全文获取类型
收费全文 | 54篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
化学 | 53篇 |
物理学 | 3篇 |
出版年
2022年 | 1篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2008年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1968年 | 4篇 |
1967年 | 9篇 |
1965年 | 3篇 |
1960年 | 1篇 |
1957年 | 4篇 |
1956年 | 2篇 |
排序方式: 共有56条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
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
5.
Tamer Shoeib Junfang Zhao Houssain EI Aribi Alan C. Hopkinson K. W. Michael Siu 《Journal of the American Society for Mass Spectrometry》2013,24(1):38-48
The fragmentations of [AA + M]+ complexes, where AA = Phe, Tyr, Trp, or His, and M is a monovalent metal (Li, Na, or Ag), have been exhaustively studied through collision-induced dissociation (CID) and through deuterium labeling. Dissociations of the Li- and Ag-containing complexes gave a large number of fragment ions; by contrast, the sodium/amino acid complexes have lower binding energies, and dissociation resulted in much simpler spectra, with loss of the entire ligand dominating. Unambiguous assignments of these fragment ions were made and formation mechanisms are proposed. Of particular interest are fragmentations in which the charge was retained on the organic fragment and the metal was lost, either as a metal hydride (AgH) or hydroxide (LiOH) or as the silver atom (Ag?). Caption for Graphical Abstract
CID products of Li+, Na+, and Ag+ complexes of Phe, Tyr, Trp, and His are reported and mechanisms by which they are formed are proposed. 相似文献
6.
7.
8.
A convenient synthesis of intermediate 4,5‐diamino‐3‐aryl‐1‐phenylpyrazoles 4a – 4c was reported. The different cyclization reactions were carried out with chalcone, 2‐mercaptoacetic acid and p‐anisialdehyde, ethyl chloroformate, glyoxal and thiourea to afford different N and S containing heterocycles. The reaction conditions were compared by conventional heating and microwave irradiation. The structures of the cyclization products were determined by analytical and spectroscopic data. All the synthesized compounds were screened for antibacterial activities in vitro. 相似文献
9.
B.A. Dolgoplosk I.A. Oreshkin S.A. Smirnov I.A. Kopieva E.I. Tinyakova 《European Polymer Journal》1979,15(3):237-240
The interaction between CD3Li and WCl6 and MoCl5 was studied at various Li/W and Li/Mo ratios. It has been shown that the decomposition of the W or Mo organometallic intermediate leads to CD4, C2D6 and C2D4. The formation of CD4 is believed to be due to CD2:carbene creation in the system, while C2D4 is a product of the recombination of methylene fragments. At Li/W = 4 mol ratio, as well as in case of MoCl5, the decomposition appears to involve the formation of carbine complexes. The trimethylsilylmethylene complex which results from WCl6-induced decomposition of Me3SiCHN2 is shown to be a poor initiator of cyclopentene polymerization. Minor amounts of trimethylvinylsilane were found to inhibit cyclopentene polymerization and pentene-2 metathesis as a result of substitution of the active RCH:alkyl carbene for the more stable Me3SiCH:. 相似文献
10.