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   312074篇
  免费   3870篇
  国内免费   739篇
电工技术   6229篇
综合类   570篇
化学工业   47302篇
金属工艺   10388篇
机械仪表   8943篇
建筑科学   8015篇
矿业工程   865篇
能源动力   8660篇
轻工业   31286篇
水利工程   2552篇
石油天然气   3690篇
武器工业   11篇
无线电   39988篇
一般工业技术   58799篇
冶金工业   56728篇
原子能技术   5479篇
自动化技术   27178篇
  2021年   2390篇
  2019年   2271篇
  2018年   3792篇
  2017年   3590篇
  2016年   3682篇
  2015年   2624篇
  2014年   4616篇
  2013年   14516篇
  2012年   7515篇
  2011年   10284篇
  2010年   8003篇
  2009年   9233篇
  2008年   9680篇
  2007年   9623篇
  2006年   8551篇
  2005年   7927篇
  2004年   7786篇
  2003年   7514篇
  2002年   7342篇
  2001年   7564篇
  2000年   7216篇
  1999年   7554篇
  1998年   17682篇
  1997年   12854篇
  1996年   10118篇
  1995年   7888篇
  1994年   7213篇
  1993年   6915篇
  1992年   5291篇
  1991年   5076篇
  1990年   4939篇
  1989年   4786篇
  1988年   4679篇
  1987年   3894篇
  1986年   4015篇
  1985年   4723篇
  1984年   4279篇
  1983年   4023篇
  1982年   3604篇
  1981年   3762篇
  1980年   3460篇
  1979年   3422篇
  1978年   3227篇
  1977年   3814篇
  1976年   4849篇
  1975年   2783篇
  1974年   2660篇
  1973年   2680篇
  1972年   2217篇
  1971年   1969篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 2, pp. 4–7, February, 1992.  相似文献   
992.
The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10?6 to 5 · 10?4 mm/y, for tantalum: 10?8 to 4 · 10?6 mm/y, and for the Ta-40Nb alloy: 2 · 10?7 to 8 · 10?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F? and at a temperature of 108°C, corrosion rates between 5.3 · 10?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10?3 mm/y at 50°C/280 ppm F? and 1.4 · 10?2 mm/y at 110°C/320 ppm F?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.  相似文献   
993.
994.
Doubly resonant Ti:sapphire laser   总被引:1,自引:0,他引:1  
A CW Ti:sapphire laser that operates simultaneously at two frequencies is described. This mode of operation was obtained with an intracavity dispersive prism and two separate feedback paths. An alternative means of achieving dual frequency operation was demonstrated using a birefringent filter. Repetitive Q-switching produced an increase in the range of wavelengths over which dual frequency operation was obtained  相似文献   
995.
A non-linear behaviour in the resistance of tellurium as a function of pressure has been observed. At each pressure the resistance shows a time variation. At lower pressures, the normalized resistance increases with time, and at higher pressures, the normalized resistance decreases exponentially as a function of time. This change in behaviour with respect to time occurs in the region of the steepest descent in the resistance versus pressure plot. However, the magnitude of the change in the resistance with time is small compared to a change in the resistance with pressure. The origin of this behaviour is suggested to be linked with the generation and annealing of localized charged defects. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
996.
Bioceramics     
Ceramics, glasses, and glass-ceramics are increasingly being tested for use in the human body. These materials often have excellent chemical properties for biomedical use, but they are brittle and show fatigue. Careful analysis of their mechanical properties is needed to determine appropriate applications. Hydroxylapatite is emerging as the most promising bioceramic because it shows no foreign body reactions and bonds strongly to bone; if properly made without pores or second phases it has excellent fatigue resistance. Glass-ceramics containing hydroxylapatite crystals also show good promise for many applications. Different forms of these materials, such as dense, granular, mixed granular with plaster of Paris, and coatings on metals are being tested and have very good potential as bioceramics.  相似文献   
997.
Gordonia amarae is a right-angled branching filament belonging to the mycolic acid-containing Actinobacteria which is commonly found in many foaming activated sludge wastewater treatment plants. Although studies on different substrates as sole carbon sources by pure cultures of G. amarae have been carried out, none have examined substrate uptake by this organism in situ. Uptake of several hydrophilic and hydrophobic substrates by G. amarae was evaluated in situ using a combination of fluorescence in situ hybridization and microautoradiography. G. amarae could assimilate a range of both hydrophilic and hydrophobic substrates. From the data, G. amarae appears to be physiologically active under aerobic, anaerobic and anoxic condition (NO2 and NO3) for some substrates. This might explain why attempts to control foaming caused by G. amarae using anoxic and anaerobic selectors have been unsuccessful. This study emphasizes that bacteria can behave differently in situ to pure cultures and that it is important to evaluate the in situ physiology of these bacteria if we are to better understand their role in the wastewater treatment process.  相似文献   
998.
999.
This paper is the result of a plenary discussion session held at the 11th European Conference on Mixing. Three perspectives on mixing research are explored: that of the industrialist, the equipment manufacturer, and the academic researcher. There was strong agreement that, while the one dimensional problems are reasonably well understood and many engineers thus perceive that mixing is simple, current practice actually requires us to address complex, multi‐dimensional problems with interactions between mixing, reaction, multi‐phase physics, surface phenomena, and transport phenomena. Understanding these multi‐scale, multi‐mechanism problems requires models which include interactions between the phenomena, and allow the effects of these interactions to emerge. Developing these models will require us to shift our perspective on mixing from one of equipment design to one of the mixing field as a fundamental physical mechanism.  相似文献   
1000.
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