全文获取类型
收费全文 | 13683篇 |
免费 | 2403篇 |
国内免费 | 1888篇 |
专业分类
化学 | 5885篇 |
晶体学 | 271篇 |
力学 | 544篇 |
综合类 | 277篇 |
数学 | 1005篇 |
物理学 | 3666篇 |
无线电 | 6326篇 |
出版年
2024年 | 58篇 |
2023年 | 283篇 |
2022年 | 510篇 |
2021年 | 560篇 |
2020年 | 531篇 |
2019年 | 537篇 |
2018年 | 497篇 |
2017年 | 585篇 |
2016年 | 655篇 |
2015年 | 780篇 |
2014年 | 906篇 |
2013年 | 1196篇 |
2012年 | 1290篇 |
2011年 | 1267篇 |
2010年 | 1065篇 |
2009年 | 1073篇 |
2008年 | 1044篇 |
2007年 | 928篇 |
2006年 | 773篇 |
2005年 | 785篇 |
2004年 | 587篇 |
2003年 | 416篇 |
2002年 | 343篇 |
2001年 | 290篇 |
2000年 | 246篇 |
1999年 | 175篇 |
1998年 | 84篇 |
1997年 | 90篇 |
1996年 | 90篇 |
1995年 | 67篇 |
1994年 | 39篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1959年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
51.
超宽带通信技术及其在军事通信方面的应用 总被引:2,自引:0,他引:2
本文给出了超宽带(Ultra-wide Bandwidth:UWB)系统的信号表示形式,分析了其具体含义、信号特点及UWB通信系统的性能,结合当前军事通信的特点及发展趋势,介绍了超宽带脉冲通信在军事通信领域的应用现状及前景。 相似文献
52.
Fiber Bragg grating (FBG) technology has been de-veloped rapidlyinrecent years ,and has beenextensivelystudied in today′s optical communication and sensingsystems . Because of the linearity between the Braggwavelength and outside environmental parameters ,theaxial strain response of FBGhas been fullyinvestigatedand usedin measurement for strain,pressure,andther-mal expansion coefficient etc . By contrast ,fewstudieshave been carried out onthe transverseload response ofFBG[1-3].Gafsi and … 相似文献
53.
Lightweight Triboelectric Nanogenerator for Energy Harvesting and Sensing Tiny Mechanical Motion 下载免费PDF全文
Tao Li Ying Xu Magnus Willander Fei Xing Xia Cao Ning Wang Zhong Lin Wang 《Advanced functional materials》2016,26(24):4370-4376
Triboelectric nanogenerators (TENGs) have shown exciting applications in mechanical energy harvesting and self‐powered sensing. Aiming at commercial applications, cost reduction and simplification of TENG structures are of great interest. In this work, a lightweight TENG based on the integration of polymer nanowires and a carbon sponge, which serves both as the substrate and an electrode, are reported. Because of the low density of the carbon sponge and the filmy nanowires, the device exhibits a total mass of less than 0.1 g for a volume of 12.5 cm3 and it produces a short‐circuit current of 6 μA, open‐circuit voltage of 75 V, and a maximum output power of 0.28 W kg?1 under light finger tapping. The device can linearly measure the acceleration at a detection limit down to 0.25 m s?2 and for a detection range from 0.25 m s?2 to 10.0 m s?2. 相似文献
54.
55.
This paper presents all-digital time-mode \(\Delta \Sigma\) modulators. The proposed modulators consist of a voltage-to-time integrator, a seven-stage gated ring oscillator functioning as a 3-bit quantizer, and seven digital differentiators. A detailed analysis of the nonlinear characteristics of the modulators is provided. Designed in IBM 130 nm 1.2 V CMOS technology with a 100 mV 100 kHz sinusoidal input and a 4.4 MHz frequency clock, the first-order modulator provides 47 dB SNR over 0–150 KHz bandwidth while consuming 1.1 mW while the second-order modulator provides 55 dB SNR over the same bandwidth while consuming consumes 1.45 mW. 相似文献
56.
文中给出回传通道调试的相关研究成果,介绍回传通道的前端信号处理、光纤链路调节、电缆分配网设置的方法,提出采用等效数字调制信号源、通过测试回传通道NPR性能评价回传通道质量的实用测试方法. 相似文献
57.
Zihao Zhang Zirong He Nan Wang Fengmei Wang Chongyu Du Jiafeng Ruan Qin Li Dalin Sun Fang Fang Fei Wang 《Advanced functional materials》2023,33(27):2214648
Rechargeable aqueous zinc batteries are promising energy storage devices because of their low cost, high safety, and high energy density. However, their performance is plagued by the unsatisfied cyclability due to the dendrite growth and hydrogen evolution reaction (HER) at the Zn anode. Herein, it is demonstrated that the concentrated hybrid aqueous/non-aqueous ZnCl2 electrolytes constitute a peculiar chemical environment for not only the Zn-ions but also water molecules. The high concentration of chloride ions substitutes the H2O molecular in the solvation structure of Zn2+, while the acetonitrile further interacts with H2O to decrease its activity. The hybrid electrolytes both inhibit the dendrite formation and HER, enabling an ultrahigh average Coulombic efficiency of 99.9% in the Zn||Cu half-cell and a highly reversible Zn plating/stripping with a low overpotential of 21 mV. Using this hybrid electrolyte, the Zn||polytriphenylamine (PTPAn) full cell deliveres a high discharge capacity of 110 mAh g−1, a high power density of 9200 W kg−1 at 100 °C and maintains 85% of the capacity for over 6000 cycles at 10 °C. This study provides a deep understanding between the solvation structure and columbic efficiency of Zn anode, thus inspiring the development for stable Zn batteries. 相似文献
58.
Jie Lian Yun Liu Zhen-Jiang Zhang Jun-Jun Cheng Fei Xiong 《电子科技学刊:英文版》2012,10(4):368-377
Based on user’s in-degree distribution, traditional ranking algorithms of user’s weight usually neglect the considerations of the differences among user’s followers and the features of user’s tweets. In order to analyze the factors which impact on user’s weight, under the analysis of the data collected from SINA Microblog network, this paper discovers that user influence and active degrees are the dominant factors for this issue. The proposed algorithm evaluates user influence by user’s follower number, the influence of user’s followers and the reciprocity between users. User’s active degree is modeled by user’s participation and the quality of user’s tweets. The models are tested by different data groups to confirm the parameters for the final calculation. Eventually, this paper compares the computational results with the user’s ranking order given by the SINA official application. The performance of this algorithm presents a stronger stability on the fluctuant range of the value of user’s weight. 相似文献
59.
时间触发以太网(TTE)将通信任务通过合理的调度定时触发发送,保证了消息的实时性和安全关键性.提出了一种基于时隙分区的时间触发以太网任务调度算法,该算法通过获取网络拓扑结构中的交换机信息,对各端系统的时刻调度表进行分区,并根据TT流量路由配置信息将其发送时刻配置在相应分区中,从而保证了TT流量在物理链路中的无冲突传输.同时,该算法使分散的网络资源得以整合,减少了RC流量的延迟并且避免了网络资源的浪费.实验结果表明,所提算法在保证TT流量可调度的同时,具有网络资源整合和运算速度方面的优势. 相似文献
60.