全文获取类型
收费全文 | 73篇 |
免费 | 0篇 |
专业分类
化学 | 60篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 2篇 |
物理学 | 6篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 1篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1969年 | 1篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1917年 | 2篇 |
1913年 | 2篇 |
排序方式: 共有73条查询结果,搜索用时 478 毫秒
61.
M. A. Beckett J. C. Tebby J. J. Thompson B. J. Williams S. C. Withington 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Through-space coupling, which may be observed when NMR active nuclei are close in space, is additive to any through-bond coupling. The magnitude of the coupling via the through-space mechanism varies according to the element, its valency and the distance between the coupled atoms-independently of the number of bonds separating the coupled atoms. The couplings between carbon-bound fluorine and phosphorus (in its three valent three coordinate state) have been studied using a series of 0-(trifluoromethyl)phenylphosphanes (1). The phosphorusfluorine coupling is lowest (29. 6Hz) for the primary phosphine (1, Y = H). It is 43 Ha for the diethylamino derivative (1, R = Et2N), rising to 53–56 Ha when Y is phenyl, heteroaromatic, alkyl and ethoxy groups, and then to 63 and 68 Hz for the phenoxy and fluoro derivatives. The PF coupling is largest (85–88 Hz) for the dichloro and dibromo compounds. The coupling constants are zero or close to aero for the corresponding salts, oxides and sulphides. The changes in the magnitude of the phoaphane couplings are discussed in terms of conformational and electronic influences on a through-space spin-spin coupling mechanism. 相似文献
62.
Danielle J. Harvey Qian Weng Laurel A. Beckett 《Statistics & probability letters》2010,80(11-12):1015-1021
We define conditions under which sums of dependent spatial data will be approximately normally distributed. A theorem on the asymptotic distribution of a sum of dependent random variables defined on a 3-dimensional lattice is presented. Examples are also presented. 相似文献
63.
Ronald Beckett Deirdre Murphy Soheyl Tadjiki David J. Chittleborough J. Calvin Giddings 《Colloids and surfaces. A, Physicochemical and engineering aspects》1997,120(1-3):17-26
Sedimentation field-flow fractionation (SdFFF) can be used to prepare fractions of very narrow mass range for electron microscopic (EM) analysis. Assuming the particle density is the same for all particles within that fraction the equivalent spherical diameter for the particles can be calculated from SdFFF theory. Integration of the micrograph image of each particle yields an area measurement which, when used in conjunction with the equivalent spherical particle diameter (from SdFFF), provides information about the particle thickness and aspect ratio. Thus SdFFF-SEM can be used to provide detailed information about clay morphology across the particle size distribution of the sample. Three clay minerals have been studied using the methodologies outlined in this paper. The aspect ratio for the Purvis School Mine kaolinite ranged from 2.8–5.9, for RM30 illite from 11.3–24.3, and for Muloorina illite from 3.1–4.3. 相似文献
64.
The synthesis of N-monoalkylhydroxylamines, N,N-dialkylhydroxylamines, nitrones, oxaziridines, nitroso and other N-oxidised products of 3,4-dimethoxyamphetamine and its N-methyl and N-benzyl derivatives is described, including a new and simple method for preparing N,N-dialkylhydroxylamines and a method for the isolation and analysis of an α-unsubstituted nitrone. 相似文献
65.
The condensation of (−)-ephedrine with acetaldehyde gives two diastereomeric 2,3,4-trimethyl-5-phenyloxazolidines, of greatly differing thermodynamic stability. The structure and configuration of both the diastereoisomers was confirmed by chemical studies and by NMR spectroscopy. 相似文献
66.
Mora JF Van Berkel GJ Enke CG Cole RB Martinez-Sanchez M Fenn JB 《Journal of mass spectrometry : JMS》2000,35(8):939-952
Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd. 相似文献
67.
Van Berkel GJ Quirke JM Adams CL 《Rapid communications in mass spectrometry : RCM》2000,14(10):849-858
A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
68.
Carl Hallmann und E. G. Beckett 《Fresenius' Journal of Analytical Chemistry》1913,52(5):316-319
Ohne Zusammenfassung 相似文献
69.
E. G. Beckett 《Fresenius' Journal of Analytical Chemistry》1917,56(5):254-255
Ohne Zusammenfassung 相似文献
70.
Recent studies published in Oncogene and Proc. Natl. Acad. Sci. USA ascribe a role for selenium, acting through wild type p53, in protecting skin cells in culture from ultraviolet radiation-induced death. While selenium clearly protects cells against ultraviolet radiation-induced death, data that we present and discuss in this letter shows that wild type p53 is not required for such protection. Moreover the non-physiologically high levels of selenium used in some studies leads us to question the relevance of such effects for selenium-induced photoprotection. 相似文献