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   1818篇
  免费   70篇
  国内免费   9篇
电工技术   45篇
综合类   1篇
化学工业   315篇
金属工艺   40篇
机械仪表   43篇
建筑科学   32篇
矿业工程   4篇
能源动力   81篇
轻工业   90篇
水利工程   12篇
石油天然气   7篇
无线电   349篇
一般工业技术   370篇
冶金工业   211篇
原子能技术   11篇
自动化技术   286篇
  2023年   19篇
  2022年   40篇
  2021年   83篇
  2020年   56篇
  2019年   72篇
  2018年   73篇
  2017年   65篇
  2016年   75篇
  2015年   33篇
  2014年   61篇
  2013年   135篇
  2012年   67篇
  2011年   73篇
  2010年   68篇
  2009年   75篇
  2008年   59篇
  2007年   62篇
  2006年   64篇
  2005年   44篇
  2004年   33篇
  2003年   28篇
  2002年   43篇
  2001年   29篇
  2000年   24篇
  1999年   37篇
  1998年   56篇
  1997年   43篇
  1996年   46篇
  1995年   32篇
  1994年   25篇
  1993年   25篇
  1992年   23篇
  1991年   25篇
  1990年   12篇
  1989年   22篇
  1988年   15篇
  1987年   21篇
  1986年   13篇
  1985年   12篇
  1984年   13篇
  1983年   12篇
  1982年   11篇
  1981年   7篇
  1980年   10篇
  1978年   8篇
  1977年   5篇
  1976年   10篇
  1975年   4篇
  1974年   6篇
  1971年   4篇
排序方式: 共有1897条查询结果,搜索用时 15 毫秒
61.
International Journal on Document Analysis and Recognition (IJDAR) - Separation of text and non-text is an essential processing step for any document analysis system. Therefore, it is important to...  相似文献   
62.
Employing first-principles density functional theory based calculations we investigated the change in electronic structure of CaCu3B4O12 compounds as one moves from 3d (Co) to 4d (Rh) to 5d (Ir) element at B site. Our study sheds light on valences of Cu and B ions as one moves from 3d to 4d to 5d based compounds. The valence of Cu in Co and Rh compound turn out to be that of less known 3+ state, while that in Ir compound turn out to be commonly known 2+ state. Our first-principles study provide microscopic understanding of these different valences of Cu, in terms of changes in the mixing of Cu x 2 − y 2 and B-a 1g states, driven by changes in the crystal field and spin splitting. The stronger crystal field splitting for 4d and 5d elements compared to 3d at B site drive the low-spin state at Rh and Ir site as opposed to intermediate spin in case of Co.  相似文献   
63.
64.
65.
66.
Feature selection through optimization techniques provides an interesting approach to minimize computational time with enhanced prediction capability, and  相似文献   
67.
Periodically fully developed two-dimensional (2D) flow in a furrowed wavy channel is investigated numerically at various Reynolds numbers (100–2123). For the laminar and transitional flow regime, the study is done for six geometrically different channels; corresponding to various nondimensional amplitude (0.05, 0.075, and 0.1) and wavelength (0.5 and 1). Critical Reynolds number—for the onset of periodic flow—decreases with increasing amplitude and wavelength. A flow regime map—demarcating steady and unsteady flow regime—is proposed. It is shown that the size of the vortex in streamlines and waviness in isotherms increase with increasing Reynolds number, amplitude and wavelength. The performance of wavy as compared to straight channel is studied with the help of ratio of Nusselt number, friction factor and area-goodness factor, and thermal-performance factor. With increasing Reynolds number, all these parameters remain almost constant in the steady regime and increase almost linearly in the unsteady regime. For the largest Reynolds number (close to 2000) studied here, the increase in the Nusselt number ratio—within the periodic flow regime—is 11.21% and 133% for the amplitude equal to 0.075 and 0.1, respectively, at a wavelength of 0.5; at a wavelength of 1.0, the increase is 101%, 134%, and 181% for the amplitude of 0.05, 0.075, and 0.1, respectively.  相似文献   
68.
Due to rapid construction, necessity for raw materials of concrete, especially coarse aggregate, tends to increase the danger of early exhaustion of the natural resources. An alternative source of raw materials would perhaps delay the advent of this early exhaustion. Recycled coarse aggregate (RCA) plays a great role as an alternative raw material that can replace the natural coarse aggregate (NCA) for concrete. Previous studies show that the properties of RCA concrete are inferior in quality compared to NCA concrete. This article attempts to study the improvement of properties of RCA concrete with the addition of bacteria named as Bacillus subtilis. The experimental investigation was carried out to evaluate the improvement of the compressive strength, capillary water absorption, and drying shrinkage of RCA concrete incorporating bacteria. The compressive strength of RCA concrete is found to be increased by about 20% when the cell concentration of B. subtilis is 106 cells/ml. The capillary water absorption as well as drying shrinkage of RCA are reduced when bacteria is incorporated. The improvement of RCA concrete is confirmed to be due to the calcium carbonate precipitation as observed from the microstructure studies carried out on it such as EDX, SEM, and XRD.  相似文献   
69.
Search of design spaces to generate solutions affects the design outcomes during conceptual design. This research aims to understand the different types of search that occurs during conceptual design and their effect on the design outcomes. Additionally, we study the effect of other factors, such as creativity, problem-solving style, and experience of designers, on the design outcomes. Two sets of design experiments, with experienced and novice designers, are used in this study. We find that designers employ twelve different types of searches during conceptual design for problem understanding, solution generation, and solution evaluation activities. Results also suggest that creativity is influenced positively by the type and amount of searches, duration of designing, and experience of designers.  相似文献   
70.
We report the preparation of polyaniline (PANI) nanoparticles dispersed in polyvinyl alcohol (PVA) matrix. From SEM picture it is seen that the particle sizes vary from 100–20 nm. Also with increase in PVA content the stability of dispersion is found to increase. Apart from SEM, spin cast films of PANI in PVA are also characterized through XRD and FTIR. XRD shows increase in crystallinity with PVA content and FTIR gives evidence of crosslinking between PANI and PVA molecules. In plane electrical conductivity (in the range of 102 Scm−1) and the exponent of nonlinear I–V are found to decrease with increase of PVA content. There is a good correlation between SEM, XRD, FTIR and electrical properties.  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