全文获取类型
收费全文 | 209304篇 |
免费 | 18599篇 |
国内免费 | 9572篇 |
专业分类
电工技术 | 12946篇 |
技术理论 | 15篇 |
综合类 | 13667篇 |
化学工业 | 34724篇 |
金属工艺 | 11618篇 |
机械仪表 | 13028篇 |
建筑科学 | 16091篇 |
矿业工程 | 6365篇 |
能源动力 | 6060篇 |
轻工业 | 14147篇 |
水利工程 | 3767篇 |
石油天然气 | 13017篇 |
武器工业 | 1614篇 |
无线电 | 25083篇 |
一般工业技术 | 25070篇 |
冶金工业 | 10144篇 |
原子能技术 | 2306篇 |
自动化技术 | 27813篇 |
出版年
2024年 | 1032篇 |
2023年 | 3865篇 |
2022年 | 7129篇 |
2021年 | 9619篇 |
2020年 | 7262篇 |
2019年 | 5756篇 |
2018年 | 6570篇 |
2017年 | 7362篇 |
2016年 | 6526篇 |
2015年 | 8686篇 |
2014年 | 10806篇 |
2013年 | 13045篇 |
2012年 | 14093篇 |
2011年 | 14948篇 |
2010年 | 12761篇 |
2009年 | 12027篇 |
2008年 | 11490篇 |
2007年 | 10617篇 |
2006年 | 10955篇 |
2005年 | 9482篇 |
2004年 | 6344篇 |
2003年 | 5348篇 |
2002年 | 4817篇 |
2001年 | 4312篇 |
2000年 | 4351篇 |
1999年 | 5100篇 |
1998年 | 4186篇 |
1997年 | 3601篇 |
1996年 | 3389篇 |
1995年 | 2733篇 |
1994年 | 2221篇 |
1993年 | 1619篇 |
1992年 | 1288篇 |
1991年 | 970篇 |
1990年 | 705篇 |
1989年 | 589篇 |
1988年 | 475篇 |
1987年 | 319篇 |
1986年 | 256篇 |
1985年 | 152篇 |
1984年 | 132篇 |
1983年 | 102篇 |
1982年 | 112篇 |
1981年 | 80篇 |
1980年 | 72篇 |
1979年 | 29篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1976年 | 28篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
ABSTRACT Contact tracing is widely considered as an effective procedure in the fight against epidemic diseases. However, one of the challenges for technology based contact tracing is the high number of false positives, questioning its trust-worthiness and efficiency amongst the wider population for mass adoption. To this end, this paper proposes a novel, yet practical smartphone-based contact tracing approach, employing WiFi and acoustic sound for relative distance estimate, in addition to the air pressure and the magnetic field for ambient environment matching. We present a model combining six smartphone sensors, prioritising some of them when certain conditions are met. We empirically verified our approach in various realistic environments to demonstrate an achievement of up to 95% fewer false positives, and 62% more accurate than Bluetooth-only system. To the best of our knowledge, this paper was one of the first work to propose a combination of smartphone sensors for contact tracing. 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.
Meifang Luo Chaozhong Guo Xinyi Luo Zhaoxu Li Yuan Qin Weizhong Zhang 《International Journal of Hydrogen Energy》2021,46(2):2117-2127
It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices. 相似文献
94.
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
95.
Baofeng Hou Hong He Ruixiu Jia Meilong Fu Yanbin Cao Shaoqun He Liwen Luo Youqing Huang 《应用聚合物科学杂志》2019,136(10):47161
The synthesis and performance of a novel temperature-tolerant foamed resin for enhanced oil recovery were investigated using various methods, including infrared, NMR, scanning electron microscopy (SEM), and displacement experiments. Polycondensation of furfuryl alcohol prepolymers was confirmed by the infrared and NMR results. The poor temperature tolerance of furfuryl alcohol prepolymers after gelation at high temperatures is mainly due to the fracture of furan rings. The addition of ester additives is an effective method of increasing the temperature tolerance of the prepared foamed resins and can effectively reduce the weight-loss rate of the polycondensation products. The SEM results show that the skeleton structure of the foamed resin remains intact after high-temperature treatment. Thus, the novel plugging agent system has excellent thermal stability and still has a high strength (>0.8 MPa) after high-temperature aging treatment for 40 days, giving the prepared foamed resin a good plugging performance (plugging rate > 91%) at 250 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47161. 相似文献
96.
97.
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
98.
基于目前中国改进型三环路压水堆(CPR1000)部分机组存在因中间量程电流饱和导致无法在48%额定功率(Pn)完成定值标定及核电厂大修经济性考虑,采用MCNP程序及核设计软件包SCIENCE,研究分析中间量程保护定值标定的新方法。分析结果表明,中间量程保护定值标定调整至30%Pn功率平台实施,采用改进方法标定的保护定值更接近于设计值。 相似文献
99.
100.