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   50125篇
  免费   2490篇
  国内免费   156篇
电工技术   708篇
综合类   65篇
化学工业   10596篇
金属工艺   2136篇
机械仪表   3242篇
建筑科学   1101篇
矿业工程   27篇
能源动力   2111篇
轻工业   3892篇
水利工程   271篇
石油天然气   91篇
武器工业   2篇
无线电   7834篇
一般工业技术   10665篇
冶金工业   4347篇
原子能技术   658篇
自动化技术   5025篇
  2024年   50篇
  2023年   570篇
  2022年   871篇
  2021年   1485篇
  2020年   1070篇
  2019年   1176篇
  2018年   1430篇
  2017年   1413篇
  2016年   1750篇
  2015年   1294篇
  2014年   2088篇
  2013年   3008篇
  2012年   3265篇
  2011年   3890篇
  2010年   2815篇
  2009年   2922篇
  2008年   2811篇
  2007年   2185篇
  2006年   2033篇
  2005年   1723篇
  2004年   1572篇
  2003年   1516篇
  2002年   1329篇
  2001年   1134篇
  2000年   996篇
  1999年   940篇
  1998年   1693篇
  1997年   1071篇
  1996年   859篇
  1995年   601篇
  1994年   499篇
  1993年   422篇
  1992年   295篇
  1991年   289篇
  1990年   266篇
  1989年   248篇
  1988年   214篇
  1987年   176篇
  1986年   124篇
  1985年   124篇
  1984年   92篇
  1983年   63篇
  1982年   40篇
  1981年   40篇
  1980年   32篇
  1979年   32篇
  1978年   30篇
  1977年   41篇
  1976年   70篇
  1973年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
汽车负载突降保护的重要性 今天,汽车中并联在供电线路上的许多电子控制器和设备与三、四十年前生产的汽车有了很大的不同。那时汽车中的唯一的电子设备就是汽车收音机。  相似文献   
92.
This paper reports an alternative method for the growth of GaN epitaxial layer on (0001) Al2O3 substrate by hot-wall vapor phase epitaxy technique. Tris (N,N-dimethyldithiocarbamato)-gallium (III), Ga(mDTC)3 was introduced as a precursor material for the seed layer formation in the growth of GaN. Optimal growth conditions with seed layers formed by the Ga(mDTC)3 concentration of 0.047 mol/L were identified: Growth temperature was found to be 850 °C, and optimal distance between the reactant outlet and substrate was determined to be 12.5 cm. Characterization results showed that this growth method produce high-crystallinity GaN epitaxial layers at a relatively lower growth temperature compared to the existing growth techniques and simplify the growth process.  相似文献   
93.
GeoFilter: Geometric Selection of Mesh Filter Parameters   总被引:1,自引:0,他引:1  
  相似文献   
94.
95.
96.
OBJECTIVE: The initially well-fixed implants of total hip replacement (THR) are in the long-term subject to aseptic loosening. Many cytokines can contribute to osteolysis due to osteoclast recruitment and/or activation. However, in this respect tumor necrosis factor-alpha (TNF-alpha) plays a pivotal role, because it upregulates interleukin-1 and 6 and granulocyte-macrophage colony stimulating factor. The aim of this study was to assess the eventual presence, cellular localization and extent of expression of TNF-alpha in the synovial-like membrane at the implant or at the cement to bone interface compared to control synovial membrane. METHODS: Twenty samples from the synovial-like membrane of the periprosthetic tissues were compared to control samples. TNF-alpha containing cells were visualized using an avidin-biotin-peroxidase complex (ABC) method and analyzed by light microscopy, double labelling and image analysis. RESULTS: TNF-alpha was found in the periprosthetic tissues in fibroblasts and vascular endothelial cells, but mainly in the macrophages was it found to coincide with areas containing implant-derived debris. TNF-alpha containing cells were more numerous in the synovial-like membrane in the interface tissue from the proximal stem area (2816 +/- 318 cells) than in the control synovial membrane (565 +/- 93 cells, p < 0.01). Interestingly, similarly high TNF-alpha expression (3452 +/- 582 cells) was also seen in the synovial-like membrane of the pseudocapsule. CONCLUSION: These findings suggest that the foreign body-type host reaction caused by THR is characterized by the high expression of TNF-alpha. Because such expression occurred in the interface tissue between the implant and surrounding bone, TNF-alpha, due to its pivotal direct and indirect role in the activation and recruitment of osteoclasts, may contribute to periprosthetic osteolysis and to the loosening of THR.  相似文献   
97.
The purpose of this study was to analyze the symbolization of colors as cultural codes, based on costume colors. In order to study the significance of colors in cultural changes, we carried out a quantitative analysis and interpreted it from the perspective of cultural semiotics. The range of this study was focused on Korean costume colors, over diverse diachronic stages of Korean culture. For this study 1535 color samples were collected, measured with a spectrophotometer, and analyzed quantitatively according their diachronic stages of origin. As a result, red, blue, and yellow were found to be the most frequently used colors during the Chosun Dynasty, a period based on Confucianism. These colors acted as cultural codes with cultural significance. During the Modern times pink, light blue, and black increased in frequency and represented the reception of western culture, the changing sex role of women in society, and utilitarianism. In these days, neutral colors and grayish tones of all colors are the most significant colors of high frequency. The use of such colors is closely related to industrialization, mechanization, functionalism, and the changes of women's sex roles in the societies. They are used as cultural codes, especially to emphasize a rational and masculine image rather than a feminine image. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 71–79, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20290  相似文献   
98.
Image flow segmentation and estimation using displaced spatial gradient   总被引:2,自引:0,他引:2  
Kim  Y.-H. Kim  S.D. 《Electronics letters》1992,28(24):2213-2215
There are two main causes of inaccuracies in estimating image flows using gradient based techniques. One is the erroneous measurement of gradients in brightness and the other is the blurring of motion boundaries which is caused by the smoothness constraint. In the Letter, the gradient measurement error of conventional methods is analysed and a new technique based on this analysis proposed.<>  相似文献   
99.
100.
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