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排序方式: 共有124条查询结果,搜索用时 46 毫秒
1.
Weiping Huang Suwen Liu Xianghai Tang Menachem Motiei Yuri Koltypin A. Gedanken 《Research on Chemical Intermediates》2004,30(7-8):793-805
Ag-TiO2, Cu-TiO2 and Ni-TiO2 were prepared by sonication. The interactions of Ti-gel with silver, copper and nickel ions under ultrasound irradiation are very different, although these ions can be dispersed very well in titania. The results of EDXA and XRD analysis indicate that Ti-gel does not react with AgCl and crystallizes unaffectedly to form rutile. M(OH)2 (M = Cu and Ni), on the other hand, favors polycondensation with Ti-gel and affects the crystallization of Ti-gel. CuO favors stabilization of the anatase phase. Ni2+ ions tend to incorporate more easily into titania than Cu2+ ions do when the samples are calcined. TEM, and BET were also used to characterize the samples. 相似文献
2.
Walker SL Redman JA Elimelech M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7736-7746
The influence of bacterial surface lipopolysaccharides (LPS) on cell transport and adhesion has been examined by use of three mutants of Escherichia coli K12 with well-characterized LPS of different lengths and molecular composition. Two experimental techniques, a packed-bed column and a radial stagnation point flow system, were employed to investigate bacterial adhesion kinetics onto quartz surfaces over a wide range of solution ionic strengths. Although the two systems capture distinct deposition (adhesion) mechanisms because of their different hydrodynamics, similar deposition kinetics trends were observed for each bacterial strain. Bacterial deposition rates were directly related to the electrostatic double layer interaction between the bacteria and quartz surfaces, in qualitative agreement with classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, DLVO theory does not fully explain the deposition behavior for the bacterial strain with the lengthy, uncharged O-antigen portion of the LPS. Neither the length nor the charge characteristics of the LPS molecule directly correlated to deposition kinetics, suggesting a complex combination of cell surface charge heterogeneity and LPS composition controls the bacterial adhesive characteristics. It is further suggested that bacterial deposition behavior is determined by the combined influence of DLVO interactions, LPS-associated chemical interactions, and the hydrodynamics of the deposition system. 相似文献
3.
Robert Glaser Menachem Twaik Shimona Geresh Jeanine Blumenfeld 《Tetrahedron letters》1977,18(52):4635-4638
Z--acetamidocinnamic acid was hydrogenated with neutral diphosphine-rhodium(I) complexes containing trans-1,2-bis(diphenylphosphinomethyl) cycloalkanes to give N-acetylphenylalanine: 86 % e.e.-(R) [(1R,2R)-cyclobutane]; 63 % e.e.-(R) [(1R,2R)-cyclopentane]; 35 % e.e.-(S) [(1S,2S)-cyclohexane]; and 82 % e.e.-(R) [(2R,3R)-DIOP]. Similarly, -acetamidoacrylic acid was hydrogenated to give N-acetylalanine: 72 % e.e.-(R) [(1R,2R)-cyclobutane]; 72 % e.e.-(R) [(1R,2R)-cyclopentane]; 40 % e.e.-(S) [(1S,2S)-cyclohexane]; and 73 % e.e.-(R) [(2R,3R)-DIOP]. 相似文献
4.
Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes 总被引:1,自引:0,他引:1
A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl2, Na2SO4, and MgSO4) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge. 相似文献
5.
Mezer A Friedman R Noivirt O Nachliel E Gutman M 《The journal of physical chemistry. B》2005,109(22):11379-11388
The surface of a protein, or a membrane, is spotted with a multitude of proton-binding sites, some of which are only a few angstroms apart. When a proton is released from one site, it propagates through the water by a random walk under the bias of the local electrostatic potential determined by the distribution of the charges on the protein. Some of the released protons disperse into the bulk, but during the first few nanoseconds, the released protons can be trapped by encounter with nearby acceptor sites. This process resembles a scenario which corresponds with the time-dependent Debye-Smoluchowski equation. In the present study, we investigated the mechanism of proton transfer between sites that are only a few angstroms apart, using as a model the proton exchange between sites on a small molecule, fluorescein, having two, spectrally distinguishable, proton-binding sites. The first site is the oxyanion on the chromophore ring structure. The second site is the carboxylate moiety on the benzene ring of the molecule. Through our experiments, we were able to reconstruct the state of protonation at each site and the velocity of proton transfer between them. The fluorescein was protonated by a few nanosecond long proton pulse under specific conditions that ensured that the dye molecules would be protonated only by a single proton. The dynamics of the protonation of the chromophore were measured under varying initial conditions (temperature, ionic strength, and different solvents (H(2)O or D(2)O)), and the velocity of the proton transfer between the two sites was extracted from the overall global analysis of the signals. The dynamics of the proton transfer between the two proton-binding sites of the fluorescein indicated that the efficiency of the site-to-site proton transfer is very sensitive to the presence of the screening electrolyte and has a very high kinetic isotope effect (KIE = 55). These two parameters clearly distinguish the mechanism from proton diffusion in bulk water. The activation energy of the reaction (E(a) = 11 kcal mol(-1)) is also significantly higher than the activation energy for proton dissociation in bulk water (E(a) approximately 2.5 kcal mol(-1)). These observations are discussed with respect to the effect of the solute on the water molecules located within the solvation layer. 相似文献
6.
