全文获取类型
收费全文 | 113438篇 |
免费 | 18127篇 |
国内免费 | 13882篇 |
专业分类
化学 | 80094篇 |
晶体学 | 1370篇 |
力学 | 6424篇 |
综合类 | 805篇 |
数学 | 13612篇 |
物理学 | 43142篇 |
出版年
2024年 | 389篇 |
2023年 | 2260篇 |
2022年 | 4068篇 |
2021年 | 4277篇 |
2020年 | 4595篇 |
2019年 | 4423篇 |
2018年 | 4106篇 |
2017年 | 3751篇 |
2016年 | 5455篇 |
2015年 | 5400篇 |
2014年 | 6630篇 |
2013年 | 8541篇 |
2012年 | 10088篇 |
2011年 | 10303篇 |
2010年 | 7283篇 |
2009年 | 6987篇 |
2008年 | 7329篇 |
2007年 | 6479篇 |
2006年 | 6127篇 |
2005年 | 5195篇 |
2004年 | 4087篇 |
2003年 | 3310篇 |
2002年 | 3070篇 |
2001年 | 2627篇 |
2000年 | 2204篇 |
1999年 | 2255篇 |
1998年 | 1862篇 |
1997年 | 1635篇 |
1996年 | 1657篇 |
1995年 | 1436篇 |
1994年 | 1320篇 |
1993年 | 1067篇 |
1992年 | 945篇 |
1991年 | 839篇 |
1990年 | 688篇 |
1989年 | 531篇 |
1988年 | 398篇 |
1987年 | 355篇 |
1986年 | 351篇 |
1985年 | 273篇 |
1984年 | 193篇 |
1983年 | 162篇 |
1982年 | 126篇 |
1981年 | 79篇 |
1980年 | 61篇 |
1979年 | 27篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
971.
972.
973.
974.
975.
Variable-energy valence and inner-valence photoelectron spectra have been recorded for the CpNiNO complex (Cp = eta(5)-C(5)H(5)) between 21.2 and 100 eV, using He I radiation and synchrotron radiation. The ground state electronic structure has been calculated by using the Xalpha-SW method. Photoionization cross sections (sigma) have also been calculated for the valence ionizations using the Xalpha-SW method. The theoretical branching ratios (sigma(i)/ summation operatorsigma) have been compared with the observed branching ratios (A(i)()/ summation operatorA) between 21.2 and 100 eV. The assignment of the photoelectron spectrum based on the analysis of intensity variations and width of vibrational peaks is consistent with the ion state orbital ordering 5e(1)(1) < 7a(1)(2) < 3e(2)(3) < 4e(1)(4) (band numbers are in parentheses) and is inconsistent with another recently proposed ordering 5e(1)(1), 5e(1)(2) < 7a(1), 3e(2)(3) < 4e(1)(4), which takes the 5e(1) vibronic effects into consideration. The experimental branching ratio results indicate a Ni 3p resonance effect around 75 eV in the photoionization process. The inner-valence spectrum has also been assigned with the aid of the Xalpha-SW calculations. 相似文献
976.
Study of free volume parameters of polystyrenes of different molecular architecture by positron annihilation lifetime measurement 总被引:1,自引:0,他引:1
H. -L. Li Y. Ujihira A. Nanasawa 《Journal of Radioanalytical and Nuclear Chemistry》1996,210(2):533-541
Differences of size, content and size distribution of free volumes in linear branched and three-armed polystyrenes, synthesized by radical and anionic processes, were observed by positron annihilation lifetime measurements. The temperature dependence of an average free volume radius was quite similar among polystyrenes of different architectures and molecular weight distributions. The free volume radius increased with temperature, from 0.27 nm (T:60 K) to 0.29 nm (T:260 K) and 0.30 nm (T
g:363 K), then to 0.35 nm (423 K), showing turning at and transition temperature. The free volume content decreased from 60 K to 220 K to 300 K showing peculiar minimum at 220 K to 300 K depending on the molecular shape, increased above 320 K, upto 340 to 360 K. The free volume contents decreased with an increase of molecular weight and by an addition of oligomer or plasticiser, suggesting differences in relaxation time or molecular motion between the edge and middle portions of molecular chain and filling effect of smaller molecules in free volumes, respectively. The apparent free volume fraction showed clear variations atT
andT
g. Size distribution of free volumes suggested more complicated behavior of free volume upon the molecular relaxations and filling effect. 相似文献
977.
Wang Tieshan Li Qiang Zhang Baoguo Wang Zhusheng Cao Zhiyuan Zhang Peixin 《Journal of Radioanalytical and Nuclear Chemistry》1996,205(1):141-145
The radio-voltaic effect is investigated to be applied radioisotopic batteries in this work. The collection rates of the electron-hole pairs are 94 percent for the alpha particles emitted by239Pu source and 65 percent for the beta particles emitted by90Sr-90Y source. The maximum energy conversion efficiency got by the silicon element is about 16%. A prototype radioisotopic battery with147Pm beta sources is constructed. Its maximum short-circuit current and off voltage are about 2 A and 190 mV respectively. The experimental data suggest that the life of the prototype battery may be more than three years. 相似文献
978.
979.
980.