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   168099篇
  免费   12223篇
  国内免费   6151篇
电工技术   8940篇
技术理论   9篇
综合类   8907篇
化学工业   27472篇
金属工艺   10096篇
机械仪表   10292篇
建筑科学   9931篇
矿业工程   3954篇
能源动力   3745篇
轻工业   9329篇
水利工程   3176篇
石油天然气   9561篇
武器工业   1062篇
无线电   17753篇
一般工业技术   26877篇
冶金工业   11008篇
原子能技术   4857篇
自动化技术   19504篇
  2023年   2199篇
  2022年   4389篇
  2021年   6199篇
  2020年   4615篇
  2019年   3985篇
  2018年   5095篇
  2017年   5528篇
  2016年   5097篇
  2015年   5651篇
  2014年   7355篇
  2013年   9003篇
  2012年   9731篇
  2011年   10440篇
  2010年   8845篇
  2009年   8698篇
  2008年   8567篇
  2007年   8034篇
  2006年   7476篇
  2005年   6410篇
  2004年   4889篇
  2003年   4810篇
  2002年   4820篇
  2001年   4400篇
  2000年   3854篇
  1999年   3466篇
  1998年   2711篇
  1997年   2283篇
  1996年   2041篇
  1995年   1772篇
  1994年   1512篇
  1993年   1276篇
  1992年   1233篇
  1991年   1086篇
  1990年   1096篇
  1989年   1018篇
  1988年   899篇
  1987年   833篇
  1986年   756篇
  1985年   712篇
  1984年   702篇
  1982年   666篇
  1981年   668篇
  1979年   737篇
  1978年   777篇
  1977年   739篇
  1976年   755篇
  1975年   713篇
  1974年   719篇
  1973年   723篇
  1972年   705篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
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   
63.
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   
64.
65.
66.
67.
68.
  Qing  Xu  Bin  Yu  Yang  Zhan  Wei  Zhao  Yu  Zheng  Jun  Ji  Jian 《Bulletin of Engineering Geology and the Environment》2021,80(8):6513-6525
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability...  相似文献   
69.
A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.  相似文献   
70.
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