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   357252篇
  免费   27890篇
  国内免费   15716篇
电工技术   20872篇
技术理论   45篇
综合类   25375篇
化学工业   59627篇
金属工艺   20783篇
机械仪表   22453篇
建筑科学   27625篇
矿业工程   11685篇
能源动力   9695篇
轻工业   23994篇
水利工程   6743篇
石油天然气   23441篇
武器工业   2797篇
无线电   38780篇
一般工业技术   39349篇
冶金工业   18532篇
原子能技术   3624篇
自动化技术   45438篇
  2024年   1456篇
  2023年   5562篇
  2022年   9858篇
  2021年   13855篇
  2020年   10429篇
  2019年   8545篇
  2018年   9848篇
  2017年   11060篇
  2016年   10128篇
  2015年   13866篇
  2014年   17446篇
  2013年   20897篇
  2012年   22690篇
  2011年   25173篇
  2010年   22242篇
  2009年   21069篇
  2008年   20651篇
  2007年   19689篇
  2006年   20053篇
  2005年   17653篇
  2004年   11965篇
  2003年   10696篇
  2002年   9895篇
  2001年   8815篇
  2000年   8758篇
  1999年   9389篇
  1998年   7179篇
  1997年   6135篇
  1996年   5811篇
  1995年   4785篇
  1994年   3888篇
  1993年   2622篇
  1992年   2072篇
  1991年   1569篇
  1990年   1233篇
  1989年   995篇
  1988年   830篇
  1987年   524篇
  1986年   410篇
  1985年   258篇
  1984年   206篇
  1983年   164篇
  1982年   128篇
  1981年   77篇
  1980年   97篇
  1979年   43篇
  1978年   17篇
  1977年   23篇
  1976年   28篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
SrMgxTi1 - xO3 nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere.  相似文献   
82.
83.
本文对弧型小方坯连铸机工艺与设备进行了分析,介绍了连铸生产的PLC控制系统。及其软件设计。  相似文献   
84.
本文介绍了用饱和蒸汽对冷凝式汽轮机进行清洗除垢时主要参数的确定、操作要点及清洗方案,清洗后的汽轮机运行正常。  相似文献   
85.
We report a detailed mapping of a 2-D dopant profile on a fully processed industrial sample with large dynamic range and high spatial resolution by utilizing a dopant-selective etching process and Atomic Force Microscopy. The experimental results show excellent agreement with those obtained from SRP and SIMS as corroborative methods. We also discuss the most critical factors which influence the applicability, reproducibility, and reliability of this method  相似文献   
86.
The effects of the plasma etching process induced gate oxide damages on device's low frequency noise behavior are investigated on MOSFET's fabricated with different field plate perimeter to gate area ratio antennas. Abnormal 1/f noise spectrum with a shoulder centered in the frequency range of 100 and to 1 kHz was frequently observed in small geometry devices, and it is attributable to a nonuniform distribution of oxide traps induced by plasma etching process  相似文献   
87.
本文实验研究了BHP的浓度对产生O2(1△)的影响。实验结果表明:当BHP浓度大于3.5M时,Cl2利用率以及O2(1△)的产率将不依赖于BHP浓度的变化而变化,同时,实验结果表明,使用低浓度的BHP对COIL的操作是可行的。  相似文献   
88.
C.S. Li  P.K. Hopke 《Indoor air》1992,2(2):84-100
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased.  相似文献   
89.
The authors reply to the comments by Koppelaar and Tolhuizen (see ibid. vol.46, no.9, p.573, 1998). They state that the optimum choice of the slopes used to perform the encoding process in a projection code always results in maximizing the minimum Hamming distance so that d=2 r  相似文献   
90.
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