蠹三维虚拟昆虫数字化模型。 相似文献
2.
AbstractIndustry 4.0 aims at providing a digital representation of a production landscape, but the challenges in building, maintaining, optimizing, and evolving digital models in inter-organizational production chains have not been identified yet in a systematic manner. In this paper, various Industry 4.0 research and technical challenges are addressed, and their present scenario is discussed. Moreover, in this article, the novel concept of developing experience-based virtual models of engineering entities, process, and the factory is presented. These models of production units, processes, and procedures are accomplished by virtual engineering object (VEO), virtual engineering process (VEP), and virtual engineering factory (VEF), using the knowledge representation technique of Decisional DNA. This blend of the virtual and physical domains permits monitoring of systems and analysis of data to foresee problems before they occur, develop new opportunities, prevent downtime, and even plan for the future by using simulations. Furthermore, the proposed virtual model concept not only has the capability of Query Processing and Data Integration for Industrial Data but also real-time visualization of data stream processing. 相似文献
3.
4.
ABSTRACT The concept of digital game-based learning (DGBL) evolves rapidly together with technological enhancements of virtual reality (VR) and smart phones. However, the mental workload (MWL) that VR-training applications demand and motivational qualities originating from user experience (UX) should be identified in order to create effective and enjoyable training/learning challenges that fit with individual users’ capabilities. This study examined the effects of reality-based interaction (RBI) and VR on measures of student motivation and MWL, in a mental arithmetic game for secondary school pupils. In a randomised controlled trial with sixty school children, a mental arithmetic game was tested with three different interaction and two different presentation methods – VR RBI, VR head-mounted-display tapping and tablet flick-gesture. Results found a significant effect of RBI on MWL but no differences in enjoyment of training were found between VR-experience and tablet training-experience. In fact, adding the gaming-context to the mental arithmetic task created an enjoyable, motivating experience regardless of presentation or interaction-style. 相似文献
5.
Undoped and fluorine doped ZnO thin films were deposited onto glass substrates using successive ionic layer adsorption and reaction (SILAR) technique and then annealed at 350 °C in vacuum ambience. The F doping level was varied from 0 to 15 at% in steps of 5 at%. The XRD analysis showed that all the films are polycrystalline with hexagonal wurtzite structure and preferentially oriented along the (002) plane. Crystallite sizes were found to increase when 5 at% of F is doped and then decreased with further doping. It was seen from the SEM images that the doping causes remarkable changes in the surface morphology and the annealing treatment results in well-defined grains with an improvement in the grain size irrespective of doping level. All the films exhibit good transparency (>70%) after vacuum annealing. Electrical resistivity of the film was found to be minimum (1.32×10−3 Ω cm) when the fluorine doping level was 5 at%. 相似文献
6.
Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure. 相似文献
7.
8.
移动通信系统中功率控制研究 总被引:2,自引:0,他引:2
在阐述功率控制在移动通信系统中的发展过程的基础上,着重研究了WCDMA系统的功率控制,最后对功率控制未来的研究方向做了简要的分析。 相似文献
9.
天然气水合物和天然气脱水新工艺探讨 总被引:3,自引:0,他引:3
探讨了天然气水合物的发展过程、形成条件以及对天然气输送管道的腐蚀堵塞作用,对我国天然气脱水创新技术———膜法脱水、汽提脱水的原理与工艺过程进行了全面论述。考察了气体处理量及操作压力等对我国1.2×105m3/d天然气膜法脱水的工业试验装置的脱水过程的影响。 相似文献
10.