全文获取类型
收费全文 | 166399篇 |
免费 | 8831篇 |
国内免费 | 4907篇 |
专业分类
电工技术 | 5806篇 |
技术理论 | 5篇 |
综合类 | 8704篇 |
化学工业 | 25337篇 |
金属工艺 | 9518篇 |
机械仪表 | 7729篇 |
建筑科学 | 9130篇 |
矿业工程 | 3054篇 |
能源动力 | 3520篇 |
轻工业 | 9429篇 |
水利工程 | 2797篇 |
石油天然气 | 5386篇 |
武器工业 | 588篇 |
无线电 | 18917篇 |
一般工业技术 | 25656篇 |
冶金工业 | 6271篇 |
原子能技术 | 1354篇 |
自动化技术 | 36936篇 |
出版年
2024年 | 425篇 |
2023年 | 1520篇 |
2022年 | 2562篇 |
2021年 | 3559篇 |
2020年 | 2751篇 |
2019年 | 2498篇 |
2018年 | 16760篇 |
2017年 | 16026篇 |
2016年 | 12209篇 |
2015年 | 3959篇 |
2014年 | 4348篇 |
2013年 | 5086篇 |
2012年 | 8238篇 |
2011年 | 14769篇 |
2010年 | 13097篇 |
2009年 | 10007篇 |
2008年 | 11120篇 |
2007年 | 11836篇 |
2006年 | 4364篇 |
2005年 | 4835篇 |
2004年 | 3987篇 |
2003年 | 4407篇 |
2002年 | 4588篇 |
2001年 | 3510篇 |
2000年 | 2463篇 |
1999年 | 2189篇 |
1998年 | 1474篇 |
1997年 | 1305篇 |
1996年 | 1286篇 |
1995年 | 1016篇 |
1994年 | 835篇 |
1993年 | 600篇 |
1992年 | 489篇 |
1991年 | 342篇 |
1990年 | 255篇 |
1989年 | 207篇 |
1988年 | 188篇 |
1987年 | 104篇 |
1986年 | 87篇 |
1985年 | 55篇 |
1984年 | 41篇 |
1982年 | 40篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1959年 | 40篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
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
35.
36.
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
37.
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
38.
Dr. Jiayao Y. Wang Dr. Jiaqi Q. Li Prof. Dr. Yumei M. Xiao Prof. Dr. Bin Fu Prof. Dr. Zhaohai H. Qin 《ChemMedChem》2020,15(5):404-410
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant. 相似文献
39.
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
40.
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