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71.
Piercarlo Fantucci Tiziana Marino Nino Russo Anna Maria Villa 《Journal of computer-aided molecular design》1995,9(5):425-438
Summary The three-dimensional structure of dolastatin-10, an extremely potent cytostatic and antineoplastic peptide extracted from the mollusc Dolabella auricularia, has not yet been fully characterized in an experimental way. By means of a systematic conformational search of the natural peptide and of two mutated analogs, carried out both in vacuo and in aqueous solution, the present work allows to obtain insights into the conformational preferences of this remarkable compound. In addition, the ability to form intra- and intermolecular H-bonds as a function both of the sequence and of the conformation is discussed. The search for the best molecular conformations has been carried out using a molecular mechanics approach, based on the CVFF potential. Dolastatin-10 contains some unusual amino acids for which no experimental structural data are available. In order to check the reliability of the CVFF potential in predicting structures of such nonconventional amino acids, geometry optimizations have been carried out using the ab initio Hartree-Fock procedure. The CVFF parameterization is found to be adequate also for nonconventional amino acids. 相似文献
72.
Beringhelli T D'Alfonso G Panigati M Mercandelli P Sironi A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(23):5340-5350
The quantitative addition of pyrazole (Hpz) to the 44 valence-electron, triangular cluster anion [Re3(mu 3-H)-(mu-H)3(CO)9]- gives the novel unsaturated anion [Re3(mu-H)4(CO)9(Hpz)]- (1, 46 valence electrons), which contains a pyrazole molecule that is terminally coordinated on a cluster vertex. Solidstate X-ray and IR analyses reveal a rather weak hydrogen-bonding interaction between the NH proton and one of the hydrides bridging the opposite triangular cluster edge (delta H degree = -3.1 kcal mol-1 from the Iogansen equation). Both IR and NMR data indicate that such a proton-hydride interaction is maintained in the major conformer present in CD2Cl2, but also provide evidence of the presence of minor conformers of 1 in which the NH proton is involved in an intermolecular hydrogen bond with the solvent. The mu-H...HN bond length evaluated in solution through the T1 minimum value (2.07 A) and that determined in the solid state by X-ray diffraction (2.05 A) are in good agreement. NMR experiments show that, in acetone, intermolecular N-H...solvent interactions replace the intramolecular dihydrogen bond. At room temperature in CH2Cl2, the pyrazole ligand in 1 is labile and 1 slowly "disproportionates" to [Re3(mu 3-H)-(mu-H)3(CO)9]- and [Re3(mu-H)3(CO)9-(mu-eta 2-pz)(Hpz)]-, with H2 evolution. Slow H2 evolution also leads to the formation of the anion [Re3(mu-H)3-(CO)9(pz)]- (5), in which the pyrazolate anion adopts a novel mu 3-eta 2-coordination mode, as revealed by a single-crystal X-ray analysis. The analysis of the bond lengths indicates that the pyrazolate anion in 5 acts as a six-electron donor, with loss of the aromaticity. The formation of 5 from 1 is much faster in solvents with a high dielectric constant, such as acetone or DMF. Anion 5 was also obtained from the reaction of pyrazole with [Re3(mu-H)3(CO)9(mu 3-CH3)]- through the intermediate formation of two isomeric addition derivatives and following CH4 evolution. 相似文献
73.
Manso MA Cattaneo TM Barzaghi S Olieman C López-Fandiño R 《Journal of AOAC International》2002,85(5):1090-1095
An interlaboratory study, with the participation of 8 laboratories, was conducted to evaluate a sodium dodecyl sulfate-capillary gel electrophoresis method for determination of adulteration of milk powder with soy and pea proteins. Calibration standards (0-8%, w/w, soy and pea protein in total protein) and adulterated skim milk powders (0-5%, w/w, soy and pea proteins in total protein) were produced. Vegetal proteins were determined after removal of milk proteins by pretreatment of the samples with tetraborate-EDTA buffer, pH 8.3. Repeatability standard deviations ranged from 9 to 15% and reproducibility standard deviations ranged from 25 to 30% in the samples containing 5% vegetal protein in total protein. 相似文献
74.
