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   241241篇
  免费   2626篇
  国内免费   427篇
电工技术   4292篇
综合类   257篇
化学工业   39369篇
金属工艺   9379篇
机械仪表   7394篇
建筑科学   5446篇
矿业工程   1391篇
能源动力   5152篇
轻工业   24808篇
水利工程   2476篇
石油天然气   5092篇
武器工业   32篇
无线电   25044篇
一般工业技术   44770篇
冶金工业   45343篇
原子能技术   5950篇
自动化技术   18099篇
  2021年   2107篇
  2019年   2017篇
  2018年   3488篇
  2017年   3424篇
  2016年   3687篇
  2015年   2235篇
  2014年   3898篇
  2013年   10184篇
  2012年   6146篇
  2011年   8297篇
  2010年   6546篇
  2009年   7232篇
  2008年   7583篇
  2007年   7712篇
  2006年   6887篇
  2005年   6045篇
  2004年   5815篇
  2003年   5598篇
  2002年   5673篇
  2001年   5560篇
  2000年   5383篇
  1999年   5302篇
  1998年   12570篇
  1997年   8895篇
  1996年   6856篇
  1995年   5329篇
  1994年   4735篇
  1993年   4624篇
  1992年   3667篇
  1991年   3387篇
  1990年   3593篇
  1989年   3472篇
  1988年   3303篇
  1987年   2895篇
  1986年   2932篇
  1985年   3373篇
  1984年   3219篇
  1983年   2892篇
  1982年   2738篇
  1981年   2821篇
  1980年   2719篇
  1979年   2624篇
  1978年   2684篇
  1977年   2948篇
  1976年   3805篇
  1975年   2368篇
  1974年   2242篇
  1973年   2376篇
  1972年   1970篇
  1971年   1858篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989.  相似文献   
64.
65.
This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm2) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V/μs in these devices  相似文献   
66.
67.
The brushless doubly fed induction machine (BDFIM) has been extensively researched for approximately 30 years, but a related machine [the brushless doubly fed reluctance machine (BDFRM)], has not. This was mainly due to the fact that reluctance rotor designs were not capable of generating saliency ratios large enough to make the BDFRM competitive with other machines. However, recent developments in reluctance rotors, spurred on by research into synchronous reluctance machines, has resulted in high saliency ratio rotors that are economic to build. This, together with the promise of higher efficiency and simpler control compared to the BDFIM, means that further investigation of the BDFRM is warranted. A relatively limited amount of work to date has been published on the BDFRM. This paper attempts to fill this void by presenting a theoretical analysis of some of the important control properties of the ideal BDFRM.  相似文献   
68.
The article presents the results of experimental investigations of critical (limit) heat fluxes upon evaporation on porous coatings, and it substantiates the physical model of the process.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 4, pp. 607–614, October, 1985.  相似文献   
69.
Structures and compositions of the monomers guanidine acrylate and guanidine methacrylate, their homopolymers, and copolymers with diallyldimethylammonium chloride enriched in acrylate comonomer units were determined. It was shown that ampholytic copolymers, owing to their ionic nature, contained comonomeric guanidine acrylate or methacrylate units and diallyldimethylammonium chloride units, as well as the acrylate comonomer with the diallyl counterion and polymeric acrylate and diallyl ion pairs. It follows from IR and 1H NMR data that guanidine methacrylate has the same structure (with two hydrogen bonds) in the solid state and in solutions. Guanidine acrylate structures in the solid state and in dimethylsulfoxide are identical and analogous to guanidine methacrylate structure in this solvent. In water, the guanidine acrylate structure has another type of hydrogen bonding (with one hydrogen bond, where the proton is shifted toward the guanidine group). These features of hydrogen bonding of guanidine acrylate and guanidine methacrylate are also retained in their homopolymers and copolymers with diallyldimethylammonium chloride. It was shown that the thermal stability of the copolymers was higher than that of their homopolymers, confirming the formation of intramolecular ion pairs of oppositely charged units of ampholytic copolymers. Moreover, the thermal stability of guanidine methacrylate-diallyldimethylammonium chloride copolymers is higher than that of guanidine acrylate-diallyldimethylammonium chloride copolymers.  相似文献   
70.
It is established that the capillary rise of a liquid has an oscillatory character, in contrast to the commonly accepted opinion that a vertical capillary is filled at a monotonically varying velocity. The value of the tangential shear stress arising in an ascending liquid is evaluated for ethyl alcohol and distilled water.  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