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161.
Biosynthetically inspired manipulation of the antibiotic paromomycin led, in six high-yielding steps, to a ring A harboring an α,β-unsaturated 6'-aldehyde and an allylic 3'-methylcarbonate group. Tsuji deoxygenation in the presence of 5 mol % Pd(2)(dba)(3) and Bu(3)P granted access to a novel series of 3',4'-dideoxy-4',5'-dehydro ring A hybrids. The neomycin-sisomicin hybrid exhibited superior in vitro antibacterial activity to the parent compound neomycin. 相似文献
162.
Thiago O. Carvalho Ana E. B. Matias Lilian R. Braga Sheila M. Evangelista Alexandre G. S. Prado 《Journal of Thermal Analysis and Calorimetry》2011,106(2):475-481
Chitosan microspheres were applied to remove the pollutants diclofenac and dipyrone from water. Adsorption studies were adjusted
to Langmuir equation. The maximum number of adsorbed moles gave 5.25 × 10−4 and 4.83 × 10−4 mol of diclofenac and dipyrone, respectively, per gram of chitosan microspheres. The interactions in solid/liquid interface
were calorimetrically followed and gave endothermic values: +22.1 ± 1.3 and +48.7 ± 1.5 kJ mol−1, respectively, for the same sequence. Both Gibbs energy values were negative. Adsorption processes were accompanied by an
increase in entropy. These interactions were studied by FTIR spectroscopy which showed a strengthening of the CN stretching
(dislocated shifts from 1,325 to 1,371 cm−1) related to a weakening of the NH stretch caused by the interaction with drugs. 相似文献
163.
Johannes Postler Marcelo M. Goulart Carolina Matias Andreas Mauracher Filipe Ferreira da Silva Paul Scheier Paulo Limão-Vieira Stephan Denifl 《Journal of the American Society for Mass Spectrometry》2013,24(5):744-752
In the present study, dissociative electron attachment (DEA) measurements with gas phase HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, C4H8N8O8, have been performed by means of a crossed electron-molecular beam experiment. The most intense signals are observed at 46 and 176 u and assigned to NO2 ? and C3H6N5O4 ?, respectively. Anion efficiency curves for 15 negatively charged fragments have been measured in the electron energy region from about 0–20 eV with an energy resolution of ~0.7 eV. Product anions are observed mainly in the low energy region, near 0 eV, arising from surprisingly complex reactions associated with multiple bond cleavages and structural and electronic rearrangement. The remarkable instability of HMX towards electron attachment with virtually zero kinetic energy reflects the highly explosive nature of this compound. Substantially different intensity ratios of resonances for common fragment anions allow distinguishing the nitroamines HMX and royal demolition explosive molecule (RDX) in negative ion mass spectrometry based on free electron capture. 相似文献
164.
Filipe Ferreira da Silva Carolina Matias Diogo Almeida Gustavo García Oddur Ingólfsson Helga Dögg Flosadóttir Benedikt Ómarsson Sylwia Ptasinska Benjamin Puschnigg Paul Scheier Paulo Limão-Vieira Stephan Denifl 《Journal of the American Society for Mass Spectrometry》2013,24(11):1787-1797
We report gas phase studies on NCO– fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO– production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO– upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition. Utilizing partially methylated thymine, we demonstrate that the remarkable site selectivity of the initial hydrogen loss as a function of the electron energy is preserved in the prompt as well as the metastable NCO– formation in DEA. Site selectivity in the NCO– yield is also pronounced after deprotonation in MALDI, though distinctly different from that observed in DEA. This is discussed in terms of the different electronic states subjected to metastable decay in these experiments. In potassium collisions with 1- and 3-methylthymine and 1- and 3-methyluracil, the dominant fragment is the NCO– ion and the branching ratios as a function of the collision energy show evidence of extraordinary site-selectivity in the reactions yielding its formation. Graphical abstract
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165.
Wiedmer SK D'Orazio G Smått JH Bourdin D Baños-Pérez C Sakeye M Kivilompolo M Kopperi M Ruiz-Jiménez J Fanali S Riekkola ML 《Journal of chromatography. A》2011,1218(30):5020-5029
The need for novel packing materials in both capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) is apparent and the development towards more selective, application-oriented chromatographic phases is under progress world-wide. In this study we have synthesized new polyethyleneimine (PEI) functionalized Mn(2)O(3), SiO(2), SnO(2), and ZrO(2) particles for the fabrication of packed capillary columns for CEC and CLC. The nanocasting approach was successful for the preparation of functionalized metal oxide materials with a controlled porosity and morphology. PEI functionalization was done using ethyleneimine monomers to create particles which are positively charged in aqueous solution below pH 9. This functionalization allowed the possibility to have both hydrophobic (due to its alkyl chain) and ionic interactions (due to positively charged amino groups) with selected compounds. For comparison aminopropyl-functionalized silica was also synthesized and tested. Both slurry pressure and electrokinetic packing procedures used gave similar results, but fast sedimentation of the material caused some problems during the packing. The high stability and wide pH range of PEI-functionalized SiO(2) material, with potential for hydrophobic and electrostatic interactions, proved to be useful for the CEC and CLC separation of some model acidic and neutral compounds. 相似文献
166.
Hugo A. Akitaya Matthew D. Jones Matias Korman Oliver Korten Christopher Meierfrankenfeld Michael J. Munje Diane L. Souvaine Michael Thramann Csaba D. Tóth 《Journal of Graph Theory》2023,102(1):35-66
Motivated by recent computational models for redistricting and detection of gerrymandering, we study the following problem on graph partitions. Given a graph and an integer , a -district map of is a partition of into nonempty subsets, called districts, each of which induces a connected subgraph of . A switch is an operation that modifies a -district map by reassigning a subset of vertices from one district to an adjacent district; a 1-switch is a switch that moves a single vertex. We study the connectivity of the configuration space of all -district maps of a graph under 1-switch operations. We give a combinatorial characterization for the connectedness of this space that can be tested efficiently. We prove that it is PSPACE-complete to decide whether there exists a sequence of 1-switches that takes a given -district map into another; and NP-hard to find the shortest such sequence (even if a sequence of polynomial lengths is known to exist). We also present efficient algorithms for computing a sequence of 1-switches that take a given -district map into another when the space is connected, and show that these algorithms perform a worst-case optimal number of switches up to constant factors. 相似文献