全文获取类型
收费全文 | 301篇 |
免费 | 2篇 |
专业分类
化学 | 151篇 |
晶体学 | 2篇 |
力学 | 13篇 |
数学 | 8篇 |
物理学 | 129篇 |
出版年
2021年 | 4篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 12篇 |
2002年 | 2篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 8篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1969年 | 5篇 |
1968年 | 7篇 |
1967年 | 5篇 |
1965年 | 5篇 |
1962年 | 2篇 |
1940年 | 3篇 |
排序方式: 共有303条查询结果,搜索用时 281 毫秒
41.
Castro-Perez J Roddy TP Nibbering NM Shah V McLaren DG Previs S Attygalle AB Herath K Chen Z Wang SP Mitnaul L Hubbard BK Vreeken RJ Johns DG Hankemeier T 《Journal of the American Society for Mass Spectrometry》2011,22(9):1552-1567
A high content molecular fragmentation for the analysis of phosphatidylcholines (PC) was achieved utilizing a two-stage [trap (first generation fragmentation) and transfer (second generation fragmentation)] collision-induced dissociation (CID) in combination with travelling-wave ion mobility spectrometry (TWIMS). The novel aspects of this work reside in the fact that a TWIMS arrangement was used to obtain a high level structural information including location of fatty acyl substituents and double bonds for PCs in plasma, and the presence of alkali metal adduct ions such as [M?+?Li]+ was not required to obtain double bond positions. Elemental compositions for fragment ions were confirmed by accurate mass measurements. A very specific first generation fragment ion m/z 577 (M-phosphoryl choline) from the PC [16:0/18:1 (9Z)] was produced, which by further CID generated acylium ions containing either the fatty acyl 16:0 (C15H31CO+, m/z 239) or 18:1 (9Z) (C17H33CO+, m/z 265) substituent. Subsequent water loss from these acylium ions was key in producing hydrocarbon fragment ions mainly from the α-proximal position of the carbonyl group such as the hydrocarbon ion m/z 67 (+H2C-HC?=?CH-CH?=?CH2). Formation of these ions was of important significance for determining double bonds in the fatty acyl chains. In addition to this, and with the aid of 13C labeled lyso-phosphatidylcholine (LPC) 18:1 (9Z) in the ω-position (methyl) TAP fragmentation produced the ion at m/z 57. And was proven to be derived from the α-proximal (carboxylate) or distant ω-position (methyl) in the LPC. 相似文献
42.
I. Mukhopadhyay R. M. Lees W. Lewis-Bevan J. W. C. Johns F. Strumia G. Moruzzi 《International Journal of Infrared and Millimeter Waves》1987,8(11):1483-1502
High-resolution infrared (IR) and far infrared (FIR) Fourier transform absorption spectra have been employed to investigate assignments of FIR laser lines reported from optically-pumped13CH3OH. The spectroscopic measurements are used in conjunction with the reported IR pump and FIR laser frequencies to form closed combination loops for several systems, serving to confirm the assignments and in some cases to improve the accuracy of the FIR laser frequencies. Frequency predictions from combination differences are also presented for a number of potential new FIR laser lines. 相似文献
43.
Mahmoud Mollabashi R. M. Lees J. W. C. Johns 《International Journal of Infrared and Millimeter Waves》1993,14(9):1727-1753
The Fourier transform far-infrared (FTFIR) spectrum of CD3OH has been obtained from 40–220 cm–1 at a resolution of 0.002 cm–1, and partially analyzed. Numerousb-type branches have been assigned in the spectrum, ranging over torsional states fromn=0 to 3. The branches have been fitted toJ(J+1) power-series energy expansions in order to obtainJ-independent branch origins. These in turn have been fitted to the torsion-rotation Hamiltonian, and improved molecular constants have been obtained for the ground vibrational state. 相似文献
44.
Abstract— Evidence is presented for the formation of a thymine hydrate upon ultraviolet (UV) or gamma irradiation of aqueous solutions. The UV quantum efficiency exhibits a dependence on pH similar to that shown for uracil hydration, but the yield is three orders of magnitude smaller than for uracil. Hydration is not affected by wavelength, oxygen, or concentration of thymine. The reversal rate of the photohydrate to thymine is similar to the reversal rates of both isomers of the thymine hydrate formed by γ radiolysis, and depends on pH in the same way as the rate for the uracil photohydrate. The photohydrate of thymine is chromatographically identical to the cis isomer of 6-hydroxy-5, 6-dihydrothymine. 相似文献
45.
46.
C. Bréchignac J.W.C. Johns A.R.W. McKellar M. Wong 《Journal of Molecular Spectroscopy》1982,96(2):353-361
The ν2 fundamental band of H2CO has been studied using a combination of sub-Doppler laser Stark spectroscopy and Doppler-limited Fourier transform spectroscopy. A combined analysis of the Stark and Fourier infrared data together with previous microwave data on the ν2 = 1 state yielded improved molecular parameters for formaldehyde, including the excited state dipole moment. A small perturbation was noted at K′a = 7 which may be ascribed to a ΔKa = 2 interaction with the v3 = 1 state. Precise treatments of ν2 with K′a > 6 will thus require a combined analysis taking into account Coriolis interactions among ν4, ν6, ν3, and ν2. 相似文献
47.
High-resolution Fourier transform spectroscopy has been applied to confirm previously proposed assignments for nine far infrared (FIR) laser lines from the CH3-deformation state of CH3OH and one line from the CH3-rocking state. Accurate frequencies are deduced for the observed and other predicted FIR laser transitions. FIR torsional branch frequencies in the ground state which were used in the confirmation are presented. Comments are also made on the OH-bending mode of CH3OH. 相似文献
48.
49.
Synthesis and reactions of 5 ,8-epidioxyandrost-6-enes 总被引:1,自引:0,他引:1
W F Johns 《The Journal of organic chemistry》1971,36(17):2391-2397
50.