全文获取类型
收费全文 | 112881篇 |
免费 | 10923篇 |
国内免费 | 6172篇 |
专业分类
电工技术 | 8016篇 |
技术理论 | 3篇 |
综合类 | 8454篇 |
化学工业 | 17409篇 |
金属工艺 | 6684篇 |
机械仪表 | 7803篇 |
建筑科学 | 9795篇 |
矿业工程 | 3660篇 |
能源动力 | 3020篇 |
轻工业 | 7768篇 |
水利工程 | 2317篇 |
石油天然气 | 5649篇 |
武器工业 | 1100篇 |
无线电 | 13600篇 |
一般工业技术 | 12468篇 |
冶金工业 | 4618篇 |
原子能技术 | 1381篇 |
自动化技术 | 16231篇 |
出版年
2024年 | 412篇 |
2023年 | 1636篇 |
2022年 | 3384篇 |
2021年 | 4782篇 |
2020年 | 3520篇 |
2019年 | 2854篇 |
2018年 | 3160篇 |
2017年 | 3545篇 |
2016年 | 3306篇 |
2015年 | 4798篇 |
2014年 | 5920篇 |
2013年 | 7051篇 |
2012年 | 8065篇 |
2011年 | 8586篇 |
2010年 | 7968篇 |
2009年 | 7778篇 |
2008年 | 7400篇 |
2007年 | 7143篇 |
2006年 | 6623篇 |
2005年 | 5669篇 |
2004年 | 3782篇 |
2003年 | 3244篇 |
2002年 | 3062篇 |
2001年 | 2714篇 |
2000年 | 2344篇 |
1999年 | 2294篇 |
1998年 | 1563篇 |
1997年 | 1421篇 |
1996年 | 1286篇 |
1995年 | 1047篇 |
1994年 | 863篇 |
1993年 | 613篇 |
1992年 | 471篇 |
1991年 | 355篇 |
1990年 | 284篇 |
1989年 | 251篇 |
1988年 | 193篇 |
1987年 | 119篇 |
1986年 | 92篇 |
1985年 | 51篇 |
1984年 | 40篇 |
1983年 | 22篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 30篇 |
1979年 | 18篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics. 相似文献
23.
Shanshan Li Bing Zhang Xuxiang Feng Yewei Wu 《International journal of remote sensing》2019,40(14):5635-5650
Feature-based methods have been developed in the past decades for the registration of optical satellite images. However, it is still a challenging problem to handle well the registration between medium and high spatial resolution images due to the large difference of the spatial structural features and local details for the same objects. In this study, an automated co-registration technique is proposed that integrates an improved SIFT (I-SIFT) and a novel matching strategy called spatial consistency constraints (SCC) to cope with the large difference in spatial resolutions between the image pair. Three constraints on angle, distance, and ratio are introduced to re the initial matching features obtained by I-SIFT. Three groups of experiments were conducted to validate the effectiveness of the proposed method. The experiments used high resolution multispectral and panoramic SPOT 5/6 images and Landsat 5/8 orthorectification images. Experimental results show that the registration error lies in about 1 pixel of high-resolution images and demonstrate that the proposed I-SIFT-SCC approach is suitable for fine registration of optical satellite images from medium spatial resolution to high spatial resolution with resolution ratio up to 6. 相似文献
24.
25.
Ting Cui Ling Xu Feng Ding Ahmed Alsaedi Tasawar Hayat 《International Journal of Adaptive Control and Signal Processing》2020,34(11):1658-1676
Parameter estimation plays an important role in the field of system control. This article is concerned with the parameter estimation methods for multivariable systems in the state-space form. For the sake of solving the identification complexity caused by a large number of parameters in multivariable systems, we decompose the original multivariable system into some subsystems containing fewer parameters and study identification algorithms to estimate the parameters of each subsystem. By taking the maximum likelihood criterion function as the fitness function of the differential evolution algorithm, we present a maximum likelihood-based differential evolution (ML-DE) algorithm for parameter estimation. To improve the parameter estimation accuracy, we introduce the adaptive mutation factor and the adaptive crossover factor into the ML-DE algorithm and propose a maximum likelihood-based adaptive differential evolution algorithm. The simulation study indicates the efficiency of the proposed algorithms. 相似文献
26.
Dan Ye Kaiyu Wang Haijiao Yang Xingang Zhao 《International Journal of Adaptive Control and Signal Processing》2020,34(11):1677-1696
In this article, an adaptive fuzzy output feedback control method is presented for nonlinear time-delay systems with time-varying full state constraints and input saturation. To overcome the problem of time-varying constraints, the integral barrier Lyapunov functions (IBLFs) integrating with dynamic surface control (DSC) are applied for the first time to keep the state from violating constraints. The effects of unknown time delays can be removed by using designed Lyapunov-Krasovskii functions (LKFs). An auxiliary design system is introduced to solve the problem of input saturation. The unknown nonlinear functions are approximated by the fuzzy logic systems (FLS), and the unmeasured states are estimated by a designed fuzzy observer. The novel controller can guarantee that all signals remain semiglobally uniformly ultimately bounded and satisfactory tracking performance is achieved. Finally, two simulation examples illustrate the effectiveness of the presented control methods. 相似文献
27.
28.
29.
Yan Jing Zhu Rongying Wu Fan Zhao Ziyin Ye Huan Hou Mengying Liu Yong Yin Lichen 《Nano Research》2020,13(10):2706-2715
Nano Research - Insufficient intratumoral penetration greatly hurdles the anticancer performance of nanomedicine. To realize highly efficient tumor penetration in a precisely and spatiotemporally... 相似文献
30.