全文获取类型
收费全文 | 341829篇 |
免费 | 31948篇 |
国内免费 | 23403篇 |
专业分类
电工技术 | 25310篇 |
综合类 | 30001篇 |
化学工业 | 41357篇 |
金属工艺 | 23013篇 |
机械仪表 | 22066篇 |
建筑科学 | 22091篇 |
矿业工程 | 9900篇 |
能源动力 | 7604篇 |
轻工业 | 35225篇 |
水利工程 | 10719篇 |
石油天然气 | 8026篇 |
武器工业 | 3677篇 |
无线电 | 36754篇 |
一般工业技术 | 38377篇 |
冶金工业 | 12176篇 |
原子能技术 | 4902篇 |
自动化技术 | 65982篇 |
出版年
2024年 | 1732篇 |
2023年 | 4392篇 |
2022年 | 10120篇 |
2021年 | 12973篇 |
2020年 | 9338篇 |
2019年 | 6513篇 |
2018年 | 21146篇 |
2017年 | 21332篇 |
2016年 | 17292篇 |
2015年 | 11913篇 |
2014年 | 14518篇 |
2013年 | 17371篇 |
2012年 | 24525篇 |
2011年 | 31732篇 |
2010年 | 29730篇 |
2009年 | 26307篇 |
2008年 | 28089篇 |
2007年 | 28828篇 |
2006年 | 18411篇 |
2005年 | 16155篇 |
2004年 | 12223篇 |
2003年 | 8431篇 |
2002年 | 7116篇 |
2001年 | 6234篇 |
2000年 | 5057篇 |
1999年 | 1787篇 |
1998年 | 533篇 |
1997年 | 403篇 |
1996年 | 298篇 |
1995年 | 231篇 |
1994年 | 176篇 |
1993年 | 204篇 |
1992年 | 193篇 |
1991年 | 170篇 |
1990年 | 130篇 |
1989年 | 149篇 |
1988年 | 112篇 |
1987年 | 82篇 |
1986年 | 80篇 |
1985年 | 58篇 |
1984年 | 49篇 |
1983年 | 54篇 |
1981年 | 45篇 |
1980年 | 92篇 |
1979年 | 52篇 |
1965年 | 59篇 |
1959年 | 86篇 |
1955年 | 63篇 |
1954年 | 68篇 |
1951年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
Chih-Chun Hsieh Tao-Chih Chang Dong-Yih Lin Ming-Che Chen Weite Wu 《Metals and Materials International》2007,13(5):411-416
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel
welds at various welding passes during a tungsten are welding (GTAW) process. The morphology, quantity, and chemical composition
of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD),
scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS),
respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless
steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding.
The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of σ→ϱ+λ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe−Cr−Si intermetallic compound found in
the fusion zone of the third pass welds during multi-pass welding. 相似文献
42.
Ivan Cimrák 《Archives of Computational Methods in Engineering》2007,15(3):277-309
The Landau-Lifshitz (LL)equation of micromagnetism governs rich variety of the evolution of magnetization patterns in ferromagnetic
media. This is due to the complexity of physical quantities appearing in the LL equation. This complexity causes also an interesting
mathematical properties of the LL equation: nonlocal character for some quantities,nonconvex side-constraints, strongly nonlinear
terms. These effects influence also the numerical approximations. In this work, recent developments on the approximation of
weak solutions, together with the overview of well-known methods for strong solutions,are addressed.
Author is supported by the Fund for Scientific Research - Flanders FWO (Belgium). 相似文献
43.
综述评述最近发展起来的陶瓷材料的烧结后冷加工热处理法“控制破碎成形加工法”,着重介绍该方法的由业,阐明其理论与实验基础,同时,介绍其应用并讨论其发展前景。 相似文献
44.
45.
基于物联网技术的监狱人员定位可视化管理系统 总被引:1,自引:0,他引:1
提出了一种监狱人员定位可视化管理系统的设计和实现方法。该系统基于WLAN的RTLS定位技术,实现对服刑人员、干警、访客等人群的可视化定位管理。文章结合监狱的应用需求,首先给出了系统的总体设计原则;同时在总体原则约束下,对系统功能、总体实现方案、实现框图、应用流程、网络安全等部分进行阐述,给出了标签软硬件设计、定位管理系统的平台选型和软件架构;最后对设计的系统进行了测试。测试结果显示,该可视化定位管理系统的定位精度达到了预期效果。在进一步优化和完善后,即可大规模推广使用。 相似文献
46.
Many video service sites headed by YouTube know what content requires copyright protection. However, they lack a copyright
protection system that automatically distinguishes whether uploaded videos contain legal or illegal content. Existing protection
techniques use content-based retrieval methods that compare the features of video. However, if the video encoding has changed
in resolution, bit-rate or codec, these techniques do not perform well. Thus, this paper proposes a novel video matching algorithm
even if the type of encoding has changed. We also suggest an intelligent copyright protection system using the proposed algorithm.
This can serve to automatically prevent the uploading of illegal content. The proposed method has represented the accuracy
of 97% with searching algorithm in video-matching experiments and 98.62% with automation algorithm in copyright-protection
experiments. Therefore, this system could form a core technology that identifies illegal content and automatically excludes
access to illegal content by many video service sites. 相似文献
47.
In this paper we have proposed a dynamic pricing scheme for the contributing peers in the Video on Demand (VoD) system. The
scheme provides an effective mechanism to maximize the profit through the residual resources of the contributing peers. A
utilization function is executed for each contributing peer to estimate the utility factor based on the parameters such as
initial setup cost, holding cost, chaining cost and salvage cost. In this paper, we urge an effective dynamic pricing algorithm
that efficiently utilizes a range of parameters with a varying degree of complexity. The key findings of the algorithm are
(i) each contributing peers are benefitted by the monetary based on its resource contributions to the VoD system and (ii)
a high degree of social optimum is established by proficiently aggregating the contributing peer’s resources with the overall
resources of the VoD system. We validate our claim by simulating the proposed dynamic pricing scheme with other standard pricing
schemes such as altruism, cost model and game theory perspective. The result of our dynamic pricing scheme shows the best
utility factor than other standard pricing schemes. 相似文献
48.
49.
关节式电分相是电气化铁路牵引供电系统较为薄弱的环节,电力机车在通过关节式电分相时经常会产生过电压现象,过电压可能会造成机车放电间隙击穿、牵引所馈线保护跳闸,严重影响铁路的安全运营.从实测结果来看,机车在过渡区和中性区行驶时过电压会持续存在一段时间,与以往对关节式电分相产生过电压的研究作对比,分析造成电磁暂态过程以及过电压延续的原因可能是机车的移动.在MATLAB/Simulink软件上建立了机车过关节式电分相的仿真模型,用多个离散过程来近似模拟机车过电分相的连续过程,最后与实测波形对比,验证等效模型是有效的. 相似文献
50.