全文获取类型
收费全文 | 246篇 |
免费 | 5篇 |
专业分类
化学 | 152篇 |
晶体学 | 4篇 |
力学 | 18篇 |
数学 | 35篇 |
物理学 | 42篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 22篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 30篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 18篇 |
2009年 | 11篇 |
2008年 | 10篇 |
2007年 | 13篇 |
2006年 | 6篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有251条查询结果,搜索用时 31 毫秒
21.
22.
Julien Legault Abderrazak Mejdi Noureddine Atalla 《Journal of sound and vibration》2011,330(24):5928-5948
This paper investigates the effects of finite dimensions on the vibro-acoustic response of orthogonally stiffened panels. Three types of excitations are considered: acoustical excitation, point force excitation and random excitation by a turbulent boundary layer. In each case, a spatially windowed periodic model is compared with a Rayleigh-Ritz model where the modes of the un-stiffened panel are used as the basis functions. The latter model accounts for the reflected wave field generated at the boundaries by assuming that the panel is simply supported. On the contrary, the windowed periodic model only accounts for finiteness on sound radiation (the assumption of an infinite periodic structure is used to calculate the panel response). Numerical studies show that when the bending wavelength becomes comparable or smaller than the stiffener spacing, the periodic model is able to reproduce the results obtained with the Rayleigh-Ritz model. To complement the study, the developed models are compared with numerical simulations (finite element method) and with experimental results. 相似文献
23.
The stability of metal vicinal surfaces with respect to faceting is investigated using empirical potentials as well as electronic structure calculations. It is proven that for a wide class of empirical potentials all vicinal surfaces between (100) and (111) are unstable at 0 K when the role of third and farther nearest neighbors is negligible. However, electronic structure calculations reveal that the answer concerning the stability of vicinal surfaces is not so clear-cut. Finally, it is shown that surface vibrations at finite temperatures have little effect on the stability of vicinal surfaces. 相似文献
24.
Fourier transform infrared spectroscopic approach to the study of the secondary cell wall development in cotton fiber 总被引:1,自引:0,他引:1
Cotton fiber maturity is a major yield component and an important fiber quality trait that is directly linked to the quantity
of cellulose deposited during the secondary cell wall (SCW) biogenesis. Cotton fiber development consists of five major overlapping
stages: differentiation, initiation, polar elongation, secondary cell wall development, and maturation. The transition period
between 16 and 21 dpa (days post anthesis) is regarded to represent a major developmental stage between the primary cell wall
and the SCW. Fourier Transform Infrared spectroscopy was used to investigate the structural changes that occur during the
different developmental stages. The IR spectra of fibers harvested at different stages of development (10, 14, 17, 18, 19,
20, 21, 24, 27, 30, 36, 46, and 56 dpa) show the presence of vibrations located at 1,733 cm−1 (C=O stretching originating from esters or amides) and 1,534 cm−1 (NH2 deformation corresponding to proteins or amino acids). The results converge towards the conclusion that the transition phase
between the primary cell wall and the secondary cell wall occurs between 17 and 18 dpa in fibers from TX19 cultivar, while
this transition occurs between 21 and 24 dpa in fibers from TX55 cultivar. 相似文献
25.
The authors describe an electrochemical sensor for the breast cancer marker α-lactalbumin (αLA). It is based on the use of printed single-walled carbon nanotube (SWCNT) electrodes that were modified with polycatechol. Impedance-derived electrochemical capacitance spectroscopy (ECS) is applied for detection at an applied potential of ?0.14 V vs. Ag/AgCl reference electrode. The electrode was prepared in a two-step process. First, a dispersion of SWCNTs was drop-cast onto the surface of a poly(ethylene terephthalate) substrate to act as the working electrode. Next, catechol was electrochemically polymerized on the SWCNTs, prior to the immobilization of lysozyme. The strong interaction between lysozyme and αLA induced changes in the redox capacitance which are detected by ECS. The latter shows the device to be capable of detecting αLA in the 20 to 80 ng·mL?1 concentration range. The limit of detection is 9.7 ng·mL?1 at an S/N ratio of 3. The device was used to detect αLA in human blood serum with good recovery results. 相似文献
26.
