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91.
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We construct an additive category where objects are embedded graphs in the 3-sphere and morphisms are geometric correspondences given by 3-manifolds realized in different ways as branched covers of the 3-sphere, up to branched cover cobordisms. We consider dynamical systems obtained from associated convolution algebras endowed with time evolutions defined in terms of the underlying geometries. We describe the relevance of our construction to the problem of spectral correspondences in noncommutative geometry.  相似文献   
94.
A template 2:2:4 condensation of 2,6-diformyl-4-methyl-phenol, triethylenetetramine and zinc acetate gave rise to the crystallisation of [{Zn4(H4L1)(OAc)4}{Zn(OAc)3(H2O)}(OAc)] · 7H2O (1 · 7H2O), being H6L1 a macrocyclic diphenolate Schiff base ligand. Changing some operation conditions, other template reactions yielded dinuclear complexes of the type Zn2(Ln)(OAc) · xH2O, where H3Ln (n = 2, 3) are podant triphenolate Schiff base ligands derived from a 3:1 condensation of the corresponding 2,6-diformyl-4-alkyl-phenol (alkyl = Me or But, respectively) and triethylenetetramine. After recrystallisation, these two latter complexes could be X-ray characterised as Zn2(L2)(OAc) · 1.25H2O · 0.5MeCN (2 · 1.25H2O · 0.5MeCN), and Zn2(L3)(OAc) (3). Furthermore, after addition of a 3:1 molar ratio of 2-amino-4-methyl-phenol to 3, this underwent imidazolidine hydrolysis and a double imine condensation, yielding Zn2(L4)(OAc)(HOAc) · 2H2O (4 · 2H2O), where H3L4 is an acyclic pentadentate Schiff base derived from the 1:2 condensation of 2,6-diformyl-4-tert-butyl-phenol and 2-amino-4-methyl-phenol.  相似文献   
95.
We report here the straightforward synthesis of some dimeric transition metal complexes of three Schiff base ligands, which were obtained by condensation of 2-tosylaminomethylaniline with 2,3-dihydroxybenzaldehyde (H2L1), 2,4-dihydroxybenzaldehyde (H2L2), and 4-formyl-3-hydroxybenzoic acid (H2L3), respectively. Both ligands and complexes were characterized by a combination of 1H NMR, infrared and mass spectrometries, and elemental analyses. Furthermore, the crystal structures of H2L2 and Pd2L22·2MeOH were elucidated by X-ray diffraction. The crystal structure of Pd2L22·2MeOH has instead of typical μ-Ophenoxo bridges, repeating units held together by unusual μ-Nsulfonamido bridges. This complex is chiral, although it crystallizes as a racemate, with C2v symmetry, where the two bridging nitrogens are asymmetric centers with identical handedness.  相似文献   
96.
The Copper(II) chelate catalyzed thermal cycloaddition of ethyl diazoacetate, dimethyl diazomalonate, ethyl-2-diazo-3-oxobutyrate, and ethyl diazopyruvate, representatives of diazocarbonyl additions that yield cyclopropanes and dihydrofurans, respectively, to olefins, has been examined in terms of the possible participation of radical species in intermediary stages. To this purpose, the title diazocarbonyl compounds were exposed to 1-methyl-1-cyclopropylethylene and 1,1-dicyclopropylethylene under catalytic conditions. The absence of cyclopropylcarbinyl radical to butenyl radical rearrangement products in cyclopropanations as well as in those reactions that furnish heterocycles suggests that intermediates of free radical nature may not be involved in the cycloaddition process. In turn, the strong electron donor capability of cyclopropyl substituents is interpreted as allusive of a non synchronous 1,3-dipolar cycloaddition of transient metal carbenes to the olefin with possible charge polarization.  相似文献   
97.
The nucleophilicity of the undissociated thiols is compared to that of thioethers in the displacement of chloride ion from the PtII complexes [Pt(bipy)(NO2)Cl] (bipy=2,2-bipyridine) and [Pt(terpy)Cl]+(terpy= 2,2-6,2- terpyridine). As far as the neutral substrate is concerned the second order rate constants for RSH and RSR nucleophiles are equally related to the inductive and steric effects of the groups linked to the sulphur donor atom. By contrast, only thiols are reactive (under standard experimental conditions) towards the cationic substrate, and the difference can be explained, in this case, by the immediate deprotonation of the substituted product forcing the reaction to completion. The reverse reaction has been examined in one case (PhSH) and the complete protonation of the coordinated thiolate species requires [H+]>2 mol·dm–3. In both series of reactions, thiol molecules also containing a second acidic group (–OH, –CO2H, –NH3+) capable of facile interaction via hydrogen bonding with the developing chloride in the transition state, exhibit a reactivity larger than that expected on the basis of electronic and steric effects alone.  相似文献   
98.
The cationic polymerization of N-vinyl carbazole, initiated by Ph3C+ AsF6? and Ph3C+ PF6? in methylene dichloride at 20 and 0°, has been studied in some detail. Reactions were very fast and rates of monomer consumption were measured using an adiabatic calorimetric technique. Initiation was relatively “slow” but complete, and termination was deduced to be insignificant during kinetic lifetimes. Values for kp were found to vary with the initial initiator concentration; this dependence is discussed in terms of current theories regarding equilibria between ion pairs and free ions in non-aqueous solvents. kp+ values estimated from two methods of extrapolation are 9.5 · 105 M?1 sec?1 at 20° and 4.8 · 105 M?1 sec?1 at 0°. Finally, it has been found that ion pairs are much less reactive than free ions in this system.  相似文献   
99.
100.
Formation in basic solution of an asymmetric pentanuclear carbonate Ni(II) complex with a compartmental ligand involves atmospheric CO(2) uptake, either by reaction of two slightly different dinuclear precursors that yield its di- and trinuclear "building blocks", or directly, by spontaneous self-organization of metal and ligand starting reactants.  相似文献   
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