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   401891篇
  免费   32543篇
  国内免费   18649篇
电工技术   23770篇
技术理论   46篇
综合类   29067篇
化学工业   66397篇
金属工艺   23339篇
机械仪表   25360篇
建筑科学   30781篇
矿业工程   12895篇
能源动力   10716篇
轻工业   28993篇
水利工程   7795篇
石油天然气   25084篇
武器工业   3228篇
无线电   43956篇
一般工业技术   44281篇
冶金工业   20309篇
原子能技术   4147篇
自动化技术   52919篇
  2024年   1701篇
  2023年   6257篇
  2022年   11264篇
  2021年   15638篇
  2020年   11793篇
  2019年   9722篇
  2018年   11174篇
  2017年   12516篇
  2016年   11508篇
  2015年   15810篇
  2014年   19863篇
  2013年   23888篇
  2012年   26076篇
  2011年   28983篇
  2010年   25741篇
  2009年   24495篇
  2008年   23980篇
  2007年   22799篇
  2006年   22886篇
  2005年   19995篇
  2004年   13633篇
  2003年   11969篇
  2002年   11115篇
  2001年   9816篇
  2000年   9533篇
  1999年   9940篇
  1998年   7512篇
  1997年   6408篇
  1996年   6041篇
  1995年   4969篇
  1994年   4043篇
  1993年   2760篇
  1992年   2171篇
  1991年   1654篇
  1990年   1288篇
  1989年   1045篇
  1988年   864篇
  1987年   559篇
  1986年   433篇
  1985年   270篇
  1984年   217篇
  1983年   174篇
  1982年   144篇
  1981年   78篇
  1980年   103篇
  1979年   54篇
  1978年   26篇
  1977年   33篇
  1976年   41篇
  1975年   15篇
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
51.
The effect of oxygen content on superconductivity of the 2212 and 2223 phase has been studied. By comparing the excess oxygen, the modulation vector, the XRD patterns, and the electric resistivity of 2212 and 2223 phase samples obtained with different post-annealing conditions, i.e., annealing at 600°C or quenching from 860°C, it was found that the super-conductivity is markedly influenced by both the defect distribution in non-Bi layers and the interstitial oxygens incorporated in the Bi-O layers. A tentative explanation for this is given.  相似文献   
52.
By using scanning polarization force microscopy,the deliquescence process and the atomic steps on the cleavage surface of CaCO3 in air were studied in situ.Under an exposure to medium umidity(-57%),the sloiw step movement has been observed.  相似文献   
53.
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   
54.
55.
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   
56.
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   
57.
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   
58.
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   
59.
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   
60.
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   
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