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   416990篇
  免费   6502篇
  国内免费   1358篇
电工技术   7868篇
综合类   356篇
化学工业   62254篇
金属工艺   16863篇
机械仪表   13823篇
建筑科学   9066篇
矿业工程   2263篇
能源动力   11783篇
轻工业   30422篇
水利工程   4372篇
石油天然气   7929篇
武器工业   17篇
无线电   50177篇
一般工业技术   87232篇
冶金工业   75330篇
原子能技术   9317篇
自动化技术   35778篇
  2021年   4199篇
  2020年   3246篇
  2019年   4077篇
  2018年   7059篇
  2017年   7052篇
  2016年   7566篇
  2015年   4872篇
  2014年   7798篇
  2013年   21336篇
  2012年   12179篇
  2011年   16178篇
  2010年   12948篇
  2009年   14440篇
  2008年   14867篇
  2007年   14620篇
  2006年   12981篇
  2005年   11532篇
  2004年   10860篇
  2003年   10792篇
  2002年   10219篇
  2001年   10040篇
  2000年   9382篇
  1999年   9719篇
  1998年   24479篇
  1997年   16876篇
  1996年   12944篇
  1995年   9663篇
  1994年   8477篇
  1993年   8467篇
  1992年   6147篇
  1991年   5767篇
  1990年   5695篇
  1989年   5315篇
  1988年   5043篇
  1987年   4430篇
  1986年   4300篇
  1985年   4895篇
  1984年   4528篇
  1983年   4034篇
  1982年   3702篇
  1981年   3797篇
  1980年   3493篇
  1979年   3381篇
  1978年   3384篇
  1977年   3781篇
  1976年   4891篇
  1975年   2916篇
  1974年   2697篇
  1973年   2766篇
  1972年   2299篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
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.
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   
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.
Combustion, Explosion, and Shock Waves - Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a...  相似文献   
8.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
9.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
10.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  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