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71.
Merlin Rosales Ysaías Alvarado Mirixa Boves Raúl Rubio Humberto Soscún Roberto A. Sánchez-Delgado 《Transition Metal Chemistry》1995,20(3):246-251
Summary A kinetic study of the regioselective homogeneous hydrogenation of quinoline (Q) to 1,2,3,4-tetrahydroquinoline (THQ) was carried out using the cationic complex [RuH(CO)(NCMe)2(PPh3)2]BF4 (1) as the precatalyst. The experimentally determined rate law wasr = {k
2
K
1/(1+K
1[H2])}[Ru0][H2]2, which becomesr = {k
2
K
1[Ru0]–[H2]2 at low hydrogen concentrations (k
2
K
1 = 28.5M
–2 s–1 at 398 K). The corresponding activation parameters were found to be H
= 42 + 6 kJ mol–1, S
= – 115 ± 2JK–1mol–1 and G
= 92 ± 8 kJ mol–1. Complex(1) was found to react with Q in CHCl3 under reflux to yield [RuH(CO)(NCMe)(N-Q)(PPh3)2]BF4
(2) which was also isolated from the hydrogenation runs. These experimental findings, together with the results ofab initio self-consistent-field molecular orbital calculations on the free organic molecules involved, are consistent with a mechanism involving a rapid and reversible partial hydrogenation of(2) to yield the corresponding dihydroquinoline (DHQ) species [RuH(CO)(NCMe)(DHQ)(PPh3)2]BF4
(4), followed by a rate-determining second hydrogenation of DHQ to yield [RuH(CO)(NCMe)(THQ)(PPh3)2]BF4
(3). 相似文献
72.
Merlin C. E. Bandeira Joseph A. Crayston Norberto S. Gonçalves Lúcia K. Noda Andrew Glidle César V. Franco 《Journal of Solid State Electrochemistry》2007,11(2):231-239
The electropolymerization of trans-[RuCl2(vpy)4] (vpy=4-vinylpyridine) on Au or Pt electrodes was studied by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) technique, and Raman spectroscopy. Cyclic voltammetry of the monomer at a microelectrode shows the typical Ru(III/II) and Ru(IV/III) waves, together with the vinyl reduction waves at −1.5 and −2.45 V and adsorption wave at −0.8 V. Electrodeposition on EQCM technique performed under potential cycling between −0.9 and −2.0 V revealed that the polymerization proceeded well in advance of the vinyl reduction waves. At potentials more positive than −0.9 V, soluble oligomers were deposited irreversibly on the electrode during the oxidative sweep. The film also showed reversible mass changes due to the oxidation and accompanying ingress of charge-balancing anions and solvent into the film. In contrast, potentiostatic growth of the polymer at −1.6 V was slower because the oligomeric material was lost completely from the electrode. Unreacted vinyl groups were detected by in situ Raman spectroscopy for films grown at −0.7, −0.9, and −1.6 V but were absent when the polymerization was carried out at −2.9 V vs Ag/Ag+. 相似文献
73.
Cornard JP Boudet AC Merlin JC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(3):591-602
Complex formation between aluminium chloride and 3'4'-dihydroxyflavone (3'4'diOHF) in methanol has been studied by UV-visible and Raman spectroscopies combined with quantum chemical calculations. Job's method of continuous variation and the molar ratio method were applied to ascertain the stoichiometry composition of the chelate in pure methanol. A 1:1 complex was indicated by both the methods. Geometry optimizations of free and complexed molecules by AMI and DFT methods show that structural modifications of the ligand, induced by complexation, are minor, and are localized on the chelating site. The good agreement between experimental and theoretical electronic spectra of both 3'4'diOHF and complex confirm the structural models. The great similarities between Raman spectra of the free and complexed form constitute an another proof of the absence of pronounced electronic and geometric changes, and notably demonstrate that the quinoidal form induced by the deprotonation of the two hydroxyl groups does not participate in the 3'4'diOHF complex structure. Whereas no complexation occurs in acidic medium, complexes of high stoichiometry are formed in alkaline medium. (Al(3'4'diOHF)2)- and (Al(3'4'diOHF)3)3- species are observed in methanol in the presence of sodium acetate or sodium methanoate. 相似文献
74.
Paulo Emilio Feuser Amanda Virtuoso Jacques Juan Marcelo Carpio Arévalo Maria Eliane Merlin Rocha Maria Claudia dos Santos-Silva Claudia Sayer Pedro H. Hermes de Araújo 《Journal of nanoparticle research》2016,18(4):104
The encapsulation of superparamagnetic nanoparticles (MNPs) in polymeric nanoparticles (NPs) with modified surfaces can improve targeted delivery and induce cell death by hyperthermia. The goals of this study were to synthesize and characterize surface modified superparamagnetic poly(methyl methacrylate) with folic acid (FA) prepared by miniemulsion polymerization (MNPsPMMA-FA) and to evaluate their in vitro cytotoxicity and cellular uptake in non-tumor cells, murine fibroblast (L929) cells and tumor cells that overexpressed folate receptor (FR) β, and chronic myeloid leukemia cells in blast crisis (K562). Lastly, hemolysis assays were performed on human red blood cells. MNPsPMMA-FA presented an average mean diameter of 135 nm and a saturation magnetization (Ms) value of 37 emu/g of iron oxide, as well as superparamagnetic behavior. The MNPsPMMA-FA did not present cytotoxicity in L929 and K562 cells. Cellular uptake assays showed a higher uptake of MNPsPMMA-FA than MNPsPMMA in K562 cells when incubated at 37 °C. On the other hand, MNPsPMMA-FA showed a low uptake when endocytosis mechanisms were blocked at low temperature (4 °C), suggesting that the MNPsPMMA-FA uptake was mediated by endocytosis. High concentrations of MNPsPMMA-FA showed hemocompatibility when incubated for 24 h in human red blood cells. Therefore, our results suggest that these carrier systems can be an excellent alternative in targeted drug delivery via FR. 相似文献
75.
