全文获取类型
收费全文 | 508篇 |
免费 | 63篇 |
国内免费 | 56篇 |
专业分类
化学 | 189篇 |
晶体学 | 3篇 |
力学 | 8篇 |
综合类 | 3篇 |
数学 | 17篇 |
物理学 | 74篇 |
无线电 | 333篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 3篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 22篇 |
2016年 | 20篇 |
2015年 | 32篇 |
2014年 | 40篇 |
2013年 | 59篇 |
2012年 | 46篇 |
2011年 | 51篇 |
2010年 | 43篇 |
2009年 | 44篇 |
2008年 | 23篇 |
2007年 | 36篇 |
2006年 | 24篇 |
2005年 | 26篇 |
2004年 | 24篇 |
2003年 | 25篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有627条查询结果,搜索用时 15 毫秒
61.
尝试对第十一届全运会主会场--济南奥林匹克体育中心体育场扩声系统工程进行分析.针对扩声系统工程设计、设备配置和工程施工、使用效果等方面进行了对比和探讨.希望能够给今后国内大型体育设施扩声系统的建设,起到借鉴和帮助作用. 相似文献
62.
东北师范大学体育馆扩声系统具备功能多、稳定性好等特点.设备配置为现场扩声,设备选型均依据国际上先进、经济上合理、使用上安全可靠、维护上便利快捷的原则,保证有良好的扩声效果.本系统采用QSCBASIS系列数字音频处理核心在完成了音频信号的处理和传输的同时,配合QSC可监控的功率放大器,实现功放网络远程监控的功能.在扬声器... 相似文献
63.
为了提高语音信号的质量,降低在语音拾取过程中背景噪声的干扰,设计了以FM1182为核心芯片的系统,该系统使用了双麦克风拾音技术。拾取到的两路信号,分别为混有背景噪声的语音信号和纯噪声信号,经过低噪的前置放大后,进入DSP芯片进行消噪运算,芯片采用AMBIN算法。通过实际电路的测试结果表明,湮没在噪声信号中的语音信号被成功提取。该系统具有集成度高,便携,成本低的特点,在保证有较高噪声处理效率的同时维持超低功耗,消噪效果十分明显,并具有较宽的噪声处理范围。 相似文献
64.
The polyamide 6 (PA6)/isotactic polypropylene (iPP) in situ fibrillation composites are prepared by a novel extrusion die with an assembly of laminating‐multiplying elements (LMEs). The scanning electron micrographs illustrate that the dividing‐multiplying processes in LMEs elongate, break, and stabilize the dispersed PA6 phase in the iPP matrix along the flowing direction (FD). The morphology development of PA6 with different LME numbers greatly affects the rheological properties, crystalline behaviors, and mechanical properties. The dynamic rheological test performed at 195°C shows that the increased spatial restriction of the high‐aspect‐ratio PA6 particles increases the viscoelastic moduli, complex viscosity, and relaxation time. The crystalline analysis reveals that the heterogeneous nucleation becomes predominant and the transcrystalline morphology is observed in those samples produced by more LMEs. The tensile tests indicate that both, breaking strength and elongation, enhanced simultaneously because of the fibrillation of dispersed phase and the improvement in interfacial adhesion between the fibers and the matrix. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
65.
Fangming Xiang Jun Wu Li Liu Ting Huang Yong Wang Chen Chen Ya Peng Chongxi Jiang Zuowan Zhou 《先进技术聚合物》2011,22(12):2533-2542
Immiscible polymer blends usually exhibit negative deviation in mechanical properties compared with the corresponding pure polymers due to the weak interfacial bonding between the two polymers. Due to the bridge effect of the oriented carbon nanotubes (CNTs) on the craze and crack development at the load of stress, CNTs have been proved to be efficient toughening agent for polymers. In this work, functionalized multiwalled carbon nanotubes (FMWCNTs) have been introduced into immiscible high density polyethylene/polyamide 6 (HDPE/PA6) blends through different sample preparation methods. The mechanical measurements demonstrate that, when the nanocomposite is prepared from the HDPE master batch, the sample exhibits excellent tensile strength and toughness simultaneously. For all the nanocomposites, FMWCNTs tend to migrate and/or maintain in PA6 particles, leading to the variation of the crystallization behavior in PA6 phase. Further results based on morphologies characterization indicate that the intensified interfacial adhesion between HDPE and PA6, which is realized by the nano‐bridge effect of FMWCNTs in the interfaces, is the main reason for the largely improved ductility. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
66.
67.
68.
针对强噪音环境中小体积应用场合下的语音增强,设计了一种基于锥型麦克风阵列结构的语音增强方法。该方法充分利用锥形结构中锥底麦克风阵列对锥顶麦克风的良好噪声抵消性能,结合端点检测器和两级自适应滤波器设计的多通道抗串扰噪声抵消算法,实现了强噪音环境中的语音增强。理论分析和仿真验证了锥形结构设计的合理性和优越性,仿真结果表明,改进的多路抗串扰噪声抵消算法应用于此锥形结构的麦克风阵列中可提高语音信号的信噪比,对语音的损伤小,在强噪音环境中语音增强效果显著。 相似文献
69.
《中国邮电高校学报(英文版)》2014,21(6):94-99
This paper studies the behaviors of power amplifier (PA) driven by a single-carrier continuous wave (CW) signal and a two-carrier CW signal both in theory and simulation, and explains why the traditional dual-band PA failed to perform satisfactory results when a two-carrier CW signal is applied to, called concurrently. Besides that, an evaluation standard of concurrent dual-band PA was presented to value its performance. Solution was given with design and fabrication of a concurrent 1.85 GHz/2.65 GHz class F PA, employing a 10W GaN HEMT device from Cree, CGH40010, whose measurement shows the saturated output power is 40.6 dBm and 40.8dBm with drain efficiencies (DE) of 77.4% and 75.3% at 1.85 GHz and 2.65 GHz, respectively. On the other hand, we see that the peak DE achieves 59.7% with an output power of 39.9 dBm in concurrent mode, which follows up with the standard. 相似文献
70.
Cu(L-glu)(bpy)(L-glu = L-glutamato; bpy = 2, 2′-bipyridine) was prepared. Its electronic absorption spectrum and photoacoustic spectrum were recorded at room temperature. They were compared with each other and compared quantitatively with ligand field theory(LFT) and the radical wave function of non-free ions[1–3]. Therefore, the electronic structure was also investigated with its spectrum behaviors and PLFT[1–3]. 相似文献