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排序方式: 共有419条查询结果,搜索用时 15 毫秒
11.
Witchayani Bungthong Parinya Amornsettachai Penporn Luangchana Boontharika Chuenjitkuntaworn Suphachai Suphangul 《Molecules (Basel, Switzerland)》2022,27(3)
This prospective clinical study aimed to evaluate the peri-implant hard tissue dimensional change at 6 months of immediate implant placement with bone graft materials in the posterior area using cone-beam computed tomography (CBCT). Twelve dental implants were placed concurrently following tooth extraction in the posterior area and filled with xenograft particles. The CBCT images were taken immediately after surgical procedures and then at 6 months follow-up. To evaluate the hard tissue changes, the vertical and horizontal bone thickness were analyzed and measured using ImageJ software. Paired t-test or Wilcoxon match-pair signed-rank test was done to analyze the changes of hard tissue values at the same level between immediately and 6 months following immediate implant placement. Independent t-test or Mann–Whitney U test was used to analyze the dimensional change in the vertical and horizontal direction in buccal and lingual aspects. The level of significance was set at p value = 0.05. All implants were successfully osseointegrated. At 6 months follow-up, the vertical bone change at the buccal aspect was −0.69 mm and at the lingual aspect −0.39 mm. For horizontal bone thickness, the bone dimensional changes at 0, 1, 5, and 9 mm levels from the implant platform were −0.62 mm, −0.70 mm, −0.24 mm, and −0.22 mm, respectively. A significant bone reduction was observed in all measurement levels during the 6 months after implant placement (p value < 0.05). It was noted that even with bone grafting, a decrease in bone thickness was seen following the immediate implant placement. Therefore, this technique can be an alternative method to place the implant in the posterior area. 相似文献
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This paper investigates the exact and approximate spectrum assignment properties associated with realizable output-feedback pole-placement type controllers for single-input single-output linear time-invariant time-delay systems with commensurate point delays. The controller synthesis problem is discussed through the solvability of a set of coupled diophantine equations of polynomials. An extra complexity is incorporated to the above design to cancel extra unsuitable dynamics being generated when solving the above diophantine equations. Thus, the complete controller tracks any arbitrary prefixed (either finite or delaydependent) closed-loop spectrum. However, if the controller is simplified by deleting the above mentioned extra complexity, then the robust stability and approximated spectrum assignment are still achievable for a certain sufficiently small amount of delayed dynamics. Finally, the approximate spectrum assignment and robust stability problems are revisited under plant disturbances if the nominal controller is maintained. In the current approach, the finite spectrum assignment is only considered as a particular case to the designer‘s choice of a (delay-dependent) arbitrary spectrum assignment objective. 相似文献
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为解决滤波器带外抑制和通带内相位波动之间的矛盾,该文介绍了一种线性相位LC滤波器的设计方法,通过对滤波器传输零点特性进行分析,根据指标要求灵活设计电路拓扑结构和零点位置,采用内、外均衡电路级联网络两种方法,来实现具有高矩形、线性相位特性的滤波器。设计了中心频率21.4 MHz、0.5 dB带宽大于10 MHz、矩形系数(45 dB/0.5 dB)小于2、带内相位波动绝对值小于5°和中心频率1 300 MHz、1 dB带宽大于200 MHz、矩形系数(35 dB/1 dB)小于2、带内相位波动绝对值小于5°两款滤波器。该方法工程实用化强,便于调试和制作,可应用于幅相特性要求高的微波系统中,提高了系统性能指标。 相似文献
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负载惯量和外界干扰是影响贴片机X,Y轴快速高精度定位的两个关键因素。本文针对负载惯量和外界干扰对控制性能的影响,提出了基于RBF神经网络的自适应滑模控制算法。利用RBF神经网络的万能逼近特性实现对外加干扰和被控对象模型信息的逼近,运用自适应控制算法计算前馈补偿量以补偿负载惯量和摩擦力对运动性能的影响,采用滑模控制算法以抑制其他不确定干扰对运动控制的影响。通过仿真分析可以得出,所采用的控制算法能够有效地补偿负载惯量和外界干扰对定位性能的影响,从而实现贴片机X,Y轴的快速高精度定位。 相似文献
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针对Openstack的高可用性问题,目前大部分的研究都集中在控制节点的高可用上,对于虚拟机的高可用研究较少.已有的虚拟机高可用方案存在无法适应多种故障场景、无法针对单个虚拟机粒度进行故障处理等问题.本文提出了一种基于Openstack的虚拟机高可用方案,方案使用控制组件和代理服务组件,配合不同故障的检测逻辑,实现多种... 相似文献
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在MEMS麦克风贴片工艺中,真空吸嘴吸取MEMS芯片以后需要进行芯片位姿的精确校正。为实现高速高精度贴片功能,提出了一种基于旋转式反射镜的飞行视觉系统,该方案利用齿轮齿条将吸嘴的升降运动转化为反射镜的旋转运动,通过设计齿轮参数,实现反射镜不干涉吸嘴的拾放功能。当反射镜旋转到与水平位置夹角呈45°时,视觉系统可以获得MEMS芯片的静止的清晰图像,CCD相机采集一幅图像后,在贴片头飞行的过程中,控制系统完成MEMS芯片的位置和角度的校正。实验结果表明,该系统可以获取高质量MEMS芯片图像。该系统结构简单紧凑,成像无失真,不限制贴片头的运动轨迹,显著提高了MEMS芯片的贴片质量和贴片效率,可广泛地应用于贴片机系统中。 相似文献
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In this paper a multi-input, multi-output (MIMO) active noise control system with the aim of global reduction of broadband noise in a telephone kiosk is addressed. The model selected for this optimization problem is the acoustic environment of an enclosure taking into account the effect of coupling of secondary sources used for control purpose. This optimization involves finding the best locations for loudspeakers and microphones inside the enclosure as well as optimizing the control signals considering secondary source coupling.Previous results show that in order to be able to reduce acoustic noise globally inside the enclosure, the frequency range of 50-300 Hz must be selected for control purpose. The mean of acoustic potential energy of the enclosure, when excited in this frequency range, is adopted as a performance measure. This performance index is penalized with the power of the signal required to excite secondary loudspeakers, in order to avoid placements that may need high voltage power amplifier for a desired performance. To find the solution of this problem, i.e. the global minimum of the performance index, several genetic algorithms are proposed and compared. In order to attain the best achievable performance in reaching the global minimum, the parameters of these genetic algorithms are tuned, and used for optimization purpose. Numerical simulations of the acoustical potential energy as well as the sound pressure at different heights of the kiosk, when active noise control (ANC) system operates, confirm the optimality of the locations proposed by the genetic algorithm. 相似文献
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