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11.
Extended studies by e.p.r. and electronic spectroscopy on the effect of different non-polar solvents, temperature and disulfide concentration on the spectral properties of bis(dithiophosphato)copper(II), Cu[(RO)2PS2]2, complexes [R = Me, Et and i-Pr] are reported. The molar absorptivity and e.p.r. intensity are very sensitive to the shape and size of the remote ligand substituents and increase in the order: Me < Et < i-Pr. The nature of the solvent and time after dissolution are also important regarding the magnitude of the e.p.r. intensity and molar absorptivity which, 1 h after dissolution, do not follow Beer's law. The molar absorptivities obtained at a given CuII(R2–dtp)2 concentration increase in the solvent order: n-hexane < n-heptane < CCl4 < PhMe < PhH < CHCl3. Twenty-four hours after dissolution the same samples exhibit: (i) linearity between absorbance and concentration of CuII(R2–dtp)2; (ii) a significant increase in molar absorptivity which is not equal for all the complexes studied and follows the same substituent and solvent orders. Beer's law is satisfied above 5 × 10–4 M for [(RO)2PS2]2Cu (R = Et, i-Pr) and above 3 × 10–3 M for [(MeO)2PS2]Cu. A significant additional increase, ca. 30–40%, of molar absorptivity, is obtained by increasing the solution temperature from 20 to 50 °C. The molar absorbtivity remains unchanged during 2–3 days after reducing the temperature. Further increase of molecular absorbtivity appears after addition of the corresponding disulfide of dithiophosphate [(RO2)PS2–S2P(RO)2] to CuII[(RO)2PS2]2. The molar absorptivity of Cu[(i-PrO)2PS2]2 increases from 4.8 × 103 cm–1 M–1, 1 h after dissolving the complex up to 2 × 104 cm–1 M–1 after addition of the corresponding disulfide. The observed effects are explained on the basis of a self-redox reaction taking place in this type of sulfur containing copper(II) complexes. 相似文献
12.
Marks JR Placone J Hristova K Wimley WC 《Journal of the American Chemical Society》2011,133(23):8995-9004
Combinatorial peptide chemistry and orthogonal high-throughput screening were used to select peptides that spontaneously translocate across synthetic lipid bilayer membranes without permeabilization. A conserved sequence motif was identified that contains several cationic residues in conserved positions in an otherwise hydrophobic sequence. This 9-residue motif rapidly translocates across synthetic multibilayer vesicles and into cells while carrying a large polar dye as a "cargo" moiety. The extraordinary ability of this family of peptides to spontaneously translocate across bilayers without an energy source of any kind is distinctly different from the behavior of the well-known, highly cationic cell-penetrating peptides, such as the HIV tat peptide, which do not translocate across synthetic bilayers, and enter cells mostly by active endocytosis. Peptides that translocate spontaneously across membranes have the potential to transform the field of drug design by enabling the delivery of otherwise membrane-impermeant polar drugs into cells and tissues. Here we describe the chemical tools needed to rapidly identify spontaneous membrane translocating peptides. 相似文献
13.
A method is developed for finding approximately the periodic solutions of nonlinear systems of difference-differential equations with impulses at fixed moments. 相似文献
14.
Changes in the elastic and viscoelastic (creep) characteristics of polymer concrete and its structural components (polyester resin, unfilled or filled with diabase flour) during a long-term exposure to water at 20°C were studied. Modeling the structural changes in polymer concrete with time showed an increase in the relative volume content of pores filled with water and a decrease in that of unfilled pores. Based on the free-volume concept and the data on swelling due to moistening and shrinkage due to physical aging of the binder, a rather accurate estimate of the time-moisture reduction function for polymer concrete was obtained. The function was found to be nonmonotonic: the interval of increase was followed by an interval of decrease. 相似文献
15.
Polina Angelova Kalina Kostova Karsten Hinrichs Dimiter Tsankov 《Central European Journal of Chemistry》2005,3(4):658-667
New 4-substituted benzyl esters of 16-mercaptohexadecanoic acid were prepared by developing a practicable synthetic procedure
and using readily available staring materials. The compounds synthesized have been characterized by NMR, MS, IR spectra and
elemental analysis. The mercapto derivatives are precursors for the formation of self-assembled monolayers on metal substrates.
Dedicated to Professor Dr. Manfred Hesse on the occasion of his 70
th
birthday 相似文献
16.
The paper deals with some linear as well as some non-linear generalizations of integral inequalities of Bellman-Bihari type for functions of several variables when the integration domain is a parallelepiped. 相似文献
17.
