全文获取类型
收费全文 | 609篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
化学 | 424篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 63篇 |
物理学 | 121篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 31篇 |
2012年 | 32篇 |
2011年 | 54篇 |
2010年 | 35篇 |
2009年 | 30篇 |
2008年 | 36篇 |
2007年 | 48篇 |
2006年 | 34篇 |
2005年 | 29篇 |
2004年 | 33篇 |
2003年 | 26篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有625条查询结果,搜索用时 250 毫秒
41.
Rüdel A Hentges R Becker U Chakraborty HS Madjet ME Rost JM 《Physical review letters》2002,89(12):125503
The dynamics of the photoionization of the two outermost orbitals of C(60) has been studied in the oscillatory regime from threshold to the carbon K edge. We show that geometrical properties of the fullerene electronic hull, such as its diameter and thickness, are contained in the partial photoionization cross sections by examining ratios of partial cross sections as a function of the photon wave number in the Fourier conjugated space. Evaluated in this unconventional manner photoemission data reveal directly the desired spatial information. 相似文献
42.
We describe the mapping of the optical transfer function (OTF) of an incoherent imaging system into a geometrical representation. We show that for defocused traditional and wavefront-coded systems the OTF can be represented as a generalized Cornu spiral. This representation provides a physical insight into the way in which wavefront coding can increase the depth of field of an imaging system and permits analytical quantification of salient OTF parameters, such as the depth of focus, the location of nulls, and amplitude and phase modulation of the wavefront-coding OTF. 相似文献
43.
Trans-hydrogen-bond deuterium isotope effects of Watson-Crick A:U and A:T base pairs of 10 homologous RNA and DNA duplexes are compared. The isotope effect at 13C2 of adenosine residues due to deuterium/protium substitution at the imino H3 site, 2hDelta13C2, is larger in RNA than in DNA. The virtually consistent larger isotope effects in RNA suggest that the N1...N3 hydrogen bonds of A:U base pairs of RNA are stronger than those of the A:T base pairs of DNA. 相似文献
44.
Design and performance evaluation of an ultrasonic motor was discussed in [Wen et al., Thin-disc piezoelectric ultrasonic motor. Part I: design and performance evaluation, Ultrasonics]. Higher precision position control of piezoceramic ultrasonic motor depends on mechanical design and servo control of a very precise and adequate metrology. This paper proposes the design of a driving circuit and controller to deal with non-linearities behavior in the model of piezoceramic-driving ultrasonic motor. The performance of the driver and the effectiveness of the proposed controller are demonstrated by command inputs of sinusoidal and step signals. For comparison purpose, the ultrasonic motor is controlled using two methods: i.e., proportional-integral-derivative (PID) and sliding-mode control (SMC). It was proven that SMC would compensate automatically for unmodeled behaviors such as piezoceramic non-linearities and mechanical stick-slip phenomena. Furthermore, SMC scheme has been successfully applied to position tracking to demonstrate the excellent robust performance in noise rejection. 相似文献
45.
Wen-Hua Zhang Sheau Wei Chien T.S. Andy Hor 《Coordination chemistry reviews》2011,255(17-18):1991-2024
This review summarises some recent developments of the metal complexes of hetero-functional hybrid ligands of C-, N-, O-, P- and S-donors. It highlights the ligand designs, synthetic pathways, structural motifs and catalytic prowess of these complexes. 相似文献
46.
47.
48.
Chyun-Chau Fuh 《Communications in Nonlinear Science & Numerical Simulation》2009,14(4):1032-1037
This paper proposes an approach for detecting unstable periodic orbits embedded in chaotic systems by using the simplex method. The simplex algorithm is easily implemented and does not require the derivatives of the function to be optimized. As a result, it is also applicable to chaotic systems with discontinuities or in which functions contain noise. 相似文献
49.
Chu‐Chang Chen Fuh‐Min Fang Yi‐Chao Li Long‐Ming Huang Cheng‐Yang Chung 《国际流体数值方法杂志》2009,60(1):79-93
The unsteady forces on a square cylinder in sinusoidally oscillating flows with non‐zero‐mean velocities are investigated numerically by using a weakly compressible‐flow method with three‐dimensional large eddy simulations. The major parameters in the analysis are Keulegan–Carpenter number (KC) and the ratio between the amplitude and the mean velocities of the approaching flow (AR). By varying the values of KC and AR the resulting drag and lift of the cylinders are analyzed systematically at two selected approaching‐flow attack angles (0 and 22.5°). In the case of the non‐zero attack angle, results show that both the drag and lift histories can be adequately described by Morison equations. However, Morison equations fail to correctly describing the lift history as the attack angle is zero. In addition, when the ratio of AR/KC is near the Strouhal number of the bluff‐body flow, the resulting drag is promoted due to the occurrence of resonance. Based on the results of systematic analyses, finally, the mean and inertia force coefficients at the two selected attack angles are presented as functions of KC and AR based on the Morison relationships. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
50.