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121.
Biscatechol-hydroxamate and catechol-bishydroxamate chelators of similar architecture were synthesized by a small set of acylation reactions, Michael additions, and domino Wittig alkenations and they were tested for siderophoric activity in various receptor-deficient mutants of Escherichia coli under iron starvation. Growth promotion occurred only in mutants featuring catecholate recognizing receptors. Simplified mimics of the natural siderophores parabactin and agrobactin, carrying an o-hydroxybenzamide instead of the 2-(o-hydroxyphenyl)oxazoline ligand, were prepared analogously. Unlike the originals these mimics are fully functional siderophores in E. coli. 相似文献
122.
Shagidullina R. A. Zakharova L. Ya. Valeeva F. G. Kudryavtseva L. A. 《Russian Chemical Bulletin》2001,50(7):1181-1185
The micellar effect of cationic surfactants in alkaline hydrolysis of O-alkyl-O-aryl-chloromethyl phosphonates involves a positive contribution of concentrating the reagents and a negative effect of the micellar environment due to a loss in the activation entropy. The reactivity of substrates in micelles depends on both electronic and hydrophobic characteristics of substituents in the aryl group. 相似文献
123.
筋骨草甾酮C是分布于植物中的植物甾酮类化合物,具有抗氧化的作用.本文标定了该化合物中所有的碳信号,并通过13C-1HCOSY和1H-1HCOSY技术纠正了文献中氢信号归属的错误. 相似文献
124.
E. A. Mareeva M. A. Orlova V. V. Doseeva D. B. Loginov A. G. Galkin I. G. Gazarina V. I. Tishok 《Applied biochemistry and biotechnology》1996,61(1-2):13-23
Two horseradish peroxidase C (HRPC) mutants with substitutions in the active center, i.e., Phe41→ His and Phel43→ Glu, were
compared to the wild-type recombinant enzyme expressed in Escherichia coli in terms of the enzymatic activity and stability
under irradiation. Both mutations caused a significant decrease in activity, but it was still possible to follow the effect
of mutations on the key steps of the reaction mechanism. Phe41 can be considered a nonpolar barrier separating histidine residues
in the active center and providing a firm noncovalent binding with the highly hydrophobic porphyrin ring. The replacement
of Phe41 with the ionizable His residue destabilizes the enzyme. The Phel43→ Glu replacement creates a negative charge at
the entrance of the heme-binding pocket, and protects the latter from both donor substrates and free radicals.
The radiolytic inactivation of the wild-type and mutant forms of recombinant HRP suggested different binding sites for iodide,
2,2′-bis(3-ethylbenzothiasoline-6-sulfonate (ABTS), guaiacol, and o-phenylene diamine. The study of kinetics and inactivation
is in agreement with the direct binding of iodide to the heme porphyrin ring. The results also suggest that the ABTS binding
site is less accessible than that for o-phenylene diamine. 相似文献
125.
D. R. Gabdrakhamanov D. A. Samarkina V. E. Semenov L. F. Saifina F. G. Valeeva V. S. Reznik 《Phosphorus, sulfur, and silicon and the related elements》2016,191(11-12):1673-1675
ABSTRACTThe series of novel pyrimidine-containing amphiphiles were examined as catalysts for cleavage of phosphonates having various hydrophobicities. Kinetic data showed marked substrate specificity of three different types (i) inhibition for both substrates, (ii) catalysis for more hydrophobic phosphonate and inhibition for less hydrophobic phosphonate, and (iii) catalysis for both substrates. The highest acceleration (more than 11 times in comparison with the reaction in the absence of amphiphile) has been reached in the case of dicationic amphiphile with three hydrophobic tails. 相似文献
126.
Moshe Kress Kyle Y. Lin Roberto Szechtman 《Mathematical Methods of Operations Research》2008,68(3):539-549
A target is hidden in one of several possible locations, and the objective is to find the target as fast as possible. One
common measure of effectiveness for the search process is the expected time of the search. This type of search optimization
problem has been addressed and solved in the literature for the case where the searcher has imperfect sensitivity (possible
false negative results), but perfect specificity (no false positive detections). In this paper, which is motivated by recent
military and homeland security search situations, we extend the results to the case where the search is subject to false positive
detections. 相似文献
127.
Veeramani Murugan Ponnusamy Parasuraman Jeyasigamani F. A. Selvin Michael M. Gromiha Kazuhiko Fukui 《Journal of carbohydrate chemistry》2017,36(2-3):111-128
In the present study, the hydroxyl groups at the C4 and C7 positions of sialic acid and C6 position of galactose in Neu5Acα(2–3)Gal (N23G) and the hydroxyl groups at the C8 position of sialic acid and C3 and C4 positions of galactose in Neu5Acα(2–6)Gal (N26G) were substituted with fluorine atoms, respectively. Molecular dynamics simulations of 100 ns duration were carried out to investigate the structural and dynamical behavior of H1 bound with the tri-fluorinated N23G and N26G (FN23G and FN26G). Based on energy analysis, it was concluded that FN26G should be a better binder for hemagglutinin (H1) than FN23G and it might act as an inhibitor for influenza. 相似文献
128.
129.
L. Ya. Zakharova F. G. Valeeva R. A. Shagidullina L. A. Kudryavtseva 《Russian Chemical Bulletin》2000,49(10):1696-1698
The reactivity of alkyl aryl chloromethylphosphonates in alkaline hydrolysis in the sodium bis(2-ethylhexyl)sulfosuccinate—decane—water
reverse micellar system is mainly determined by the electronic properties of substituents and depends only slightly on their
hydrophobicity.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1715, October, 2000. 相似文献
130.
Se Geun Lee Jae Pil Kim Ick Chan Kwon Ki Hong Park Seok Kyun Noh Sung Soo Han Won Seok Lyoo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3567-3576
Poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) microspheres with a skin/core structure were prepared through the heterogeneous surface saponification of PVAc microspheres suspension‐polymerized. The PVA skin formed through the heterogeneous saponification was hydrogel swellable in water. In addition, to obtain monodisperse PVA/PVAc microspheres having various skin/core ratios and morphologies, the ion‐specificities to the heterogeneous saponification were investigated using SO, Cl?, NO, Br?, and I? for anions and Li+, Na+, and K+ for cations, respectively. The ions were not specific significantly to the rate of the heterogeneous saponification, while were related to the degree of saponification (DS). DSs had different values between by weight loss (DSw) and by proton nuclear magnetic resonance spectroscopy (DSNMR) measurements. The order of DSws was SO < Cl? < NO < Br? < I? for anions and K+ < Na+ < Li+ for cations, and that of DSNMRs, I? < Br? < NO < Cl? < SO for anions and Li+ < Na+ < K+ for cations. The differences in values between DSws and DSNMRs were caused by the dissolution of PVA skin and were significantly decreased for SO. The peaks at melting temperature of PVA were sharp and their areas were large for ions deswelling PVA skins. 相似文献