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   416402篇
  免费   31888篇
  国内免费   17800篇
电工技术   24091篇
技术理论   50篇
综合类   29100篇
化学工业   69337篇
金属工艺   23823篇
机械仪表   26403篇
建筑科学   32056篇
矿业工程   13636篇
能源动力   11449篇
轻工业   27818篇
水利工程   7585篇
石油天然气   27578篇
武器工业   3185篇
无线电   44832篇
一般工业技术   46480篇
冶金工业   21689篇
原子能技术   4194篇
自动化技术   52784篇
  2024年   1659篇
  2023年   6363篇
  2022年   11278篇
  2021年   15869篇
  2020年   11975篇
  2019年   9882篇
  2018年   11469篇
  2017年   12928篇
  2016年   11663篇
  2015年   15908篇
  2014年   20152篇
  2013年   24255篇
  2012年   26099篇
  2011年   29032篇
  2010年   25655篇
  2009年   24238篇
  2008年   23773篇
  2007年   22773篇
  2006年   23227篇
  2005年   20552篇
  2004年   13868篇
  2003年   12468篇
  2002年   11493篇
  2001年   10245篇
  2000年   10327篇
  1999年   11126篇
  1998年   8699篇
  1997年   7358篇
  1996年   7008篇
  1995年   5831篇
  1994年   4740篇
  1993年   3260篇
  1992年   2557篇
  1991年   1948篇
  1990年   1526篇
  1989年   1228篇
  1988年   1034篇
  1987年   652篇
  1986年   519篇
  1985年   348篇
  1984年   260篇
  1983年   200篇
  1982年   168篇
  1981年   102篇
  1980年   120篇
  1979年   56篇
  1978年   20篇
  1977年   30篇
  1976年   36篇
  1970年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented  相似文献   
112.
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   
113.
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   
114.
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   
115.
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   
116.
This paper reports a new, highly integrated modular design approach for pulsewidth-modulation AC-AC converters based on a modular phase-bank structure. Novel high-power 3-in-1 integrated bi-directional power modules (IBPM) rated at 1200-V AC and 150 A and the 3-to-1 phase bank circuits have been successfully developed, fabricated and tested. This enables the modularity design of the multiphase converter systems and reduces the critical parasitic inductance. A theoretical analysis of the IBPM's silicon utilization for this new breed of direct power converters has been outlined. A lab prototype at medium power level has been successfully designed, implemented, and tested with good results. A nearly 460-VRMS out voltage at a 1:0.955 voltage transfer ratio, which, perhaps, is the highest performance reported so far in the literature, has been achieved by the novel two-side modulation control system. The converter-fed AC motor system is able to operate over the 0-240 Hz range with inherent regenerative capability and four-quadrant operation. Potential industrial applications are also briefly highlighted in this paper  相似文献   
117.
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   
118.
119.
120.
本文讨论了温度、搅拌和时间三要素对感光乳剂和工艺过程的影响,指出了上述影响的后果和严格过程控制的重要性,提出克服影响的措施。  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