全文获取类型
收费全文 | 142920篇 |
免费 | 11389篇 |
国内免费 | 5859篇 |
专业分类
电工技术 | 8338篇 |
技术理论 | 8篇 |
综合类 | 9472篇 |
化学工业 | 24411篇 |
金属工艺 | 8541篇 |
机械仪表 | 9175篇 |
建筑科学 | 12065篇 |
矿业工程 | 4280篇 |
能源动力 | 3962篇 |
轻工业 | 8925篇 |
水利工程 | 2538篇 |
石油天然气 | 8873篇 |
武器工业 | 1187篇 |
无线电 | 15119篇 |
一般工业技术 | 16943篇 |
冶金工业 | 6819篇 |
原子能技术 | 1603篇 |
自动化技术 | 17909篇 |
出版年
2024年 | 466篇 |
2023年 | 2293篇 |
2022年 | 3769篇 |
2021年 | 5476篇 |
2020年 | 4331篇 |
2019年 | 3541篇 |
2018年 | 4042篇 |
2017年 | 4567篇 |
2016年 | 3931篇 |
2015年 | 5370篇 |
2014年 | 6869篇 |
2013年 | 8149篇 |
2012年 | 8948篇 |
2011年 | 9790篇 |
2010年 | 8348篇 |
2009年 | 8106篇 |
2008年 | 7835篇 |
2007年 | 7443篇 |
2006年 | 7821篇 |
2005年 | 6807篇 |
2004年 | 4681篇 |
2003年 | 4060篇 |
2002年 | 3854篇 |
2001年 | 3380篇 |
2000年 | 3552篇 |
1999年 | 4148篇 |
1998年 | 3413篇 |
1997年 | 2849篇 |
1996年 | 2747篇 |
1995年 | 2256篇 |
1994年 | 1834篇 |
1993年 | 1317篇 |
1992年 | 1086篇 |
1991年 | 795篇 |
1990年 | 591篇 |
1989年 | 479篇 |
1988年 | 378篇 |
1987年 | 248篇 |
1986年 | 162篇 |
1985年 | 119篇 |
1984年 | 81篇 |
1983年 | 56篇 |
1982年 | 67篇 |
1981年 | 44篇 |
1980年 | 38篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1965年 | 3篇 |
1940年 | 3篇 |
1928年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
针对大型旋转机械通过临界转速时振动过大及运行中故障频发等问题,搭建转子试验台,模拟启停机过程和碰摩、不对中故障。不改变原有支撑形式,安装自主设计的磁流变阻尼器,在不停机的情况下,试验研究阻尼器抑制转子通过临界转速时振动过大及各类故障振动。试验结果表明,阻尼器可以有效抑制转子系统临界转速附近的振动,降幅在60%以上;转子发生碰摩或不对中故障时,阻尼器可以降低其高倍频振动。 相似文献
94.
Pyrochlore-type WO_3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid,from which films were made by dip coating process with indium-tin oxide(ITO).The obtained films were characterized by thermogravimetric and differential thermal analysis(TG-DTA), X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM), cyclic voltammetry(CV), chronoamperometry(CA) and ultravioletvisible(UV-Vis) absorption. Results show that the crystal of the pyrochlore-type WO_3 powder is perfect. When the calcination temperature rises from room temperature to500 ℃,the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase,finally it will completely convert to WO_3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300 ℃ exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm~2 C~(-1) at 884 nm. 相似文献
95.
Synergistic flame retardant effects of activated carbon and molybdenum oxide in poly(vinyl chloride)
下载免费PDF全文
![点击此处可从《Polymer International》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mengjiao Zhang Weihong Wu Shaorui He Xue Wang Yunhong Jiao Hongqiang Qu Jianzhong Xu 《Polymer International》2018,67(4):445-452
The synergistic effects of activated carbon (AC) and molybdenum oxide (MoO3) in improving the flame retardancy of poly(vinyl chloride) (PVC) were investigated. The effects of AC, MoO3 and their mixture with a mass ratio of 1:1 on the flame retardancy and smoke suppression properties of PVC were studied using the limiting oxygen index and cone calorimeter tests. It was found that the flame retardancy of the relatively cheaper AC was slightly weaker than that of MoO3. In addition, the incorporation of AC and MoO3 greatly reduced the total heat release and improved smoke suppressant property of PVC composites. When the total content of AC and MoO3 was 10 phr, PVC/AC/MoO3 had the lowest peak heat release rate and peak smoke production rate values of 173.80 kW m?2 and 0.1472 m2 s?1, which represented reductions of 47.3 and 59.9%, respectively, compared with those of PVC. Furthermore, thermogravimetric analysis and gel content tests were used to analyze the flame retardant mechanism of AC and MoO3, with results showing that AC could promote early crosslinking in PVC. Char residue left after heating at 500 °C was analyzed using scanning electron microscopy and Raman spectroscopy, and the results showed that MoO3 produced the most compact char, with the smallest and most organized carbonaceous microstructures. © 2017 Society of Chemical Industry 相似文献
96.
97.
设计了一种以STM32F103微控制器为控制核心,基于24位高精度模数转换器的钻孔深度测量仪器。利用弹性波回波测距原理,通过测量出钻孔中钻杆的长度,实现钻孔深度的快速、无损、准确的测量,主要用于井下瓦斯抽放钻孔、探放水钻孔等煤矿通防工作的施工验收。仪器小巧轻便,操作简单,单人即可完成测量工作,节约下井的人力物力,提高生产效率,最长测量长度可达250米,误差不超过1米。 相似文献
98.
Shouguang Wang Mengdi Gan Mengchu Zhou Dan You 《IEEE/CAA Journal of Automatica Sinica》2015,2(4):345-352
As a powerful analysis tool of Petri nets, reachability trees are fundamental for systematically investigating many characteristics such as boundedness, liveness and reversibility. This work proposes a method to generate a reachability tree, called ωRT for short, for a class of unbounded generalized nets called ω-independent nets based on new modified reachability trees (NMRTs). ωRT can effectively decrease the number of nodes by removing duplicate and ω-duplicate nodes in the tree, and verify properties such as reachability, liveness and deadlocks. Two examples are provided to show its superiority over NMRTs in terms of tree size. 相似文献
99.
100.