全文获取类型
收费全文 | 438篇 |
免费 | 7篇 |
专业分类
化学 | 184篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 18篇 |
物理学 | 230篇 |
出版年
2020年 | 3篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 22篇 |
2012年 | 10篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 11篇 |
2004年 | 17篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1997年 | 7篇 |
1996年 | 17篇 |
1995年 | 6篇 |
1994年 | 21篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 21篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 17篇 |
1985年 | 5篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 14篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1962年 | 2篇 |
1938年 | 2篇 |
1932年 | 2篇 |
1920年 | 2篇 |
1885年 | 2篇 |
排序方式: 共有445条查询结果,搜索用时 15 毫秒
51.
Jian Fang Evan M. Howard Prof. Dr. Matthias Brewer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12927-12931
Structurally complex diazo-containing scaffolds are formed by conjugate addition to vinyl diazonium salts. The electrophile, a little studied α-diazonium-α,β-unsaturated carbonyl compound, is formed at low temperature under mild conditions by treating β-hydroxy-α-diazo carbonyls with Sc(OTf)3. Conjugate addition occurs selectively at the 3-position of indole to give α-diazo-β-indole carbonyls, and enoxy silanes react to give 2-diazo-1,4-dicarbonyl products. These reactions result in the formation of tertiary and quaternary centers, and give products that would be otherwise difficult to form. Importantly, the diazo functional group is retained within the molecule for future manipulation. Treating an α-diazo ester indole addition product with Rh2(OAc)4 caused a rearrangement to occur to give a 2-(1H-indol-3-yl)-2-enoate. In the case of diazo ketone compounds, this shift occurred spontaneously on prolonged exposure to the Lewis acidic reaction conditions. 相似文献
52.
53.
54.
55.
We report experiments on Co alloys by β and γ nuclear orientation measurements. We discuss the link between susceptibility and hyperfine measurements and the possibility of separating the orbital and spin contribution. 相似文献
56.
Ronald C. Scherer Moderator Editor David W. Brewer Raymond Colton Lucille S. Rubin Bonnie N. Raphael Richard Miller Elizabeth Howell G. Paul Moore 《Journal of voice》1994,8(4):359-374
The integration of voice science, voice pathology, medicine, public speaking, acting, and singing has been central to evolution in all fields. The Voice Foundation Symposia have played a seminal and central role in fostering integration among disciplines. The result has been an improvement in the knowledge and practice in each field. And the future promises to be even more informative and exciting. 相似文献
57.
D. R. Harshman R. Keitel M. Senba E. J. Ansaldo J. H. Brewer 《Hyperfine Interactions》1984,18(1-4):557-561
The behavior of muonium on the surface of finely divided silica (amorphous SiO2) powder (mean grain diameter 70 Å) has been studied as a function of the surface concentration of hydroxyl groups. The temperature dependence of the Mu relaxation rate in transverse field was measured for samples prepared with 0%, 50% and 70% of the surface hydroxyl groups removed over the temperature range 4 K <T < 300 K. The relaxation rate shows a distinct maximum at about 25 K and a minimum at about 16 K for all three samples, and shows a dramatic decrease below 16 K as the concentration of surface hydroxyls is reduced. A three-state nonequilibrium model describing the diffusion and trapping of muonium on the silica surface is used to interpret the data.On leave from Department of Physics, University of Saskatchewan, Saskatoon, Sask. S7N OWO, Canada. 相似文献
58.
Anthony L Fitzhugh Richard S Strauss Elizabeth N Brewer Steven D Glassman Maitland Jones 《Tetrahedron letters》1985,26(33):3911-3914
Oxalacetic esters undergo ester exchange at 120°C, at which temperature loss of CO does not occur. A new mechanism is proposed for the decarbonmonoxylation reaction. 相似文献
59.
In order to provide a larger data base for understanding the whys and why nots of muonium formation in solids, we have been searching for Mu in predominantly crystalline environments. We have observed muonium in room temperature diamond, and report on a brief study of the temperature behaviour of its asymmetry and relaxation. These results are radically different from all previous diamond results. We have not been able to detect any Mu in SrTiO3, ZrSiO4, or TiO2, but in GeO2 there is a tiny signal in both a fused sample and a hexagonal single crystal, but none in a tetragonal crystal. Since hexagonal GeO2 is structurally similar to quartz, one would naively expect similar amounts of Mu. Such is not the case, the reasons for which are not understood at this time. In SrTiO3, the muon asymmetry is a strong function of temperature. 相似文献
60.
The flexible fiberoptic laryngoscope is a valuable tool in the examination of laryngeal and supraglottic structure and function. Nevertheless, persistent questions remain about the validity of the perceived image, and a variety of concerns arise relative to the equipment used, the difficult to examine patient, and the difficulty in obtaining measurable objective data. All of these areas are discussed. Distortions of the video image that result from the wideangle lens effect are described. Given an awareness of the distortions that may be present in the fiberoptic video image, it is clear that it is necessary to exercise caution in making judgments of anatomic or physiologic integrity based on fiberoptic information alone. 相似文献