全文获取类型
收费全文 | 11981篇 |
免费 | 1729篇 |
国内免费 | 1588篇 |
专业分类
化学 | 6686篇 |
晶体学 | 144篇 |
力学 | 468篇 |
综合类 | 77篇 |
数学 | 869篇 |
物理学 | 3092篇 |
无线电 | 3962篇 |
出版年
2024年 | 83篇 |
2023年 | 327篇 |
2022年 | 455篇 |
2021年 | 550篇 |
2020年 | 557篇 |
2019年 | 529篇 |
2018年 | 408篇 |
2017年 | 474篇 |
2016年 | 524篇 |
2015年 | 626篇 |
2014年 | 692篇 |
2013年 | 942篇 |
2012年 | 979篇 |
2011年 | 1031篇 |
2010年 | 767篇 |
2009年 | 721篇 |
2008年 | 779篇 |
2007年 | 652篇 |
2006年 | 620篇 |
2005年 | 504篇 |
2004年 | 366篇 |
2003年 | 334篇 |
2002年 | 359篇 |
2001年 | 261篇 |
2000年 | 260篇 |
1999年 | 212篇 |
1998年 | 163篇 |
1997年 | 138篇 |
1996年 | 144篇 |
1995年 | 131篇 |
1994年 | 124篇 |
1993年 | 103篇 |
1992年 | 87篇 |
1991年 | 71篇 |
1990年 | 61篇 |
1989年 | 58篇 |
1988年 | 37篇 |
1987年 | 30篇 |
1986年 | 31篇 |
1985年 | 36篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1959年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
本文根据ITU-T最新的Q.2971协议,以及笔者所从事的实际课题,提出一整套B-ISDN第三层UNI信令的软件实现策略,其特点是能同时满足用户对点到点以及点到多点广播这两种通信方式的要求,而且可以动态配置。 相似文献
12.
13.
提出一种极近距离雷达概念,并导出其作用距离公式,在此基础上研制出一台3mm波段极近距离多普勒雷达样机.试验结果表明该雷达结构简单,成本低廉,在作用距离为零点几米至几米范围内可获得较高的定距精度. 相似文献
14.
Chan C.C. Zheng Ming Zhao Qian C. Meng S. 《Industrial Electronics, IEEE Transactions on》2002,49(6):1342-1344
Based on the concepts of cascade multilevel converters and one-cycle technique, comparisons are conducted to characterize the distortion of the pulsewidth modulation (PWM) and one-cycle control methods that were applied to converters. Simulation results for the different control schemes are obtained in PSIM software initially to see the effect of one-cycle control different from that of PWM control. Through the comparisons, the advantages and disadvantages are identified for each method. The one-cycle scheme is better than PWM control in reducing undesirable harmonics and tracing dynamic waveforms. Simulation and experimental results are also provided to verify the conclusions. 相似文献
15.
Leung V.C.M. Qian N. Malyan A.D. Donaldson R.W. 《Selected Areas in Communications, IEEE Journal on》1994,12(8):1376-1388
A distributed circuit-switched approach for supporting the deployment of high speed wireless personal communication services in urban areas through the interconnection of base stations via metropolitan area networks (MANs) is proposed. Broadband MANs minimize traffic congestion by dynamic sharing of link capacity and by serving as distributed switches for partitioning call control functions. While the DQDB protocol readily supports distributed packet-switching over the IEEE 802.6 MAN, isochronous traffic such as voice and video is best supported by circuit-switched connections. The authors present an enhanced bi-state pre-arbitrated (PA) transport mechanism, and associated call control and handoff management techniques, which enable distributed circuit-switching over the MAN. These capabilities are not currently addressed in the 802.6 standards. The bi-state PA transport mechanism facilitates statistical multiplexing of variable rate isochronous traffic sources. The network capacity is constrained by the call setup delay performance, and is analyzed by simulations. Alternative signaling architectures, involving different placements of call control network elements, are evaluated. The effects of erasure nodes, and close bus versus open bus architectures, are considered. The overlap inter-MAN call setup procedure is proposed to reduce delays. Different call handoff procedures are formulated according to the type of handoff and the resulting change in call connectivity. Most handoffs are intra-MAN, requiring simple procedures with short delays 相似文献
16.
坦克红外特征控制技术评述 总被引:2,自引:1,他引:1
坦克红外特征控制对于提高坦克的战场生存能力具有重要意义。控制的主要方法有遮障、表面处理、外形技术、主动冷却、总体设计等。坦克红外特征的控制必须与其他波段,特别是射频波段的特性控制兼容。遮障和低发射率涂料是现役坦克红外特征控制的主要措施。而对未来的主战坦克,设计应是减少其系统特性的重要途径。 相似文献
17.
采用自行研制的LB自动提膜装置,制备出大面积(10×8cm2)、高质量的PMMA超薄抗蚀剂膜,并将其用于高分辨率铬掩模版的研制。通过电子束曝光,湿法蚀刻,制作了分辨率优于0.5μm,特征线宽0.38μm的4(100mm)铬掩模版。 相似文献
18.
The propagation and dispersion characteristics of picosecond electrical pulses in a suspended coplanar waveguide (SCPW) are investigated, and it is shown that the SCPW is a very promising transmission structure for ultrashort pulses. Numerical results for the modal dispersion of the SCPW are presented and compared to those of the conventional CPW, and a field-coupling theory is used to explain the evolution in the dispersion behavior. An evaluation based on the numerical analysis shows that a SCPW with properly controlled dispersion can exhibit a five times improvement in pulse transmission capability compared to the conventional CPW. Both computer simulations and experimental measurements show a substantial suppression in pulse distortion as well, compared to conventional CPWs 相似文献
19.
20.