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71.
72.
The synthesis of branched poly(ethylene glycol) (PEG) derivatives, namely star PEG and dendronized PEG, can be challenging and their purity can be difficult to ascertain using traditional techniques, such as NMR and GPC. Herein, the detailed characterization of these branched PEGs using MALDI-ToF MS was investigated in order to confirm their structural purity. In this light, mass spectrometry offers a number of advantages for polymer characterization, including the ability to get detailed structural data, such as end group masses, from microgram-scale samples. In addition, the ability to rapidly acquire data from crude reaction aliquots makes MALDI-ToF MS ideal for monitoring end group transformations. 相似文献
73.
Boyu Zhang Hong ZhangBrittany K. Myers Ravinder ElupulaJanarthanan Jayawickramarajah Scott M. Grayson 《Analytica chimica acta》2014
End groups play a critical role in macromolecular coupling reactions for building complex polymer architectures, yet their identity and purity can be difficult to ascertain using traditional analytical technique. Recent advances in mass spectrometry techniques have made matrix-assisted laser desorption/ionization time-of-fight (MALDI-TOF) mass spectrometry a rapid and powerful tool for providing detailed information about the identity and purity of homopolymer end groups. In this work, MALDI-TOF mass spectrometry was used to study end groups of linear polyethylene glycols. In particular, the identifications of alcohol, amine and thiol end groups are investigated because these nucleophilic moieties are among the most common within biological and synthetic macromolecules. Through comparative characterization of alcohol, amine, and thiol end groups, the exact identification of these end groups could be confirmed by selective and quantitative modification. The precision of this technique enables the unambiguous differentiation of primary amino groups relative to hydroxyl groups, which differ by only 1 mass unit. In addition, the quantitative conversion of various polyethylene glycol end groups using highly efficient coupling reactions such as the thiol-ene and azide-alkyne click reactions can be confirmed using MALDI-TOF mass spectrometry. 相似文献
74.
75.
Daniel R. Grayson 《K-Theory》1992,6(2):97-111
We construct Adams operations on higher algebraicK-groups induced by operations such as symmetric powers on any suitable exact category, by constructing an explicit map of spaces, combinatorially defined. The map uses theS-construction of Waldhausen, and deloops (once) earlier constructions of the map.Supported by NSF grant DMS 90-02715 相似文献
76.
77.
The recently observed collider events with large missing PT are analysed in terms of a supersymmetric model with a light photino and scalar quarks with mass in the range 20 to 35 GeV. A lower bound of O(60 GeV) on the gluino mass in this scenario is found. 相似文献
78.
Michael A. Grayson 《Journal of Polymer Science.Polymer Physics》1986,24(8):1747-1754
A method of correcting gravimetric data for diffusion through the sample edges to obtain true diffusion coefficients is presented. This method is compared with existing methods to show that it has the best accuracy for thick slab or cubic sample geometries. 相似文献
79.
The reaction of PtCl2en (en = ethane-1,2-diamine) with TlO2CC6F5 in boiling pyridine unexpectedly yielded a polyfluorophenyl-stabilized ethane-1,2-diaminatoplatinum(II) complex, Pt[N(p-HC6F4)CH2]2(py)2, 1a, the structure of which has been established by X-ray crystallography. 相似文献
80.
Michael A. Grayson Peter S. Pao Clarence J. Wolf 《Journal of Polymer Science.Polymer Physics》1987,25(4):935-945
The sorption of methylene chloride in neat PEEK was investigated as a function of temperature, sample thickness, surface treatment, and thermal history. The solubility of H2CCl2 in neat PEEK is 23 wt.% and is independent of thickness. Both surface treatment and thermal annealing strongly affect the rate of penetration; the as-Received material sorbs H2CCl2 more rapidly than abraded or annealed samples; however, the bulk solubility is independent of surface treatment. The sorption and desorption processes are considerably different, and the diffusion process is not simple Fickian Case I. The penetrant advances as a sharp front, suggesting a two-step, relaxation-controlled diffusion mechanism. 相似文献