全文获取类型
收费全文 | 52篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学 | 16篇 |
力学 | 2篇 |
数学 | 1篇 |
物理学 | 34篇 |
出版年
2023年 | 1篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2013年 | 1篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2005年 | 1篇 |
2003年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1963年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有53条查询结果,搜索用时 0 毫秒
41.
42.
+ ions. The Ca+ ions are trapped in a miniature rf Paul trap and irradiated by light from a frequency-doubled diode laser at 397 nm and by
light from a diode laser at 866 nm. We are able to cool a single ion and observe its fluorescence continuously with the laser
diode locked to the external frequency-doubling cavity. Quantum jumps in the fluorescence light of a single ion and of a small
cloud of five ions have been induced by driving the “clock” transition at 729 nm. We were able to resolve the influence of
the micromotion on the excitation spectrum of the small ion cloud.
Received: 10 July 1997/Revised version: 17 November 1997 相似文献
43.
U. Eichmann J. L. Dexter E. Y. Xu T. F. Gallagher 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,11(3):187-197
We have investigated ionization and excitation of the Ba 6s n s 1 S 0 and 6s n d 1,3 D 2 series in strong microwave fields. The observed microwave ionization threshold fields, scaling as 0.28n ?5, and the state mixing fields cannot be completely explained in terms of a single cycle Landau-Zener model. However, by taking into account multiphoton resonant transitions driven by many cycles of the microwave field we have been able to interpet the data. In particular, multi-photon transitions have been found to be responsible for apparent resonance structures and for the unexpectedly low mixing fields. Not surprisingly, doubly excited valence states introduce irregularities into both the microwave ionization and the state mixing field values. 相似文献
44.
45.
T lymphocytes (T cells) are the central cell type initiating all immune responses. They are able to recognize other cells in the body that have been invaded by foreign living or nonliving matter. In such cells, foreign peptides generated by intracellular breakdown are complexed with molecules of the major histocompatibility complex (MHC) specially designed for peptide binding. Peptide-loaded MHC molecules appear on the surface of these cells and alert the immune system. The molecular complex which T cells use for recognition of peptide-loaded MHC molecules is among the most sophisticated and versatile receptor systems in biology. It consists of specific and nonspecific transmembrane components which assemble to a functional signal transduction unit as the result of ligand binding. Correct assembly leads to activation and relocation of enzymes including membrane-associated, tyrosin-specific protein kinases and phosphatases. Transmembrane signaling in T cells depends on the correct assembly and cooperation among multiple molecular components. This may be related to a multitude of different cellular responses of T cells at different stages of differentiation, all elicited through the T cell receptor complex. 相似文献
46.
Polyethylene glycols react with CH3OCH2+ ions from dimethyl ether to form [M + 13]+ products. The [M + 13]+ ions are stabilized by intramolecular interactions involving the internal ether oxygen atoms and the terminal methylene group. Collisionally activated dissociation (CAD), including MSn and deuterium labeling experiments show that fragmentation reactions involving intramolecular cyclization are predominant. Scrambling of hydrogen and deuterium atoms in the ion-molecule reaction products is not indicated. The CAD spectra of the [M + 13]+ ions provide unambiguous assignment of the glycol size. 相似文献
47.
Erika S. Eichmann Jennifer S. Brodbelt 《Journal of the American Society for Mass Spectrometry》1993,4(2):97-105
The selective methylation and methylene substitution reactions of dimethyl ether ions with ethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol dimethyl ether were investigated in a quadrupole ion trap mass spectrometer. Whereas the reactions of ethylene glycol and ethylene glycol monomethyl ether with the methoxymethylene cation 45+ gave only [M + 13]+ product ions, the reaction of ethylene glycol dimethyl ether with the same reagent ion yielded exclusively [M + 15]+ ions. The relative rates of formation of these products and those from competing reactions were examined and rationalized on the basis of structural and electronic considerations. The heats of formation for various relevant species were estimated by computational methods and showed that the reactions leading to the [M + 13]+ ions were more energetically favorable than those leading to the [M + 15]+ products for cases in which both reactions are possible. Finally, the collision-induced dissociation behavior of the [M + H]+, [M + 13]+, and [M + 15]+ ions indicated that the and [M + H]+ rons dissociated by analogous pathways and were thus structurally similar, whereas the [M + 13]+ ions possessed distinctly different structural characteristics. 相似文献
48.
49.
Functional group interactions within biologically relevant molecules are among the most influential yet least understood factors in determining their reactive behaviors. Reactions of dimethyl ether ions, which have previously been shown to be site-selective, with four cinchona alkaloids, cinchonine, cinchonidine, quinine and quinidine, have been examined. These reactions are each shown to produce qualitatively similar spectra for the stereoisomeric pairs cinchonidine–cinchonine and quinidine–quinine, but small variations in the relative abundances of the products indicate that some stereoselectivity can be observed. The site selectivity of each of the reagents was investigated by observing the reactions occurring with model subunits of the alkaloids. 相似文献
50.