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   19396篇
  免费   955篇
  国内免费   141篇
电工技术   341篇
综合类   33篇
化学工业   4265篇
金属工艺   597篇
机械仪表   641篇
建筑科学   382篇
矿业工程   49篇
能源动力   1372篇
轻工业   1196篇
水利工程   156篇
石油天然气   84篇
武器工业   1篇
无线电   2408篇
一般工业技术   4485篇
冶金工业   1506篇
原子能技术   179篇
自动化技术   2797篇
  2024年   80篇
  2023年   420篇
  2022年   959篇
  2021年   1169篇
  2020年   926篇
  2019年   959篇
  2018年   1239篇
  2017年   970篇
  2016年   935篇
  2015年   606篇
  2014年   855篇
  2013年   1547篇
  2012年   912篇
  2011年   1097篇
  2010年   878篇
  2009年   829篇
  2008年   733篇
  2007年   593篇
  2006年   497篇
  2005年   389篇
  2004年   280篇
  2003年   252篇
  2002年   203篇
  2001年   183篇
  2000年   177篇
  1999年   173篇
  1998年   299篇
  1997年   246篇
  1996年   231篇
  1995年   180篇
  1994年   165篇
  1993年   156篇
  1992年   107篇
  1991年   141篇
  1990年   101篇
  1989年   106篇
  1988年   86篇
  1987年   95篇
  1986年   79篇
  1985年   87篇
  1984年   76篇
  1983年   77篇
  1982年   66篇
  1981年   72篇
  1980年   49篇
  1979年   32篇
  1978年   28篇
  1977年   26篇
  1976年   36篇
  1971年   14篇
排序方式: 共有10000条查询结果,搜索用时 835 毫秒
31.
32.
Gel state reactions offer new direction for the reactivity of the organic molecules or metal‐organic materials upon photoirradiation with shorter reaction times and high yields compared to solid and solution states. The restricted molecular movement among the molecules in the soft solids control the stereoselectivity of the photoproducts in the gel state reactions. To date, most of the strategies based on self‐assembly have been demonstrated in the solid state, in particular for [2+2] reactions of olefins and polymerization reactions of diacetylenes via 1,4 addition. The soft materials are of emerging materials in recent days given their many applicative day‐to‐day aspects. This review gives a glimpse of recent reports on pericyclic reactions in the gel state that are designed based on the self‐assembly concept. Also it highlights how such reactions accompany the physical changes in the structure of the gels and stereo controlled products with high yields.  相似文献   
33.
The current work explores the usage of novel synthesized Deep Eutectic Solvent (DES) as a catalyst cum solvent media for the thermal dehydrogenation of chemical hydrides, namely Ammonia Borane (AB) and Ethylene diamine bisborane (EDAB). In the first instance, the quantum chemistry based COSMO-SAC (COnductor like Screening MOdel Segment Activity Coefficient) model was used for the selection of the pertinent solvent. 1-Butyl-3-methylimidazolium methanesulfonate: Imidazole ([BMIM][MeSO3]:[Im]) turned out to be an ideal eutectic mixture with the highest predicted solubility with amine boranes. The DES was synthesized by combining the Hydrogen Bond Acceptor (HBA), namely 1-Butyl-3-methylimidazolium methanesulfonate and Imidazole as Hydrogen Bond Donor (HBD) at a molar ratio of 1:2 and T = 70 °C. The formation of DES was confirmed by recording the NMR spectra. Further, the thermal dehydrogenation study was performed at a vacuum of 4 × 10?2 mbar (gauge pressure) of AB/DES and EDAB/DES systems at 105 °C, where a hydrogen equivalent of 1.40 and 2.55 was produced, respectively. The residual samples were further analyzed through 1H NMR analysis for the reaction mechanism and to confirm the role of Ionic Liquid-based DES as catalyst cum solvent media.  相似文献   
34.
35.
Lund  Brady D.  Maurya  Sanjay Kumar 《Scientometrics》2020,125(3):2491-2504
Scientometrics - This study investigates a potential relationship between highly-cited scholarly papers and the number of citations received by other papers with which they share a journal issue....  相似文献   
36.
Wireless Personal Communications - A relatively new area of research and development is Swarm Robotics. It is a part of the swarm intelligence field. In the proposed paper, we shall use swarm...  相似文献   
37.
Wireless Personal Communications - In this article compact multiple input multiple output (MIMO) antenna with triple notch at the ultra-wideband application having two identical monopole antennas...  相似文献   
38.
39.
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   
40.
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