全文获取类型
收费全文 | 1451篇 |
免费 | 17篇 |
国内免费 | 13篇 |
专业分类
化学 | 920篇 |
晶体学 | 5篇 |
力学 | 19篇 |
综合类 | 1篇 |
数学 | 297篇 |
物理学 | 239篇 |
出版年
2021年 | 11篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 19篇 |
2013年 | 71篇 |
2012年 | 61篇 |
2011年 | 70篇 |
2010年 | 41篇 |
2009年 | 29篇 |
2008年 | 67篇 |
2007年 | 65篇 |
2006年 | 68篇 |
2005年 | 65篇 |
2004年 | 61篇 |
2003年 | 55篇 |
2002年 | 62篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 22篇 |
1998年 | 8篇 |
1997年 | 18篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 23篇 |
1984年 | 39篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 9篇 |
1979年 | 26篇 |
1978年 | 29篇 |
1977年 | 25篇 |
1976年 | 28篇 |
1975年 | 26篇 |
1974年 | 23篇 |
1973年 | 20篇 |
1972年 | 14篇 |
1971年 | 8篇 |
1968年 | 9篇 |
排序方式: 共有1481条查询结果,搜索用时 62 毫秒
31.
Allwyn G Cole Laurie M Yoder Joseph J Shiang Neil A Anderson Larry A Walker Mark M Banaszak Holl Roseanne J Sension 《Journal of the American Chemical Society》2002,124(3):434-441
An ultrafast transient absorption study of the primary photolysis of ethyl- and n-propylcobalamin in water is presented. Data have been obtained for two distinct excitation wavelengths, 400 nm at the edge of the UV gamma-band absorption, and 520 nm in the strong visible alphabeta-band absorption. These data are compared with results reported earlier for the B(12) coenzymes, methyl- and adenosylcobalamin. The data obtained for ethylcobalamin and n-propylcobalamin following excitation at 400 nm demonstrate the formation of one major photoproduct on a picosecond time scale. This photoproduct is spectroscopically identifiable as a cob(II)alamin species. Excitation of methyl-, ethyl-, and n-propylcobalamin at 520 nm in the low-lying alphabeta absorption band results in bond homolysis proceeding via a bound cob(III)alamin MLCT state. For all of the cobalamins studied here competition between geminate recombination of caged radical pairs and cage escape occurs on a time scale of 500 to 700 ps. The rate constants for geminate recombination in aqueous solution fall within a factor of 2 between 0.76 and 1.4 ns(-1). Intrinsic cage escape occurs on time scales ranging from 相似文献
32.
Larry I. Amstutz Horst Meyer Samuel M. Myers
Robert L. Mills
《Journal of Physics and Chemistry of Solids》1969,30(12):2693-2697Measurements of T1 in the hep phase of H2, over the temperature range 2°–12°K and the ortho concentration range between 0.5 and 0.97 are presented. At temperatures below 10°K, the thermally activated self-diffusion is negligible and the mechanism for nuclear relaxation is that attributed by Moryia and Motizuki and by Harris to intramolecular dipolar interaction, modulated by intennolecular electric quadrupole-quadrupole (EQQ) interaction. The gaussian approximation for the correlation function was used by these authors to predict T1. From the comparison between experiment and theory, we determine the EQQ parameter Γ/kB to be 0.67°K. Above 10°K the effect of diffusion influences T1, and the experimental results for an 88 per cent ortho H2 sample up to the melting point suggest that the relaxation mechanisms resulting from EQQ interaction and diffusion are not independent of one another. 相似文献
33.
34.
A. D. Al-Rawwas C. E. Johnson M. F. Thomas S. E. Dann M. T. Weiler 《Hyperfine Interactions》1994,93(1):1521-1529
Mössbauer spectra have been recorded at 4.2 and 300 K on the series La1–x
Sr
x
FeO3, wherex varies from 0 to 1.0 in steps of 0.1. Neutron diffraction experiments have shown that the crystal structure is orthorhombic for 0x<0.3, rhombohedral for 0.4x0.7, and cubic for 0.8<x1.0. Mössbauer spectra at 4.2 K are composed of magnetic sextet components arising from different charge states of iron ions. In the orthorhombic and rhombohedral phases, the charge states Fe3+ and Fe5+ coexist. In the cubic phase, iron is present as Fe3+ and Fe4+ states. At 300 K, the samples are magnetically ordered in the range 0 x0.3 and the coexistence of Fe3+ and Fe5+ remains. For samples 0.4x1.0, the samples are paramagnetic. Fits to these spectra require two components, one corresponding to an Fe4+ state, the other being best described as an Fe3+ ion forx0.7 but forx>0.7 having a mean charge state which increases to 3.5 forx=1.0. 相似文献
35.
36.
37.
38.
39.
The change in fluorescence quantum yield for indole as a function of excitation wavelength between 250 and 220 nm is found to vary with the static dielectric constant of various alcohol—water mixtures at 296 K. The supports the intermediacy of a CTTS state in the photoionization process. 相似文献
40.