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   419776篇
  免费   14709篇
  国内免费   6645篇
电工技术   13364篇
技术理论   9篇
综合类   8891篇
化学工业   62276篇
金属工艺   23393篇
机械仪表   20274篇
建筑科学   15647篇
矿业工程   5718篇
能源动力   9256篇
轻工业   27180篇
水利工程   6223篇
石油天然气   14010篇
武器工业   1056篇
无线电   45651篇
一般工业技术   81112篇
冶金工业   51815篇
原子能技术   9987篇
自动化技术   45268篇
  2023年   2526篇
  2022年   4896篇
  2021年   7561篇
  2020年   5643篇
  2019年   5388篇
  2018年   14754篇
  2017年   15629篇
  2016年   11783篇
  2015年   7705篇
  2014年   10205篇
  2013年   17532篇
  2012年   16633篇
  2011年   24072篇
  2010年   20940篇
  2009年   20441篇
  2008年   20332篇
  2007年   21630篇
  2006年   12735篇
  2005年   14339篇
  2004年   11334篇
  2003年   10910篇
  2002年   9739篇
  2001年   8913篇
  2000年   8305篇
  1999年   7952篇
  1998年   13857篇
  1997年   10213篇
  1996年   8300篇
  1995年   6325篇
  1994年   5670篇
  1993年   5239篇
  1992年   4339篇
  1991年   4060篇
  1990年   3822篇
  1989年   3806篇
  1988年   3604篇
  1987年   3126篇
  1986年   2937篇
  1985年   3312篇
  1984年   3083篇
  1983年   2870篇
  1982年   2645篇
  1981年   2768篇
  1980年   2563篇
  1979年   2732篇
  1978年   2754篇
  1977年   2982篇
  1976年   3819篇
  1975年   2415篇
  1973年   2362篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
81.
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   
82.
83.
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   
84.
Sun  Yue  Zhu  Yu  Li  Ying  Zhang  Mingyu 《Wireless Personal Communications》2020,111(1):83-96
Wireless Personal Communications - The existing long term evolution networks originally designed for human-to-human communications are hard to tackle numerous and bursty random access requests from...  相似文献   
85.
86.
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels.  相似文献   
87.

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

  相似文献   
88.
89.
Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015  相似文献   
90.
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