全文获取类型
收费全文 | 145篇 |
免费 | 8篇 |
专业分类
化学 | 106篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 19篇 |
物理学 | 16篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 16篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 2篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 1篇 |
排序方式: 共有153条查询结果,搜索用时 15 毫秒
131.
In the present paper, we prove quantitative q‐Voronovskaya type theorems for q‐Baskakov operators in terms of weighted modulus of continuity. We also present a new form of Voronovskaya theorem, that is, q‐Grüss‐Voronovskaya type theorem for q‐Baskakov operators in quantitative mean. Hence, we describe the rate of convergence and upper bound for the error of approximation, simultaneously. Our results are valid for the subspace of continuous functions although classical ones is valid for differentiable functions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
132.
Serkan Demirci Selin Kinali‐Demirci Tuncer Caykara 《Journal of polymer science. Part A, Polymer chemistry》2013,51(7):1612-1619
In this study, we report on the fabrication of tunable mixed‐charged copolymer brushes consisting of negatively charged carboxylic acid monomer (4‐vinylbenzoic acid, VBA) and positively charged quaternary amine monomer ((ar‐vinylbenzyl)trimethylammonium chloride) via reversible addition–fragmentation chain transfer‐mediated polymerization. The copolymer brushes have negative charge under neutral and basic conditions, and are positively charged under acidic conditions owing to the protonation of the carboxylate groups. The copolymer brushes revealed a unique reversible wetting behavior with pH. The reversible properties of the copolymer brushes can be employed to regulate the adsorption of charged biomacromolecules such as DNA and proteins. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
133.
Dicarboxylic acid-terminated monolayers on hydroxylated silicon wafer were prepared via the chemisorption of 3-glycidoxypropyldimethylethoxysilane (GPDMES) molecules and subsequent reaction of the epoxy groups with iminodiacetic acid (IDA). The structure and surface composition of the monolayers were characterized by the means of contact-angle measurement, ellipsometric thickness measurement, reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Moreover, we found that the dicarboxylic acid-terminated monolayers on silicon wafer exhibit well-defined contact angle titration curve from which the surface acid dissociation constants were determined. The results were compared with the pKa values reported in the literature for IDA in aqueous solution. Small difference in the surface pKa values was attributed to variations of the microenvironment of the acid moieties. These experimental findings provide fundamental knowledge at the molecular level for the preparation of bioactive surfaces of controlled reactivity on silicon substrates. 相似文献
134.
135.
Adem Zengin Ertan Yildirim Tuncer Caykara 《Journal of polymer science. Part A, Polymer chemistry》2013,51(4):954-962
Well‐defined, high‐density poly(2‐(2‐methoxyethoxy)ethyl methacrylate) [poly(MEO2MA)] brushes were fabricated through a reliable strategy by the combination of self‐assembly of a monolayer of 3‐aminopropyltrimethoxy silane on silicon surface to immobilize 4‐cyano‐4‐(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid chain transfer agent and reversible addition‐fragmentation chain transfer‐mediated polymerization of MEO2MA. The whole fabrication process of the poly(MEO2MA) brushes was followed by water contact angle, grazing angle‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and atomic force microscopy. Characterization of the poly(MEO2MA) brushes, such as molecular weight and thickness determination, were measured by gel permeation chromatography and ellipsometry, and the grafting density was estimated. The temperature‐responsive property of the poly(MEO2MA) brushes was further investigated and the result verified the brush‐to‐mushroom phase transition of the poly(MEO2MA) chains from low to high temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
136.
The complexing of Eu(fod)3 with macrocyclic ethers, benzo[15]crown-5, benzo[12]crown-4, dibenzo[20]crown-6, dibenzo[23]crown-7 and dibenzo[26]crown-8 was observed on their 1H-NMR spectra and the selective binding constants at 400 MHz and 305 K in CDCl3 were reported. The Eu(fod)3 interaction displayed the selective binding role of oxygen on macrocyclic, H2COCH2, backbones with o- or m-dioxyphenyl groups referring the 1H chemical shifts. The estimated equilibrium constants, Ka of 1:1 ratio of interactions were in accordance with the Eu3+ ionic radii to bind the oxygen sites depending on the macrocyclic size and conformation of the ethers. The minimum lanthanide-macrocyclic ether distance displayed the maximum stability so that benzo[3n]crown-n (n=4, 5) group was found to bind the Eu(fod)3 moderately whilst dibenzo[3n+2]crown-n (n=6-8) oligomer chemical shifts were induced largely since the such Eu3+ complexes are more stable with larger ethyleneoxy groups. 相似文献
137.