Tiziana Beringhelli Gianfranco Ciani Giuseppe DAlfonso Angelo Sironi Maria Freni 《Journal of organometallic chemistry》1982,233(3):C46-C50
The novel anions [Re3H3(CO)10(μ-O2CR)]? (R = H, CH3, CF3), obtained by reaction of [Re3H4(CO)10]? with the corresponding car?ylic acids, have been characterized by IR and NMR spectra and by X-ray analysis of the formate and trifluoroacetate derivatives. They contain a triangle of rhenium atoms, with the car?ylate group diaxially bridging on the shorter ReRe edge. 相似文献
75.
Francesca Cardullo Paul Seiler Lyle Isaacs Jean-Franois Nierengarten Richard F. Haldimann Franois Diederich Tiziana Mordasini-Denti Walter Thiel Corinne Boudon Jean-Paul Gisselhrccht Maurice Gross 《Helvetica chimica acta》1997,80(2):343-371
By the tether-directed remote functionalization method, a series of bis- to hexakis-adducts of C60, i.e., 1 – 7 (Fig. 1), had previously been prepared with high regioselectivity. An efficient method for the removal of the tether-reactive-group conjugate was now developed and its utility demonstrated in the regioselective synthesis of bis- to tetrakis(methano)fullerenes ( = di- to tetracyclopropafullerenes-C60-Ih) 9 – 11 starting from 4, 5, and 7, respectively (Schemes 2, 4, and 5). This versatile protocol consists of a 1O2 ene reaction with the two cyclohexene rings in the starting materials, reduction of the formed mixture of isomeric allylic hydroperoxides to the corresponding alcohols, acid-promoted elimination of H2O to cyclohexa-1,3-dienes, Diels-Alder addition of dimethyl acetylenedicarboxylate, retro-Diels-Alder addition, and, ultimately, transesterification. In the series 9 – 11 , all methano moieties are attached along an equatorial belt of the fullerene. Starting from C2v-symmetrical tetrakis-adduct 15 , transesterification with dodecan-1-ol or octan-1-ol yielded the octaesters 16 and 17 , respectively, as noncrystalline fullerene derivatives (Scheme 3). The X-ray crystal structure of a CHCl3 solvate of 11 (Fig. 3) showed that the residual conjugated π-chromophore of the C-sphere is reduced to two tetrabenzopyracylene substructures connected by four biphenyl-type bonds (Fig. 5). In the eight six-membered rings surrounding the two pyracylene (= cyclopent[fg]acenaphthylene) moieties, 6–6 and 6–5 bond-length alteration (0.05 Å) was reduced by ca. 0.01 Å as compared to the free C60 skeleton (0.06 Å) (Fig. 4). The crystal packing (Fig. 6) revealed short contacts between Cl-atoms of the solvent molecule and sp2- and sp3-C-atoms of the C-sphere, as well as short contacts between Cl-atoms and O-atoms of the EtOOC groups attached to the methano moieties of 11 . The physical properties and chemical reactivity of compounds 1 - 11 were comprehensively investigated as a function of degree and pattern of addition and the nature of the addends. Methods applied to this study were UV/VIS (Figs. 7–11), IR, and NMR spectroscopy (Table 2), cyclic (CV) and steady-state (SSV) voltammetry (Table 1), calculations of the energies of the lowest uunoccupied mmolecular orbitals (LUMOs) and electron affinities (Figs. 12 and 13), and evaluation of chemical reactivity in competition experiments. It was found that the properties of the fullerene derivatives were not only affected by the degree and pattern of addition but also, in a remarkable way, by the nature of the addends (methano vs. but-2-ene-1, 4-diyl) anellated to the C-sphere. Attachment of multiple thano moieties along an equatorial belt as in the series 8 – 11 induces only a small perturbation of the original fullerene π-chromophore. In general, with increasing attenuation of the conjugated fullerene π-chromophore, the optical (HOMO-LUMO) gap in the UV/VIS spectrum is shifted to higher energy, the number of reversible one-electron reductions decreases, and the first reduction potential becomes increasingly negative, the computed LUMO energy increases and the electron affinity decreases, and the reactivity of the fullerene towards nucleophiles and carbenes and as dienophile in cycloadditions decreases. 相似文献
76.
