全文获取类型
收费全文 | 844篇 |
免费 | 85篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 33篇 |
综合类 | 111篇 |
化学工业 | 55篇 |
金属工艺 | 10篇 |
机械仪表 | 31篇 |
建筑科学 | 1篇 |
矿业工程 | 3篇 |
能源动力 | 3篇 |
轻工业 | 10篇 |
石油天然气 | 1篇 |
武器工业 | 19篇 |
无线电 | 461篇 |
一般工业技术 | 68篇 |
冶金工业 | 6篇 |
原子能技术 | 1篇 |
自动化技术 | 158篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 11篇 |
2021年 | 23篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 25篇 |
2016年 | 33篇 |
2015年 | 42篇 |
2014年 | 46篇 |
2013年 | 40篇 |
2012年 | 63篇 |
2011年 | 71篇 |
2010年 | 60篇 |
2009年 | 49篇 |
2008年 | 50篇 |
2007年 | 69篇 |
2006年 | 62篇 |
2005年 | 46篇 |
2004年 | 28篇 |
2003年 | 24篇 |
2002年 | 30篇 |
2001年 | 25篇 |
2000年 | 27篇 |
1999年 | 8篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有971条查询结果,搜索用时 31 毫秒
71.
跳频同步信号的最佳干扰 总被引:1,自引:0,他引:1
跳频同步法较普遍以时间信息作为发方发送同步信息,具有跳频周期短、跳频点少、周期性循环规律明显等特点。基于这些特点用干扰同步信号的方式来对跳频同步信号实施同步瞄准式干扰。并探讨了跳频同步信号最佳干扰。 相似文献
72.
73.
在简述重排时频分布主要理论的基础上,具体分析了基于平滑伪Wigner-Ville分布的时频重排(rearrangement of the smooth pseudo Wigner-Ville distribution,RSPWVD)算法和基于Morlet小波的尺度图重排(rearrangement of the Morlet scale chart,RMSC)算法识别信号的基本原理,并导出了各自的重排算法表达式。分析结果表明,RMSC算法不仅可以获得比RSPWVD更为理想的抗干扰效果,而且可进一步提高信号时频分布的时频聚集性,从而更加精确地对跳频信号参数进行盲估计。最后给出了计算机仿真结果,并验证了其可行性和有效性。 相似文献
74.
75.
Takuya Otani Kenji Hashimoto Takaya Isomichi Akira Natsuhara Masanori Sakaguchi Yasuo Kawakami 《Advanced Robotics》2013,27(22):1197-1206
In previous studies, various stabilizing control methods for humanoids during the stance phase while hopping and running were proposed. Although these methods contribute to stability while hopping and running, it is possibility that the control during the flight phase could also affect the stability. In this study, we investigated whether the control during the flight phase can affect the stability of a humanoid while running. To achieve stable hopping, we developed a control system that accounts for the angular momentum of the whole body during the flight phase. In this system, the angular momentum generated by the motion of the lower body in each time interval is calculated during the flight phase, and the trunk joints are controlled to generate the angular momentum necessary to compensate for the deviation of the waist posture, which is used as the reference point for the motion coordinate system of the robot. Once the proposed control system was developed and simulated, we found that the hopping duration in the unconstrained state was extended. 相似文献
76.
A T Oza 《Bulletin of Materials Science》1985,7(5):491-497
The electrical resistivities of organic charge transfer complexes namely dithionaphthalene-iodine (1:1), anthracene-trinitrobenzene
(1:1), pyrene-2I2 and benzidine-tcnq (dichloromethane) have been studied upto 2–8 GPa pressure. An increase in the electrical resistivities shows that the conduction
is due to a hopping mechanism involving localized levels near the band edges or is trap-limited. Pressure can increase both
the density of defects and intermolecular orbital overlap as opposite effects. 相似文献
77.
78.
Polyaniline (PANI) has been blended with cellulose triacetate (CTA) to obtain both good mechanical properties and good electrical
properties. The effects of PANI weight percentage on the optical, structural, morphological and electrical properties in the
blend films of polyaniline and cellulose triacetate (PANI/CTA) have been investigated. The phenomenon of percolation was observed
in these blend films. It is found that the electrical conductivity of the blend films increases with the increase of polyaniline
content up to a value of 10−4 S cm−1 at 84 weight percentage of PANI. The experimental percolation threshold of the dried blend films is obtained at 9.5 wt% of
polyaniline. The values of Mott’s temperature, density of states at the Fermi level [N (E
f)], hopping distance (R
hop), and barrier height (W
hop) for PANI/CTA blend films are calculated. By applying Mott’s theory, it is found that the PANI/CTA blend films obey the three
dimensional variable range hopping mechanism. 相似文献
79.
In this paper, we propose and give the performance of a novel uplink system based on the combination of multi-carrier (MC),
code division multiple access (CDMA) and multiple input multiple output (MIMO) techniques. First, we describe the interests
of spread-spectrum multi-carrier multiple access (SS-MC-MA) scheme for uplink, especially compared to MC-CDMA. Classically,
with SS-MC-MA, each user spreads its data symbols on a specific subset of adjacent or multiplexed subcarriers, to facilitate
the channel estimation and reduce complexity at the reception. In order to compensate for the lack of frequency diversity
of SS-MC-MA with adjacent subcarriers, we first combine it with an orthogonal space-time block code (STBC) and demonstrate
the resulting spatial diversity gain. Then, we propose to allocate the subsets to the different users by applying a frequency
hopping pattern (FH). In that case, each user benefits from the frequency diversity linked to the total bandwidth as with
the multiplexed subcarriers solution, while keeping the advantages of the adjacent subcarriers solution. The gain provided
by the use of the frequency hopping is stressed on. Finally, the performance of this scheme is evaluated over realistic MIMO
channel with channel turbo coding for systems offering asymptotic spectrum efficiency of 1, 2, 3 and 4.5 bit/s/Hz. Thus, the
efficiency of the novel proposed STBC FH SS-MC-MA system as a very promising multiple access and modulation scheme for the
uplink of the future wideband wireless networks is successfully demonstrated. 相似文献
80.
探讨了一种基于FPGA的跳频通信频率合成器的实现方案,重点介绍其原理和电路设计,并给出了FPGA的仿真结果。结果表明该设计行之有效,实现了高度集成化。 相似文献