Abdul Rob Manuel Hernandez Andrew S. Ball Munir Tuncer Maria E. Arias Michael T. Wilson 《Applied biochemistry and biotechnology》1997,62(2-3):159-174
The effect of a number of environmental parameters (pH, temperature, carbon and nitrogen ratio of nutrient) on the production
of extracellular peroxidase enzymes byStreptomyces avermitilis UAH30 was examined. Maximum specific peroxidase activity (0.12 U/mg of protein) was obtained after 72 hours of 1 incubation
at 45‡C in a minimal salt medium (pH 7.5) containing 0.6% (w/v) yeast extract and 0.6% (w/v) xylan corresponding to a C:N
ratio of 4 to 1. A study of the effect of incubation on peroxidase activity showed that the enzyme was stable and active for
at least one hour after incubation at 50‡C while at higher temperatures the stability and activity of the peroxidase was reduced
such that at 60‡C the peroxidase activity has a half life of 20 min while at 80‡C the half life was reduced to 5 min. The
activation energy for deactivation as a result of thermal denaturation of the enzyme was calculated to be 80 ±7 kJ/mol. The
optimum pH for the activity occurred between a pH range of 6.5–8.5 with pKa1 and pKa2 of 5.1 ±0.1 and 9.7 ±0.1, respectively. The Km and Vmax for the peroxidase activity were determined to be 1.45 mM and 0.31 unit per mg protein respectively using 2,4dicholorophenol
(2,4-DCP) as a substrate. Characterization of the peroxidase activity revealed activity against L,3–4 dihydroxyphenylalanine
and guaiacol, while no inhibition of peroxidase activity could be detected with the haem inhibitors such as potassium cyanide
and sodium azide, suggesting the lack of haem component in the tertiary structure. Aspects of using the crude peroxidase preparation
in the pulp and paper industry are discussed. 相似文献
138.
Hydrogels based on N,N-dimethylacrylamide (DMAAm), allylthiourea (ATU), and maleic acid (MA) were synthesized by free-radical cross-linking copolymerization in water with N,N-methylene-bis(acrylamide) (BAAm) as the cross-linker, ammonium persulfate (APS) as the initiator, and N,N,N′,N′-tetramethylenediamine (TEMED) as the activator. Since Se(IV) is the most serious interfering element in the electroanalytical (polarographic or voltammetric) determination of lead and cadmium, a new method for their correct determination after selective separation of the interfering ion (selenite) was developed by using poly(N,N-dimethylacrylamide-co-allylthiourea) [P(DMAAm-co-ATU)] hydrogels containing reducing pedant groups like allylthiourea. The proposed method showed good reproducibility and accuracy with relative standard deviations of 8.5 and 3.4% and relative errors of ?6.0 and ?5.4% for the determination of 5.0 × 10?5 M Pb(II) and Cd(II), respectively, next to 3.0 × 10?5 M Se(IV). 相似文献
139.
The reaction of etheral methyllithium with 3,3-dibromo-2,7,7-trimethyl-tricyclo[4.1.1.0(2,4)]octane (2) was investigated. The generated carbene 12 undergoes intramolecular C-H insertion to provide the tetracyclic hydrocarbon 3 and the bicyclic allene 15, which undergoes [2+2] cyclodimerization. The structures of the formed allene dimers 16, 17, and 18 were elucidated by spectral means. The activation barriers for all possible C-H insertion products 3, 13, and 14 and the allene 15 were investigated by using density functional theory computations at the B3LYP/6-31G(d) level. It was found that the activation barriers for the formation of 3 and 15 (6.2 and 6.3 kcal mol(-1)) are much lower than that for the insertion products 13 and 14 (17.5 and 12.6 kcal mol(-1)), respectively. This prediction was completely in agreement with our experimental results. 相似文献
140.
Hülya Tuncer Çakil Erk 《Journal of inclusion phenomena and macrocyclic chemistry》2003,45(3-4):271-274
Some novel bis-(substituted-phenoxy) ended glycols were synthesised usinghydroxy aromatics of vanillin, o-vanillin, iso-vanillin and 4-hydroxy coumarin which reacted with bis-dihalides of polyglycols in the presence ofDMSO/alkali carbonate. The novel podands, Ar-(CH2CH2O)m-Ar,(m = 1–4), were identified with IR, 1H-NMR, 13C-NMR and mass spectrometry. The various (formyl-methoxy)phenyl and 4-oxycoumarin derivatives of glycols were studied to estimate the cation binding selectivity of SCN- salts ofLi+, Na+, K+ and Zn2+ cations in acetonitrile using steady statefluorescence spectroscopy. The relevant structures of podands have shown goodselectivity depending on the cation and the glycollength, although the chromophoreend groups have no specific contribution on binding. 相似文献