首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14142篇
  免费   730篇
  国内免费   172篇
化学   8828篇
晶体学   105篇
力学   596篇
综合类   4篇
数学   1627篇
物理学   2092篇
无线电   1792篇
  2024年   34篇
  2023年   151篇
  2022年   547篇
  2021年   697篇
  2020年   583篇
  2019年   656篇
  2018年   649篇
  2017年   526篇
  2016年   832篇
  2015年   543篇
  2014年   758篇
  2013年   1416篇
  2012年   1031篇
  2011年   1013篇
  2010年   696篇
  2009年   591篇
  2008年   641篇
  2007年   583篇
  2006年   428篇
  2005年   426篇
  2004年   287篇
  2003年   270篇
  2002年   224篇
  2001年   127篇
  2000年   85篇
  1999年   101篇
  1998年   60篇
  1997年   71篇
  1996年   80篇
  1995年   48篇
  1994年   57篇
  1993年   40篇
  1992年   58篇
  1991年   53篇
  1990年   48篇
  1989年   47篇
  1988年   43篇
  1987年   48篇
  1986年   49篇
  1985年   51篇
  1984年   44篇
  1983年   36篇
  1982年   38篇
  1981年   20篇
  1980年   35篇
  1979年   31篇
  1978年   30篇
  1976年   20篇
  1975年   18篇
  1974年   18篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
In present study, a simultaneous derivatization and air‐assisted liquid–liquid microextraction method combined with gas chromatography–nitrogen phosphorous detection has been developed for the determination of some phenolic compounds in biological samples. The analytes are derivatized and extracted simultaneously by a fast reaction with 1‐flouro‐2,4‐dinitrobenzene under mild conditions. Under optimal conditions low limits of detection in the range of 0.05–0.34 ng mL?1 are achievable. The obtained extraction recoveries are between 84 and 97% and the relative standard deviations are less than 7.2% for intraday (n = 6) and interday (n = 4) precisions. The proposed method was demonstrated to be a simple and efficient method for the analysis of phenols in biological samples. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
12.
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...  相似文献   
13.
Journal of Thermal Analysis and Calorimetry - Modeling and computations are performed to study the ND-Co3O4/EG hybrid nanoliquid mixed convective flow past a vertical porous cylinder. The flow...  相似文献   
14.
15.
Ahmad  Bilal  Jian  Wang  Enam  Rabia Noor  Abbas  Ali 《Wireless Personal Communications》2021,118(2):1055-1073

As per the most recent literature, Orthogonal Frequency Division Multiplexing (OFDM), a multi access technique, is considered most suitable for the 3G, 4G and 5G techniques in high speed wireless communication. What made OFDM most popular is its ability to deliver high bandwidth efficiency and superior data rate. Besides it, high value of peak to average power ratio (PAPR) and Inter Carrier Interference (ICI) are the challenges to tackle down via appropriate mitigation scheme. As a research contribution in the present work, an improved self-cancellation (SC) technique is designed and simulated through Simulink to mitigate the effect of ICI. This novel proposed technique (Improved SC) is designed over discrete wavelet transform (DWT) based OFDM and compared with conventional SC scheme over different channel conditions i.e. AWGN and Rayleigh fading environments. It is found that proposed DWT-OFDM with Improved SC scheme outperforms conventional SC technique significantly, under both AWGN and Rayleigh channel conditions. Further, in order to justify the novelty in the research contribution, a Split-DWT based Simulink model for Improved SC scheme is investigated to analyse the BER performance. This Split-DWT based Simulink model presented here foretells the future research potential in wavelet hybridization of OFDM to side-line ICI effects more efficiently.

  相似文献   
16.
Wireless Networks - The original version of this article unfortunately contained a mistake in the title. The correct title has been published with this erratum.  相似文献   
17.
Research on Chemical Intermediates - A theoretical study on four organic dyes based on bis(4-hexyloxy)triphenylamine as donor and electron acceptor cyanoacrylic acid with a...  相似文献   
18.
In this paper, the deformation of the Heisenberg algebra, consistent with both the generalized uncertainty principle and doubly special relativity, has been analyzed. It has been observed that, though this algebra can give rise to fractional derivative terms in the corresponding quantum mechanical Hamiltonian, a formal meaning can be given to them by using the theory of harmonic extensions of function. Depending on this argument, the expression of the propagator of the path integral corresponding to the deformed Heisenberg algebra, has been obtained. In particular, the consistent expression of the one dimensional free particle propagator has been evaluated explicitly. With this propagator in hand, it has been shown that, even in free particle case, normal generalized uncertainty principle and doubly special relativity show very much different result.  相似文献   
19.
Journal of Thermal Analysis and Calorimetry - The operating temperature of Li-ion batteries used in modern electric vehicles should be maintained within an allowable range to avoid thermal runaway...  相似文献   
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号