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41.
42.
Michael C. Zerner Walter M. F. Fabian Renate Dworczak Dietmar W. Kieslinger Gert Kroner Hans Junek Max E. Lippitsch 《International journal of quantum chemistry》2000,79(4):253-266
The effect of conformation (E/Z isomerism), nature (donor/acceptor) of substituents, and endgroups (indandione, pyrazolone, pyrazoledione) on the molecular hyperpolarizability βvec of dicyanomethylene (hetero)aromatic dyes is investigated by means of semiempirical (AM1, ZINDO) molecular orbital calculations. Unless Z isomers are stabilized by intramolecular hydrogen bonding, generally E conformers have larger βvec's. Replacement of one nitrile group of the dicyanomethylene moiety by p‐aminoaryl rather than p‐R‐arylamino (R=NMe2, MeO, H, NO2) is found to be advantageous. Increasing the acceptor strength of 29 by successively replacing the carbonyl with dicyanovinyl groups leads to a maximum of βvec for the derivative with one rather than two C(CN)2 groups. With respect to endgroups, the indandione moiety generally is the least active group. Solvent effects are treated within the framework of the self‐consistent reaction field approximation. In most cases gas‐phase tendencies are either parallel or even reinforced if solvent effects are taken into account. The calculated results are compared with electric field induced second harmonic generation (EFISH) measurements. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 253–266, 2000 相似文献
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44.
Renate Geßmann Norbert Schiemann Hans Brückner Kyriacos Petratos 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):o413-o415
The intramolecular hydrogen‐bonding pattern of Z‐Leu‐Aib‐Pro‐Val‐OBg monohydrate [(N‐benzhydrylamino)carbonylmethyl N‐benzyloxycarbonyl‐α‐aminoisobutyrylprolylvalinate monohydrate], C43H55N5O8·H2O, is unusual for a tetrapeptide because, in addition to a 14 hydrogen bond, a second hydrogen bond of the type 15 is formed. This folding reflects the intramolecular hydrogen‐bonding pattern that this amino acid sequence adopts in the naturally occurring peptaibol alamethicin. 相似文献
45.
N,N -Dimethylglycinato Complexes of Platinum(IV) The aquapentachloroplatinic acid (H3O)-[PtCl5(H2O)] · 2(18-cr-6) · 6 H2O ( 1 ) reacts with N,N-dimethylglycine (Me2glyH) to give cis-[PtCl2(N,O-Me2gly)2] · (18-cr-6) ( 6 ) and (Me2glyH2)[PtCl4(N,O-Me2gly)] ( 7 ). Complexes 6 and 7 are characterized by microanalysis, 1H-NMR and IR spectroscopy as well as by X-ray structure analysis. In both complexes the N,N-dimethylglycinato ligands are N,O-coordinated. In 6 , the amino groups are mutually trans and the carboxylato groups are cis (configuration index: OC-6–22). In the crystal, there are only weak C–H…O interactions between the N-methyl groups of the [PtCl2(N,O-Me2gly)2] complex and the oxygen atoms of the crown ether (shortest C…O contacts: 3.10(2) Å and 3.21(2) Å). In the solid state, 7 exhibits strong cation-anion interactions: The carboxyl group of the cation (Me2glyH2)+ forms a strong O–H…O bridge to the exocyclic oxygen atom of the carboxylate group of the glycinato ligand (O…O 2.61(1) Å). 相似文献
46.
Silvia Anthoine Dietrich Renate Lindauer Claire Stierlin Jürg Gertsch Dr. Ruth Matesanz Dr. Sara Notararigo José Fernando Díaz Dr. Karl‐Heinz Altmann Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10144-10157
A series of epothilone B and D analogues bearing isomeric quinoline or functionalized benzimidazole side chains has been prepared by chemical synthesis in a highly convergent manner. All analogues have been found to interact with the tubulin/microtubule system and to inhibit human cancer cell proliferation in vitro, albeit with different potencies (IC50 values between 1 and 150 nM ). The affinity of quinoline‐based epothilone B and D analogues for stabilized microtubules clearly depends on the position of the N‐atom in the quinoline system, while the induction of tubulin polymerization in vitro appears to be less sensitive to N‐positioning. The potent inhibition of human cancer cell growth by epothilone analogues bearing functionalized benzimidazole side chains suggests that these systems might be conjugated with tumor‐targeting moieties to form tumor‐targeted prodrugs. 相似文献
47.
