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101.
R. Kaiser M. Friedrich T. Schmitz-Hübsch F. Sellam T. U. Kampen K. Leo D. R. T. Zahn 《Fresenius' Journal of Analytical Chemistry》1999,363(2):189-192
3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) was deposited using organic molecular beam deposition (OMBD) onto various
substrates, i.e. mica(0001), Au(111) layers on mica, and Se-passivated GaAs(100). Layer thicknesses were from 2 to 30 nm.
Reflectance and transmittance measurements were performed in order to identify PTCDA absorption features and find suitable
laser wavelengths for subsequent Raman investigations. Despite the low thicknesses the Raman spectra reveal strong scattering
by the molecular vibrational modes, in particular above 1200 cm–1. Frequency shifts of various modes in the layers from their values in PTCDA source material may indicate the influence of
the substrates. Similar shifts were also observed in infrared spectra of the same materials.
Received: 5 August 1998 / Received: 25 October 1998 / Accepted: 26 October 1998 相似文献
102.
Alexander L. Stroyuk Alexandra E. Raevskaya Stepan Ya. Kuchmiy Vladimir M. Dzhagan Dietrich R.T. Zahn Steffen Schulze 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,320(1-3):169-174
Colloidal selenium nanoparticles (NPs) were synthesized via acidic decomposition of sodium selenosulfate. The effects of synthesis and post-synthesis treatment conditions on the size, structure and size distribution of the Se nanoparticles are discussed. It is shown that the decomposition of sodium selenosulfate with non-oxidative acids (e.g., HCl) in aqueous solutions of polymers (sodium polyphosphate, gelatin, polyvinyl alcohol, polyethyleneglycole) and surfactants (sodium dodecylsulfonate, cetylpyridinium chloride) results in the formation of amorphous 25–200 nm Se nanoparticles converting upon ageing at 90 °C into trigonal 150–250 nm Se nanocrystals. Optical properties (absorption and Raman spectra) of freshly prepared and aged Se nanoparticles both in colloidal solutions and in polymeric (polyvinyl alcohol) films are analyzed. 相似文献
103.
104.
Dorothea Bahns Katarzyna Rejzner Jochen Zahn 《Communications in Mathematical Physics》2014,327(3):779-814
We show that the Nambu–Goto string, and its higher dimensional generalizations, can be quantized, in the sense of an effective theory, in any dimension of the target space. The crucial point is to consider expansions around classical string configurations. We are using tools from perturbative algebraic quantum field theory, quantum field theory on curved spacetimes, and the Batalin–Vilkovisky formalism. Our model has some similarities with the Lüscher–Weisz string, but we allow for arbitrary classical background string configurations and keep the diffeomorphism invariance. 相似文献
105.
Using positional data from video microscopy, we determine the elastic moduli of two-dimensional colloidal crystals as a function of temperature. The moduli are extracted from the wave-vector-dependent normal-mode spring constants in the limit q-->0 and are compared to the renormalized Young's modulus of the Kosterlitz-Thouless-Halperin-Nelson-Young theory. An essential element of this theory is the universal prediction that Young's modulus must approach 16 pi at the melting temperature. This is indeed observed in our experiment. 相似文献
106.
V. N. Bessolov E. V. Konenkova M. V. Lebedev D. R. T. Zahn 《Physics of the Solid State》1999,41(5):793-795
The electronic properties of the (100) surface of n-GaAs, p-GaAs, and n-InP semiconductors treated with various sulfide solutions have been studied. Sulfide treatment was shown to increase the
photoluminescence intensity, decrease the depth of the near-surface depleted region in the semiconductor, and shift the surface
Fermi level toward the conduction band. These effects are the stronger, the higher the sulfur chemical activity in the solution.
Fiz. Tverd. Tela (St. Petersburg) 41, 875–878 (May 1999) 相似文献
107.
One-electron reduction inverts the helicity of copper complexes formed from derivatives of S-methylcysteine and methioninol. The change in conformation of the organic ligand is followed in the exciton-coupled circular dichroism (ECCD) spectra of the complexes. 相似文献
108.
