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   72752篇
  免费   8302篇
  国内免费   4117篇
电工技术   23108篇
技术理论   2篇
综合类   6297篇
化学工业   6487篇
金属工艺   3749篇
机械仪表   2972篇
建筑科学   6829篇
矿业工程   2368篇
能源动力   1905篇
轻工业   2188篇
水利工程   2786篇
石油天然气   2603篇
武器工业   473篇
无线电   7863篇
一般工业技术   4225篇
冶金工业   2806篇
原子能技术   979篇
自动化技术   7531篇
  2024年   254篇
  2023年   819篇
  2022年   1582篇
  2021年   2092篇
  2020年   2040篇
  2019年   1660篇
  2018年   1588篇
  2017年   2238篇
  2016年   2521篇
  2015年   2817篇
  2014年   5010篇
  2013年   4016篇
  2012年   5743篇
  2011年   6197篇
  2010年   4629篇
  2009年   4835篇
  2008年   4416篇
  2007年   5284篇
  2006年   4886篇
  2005年   3922篇
  2004年   3263篇
  2003年   2905篇
  2002年   2363篇
  2001年   2018篇
  2000年   1768篇
  1999年   1372篇
  1998年   976篇
  1997年   751篇
  1996年   668篇
  1995年   559篇
  1994年   411篇
  1993年   295篇
  1992年   263篇
  1991年   190篇
  1990年   142篇
  1989年   139篇
  1988年   102篇
  1987年   71篇
  1986年   51篇
  1985年   53篇
  1984年   60篇
  1983年   32篇
  1982年   39篇
  1981年   29篇
  1980年   10篇
  1979年   9篇
  1977年   9篇
  1964年   10篇
  1963年   6篇
  1959年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
I.H. Song 《Thin solid films》2007,515(19):7598-7602
This paper is a report on the effect of a single perpendicular grain boundary on the hot-carrier and high current stability in high performance polycrystalline silicon (poly-Si) thin film transistors (TFTs). Under a hot carrier stress condition (Vg = Vth + 1 V, Vd = 12 V), the poly-Si TFT with a single grain boundary is superior to the poly-Si without any grain boundary because of the smaller free carriers available for electric conduction. The shift of transconductance in poly-Si TFT with a single grain boundary is less than 5% after hot carrier stress during a period of 1000 s. The shift of transconductance is about 25% in the case of the poly-Si TFTs without a grain boundary in the channel. On high current stress, the poly-Si TFT without the grain boundary is less degraded than the poly-Si TFT with the grain boundary because the concentrated electric field near the drain junction is lower.  相似文献   
92.
A long thin conducting stripline embedded in a dielectric and centered between two large conducting plates, i.e., the stripline environment, is considered. The stripline is modeled as infinitely long, infinitely thin, and perfectly conducting by first considering a stripline of finite length, thickness, and conductivity in a dielectric layer. Starting from Maxwell's equations and assuming that the current on the stripline is a propagating wave in length direction, asymptotic expressions for the fields inside and in the neighbourhood of the stripline are deduced. These expressions are used to model the stripline in the stripline environment, which leads to a boundary-value problem for the electric potential. This problem is solved by two different approaches, leading to integral equations for the current and for an auxiliary function describing the electric potential. A relation between the current and the auxiliary function is deduced, which is used to obtain asymptotic expressions for current and impedance. Results are compared with a numerical solution of the integral equation for the current and with results in literature.  相似文献   
93.
随着电容测量技术的迅速发展,电容传感器在非电量测量和自动检测中得到广泛应用,但它在使用过程中也存在一些问题,针对在使用电容传感器过程中存在的几个问题,从电容传感器的原理和工作过程两个方面进行了讨论,并提出行之有效的处理方法。  相似文献   
94.
The current study prospectively followed girls with attention-deficit/hyperactivity disorder (ADHD), along with a matched comparison sample, 5 years after childhood neuropsychological assessments. Follow-up neuropsychological measures emphasized attentional skills, executive functions, and language abilities. Paralleling childhood findings, the childhood-diagnosed ADHD group displayed moderate to large deficits in executive/attentional performance as well as in rapid naming relative to the comparison group at follow up (Mage 14.2 years). ADHD-inattentive versus ADHD-combined contrasts were nonsignificant and of negligible effect size, even when a refined, sluggish cognitive tempo subgroup of the inattentive type was examined. Although ADHD versus comparison group differences largely withstood statistical control of baseline demographics and comorbidities, control of childhood IQ reduced executive function differences to nonsignificance. Yet when the subset of girls meeting diagnostic criteria for ADHD in adolescence was compared with the remainder of the participants, neuropsychological deficits emerged even with full statistical control. Overall, childhood ADHD in girls portends neuropsychological and executive deficits that persist for at least 5 years. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
95.
Using conventional high‐temperature superconducting wire, a model superconducting fault current limiter (SFCL) is made and tested. Solenoid coil using Bi2223 silver sheath wire is so made that inductance is as small as possible and a vacuum interrupter is connected in series to it. A conventional reactor coil is connected in parallel. When the fault current flows in this equipment, superconducting wire is quenched and current is transferred into the parallel coil because of voltage drop of superconducting wire. This large current in parallel coil actuates magnetic repulsion mechanism of vacuum interrupter. Due to opening of vacuum interrupter, the current in superconducting wire is broken. By using this equipment, current flow time in superconducting wire can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of parallel coil. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 52–61, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20315  相似文献   
96.
提出一种配电网电容电流测量的新方法,在零序电压互感器的开口三角侧串联一个可调电感,通过注入一个变频恒流信号寻找配电网的谐振频率,改变可调电感的数值后寻找另一谐振频率,联立2个谐振方程求解电容电流,该方法消除了电压互感器漏抗对测量的影响。开发了配电网电容电流测量仪,经模拟试验和现场测试表明,该方法具有安全、快捷、准确等特点,适用于中性点不接地或经随调式消弧线圈接地配电网。  相似文献   
97.
This paper presents the mass transfer results from an impinging liquid jet to a rotating disk. The mass transfer coefficients were measured using the electrochemical limiting diffusion current technique (ELDCT). Rotational Reynolds number (Rer) in the range of 3.4 × 104–1.2 × 105, jet Reynolds number (Rej) 1.7 × 104–5.3 × 104 and non-dimensional jet-to-disk spacing (H/d) 2–8 were taken into consideration as parameters. It was found that the jet impingement resulted in a substantial enhancement in the mass transfer compared to the case of the rotating disk without jet.  相似文献   
98.
光纤复合架空地线雷击断股的分析及试验   总被引:4,自引:2,他引:2  
介绍了光纤复合架空地线(0PGW)雷击断股的特征,讨论了其原因和机理,并进行了0PGW的雷电冲击电波试验,分析了造成断股的影响因素,提出了防止雷击造成0PGW断股的措施。  相似文献   
99.
关于征地制度的思考   总被引:20,自引:0,他引:20  
针对当前农村土地问题的现状.认为调整农村土地关系改革土地制度是解决当前农村问题的关键之一。介绍苏格兰土地改革的经验.提出农村土地转为非农用地的交易中国家应实行限制性措施.可尝试建立“国家失地农民账户”和“国家失地农民保障基金”.从而合理分配土地交易产生的级差收益保障失地农民的合法利益。  相似文献   
100.
The error of solution of Cauchy problems for systems of ordinary differential equations is estimated in the case where the input data are approximate. It is shown how to prepare a program for computing the right-hand sides of the system automatically and simultaneously. Diagrams are presented to illustrate the efficiency of parallelization. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 175–182, March–April 2007.  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