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排序方式: 共有322条查询结果,搜索用时 156 毫秒
61.
Stefan Laumann Matthias Ikeda Herbert Sassik Andrey Prokofiev Prof. Dr. Silke Paschen 《无机化学与普通化学杂志》2012,638(2):294-301
Intermetallic clathrates are promising materials for thermoelectric applications. This is not only due to their low thermal and high electrical conductivities (“phonon glass – electron crystal”) but also due to the expectation that they are semiconductors and thus have large thermopower values. Band structure calculations of the stoichiometric compound Eu8Ga16Ge30 indeed yield a semiconducting ground state. However, with conventional synthesis methods the exact 8:16:30 stoichiometry could not be reached. Herein we use the melt‐spinning technique to obtain Eu8Ga16–xGe30+x samples with smaller x than previously realized. The quenching procedure and the results of the characterization of the quenched phases by X‐ray powder diffraction and electron microscopy are presented. The electrical resistivity shows that, in contrast to conventional synthesis procedures, semiconducting compounds can be produced. 相似文献
62.
Silke Biedasek Mohammed Abboud Hans-Ulrich Moritz Achim Stammer 《Macromolecular Symposia》2007,259(1):390-396
Summary: Aqueous solutions of acrylic acid were levitated in a 40 kHz acoustic levitator. The monomer amount in the levitated droplets was monitored by Raman spectroscopy relating to an internal standard. Thus evaporation of the monomer as well as polymerization reactions initiated by a redox system were investigated by Raman spectroscopy and resultant data were compared to HPLC data. Decreases in monomer amount due to evaporation can be clearly distinguished from polymerization reactions. Additionally, temperature measurement within the droplet throughout a polymerization reaction shows the typical temperature course originating from the heat of polymerization. 相似文献
63.
Summary: A new class of poly(arylene ethynylene)s (PAEs) containing an electron‐deficient N‐alkylphthalimide unit was prepared by means of a Sonogashira reaction. Complete solubility of the PAEs was observed by utilizing a 2,6‐diisopropylphenyl side chain. The chemical structure of the novel soluble polymer 3c was confirmed by NMR spectra, whereas the insoluble polymers were characterized by elemental analysis and IR spectra. Fluorescence measurements of 3c indicate a rigid structure and high symmetry in the excited state.
64.
Since the symmetries of fluid motion are admitted by all statistical quantities of turbulent flows as can be taken from the multipoint equations, we can derive conditions for turbulence models so that they capture the proper flow physics. Concerning these constraints we will exemplary investigate the k – ϵ – model for its capability to reproduce new scaling laws derived from symmetry methods. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
65.
Johannes Wellmann Beate Hartmann Esther-Corinna Schwarze Silke Hillebrand Stephan I. Brueckner Jakob Ley Gerold Jerz Peter Winterhalter 《Molecules (Basel, Switzerland)》2022,27(11)
Previously, different Hydrangea macrophylla ssp. serrata cultivars were investigated by untargeted LC-MS analysis. From this, a list of tentatively identified and unknown compounds that differ significantly between these cultivars was obtained. Due to the lack of reference compounds, especially for dihydro-isocoumarins, we aimed to isolate and structurally characterise these compounds from the cultivar ‘Yae-no-amacha’ using NMR and LC-MS methods. For purification and isolation, counter-current chromatography was used in combination with reversed-phase preparative HPLC as an orthogonal and enhanced purification workflow. Thirteen dihydro-isocoumarins in combination with other metabolites could be isolated and structurally identified. Particularly interesting was the clarification of dihydrostilbenoid glycosides, which were described for the first time in H. macrophylla ssp. serrata. These results will help us in further studies on the biological interpretation of our data. 相似文献
66.
67.
In the case of existence the smallest numberN=Rakis called a Rado number if it is guaranteed that anyk-coloring of the numbers 1, 2, …, Ncontains a monochromatic solution of a given system of linear equations. We will determine Rak(a, b) for the equationa(x+y)=bzifb=2 andb=a+1. Also, the case of monochromatic sequences {xn} generated bya(xn+xn+1)=bxn+2 is discussed. 相似文献
68.
M. Sc. Ibrahim Halil Öner M. Sc. Christine Joy Querebillo Dr. Christin David Dipl.‐Ing. Ulrich Gernert M. Sc. Carsten Walter Prof. Dr. Matthias Driess Prof. Dr. Silke Leimkühler Dr. Khoa Hoang Ly Prof. Dr. Inez M. Weidinger 《Angewandte Chemie (International ed. in English)》2018,57(24):7225-7229
We present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface‐enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochrome b5 were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 °C. For the first time, such high values are reported for non‐directly surface‐interacting probes, for which the involvement of charge‐transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode. 相似文献
69.
We investigated the generation dependent shape and internal structure of star-burst dendrimers under good solvent conditions using small angle x-ray scattering and molecular modeling. Measurements have been performed on poly(amidoamine) dendrimers with generations ranging from g=0 up to g=8 at low concentrations in methanol. We described the static form factor P(q) by a model taking into account the compact, globular shape as well as the loose, polymeric character of dendrimers. Monomer distributions within dendrimers are of special interest for potential applications and have been characterized by the pair correlation function gamma(r), as well as by the monomer and end-group density profile, rho(r) and rho(e)(r), respectively. Monomer density profiles and gamma(r) can be derived from P(q) by modeling and via a model independent approach using the inverse Fourier transformation algorithm first introduced by Glatter. Experimental results are compared with computer simulations performed for single dendrimers of various generations using the cooperative motion algorithm. The simulation gives direct access to gamma(r) and rho(r), allows an independent determination of P(q), and yields in addition to the scattering experiment information about the distribution of the end groups. Excellent qualitative agreement between experiment and simulation has been found. 相似文献
70.
Silke Schmetzer Paulette Greenidge Karl-Artur Kovar Meike Schulze-Alexandru Gerd Folkers 《Journal of computer-aided molecular design》1997,11(3):278-292
A cannabinoid pseudoreceptor model for the CB1-receptor has been constructed for 31 cannabinoids using the molecular modelling software YAK. Additionally, two CoMFA studies were performed on these ligands, the first of which was conducted prior to the building of the pseudoreceptor. Its pharmacophore is identical with the initial superposition of ligands used for pseudoreceptor construction. In contrast, the ligand alignment for the second CoMFA study was taken directly from the final cannabinoid pseudoreceptor model. This altered alignment gives markedly improved cross-validated r2 values as compared to those obtained from the original alignment with
values of 0.79 and 0.63, respectively, for five components. However, the pharmacophore alignment has the better predictive ability. Both the CoMFA and pseudoreceptor methods predict the free energy of binding of test ligands well. 相似文献