Noureddine Issaoui Najeh Rekik Brahim Oujia Marek J. Wójcik 《International journal of quantum chemistry》2010,110(14):2583-2602
In this article, we extend a previous work toward presenting a theoretical study of the effects of Fermi resonances and the fundamental anharmonic coupling parameter α between the high‐frequency mode and the H‐bond bridge. The model incorporates (i) both intrinsic anharmonicities of the fast mode (double well potential) and the H‐bond Bridge (Morse potential), (ii) strong anharmonic coupling theory, (iii) Fermi resonances by the aid of an anharmonic coupling between the fast mode and one or several harmonic bending modes, (iv) quadratic modulation of both the angular frequency and the equilibrium position of the X? …Y stretching mode on the intermonomer ? H… motions, and (v) the quantum direct (fast and bending modes) and indirect dampings (slow mode). The IR spectral density is obtained by Fourier transform of the autocorrelation function of the transition dipole moment operator of the X? H bond. The numerical calculation shows that Fermi resonances generate very complicated profiles with multisubstructure and also provide a direct evidence of Fermi resonances which were predicted to be a major feature of H‐bonds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
27.
Noureddine Barka Samir Qourzal Ali Assabbane Abderrahman Nounah Yhya Ait-Ichou 《Arabian Journal of Chemistry》2010,3(4):279-283
The photocatalytic degradation of an azo reactive dye, Reactive Yellow 84 (RY84), in aqueous solutions using industrial titanium dioxide coated non-woven paper was studied. The experiments were carried out to investigate the factors that influence the dye photocatalytic degradation, such as adsorption, initial concentration of dye, temperature, and solution pH. The experimental results show that adsorption is an important parameter controlling the apparent kinetics constant of degradation. The photocatalytic degradation rate was favored by a high concentration of solution in respect to Langmuir–Hinshelwood model. The degradation was enhanced by the temperature and was favored in acidic pH range. 相似文献
28.
A nonlocal Levinson beam model is developed to study the free vibrations of a zigzag single-walled carbon nanotube (SWCNT) in thermal environments. The equivalent Young’s modulus and shear modulus for a zigzag SWCNT are derived using an energy-equivalent model. The present study illustrates that the vibration characteristics of an SWCNT are strongly dependent on the temperature change and on the chirality of a zigzag carbon nanotube. The investigation of the chirality and temperature effects on free vibration of carbon nanotubes may be used as a useful reference for the application and the design of nanoelectronic and nanodrive devices, nano-oscillators, and nanosensors, in which carbon nanotubes act as basic elements. 相似文献
29.
Noureddine Mehidi 《Meccanica》2007,42(4):403-407
We first approximate the solutions of the nonautonomous oscillating suspension point pendulum equation by the solutions of
a second order autonomous differential equation. Using the strict monotonicity of the periodic solutions of the approximating
equation, we prove the existence of a large number of subharmonic periodic solutions of the plane pendulum when its point
of suspension is excited parametrically. 相似文献
30.
El Mostafa Daya Bouazza Braikat Noureddine Damil Michel Potier-Ferry 《Comptes Rendus Mecanique》2002,330(5):333-338
By homogenization theory, one can predict the vibrations of long repetitive structures in the low frequency range. Beyond this range, many modes have a modulated shape. Based on a multiple scale analysis, a continuum model is presented, that is able to account for this class of modes. This model involves a real coefficient that can be computed from the finite element resolution of problems defined on a few basic cells. An application in 2D elasticity is presented. To cite this article: E.M. Daya et al., C. R. Mecanique 330 (2002) 333–338. 相似文献