全文获取类型
收费全文 | 100787篇 |
免费 | 18449篇 |
国内免费 | 20993篇 |
专业分类
化学 | 41296篇 |
晶体学 | 2382篇 |
力学 | 4385篇 |
综合类 | 2201篇 |
数学 | 9081篇 |
物理学 | 28481篇 |
无线电 | 52403篇 |
出版年
2024年 | 519篇 |
2023年 | 1557篇 |
2022年 | 3667篇 |
2021年 | 3520篇 |
2020年 | 3198篇 |
2019年 | 2963篇 |
2018年 | 2820篇 |
2017年 | 4088篇 |
2016年 | 3263篇 |
2015年 | 4963篇 |
2014年 | 6055篇 |
2013年 | 7538篇 |
2012年 | 8204篇 |
2011年 | 8369篇 |
2010年 | 8433篇 |
2009年 | 8684篇 |
2008年 | 9174篇 |
2007年 | 8839篇 |
2006年 | 8408篇 |
2005年 | 6969篇 |
2004年 | 5522篇 |
2003年 | 3999篇 |
2002年 | 3639篇 |
2001年 | 3545篇 |
2000年 | 3360篇 |
1999年 | 1750篇 |
1998年 | 906篇 |
1997年 | 704篇 |
1996年 | 651篇 |
1995年 | 567篇 |
1994年 | 633篇 |
1993年 | 607篇 |
1992年 | 479篇 |
1991年 | 360篇 |
1990年 | 327篇 |
1989年 | 345篇 |
1988年 | 283篇 |
1987年 | 229篇 |
1986年 | 177篇 |
1985年 | 140篇 |
1984年 | 126篇 |
1983年 | 149篇 |
1982年 | 117篇 |
1981年 | 99篇 |
1980年 | 72篇 |
1979年 | 64篇 |
1978年 | 27篇 |
1977年 | 21篇 |
1971年 | 17篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
用长脉冲激光(脉冲宽度150μs,波长1.06μm)辐照高温烧结的YBa_2Cu_3O_(7-x)靶,在6Pa的氧气压强下,巳在(100)YSZ单晶衬底上原位生成YBa_2Cu_(?)O_(7-x)超导膜。衬底置于750℃的加热器上,衬底与靶之间的距离5cm,用该法制得的薄膜光亮坚实,正常态呈金属性,零电阻温度为84.7K。用XRD和SEM对薄膜进行了分析研究。 相似文献
112.
Electroluminescence of a Multi-Layered Organic Light-Emitting Diode Utilizing Trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-Methylphridinium Tetraphenylborate as the Active Layer 下载免费PDF全文
Employing an organic dye salt of trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-methylphridinium tetra\-phenylborate (ASPT) as the active layer, 8-hydrocyquinoline aluminium (Alq3) as the electron transporting layer and N,N’-diphenyl-N,N’-bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD) as the hole transporting layer, respectively, we fabricate a multi-layered organic light-emitting diode and observe the colour tunable electroluminescence (EL). The dependence of the EL spectra on the applied voltage is investigated in detail, and the recombination mechanism is discussed by considering the variation of the hole-electron recombination region. 相似文献
113.
This paper reports on the major progress in the development of an intelligent, interactive and automated system, based on the vector finite element method, and implemented within PDE/Protran problem solving environment. The system is known as WAVEGIDE and was originally developed by the authors for an efficient solution of inhomogeneous dielectric waveguides. In this paper, it has been further extended to the solution of anisotropic waveguiding structures. With our system, through an interactive “question-and-answer” session, which requires minimal knowledge of programming, the problem can be defined using high level PDE/Protran commands. It can then be simply and quickly solved by the main processor within this intelligent environment. To verify the convergence and accuracy of the present approach, numerical results (with respect to the grid density and element order) for a rectangular metallic waveguide half filled with dielectric are given and compared with other finite element methods. Numerical results for an anisotropic dielectric rectangular waveguide are also presented. These results clearly illustrate the accuracy and the ease of use of the modified WAVEGIDE program 相似文献
114.
Ping Liu Zheng-Fan Li Guo-Bing Han 《Electromagnetic Compatibility, IEEE Transactions on》2006,48(3):485-492
In this paper, the asymptotic waveform evaluation (AWE) technique is first applied to the conventional eigenmode expansion method for characterizing a power/ground (P/G) plane pair and analyzing the simultaneous switching noise on such plane pairs for printed circuit boards or multichip modules. The application of AWE avoids a large number of iterations in computing the impedance frequency response of a P/G plane pair structure and greatly reduces the computation time. Meanwhile, to obtain an accurate solution in an entire frequency range, we employ the complex frequency hopping technique which can help select multiple expansion points. In addition, the proposed approach can also be used to characterize the P/G plane pair structures with irregular shapes. Three examples demonstrate its high efficiency and good accuracy. 相似文献
115.
ZHANG Zu-fan DU Hui-ping JIANG Ze Chongqing University of Posts Telecommunications Chongqing China University of Electronic Science Technology of China Chengdu China 《中国邮电高校学报(英文版)》2006,13(4):29-33
1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar… 相似文献
116.
117.
118.
基于移动端多天线系统的无线衰落信道模型 总被引:11,自引:11,他引:0
根据当前无线移动通信对多天线移动接收端性能仿真的要求,讨论并建立了适于空时信号处理的移动端矢量信道模型。通过分析无线移动信道特点。研究了影响接收信号幅度相位的诸多因素,建立了相应的数学模型。并对随机参数选取进行了探讨。其中考虑到移动端接收信号到达角扩散的特点,采用GBSB椭圆模型产生了适于移动端接收信号仿真的随机角度,改进了一种瑞利衰落生成算法。最后信道的数值仿真结果符合理论和经验。同时,通过TD-SCDMA系统链路级仿真,也证明了该信道模型的有效性。 相似文献
119.
120.
The Effects of Filtered Channel Quality Feedback on Throughput of Proportional Fair Algorithm 总被引:1,自引:0,他引:1
1 IntroductionSchedulingalgorithmsarewidelystudiedforwirelesspacketdatasystems,whichgenerallyhavetwobasiccategories,oneisoptimizedforsystemthroughputandfairness[1~ 2 ] ,andtheotherisforthequalityofservice[3~6] .Forsystemswherepack etdataaretimedivisionmultiplexedacrossusersonthedownlink ,orfromBaseStation (BS)tomultipleMobileStations(MS) ,theBSusesschedulingalgo rithmstodecidewhichuseristransmittedto .ItisindicatedinRefs.[7,8]thatschedulingonlyoneus eratatimeisoptimalfromthepointofviewo… 相似文献