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61.
Klaus Grasshoff und Harry Hahn 《Fresenius' Journal of Analytical Chemistry》1959,168(4):247-263
Zusammenfassung Es wird das polarographische Verhalten der Molybdatokieselsäure (-Form) näher untersucht. Sie gibt eine charakteristische Reduktionsstufe, deren Halbstufenpotential gesetzmäßig vom pH-Wert der Trägerlösung abhängig ist. Die Ausbildung dieser Stufe ist von der Zusammensetzung der Trägerlösung abhängig. Sie ist am besten in einer Pufferlösung aus Natriumcitrat und Salzsäure vom pH 2,5 ausgebildet. Anwesenheit von Methyläthylketon verbessert die Form der Stufe. Die Reduktion der Molybdatokieselsäure verläuft an der Quecksilbertropf-elektrode reversibel. Auf Grund der polarographischen Untersuchung wird eine auch durch präparative Versuche gestützte Formulierung des Reduktionsverlaufs vorgeschlagen. Die Molybdatokieselsäure zerfällt beim Lösen im wäßrigen Medium zu über 50% in Kieselsäure und Hexamolybdänsäure. Ihre Unbeständigkeitskonstante wird aus den polarographischen Daten zu K=1,5 · 10–11 bestimmt. Die polarographische Reduktion der Molybdatokieselsäure ist für eine quantitative Bestimmung kleiner Mengen Silicium voll geeignet.Wir danken der Deutschen Forschungsgemeinschaft sowie dem Fonds der Chemischen Industrie für die Unterstützung dieser Arbeit. 相似文献
62.
Armstrong TA Bettoni D Bharadwaj V Biino C Borreani G Broemmelsiek D Buzzo A Calabrese R Ceccucci A Cester R Church M Dalpiaz P Dalpiaz PF Dibenedetto R Dimitroyannis D Fabbri MG Fast J Gianoli A Ginsburg CM Gollwitzer K Hahn A Hasan M Hsueh S Lewis R Luppi E Macrí M Majewska AM Mandelkern M Marchetto F Marinelli M Marques J Marsh W Martini M Masuzawa M Menichetti E Migliori A Mussa R Palestini S Pallavicini M Pastrone N Patrignani C Peoples J Pesando L Petrucci F Pia MG Pordes S Rapidis P 《Physical review letters》1992,69(16):2337-2340
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64.
The luminescence of solid xenon at 20 K has been excited optically in the wavelength range 1550Åto 1150Å. The 1760Å emission band due to a transition of the molecule is found in agreement with α? or e?-excitation. The excitation spectrum yields a relatively high quantum efficiency of the Γ(3/2) exciton series indicating efficient self-trapping. The Γ(1/2) exciton series and conduction band states have a low quantum efficiency. 相似文献
65.
Markus Follmann Nils Griebenow Michael G. Hahn Ingo Hartung Franz‐Josef Mais Joachim Mittendorf Martina Schfer Hartmut Schirok Johannes‐Peter Stasch Friederike Stoll Alexander Straub Peter Jeschke Ralf Nauen Michael Edmund Beck Hans‐Wilhelm Engels Hans‐Georg Pirkl Reinhard Albers Rolf W. Albach Jens Krause Andreas Hoffmann Holger Casselmann Jeff Dormish 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(36):9503-9503
66.
Marine Rémy Dr. Iwona Nierengarten Boram Park Dr. Michel Holler Dr. Uwe Hahn Dr. Jean-François Nierengarten 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(33):8492-8499
Stable pillar[5]arene-containing [2]rotaxane building blocks with pentafluorophenyl ester stoppers have been efficiently prepared on a multi-gram scale. Reaction of these building blocks with various nucleophiles gave access to a wide range of [2]rotaxanes with amide, ester or thioester stoppers in good to excellent yields. The rotaxane structure is fully preserved during these chemical transformations. Actually, the addition-elimination mechanism at work during these transformations totally prevents the unthreading of the axle moiety of the mechanically interlocked system. The stopper exchange reactions were optimized both in solution and under mechanochemical solvent-free conditions. While amide formation is more efficient in solution, the solvent-free conditions are more powerful for the transesterification reactions. Starting from a fullerene-functionalized pillar[5]arene derivative, this new strategy gave easy access to a photoactive [2]rotaxane incorporating a C60 moiety and two Bodipy stoppers. Despite the absence of covalent connectivity between the Bodipy and the fullerene moieties in this photoactive molecular device, efficient through-space excited state interactions have been evidenced in this rotaxane. 相似文献
67.
Julien Iehl Thi Le Anh Nguyen Stéphane Frein Uwe Hahn Joaquín Barberá Jean-François Nierengarten 《Liquid crystals》2017,44(12-13):1852-1860
ABSTRACTLiquid-crystalline [60]fullerodendrimers were constructed via click chemistry based on the reaction between hexa-adducts of [60]fullerene (C60) bearing 12 azide groups and alkyne-terminated cyanobiphenyl dendrons of first- and second-generation. The structure of all the new compounds was confirmed by IR, UV, 1H and 13C NMR spectroscopies and mass spectrometry. The mesomorphic properties were studied by polarised optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. The hexa-adduct of C60 functionalised with the first-generation dendrons gave rise to the formation of a smectic A phase and a rectangular columnar phase (c2mm symmetry) while the hexa-adduct of C60 decorated with the second-generation dendrons displayed only a rectangular columnar phase (c2mm symmetry). Our results show that the hexa-adduct of C60 is a unique synthetic platform for the design of fullerodendrimers and dendronised materials. 相似文献
68.
Marcus Richter Sebastian Hahn Dr. Evgenia Dmitrieva Dr. Frank Rominger Dr. Alexey Popov Prof. Dr. Uwe H. F. Bunz Prof. Dr. Xinliang Feng Dr. Reinhard Berger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(5):1345-1352
Polycyclic aromatic azomethine ylides (PAMYs) are powerful building blocks in the bottom-up synthesis of internally nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) through 1,3-cycloaddition reactions. In this work, the cycloaddition reaction of PAMYs to asymmetric ortho-quinones is presented, which, in contrast to the addition to symmetric para-quinones, facilitates subsequent condensation reactions and allows the synthesis of three helical N-PAHs with ullazine-quinoxaline ( UQ - 1 – 3 ) backbones. UQ - 1 and UQ - 2 possess two helical centers; however, single-crystal X-ray analysis together with the computational modeling of UQ - 3 elucidate the formation of only the thermodynamically most stable geometry with four helical centers in a (P,P,M,M) configuration. For the series UQ - 1 – 3 , the number of redox steps is directly correlated with the number of ullazine or quinoxaline units incorporated into the targeted molecular backbones. A detailed investigation of the spectroscopic and magnetic properties of the radical cation and anion as well as the dication and dianion species by in situ EPR/UV/Vis-NIR spectroelectrochemistry is provided. The excellent optical and redox properties combined with helical geometries render them possibly applicable as chiral emitter or ambipolar charge transport material in organic electronics. 相似文献
69.
Bousquet, Lochet and Thomassé recently gave an elegant proof that for any integer , there is a least integer such that any tournament whose arcs are coloured with colours contains a subset of vertices of size with the property that any vertex not in admits a monochromatic path to some vertex of . In this note we provide a lower bound on the value . 相似文献
70.