全文获取类型
收费全文 | 295篇 |
免费 | 3篇 |
国内免费 | 6篇 |
专业分类
化学 | 122篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 41篇 |
物理学 | 131篇 |
出版年
2022年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2016年 | 3篇 |
2014年 | 6篇 |
2013年 | 7篇 |
2012年 | 15篇 |
2011年 | 6篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 10篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1969年 | 2篇 |
1942年 | 2篇 |
1933年 | 2篇 |
1931年 | 2篇 |
1923年 | 2篇 |
1893年 | 2篇 |
排序方式: 共有304条查询结果,搜索用时 9 毫秒
61.
62.
Interaction between a partially fluorinated alkyl sulfate and gelatin in aqueous solution 总被引:1,自引:0,他引:1
Griffiths PC Cheung AY Jenkins RL Howe AM Pitt AR Heenan RK King SM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1161-1167
The interaction of a partially fluorinated alkyl sulfate, sodium 1H,1H,2H,2H-perfluorooctyl sulfate (C6F13CH2CH2OSO3Na), with the polyampholyte gelatin has been examined in aqueous solution using surface tension and small-angle neutron scattering (SANS). The 19F chemical shift of each fluorine environment in the surfactant is unaltered by the addition of gelatin, indicating that there is no contact between the gelatin and the fluorocarbon core of the micelle. The chemical shift of the two methylene groups closest to the headgroup is altered when gelatin is present, disclosing the location of the polymer. The critical micelle concentration (cmc) of the surfactant, cmc = 17+/-1 mM, corresponds to an effective alkyl chain (CnH2n+1) length of n = 11. In the presence of gelatin, the cmc is substantially reduced as expected, cmc(1) = 4+/-1 mM, which is also consistent with an effective alkyl chain length of n = 11. In the presence of the fluorosurfactant, the monotonic decay of the SANS from the gelatin-only system is replaced by a substantial peak at an intermediate Q value mirroring the micellar interaction. At low ionic strengths, the gelatin/micelle complex can be described by an ellipsoid. At higher ionic strengths, the electrostatic interaction between the micelles is screened and the peak in the gelatin scattering disappears. The correlation length describing the network structure decreases with increasing SDS concentration as the bound micelles promote a collapse of the network. 相似文献
63.
The Mössbauer spectrum of the iron analog of K-β-alumina, K1+xFe11O17, where x = 0.35 to 0.86, has been obtained. Four magnetically split Fe3+ components can be resolved. At 295°K the magnetic flux densities at the nuclei are, for the 2a octahedral site 51.8 T, for the 12k octahedral site 43.8 T, and for the two tetrahedral sites, for which an assignment is suggested, 49.5 and 38.7 T. The random distribution of the excess potassium ions resulted in line broadening of the 12k octahedral, and bridging tetrahedral, spectra.Spin flopping in the antiferromagnetic lattice at 4.2°K in an applied magnetic flux density of 2.5 T was inferred from the absence of any effect of the applied field on the spectrum. The consequently low values of the magnetocrystalline anisotropy constants are compared and contrasted with those of the similarly structured ferrimagnetic hexagonal ferrites, and the possible role of Fe2+ in reducing the anisotropy is discussed. 相似文献
64.
Santhana K Eswaramoorthy James M Howe Fritz Phillipp 《Microscopy and microanalysis》2007,13(4):291-295
This article describes a simple shield that can be placed on typical commercial heating holders to reduce the thermal signal during heating to reasonable levels for in situ energy-dispersive X-ray spectroscopy analysis. The improved temperature capability provided by the shield is demonstrated by initial compositional analysis results obtained across a solid-liquid interface on Al-Si-Cu-Mg alloy powder particles. Considerations in the design of and improvement for the shield are discussed. 相似文献
65.
66.
67.
68.
Malcolm S. Cole Michael D. Howe Dr. Joseph A. Buonomo Dr. Sachin Sharma Dr. Elise A. Lamont Scott I. Brody Dr. Neeraj K. Mishra Dr. Yusuke Minato Dr. Joshua M. Thiede Dr. Anthony D. Baughn Dr. Courtney C. Aldrich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(51):e202200995
Tuberculosis (TB) is a leading source of infectious disease mortality globally. Antibiotic-resistant strains comprise an estimated 10 % of new TB cases and present an urgent need for novel therapeutics. β-lactam antibiotics have traditionally been ineffective against M. tuberculosis (Mtb), the causative agent of TB, due to the organism's inherent expression of β-lactamases that destroy the electrophilic β-lactam warhead. We have developed novel β-lactam conjugates, which exploit this inherent β-lactamase activity to achieve selective release of pyrazinoic acid (POA), the active form of a first-line TB drug. These conjugates are selectively active against M. tuberculosis and related mycobacteria, and activity is retained or even potentiated in multiple resistant strains and models. Preliminary mechanistic investigations suggest that both the POA “warhead” as well as the β-lactam “promoiety” contribute to the observed activity, demonstrating a codrug strategy with important implications for future TB therapy. 相似文献
69.
ER Badman GE Patterson JM Wells RE Santini RG Cooks 《Journal of mass spectrometry : JMS》1999,34(8):889-894
Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
70.
Peter W. A. Howe 《Magnetic resonance in chemistry : MRC》2010,48(11):837-841
The HSQC sequence provides a sensitive way of determining the 13C chemical shift of protonated carbons. It uses INEPT elements for magnetization transfer, which can only be optimized for one value of 1JCH, but small organic molecules contain a wide range of 1JCH values. One popular method of compensating for 1JCH variation is to incorporate adiabatic pulses into the INEPT elements. This article shows that this method fails for a significant subset of functional groups. It also shows that the effects of this failure can be reduced by avoiding refocusing delays and by using a J‐compensated excitation element. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献