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71.
Smitrovich JH DiMichele L Qu C Boice GN Nelson TD Huffman MA Murry J 《The Journal of organic chemistry》2004,69(6):1903-1908
The stereochemical outcome of the asymmetric Michael reaction of pseudoephedrine amide enolates changes dramatically in the presence of LiCl. Reaction of the enolate in the absence of LiCl results in formation of the anti Michael adduct with high selectivity, whereas in the presence of lithium chloride the syn adduct is favored. This method provides access to enantiomerically enriched trans-3,4-disubstituted delta-lactones from the anti Michael adducts by a two step reduction/lactonization sequence. Information obtained from NMR studies indicates that, under both enolization conditions, the (Z)-enolate is formed. A model to explain the turnover in selectivity based on NMR evidence is presented. 相似文献
72.
Loren G. Hepler Zorawar S. Kooner Geneviève Roux-Desgranges Jean-Pierre E. Grolier 《Journal of solution chemistry》1985,14(8):579-594
In the ideal associated solution model, activity coefficients of all species (labelled A, B, and AB here) are taken to be unity at all mole fractions and all temperatures, with several derivative consequences that have not previously been investigated. We have applied this model to an analysis of the thermodynamic properties (vapor pressures, excess volumes, excess enthalpies, partial molar enthalpies of solution, and excess heat capacities) of the chloroform + triethylamine system in terms of K, V, H, and C
p
for the equilibrium represented by A+B=AB. It is shown that there is good consistency between the relatively simple chemical ideal associated solution model and all available thermodynamic data except heat capacities, for which the consistency between model and data is less good. Some limitation of the ideal associated solution model are discussed, along with the relationship of this model to hydrogen bonding in the AB complex and to spectroscopic investigations. New thermal (partial molar enthalpies of solution and excess heat capacities) and volumetric data are presented. 相似文献
73.
Hureau C Blanchard S Nierlich M Blain G Rivière E Girerd JJ Anxolabéhère-Mallart E Blondin G 《Inorganic chemistry》2004,43(14):4415-4426
Two heptacoordinated Mn(II) complexes are isolated and X-ray characterized using the well-known tpen ligand (tpen = N,N,N',N'-tetrakis(2-pyridylmethyl)-1,2-ethanediamine): [(tpen)Mn(OH(2))](ClO(4))(2) (1(ClO(4))(2)) and [(tpen)Mn(micro-OAc)Mn(tpen)](ClO(4))(3).2H(2)O (2(ClO(4))(3).2H(2)O). Crystallographic data for 1(ClO(4))(2) at 110(2) K (respectively at 293(2) K): monoclinic, space group C2/c, a = 15.049(3) A (15.096(3) A), b = 9.932(2) A (10.105(2) A), c = 19.246(4) A (19.443(4) A), beta = 94.21(3) degrees (94.50(3) degrees ), Z = 4. Crystallographic data for 2(ClO(4))(3).0.5(C(2)H(5))(2)O at 123(2) K: triclinic, space group P, a = 12.707(3) A, b = 12.824(3) A, c = 19.052(4) A, alpha = 102.71(3) degrees, beta = 97.83(3) degrees, gamma = 98.15(3) degrees, Z = 2. Investigation of the variation upon temperature of the molar magnetic susceptibility of compound 2(ClO(4))(3).2H(2)O reveals a weak antiferromagnetic exchange interaction between the two high-spin Mn(II) ions (J = -0.65 +/- 0.05 cm(-)(1), H = -JS(1).S(2)). EPR spectra are recorded on powder samples and on frozen acetonitrile solutions, demonstrating the maintenance upon dissolution of the heptacoordination of Mn in complex 1 while complex 2 partially dissociates. Electrochemical responses of complexes 1 and 2 are investigated in acetonitrile, and bulk electrolyses are performed at oxidative potential in the presence of various amounts of 2,6-lutidine (0-2.65 equiv per Mn ion). The formation from either 1 or 2 of the mixed-valent complex [(tpen)Mn(III)(micro-O)(2)Mn(IV)(tpen)](3+) (3) is established from mass spectrometry and EPR and IR spectroscopy measurements. When reaction is started from 2, formation of [(tpen)Mn(IV)(micro-O)(2)(micro-OAc)Mn(IV)](3+) (4) is evidenced from cyclic voltammetry, EPR, and UV-vis data. The Mn vs tpen ratio in the electrogenerated complexes is accurately controlled by the quantity of additional 2,6-lutidine. The role of tpen as a base is discussed. 相似文献
74.
