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81.
Jakob Blom Gabriel J. Reyes‐Rodríguez Henriette N. Tobiesen Johannes N. Lamhauge Marc V. Iversen Casper L. Barlse Niels Hammer Matilde Rusbjerg Karl Anker Jrgensen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):18020-18026
Nucleophile–nucleophile coupling is a challenging transformation in organic chemistry. Herein we present a novel umpolung strategy for α‐functionalization of aldehydes with nucleophiles. The strategy uses organocatalytic enamine activation and quinone‐promoted oxidation to access O‐bound quinol‐intermediates that undergo nucleophilic substitution reactions. These quinol‐intermediates react with different classes of nucleophiles. The focus is on an unprecedented organocatalytic oxidative α‐thiolation of aldehydes. The reaction scope is demonstrated for a broad range of thiols and extended to chemoselective bioconjugation, and applicable to a large variety of aldehydes. This strategy can also encompass organocatalytic enantioselective coupling of α‐branched aldehydes with thiols forming quaternary thioethers. Studies indicate a stereoselective formation of the intermediate followed by a stereospecific nucleophilic substitution reaction at a quaternary stereocenter, with inversion of configuration. 相似文献
82.
Matilde Lalín 《Geometriae Dedicata》2004,107(1):211-234
83.
Fondo M Ocampo N García-Deibe AM Corbella M El Fallah MS Cano J Sanmartín J Bermejo MR 《Dalton transactions (Cambridge, England : 2003)》2006,(41):4905-4913
The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium. 相似文献
84.
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
85.
Jesús Sanmartín-Matalobos Cristina Portela-García Matilde Fondo Ana M. García-Deibe Antonio L. Llamas-Saiz 《Journal of Coordination Chemistry》2016,69(8):1358-1370
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
86.
87.
Miguel E. Alonso Maria I. Hernández Matilde Gómez Patricia Jano Sarah Pekerar 《Tetrahedron》1985,41(12):2347-2354
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
88.
Annibale Giuliano Brandolisio Matilde Bugarcic Zivadin Cattalini Lucio 《Transition Metal Chemistry》1998,23(6):715-719
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
89.
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