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   397篇
  免费   10篇
  国内免费   11篇
化学   71篇
力学   5篇
数学   4篇
物理学   27篇
无线电   311篇
  2024年   1篇
  2023年   2篇
  2022年   7篇
  2021年   9篇
  2020年   6篇
  2019年   6篇
  2018年   6篇
  2017年   6篇
  2016年   6篇
  2015年   10篇
  2014年   22篇
  2013年   27篇
  2012年   23篇
  2011年   24篇
  2010年   22篇
  2009年   44篇
  2008年   23篇
  2007年   32篇
  2006年   32篇
  2005年   23篇
  2004年   17篇
  2003年   17篇
  2002年   13篇
  2001年   12篇
  2000年   4篇
  1999年   5篇
  1998年   3篇
  1996年   3篇
  1995年   2篇
  1992年   1篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1987年   1篇
  1985年   1篇
  1977年   2篇
  1976年   1篇
排序方式: 共有418条查询结果,搜索用时 15 毫秒
151.
基于CMOS摄像头的智能车路径跟踪系统设计   总被引:3,自引:1,他引:3  
李国柱 《现代电子技术》2011,34(18):12-14,17
设计了一种能自动识别和跟踪路径的智能车系统。用以MC9S12XS128作为核心控制器,利用COMS图像传感器OV6620作为路径信息采集装置,通过对采集图像进行二值化处理、去噪操作、边缘检测和断点修补后提取出路径中心信息。利用最小二乘法对路径中心信息进行直线拟合,根据拟合直线的参数计算舵机控制量。对舵机采用PD控制算法,根据舵机转向角设定小车的速度,并对小车实行转角和速度的实时控制。实验证明,该智能车系统能够沿着黑色赛道快速稳定地自动行驶,实现了路径识别与跟踪。  相似文献   
152.
Adaptive systems identification has been widely studied, but most studies have focused on the convergence of these methods. Applications of equalization systems have also received much attention. This paper presents a new combination of adaptive Broadband Radio Access Networks (BRAN) channel identification algorithms for multicarrier code division multiple access (MC‐CDMA) systems downlink equalization. In fifth‐generation (5G) wireless communications, MC‐CDMA is expected to support the associated networks. The BRAN E channel parameters, representing an outdoor scenario normalized for MC‐CDMA systems, are identified using a recursive least mean pth power algorithm with logarithmic transformation (RlogLMP). For validity and test aim, this algorithm is compared with the existing recursive least square (RLS) and least mean square (LMS) algorithms. Moreover, we use the estimated coefficients in the adaptive equalization problem. We give a review of the threshold orthogonality restoring combining (TORC) equalizer, which is coupled with the presented algorithms to counteract channel fading, as evaluated by the bit error rate (BER). Our performance results show that the RlogLMP algorithm can estimate the measured BRAN E channel with good efficiency for various values of the signal‐to‐noise ratio (SNR), as compared with the classical algorithms RLS and LMS. In adaptive equalization problems, the achieved results demonstrate that two thresholds ρTH in the TORC equalizer minimize the performance degradation, in terms of the BER, of the MC‐CDMA system under multipath channel fading with very good accuracy, especially if the coefficients are estimated with the specific case of the power p in the RlogLMP algorithm.  相似文献   
153.
基于锁相环的低频函数发生器   总被引:1,自引:0,他引:1  
介绍了锁相环的原理以及Freeseale公司的锁相环频率合成器件MC145151-2的主要特点,给出了MC145151-2和ICL8038低频锁相环函数发生器的工作原理、设计思想、电路结构、模块设计方法及其电路原理图。  相似文献   
154.
陈卫民  李曦  张保平 《电子工程师》2004,30(9):i006-i008
介绍了以Motoro1a MC683 32单片机为基础,由作者自行开发的电力信号检测监控系统.首先简单讲述MC68332单片机和电力信号的特点,然后从总体框架基础上介绍了本系统的硬件和软件结构以及相关的实现方法.  相似文献   
155.
介绍MOTOROLA公司锁相频率合成器MC145170的内部结构及特点,实际应用中的问题考量,基于MC145170的环路滤波器的设计方案,该方案可较好地满足工程设计中对相位噪声的要求。  相似文献   
156.
A theoretical treatment is proposed for the determination of the distribution characteristics of a solubilizate between micellar and aqueous phases from the variation of the critical micelle concentration (CMC) with the molar ratio of components in the system. The theory has been tested by determining the distribution coefficient and free energy of solubilization of n-butanol in the n-butanol/sodium dodecyl sulphate/water system from CMC values determined by conductimetric techniques.  相似文献   
157.
Three polycaprolactam samples modified by 0.05—0.50% polyphenylquinoxaline(PPQ)by weight were prepared.Their structure and mechanical properties were characterized by FT-IR, SEM, density, tensile, impact, DTAand visco-elastic method, PPQ induced the formation of "crystal grains" distributed evenly over nylon spherulites in modified samples, which were observed for the first time, and strengthened modified samples. Modified nylons had higher crystallinities, higher T_g, more nearly perfect spherulites than MC nylon itself, and showed typical reinforcing effect on mechanical properties.  相似文献   
158.
From the past decade, the multicarrier code division multiple access (MC‐CDMA) transmission schemes have placed major role in wireless communications. It is providing a secured wireless communication to the users with guaranteed performance. In many situations, the performance of the MC‐CDMA is restricted due to the interference caused by multiple access interference (MAI), which also influences the frameworks of CDMA. To overcome this issue, we concentrated on developing the efficient technique for data transmission with interference cancellation for downlink MC‐CDMA. In the proposed method, the interference cancellation procedure is done by using the regeneration and subtraction of MAI from the signal. The simulation results are evaluated using the MC‐CDMA system with different decision functions. Results proved that the proposed system is efficient in reducing the MAI along with an improved bit error rate (BER).  相似文献   
159.
Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm–3 and 0.25 mol dm–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below.  相似文献   
160.
An electrochemical biosensor for the detection of microcystin has been developed based on the inhibition of the protein phosphatase 2A (PP2A) by this cyanobacterial toxin. The enzyme has been immobilised by entrapment using a poly(vinyl alcohol) azide-unit pendant water-soluble photopolymer (PVA-AWP). Electrode supports and immobilisation conditions have been optimised by colorimetric assays, the highest immobilisation yields being obtained with screen-printed graphite electrodes and the 1:2 PP2A:PVA ratio. Catechyl monophosphate (CMP), α-naphthyl phosphate (α-NP) and 4-methylumbelliferyl phosphate (4-MUP) have been used as phosphorylated substrates to monitor the protein phosphatase activity by electrochemical methods, the former providing the highest chronoamperometric currents at appropriate working potentials (+450 mV versus Ag/AgCl). Incubation with standard microcystin solutions has demonstrated the inhibition of the immobilised enzyme, proportional to the toxin concentration. The standard inhibition curve has provided a 50% inhibition coefficient (IC50) of 83 μg L−1, a limit of detection (LOD; 35% inhibition) of 37 μg L−1, and 100% inhibition at about 1000 μg L−1. Real samples of cyanobacterial blooms from the Tarn River (Midi-Pyrénées, France) have been analysed using the developed amperometric biosensor and the toxin contents have been compared to those obtained by a conventional colorimetric protein phosphatase inhibition (PPI) assay and high-performance liquid chromatography (HPLC). The results clearly justify the use of the developed amperometric biosensor as screening method for microcystin detection.  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