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1.
A.Q.H. Habets-Crützen S.J.N. Carlier J.A.M. de Bont D. Wistuba V. Schurig S. Hartmans J. Tramper 《Enzyme and microbial technology》1985,7(1):17-21
Resting cells of ethene grown Mycobacterium 2W produced 1,2-epoxypropane stereospecifically from propene as revealed by optical rotation, 1H n.m.r. using a chiral shift reagent, and also by complexation gas chromatography involving a glass capillary column coated with an optically active metal chelate. The gas-liquid chromatography method allowed the rapid screening of 11 strains with regard to stereospecific formation of 1,2-epoxypropane, 1,2-epoxybutane and 1-chloro-2,3-epoxypropane. Bacteria grown on either ethene, propene or butadiene all predominantly produced the R form of 1,2-epoxypropane from propene and 1,2-epoxybutane from 1-butene while the strains tested for 1-chloro-2,3-epoxypropane production from 3-chloro-1-propene predominantly accumulated the S enantiomer. 相似文献
2.
Svetlana V. Shilova Grigory M. Mirgaleev Ksenia A. Romanova Yury G. Galyametdinov 《Biopolymers》2023,114(10):e23555
This work reports synthesis of pH-responsive alginate/chitosan hydrogel spheres with the average diameter of 2.0 ± 0.05 mm, which contain cefotaxime that is an antibiotic of the cefalosporine group. The spheres provided the cefotaxime encapsulation efficiency of 95 ± 1%. An in vitro release of cefotaxime from the spheres in the media that simulate human biological fluids in peroral delivery conditions was found to be a pH-dependent process. The analysis of cefotaxime release kinetics by the Korsmeyer–Peppas model revealed a non-Fickian mechanism of its diffusion, which may be related to intermolecular interactions occurring between the antibiotic and chitosan. Conductometry, UV spectroscopy, and IR spectroscopy were used to study complexation of chitosan with cefotaxime in aqueous media with varied pH, characterize the composition of the complexes, and calculate their stability constants. The composition of the cefotaxime–chitosan complexes was found to correspond to the 1.0:4.0 and 1.0:2.0 molar ratios of the components at pH 2.0 and 5.6, respectively. Quantum chemical modeling was used to evaluate energy characteristics of chitosan–cefotaxime complexation considering the influence of a solvent. 相似文献
3.
Darja Fer
ej-Temeljotov Matev Kmet Darko Kocjan Sonja Kotnik Aleksander Resman Uro Urleb Katarina Verhnjak Igor Zver Janko
mitek 《Chirality》1993,5(4):288-292
Structure–interaction relationships, stereoselectivity, and solubility enhancement in inclusion compexation of β-cyclodextrins (CDs) with some racemic and enantiomerically pure 1,4-dihydropyridine derivatives (DHPs) were investigated. 1:1 and 1:2 (mole ratio) complexes were prepared and characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), MS-FAB spectrometry, 1H-NMR spectroscopy, water and phase solubility. The solubility studies have revealed different complexation equilibria for optically pure DHP enantiomers, and corresponding racemic mixtures in water solutions. By means of 1H-NMR chemical shift measurements, the inclusion of aromatic fragments of racemic and enantiomerically pure DHP molecules within the cavities of different CDs was elucidated. Considerable stereoselectivity in complexation interactions was observed. The results indicate the potential use of cyclodextrins as chiral selectors for enantiomeric resolution of 1,4-DHP calcium antagonists. © 1993 Wiley-Liss, Inc. 相似文献
4.
The selective precipitation of alpha-lactalbumin (alpha-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. As precipitation is a phenomenon dependent on the protein hydrophobicity, and as the release of the tightly bound calcium occurring at pH around 4 modifies the alpha-LA hydrophobicity, the specific role of calcium on isoelectric precipitation is investigated. A study of the extent of alpha-LA precipitation in a whey protein concentrate under various operating conditions of pH, temperature, protein concentration, and calcium content is presented. We propose a mechanism for this phenomenon as a combination of a complexation equilibrium and of an irreversible precipitation, to account for the influence of temperature, alpha-LA concentration total ionic content, and calcium concentration, and also to estimate the complexation equilibrium constant. (c) 1995 John Wiley & Sons, Inc. 相似文献
5.
X-ray analysis of the crystalline product obtained by reaction of 2,3,4,6-Tetra-O-acetyl-D-glycopyranose with phenylethylamine revealed the formation of a real one-to-one inclusion complex. This complexaion is highly stereoselective, because only the (+)-R-enantiomeric form of the amine is included. Analogies to the mode of complexation of cellulose triaceate with chiral molecules in ?inclusion chromatography”? are discussed. 相似文献
6.
