首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   490227篇
  免费   15555篇
  国内免费   7303篇
电工技术   14536篇
技术理论   9篇
综合类   9249篇
化学工业   72105篇
金属工艺   25833篇
机械仪表   22114篇
建筑科学   17144篇
矿业工程   5880篇
能源动力   11111篇
轻工业   32399篇
水利工程   6897篇
石油天然气   15450篇
武器工业   1092篇
无线电   55167篇
一般工业技术   95595篇
冶金工业   64834篇
原子能技术   11986篇
自动化技术   51684篇
  2022年   5058篇
  2021年   8022篇
  2020年   6043篇
  2019年   5808篇
  2018年   15198篇
  2017年   16060篇
  2016年   12487篇
  2015年   8295篇
  2014年   11318篇
  2013年   20363篇
  2012年   18349篇
  2011年   26317篇
  2010年   22540篇
  2009年   22356篇
  2008年   22599篇
  2007年   23718篇
  2006年   14826篇
  2005年   16145篇
  2004年   13338篇
  2003年   12830篇
  2002年   11793篇
  2001年   11008篇
  2000年   10119篇
  1999年   9888篇
  1998年   18734篇
  1997年   13614篇
  1996年   10751篇
  1995年   8467篇
  1994年   7390篇
  1993年   7177篇
  1992年   5467篇
  1991年   5146篇
  1990年   4992篇
  1989年   4892篇
  1988年   4491篇
  1987年   4045篇
  1986年   4001篇
  1985年   4304篇
  1984年   3991篇
  1983年   3712篇
  1982年   3517篇
  1981年   3529篇
  1980年   3497篇
  1979年   3329篇
  1978年   3437篇
  1977年   3670篇
  1976年   4633篇
  1975年   2954篇
  1974年   2888篇
  1973年   2894篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
92.
Lobster krill (Munida genus) represents an under‐valued crustacean frequently caught on European fishing banks. In this work, its sensory, microbiological and biochemical qualities were evaluated during chilled storage. Additionally, the effects of a prestorage antimelanosic treatment consisting of soaking in sodium metabisulphite (SMB) solutions at two different concentrations (0.25% and 0.75%) were also studied. SMB prestorage treatment provided lobster specimens that still exhibited acceptable sensory quality after 10 days of storage, while control specimens were unacceptable at that time. SMB treatment also resulted in a significant (P < 0.05) inhibition of microbial growth, mainly of Enterobacteriaceae, psychrotrophes and proteolytic bacteria. Low lipid oxidation levels were observed for all batches; however, a significantly higher (P < 0.05) retention of polyunsaturated fatty acids was found in SMB‐treated lobster, especially in the 0.75% SMB batch. The results presented here open the way to the potential commercialisation of currently under‐utilised lobster krill as a chilled product.  相似文献   
93.
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets.  相似文献   
94.
Ni2P nanoparticles and CdS nanorods were grew together on a mesoporous g-C3N4 through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni2P composite displays a high H2 evolution rate with 2905.86 μmol g?1 h?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni2P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni2P. Meanwhile, Ni2P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni2P composite exerts good stability in 12-h cycles.  相似文献   
95.
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings.  相似文献   
96.
Fefelov  S. A.  Kazakova  L. P.  Bogoslovskiy  N. A.  Bylev  A. B.  Yakubov  A. O. 《Semiconductors》2020,54(4):450-453
Semiconductors - The current–voltage characteristics measured on Ge2Sb2Te5 thin films in the current mode are studied. The effect of multilevel recording is established when applying...  相似文献   
97.
Journal of Communications Technology and Electronics - Abstract—The article considers the two-dimensional diffraction problem of a TM-type plane electromagnetic wave on a cylindrical silver...  相似文献   
98.
ABSTRACT

This paper deals with asymptotic stabilisation of a class of nonlinear input-delayed systems via dynamic output feedback in the presence of disturbances. The proposed strategy has the structure of an observer-based control law, in which the observer estimates and predicts both the plant state and the external disturbance. A nominal delay value is assumed to be known and stability conditions in terms of linear matrix inequalities are derived for fast-varying delay uncertainties. Asymptotic stability is achieved if the disturbance or the time delay is constant. The controller design problem is also addressed and a numerical example with an unstable system is provided to illustrate the usefulness of the proposed strategy.  相似文献   
99.
Powder Metallurgy and Metal Ceramics - The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was...  相似文献   
100.
贾宇 《现代导航》2020,11(4):272-276
卫星导航地基增强系统(GBAS)是国际民航组织重点推进的新技术。为全面借鉴国际上 GBAS 技术的发展与应用,本文介绍了 GBAS 组成、原理和优缺点,研究了国内外 GBAS 研究与应用的发展,结合中国民航目前的运行需求提出了 GBAS 应用建议,为 GBAS 发展应用提供了参考。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号