全文获取类型
收费全文 | 1189篇 |
免费 | 239篇 |
国内免费 | 51篇 |
专业分类
化学 | 64篇 |
晶体学 | 5篇 |
力学 | 360篇 |
综合类 | 9篇 |
数学 | 396篇 |
物理学 | 645篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 22篇 |
2021年 | 33篇 |
2020年 | 39篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 32篇 |
2016年 | 59篇 |
2015年 | 42篇 |
2014年 | 75篇 |
2013年 | 94篇 |
2012年 | 65篇 |
2011年 | 90篇 |
2010年 | 71篇 |
2009年 | 73篇 |
2008年 | 70篇 |
2007年 | 63篇 |
2006年 | 70篇 |
2005年 | 69篇 |
2004年 | 60篇 |
2003年 | 56篇 |
2002年 | 51篇 |
2001年 | 49篇 |
2000年 | 29篇 |
1999年 | 33篇 |
1998年 | 31篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 6篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1479条查询结果,搜索用时 15 毫秒
91.
架设阶段悬索桥静力问题的随机有限元分析 总被引:5,自引:0,他引:5
架设阶段的悬索桥不仅具有显著的几何非线性行为,而且存在材料特性的变异。本文建立了以增量形式表达的非线性摄动法随机有限元列式,并编制了悬索桥静力分析程序SNAP。针对一座国内在建的悬索桥,计算了该桥在某一施工阶段考虑缆索弹性模量随机性时主梁跨中点位移的变化。结果表明,材料随机性的影响十分明显。 相似文献
92.
Changming Huang 《Optics Communications》2011,284(18):4225-17188
We report on the dynamics of semi-localized nonlinear optical modes supported by an interface separating a uniform defocusing saturable medium and an imprinted semi-infinite photonic lattice. Out-of-phase and in-phase kink solitons composed by dark-soliton-like pedestals and oscillatory tails are found. Two branches of out-of-phase kink solitons exist in shallow lattices. Saturable nonlinearity enhances the pedestal height and renormalized energy flow of kink solitons evidently. While in-phase kink solitons are always unstable, out-of-phase kink solitons will be completely stable provided that lattice depth exceeds a critical value. Furthermore, stable kink solitons in the higher band gaps are also possible. Our results may give a helpful hint for understanding the dynamics of kink solitons with high pedestals in other fields. 相似文献
93.
The nonlinear response of the experimental system and the saturation of fringe patterns can induce the fluctuating phase error in the projection grating phase-shifting profilometry. Two major factors of the fluctuating phase error are discussed by simulation. The fluctuating phase error caused by the nonlinear response of the system is four times the frequency of the fringe pattern when the conventional four-frame phase extracting algorithm is used. However, such error can be decreased by five-frame algorithm. On the other hand, the fluctuating phase error caused by the fringe saturation is five times the frequency of the fringe pattern by using conventional five-frame phase extracting algorithm. A novel phase recovering algorithm is used to decrease the phase error caused by the saturation. Furthermore, the applicability range of the proposed phase recovering algorithm is analyzed by simulation and experiments with different saturation degree of the fringe pattern and nonlinearity of the measurement system. 相似文献
94.
ZHAO ChunRan & YE Liu School of Physics & Materials Science Anhui University Hefei China School of Physics & Electronic Information Huaibei Normal University Huaibei 《中国科学:物理学 力学 天文学(英文版)》2011,(3)
A scheme is proposed for generating a multiphoton entangled cluster state among four modes. The scheme only uses Kerr medium, beam splitter and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. The photon in the signal mode is prepared in a superposition state of the vacuum state and one-photon state while the probe beam is initially set in a coherent state superposition. The strong probe mode interacts successively with multiple signal-mode photo... 相似文献
95.
Xiao-Fei ZhangQing Xu Han-Xing LiuWen Chen Min Chen Bok-Hee Kim 《Physica B: Condensed Matter》2011,406(8):1571-1576
Nonlinear dielectric properties of Ba0.6Sr0.4TiO3 ceramics prepared by citrate method were investigated under bias electric field with respect to field history. X-ray diffraction analysis and temperature dependence of the dielectric constant (εr) confirmed a macroscopically paraelectric state for the specimen at room temperature. A slim polarization versus electric field (P-E) hysteresis loop of the specimen at room temperature indicated the existence of polar nano-regions (PNRs) superimposed on the paraelectric background. The nonlinear dielectric properties in continuous cycles of bias field sweep displayed a strong sensitivity to the field history. This phenomenon was qualitatively explained in terms of an irreversible polarization evolution of the PNRs under the bias fields. A considerable decline of the tunability with the cycle number suggests an appreciable contribution of the PNRs to the dielectric nonlinearity. The polarization and size of the PNRs were determined by fitting the dielectric constants to a multipolarization mechanism model. 相似文献
96.
Mitri FG 《Ultrasonics》2011,51(4):496-502
Background and motivation
Generalized Bessel vortex beams are regaining interest from the standpoint of acoustic scattering and radiation force theories for applications in particle rotation, mixing and manipulation. Other possible applications may include medical and nondestructive imaging. To manipulate heavy particles in a host medium, a minimum threshold of the incident sound field intensity is required at relatively high wave amplitudes such that nonlinear wave propagation occurs and the generation of harmonics may be detected. Thus, predictions of the harmonics generation become crucial from the standpoint of experimental design, and the present analysis should assist in the development of more complete models related to the (nonlinear) scattering and radiation forces under such circumstances. The purpose of this research is to construct a theoretical model for the second-harmonic pressure generation associated with a category of non-diffracting Bessel vortex beams known as high-order Bessel vortex beams of fractional typeα (HOBVBs-Fα).Method
The weakly nonlinear wave propagation of a HOBVB-Fα is investigated based on Lighthill’s formalism. Analytical solutions up to the second-order level of approximation are derived and discussed. Closed-form solutions are obtained, which are expressed as a function of first-order quantities available from the classical linear theory. Lateral profiles of the HOBVB-Fα are computed and compared.Results and conclusion
The results show that the beam’s width reduces and becomes narrower, the side-lobes decrease in magnitude, and the hollow region diameter (or null in magnitude) increases as the order of nonlinearity increases. Furthermore, the nonlinearity of the medium preserves the non-diffracting feature of the beam’s second-harmonic generation within the pre-shock range. 相似文献97.
D. Madhavi LathaV.G.K.M. Pisipati C. Rama Chandra PrabhuP.V. Datta Prasad 《Journal of Molecular Liquids》2011,164(3):187-190
The thermodynamic parameters like Moelwyn-Hughes parameter (C1), reduced molar volume (V~), isochoric temperature coefficient of internal pressure (X), Huggin's parameter (F), Gruneisen parameter (Γp), isothermal microscopic Gruneisen parameter, Sharma parameter (So), fraction free volume (f) and (A?) a dimensionless thermal parameter, etc and the Beyer's nonlinearity parameter (B/A) were deduced employing the thermal expansion coefficient derived from density data for the homologues series of compounds terephthalyidene-bis-p-n-alkyl anilines, TBnA with n = 5 to 10,12,14,16 and 18. Further, it is found that the variation of molecular radius, Mr increases with the increase of alkyl chain number, with a core radius of 4.78 Å and the increment for methylene unit is 0.086 Å . The results were discussed with the body of the data available. 相似文献
98.
99.
100.
A scheme is proposed for generating maximally entangled Dicke states among four modes. The scheme only uses Kerr medium and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. The scheme can be generalized to produce maximally entangled 2k-qubit states. 相似文献