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981.
Kobr L Zhao K Shen Y Comotti A Bracco S Shoemaker RK Sozzani P Clark NA Price JC Rogers CT Michl J 《Journal of the American Chemical Society》2012,134(24):10122-10131
We describe an approach to regular triangular arrays of dipolar molecular rotors based on insertion of dipolar rotator carrying shafts as guests into channels of a host, tris(o-phenylenedioxy)cyclotriphosphazene (TPP). The rotor guests can either enter the bulk of the host or stay at or near the surface, if a suitable stopper is installed at the end of the shaft. Differential scanning calorimetry, solid-state NMR, and powder X-ray diffraction were used to examine the insertion of a dipolar rotor synthesized for the purpose, 1-n-hexadecyl-12-(2,3-dichlorophenyl)-p-dicarba-closo-dodecaborane, and it was found that it forms a surface inclusion compound. Rotational barriers from 1.2 to 9 kcal/mol were found by dielectric spectroscopy and were attributed to rotors inserted into the surface to different degrees, some rubbing the surface as they turn. 相似文献
982.
Falus P Porcar L Fratini E Chen WR Faraone A Hong K Baglioni P Liu Y 《J Phys Condens Matter》2012,24(6):064114
Recent combined experiments by small angle neutron scattering (SANS) and neutron spin echo (NSE) have demonstrated that dynamic clusters can form in concentrated lysozyme solutions when the right combination of a short-ranged attraction and a long-ranged electrostatic repulsion exists. In this paper, we investigate the temperature effect on the dynamic cluster formation and try to pinpoint the transition concentration from a monomeric protein phase to a cluster phase. Interestingly, even at a relatively high concentration (10% mass fraction), despite the significant change in the SANS patterns that are associated with the change of the short-ranged attraction among proteins, the normalized short-time self-diffusion coefficient is not affected between 5 and 40?°C. This is interpreted as a lack of cluster formation in this condition. However, at larger concentrations such as 17.5% and 22.5% mass fraction, we show that the average hydrodynamic radius increases significantly and causes a large decrease of the normalized self-diffusion coefficient as a result of cluster formation when the temperature is changed from 25 to 5?°C. 相似文献
983.
Giovanna Colucci Anna Di Gianni Roberta Bongiovanni Aldo Priola Francesca Torello Silvia Bracco Piero Sozzani 《Macromolecular Symposia》2010,296(1):550-556
Summary : The present work describes a method to modify the surface of silica, reducing its polar character and making it compatible and dispersible into hydrocarbon based elastomers. A liquid low molar mass polybutadiene (PB) was grafted with mercaptopropyltrimethoxysilane (MPTS) via radical addition of the thiol group to the double bonds. The silanized PB was reacted with silica via thermal condensation with its silanol groups. 29Si NMR spectra showed that the condensation reaction of the trifunctional silane involved one or two alkoxy groups, while the third alkoxy group remained unreacted, probably for steric reasons. The characterization of the functionalized silica particles was performed by contact angle measurements and TGA analysis. 相似文献
984.
Bianca F Bonini aetano Maccagnani ermana Mazzanti Piero Piccinelli 《Tetrahedron letters》1979,20(41):3987-3990
The reaction of organolithium compounds with stilbene episulphoxides and episulphides leads to stereospecific desulphurization and to ring opening. The stereochemistry of the latter reaction depends on the structural features. 相似文献
985.
Piero Villaggio 《International Journal of Solids and Structures》1977,13(4):279-292
The paper presents an extension to unilateral problems of the classical method of bounding (above and below) the solutions of linear self-adjoint boundary value problems. Using this extension the solution of the general unilateral problem in linear elasticity is bounded in energy by two suitable defined admissible states belonging to two complementary convex sets. 相似文献
986.
Ionization potentials of small molecules are calculated by the MS Xα and LCAO Xα methods. The results are compared with the experimental values and the results of previous accurate calculations. The Xα method proves to be rather accurate and potentially superior to the HF method. Indication is found of a possible failure of the method in the fluoromethanes. The limitation of the MS Xα method is discussed. 相似文献
987.
Unsymmetric cyclic ketenes were generated from N‐acyl‐1,3‐thiazolidine‐2‐carboxylic acids 1a – c by means of Mukaiyama's reagent, and then reacted with imines 2a – c to the new, isomeric spiro‐β‐lactams 3 and 4 via [2+2] cycloaddition (Staudinger ketene–imine reaction; Scheme 1). The reactions were stereoselective (Table 1) and mainly afforded the spiro‐β‐lactams with a relative trans configuration. The spiro‐β‐lactams could be transformed into the corresponding monocyclic β‐lactams by means of thiazolidine ring opening or into substituted thiazolidines via hydrolysis of the β‐lactam ring. 相似文献
988.
989.
The asymmetric hydroformylation of the straight chain butenes with the [(?)-DIOP]PtCl2-SnCl2 catalytic system shows that asymmetric induction, contrary to the rhodium-(?)-DIOP catalytic system, takes place after the intermediate metal-alkyl-complex formation. 相似文献
990.
Summary The acetate scrambling processes (, conversion and N inversion) occurring in the complexes formed from meso-(2,3-butylenediamine)tetraacetic acid (BDTA) with zinc(II), cadmium(II), mercury(II), scandium(III), yttrium(III) and lanthanum(III) ions have been investigated by line shape analysis of their n.m.r. spectra. Between 308 and 373 K fast conversion between and isomers and slow nitrogen inversion occur except for mercury(II) and yttrium(III) in the latter case. H* = 2.3±0.1 kJ mol–1 and S* = –6.9±0.2 mol–1 J K–1 for the mercury complex; H* = 2.6 ±0.2 kJ mol–1 and S* = –5.5±0.5 mol–1 JK–1 for the yttrium complex. Exchange mechanisms proceeding through different reaction intermediates are discussed on the light of the results obtained in this work as well as previously on other polyaminepolycarboxylate complexes of the same ions. 相似文献