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   1538212篇
  免费   27537篇
  国内免费   7087篇
电工技术   34603篇
综合类   6555篇
化学工业   272028篇
金属工艺   65252篇
机械仪表   43773篇
建筑科学   46788篇
矿业工程   11520篇
能源动力   50305篇
轻工业   116760篇
水利工程   15642篇
石油天然气   37783篇
武器工业   156篇
无线电   197321篇
一般工业技术   287700篇
冶金工业   182201篇
原子能技术   34143篇
自动化技术   170306篇
  2021年   15512篇
  2019年   14625篇
  2018年   16213篇
  2017年   15477篇
  2016年   21510篇
  2015年   17421篇
  2014年   28740篇
  2013年   87917篇
  2012年   36044篇
  2011年   48942篇
  2010年   43145篇
  2009年   51347篇
  2008年   45738篇
  2007年   43104篇
  2006年   45295篇
  2005年   40232篇
  2004年   42252篇
  2003年   42031篇
  2002年   41139篇
  2001年   38025篇
  2000年   36306篇
  1999年   35760篇
  1998年   50525篇
  1997年   42317篇
  1996年   37535篇
  1995年   32074篇
  1994年   29847篇
  1993年   29693篇
  1992年   26461篇
  1991年   23717篇
  1990年   23967篇
  1989年   23059篇
  1988年   21564篇
  1987年   19821篇
  1986年   19178篇
  1985年   22550篇
  1984年   22527篇
  1983年   20509篇
  1982年   19452篇
  1981年   19551篇
  1980年   18238篇
  1979年   18697篇
  1978年   17971篇
  1977年   18224篇
  1976年   20156篇
  1975年   16198篇
  1974年   15675篇
  1973年   15779篇
  1972年   13229篇
  1971年   11896篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
In optimization of transient problems, a robust, stable, and efficient numerical scheme for time integration is of much importance. Recently, the mixed Lag  相似文献   
912.
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   
913.
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   
914.
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   
915.
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   
916.
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   
917.
918.
919.
920.
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