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91.
Peter Niedbalski Christopher Parish Andhika Kiswandhi Lloyd Lumata 《Magnetic resonance in chemistry : MRC》2016,54(12):962-967
The nitroxide‐based free radical 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) is a widely used polarizing agent in NMR signal amplification via dissolution dynamic nuclear polarization (DNP). In this study, we have thoroughly investigated the effects of 15N and/or 2H isotopic labeling of 4‐oxo‐TEMPO free radical on 13C DNP of 3 M [1‐13C] sodium acetate samples in 1 : 1 v/v glycerol : water at 3.35 T and 1.2 K. Four variants of this free radical were used for 13C DNP: 4‐oxo‐TEMPO, 4‐oxo‐TEMPO‐15N, 4‐oxo‐TEMPO‐d16 and 4‐oxo‐TEMPO‐15N,d16. Our results indicate that, despite the striking differences seen in the electron spin resonance (ESR) spectral features, the 13C DNP efficiency of these 15N and/or 2H‐enriched 4‐oxo‐TEMPO free radicals are relatively the same compared with 13C DNP performance of the regular 4‐oxo‐TEMPO. Furthermore, when fully deuterated glassing solvents were used, the 13C DNP signals of these samples all doubled in the same manner, and the 13C polarization buildup was faster by a factor of 2 for all samples. The data here suggest that the hyperfine coupling contributions of these isotopically enriched 4‐oxo‐TEMPO free radicals have negligible effects on the 13C DNP efficiency at 3.35 T and 1.2 K. These results are discussed in light of the spin temperature model of DNP. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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96.
We extend a result of Roth dealing with fixed points of lattice mappings which satisfy certain constraints.
Presented by J. Mycielski. 相似文献
97.
Enju Wang Kwok-Fan Chow Crystal Wong Alvin Persad Andrew Bocarsly 《Analytica chimica acta》2005,534(2):301-306
A dye doped sol-gel for the sensing of hydrochloric acid in solution and/or gaseous phase is described. The sol-gel is obtained by acidic hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (Ph-TriEOS) in the presence of phenol red (PR) and further spin-coating onto glass slides. The sensitive response is based on an increase of the absorption band at 510 nm of phenol red entrapped in the sol-gel casting when exposed to HCl solution or gas, due to protonation of the dye. The detection limit of the sol-gel response to moisturized gaseous HCl is below 12 ppm, and its response to HCl in solution falls in the range of 0.01-6 M. The sol-gel coating has a response time of less than 40 s in steady-state, and life-time of more than a year. Weak acids such as acetic acid, benzoic acid, salicylate acid, citrate acid, and carbonic acid do not interfere the response. The responses in acid solutions are completely reversible. In the gaseous phase, response of HCl appears to be moisture sensitive. 相似文献
98.
Alvin D. Delman Hanna Nagy Kovacs Bernard B. Simms 《Journal of polymer science. Part A, Polymer chemistry》1968,6(8):2117-2126
Studies were undertaken to ascertain the thermal stability of several types of silicon-containing polymers. Results of thermal analysis investigations indicate that all of the polymers are unusually heat-resistant when heated in air at elevated temperatures. Solution-cast films of the polymers on aluminum showed excellent flexibility and adhesion characteristics after being heated in air for 100 hr. at 300°C. and then for 3.5 hr. at 400°C. Visual examination of the films after the heating sequence indicated that the silicon-containing polyamides and polybenzimidazole had darkened slightly, while the polyoxadiazole appeared to be unaffected in this respect. Infrared spectroscopy studies showed that all of the polymers underwent only very minor structural changes during the prolonged heating process. 相似文献
99.
The decay rates and spin-lattice relaxation rates are presented for the lowest excited triplet state in tryptophan and in tyrosinate in zero-field at 1.34 K. 相似文献
100.
Alvin P. Kennedy David A. Babb Jeffrey N. Bremmer Andrew J. Pasztor 《Journal of polymer science. Part A, Polymer chemistry》1995,33(11):1859-1865
The results of thermal and oxidative stability studies are reported for one perfluorocyclo-butane aromatic ether thermoset polymer. The polymer was prepared from 1,1,1-tris (4-trifluorovinyloxyphenyl)ethane by the thermal cyclodimerization of the trifluorovinyl either functionality, resulting in a network polymer comprising alternating perfluorocy-clobutane and aromatic either groups. The results of isothermal and dynamic thermal gravimetric analysis (TGA) studies are reported with kinetic approximations for de-composition in nitrogen, along with FTIR studies of the oxidative process in air and TGA/mass spec determination of the gasses evolved from decomposition in air. Based on these results, thermal and oxidative decomposition mechanisms are proposed. © 1995 John Wiley & Sons, Inc. 相似文献