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141.
Claudia Broecker Ralph-Hardo Schulz Gernot Stroth 《Designs, Codes and Cryptography》1997,10(2):137-143
We show that the Sylow 2-subgroups of nearly all Chevalley groups in even characteristic allow the definition of a check-character-system which detects all single and the most important double errors. 相似文献
142.
Formal syntheses of hirsutic acid C and complicatic acid via cycloaddition of cyclohexa-2,4-dienone with methyl methacrylate and a triplet sensitized 1,2-acyl shift are described. The X-ray crystal structure of one of the key intermediates is also reported. 相似文献
143.
C. W. Stark 《K-Theory》1991,5(4):333-354
We exhibit infinitely many commensurability classes of smooth closed manifolds M
m
, for all m 12, such that the universal cover of M is the product of a sphere and a Euclidean space and such that 1(M) contains finite dihedral subgroups. 相似文献
144.
Guillermo Durán-Solares Walter Fugarolas-Gómez Naytzé Ortíz-Pastrana Horacio López-Sandoval Tayde Osvaldo Villaseñor-Granados Angelina Flores-Parra 《Journal of Coordination Chemistry》2018,71(11-13):1935-1958
AbstractSpectroscopic and single crystal X-ray diffraction studies of coordination compounds of CoII, NiII, ZnII, and PdII with phenylsulfonyl imidazole and benzimidazole derivatives (2-mfsiz, 2-mfsbz) were performed. The relevance of non-covalent interactions on the stabilization of intra and intermolecular arrangements in the ligands and their coordination compounds was investigated. The imidazole 2-mfsiz ligand presents two enantiomeric conformers, where the ethylphenylsulfone moiety stabilizes intermolecular lone pair···π (S–O···π(phe)) and H···π contacts, while its tetrahedral coordination compounds, [M(2-mfsiz)2X2] (M2+?=?Co, Ni, Zn; X?=?Cl, Br) showed intramolecular lone pair···π interactions (S–O···π(iz)). On the other hand, compounds [Cu2(2-mfsiz)2(µ2-AcO)4] and trans-[Pd(2-mfsiz)2Cl2] do not present lone pair···π interactions due to the metal ion geometry (square base pyramidal or square planar), which leads to formation of π(iz)···π(phe) interactions. For the benzimidazole ligand 2-mfsbz, an intramolecular, H(phe)···π(bz) contact was observed, remaining in its tetrahedral and octahedral coordination compounds, [M(2-mfsbz)2X2] (M2+?=?Co, Zn; X?=?Cl, Br, NO3). This interaction limits the free rotation of the ethylphenylsulfone moiety for stabilization of an intermolecular lone pair···π interaction (S–O···π(iz)). The dimeric [Zn2(2-mfsiz)2(µ2-AcO)4] compound has a π(bz)···π(phe) contact. Theoretical calculations confirmed the non-covalent interactions in the ligands and their coordination compounds. 相似文献
145.
Resonance Raman and UV–vis characterization of charge transfer complexes of TCNQ and aromatic amines
Although the molecular charge transfer complexes formed by 7,7,8,8-tetracyanoquinodimethane (TCNQ) and several different donors have been widely investigated in the past, in this paper it is shown for the first time the vibrational spectroscopic characterization of the complexes formed by TCNQ and the simplest series of substituted anilines in solution. The UV–vis spectra indicate the formation of TCNQ complexes stabilized by two aromatic amines in a sandwich π type complex. It was observed that the charge transfer transition energies of the complexes follow a linear correlation with the ionization potential of the amines. The resonance Raman spectra revealed, by the analysis of the ν(CC) and ν(CN) stretching modes of TCNQ, that the complexes keep their neutral character in the ground electronic state, and not as a TCNQ2− dianion species as reported before. The observed enhancement of the TCNQ bands as the amine donor capacity increases, confirmed the charge transfer nature of the electronic transitions. The DFT and TDDFT results were obtained and the theoretical Raman and electronic spectra data supported the experimental findings. The results of the model systems presented herein can contribute to a deep understanding of the photoinduced charge transfer process in complexes of TCNQ, which is a key step in the designing of organic molecular devices. 相似文献
146.