Rainer Lubig Peter Kusch Karin Röper Helmut Zahn 《Monatshefte für Chemie / Chemical Monthly》1981,112(11):1313-1323
The interaction of glutaraldehyde with model aliphatic amines was studied in order to understand the crosslinking reaction of glutaraldehyde with proteins. The reaction in organic solvents gave N-alkyl-1,4-dihydropyridines and N,N-dialkyl-1,5-diiminopentanes. The isolated products are new or were previously described by us for the first time1. Hydration of the reaction products led to stable N-alkylpiperidines and N,N-dialkyl-1,5-diaminopentanes. In aqueous solution the reaction depends on thepH: at apH above 7, N-alkyl-1,4-dihydropyridines and at apH below 7, polymers were obtained. For the crosslinking reaction of proteins with glutaraldehyde the following mechanism is proposed: Monomeric glutaraldehyde reacts with the protein to give intermediate N-alkyl-2,6-dihydroxypiperidines. Intramolecular dehydration leads to the corresponding N-alkyl-1,4-dihydropyridines. Condensation of the cyclic monohydrate of glutaraldehyde and N-alkyl-2,6-dihydroxypiperidines gives linear polymeric crosslinks containing -oxo-N-alkylpiperidine units.
Lubig R., Dissertation, RWTH Aachen, 1974. 相似文献
109.
Dietrich R. T. Zahn 《Analytical and bioanalytical chemistry》1997,358(1-2):10-14
The potential of optical techniques for semiconductor interfaces and growing layers is demonstrated using in particular the example of Raman spectroscopy in combination with molecular beam epitaxial (MBE) growth. Recent developments allow this method to be applied not only in situ but while growth progresses. This application critically depends on the resonant excitation which provides the required sensitivity for layers in the nanometre range. Here the heteroepitaxy of II–VI compound semiconductors on III–V substrates serves as an example to illustrate the wealth of information, e.g. on layer composition, crystallinity, growth rate, and interfacial reactivity. Very recent results on gallium nitride growth clearly reveal that such experiments can be performed even at temperatures as high as 685?°C. 相似文献
110.
Zusammenfassung Das Molekulargewicht der aus der Forellenmilch gewonnenen Desoxyribonucleins?ure wurde mit Hilfe der Ultrazentrifuge untersucht.
Wegen der hohen Viskosit?t mu?te man eine sehr verdünnte L?sung von 0,002% DNS inMcIlvaine- Puffer (pH 4,97) anwenden. Die experimentellen Konzentrationskurven wurden mit UV-Absorptionsoptik aufgenommen, und danach lie?en sich
auch die theoretischen Gradientenkurven ableiten.
Es hat sich gezeigt, da? DNS mehrere polydisperse Fraktionen enth?lt, die erne mehrgipfelige charakteristische Verteilung
darstellen mit einer mittleren Sedimentationskonstante von 19,35 sved. Auf Grund dieser Konstante sowie auch aus den Viskosit?tsmessungen,
die die „intrinsic viscosity“ 〈[π]Φ=0〉=6541 liefern, wurde der Mittelwert für das Achsenverh?ltnis 〈p〉= 380 und für das Molekulargewicht 〈M〉=6100000 festgestellt.
Die mittlere Dicke der DNS-Moleküle ist 25 ? und die L?nge 1,178μ.
Die Bestimmung der Molekulargewichtsverteilung kann nach dieser Methode sowie auch nach der neuen Momentenmethode bzw. nach
der „Dreipunktmethode“ unmittelbar aus der experimentellen Gradientenkurve abgeleitet werden.
Mit Unterstützung der Deutschen Forschungsgemeinschaft.
Frl. Dr.L. Hübner aus dem Paul-Ehrlich-Institut, Frankfurt a. M., und HerrnG. Zwarg aus dem Beckman-Werk in München danken wir für die Hilfe und die Mitarbeit bei der Durchführung der Sedimentationsversuche. 相似文献