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11.
12.
This article describes a new synthesis strategy to prepare diblock copolymers as model compounds for industrially produced cellulose ethers exemplified with methylcellulose (MC). To elucidate a key structure for thermoreversible gelation of MC, five regioselectively methylated celluloses 1 – 5 (236, 23, 26, 3, and 6 MC), five corresponding methyl‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 6 – 10 , and five equiv methyl‐β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 11 – 15 were synthesized for the first time via combination of the glycosyl trichloroacetimidate method and the acid‐catalyzed methanolysis method. The structure of compounds 1 – 15 was confirmed by means of NMR spectroscopy and MALDI‐TOF MS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   
13.
We obtained, for the first time, high-resolution rotational distribution of CO2 collisionally excited by N2. The rotational distribution is non-Boltzmann, and the initial results suggest that surprisingly large impact parameter collisions contribute substantially to the collisional excitation, even though small impact parameter collisions are more effective, as expected.  相似文献   
14.
This article describes detailed structure‐property relationships of 5 regioselectively methylated celluloses and 10 diblock cellulose derivatives with regioselective functionalization patterns: methyl 2,3,6‐tri‐O‐ ( 1 , 236MC), methyl 2,3‐di‐O‐ ( 2 , 23MC), methyl 2,6‐di‐O‐ ( 3 , 26MC), methyl 3‐O‐ ( 4 , 3MC), methyl 6‐O‐methyl‐cellulosides ( 5 , 6MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐methyl‐ ( 6 , G‐236MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,3‐di‐O‐methyl‐ ( 7 , G‐23MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,6‐di‐O‐methyl‐ ( 8 , G‐26MC), methyl β‐D‐glucopyranosyl‐(1→4)‐3‐O‐methyl‐ ( 9 , G‐3MC), methyl β‐D‐glucopyranosyl‐(1→4)‐6‐O‐methyl‐ ( 10 , G‐6MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐methyl‐ ( 11 , GG‐236MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,3‐di‐O‐methyl‐ ( 12 , GG‐23MC), methyl β‐D‐glucopy‐ranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,6‐di‐O‐methyl‐ ( 13 , GG‐26MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐3‐O‐methyl‐ ( 14 , GG‐3MC), and methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐6‐O‐methyl‐cellulosides ( 15 , GG‐6MC). Surface tension, differential scanning calorimetry, fluorescence, and dynamic light scattering measurements of aqueous solutions of compounds 1 – 15 revealed that there was no relationship between aggregation behaviors and gel formation, gelation occurred only when the hydrophobic environments formed by hydrophobic interactions between the sequences of 2,3,6‐tri‐O‐methyl‐glucopyranosyl units upon heating. The diblock structure consisting of cellobiosyl block and approx. ten 2,3,6‐tri‐O‐methyl‐glucopyranosyl units was of crucial importance for thermoreversible gelation of methylcellulose. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1539–1546, 2011  相似文献   
15.
An uncollimated molecular beam (free jet) of CO and O2 molecules incident on a polycrystalline Pt surface at 775 K in vacuo produces vibrationally hot CO2 molecules at a density sufficient for infrared emission spectrometry. Analysis of spectra at a resolution of 0.1 cm?1 clearly shows that nascent product molecules have much more internal excitation than would be the case for equilibrium at the surface temperature.  相似文献   
16.
Summary: The paper reviews recent developments in synthesis and characterization of regioselectively functionalized cellulose derivatives. It demonstrates the importance of protecting groups like triphenylmethyl- and thexyldimethylsilyl (TDMS) ethers in cellulose chemistry. The protected cellulose derivatives can be used for the preparation of 2,3-O-functionalized polymers. Moreover, the TDMS group opens up the synthesis of 3-O-ethers of cellulose that possess interesting properties in terms of structure in solution, water-solubility, and thermoreversible gelation.  相似文献   
17.
18.
Infrared laser spectroscopy and time-of-flight mass spectrometry have been used to measure the rotational and translational distributions of HF and NH3 subliming from a polycrystalline sample of NH4F. The results of this study are compared with thermal desorption and gas-surface scattering experiments.  相似文献   
19.
Experiments are described in which bare (completely desolvated) ions are separated from their source gas and mixed with a bath gas of any desired temperature and precisely controlled composition. The resulting mixture of ions and bath gas is transported by free jet expansion into a vacuum system for mass analysis to reveal the extent to which the ions have formed adducts with other species in the bath gas. Because the ions are separated from their source gas or vapor before they are mixed with the bath gas, the compositions of the bath gas and source gas are completely independent. Thus, one can examine solvation or adduction by any desired species contained in the bath gas without any interference from other species that might be present in the source gas. Reported here are results obtained on the solvation of electrospray ions of a small peptide, leucine-enkephalin, by water and several alkanols. One provocative finding is that a substantial fraction of ions thought to be singly charged monomers turned out to be doubly charged dimers.  相似文献   
20.
The rack space     
The main result of this paper is a new classification theorem for links (smooth embeddings in codimension 2). The classifying space is the rack space and the classifying bundle is the first James bundle.

We investigate the algebraic topology of this classifying space and report on calculations given elsewhere. Apart from defining many new knot and link invariants (including generalised James-Hopf invariants), the classification theorem has some unexpected applications. We give a combinatorial interpretation for of a complex which can be used for calculations and some new interpretations of the higher homotopy groups of the 3-sphere. We also give a cobordism classification of virtual links.

  相似文献   

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