Highly Strained Heterocycles Constructed from Boron–Boron Multiple Bonds and Heavy Chalcogens 下载免费PDF全文
Prof. Dr. Holger Braunschweig Philipp Constantinidis Theresa Dellermann Dr. William C. Ewing Prof. Dr. Ingo Fischer Merlin Hess Dr. Fergus R. Knight Anna Rempel Christoph Schneider Stefan Ullrich Dr. Alfredo Vargas Prof. J. Derek Woollins 《Angewandte Chemie (International ed. in English)》2016,55(18):5606-5609
The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B?B double bond enables reactions with Se0 and Te0. The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions. 相似文献
76.
Salviachinensine A, a natural product obtained from the Chinese medicinal plant Salvia chinensis, was synthesized for the first time by employing Donald Matteson's boronic ester homologation. The use of (R,R)-dicyclohexylethane-1,2-diol (DICHED) enabled the generation of the required stereogenic centers in a highly stereoselective fashion. Salviachinensine A was formed in a one-pot protecting group cleavage/lactonization/ intramolecular Friedel–Crafts alkylation, followed by Lewis acid-catalysed cleavage of the acetal protecting groups. 相似文献
77.
Ying Zheng Merlin L. Bruening Gregory L. Baker 《Journal of Polymer Science.Polymer Physics》2010,48(18):1955-1959
Isothermal crystallization rates of semicrystalline poly(methoxypoly(ethylene glycol) methacrylate) brushes on gold‐coated substrates were measured by polarized optical microscopy. Growth rates for crystal radii, which were essentially constant for each film, initially increased with film thickness and then leveled off for film thicknesses >300 nm. Avrami–Evans theory suggests that the spherulites exhibit one‐dimensional growth with heterogeneous nucleation. Compared with physisorbed analogs, polymer brushes crystallized slower due to the restriction of chain mobility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1955–1959, 2010 相似文献
78.
The composition and conformation of complexes of aluminium(III) with isoquercitrin (Iso) have been studied in methanol solution. This molecule presents two potential chelating sites in competition. UV–Vis spectroscopy provides evidence of three different species in neutral solution: Al(Iso)2+ Al(Iso)2 + and Al2(Iso)3+. This last one is formed only if a great quantity of Al(III) is presented in the medium. The first site involved in complexation is the 5-hydroxy-4-keto group. FT-Raman spectroscopy has allowed to confirm this mechanism. The stability constants of this complexes have been determined using the
program. In acidic condition, only the first complex is obtained. In alkaline medium, Al(Iso)+ and Al(Iso)2 − complexes are formed, the catechol group is then the chelating site involved in these species To propose a molecular conformation for the free isoquercitrin and its complexes in neutral medium, both semiempirical molecular orbital and DFT calculations have been performed. It has been showed that the participation of cynnamoyl and benzoyle mesomeric forms stabilise the structure of Al(Iso)2+. The structural models have been validated by the good agreement between theoretical and experimental electronic spectra. 相似文献
79.
Infinite Time Register Machines (ITRM's) are a well-established machine model for infinitary computations. Their computational strength relative to oracles is understood, see e.g. , and . We consider the notion of recognizability, which was first formulated for Infinite Time Turing Machines in [6] and applied to ITRM's in [3]. A real x is ITRM-recognizable iff there is an ITRM-program P such that Py stops with output 1 iff y=x, and otherwise stops with output 0. In [3], it is shown that the recognizable reals are not contained in the ITRM-computable reals. Here, we investigate in detail how the ITRM -recognizable reals are distributed along the canonical well-ordering <L of Gödel's constructible hierarchy L . In particular, we prove that the recognizable reals have gaps in <L, that there is no universal ITRM in terms of recognizability and consider a relativized notion of recognizability. 相似文献
80.
Nicolas Preux Aurélie Rolle Cindy Merlin Messaoud Benamira Marcin Malys Claude Estournes Annick Rubbens Rose-Noëlle Vannier 《Comptes Rendus Chimie》2010,13(11):1351-1358
In this study, with the aim to enhance the ionic conduction of known structures by defect chemistry, the La2O3-Ta2O5 system was considered with a focus on the La3TaO7 phase whose structure is of Weberite type. In order to predict possible preferential substitution sites and substitution elements, atomistic simulation was used as a first approach. A solid solution La3−xSrxTaO7−x/2 was confirmed by X-ray diffraction and Raman spectroscopy; it extends for a substitution ratio up to x = 0.15. Whereas La3TaO7 is a poor oxide ion conductor (σ700 °C = 2 × 10−5S.cm−1), at 700 °C, its ionic conductivity is increased by more than one order of magnitude when 3.3% molar strontium is introduced in the structure (σ700 °C = 2 × 10−4S.cm−1). 相似文献