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61.
Relaxing nonequilibrated polymers in thin films at temperatures slightly above the glass transition
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Mithun Chowdhury Samer Al Akhrass Falko Ziebert Günter Reiter 《Journal of Polymer Science.Polymer Physics》2017,55(6):515-523
We have studied the dewetting process of thin polystyrene films on nonwettable substrates in the viscoelastic regime slightly above the glass transition temperature. The evolution of the shape of the dewetting rim for varying film thickness, molecular weights and dewetting temperatures allowed us to determine the relaxation rates of residual stresses, which originated from nonequilibrated polymer chain conformations formed during film preparation by spin‐coating. For long chain polymers, we found rates notably faster than the longest bulk relaxation processes, highly independent of molecular weight and temperature. Our study demonstrates that dewetting is a powerful tool for sensitive characterization of nonequilibrium properties of thin polymer films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 515–523 相似文献
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Robert I. R. Blyth Renate Duschek Georg Koller Falko P. Netzer Michael G. Ramsey 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):509-518
Summary. 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.
Received May 30, 2000. Accepted September 21, 2000 相似文献
64.
Wolf R Ehlers AW Khusniyarov MM Hartl F de Bruin B Long GJ Grandjean F Schappacher FM Pöttgen R Slootweg JC Lutz M Spek AL Lammertsma K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(48):14322-14334
The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K([18]crown-6)(thf)(2)][Fe(η(4)-P(2)C(2)tBu(2))(2)] (K1), [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)tBu(2))(2)] (K2), and [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)Ad(2))(2)] (K3, Ad = adamantyl) were obtained from reactions of [K([18]crown-6)(thf)(2)][M(η(4)-C(14)H(10))(2)] (M = Fe, Co) with tBuC[triple bond]P (1, 2), or with AdC[triple bond]P (3). Neutral sandwiches [M(η(4)-P(2)C(2)tBu(2))(2)] (4: M = Fe 5: M = Co) were obtained by oxidizing 1 and 2 with [Cp(2)Fe]PF(6). Cyclic voltammetry and spectro-electrochemistry indicate that the two [M(η(4)-P(2)C(2)tBu(2))(2)](-)/[M(η(4)-P(2)C(2)tBu(2))(2)] moieties can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1-5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and M?ssbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1-3). The molecular structures of 1-5 were determined by using X-ray crystallography. Essentially D(2d)-symmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal-ligand π bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed. 相似文献
65.
Varghese Swamy Leonid S. Dubrovinsky Falko Langenhorst Michael Drakopoulos Hans-Peter Weber 《Solid State Communications》2005,134(8):541-546
High-pressure structural transitions in nanocrystalline systems are of significant interest as models of first-order phase transitions. We demonstrate size-induced lattice expansion and significant atomic rearrangements in the crystal structure of nanocrystalline high-pressure baddeleyite-TiO2. The α-PbO2 structured TiO2 recovered after dozens of pressure cycles in the α-PbO2-baddeleyite pressure field displayed elongate 25-35 nm crystallites, compared to starting 34-nm anatase crystallites, suggesting crystallite coherency across anatase, baddeleyite, and α-PbO2 structures and ‘single structural domain’ behavior of the nanocrystalline system. 相似文献
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67.
Falko M. Schappacher 《Journal of solid state chemistry》2009,182(2):265-7039
The ternary intermetallic compounds RE2Cu2Cd (RE=Y, Sm, Gd-Tm, Lu) were synthesized by induction-melting of the elements in sealed tantalum tubes. The samples were characterized by X-ray powder diffraction. The structure of Gd2Cu2Cd was refined from single crystal X-ray diffractometer data: Mo2FeB2 type, space group P4/mbm, a=756.2(3), c=380.2(3) pm, wR2=0.0455, 321 F2 values, 12 variables. The structures are 1:1 intergrowth variants of slightly distorted CsCl and AlB2 related slabs of compositions RECd and RECu2. The copper and cadmium atoms build up two-dimensional [Cu2Cd] networks (257 pm Cu-Cu and 301 pm Cu-Cd in Gd2Cu2Cd) which are bonded to the rare earth atoms via short RE-Cu contacts (290 pm in Gd2Cu2Cd). Temperature dependent susceptibility measurements of RE2Cu2Cd with RE=Gd, Tb, Dy, and Tm show experimental magnetic moments which are close to the free RE3+ ion values. The four compounds show ferromagnetic ordering at TC=116.7(2), 86.2(3), 48.4(1), and 14.5(1) K, respectively, as confirmed by heat capacity measurements. Dy2Cu2Cd shows a spin reorientation at TN=16.9(1) K. 相似文献
68.
Falko Pippig Sanaa Sarghini Andreas Holländer Sabine Paulussen Herman Terryn 《Surface and interface analysis : SIA》2009,41(5):421-429
The determination of functional groups on complex polymer surfaces by X‐ray photoelectron spectroscopy (XPS) can be improved considerably by derivatization reactions. Simple polymers containing hydroxyl groups or amino groups were investigated as reference materials for the derivatization with trifluoroacetic anhydride (TFAA). ‐1 Poly(vinyl alcohol) (PVA), poly(hydroxyethyl methacrylate) (PHEMA), poly(vinyl butyral) (PVB), poly(allylamine) (PAAm), and poly(diallyl amine) (PDAAm) were derivatized using TFAA and analyzed with XPS. Polyethylene (PE) was used as an independent external reference for the binding energy (BE). Applying this procedure, the BE scales of all measurements were referenced to the carbon atoms of PE. It was found that the BE of the CF3 component in the C1s region is different when bonded as an acetate or as an amide. The CF3 BE is also influenced by the density of these groups in the polymer molecule. In TFAA‐PVA, where every second main chain carbon atom carries a trifluoroacetate (TFAc) group, the BE is 294.3 eV while in TFAA‐PVB with only isolated groups, the BE is 293.6 eV. The BE of the CF3 component in the trifluoroacetamides (TFAAms) prepared from PAAm and PDAAm was found to be 292.5 and 292.3 eV, respectively. Compared with the analog fluorine free compounds, the BE is shifted toward higher values also for the ester carbon atom, the amide carbon atom, and the carbon atom to which the ester or amide is bonded. The data suggest that the gas phase reaction of TFAA with a polymer surface is diffusion limited. The actual ester or amide formation is a fast reaction and runs as a wave into the surface. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
69.
Bing Wu Sebastian von der Ecken Ian Swyer Chunliang Li Amy Jenne Franck Vincent Daniel Schmidig Till Kuehn Armin Beck Falko Busse Henry Stronks Ronald Soong Aaron R. Wheeler Andr Simpson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(43):15516-15520
Microcoil nuclear magnetic resonance (NMR) has been interfaced with digital microfluidics (DMF) and is applied to monitor organic reactions in organic solvents as a proof of concept. DMF permits droplets to be moved and mixed inside the NMR spectrometer to initiate reactions while using sub‐microliter volumes of reagent, opening up the potential to follow the reactions of scarce or expensive reagents. By setting up the spectrometer shims on a reagent droplet, data acquisition can be started immediately upon droplet mixing and is only limited by the rate at which NMR data can be collected, allowing the monitoring of fast reactions. Here we report a cyclohexene carbonate hydrolysis in dimethylformamide and a Knoevenagel condensation in methanol/water. This is to our knowledge the first time rapid organic reactions in organic solvents have been monitored by high field DMF‐NMR. The study represents a key first step towards larger DMF‐NMR arrays that could in future serve as discovery platforms, where computer controlled DMF automates mixing/titration of chemical libraries and NMR is used to study the structures formed and kinetics in real time. 相似文献
70.