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   288429篇
  免费   6665篇
  国内免费   3227篇
电工技术   7148篇
技术理论   6篇
综合类   3145篇
化学工业   46624篇
金属工艺   12437篇
机械仪表   9516篇
建筑科学   8741篇
矿业工程   2571篇
能源动力   6353篇
轻工业   28252篇
水利工程   3427篇
石油天然气   7746篇
武器工业   449篇
无线电   30536篇
一般工业技术   52071篇
冶金工业   48491篇
原子能技术   5931篇
自动化技术   24877篇
  2022年   2357篇
  2021年   3664篇
  2020年   2521篇
  2019年   2855篇
  2018年   4214篇
  2017年   4280篇
  2016年   4494篇
  2015年   3890篇
  2014年   6041篇
  2013年   13122篇
  2012年   9530篇
  2011年   12307篇
  2010年   9926篇
  2009年   10418篇
  2008年   11229篇
  2007年   11175篇
  2006年   9952篇
  2005年   8758篇
  2004年   7567篇
  2003年   6954篇
  2002年   6913篇
  2001年   6935篇
  2000年   6511篇
  1999年   6447篇
  1998年   13294篇
  1997年   9938篇
  1996年   7612篇
  1995年   5805篇
  1994年   5331篇
  1993年   5114篇
  1992年   4090篇
  1991年   3833篇
  1990年   3888篇
  1989年   3807篇
  1988年   3575篇
  1987年   3047篇
  1986年   3065篇
  1985年   3415篇
  1984年   3334篇
  1983年   3082篇
  1982年   2706篇
  1981年   2909篇
  1980年   2649篇
  1979年   2841篇
  1978年   2736篇
  1977年   2841篇
  1976年   3693篇
  1975年   2457篇
  1974年   2290篇
  1973年   2320篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp2 content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters  相似文献   
102.
This paper studies a particular single-stage power-factor-correction (PFC) switching regulator employing a discontinuous-conduction-mode (DCM) boost-input cell and a continuous-current-mode (CCM) forward output cell. Although this single-stage PFC regulator can provide a reasonably high power factor when its PFC stage is operating in discontinuous mode, substantial reduction in line-current harmonics is possible by applying a suitable frequency-modulation scheme. This paper derives a frequency-modulation scheme and proposes a practical implementation using a simple translinear analog circuit. A quantitative analysis on the total harmonic distortion (THD) of the line current when the circuit is subject to a limited range of frequency variations is presented along with some considerations for practical design. Experimental data obtained from a prototype confirms the effectiveness of the proposed frequency-modulation scheme. The proposed analog translinear circuit allows custom integrated circuit implementation, making it a viable low-cost solution to the elimination of line-current harmonics in switching regulators  相似文献   
103.
104.
105.
We prospectively studied 10 patients with stable exertional ischaemia, selected from a larger group of patients referred for suspected coronary artery disease or to detect residual ischaemia after myocardial infarction, to evaluate pharmacokinetic changes during chronic treatment with gallopamil and its correlation with clinical efficacy in patients with coronary artery disease. Our study consisted of a 1-week run-in single-blind placebo treatment and a 4-week single-blind gallopamil treatment. At the end of the run-in period patients underwent two different exercise tests, the first 2 hours and the second 7 hours after placebo administration. During active treatment all patients underwent two different exercise tests, the first 2 hours and the second 7 hours after gallopamil (50 mg) administration on the 1st and 28th days of gallopamil therapy. On the same days in eight of the patients we evaluated gallopamil pharmacokinetic changes. Our data revealed a rapid increase of unchanged gallopamil and its metabolite (norgallopamil) in the plasma, and a peak concentration of these substances about 2 hour after oral administration on both the 1st and 28th day of observation. Moreover, our results demonstrated an increase between the first and 28th day of treatment in peak concentration of unchanged gallopamil in the plasma, and of AUC 0-infinity and AUC o-c values during chronic treatment with gallopamil. Our clinical data showed an improvement in exercise results during gallopamil therapy related to increased concentration of the drug.  相似文献   
106.
107.
108.
A Biologically-Parameterized Feather Model   总被引:1,自引:0,他引:1  
Feathers, unlike other cutaneous appendages such as hair, fur, or scales have a definite structure. Variation in feather structure creates a wide range of resulting appearances. Collectively, feather structure determines the appearance of the feather coat, which can largely affect the resulting look of a feathered object (bird). In this paper we define the structure of individual feathers using a parameterization based on biological structure and substructures of actual feathers. We show that our parameterization can generate a large variety of feathers at multiple levels of detail and provide an initial step to semi‐automatically generating a wide range of feather coats. his is achieved by specifying an intuitive interpolation between different structures and ages of feathers.  相似文献   
109.
The authors report an exceedingly rare complication of rheumatoid arthritis, i.e. acquired hemophilia due to anti-factor VIII autoantibody production. Treatment with intravenous immune globulin ensured control of hemorrhagic manifestations by inducing a transient rise in factor VIII level.  相似文献   
110.
A solution to autonomous lateral vehicle guidance using a neurocontroller that can learn from measured human-driving data without knowledge of the physical car parameters is discussed. Simulations and practical tests confirm that a small-size feedforward autonomous neural network (21 neurons) can learn to steer a vehicle at high speeds only from looking at human-driving examples. In this way, the network learns the total closed-loop behavior, including the nonlinear dynamics of the vehicle and the driver's individual driving style. The main result of practical investigations is that the neutral controller trained on human-driving examples exhibits an aperiodic behavior that does not vanish at higher speeds (tests performed up to 130 km/h) and produces fewer lateral deviations than the linear state controller  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