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   25267篇
  免费   1927篇
  国内免费   862篇
电工技术   1329篇
技术理论   1篇
综合类   1381篇
化学工业   4505篇
金属工艺   1324篇
机械仪表   1321篇
建筑科学   1868篇
矿业工程   578篇
能源动力   885篇
轻工业   1640篇
水利工程   339篇
石油天然气   1345篇
武器工业   123篇
无线电   3123篇
一般工业技术   3245篇
冶金工业   1442篇
原子能技术   314篇
自动化技术   3293篇
  2024年   84篇
  2023年   408篇
  2022年   702篇
  2021年   1033篇
  2020年   722篇
  2019年   674篇
  2018年   694篇
  2017年   808篇
  2016年   762篇
  2015年   929篇
  2014年   1245篇
  2013年   1588篇
  2012年   1588篇
  2011年   1725篇
  2010年   1400篇
  2009年   1442篇
  2008年   1341篇
  2007年   1241篇
  2006年   1351篇
  2005年   1165篇
  2004年   843篇
  2003年   760篇
  2002年   762篇
  2001年   543篇
  2000年   523篇
  1999年   604篇
  1998年   572篇
  1997年   464篇
  1996年   449篇
  1995年   345篇
  1994年   281篇
  1993年   190篇
  1992年   175篇
  1991年   117篇
  1990年   92篇
  1989年   72篇
  1988年   88篇
  1987年   48篇
  1986年   44篇
  1985年   25篇
  1984年   33篇
  1983年   19篇
  1982年   27篇
  1981年   13篇
  1980年   10篇
  1979年   15篇
  1977年   4篇
  1976年   9篇
  1975年   4篇
  1965年   5篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Centimeter-size multi-branched tree-like carbon structures have been generated by the catalytic chemical vapor deposition of toluene using ferrocene as the catalyst precursor and investigated by means of SEM, TEM, and EDX. It is found that a temperature of 1000-1200 °C and a carrier gas flow rate of 1000-2500 ml/min are necessary for the generation of the carbon trees. Their morphologies and microstructures change greatly with the changing reaction conditions. The fractal dimensions of the trees are calculated to quantitatively investigate the influence of different reaction temperatures on the morphologies.  相似文献   
22.
Copolythiophenes (Co‐PTs), poly(3‐hexylthiophene‐co‐3‐thiophene carboxylic acid) (P3HT‐TCa), poly(3‐hexyloxylthiophene‐co‐3‐thiophene carboxylic acid) (P3HOT‐TCa), and poly(3‐phenylthiophene‐co‐3‐thiophene carboxylic acid) (P3PhT‐TCa), were synthesized by chemical oxidized polymerization to investigate the effect of copolymerization on the properties of polythiophenes (PTs). Gel permeation chromatography showed that the molecular weight (MW) of Co‐PT was lower than that of homopolythiophene. Fourier transform infrared (FTIR) spectra indicated that the copolymerization was successful between the monomers. The λmax of Co‐PTs gave a “blue shift” in ultraviolet‐visible (UV‐VIS) spectra. Photoluminescence (PL) spectra showed that the PL intensity of Co‐PT became weaker than that of homopolythiophene and the disappearance of PL had been observed in P3HOT‐TCa. The thermal stability of Co‐PT was influenced by the carboxyl for its low decomposition temperature. Furthermore, the copolymerization between multi‐wall carbon nanotube containing thiophene ring (MWNT‐Th) and 3‐hexyloxylthiphene could also take place successfully. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007  相似文献   
23.
Automatic detection and precise localization of human eye centers are the essential processes in photo related multimedia applications. Since eye center points are used as reference base points for further intelligent processing, precise eye center localization is very important. In face recognition the accuracy of localization of eye centers directly influences the identification accuracy. A multiple stage approach with multiple cues for detection and precise localization of eye centers is presented in this paper. Multiple scopes searching strategy is used for correctly extracting eye patch images from the background. Dedicated gradient based features and curvelet based features are constructed and used for comprehensively revealing the intensity distribution characteristics and the edge based texture around eye centers. A rebuilt score calculation mechanism is proposed and the rebuilt scores are used as a specific measurement index reflecting the matching accuracy. The final localizations of eye centers are determined with integrating the gradient based scores and curvelet based scores. The experiment results testing on public face datasets show that the localization accuracy of proposed approach outperforms the accuracy with other state of the art methods.  相似文献   
24.
This study is to investigate the factors influencing the alcohol production byKluyveromyces fragilis using the juice of Jerusalem Artichoke tubers. The cell growth rate and ethanol production rate were stimulated by aeration and by the addition of unsaturated fatty acids and the cell mass production and the ethanol production were substantially improved. It was found that oxygen and unsaturated fatty acids added played a decisive role on the increase of alcohol tolerance of yeast.  相似文献   
25.
现代科学技术,尤其是生物技术和计算机技术的飞速发展和广泛应用,给化妆品行业带来了全新的发展机遇,赋予化妆品以一定的功效性是新世纪化妆品发展的重要趋势.近20年来,人们对化妆品的要求已从洁肤、润肤为目的的基础护肤品向美白、祛皱为目的的功效性化妆品方向发展.  相似文献   
26.
The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005  相似文献   
27.
从实践论的视角分析马克思主义真理观.通过对真理的属性及其检验标准、真理和价值的关系问题的讨论,阐述了实践在马克思主义真理观中的作用和地位.  相似文献   
28.
本文分析了乳胶制品的生产过程,并对工序能力指数进行了分析,从而推断出产品的质量。  相似文献   
29.
Liu  Tang-hong  Su  Xin-chao  Zhang  Jie  Chen  Zheng-wei  Zhou  Xi-sai 《中南大学学报(英文版)》2016,23(9):2419-2428
This work used the computational fluid dynamics method combined with full-scale train tests to analyze the train aerodynamic performance on special slope topography. Results show that with the increment in the slope gradient, the aerodynamic forces and moment increase sharply. Compared with the flat ground condition, the lateral force, lift force, and overturning moment of the train on the first line increase by 153.2%, 53.4% and 124.7%, respectively, under the slope gradient of 20°. However, with the increment of the windward side's depth, the windbreak effect is improved obviously. When the depth is equal to 10 m, compared with the 0 m, the lateral force, lift force and overturning moment of the train on the first line decrease by 70.9%, 77.0% and 70.6%,respectively. Through analyzing the influence of slope parameters on the aerodynamic performance of the train, the relationships among them are established. All these will provide a basic reference for enhancing train aerodynamic performances under different slope conditions and achieve reasonable train speeds for the operation safety in different wind environments.  相似文献   
30.
Wei  Shikui  Jiang  Su  Jin  Wenxian  Zhao  Yao  Ni  Rongrong  Zhu  Zhenfeng 《Multimedia Systems》2015,21(2):207-216
Multimedia Systems - Recently, the frame fusion based video copy detection scheme provides a possibility to detect copies in a continuous query video stream. However, its computational complexity...  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