全文获取类型
收费全文 | 105篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
化学 | 21篇 |
力学 | 5篇 |
数学 | 3篇 |
物理学 | 29篇 |
无线电 | 50篇 |
出版年
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 7篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有108条查询结果,搜索用时 0 毫秒
1.
Hamid Reza Momenian Sousan Gholamrezaei Masoud Salavati-Niasari Behnam Pedram Farhang Mozaffar Davood Ghanbari 《Journal of Cluster Science》2013,24(4):1031-1042
In this work Mg(OH)2, Ca(OH)2, CaCO3, SrCO3 and BaCO3 nanoparticles were synthesized via a simple sonochemical reaction at room temperature. Nanoparticles were synthesized via a surfactant-free reaction solvent water. Nanostructures materials were characterized by scanning electron microscopy, X-ray diffraction and fourier transform infrared spectroscopy. The photocatalytic behavior of nanoparticles was evaluated using the degradation of a methyl orange aqueous solution under ultraviolet light irradiation. The results show that metal hydroxide and metal carbonate nanoparticles are promising materials with excellent performance in photocatalytic applications. 相似文献
2.
3.
Rahim Hekmat Shoar Majid M. Heravi Leila Pedram Shadi Hasan Raeiat Zeinab Jaddi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2563-2567
A facile and rapid synthesis of thio compounds, analogues to ciprofloxacin, and norfloxacin is described. 相似文献
4.
This paper presents a low-power low-noise fully integrated bandpass operational amplifier for a variety of biomedical neural recording applications. A standard two-stage CMOS amplifier in a closed-loop resistive feedback configuration provides a stable ac gain of 39.3 dB at 1 kHz. A subthreshold PMOS input transistor is utilized to clamp the large and random dc open circuit potentials that normally exist at the electrode-electrolyte interface. The low cutoff frequency of the amplifier is programmable up to 50 Hz, while its high cutoff frequency is measured to be 9.1 kHz. The tolerable dc input range is measured to be at least +/- 0.25 V with a dc rejection factor of at least 29 dB. The amplifier occupies 0.107 mm2 in die area, and dissipates 115 microW from a 3 V power supply. The total measured input-referred noise voltage in the frequency range of 0.1-10 kHz is 7.8 microVrms. It is fabricated using AMI 1.5 microm double-poly double-metal n-well CMOS process. This paper presents full characterization of the dc, ac, and noise performance of this amplifier through in vitro measurements in saline using two different neural recording electrodes. 相似文献
5.
The wake in the flow past a circular cylinder has posed a long-standing challenge to scientists since the late 19th century. Many aspects of this seemingly simple phenomenon remain unexplained. Of particular interest is the relationship between the dimensionless vortex shedding frequency (the Strouhal number St) and the ratio of inertial to viscous forces in the fluid (the Reynolds number Re). We propose a new St-Re relation based on the observations of the structure of a vortex street in flowing soap films. The measurements suggest a simple two-parameter form St=1/(A+B/Re) that describes laminar vortex shedding remarkably well for bulk fluids as well as for two-dimensional flowing soap films. 相似文献
6.
An all-fiber, narrowband, tunable polarization controller is proposed and demonstrated. The device is based on coherent acousto-optic mode coupling induced by two orthogonal acoustic waves on a dispersion-compensating fiber. The cooperative coupling between the two polarizations of the core mode and the TE01 cladding mode through the two gratings permits indirect coupling between the two polarizations of the core mode with nearly 100% efficiency, which makes the polarization-controlling function possible. Experimental results verify the operation of the polarization controller with an insertion loss of <1 dB. 相似文献
7.
P. Pedram S. Jalalzadeh S. S. Gousheh 《International Journal of Theoretical Physics》2007,46(12):3201-3208
We present a Chaplygin gas Friedmann–Robertson–Walker quantum cosmological model. In this work the Schutz’s variational formalism is applied with positive, negative, and zero constant spatial curvature. In this approach the notion of time can be recovered. These give rise to Schrödinger–Wheeler–DeWitt equation for the scale factor. We use the eigenfunctions in order to construct wave packets for each case. We study the time dependent behavior of the expectation value of the scale factor, using the many-worlds interpretations of quantum mechanics. 相似文献
8.
Mohammad Reza Majma Hossein Pedram Mehdi Dehghan 《Wireless Personal Communications》2014,78(1):687-714
Lifetime and energy efficiency are important factors in the design of wireless sensor network. A critical issue during data collection is the formation of energy holes near the sink. Sensors which are located near the sink have to participate in relaying data on behalf of other sensors and thus their energy will be depleted very quickly. Mobile sink movement yields the significant performance gained by decreasing the amount of energy consumption. In this paper, we propose an Intelligent Grid Based Data Disseminating protocol for mobile sink in wireless sensor networks. We have utilized a virtual grid as the protocol’s substructure. In our proposed method, cell heads (CHs) will be selected based on the locations of virtual cross points (CPs) and CPs selection is needless to transfer any required data between neighbor nodes. We have optimized CPs selection using linear programming technique in order to increase network lifetime. By selecting the CHs based on our proposed algorithm, data will be disseminated toward the sink. Our data dissemination protocol is simple and has low overhead to construct and maintain. Also, we have presented a new method for sink location update which leads to the least cost in data transfer. Simulation results illustrate that by utilizing hierarchical functionality and selecting appropriate CPs and consequently selecting CHs, energy consumption will be decreased in comparison with other presented methods which directly lead to network lifetime increment. Also by determining an optimal cell size, packet delivery rate will be improved noticeably. 相似文献
9.
Khalili B Jajarmi P Eftekhari-Sis B Hashemi MM 《The Journal of organic chemistry》2008,73(6):2090-2095
New 2-alkyl-5-aryl-(1H)-pyrrole-4-ol derivatives were synthesized via three-component reaction of beta-dicarbonyl compounds with arylglyoxals in the presence of ammonium acetate in water at room temperature. 相似文献
10.
Samples of head-to-head polypropylene have been prepared by the hydrogenation of two polydienes; 1,4-poly(2,4-hexadiene) and 1,4-poly(2,3-dimethyl-1,3-butadiene). Glass transition temperatures were found to be marginally lower than for conventional polypropylene suggesting that the head-to-head placements in the chain increased the polymer flexibility. 相似文献