You-Bin Si Yan Xiang Chao Tian Xiong-Yuan Si Jing Zhou Dong-Mei Zhou 《Soil & Sediment Contamination》2013,22(1):72-84
Glyphosate [N-(phosphonomethyl)-glycine] is a herbicide widely used in large quantities in agricultural applications. It is also known to form complexes with metal ions, although its influence on metal behavior, such as lead (Pb) in soil, is not well understood. In this study, the adsorption and co-adsorption of Pb and glyphosate were determined on two soils [a red (RS) soil, Udic Ferrisol, and a yellow-brown (YB) soil, Udic Luvisol] of distinctly different chemical characteristics at varying pH conditions. Results indicate that the adsorption of lead and glyphosate strongly depends on soil types: the RS soil, characterized by a relatively high iron/aluminum content but a low pH and organic matter content, shows a much lower adsorption capacity for Pb but a higher sorption for glyphosate than the YB soil. The co-existence of Pb and glyphosate in soils resulted in complex interactions among Pb, glyphosate, Pb-glyphosate complexes, and soil minerals. The presence of glyphosate decreased Pb adsorption on the two soils, which was attributed primarily to the formation of soluble Pb-glyphosate complexes having relatively low affinities to soil surfaces. On the other hand, addition of Pb increased the adsorption of glyphosate on both soils, which was attributed to: (1) a decreased solution pH due to the ion exchange between Pb2+ and H+ on soil surfaces; and (2) increased sorption sites where Pb was adsorbed and acted as a bridge between glyphosate and the soil. The present study illustrates that the complex interactions among glyphosate, Pb, and soil may have important implications for the mobility and bioavailability of Pb in soil and should thus be considered in future environmental risk assessments. 相似文献
7.
Roya R.R. Sardari Tarek Dishisha Sang‐Hyun Pyo Rajni Hatti‐Kaul 《Biotechnology and bioengineering》2013,110(4):1243-1248
3‐Hydroxypropionaldehyde (3HPA) is an important specialty chemical which can be produced from glycerol using resting cells of Lactobacillus reuteri. This biocatalytic route, however, suffers from substrate‐ and product‐mediated loss of enzyme activity within 2 h of biotransformation. In order to overcome the inhibitory effects of 3HPA, complex formation with sodium bisulfite was investigated, optimized and applied for in situ capture of the aldehyde during biotransformation of glycerol in a fed‐batch process. As a result, the activity of the cells was maintained for at least 18 h. The 3HPA produced per gram cell dry weight was increased 5.7 times compared to the batch production process, and 2.2 times compared to fed‐batch process without in situ complex formation. This approach may have potential for production and in situ removal of 3HPA after further process development. Biotechnol. Bioeng. 2013; 110: 1243–1248. © 2012 Wiley Periodicals, Inc. 相似文献
8.
The interaction of a number of phenolic compounds, being ‘model fragments’ of humic acids, with cadmium ions was investigated. The fluorescence quenching method was used to determine the complexation constants of these compounds with cadmium ions. It was established that bonding of phenolic compounds by cadmium ions at рН 7 is weak and reaches a maximum value of 15% for interaction with resorcinol. It was demonstrated that modification of humic acids by the mechanoactivation method increases by three times bonding of cadmium ions, which is caused by strengthening the acid properties of carboxyl and hydroxyl groups at the aromatic ring. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
9.
DigA16 is an artificial digoxigenin-binding protein, which was derived from the bilin-binding protein, a lipocalin of Pieris brassicae, via reshaping of its natural ligand pocket. Here we report the crystal structures of DigA16 in the presence of either digoxigenin or digitoxigenin and for the apo-protein at resolutions below 1.9A. As a consequence of the altogether 17 amino acid substitutions within the binding site significant structural changes have occurred in the four loops that form the entrance to the ligand pocket on top of the structurally conserved beta-barrel framework. For example, one loop adopts a new alpha-helical backbone structure, which seems to be induced by few critical side-chain contacts. Digoxigenin becomes almost fully buried (by 95%) upon complexation, whereby specificity for the hydrophilic steroid is maintained through hydrogen-bonding networks and shape complementarity. The differential binding of the related steroid digitoxigenin is mainly governed by an internal histidine residue, whose side-chain undergoes significant induced fit. Among those amino acids that line the ligand pocket two tyrosine and one tryptophan residue provide the largest contacts. Interestingly, corresponding three side-chains are found with the same mutual orientation in the anti-digoxigenin antibody 26-10, even though the hapten orientation is quite different there and only 66% of the steroid surface is buried in the combining site. Hence, in the case of the engineered lipocalin DigA16 an example of convergent in vitro evolution is observed. Generally, the remarkable structural plasticity of the loop region and the role of polar residues in the binding site illustrate the potential of the lipocalin scaffold for the generation of specific receptor proteins towards a variety of ligands. 相似文献
10.
A plant flavone, luteolin is a well-known inducer of nod genes in the Rhizobium meliloti. Its poor aqueous solubility was
greatly enhanced by the complexation with a family of cyclosophoraoses synthesized in R .meliloti. Nuclear magnetic resonance
(NMR) spectroscopic analysis showed that the chemical shifts of the aromatic ring moieties of the luteolin were changed greatly
by the complexation with cyclosophoraoses. Fourier transform infrared (FTIR) spectroscopic analysis also showed a restricted
vibrational pattern in carbonyl stretching region of the luteolin due to the complexation. This effective complex formation
of cyclosophoraoses with a plant flavone, luteolin, suggests that rhizobial cyclosophoraoses play an important role as a solubility
enhancer of the hydrophobic legume-derived flavonoids.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献