Kunze J Leitch J Schwan AL Faragher RJ Naumann R Schiller S Knoll W Dutcher JR Lipkowski J 《Langmuir : the ACS journal of surfaces and colloids》2006,22(12):5509-5519
For a monolayer of 2,3-di-phytanyl-sn-glycerol-1-tetraethylene glycol-D,L-a-lipoic acid ester lipid (DPTL) self-assembled (SAM) at a gold electrode surface we propose a new method to determine the charge number per adsorbed molecule and the packing density (area per molecule) in the monolayer. The method relies on chronocoulometry to measure the charge density at the SAM covered gold electrode surface. Two series of measurements have to be performed. In the first series, charge densities are measured for a monolayer transferred from the air-solution to the metal-solution interface using the Langmuir-Blodgett (LB) technique. This series of measurements allows one to determine charge numbers per adsorbed DPTL molecule. The second series is performed using a gold electrode covered with a self-assembled monolayer. The charge densities obtained in this series are then used to calculate the packing density with the help of charge numbers per adsorbed DPTL determined in the first series. The area per adsorbed molecule determined by the new method was compared to the area per molecule determined by the popular reductive desorption method. The molecular area determined with the new method is about 20% larger than the area calculated from the van der Waals model, which is a physically reasonable result. In contrast, the popular reductive desorption method gives an area per molecule 20% lower than the minimum estimated based on a van der Waals model. This is a physically unreasonable result. It is also shown that the charge numbers per adsorbed molecule depend on the electrode potential and may assume values smaller than the number of electrons participating in the reductive desorption step. An explanation of the origin of the "partial charge numbers" is provided. We recommend the new method be used in future studies of thiol adsorption at metal surfaces. 相似文献
48.
Robert I. R. Blyth Renate Duschek Georg Koller Falko P. Netzer Michael G. Ramsey 《Monatshefte für Chemie / Chemical Monthly》2001,11(3):509-518
We highlight the importance of interfacial properties in determining the performance of devices based on electroactive organic materials. Investigations of the interfaces of benzene with Al(111) and In2O3 are presented as a model of interface properties for devices based on complex aromatic molecules. At both interfaces the binding is shown to be electrostatic, with the resulting interface dipole determining the band alignment. It is also argued that chemical modification of substrates can be used to tailor both electronic and structural properties. 相似文献
49.
Fani Fountoulaki Renate Geßmann Hans Brückner Michael Kokkinidis 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):e578-e579
The structure of the synthetic protected dipeptide (Z)‐Pro–Leuol [systematic name: benzyl 2‐(1‐hydroxymethyl‐3‐methylbutylaminocarbonyl)pyrrolidine‐1‐carboxylate], C19H28N2O4, was determined by X‐ray crystallography. The peptide adopts a novel backbone conformation compared with other longer oligopeptides containing Pro–Leuol. 相似文献
50.
Robert Kohler Rainer Alex Renate Brielmann Bernhard Ausperger 《Macromolecular Symposia》2006,244(1):89-96
Summary: Some natural fibres like flax, hemp and others show excellent mechanical properties which make them a promising choice for the reinforcement of polymers. For natural fibre reinforced composites, hydrophilicity is a problem with respect to dimensional changes, fibre to matrix adhesion and long term stability. The interaction of differently prepared and modified fibres with water vapour has been investigated by dynamic vapour sorption. It has been found that the sorption and desorption kinetics of cellulosic fibres can be excellently fitted by assuming two parallel, independent first order processes. This empirical model, defined here as the “Parallel Exponential Kinetics” model (PEK-model), reveals two distinct mechanisms with slow and fast exchange of water vapour respectively, related to different sorption sites. The specific sorption mechanisms are represented by individual sorption-desorption isotherms as components of the total isotherms. The results suggest a relation to the differing types of amorphous regions in the fibres and/or to the different states of “bound” or “free” water, discussed for hydrophilic materials. The PEK-model proved to be consistently applicable for sorption and desorption over the whole humidity range, and also for all tested cellulose fibres. It is especially useful for a clearer distinction of different fibre types or modifications and can be successfully used for an extended fibre characterization. 相似文献