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   19876篇
  免费   994篇
  国内免费   139篇
电工技术   370篇
综合类   29篇
化学工业   4297篇
金属工艺   613篇
机械仪表   650篇
建筑科学   386篇
矿业工程   46篇
能源动力   1473篇
轻工业   1210篇
水利工程   152篇
石油天然气   87篇
武器工业   1篇
无线电   2468篇
一般工业技术   4552篇
冶金工业   1586篇
原子能技术   189篇
自动化技术   2900篇
  2024年   77篇
  2023年   427篇
  2022年   874篇
  2021年   1187篇
  2020年   940篇
  2019年   980篇
  2018年   1258篇
  2017年   993篇
  2016年   968篇
  2015年   629篇
  2014年   876篇
  2013年   1602篇
  2012年   937篇
  2011年   1135篇
  2010年   914篇
  2009年   863篇
  2008年   753篇
  2007年   617篇
  2006年   507篇
  2005年   382篇
  2004年   296篇
  2003年   274篇
  2002年   205篇
  2001年   197篇
  2000年   195篇
  1999年   184篇
  1998年   326篇
  1997年   268篇
  1996年   240篇
  1995年   176篇
  1994年   172篇
  1993年   164篇
  1992年   115篇
  1991年   137篇
  1990年   106篇
  1989年   103篇
  1988年   89篇
  1987年   94篇
  1986年   77篇
  1985年   93篇
  1984年   77篇
  1983年   76篇
  1982年   64篇
  1981年   75篇
  1980年   53篇
  1979年   37篇
  1978年   33篇
  1977年   34篇
  1976年   41篇
  1975年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
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   
44.
45.
46.
47.
The present study attempts quantitative determination of changes in the morphological surface features viz. fractal dimension, lower and upper cut off length scale through Power Spectral Density analysis prior to and after irradiation of 100 KeV Ar+ ion beam at incidence angles of 0°, 40° and 60° on ZnO thin films. All the unirradiated and irradiated samples are subjected to photoelectrochemical characterization and a correlation between photoelectrochemical performance and morphological parameters is established. Sample irradiated at 40° angle at the fluence of 5 × 1016 ions/cm2 is found to possess maximum fractal dimension of 2.72, lower and upper cut off length scale of 3.16 nm and 63.00 nm respectively. This sample exhibits maximum photocurrent density of 3.19 mA/cm2 and applied bias photon-to-current efficiency of 1.12% at 1.23 V/RHE. Hydrogen gas collected for duration of 1 h for the same sample was ~4.83 mLcm?2.  相似文献   
48.

Floods are common and recurring natural hazards which damages is the destruction for society. Several regions of the world with different climatic conditions face the challenge of floods in different magnitudes. Here we estimate flood susceptibility based on Analytical neural network (ANN), Deep learning neural network (DLNN) and Deep boost (DB) algorithm approach. We also attempt to estimate the future rainfall scenario, using the General circulation model (GCM) with its ensemble. The Representative concentration pathway (RCP) scenario is employed for estimating the future rainfall in more an authentic way. The validation of all models was done with considering different indices and the results show that the DB model is most optimal as compared to the other models. According to the DB model, the spatial coverage of very low, low, moderate, high and very high flood prone region is 68.20%, 9.48%, 5.64%, 7.34% and 9.33% respectively. The approach and results in this research would be beneficial to take the decision in managing this natural hazard in a more efficient way.

  相似文献   
49.
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   
50.
Application of brown titanium dioxide (TiO2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO2-x nanoparticles with g-C3N4, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO2-x nanocomposite with high rate constants of 0.075 min?1, 0.083 min?1 and 0.093 min?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e?)/hole (h+) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO2-x is carried out.  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