全文获取类型
收费全文 | 1049篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 801篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 51篇 |
物理学 | 222篇 |
出版年
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 26篇 |
2015年 | 19篇 |
2014年 | 30篇 |
2013年 | 36篇 |
2012年 | 66篇 |
2011年 | 78篇 |
2010年 | 41篇 |
2009年 | 41篇 |
2008年 | 49篇 |
2007年 | 74篇 |
2006年 | 62篇 |
2005年 | 47篇 |
2004年 | 46篇 |
2003年 | 41篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 4篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 12篇 |
1971年 | 4篇 |
排序方式: 共有1091条查询结果,搜索用时 15 毫秒
91.
92.
93.
N. Nücker P. Adelmann M. Alexander H. Romberg S. Nakai J. Fink H. Rietschel G. Roth H. Schmidt H. Spille 《Zeitschrift für Physik B Condensed Matter》1989,75(4):421-422
We present results from electron energy-loss spectroscopy on Nd2–xCexCuO4. There is no clear evidence for Cu1+ but for holes at the oxygen sites. The valency of Ce is found to be close to 3.4. Thus our results do not corroboraten-type superconductivity in this compound. 相似文献
94.
Steady-progressive-wave solutions are sought to the nonlinear wave equation derived previously [J. Fluids Struct. 16 (2002) 597] for flexural motions of an elastic beam traveling in an air-filled tube along its center axis at a subsonic speed. Fluid-structure interactions are taken into account through aerodynamic loading on the lateral surface of the beam subjected to small but finite deflection but end effects and viscous effects are neglected. Linear dispersion characteristics are first examined by exploiting the small ratio of the induced mass to the mass of the beam per unit length. Centered around the traveling speed of the beam, there exists such a narrow range of propagation velocity that the linear steady propagation is prohibited. In this range, it is revealed that some interesting nonlinear solutions exist. The periodic wavetrain is found to exist as the exact solution. Asymptotic analysis is then made by applying the method of multiple scales and the stationary nonlinear Schrödinger equation is derived for a complex amplitude. A monochromatic solution to this equation corresponds to the exact periodic solution. Imposing undisturbed boundary conditions at infinity, it is revealed that the localized solution exists as a result of balance between the linear instability and the nonlinearity. This solution is checked by solving the nonlinear equation numerically. It is further revealed that the amplitude-modulated wavetrain exists not only in the range of the velocity mentioned above but also outside of it. 相似文献
95.
In this paper, we propose a genetic algorithm‐based wavelength selection (GAWLS) method for visible and near‐infrared (Vis/NIR) spectral calibration. The objective of GAWLS is to construct robust and predictive regression models by selecting informative wavelength regions. To demonstrate the ability of the proposed method, regression models for soil properties and sugar content of apples are constructed by using GAWLS and other variable selection methods. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
96.
97.
The ground state absorption (GSA), photoluminescence (PL) and photoluminescence excitation (PLE) spectra for Er(1.0 at%):YAP and Er(0.5 at%):LSO were measured at room temperature. Based on the GSA spectra, the radiative transition rates and luminescence branch ratios of erbium ions were determined by the Judd-Ofelt (J-O) method. In the range of 1400-1700 nm Er(1.0 at%):YAP has intense absorption at 1509 nm (0.96×10−20 cm2), which is almost two times larger than the peak absorption of Er(0.5 at%):LSO. From the PL and PLE spectra, four intense emission bands around 850 nm (4S3/2→4I13/2), 980 nm (4I11/2→4I15/2), 1230 nm (4S3/2→4I11/2) and 1520 nm (4I13/2→4I15/2) were observed. The stimulated emission cross-sections of the four bands were calculated by the Fuchtbauer-Ladenberg (F-L) equation. The results suggest that Er(1.0 at%):YAP has potential to realize laser oscillation at 858 nm because of the relatively large simulated emission cross-section (1.76×10−20 cm2). The temperature dependences of the PL spectra for the two crystals were also investigated in the range of 290-12 K. The ∼1520 nm emission presents continuous increase with temperature, while the emissions around 850, 1230 and 980 nm firstly increase with temperature, then reach their own largest values at the transition temperatures (about 100 K), and finally decrease with temperature. These results were well interpreted by the temperature dependence of multi-phonon process. 相似文献
98.
N. Nakai Y. Nagai M. Machida 《Physica C: Superconductivity and its Applications》2011,471(21-22):743-746
We have performed numerical calculations for low-lying excitations induced by a single non-magnetic impurity in a d-wave superconductor on the basis of two different frameworks. One is the Bogoliubov–de Gennes theory in real coordinates, while the other is the Born approximation in wave-number coordinates. This paper shows that these results for low-lying excitations are identical by using Fourier transformations. 相似文献
99.
Tomoyuki Miyazawa Haruka Abe Takayuki Suzuki Yosuke Togashi Kazuhiro Koshiji Yuki Nonaka 《Journal of carbohydrate chemistry》2013,32(5):252-266
We evaluated the potential of a linear β-1,3-glucan (curdlan) as a starting material to access C6-modified glucose derivatives and found that 6-bromo-6-deoxyglucose, 6-azide-6-deoxyglucose, and 6-acetamido-6-deoxyglucose could be readily prepared from curdlan through its C6-selective and quantitative modifications and subsequent acid-catalyzed hydrolysis. 相似文献
100.
Yosuke Miyamoto 《Geometriae Dedicata》1991,40(2):223-236
A truncated tetrahedron is a building block of hyperbolic 3-manifolds with totally geodesic boundary. We study the relation between the volume of a truncated tetrahedron and the area of its faces which form the boundary of manifolds. 相似文献