全文获取类型
收费全文 | 218455篇 |
免费 | 20409篇 |
国内免费 | 10584篇 |
专业分类
电工技术 | 14409篇 |
技术理论 | 14篇 |
综合类 | 14946篇 |
化学工业 | 35354篇 |
金属工艺 | 12116篇 |
机械仪表 | 13808篇 |
建筑科学 | 16960篇 |
矿业工程 | 6594篇 |
能源动力 | 6387篇 |
轻工业 | 15908篇 |
水利工程 | 4043篇 |
石油天然气 | 12767篇 |
武器工业 | 1849篇 |
无线电 | 26333篇 |
一般工业技术 | 25465篇 |
冶金工业 | 10407篇 |
原子能技术 | 2653篇 |
自动化技术 | 29435篇 |
出版年
2024年 | 1127篇 |
2023年 | 4139篇 |
2022年 | 7883篇 |
2021年 | 10433篇 |
2020年 | 7901篇 |
2019年 | 6238篇 |
2018年 | 7042篇 |
2017年 | 7829篇 |
2016年 | 6990篇 |
2015年 | 9292篇 |
2014年 | 11542篇 |
2013年 | 13622篇 |
2012年 | 14930篇 |
2011年 | 15691篇 |
2010年 | 13595篇 |
2009年 | 12856篇 |
2008年 | 12374篇 |
2007年 | 11443篇 |
2006年 | 11553篇 |
2005年 | 9865篇 |
2004年 | 6592篇 |
2003年 | 5660篇 |
2002年 | 5294篇 |
2001年 | 4756篇 |
2000年 | 4447篇 |
1999年 | 4877篇 |
1998年 | 3890篇 |
1997年 | 3377篇 |
1996年 | 3143篇 |
1995年 | 2489篇 |
1994年 | 2054篇 |
1993年 | 1488篇 |
1992年 | 1218篇 |
1991年 | 882篇 |
1990年 | 641篇 |
1989年 | 537篇 |
1988年 | 428篇 |
1987年 | 295篇 |
1986年 | 236篇 |
1985年 | 146篇 |
1984年 | 133篇 |
1983年 | 101篇 |
1982年 | 99篇 |
1981年 | 76篇 |
1980年 | 72篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Weikang Dong Ruishi Qi Tiansheng Liu Yi Li Ning Li Ze Hua Zirui Gao Shuyuan Zhang Kaihui Liu Jiandong Guo Peng Gao 《Advanced materials (Deerfield Beach, Fla.)》2020,32(46):2002014
Hyperbolic phonon polaritons (HPhPs) in orthorhombic-phase molybdenum trioxide (α-MoO3) show in-plane hyperbolicity, great wavelength compression, and ultralong lifetime, therefore holding great potential in nanophotonic applications. However, its polaritonic response in the far-infrared (FIR) range remains unexplored due to challenges in experimental characterization. Here, monochromated electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) is used to probe HPhPs in α-MoO3 in both mid-infrared (MIR) and FIR frequencies and correlate their behaviors with microstructures and orientations. It is found that low structural symmetry leads to various phonon modes and multiple Reststrahlen bands (RBs) over a broad spectral range (over 70 meV) and in different directions (55–63 meV and 119–125 meV along the b-axis, 68–106 meV along the c-axis, and 101–121 meV along the a-axis). These HPhPs can be selectively excited by controlling the direction of swift electrons. These findings provide new opportunities in nanophotonic and optoelectronic applications, such as directed light propagation, hyperlenses, and heat transfer. 相似文献
92.
Adaptive backstepping repetitive learning control design for nonlinear discrete‐time systems with periodic uncertainties
下载免费PDF全文
![点击此处可从《International Journal of Adaptive Control and Signal Processing》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Qiao Zhu Jian‐Xin Xu Shiping Yang Guang‐Da Hu 《International Journal of Adaptive Control and Signal Processing》2015,29(4):524-535
This paper addresses a tracking problem for uncertain nonlinear discrete‐time systems in which the uncertainties, including parametric uncertainty and external disturbance, are periodic with known periodicity. Repetitive learning control (RLC) is an effective tool to deal with periodic unknown components. By using the backstepping procedures, an adaptive RLC law with periodic parameter estimation is designed. The overparameterization problem is overcome by postponing the parameter estimation to the last backstepping step, which could not be easily solved in robust adaptive control. It is shown that the proposed adaptive RLC law without overparameterization can guarantee the perfect tracking and boundedness of the states of the whole closed‐loop systems in presence of periodic uncertainties. In addition, the effectiveness of the developed controller is demonstrated by an implementation example on a single‐link flexible‐joint robot. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
93.
