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71.
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Abdelkader Krifa 《Journal of Difference Equations and Applications》2019,25(1):84-96
In this paper, we prove the possibility of optimization of some free parameters of Meixner-like discrete-time linear filters using orthonormal basis functions (OBF) in an analytical way. Since the z-transform of the Meixner filters is impossible and it is possible for Meixner-like filters, we are motivated to study closely the optimization of the Meixner-like's pole. As a result, the differential equation associated with Meixner-like filters has been developed. On the other hand, the effective width of the energy distribution in the transformation domain is a function of the free parameter (Meixner-like pole) and simple signal measurements and can be calculated by the second-order moment. Analytic minimization of the second-order moment gives an optimal value of the free parameter. To validate the effectiveness of the proposed approach, numerical results are used to determine the free parameters. 相似文献
73.
为提高三相逆变器的转换效率,提出了一种新型三相谐振极软开关逆变器拓扑结构,通过在每相桥臂上增加结构简单的辅助电路,实现了主开关的零电压软开通和零电流软关断.逆变器主开关采用金属氧化物半导体场效应晶体管(Metal Oxide Semiconductor Field Effect Transistor,MOSFET)或者绝缘栅双极型晶体管(Insulated Gate Bipolar Transistor,IGBT)时,都能实现无损耗切换,解决了MOSFET内部结电容造成的容性开通损耗问题和IGBT拖尾电流造成的关断损耗问题.分析了电路的工作过程,实验结果表明开关器件完成了软切换.因此,该拓扑结构对于提高逆变器的性能具有重要意义. 相似文献
74.
This paper presents the design of space–time block codes (STBCs) over maximum rank distance (MRD) codes, energy‐efficient STBCs, STBCs using interleaved‐MRD codes, the use of Gaussian integers for STBCs modulation, and Gabidulin's decoding algorithm for decoding STBCs. The design fundamentals of STBCs using MRD codes are firstly put forward for different number of transmit antennas. Extension finite fields (Galois fields) are used to design these linear block codes. Afterward, a comparative study of MRD‐based STBCs with corresponding orthogonal and quasi‐orthogonal codes is also included in the paper. The simulation results show that rank codes, for any number of transmit antennas, exhibit diversity gain at full rate contrary to orthogonal codes, which give diversity gain at full rate only for two transmit antennas case. Secondly, an energy‐efficient MRD‐STBC is proposed, which outperforms orthogonal STBC at least for 2 × 1 antenna system. Thirdly, interleaved‐MRD codes are used to construct higher‐order transmit antenna systems. Using interleaved‐MRD codes further reduces the complexity (compared with normal MRD codes) of the decoding algorithm. Fourthly, the use of Gaussian integers is utilized in mapping MRD‐based STBCs to complex constellations. Furthermore, it is described how an efficient and computationally less complex Gabidulin's decoding algorithm can be exploited for decoding complex MRD‐STBCs. The decoding results have been compared against hard‐decision maximum likelihood decoding. Under this decoding scheme, MRD‐STBCs have been shown to be potential candidate for higher transmit antenna systems as the decoding complexity of Gabidulin's algorithm is far less, and its performance for decoding MRD‐STBCs is somewhat reasonable. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
75.
Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications. 相似文献
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为了实现大直径螺柱焊的自动化,提出了一种基于三菱可编程控制器MELSEC IQ-F驱动伺服电机驱动系统以及气动装置的自动化螺柱焊系统,在详细分析螺柱焊确定自动焊接的过程,给出系统整体实现方案.给出了三台PLC控制11台伺服电机的的拓扑图.给出单工位工作时的系统的动作顺序图,提供了一个良好的操作界面.经实际运行证明设计可行.针对焊接中弧偏吹现象、焊缝受材料及外界干扰等现象,采取齿型双铜极来实现左右电极接触面相等,提升焊接效果,加装软橡胶实现自动纠正接触面不平等情况,产品经厂家使用证明,焊接的产品达到了企业的要求,极大的提升了焊接的质量和工作效率. 相似文献
79.
Laplacian growth without surface tension in filtration combustion: Analytical pole solution
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Oleg Kupervasser 《Complexity》2016,21(5):31-42
Filtration combustion (FC) is described by Laplacian growth without surface tension. These equations have elegant analytical solutions that replace the complex integro‐differential motion equations by simple differential equations of pole motion in a complex plane. The main problem with such a solution is the existence of finite time singularities. To prevent such singularities, nonzero surface tension is usually used. However, nonzero surface tension does not exist in FC, and this destroys the analytical solutions. However, a more elegant approach exists for solving the problem. First, we can introduce a small amount of pole noise to the system. Second, for regularization of the problem, we throw out all new poles that can produce a finite time singularity. It can be strictly proved that the asymptotic solution for such a system is a single finger. Moreover, the qualitative consideration demonstrates that a finger with of the channel width is statistically stable. Therefore, all properties of such a solution are exactly the same as those of the solution with nonzero surface tension under numerical noise. The solution of the Saffman–Taylor problem without surface tension is similar to the solution for the equation of cellular flames in the case of the combustion of gas mixtures. © 2014 Wiley Periodicals, Inc. Complexity 21: 31–42, 2016 相似文献
80.
交错稀疏阵列天线的设计需要实现“稀疏布阵”和“子阵交错机制”两个关键技术的有机“协同”.提出一种基于改进迭代快速傅里叶变换(Fast Fourier Transformation, FFT)算法的均匀面阵交错稀疏布阵机制.鉴于均匀矩形平面阵列天线激励与方向图存在二维傅里叶变换的关系, 该方法通过对均匀面阵方向图采样的频谱能量分析, 采用交错选取子阵激励的方法, 实现了面阵天线方向图频谱能量的均匀分配, 获得了近似相同方向图的交错子阵设计.在此基础上, 采用迭代FFT算法对交错子阵激励进行迭代循环, 有效降低了交错子阵的峰值旁瓣电平.理论分析与实验仿真证明, 相对于基于循环差集和互补差集的稀疏交错优化方法, 该算法实现的交错稀疏阵列设计具有方向图近似程度更高, 且峰值旁瓣电平更低的优点. 相似文献