John Asplund Kossi Edoh Ruth Haas Yulia Hristova Beth Novick Brett Werner 《Discrete Mathematics》2018,341(10):2938-2948
For a graph and, the shortest path reconfiguration graph of with respect to and is denoted by . The vertex set of is the set of all shortest paths between and in . Two vertices in are adjacent, if their corresponding paths in differ by exactly one vertex. This paper examines the properties of shortest path graphs. Results include establishing classes of graphs that appear as shortest path graphs, decompositions and sums involving shortest path graphs, and the complete classification of shortest path graphs with girth 5 or greater. We include an infinite family of well structured examples, showing that the shortest path graph of a grid graph is an induced subgraph of a lattice. 相似文献
18.
Kalina Mambourg Laurie Bodart Nikolay Tumanov Steve Lanners Johan Wouters 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(3):205-211
The condensation reaction of 2‐mercapto‐3‐methoxybenzaldehyde with 3‐aminopyridine afforded an unexpected N‐alkylated [1,5]dithiocine instead of the N‐salicylideneaniline. The proposed mechanism for this condensation involves a strong intramolecular hydrogen bond between the thiol and the amine groups, leading to a second condensation. The corresponding product, i.e. 4,10‐dimethoxy‐13‐(pyridin‐3‐yl)‐6H,12H‐6,12‐epiminodibenzo[b,f][1,5]dithiocine methanol 0.463‐solvate, C21H18N2O2S2·0.463CH3OH, was characterized by single‐crystal X‐ray diffraction analysis. The supramolecular structure shows π–π stacking and S…S interactions in the crystal packing. Within the asymmetric unit, two geometries of the N atom are observed. Although a planar geometry should be expected, a pyramidal one is observed due to the crystal packing. The presence of the two geometries was further supported by density functional theory (DFT) calculations that show an electronic energy difference of less than 2 kJ mol?1 between the two conformers. 相似文献
19.
Hristova E Dong Y Grigoryan VG Springborg M 《The journal of physical chemistry. A》2008,112(34):7905-7915
The lowest-energy structures for all compositions of Ni n Cu m bimetallic clusters with N = n + m up to 20 atoms, N = 23, and N = 38 atoms have been determined using a genetic algorithm for unbiased structure optimization in combination with an embedded-atom method for the calculation of the total energy for a given structure. Comparing bimetallic clusters with homoatomic clusters of the same size, it is shown that the most stable structures for each cluster size are composed entirely of Ni atoms. Among the bimetallic clusters in the size range N = 2-20, the Ni N-1 Cu 1 clusters possess the highest stability. Further, it has been established that most of the bimetallic cluster structures have geometries similar to those of pure Ni clusters. The size N = 38 presents a special case, as the bimetallic clusters undergo a dramatic structural change with increasing atom fraction of Cu. Moreover, we have identified an icosahedron, a double, and a triple icosahedron with one, two, and three Ni atoms at the centers, respectively, as particularly stable structures. We show that in all global-minimum structures Ni atoms tend to occupy mainly high-coordination inner sites, and we confirm the segregation of Cu on the surface of Ni-Cu bimetallic clusters predicted in previous studies. Finally, it is observed that, in contrast to the bulk, the ground-state structures of the 15-, 16-, and 17-atom bimetallic clusters do not experience a smooth transition between the structures of the pure copper and the pure nickel clusters as a function of the relative number of the two types of atoms. For these sizes, the concentration effect on energy is more important than the geometric one. 相似文献
20.
Electrical measurements of bilayer membranes formed by Langmuir-Blodgett deposition on single-crystal silicon 总被引:1,自引:0,他引:1
Nikolov V Lin J Merzlyakov M Hristova K Searson PC 《Langmuir : the ACS journal of surfaces and colloids》2007,23(26):13040-13045
Bilayer membranes on solid supports are used for fundamental studies of biophysical properties and for the development of biosensors and other devices. Here we report on electrically addressable bilayer membranes formed by Langmuir-Blodgett (LB)-based deposition on single-crystal silicon. The incorporation of a polymer cushion ensures high lipid mobility in both the lower and upper leaflet, allowing the potential for combined investigations of electrical, structural, and dynamic characteristics of membrane-associated proteins. Impedance spectroscopy is used to demonstrate that the lipid bilayers are robust and reproducible with an impedance of about 10(4) Omega cm2 and a capacitance of about 0.8 microF cm(-2). The ability to characterize ion channels is demonstrated using the model system gramicidin. These results demonstrate that artificial bilayers formed by LB deposition have many unique advantages for electrical measurements of membranes and their components. 相似文献