全文获取类型
收费全文 | 227篇 |
免费 | 41篇 |
国内免费 | 36篇 |
专业分类
化学 | 121篇 |
晶体学 | 4篇 |
力学 | 3篇 |
综合类 | 3篇 |
数学 | 30篇 |
物理学 | 143篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 17篇 |
2012年 | 8篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 15 毫秒
1.
本文对广义风险过程中的渐近方差作了非参数估计,得出并证明了两个定理,为广义风险过程中破产概率的区间估计作了理论准备. 相似文献
2.
3.
K. Dzilinski G. N. Synyakov A. M. Shulga I. V. Filatov G. P. Gurinovich 《Radiation Physics and Chemistry》1995,45(6):923-928
Radical anions of Zn-chlorin, Zn-octaethylchlorin complexes and their 15N and deuterium substituted analogues have been studied by EPR spectroscopy and the INDO molecular orbital method in the unrestricted Hartree-Fock procedure. Parameters of experimental spectra, determined by using the iterative least-squares fitting method, have been compared with those calculated on the basis of spin density distribution. A satisfactory agreement between the experimental hyperfine coupling constants and theoretical ones for the systems studied has been obtained. 相似文献
4.
高效液相色谱氮杂冠醚键合固定相的合成及性能研究 总被引:2,自引:0,他引:2
我们曾用γ-氯丙基键合硅胶(CPS),在氢化钠(NaH)作用下合成了3-(氮杂-18-冠-6)丙基键合固定相(BCP)[1].该固定相对碱基、核苷酸、硝基苯酚等有较好的分离选择性,但由于NaH对硅胶基质腐蚀作用较大,导致BCP柱效及渗透性较低.本文采... 相似文献
5.
Simultaneous thermogravimetry–differential thermal analysis (TG–DTA) and gas and liquid chromatography with mass spectrometry detection have been used to study the kinetics and decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester, commercially known as salsalate. Samples of salsalate were heated in the TG–DTA apparatus in an inert atmosphere (100 ml min−1 nitrogen) in the temperature range 30–500 °C. The data indicated that the decomposition of salsalate is a two-stage process. The first decomposition stage (150–250 °C) had a best fit with second-order kinetics with Ea=191–198 kJ/mol. The second decomposition stage (300–400 °C) is described as a zero-order process with Ea=72–80 kJ/mol. The products of the decomposition were investigated in two ways:
- (a)Salsalate was heated in a gas chromatograph at various isothermal temperatures in the range 150–280 °C, and the exit gas stream analyzed by mass spectrometry (GC–MS). This approach suggested that salsalate decomposes with the formation of salicylic acid, phenol, phenyl salicylate, and cyclic oligomers of salicylic acid di- and tri-salicylides.
- (b)One gram samples of salsalate were heated in a vessel under nitrogen to 150 °C, and the residues were analyzed by liquid chromatography–mass spectrometry (LC–MS). The major compound detected was a linear tetrameric salicylate ester.
6.
Y. M. Shulga A. A. Startsev Y. I. Yermakov B. N. Kuznetsov Y. G. Borod'ko 《Reaction Kinetics and Catalysis Letters》1977,6(3):377-383
By the XPS method it has been shown that in the catalysts obtained by interacting W(-C4H7)4 with SiO2 several oxidation states of the supported tungsten are realized together with a higher coverage of the silica surface with tungsten compounds, as compared with the catalysts prepared by impregnation of SiO2 with an aqueous solution of (NH4)2 WO4.
, , W(-C4H7)4 SiO2, , , SiO2 (NH4)2 WO4.相似文献
7.
8.
9.
Focusing on the rapid prediction of acoustic field uncertainty in environment with temporal and spatial sound speed perturbation, evolvement of sound speed structure over time is predicted based on the ocean-acoustic coupled model to obtain the uncertainty distribution of the vertical structure of sound speed. Further, a method combining the arbitrary polynomial chaos expansion with the empirical orthogonal function is proposed to reduce the dimensionality of uncertain parameters and to obtain the uncertainty distribution of the acoustic field. Simulations have shown that the computational complexity can be reduced by 2 orders of magnitude compared to the conventional polynomial chaos expansion while ensures the same precision.Moreover, the computational complexity is not influenced by the complexity of the sound speed profile. The acoustic field and uncertainty predicted in uncertain environment by proposed method also have been tested with the experimental data. 相似文献
10.