Bernat V Ringard-Lefebvre C Bas GL Perly B Djedaïni-Pilard F Lesieur S 《Langmuir : the ACS journal of surfaces and colloids》2008,24(7):3140-3149
Complex formation between octyl beta-D-glucopyranoside (OG) and alpha-cyclodextrin (alphaCD) was investigated on the basis of three highly accurate and appropriate experimental techniques. First, surface tension measurements showed that alphaCD directly acts on the surfactant monomers in the aqueous phase, leading to progressive depletion of the air-water interface with increasing cyclodextrin contents. Significant shift of OG critical micelle concentration (cmc) was consequently observed: the higher alphaCD concentration, the higher the cmc value. Experiments performed at surfactant and cyclodextrin concentrations in the Gibbs regime of surface tension versus OG content were performed on one hand to establish Job's plot that showed 1:1 stoichiometry of the OG-alphaCD complex and on the other hand to calculate the association constant found equal to (1.85 +/- 0.35) x 10(3) L mol(-1). An inclusion process of the surfactant alkyl residue within the cyclodextrin cavity was confirmed by one-dimensional (1)H NMR, and the structure of the mixed assembly was extensively characterized by two-dimensional NOESY (1)H NMR. OG penetrates alphaCD so that its hydrocarbon chain is embedded inside the cyclodextrin cavity, and its polar head as well as the alpha-methylene group emerges outside the alphaCD secondary face. Solubility behavior of the OG-alphaCD complex in a wide range of host-guest ratios and concentrations was finally examined by turbidity recording and optical microscopy. At very low free cyclodextrin levels in the solution, the complex presented high solubility behavior up to more than 70 mM. By increasing nonassociated alphaCD in the mixture, propensity of the cyclodextrin molecules to crystallize was observed at concentrations far below the 100 mM aqueous solubility of the pure cyclodextrin. The hexagonal shape of the crystals seen in the optical microscopy images suggested they were, partially at least, composed of the solid complex. 相似文献
75.
76.
77.
Bridging β‐Cyclodextrin Prevents Self‐Inclusion,Promotes Supramolecular Polymerization,and Promotes Cooperative Interaction with Nucleic Acids 下载免费PDF全文
Dr. Pierre Evenou Dr. Julien Rossignol Dr. Gaëlle Pembouong Adélie Gothland Dr. Dmitri Colesnic Dr. Renaud Barbeyron Dr. Sergii Rudiuk Prof. Anne‐Geneviève Marcelin Dr. Mickaël Ménand Prof. Damien Baigl Prof. Vincent Calvez Dr. Laurent Bouteiller Prof. Matthieu Sollogoub 《Angewandte Chemie (International ed. in English)》2018,57(26):7753-7758
78.
William Gagné-Monfette Jean-François Vincent-Rocan Owen C. Lutes Geneviève F. O'Keefe Alexandria D. M. Jeanneret Claire Blanger Ryan A. Ivanovich Prof. Dr. André M. Beauchemin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(56):14051-14056
In contrast to carbon-substituted isocyanates that are common building blocks, N-substituted isocyanates remain underdeveloped and reports on their N-acyl derivatives (i. e. amido-isocyanates) are exceedingly rare. Herein, amido-isocyanates were investigated in the context of syntheses of aza-tripeptide and hydantoins subunits starting from simple bench-stable precursors. A key finding is that the amido-isocyanate formed in situ cyclized to yield an oxadiazolone, and that under suitable reaction conditions this heterocycle is a traceless blocked (masked) N-isocyanate. Using organic bases as catalysts and upon heating, oxadiazolone formation is observed, and various nucleophiles to provide the desired aza-dipeptides or hydantoins in moderate to high yields. Further support for an amido-isocyanate intermediate was obtained using carboxylic acids as nucleophiles, affording N-acylhydrazide products. 相似文献
79.
Guanosine in a Single Stranded Region of Anticodon Stem–Loop tRNA Models is Prone to Oxidatively Generated Damage Resulting in Dehydroguanidinohydantoin and Spiroiminodihydantoin Lesions 下载免费PDF全文
Dr. Agnieszka Tomaszewska‐Antczak Dr. Piotr Guga Prof. Barbara Nawrot Dr. Geneviève Pratviel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6381-6385
Oxidation of RNA hairpin models corresponding to anticodon stem–loop (ASL) of transfer RNA led to RNA damage consisting solely of a unique loop guanine oxidation. Manganese porphyrin/oxone treatment of RNA resulted in dehydroguanidinohydantoin ( DGh ; major) and/or spiroiminodihydantoin ( Sp ) lesions. Ribose damage was not observed. This two‐electron transfer oxidation reaction allowed the identification of guanine oxidation products for further study of RNA species carrying a unique lesion at a single G to investigate their biological impact. 相似文献
80.