全文获取类型
收费全文 | 211篇 |
免费 | 0篇 |
专业分类
化学 | 142篇 |
晶体学 | 2篇 |
数学 | 15篇 |
物理学 | 52篇 |
出版年
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 14篇 |
2012年 | 4篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有211条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
The enthalpies of combustion (ΔH
comb) of five primary, secondary, and tertiary alkyl(aryl)arsines in the condensed state were calculated using the equation ΔH
comb = −385.8–110.3N, where N is the number of bond-forming electrons. The dependence presented is used for the calculation of the enthalpies of combustion
of full esters and amidoesters of arsinous acid of noncyclic and cyclic structures.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1042–1043, May, 2007. 相似文献
5.
Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
6.
U. S. Andropova N. A. Tebeneva A. N. Tarasenkov M. S. Parshin A. A. Askadskii O. A. Serenko A. M. Muzafarov 《Polymer Science Series B》2017,59(2):202-209
Amorphous polyaryleneetherketone tetrakis(phenyldiethoxysiloxy)hafnium or tetrakis(methyldiethoxysiloxy) hafnium are used as precursors of disperse phase of composites. One of the factors determining the morphology of filled polymer films and the size and shape of particles forming in polymer in situ is the activity of alkoxy groups of metal alkoxysiloxane precursor in hydrolysis and condensation reactions. When using tetrakis(phenyldiethoxysiloxy)hafnium instead of tetrakis(methyldiethoxysiloxy)hafnium, nanocomposites obtained via the sol-gel method are characterized by a uniform distribution of spherical particles of disperse phase. 相似文献
7.
EI Rodriguez Martinez CI Barriga-Paulino MI Zapata CC Chinchilla AM López-Jiménez CM Gómez 《BMC neuroscience》2012,13(1):104-23
ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages. 相似文献
8.
9.
Dr. Anton A. Anisimov Dr. Fedor V. Drozdov Yulia S. Vysochinskaya Ekaterina O. Minyaylo Prof. Alexander S. Peregudov Prof. Fedor M. Dolgushin Dr. Olga I. Shchegolikhina Prof. Aziz M. Muzafarov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11404-11407
This study presents the synthesis of organoboron derivatives of stereoregular 4-, 6-, and 12-unit phenylcyclosilsesquioxanes. All compounds obtained were isolated in good yields (70–80 %) and were fully characterized by 1H, 13C, 29Si, 11B NMR, IR spectroscopy, HRMS ESI, and elemental microanalysis. The structure of the key modifier, obtained for the first time, 4-(tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl) dimethylvinylsilane, was also confirmed by single-crystal XRD. 相似文献
10.
V. E. Smirnova E. N. Popova V. M. Svetlichnyi L. A. Myagkova A. N. Orekhov V. E. Yudin A. M. Muzafarov E. A. Tatarinova 《Russian Journal of Applied Chemistry》2011,84(10):1800-1804
The effect exerted by thermal aging in air at 350°C on the thermal and mechanical properties of composite films prepared on
the basis of heat-resistant polyimide PM and non-film-forming polymethylphenylsiloxane (PMPS) was examined. The phase segregation
of polymeric composites of various compositions and the thermal aging rate were evaluated. 相似文献