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   247111篇
  免费   18114篇
  国内免费   9191篇
电工技术   13223篇
技术理论   13篇
综合类   14131篇
化学工业   40776篇
金属工艺   14875篇
机械仪表   15202篇
建筑科学   17134篇
矿业工程   6295篇
能源动力   5850篇
轻工业   14048篇
水利工程   4616篇
石油天然气   14362篇
武器工业   1705篇
无线电   25818篇
一般工业技术   36156篇
冶金工业   14939篇
原子能技术   5820篇
自动化技术   29453篇
  2023年   3374篇
  2022年   5839篇
  2021年   8891篇
  2020年   6882篇
  2019年   5793篇
  2018年   7251篇
  2017年   8035篇
  2016年   7228篇
  2015年   8567篇
  2014年   11006篇
  2013年   13539篇
  2012年   14707篇
  2011年   15795篇
  2010年   13435篇
  2009年   13193篇
  2008年   12929篇
  2007年   12250篇
  2006年   11973篇
  2005年   10408篇
  2004年   7544篇
  2003年   7070篇
  2002年   6914篇
  2001年   6241篇
  2000年   5938篇
  1999年   5840篇
  1998年   4705篇
  1997年   3874篇
  1996年   3652篇
  1995年   3123篇
  1994年   2598篇
  1993年   2052篇
  1992年   1858篇
  1991年   1587篇
  1990年   1451篇
  1989年   1314篇
  1988年   1144篇
  1987年   1000篇
  1986年   857篇
  1985年   787篇
  1984年   746篇
  1982年   703篇
  1981年   695篇
  1979年   742篇
  1978年   779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
101.
102.
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   
103.
104.
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   
105.
106.
综述了国内外聚酯增塑剂的合成及应用的最新研究进展,重点介绍了超支化、生物基、石油基聚酯增塑剂的合成与制备方法以及不同类型聚酯增塑剂在聚氯乙烯(PVC)、淀粉、聚乳酸、聚氨酯弹性体与橡胶制品中的最新应用研究进展;并对聚酯增塑剂未来发展方向做了展望。  相似文献   
107.
108.
109.
110.
Proton exchange membrane fuel cells (PEMFCs) have become the most attractive power supply units for stationary and mobile applications. The operation, design characteristics, as well as performance of PEMFCs, are closely related to the multiphase transport of mass, heat, and electricity in the cell, a critical of which is the gas diffusion layer (GDL). It is very important to guarantee the transmission of water and gasses under high current density, and which is the weakness of PEMFCs at present. Microporous layer (MPL) is considered to be the key variable for mass transfer, so varieties of works focus on modification of MPL materials and its structure design. However, there is still a lack of special review to summarize and prospect the progress of MPL in recent years. This review article therefore focuses on the insights and comprehensive understanding of four critical issues of the MPL, the porosity, pore size distribution, wettability, structural design and the durability of MPL. At last, the conclusion and recommendations section summarized the future prospects and recommendations for possible research opportunities.  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