Bing Yang Yu Zhou Wenjie Yu Song Zhang Hongxiang Chen Ju Ye 《Polymer International》2019,68(4):675-683
In order to improve the dispersity and stability of the nano‐SiO2 aqueous system with high solid content, a kind of polyacrylic acid dispersant with methoxysilicon end groups (KH590‐PAA) was synthesized by photopolymerization of acrylic acid (AA) initiated with (3‐mercaptopropyl)trimethoxysilane (KH590). After adding KH590‐PAA into the nano‐SiO2 aqueous dispersion system (20 wt% solid content), the viscosity and the curing time of the system were measured with a rotational viscometer and the inverted bottle method. Moreover, the dispersion mechanism of KH590‐PAA for the nano‐SiO2 aqueous system was researched by measuring the adsorption capacity, the particle size and the zeta potential of the nanoparticles with a conductivity meter, dynamic light scattering, SEM and TEM, respectively. The results showed that the methoxysilicon groups in KH590‐PAA could react with hydroxyl groups on the surface of nano‐SiO2 in the process of stirring, which enhanced the adsorption capacity of the dispersant and then increased the surface charge of the particles. Therefore, electrostatic repulsion and steric hindrance effects between the SiO2 nanoparticles could be further enhanced by adding the KH590‐PAA dispersant, and then the nano‐SiO2 aqueous system exhibited better dispersity and stability. Besides, the dispersion properties of SiO2 nanoparticles in water were closely related to the addition amount and the molecular weight of the KH590‐PAA dispersant. © 2018 Society of Chemical Industry 相似文献
94.
95.
96.
Anxiang Su Gaoxing Ma Minhao Xie Yang Ji Xiangfei Li Liyan Zhao Qiuhui Hu 《International Journal of Food Science & Technology》2019,54(6):2277-2287
In this study, in vitro digestion and fermentation of Flammulina velutipes -derived polysaccharides (FVP) were investigated. It was found that FVP mainly consisted of 48.45% glucose, 15.40% mannose, 14.60% xylose, 11.80% fucose and 9.90% galactose. The -human saliva, simulated gastric and small intestinal juices conditions did not break down the FVP. Based on in vitro fermentation tests, FVP modulated the composition of gut microbiota by elevating the amounts of Bifidobacteriaceae and Bacteroidaceae and reducing the numbers of genera Lachnospiraceae and Enterococcaceae. Meanwhile, FVP affected the synthesis of short-chain fatty acids derived from gut microbiota. 相似文献
97.
带关键字搜索的公钥加密(PEKS)是一种有用的加密原语,它允许用户将在加密数据上搜索的功能委托给不可信的第三方服务器,而不影响原始数据的安全性和隐私性。但是,由于缺乏对于数据的加密以及解密能力,PEKS方案不能单独进行使用,必须与标准的公钥加密方案(PKE)相结合。因此,Baek等人在2006年引入了一种新的加密原语,称为结合PKE和PEKS的加密方案(PKE+PEKS),它同时提供了PKE和PEKS的功能。目前,已有文献提出了几种PKE+PEKS方案。然而,他们都没有考虑关键字猜测攻击的问题。本文提出一个新的高效且能够抵抗关键字猜测攻击的PKE+PEKS方案,与已有方案相比,该方案在性能上有很大的提升,并且在生成关键字和数据密文时,不需要使用双线性对,极大地降低了计算和存储成本。安全性分析表明,本文中所提出的方案能够满足密文隐私安全性、陷门不可区分性和抗关键字猜测攻击的安全性。效率分析表明,本分提出的方案更加高效。 相似文献
98.
99.
100.