全文获取类型
收费全文 | 131742篇 |
免费 | 22068篇 |
国内免费 | 16155篇 |
专业分类
化学 | 92587篇 |
晶体学 | 1666篇 |
力学 | 7848篇 |
综合类 | 1007篇 |
数学 | 16062篇 |
物理学 | 50795篇 |
出版年
2024年 | 424篇 |
2023年 | 2484篇 |
2022年 | 4473篇 |
2021年 | 4697篇 |
2020年 | 5072篇 |
2019年 | 4985篇 |
2018年 | 4596篇 |
2017年 | 4219篇 |
2016年 | 6281篇 |
2015年 | 6241篇 |
2014年 | 7597篇 |
2013年 | 9861篇 |
2012年 | 11871篇 |
2011年 | 12079篇 |
2010年 | 8591篇 |
2009年 | 8261篇 |
2008年 | 8839篇 |
2007年 | 7839篇 |
2006年 | 7414篇 |
2005年 | 6307篇 |
2004年 | 4909篇 |
2003年 | 3958篇 |
2002年 | 3744篇 |
2001年 | 3098篇 |
2000年 | 2687篇 |
1999年 | 2661篇 |
1998年 | 2206篇 |
1997年 | 1922篇 |
1996年 | 1938篇 |
1995年 | 1737篇 |
1994年 | 1528篇 |
1993年 | 1241篇 |
1992年 | 1109篇 |
1991年 | 980篇 |
1990年 | 806篇 |
1989年 | 640篇 |
1988年 | 495篇 |
1987年 | 417篇 |
1986年 | 400篇 |
1985年 | 328篇 |
1984年 | 226篇 |
1983年 | 192篇 |
1982年 | 149篇 |
1981年 | 108篇 |
1980年 | 76篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1976年 | 24篇 |
1975年 | 25篇 |
1957年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper reports that the growth of RuOx(110) thin layer growth on Ru(0001)
has been investigated by means of scanning tunnelling microscope (STM). The STM
images showed a domain structure with three rotational domains of RuOx(110)
rotated by an angle of 120℃.
The as-grown RuOx(110) thin layer is expanded from the bulk-truncated
RuOx(110) due to the large mismatch between RuOx(110) and the
Ru(0001) substrate. The results also indicate that growth of RuOx(110)
thin layer on the Ru(0001) substrate by oxidation tends first to formation
of the Ru-O (oxygen) chains in the [001] direction of RuOx(110). 相似文献
62.
63.
64.
Incomplete LU factorization preconditioning techniques often have difficulty on indefinite sparse matrices. We present hybrid reordering strategies to deal with such matrices, which include new diagonal reorderings that are in conjunction with a symmetric nondecreasing degree algorithm. We first use the diagonal reorderings to efficiently search for entries of single element rows and columns and/or the maximum absolute value to be placed on the diagonal for computing a nonsymmetric permutation. To augment the effectiveness of the diagonal reorderings, a nondecreasing degree algorithm is applied to reduce the amount of fill-in during the ILU factorization. With the reordered matrices, we achieve a noticeable improvement in enhancing the stability of incomplete LU factorizations. Consequently, we reduce the convergence cost of the preconditioned Krylov subspace methods on solving the reordered indefinite matrices. 相似文献
65.
R. A. Ganeev A. I. Ryasnyanskii M. K. Kodirov Sh. R. Kamalov V. A. Li R. I. Tugushev T. Usmanov 《Technical Physics》2002,47(8):991-995
Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported. 相似文献
66.
Chunguang Du Hongyi Chen Shiqun Li 《量子光学学报》2006,12(B08):70-71
Recently, research on left-handed materials (LHMs) has attracted considerable attentions. The LHMs are a kind of metameterial which have negative permittivity and negative permeability, which lead to negative refractive index in a frequency range. The LHMs that have been available so far are in the microwave range and are usually composed of classical particles, such as split-ring resonators. Some quantum phenomena such as spontaneous emission of atoms in the LHMs which are considered to be 'classical background' have also been investigated. Many potential applications of LHMs have been proposed, such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. 相似文献
67.
A FUNDAMENTAL SOLUTION FOR THE LAPLACE OPERATOR ON THE QUATERNIONIC HEISENBERG GROUP 总被引:2,自引:0,他引:2
朱理 《数学物理学报(B辑英文版)》2002,22(3)
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献
68.
69.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
70.
Proton conductivity of phosphoric acid derivative of fullerene 总被引:1,自引:0,他引:1
The proton conductive property of methano [60] fullerene diphosphoric acid has been investigated under various humidity conditions at the temperature range between 15 and 45 °C. It shows proton conductivity as high as 10−2 S cm−1 at 25 °C under relative humidity of 95%. Thermal analyses including TG–DTA and thermal desorption mass spectroscopy (TDS) confirm that the compound is thermally stable up to 200 °C. Proton conduction of the compound depends very much on humidity or water content. The logarithmic conductivity at 25 °C is increased linearly with increasing relative humidity. The activation energy (Ea) estimated from the slope of log(σT) vs. 1/T is decreased from 1.08 to 0.52 eV, as the relative humidity is increased from 40% to 75%. The humidity dependence of conductivity is discussed in the light of the observed hydration isotherm. 相似文献