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   274381篇
  免费   4026篇
  国内免费   963篇
电工技术   5549篇
综合类   1225篇
化学工业   40382篇
金属工艺   10567篇
机械仪表   8310篇
建筑科学   7325篇
矿业工程   1472篇
能源动力   6032篇
轻工业   18791篇
水利工程   2712篇
石油天然气   4171篇
武器工业   25篇
无线电   35756篇
一般工业技术   50665篇
冶金工业   55548篇
原子能技术   4236篇
自动化技术   26604篇
  2022年   4353篇
  2021年   5636篇
  2020年   4230篇
  2019年   5357篇
  2018年   3943篇
  2017年   3455篇
  2016年   3327篇
  2015年   2543篇
  2014年   3907篇
  2013年   10844篇
  2012年   6508篇
  2011年   9526篇
  2010年   7639篇
  2009年   8518篇
  2008年   8439篇
  2007年   8465篇
  2006年   7865篇
  2005年   7493篇
  2004年   8332篇
  2003年   7945篇
  2002年   7782篇
  2001年   7521篇
  2000年   6436篇
  1999年   6794篇
  1998年   16917篇
  1997年   11508篇
  1996年   8914篇
  1995年   6723篇
  1994年   6057篇
  1993年   5911篇
  1992年   4259篇
  1991年   3818篇
  1990年   3893篇
  1989年   3778篇
  1988年   3417篇
  1987年   2804篇
  1986年   2915篇
  1985年   3287篇
  1984年   2886篇
  1983年   2636篇
  1982年   2417篇
  1981年   2498篇
  1980年   2167篇
  1979年   2030篇
  1978年   2112篇
  1977年   2491篇
  1976年   3090篇
  1975年   1808篇
  1974年   1698篇
  1973年   1568篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
2.
Journal of Communications Technology and Electronics - A quantitative comparison of the spectral characteristics of the human visual system and matrix photodetectors is carried out. Criteria for a...  相似文献   
3.
4.
Xiao  Zhu  Chen  Yanxun  Jiang  Hongbo  Hu  Zhenzhen  Lui  John C. S.  Min  Geyong  Dustdar  Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of...  相似文献   
5.
6.
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated.  相似文献   
7.
Virtual Reality - It is generally accepted that natural environments reduce stress and improve mood. Since access to natural environments is sometimes limited, virtual natural environments,...  相似文献   
8.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast...  相似文献   
9.
Food Science and Biotechnology - A rich source of nutrients, figs have a number of clinically validated benefits. This study aimed to evaluate the in vitro simulated gastrointestinal digestion, and...  相似文献   
10.
Objective

Neonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T.

Methods

The 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array.

Results

The 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom.

Conclusion

The 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.

  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