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151.
Jordan Meyet Keith Searles Mark A. Newton Michael Wrle Alexander P. vanBavel Andrew D. Horton Jeroen A. vanBokhoven Christophe Copret 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):9946-9950
Monomeric CuII sites supported on alumina, prepared using surface organometallic chemistry, convert CH4 to CH3OH selectively. This reaction takes place by formation of CH3O surface species with the concomitant reduction of two monomeric CuII sites to CuI, according to mass balance analysis, infrared, solid‐state nuclear magnetic resonance, X‐ray absorption, and electron paramagnetic resonance spectroscopy studies. This material contains a significant fraction of Cu active sites (22 %) and displays a selectivity for CH3OH exceeding 83 %, based on the number of electrons involved in the transformation. These alumina‐supported CuII sites reveal that C?H bond activation, along with the formation of CH3O‐ surface species, can occur on pairs of proximal monomeric CuII sites in a short reaction time. 相似文献
152.
153.
Luke Green Keith Livingstone Dr. Sophie Bertrand Dr. Simon Peace Dr. Craig Jamieson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14866-14870
A range of 1,3,4-oxadiazoles have been synthesized using a UV-B activated flow approach starting from carboxylic acids and 5-substituted tetrazoles. The application of UV light represents an attractive alternative to the traditional thermolytic approach and has demonstrated comparable efficiency and versatility, with a diverse substrate scope, including the incorporation of highly substituted amino acids. 相似文献
154.
Dey A Peng Y Broderick WE Hedman B Hodgson KO Broderick JB Solomon EI 《Journal of the American Chemical Society》2011,133(46):18656-18662
S K-edge X-ray absorption spectroscopy on the resting oxidized and the S-adenosyl-l-methionine (SAM) bound forms of pyruvate formate-lyase activating enzyme are reported. The data show an increase in pre-edge intensity, which is due to additional contributions from sulfide and thiolate of the Fe(4)S(4) cluster into the C-S σ* orbital. This experimentally demonstrates that there is a backbonding interaction between the Fe(4)S(4) cluster and C-S σ* orbitals of SAM in this inner sphere complex. DFT calculations that reproduce the data indicate that this backbonding is enhanced in the reduced form and that this configurational interaction between the donor and acceptor orbitals facilitates the electron transfer from the cluster to the SAM, which otherwise has a large outer sphere electron transfer barrier. The energy of the reductive cleavage of the C-S bond is sensitive to the dielectric of the protein in the immediate vicinity of the site as a high dielectric stabilizes the more charge separated reactant increasing the reaction barrier. This may provide a mechanism for generation of the 5'-deoxyadenosyl radical upon substrate binding. 相似文献
155.
Keith B. Dillon Judith A. K. Howard Philippa K. Monks Michael R. Probert Helena J. Shepherd 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(4):m111-m114
The title compound, cis‐dichloridobis(triethylphosphane)platinum(II) chloroform monosolvate, [PtCl2(C6H15P)2]·CHCl3, has been obtained from ligand scrambling in the cis‐[PtCl2(Cyp2PCl)(PEt3)] (Cyp = cyclopentyl) system in CHCl3 solvent. Unlike the two previously reported unsolvated polymorphs, which are both monoclinic, the compound crystallizes in an orthorhombic setting. Furthermore, the system exhibits a reversible temperature‐dependent structural phase transition, coupling a reduction in anisotropic displacement parameters and a reduction in crystallographic symmetry on cooling. The high‐temperature phase adopts space group Pnma with the complex and solvent molecules sitting across a crystallographic mirror plane (Z′ = 0.5). The low‐temperature phase adopts the space group P212121 with Z′ = 1. 相似文献
156.
Ian A. Gass Stuart R. Batten Craig M. Forsyth Boujemaa Moubaraki Caspar J. Schneider Keith S. Murray 《Coordination chemistry reviews》2011,255(17-18):2058-2067
The synthesis, structures and magnetism of the complexes [FeII(3-bpp)2][bpmdcK](SeCN)1.7(ClO4)1.3·MeOH·H2O (1), [FeII(3-bpp)2]4[bpmdcH2(H2O)2](ClO4)10·7H2O·3MeOH (2) and cis-[FeII2(NCSe)2((3,5-Me2pz)3CH)2(μ-bpmdc)]·2MeCN (3) (where 3-bpp = 2,6-di(pyrazole-3yl)pyridine, bpmdc = N,N′-bis(4-pyridyl-methyl)diaza-18-crown-6) and (3,5-Me2pz)3CH = tris(3,5-dimethylpyrazole)methane, are presented. These compounds form a study of the supramolecular influence of host–guest/crown-ether interactions and cation-to-crown hydrogen-bonding effects upon d6 spin transitions, the latter occurring above, or near to, room temperature in 1 and 2. Desolvation effects also influence the T1/2 values. The dinuclear compound 3 contains covalent pyridyl (crown) N to Fe bridge bonding and remains high spin. 相似文献
157.
