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   1567377篇
  免费   36625篇
  国内免费   6992篇
电工技术   35032篇
综合类   6425篇
化学工业   280651篇
金属工艺   65014篇
机械仪表   44047篇
建筑科学   47971篇
矿业工程   11483篇
能源动力   50787篇
轻工业   120916篇
水利工程   15963篇
石油天然气   37552篇
武器工业   143篇
无线电   201730篇
一般工业技术   295381篇
冶金工业   190005篇
原子能技术   34068篇
自动化技术   173826篇
  2021年   15647篇
  2020年   12850篇
  2019年   16844篇
  2018年   18057篇
  2017年   17629篇
  2016年   24032篇
  2015年   19814篇
  2014年   31047篇
  2013年   91164篇
  2012年   37815篇
  2011年   50338篇
  2010年   44442篇
  2009年   52614篇
  2008年   46951篇
  2007年   44067篇
  2006年   46239篇
  2005年   40952篇
  2004年   43079篇
  2003年   42753篇
  2002年   41698篇
  2001年   38741篇
  2000年   37047篇
  1999年   36327篇
  1998年   53146篇
  1997年   44113篇
  1996年   38594篇
  1995年   32689篇
  1994年   30401篇
  1993年   30239篇
  1992年   26590篇
  1991年   23906篇
  1990年   24064篇
  1989年   23206篇
  1988年   21682篇
  1987年   19898篇
  1986年   19322篇
  1985年   22676篇
  1984年   22544篇
  1983年   20522篇
  1982年   19464篇
  1981年   19580篇
  1980年   18259篇
  1979年   18701篇
  1978年   17947篇
  1977年   18292篇
  1976年   20295篇
  1975年   16162篇
  1974年   15631篇
  1973年   15719篇
  1972年   13180篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
961.
Bacterial cellulose membranes were employed as templates for calcium phosphates deposition by successive immersion in solutions of Ca(NO3)2·4H2O and (NH4)2HPO4, under ultrasonication. During the wet chemical reaction, mineral phases were loaded on bacterial cellulose fibrils, leading to precursor hybrid composites. These were subjected to a lyophilisation procedure in order to preserve the 3D porous aspect and afterwards to a thermal treatment with the aim of removing the polymeric phase and generating well crystallized structures. Different types of morphologies were achieved by varying the heating rate, as well as the calcination temperature and period. The as-prepared samples and the final ones were investigated from compositional and structural point of view through X-ray diffraction and Fourier-transform infrared spectroscopy and morphologically concerning by scanning electron microscopy. The magnetic properties were also evaluated in order to demonstrate the suitability of the obtained materials for the development of magnetic scaffolds dedicated to hard tissue applications.  相似文献   
962.
Nahrawy  A. M. El  Moez  A. Abdel  Saad  A. M. 《SILICON》2018,10(5):2117-2122
Silicon - Thin film nanocomposites of sodium silicate (80 SiO2 –20 Na2O)/ tartrazine dye (E102) prepared using sol gel process in acidic system. The change in the physicochemical properties...  相似文献   
963.
964.
ABSTRACT

This paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance.  相似文献   
965.
Abdellah  W. M. 《Radiochemistry》2020,62(3):347-358
Radiochemistry - The study deals with separation of uranium, thorium, and yttrium with highest possible purity from El-Garaa El-Hamara sulfate leach liquor. From the latter, almost complete...  相似文献   
966.
The ability of bacterial species to colonize and infect host organisms is critically dependent upon their capacity to adhere to cellular surfaces of the host. Adherence to cell surfaces is known to be essential for the activation and delivery of certain virulence factors, but can also directly affect host cell signaling to aid bacterial spread and survival. In this review we will discuss the recent advances in the field of bacterial adhesion, how we are beginning to unravel the effects adhesins have on host cell signaling, and how these changes aid the bacteria in terms of their survival and evasion of immune responses. Finally, we will highlight how the exploitation of bacterial adhesins may provide new therapeutic avenues for the treatment of a wide range of bacterial infections.  相似文献   
967.
968.
969.
970.
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