Alunni S Del Giacco T De Maria P Fontana A Gasbarri C Ottavi L 《The Journal of organic chemistry》2004,69(18):6121-6123
Second-order rate constants have been determined for the title reactions in OH(-)/H(2)O and in OH(-)/ (CH(3)CN/H(2)O) [30/70, 60/40, and 85/15 (v/v) mixtures]. A relatively small increase in reactivity is observed for the four substrates upon increasing the percentage of CH(3)CN in the solvent mixture. The methyl activating factors (/) are also slightly affected by the solvent composition. On the other hand, the high acceleration of the reaction by methylation of the pyridine ring amounts to 10(4)-10(6) according to an E1cb mechanism. 相似文献
77.
Benaglia M Benincori T Mussini P Pilati T Rizzo S Sannicolò F 《The Journal of organic chemistry》2005,70(19):7488-7495
[structure: see text] The role played by the electronic properties and the steric features of bis(oxazoline) ligands in the Cu(I)-catalyzed cyclopropanation of styrene effected with ethyl diazoacetate was investigated. Two pairs of new bis(oxazolines) displaying flexible and atropisomeric 3,3'-bithiophene backbones were synthesized and structurally and electronically characterized. For the first time, the electrochemical oxidative potential was used as a reliable index of the electronic density on the nitrogen atom of the chelating groups of new and, for comparative purposes, of already known bis(oxazolines). The Cu(I) complexes of the new ligands were prepared, and their enantioselection ability and catalytic efficiency were tested. This investigation suggests that steric factors and catalyst geometrical features are clearly more important than any consideration of the electronic properties of the chiral ligands. 相似文献
78.
79.
Antonio Qualtieri Giovanni Morello Piernicola Spinicelli Maria T. Todaro Tiziana Stomeo Luigi Martiradonna Milena De Giorni Xavier Quélin Stéphanie Buil Alberto Bramati Jean P. Hermier Roberto Cingolani Massimo De Vittorio 《Superlattices and Microstructures》2010
Direct lithography of resist blends, embedding semiconductor colloidal nanocrystals (NCs) is an innovative way to achieve nanopositioning of NCs in quantum-confined optical resonators. In this work, we show a new appealing approach for the fabrication of single-photon sources operating at room temperature by localizing semiconductor colloidal NCs into vertical planar microcavities with lithographic techniques. 相似文献
80.
Rosanna Inzitari Tiziana Cabras Elisabetta Pisano Chiara Fanali Barbara Manconi Emanuele Scarano Antonella Fiorita Gaetano Paludetti Armando Manni Sonia Nemolato Gavino Faa Massimo Castagnola Irene Messana 《Journal of separation science》2009,32(1):57-63
Thymosin β4 (Tβ4), its sulfoxide, and thymosin β10 (Tβ10) were detected in human saliva and identified by different strategies based on RP HPLC coupled to electrospray multidimensional IT MS. Tβ4 was almost always detected in whole saliva, its sulfoxide sporadically, Tβ10 rarely. Tβ4 was undetectable in parotid saliva and less concentrated in submandibular/sublingual saliva than in whole saliva. Analysis of gingival crevicular fluid revealed high relative amounts of Tβ4, Tβ4 sulfoxide, and Tβ10 in all the samples. Tβ4 mean concentration was 200 times higher in crevicular fluid (20 μmol/L, N = 9) than in whole saliva (0.1 μmol/L, N = 9). Crevicular fluid concentration of Tβ4 (ca. 5% represented by its sulfoxide) and β10 significantly correlated (r = 0.856; N = 9), and their ratio was about 5. A significant correlation was also observed between Tβ4 concentrations in whole saliva and gingival crevicular fluid (r = 0.738; N = 9). Immunohistochemical analysis of the major salivary glands showed that immunoreactivity for Tβ4 is restricted to ductal cells, with minor degree of focal positivity in some acinar cells. On the whole, results indicate that gingival sulcus is a main, although not the sole, source for oral Tβ4 and Tβ10. 相似文献