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   675869篇
  免费   11242篇
  国内免费   2051篇
电工技术   11935篇
综合类   710篇
化学工业   103774篇
金属工艺   26144篇
机械仪表   20760篇
建筑科学   15974篇
矿业工程   3735篇
能源动力   18346篇
轻工业   57134篇
水利工程   7168篇
石油天然气   13055篇
武器工业   39篇
无线电   75590篇
一般工业技术   133798篇
冶金工业   126587篇
原子能技术   14513篇
自动化技术   59900篇
  2021年   6907篇
  2020年   5293篇
  2019年   6545篇
  2018年   10871篇
  2017年   10791篇
  2016年   11675篇
  2015年   7610篇
  2014年   12164篇
  2013年   32955篇
  2012年   19415篇
  2011年   25478篇
  2010年   20202篇
  2009年   22544篇
  2008年   22949篇
  2007年   22366篇
  2006年   19671篇
  2005年   17932篇
  2004年   16977篇
  2003年   16650篇
  2002年   16052篇
  2001年   15581篇
  2000年   14589篇
  1999年   15016篇
  1998年   38921篇
  1997年   27512篇
  1996年   21010篇
  1995年   15622篇
  1994年   13806篇
  1993年   13768篇
  1992年   9835篇
  1991年   9485篇
  1990年   9289篇
  1989年   8874篇
  1988年   8594篇
  1987年   7350篇
  1986年   7332篇
  1985年   8297篇
  1984年   7705篇
  1983年   6962篇
  1982年   6570篇
  1981年   6709篇
  1980年   6343篇
  1979年   6104篇
  1978年   6222篇
  1977年   7294篇
  1976年   9664篇
  1975年   5451篇
  1974年   5091篇
  1973年   5259篇
  1972年   4430篇
排序方式: 共有10000条查询结果,搜索用时 62 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.
3.
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   
4.
Koroteev  A. S. 《Atomic Energy》2021,130(4):202-208
Atomic Energy - The history and direction of further development of space nuclear energetics are examined. The functional diagram and principle of operation of a promising, powerful,...  相似文献   
5.
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   
6.
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed.  相似文献   
7.
8.
9.
10.
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   
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