Antonella Cartoni Andrea MadamiDaniela Palomba Marco MarrasMarco Berettoni Lauso OlivieriAlessandro Ettorre Amalia CipolloneFabio Animati Carlo Alberto MaggiEdith Monteagudo 《Tetrahedron》2003,59(8):1309-1316
NMR-Spectroscopic, computational and mass-spectrometric studies of the cis/trans isomers of N-[8-(acetylamino)-4-(2,2-dimethyl-1,1-diphenyl-silapropoxy)-6-fluoro-5-methyl-1-one-2,3,4-trihydronaphthyl]acetamide (1a and 1b), obtained as intermediates in the synthesis of an important class of alkaloid molecules, are reported. 1H and 13C NMR analyses show an unusual axial preference of the TBDPSi- (tert-butyldiphenylsilyl) group in position 4 in both the isomers. Mass spectrometric evidence demonstrates that trans isomer has a higher affinity for ammonium ions than the cis isomer and that only the ammonium adduct [1b+NH4]+ and the protonated molecule [1b+H]+ show the fragmentation in which loss of benzene is observed. Moreover, molecular mechanics and semi-empirical calculations indicate that a group of trans conformers tend to place one of the phenyl rings of the TBDPSiO- group in a offset π-stacked geometry with the compound's aromatic ring. The combination and the detailed analyses of these experimental and theoretical results could support the π-π interaction obtained as a conformational preference in the trans isomer. 相似文献
147.
Baris Yücel 《Tetrahedron》2005,61(48):11355-11373
Palladium-catalyzed cross-coupling of bicyclopropylidene (1) with iodoethene (11) in the presence of a secondary amine 12 provides allylidenecyclopropanes 13 which undergo immediate Diels-Alder reactions upon addition of dienophiles 14-18 to provide 8-(1′-aminoethyl)-substituted spiro[2.5]oct-7-ene derivatives 23a-26a in 29-66% yield. The same one-pot, two-step queuing cascade can be carried out with other iodoalkenes including cyclic ones and with cyclic dienophiles such as N-arylmaleinamides 19-22 and N-phenyl-triazolinedione 37 to furnish highly substituted spiro[2.5]oct-4-enes and spirocyclopropanated heterobicycles 47a-49a, 41a-46a (17-50%). Spirocyclopropanated heterobicycles such as 55, 56 (25 and 38% yield, respectively) can also be obtained by an inter-intra-intra-intermolecular version of this queuing cascade involving 1-hydroxyethyl- and 1-aminoethyl-substituted iodoethenes 53, 54. 相似文献
148.
Mario Amati Rosalba Liantonio Silvia Luzzati Giuseppe Resnati 《Journal of fluorine chemistry》2004,125(4):629-640
α,ω-Diiodoperfluoralkanes self-assemble in solution and in the solid phase with (S)-(−)-N,N-dimethyl-1-ferrocenylethylamine. The formed adducts have been characterized by DSC, IR, Raman, and NMR techniques. Single crystal X-ray analysis of one of the obtained adducts shows that perfluorinated and organometallic modules alternate giving rise to infinite one-dimensional (1D) chains. The interacting modules are connected through strong n-type halogen bondings, involving nitrogen and iodine atoms, and weak π-type halogen bondings, involving Cp rings and iodine atoms. Both interactions are the shortest reported to now in their respective classes. Theoretical calculations have been performed to quantify the observed π-type halogen bonding. For the first time a metallocene-perfluorocarbon (PFC) hybrid material is described. 相似文献
149.
Teresa M.V.D. Pinho e Melo Maria I.L. Soares António M.d’A. Rocha Gonsalves 《Tetrahedron letters》2006,47(5):791-794
Diazafulvenium methides generated from the solution pyrolysis of pyrazolo[1,5-c][1,3]thiazole-2,2-dioxides participate in [8π+2π] cycloadditions giving pyrazolo[1,5-a]pyridine derivatives. 1-Methyl-diazafulvenium, generated under flash vacuum pyrolysis reaction conditions, undergoes an intramolecular sigmatropic [1,8]H shift giving 1-vinyl-1H-pyrazoles. 相似文献
150.
Donor-acceptor molecules containing thiophene chromophore with remarkably large Stokes shift (>210 nm) have been found to exhibit strong and stable ECL emission via the singlet excited state without the addition of any co-reactant or a second compound. 相似文献