Reactions of trialkylboranes with 2-lithio-2-alkyl-1,3-benzodithioles followed by oxidation give ketones in good yields. This method is far less subject to steric hindrance than the analogous reactions using anions derived from bis(phenylthio)alkanes. 相似文献
158.
John T. Shaw Christine E. Brotherton Robert W. Moon Mark D. Winland Mark D. Anderson Keith S. Kyler 《Journal of heterocyclic chemistry》1980,17(1):11-16
A much improved synthesis of the heretofore difficultly obtainable 2,6-diaminopyrazine (4) was afforded by the low-pressure catalytic hydrogenation (palladium on carbon) of 2,6-diazido-pyrazine (2) ; reaction of 2,6-dichloropyrazine (1) and sodium azide gave 2 in 84% yield. The outcome of the reduction was found to be solvent dependent: 1,2-dimethoxyethane containing aqueous ammonia gave 4 in 83% yield; 1,2-dimethoxyethane alone gave 5-aminotetrazolo[1,5-a]-pyrazine (3) in 26% yield. Additional alternative syntheses of 3 and 4 are described. A number of acyl and azo derivatives of 4 were prepared. Reactions of 2 with dimethyl acetylenedicarboxylate and ethyl acetate (base catalyzed) leading to vic-triazole derivatives are also described. 相似文献
159.
Effects of petroleum resins on asphaltene aggregation and water-in-oil emulsion formation 总被引:4,自引:0,他引:4
P. Matthew Spiecker Keith L. Gawrys Chad B. Trail Peter K. Kilpatrick 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,220(1-3):9-27
Asphaltenes from four crude oils were fractionated by precipitation in mixtures of heptane and toluene. Solubility profiles generated in the presence of resins (1:1 mass ratio) indicated the onset of asphaltene precipitation occurred at lower toluene volume fractions (0.1–0.2) than without resins. Small-angle neutron scattering (SANS) was performed on solutions of asphaltene fractions in mixtures of heptane and toluene with added resins to determine aggregate sizes. Water-in-oil emulsions of asphaltene–resin solutions were prepared and separated by a centrifuge method to determine the vol.% water resolved. In general, the addition of resins to asphaltenes reduced the aggregate size by disrupting the π–π and polar bonding interactions between asphaltene monomers. Interaction of resins with asphaltenic aggregates rendered the aggregates less interfacially active and thus reduced emulsion stability. The smallest aggregate sizes observed and the weakest emulsion stability at high resin to asphaltene (R/A) ratios presumably corresponded to asphaltenic monomers or small oligomers strongly interacting with resin molecules. It was often observed that, in the absence of resins, the more polar or higher molecular weight asphaltenes were insoluble in solutions of heptane and toluene. The addition of resins dissolved these insolubles and aggregate size by SANS increased until the solubility limit was reached. This corresponded approximately to the point of maximum emulsion stability. Asphaltene chemistry plays a vital role in dictating emulsion stability. The most polar species typically required significantly higher resin concentrations to disrupt asphaltene interactions and completely destabilize emulsions. Aggregation and film formation are likely driven by polar heteroatom interactions, such as hydrogen bonding, which allow asphaltenes to absorb, consolidate, and form cohesive films at the oil–water interface. 相似文献
160.
Reaction of the phosphavinyl Grignard reagent [Z-MesP=C(Bu(t))MgBr.OEt2]2 (Mes = 2,4,6-Me3C6H2) with MesPCl2 affords the corresponding 1,3-diphosphapropene compound [Z-MesP=C(Bu(t))P(X)Mes] (X = Cl, Br); subsequent reaction with two equivalents of elemental lithium in thf affords the title compound [[Bu(t)C(PMes)2]Li(thf)3], which contains an asymmetric eta1-1,3-diphosphaallyl ligand. 相似文献