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81.
The reduction of [Co(III)(tmsalen)(py)2]+ with NaBH4/PdCl2 and the successive oxidative addition of CH2ClI, carried out in neutral methanolic solution and followed by the addition of NaOH, afford a new dinuclear complex. The molecular structure reveals that it is formed by an octahedral [Co(tmsalen)(py)(OH)] unit connected to a β-folded [Co(tmsalenCH2)]+ fragment, in such a way that the latter metal completes the coordination sphere with the hydroxo group and a tmsalen oxygen from the former unit.  相似文献   
82.
The rate constants of ortho- into para-positronium conversion reactions promoted by paramagnetic 3d complexes were found to be linearly correlated with the delocalization, of unpaired metal electrons caused by ligands. It is shown here that s, usually obtained by UV/Vis absorption spectroscopy, may also be deduced from the correlations mentioned above.  相似文献   
83.
The paper reports the synthesis of a-cyclodextrin (-CD) derivative (1) functionalized with a ligand subunit at the secondary-hydroxyl rim. The ligand subunit is 2-hydroxymethyl-6-thiomethyl pyridine connected to the macrocycle via a thioether bond. In the presence of Cu(II) ions1 accelerates the cleavage of thep-nitrophenyl esters of picolinic acid (PNPP), quinaldic acid (PNPQ) and its 6-phenyl derivative (PNPQPh) via the nucleophilic attack of the hydroxyl of the pyridine subunit. However, the-CD derivative is less effective than the ligand 2-hydroxymethyl-6-methylthiomethyl pyridine (2), indicating no cooperation between the hydrophobic and metal ion recognition sites. However, in the case of PNPQPh, the observed rate constants in the presence of Cu(II) ions are close to that of model2 and this suggests we are approaching a binding mode appropriate for taking advantage of the two binding sites of the metal receptor1 · Cu(II). Interestingly, the most reactive derivative with native-CD is thep-nitrophenyl quinaldate (PNPQ) in accord with its mode of complexation to the macrocycle and the location of the actual nucleophile (one of the secondary hydroxyls of-CD).  相似文献   
84.
The ortho- (o-Ps) to para-positronium (p-Ps) conversion reactions promoted by ten Cr(III) complexes were investigated at several temperatures. The results obtained are discussed together with those of three other Cr(III) complexes measured previously.It was found that all the reactions studied are diffusion controlled and that their rate constants,k SE, increased as the corresponding ratiosB/B o between the Racah interelectronic repulsion parameters of Cr(III) complexes and Cr(III) gaseous ion decrease; that is,K SE increases as 3d electron cloud expansion promoted by ligands, increases. Therefore the o-Ps to p-Ps conversion reactions can be considered a complementary probe for the spectroscopic method in investigating the ligand capabilities to cause 3d cloud expansion. The effect is called nephelauxetic which means expanding (electron) cloud.Finally an empirical average environmental rule, similar to that hypothesized for B/Bo ratios, is proposed for estimating the rate constants,K SE, of complexes formed with mixed ligand sets.This work was supported by Ministero Universitá e Ricerca Scientifica e Tecnologica (M.U.R.S.T.) and by Consiglio Nazionale Ricerche (C.N.R.).  相似文献   
85.
In the Hilbert space formulation of classical mechanics, pioneered by Koopman and von Neumann, there are potentially more observables than in the standard approach to classical mechanics. In this Letter, we show that actually many of those extra observables are not invariant under a set of universal local symmetries which appear once the Koopman and von Neumann formulation is extended to include the evolution of differential forms. Because of their noninvariance, those extra observables have to be removed. This removal makes the superposition of states in the Koopman and von Neumann formulation, and as a consequence also in classical mechanics, impossible.  相似文献   
86.
Chiral non-racemic 1,4-dihydropyridazines were prepared by the reaction of 1,2-diaza-1,3-dienes with arylacetaldehydes under organocatalytic conditions. l-Proline and (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine coupled with trifluoroacetic acid were used as organocatalysts. Enantiomeric excesses ranged from 25% to 78%.  相似文献   
87.
Resonant photoemission was used to investigate the EuF3 ultrathin layer for the photon energies within the Eu 4d → 4f excitation region. Photoemission from the valence band in resonance showed the lines which can be attributed to two Eu valence states (Eu+3 and Eu+2) whereas the off resonance spectra of EuF3 ultrathin layer do not exhibit divalent states of Eu. An explanation of that effect is proposed which is based on the charge transfer from the ligand.  相似文献   
88.
In this paper models and algorithms for the optimization of signal settings on urban networks are proposed. Two different approaches to the solution of the problem may be identified: a global approach (optimization of intersection signal settings on the whole network) and a local approach (optimization of signal settings intersection by intersection). For each approach a different optimization model and some solution algorithms are proposed; both models and algorithms are based on the assumptions of within-day static system and stochastic user equilibrium assignment models. The paper includes numerical results on test networks and a comparison between the two approaches.  相似文献   
89.
Zinc(II) complexes of the formula [Zn(L)(X)2] (where X = Cl, N3, NCO and SCN (1a-d, respectively)) and {[Zn(L)(ClO4)(H2O)](ClO4)}n (2), were isolated in the pure form on the reaction of 1,3-bis(2-pyridylmethylthio)propane (L) with different zinc(II) salts. All the complexes were characterized by physicochemical and spectroscopic tools. The X-ray crystallographic analyses of the complexes 1d and 2 showed that the former is mononuclear while complex 2 is a 1D coordination polymer, {[Zn(L)(ClO4)(H2O)](ClO4)}n, due to a different coordination mode of the tetradentate ligand L. The zinc(II) ions present an octahedral coordination geometry in both compounds, which is more distorted in the mononuclear complex 1d. The study indicates that the counter anion of the zinc(II) salt used as reactant leads to a different type of complex when isolated as a crystalline material. A spectroscopic study of the interaction of complex, 2 with calf thymus-DNA (CT-DNA) in Tris-HCl buffer showed a significant non-intercalative interaction with a binding constant (Kb) of 4.7 × 104 M−1, and the linear Stern-Volmer quenching constant (Ksv) and the binding sites (n) were found to be 1.3 × 103 and 0.92 respectively, calculated from ethidium bromide (EB) fluorescence displacement experiments.  相似文献   
90.
In the title compound, [Pd(C23H29N2OS2)2], the PdII atom displays the expected square‐planar coordination geometry. However, the trans configuration, which allows the PdII atom to be located on a crystallographic inversion centre, is unusual with respect to the cis arrangement found in analogous Pd complexes comprising similar N,S‐chelating ligands.  相似文献   
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