全文获取类型
收费全文 | 17629篇 |
免费 | 3180篇 |
国内免费 | 525篇 |
专业分类
电工技术 | 682篇 |
综合类 | 1826篇 |
化学工业 | 155篇 |
金属工艺 | 135篇 |
机械仪表 | 1093篇 |
建筑科学 | 411篇 |
矿业工程 | 168篇 |
能源动力 | 45篇 |
轻工业 | 28篇 |
水利工程 | 140篇 |
石油天然气 | 56篇 |
武器工业 | 863篇 |
无线电 | 12329篇 |
一般工业技术 | 559篇 |
冶金工业 | 73篇 |
原子能技术 | 57篇 |
自动化技术 | 2714篇 |
出版年
2024年 | 126篇 |
2023年 | 285篇 |
2022年 | 447篇 |
2021年 | 449篇 |
2020年 | 611篇 |
2019年 | 701篇 |
2018年 | 621篇 |
2017年 | 691篇 |
2016年 | 714篇 |
2015年 | 898篇 |
2014年 | 1252篇 |
2013年 | 1136篇 |
2012年 | 1595篇 |
2011年 | 1580篇 |
2010年 | 1187篇 |
2009年 | 1144篇 |
2008年 | 992篇 |
2007年 | 1299篇 |
2006年 | 1083篇 |
2005年 | 911篇 |
2004年 | 720篇 |
2003年 | 659篇 |
2002年 | 482篇 |
2001年 | 428篇 |
2000年 | 338篇 |
1999年 | 218篇 |
1998年 | 185篇 |
1997年 | 106篇 |
1996年 | 120篇 |
1995年 | 80篇 |
1994年 | 86篇 |
1993年 | 37篇 |
1992年 | 34篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1979年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1962年 | 2篇 |
1961年 | 4篇 |
1960年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
2.
Very high resolution inverse synthetic aperture radar (ISAR) imaging of fast rotating targets is a complicated task. There may be insufficient pulses or may introduce migration through range cells (MTRC) during the coherent processing interval (CPI) when we use the conventional range Doppler (RD) ISAR technique. With compressed sensing (CS) technique, we can achieve the high-resolution ISAR imaging of a target with limited number of pulses. Sparse representation based method can achieve the super resolution ISAR imaging of a target with a short CPI, during which the target rotates only a small angle and the range migration of the scatterers is small. However, traditional CS-based ISAR imaging method generally faced with the problem of basis mismatch, which may degrade the ISAR image. To achieve the high resolution ISAR imaging of fast rotating targets, this paper proposed a pattern-coupled sparse Bayesian learning method for multiple measurement vectors, i.e. the PC-MSBL algorithm. A multi-channel pattern-coupled hierarchical Gaussian prior is proposed to model the pattern dependencies among neighboring range cells and correct the MTRC problem. The expectation-maximization (EM) algorithm is used to infer the maximum a posterior (MAP) estimate of the hyperparameters. Simulation results validate the effectiveness and superiority of the proposed algorithm. 相似文献
3.
4.
A flower‐shaped ultra‐wideband fractal antenna is presented. It comprises a fourth iterative flower‐shaped radiator, asymmetrical stub‐loaded feeding line, and coplanar quarter elliptical ground planes. A wide operating band of 12.12 GHz (4.58‐16.7 GHz) for S 11 ≤ ? 10 dB is achieved along with an overall antenna footprint of 15.7 × 11.4 mm2. In addition, other desirable characteristics, that is, omnidirectional radiation patterns, peak gain upto 5 dB, and fidelity factor more than 75% are achieved. A good agreement exists between the simulation and measured results. The obtained results illustrate that this antenna has wide operating range and compact dimensions than available structures. 相似文献
5.
6.
In this paper, we propose a novel change detection method for synthetic aperture radar images based on unsupervised artificial immune systems. After generating the difference image from the multitemporal images, we take each pixel as an antigen and build an immune model to deal with the antigens. By continuously stimulating the immune model, the antigens are classified into two groups, changed and unchanged. Firstly, the proposed method incorporates the local information in order to restrain the impact of speckle noise. Secondly, the proposed method simulates the immune response process in a fuzzy way to get an accurate result by retaining more image details. We introduce a fuzzy membership of the antigen and then update the antibodies and memory cells according to the membership. Compared with the clustering algorithms we have proposed in our previous works, the new method inherits immunological properties from immune systems and is robust to speckle noise due to the use of local information as well as fuzzy strategy. Experiments on real synthetic aperture radar images show that the proposed method performs well on several kinds of difference images and engenders more robust result than the other compared methods. 相似文献
7.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
8.
对空监视雷达探测威力检飞的几个问题 总被引:5,自引:0,他引:5
以新的观点论证了对空监视雷达探测威力检验飞行中所需的采样点数和飞行架次,讨论了预警机雷达威力检飞的特殊问题,包括地区选择、航线设计和目标机标定等。 相似文献
9.
介绍了某伪码连续波交会对接雷达信号处理机设计.在测距中,提出用噪声较小的载波相位△伪距测量值对伪距进行处理,得到高精度测距值.在测角中,提出了一种干涉仪天线阵结构和干涉仪解模糊算法,针对通道载波相位误差可能引起的解模糊错误,又提出了一种纠正方法,仿真显示,在发生解模糊错误的概率高达0.42的情况下,该方法仍然可以识别并纠正所有解模糊错误.实验表明,该信号处理机可以满足空间航天器交会对接的要求. 相似文献
10.