de Kerchove AJ Elimelech M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(14):6462-6472
Bacterial cells and other biological particles carry charged macromolecules on their surface that form a "soft" ion-permeable layer. In this paper, we test the applicability of an electrokinetic theory for soft particles to characterize the electrophoretic mobility (EPM) and adhesion kinetics of bacterial cells. The theory allows the calculation of two parameters--the electrophoretic softness and the fixed charged density--that define the characteristics of the polyelectrolyte layer at the soft particle surface. The theory also allows the calculation of an outer-surface potential that may better predict the electrostatic interaction of soft particles with solid surfaces. To verify its relevance for bacterial cells, the theory was applied to EPM measurements of two well-characterized Escherichia coli K12 mutants having lipopolysaccharide (LPS) layers of different lengths and molecular compositions. Results showed that the obtained softness and fixed charge density were not directly related to the known characteristics of the LPS of the selected strains. Interaction energy profiles calculated from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were used to interpret bacterial deposition (adhesion) rates on a pure quartz surface. The outer surface potential failed to predict the low attachment efficiencies of the two bacterial strains. The lack of success in the application of the theory for soft particles to bacterial cells is attributed to chemical and physical heterogeneities of the polyelectrolyte layer at the cell surface. 相似文献
7.
Miklós Banai 《International Journal of Theoretical Physics》1981,20(3):147-169
We investigate prepositional systems for local field theories, which reflect intrinsically the uncertainties of measurements made on the physical system, and satisfy the isotony and local commutativity postulates of Haag and Kastler. The space-time covariance can be implemented in a natural way in these propositional systems. New techniques are introduced to obtain these propositional systems: the lattice-valued logics. The decomposition of the complete orthomodular lattice-valued logics shows that these logics are more general than the usual two-valued ones and that in these logics there is enough structure to characterize the classical and quantum, nonrelativistic and relativistic local field theories in a natural way. The Hubert modules give the natural inner product spaces (modules) for the realization of the lattice-valued logics.The author is also with the Publishing House of the Hungarian Academy of Sciences, H-1363, Budapest, P.O.B. 24. 相似文献
8.
Miller's 1937 splitting theorem was proved for every finite n>0 for all ρ-uniform families of sets in which ρ is infinite. A simple method for proving Miller-type splitting theorems is presented here and an extension of Miller's theorem is proved in ZFC for every cardinal ν for all ρ -uniform families in which ρ≥?ω(ν). The main ingredient in the method is an asymptotic infinitary Löwenheim–Skolem theorem for anti-monotone set functions. 相似文献
9.
Mariana Pokrass Doron Azulay Isaac Balberg Nurit Atar Raz Gvishi Menachem Nathan 《Journal of Sol-Gel Science and Technology》2014,70(3):517-527
Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? c = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10?3(Ω cm)?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating. 相似文献
10.
Menachem Kojman 《Proceedings of the American Mathematical Society》2002,130(6):1597-1602
A topological space is Hindman if for every sequence in there exists an infinite so that the sequence , indexed by all finite sums over , is IP-converging in . Not all sequentially compact spaces are Hindman. The product of two Hindman spaces is Hindman.
Furstenberg and Weiss proved that all compact metric spaces are Hindman. We show that every Hausdorff space that satisfies the following condition is Hindman:
Consequently, there exist nonmetrizable and noncompact Hindman spaces. The following is a particular consequence of the main result: every bounded sequence of monotone (not necessarily continuous) real functions on has an IP-converging subsequences.