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   29561篇
  免费   1211篇
  国内免费   175篇
电工技术   544篇
综合类   45篇
化学工业   6066篇
金属工艺   893篇
机械仪表   922篇
建筑科学   542篇
矿业工程   110篇
能源动力   1924篇
轻工业   2131篇
水利工程   305篇
石油天然气   150篇
武器工业   1篇
无线电   3671篇
一般工业技术   6576篇
冶金工业   2884篇
原子能技术   332篇
自动化技术   3851篇
  2024年   125篇
  2023年   545篇
  2022年   1315篇
  2021年   1475篇
  2020年   1178篇
  2019年   1210篇
  2018年   1590篇
  2017年   1312篇
  2016年   1284篇
  2015年   807篇
  2014年   1182篇
  2013年   2224篇
  2012年   1304篇
  2011年   1616篇
  2010年   1285篇
  2009年   1235篇
  2008年   1119篇
  2007年   911篇
  2006年   762篇
  2005年   596篇
  2004年   494篇
  2003年   440篇
  2002年   358篇
  2001年   314篇
  2000年   307篇
  1999年   314篇
  1998年   629篇
  1997年   456篇
  1996年   462篇
  1995年   381篇
  1994年   334篇
  1993年   317篇
  1992年   244篇
  1991年   275篇
  1990年   210篇
  1989年   203篇
  1988年   201篇
  1987年   194篇
  1986年   164篇
  1985年   197篇
  1984年   165篇
  1983年   177篇
  1982年   159篇
  1981年   151篇
  1980年   123篇
  1979年   84篇
  1978年   72篇
  1977年   81篇
  1976年   109篇
  1975年   44篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Many occupations require workers to stand for long periods of time without proper interventions, which causes discomfort in the back and lower limbs. Therefore, this study aims to assess the effectiveness in alleviating body muscle discomfort during prolonged standing through the use of a calf massager. This study was conducted among male workers at a manufacturer with production line workers and the list was obtained from the HR Department and simple random sampling was done by number categorization. A total of 100 respondents (50 respondents for both the control and the experimental groups) participated in this study. The experiment took place in a room with a similar setup for the production line. Each respondent was requested to perform the simulated task for 2 hr. For the experimental group, the calf massager was turned on every 15 min. At every 15‐min interval after turning on the calf massager, respondents from both groups were required to evaluate their discomfort level on a Borg's scale CR‐10 questionnaire. The results showed that the level of body discomfort among respondents in the experimental group reduced (20–30%) compared with that of the control group. Multivariate analysis results revealed that the discomfort rating for the lower back, knees, thighs, calves, and feet was significantly lower (p < .05) among the experimental group compared with the control group. For lower body parts, the lower back region was statistically significant (p < .05) at the 90th, 105th, and 120th min; the thigh region was statistically significant (p < .05) at the 120th min; the knee region was statistically significant (p < .05) at the 105th and 120th min; the calf region was statistically significant (p < .05) at all minute intervals except the 15th and 45th min, while the feet region, was statistically significant at the 105th and 120th min. Therefore, this study indicates that calf massage treatment is capable of reducing body muscle discomfort during prolonged standing and highlights the significance of calf massage.  相似文献   
6.
7.
8.
Wireless Personal Communications - Data security is currently become a serious concern in wireless communication system for both the users and providers. Without a secure medium, the data...  相似文献   
9.
Microsystem Technologies - The strategy for analysis of noise generated in the analog circuit is presented here. Further, methodology for optimization of noise to improve the performance of the...  相似文献   
10.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures.  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