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991.
Dr. M. Qadri E. Mubarak Dr. Hafiz Saqib Ali Jimei Zhou Prof. Chaoqun Li Prof. Jianliang Xiao Dr. Sam P. de Visser 《欧洲无机化学杂志》2023,26(5):e202200621
High-valent metal-oxo species are typical catalytic cycle intermediates in mono-oxygenases and dioxygenases and commonly react through oxygen atom transfer to substrates. In this work we study a biomimetic model complex with a 1,1’-bis((3,5-dimethylpyridin-2-yl)methyl)-2,2’-bipiperidine ligand system bound to a manganese(IV)-oxo(hydroxo) species and study its formation from manganese(II)-hydroxo and H2O2 as well as its reaction with (S)-1-phenylisochromane through dehydrogenative α-oxygenation. The work utilizes density functional theory methods to explore its catalytic cycle and its reactivity patterns. We show that the manganese(IV)-oxo(hydroxo) species is an active oxidant and preferentially the oxo group abstracts a hydrogen atom from substrate with barriers well lower in energy than those found for hydrogen atom abstraction by the hydroxo group. Interestingly, the rate-determining step is the OH rebound rather than the hydrogen atom abstraction, which would imply they would have limited kinetic isotope effect for the replacement of the transferring hydrogen atom by deuterium. 相似文献
992.
Francis Bru Dr. Mathieu Lesieur Dr. Albert Poater Prof. Dr. Alexandra M. Z. Slawin Prof. Dr. Luigi Cavallo Prof. Dr. Catherine S. J. Cazin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(67):e202201917
The synthesis and isolation of [Pd(NHC)(PhC≡CPh)] complexes are reported. These new 14-electron Pd(0)-complexes are key synthons leading to known palladium(0) and palladium(II) species, as well as permitting access to unprecedented mixed NHC-phosphite palladium(0) complexes. This motif permits the facile catalytic hydrosilylation of allenes. DFT calculations have allowed the characterization of the relatively weak interaction between the metal and the diphenylacetylene ligand, with a comparison with a series of ligands with more or less coordinating power, bearing varied structural and electronic properties. 相似文献
993.
Liu Ming Granados Albert Reyes-Mesa David Arosemena-Angulo E. Leonardo Calvo-Torras María Ángeles Pleixats Roser Vallribera Adelina 《Cellulose (London, England)》2022,29(16):8889-8905
Cellulose - The preparation of antifungal-functionalized silica nanoparticles by covalent attachment of several silylated derivatives based on the topical antifungal agent Micozanole is described.... 相似文献
994.
PROOXIDANT and ANTIOXIDANT EFFECTS OF ASCORBATE ON PHOTOSENSITIZED PEROXIDATION OF LIPIDS IN ERYTHROCYTE MEMBRANES 总被引:1,自引:0,他引:1
Albert W. Girotti James P. Thomas John E. Jordan 《Photochemistry and photobiology》1985,41(3):267-276
Abstract— Continuous blue light irradiation of resealed erythrocyte ghosts at 37°C in the presence of uroporphyrin or protoporphyrin results in 1 O2 -mediated (azide inhibitable) lipid peroxidation and membrane lysis. Lipid peroxidation was assessed by thiobarbituric acid reactivity and by quantitation of total hydroperoxides, while lysis was measured in terms of trappedglucose–6-P release. Low concentrations of ascorbate, AH- (e.g. 0.5 m M ). present at the start of irradiation, significantly enhanced the rates of lysis and peroxidation, whereas relatively high concentrations of AH- (e.g. 15 m M ) inhibited both processes. By way of contrast. AH- produced only a dose-dependent inhibition of the photoinactivation of lysozyme, added as an extramembranous target. No significant AH- induced lipid peroxidation was observed in dark or light controls, plus porphyrin or minus porphyrin, respectively. Stimulation of peroxidation and lysis by low levels of AH- was enhanced by added Fe(III), abolished by EDTA. but unaffected by catalase or superoxide dismutase. A plausible explanation for these results is as follows. At low concentrations of AH- prooxidant activity is favored. Redox metal-mediated breakdown of photoperoxides occurs, which tends to amplify lipid peroxidation. Neither O2 - nor H2 O2 appears to be involved. At significantly high concentrations, AH- acts predominantly as an antioxidant by intercepting 1 O2 and/or sensitizer triplet, or by scavenging free radical intermediates of lipid peroxidation. 相似文献
995.
Elena Carceller Víctor Centellas Albert Moyano Miquel A. Pericàs Fèlix Serratosa 《Tetrahedron letters》1985,26(20):2475-2476
The perhydrotriquinacene skeleton has been synthesized by a Pauson-Khand bis-annulation process. 相似文献
996.
Albert J. Fry Thomas A. Powers Klaus Müllen Wolfgang Irmen 《Tetrahedron letters》1985,26(40):4879-4882
The cyclic voltammetric behavior of a series of dimeric [14] annulenes was examined and compared with the monomer. The data suggest a signigficant degree of interaction between the annulene rings when a three-carbon chain connects them, little or no interaction with an eight-carbon chain, and weak interaction with a four-carbon chain. 相似文献
997.
α-MSH and ACTH(1–24) were tritiated to high specific radioactivity (> 100 Ci/mmol) using a new tritiation apparatus with which the tritiation reaction can be performed at slightly elevated pressure. This allows short reaction times with the least possible damage to the molecule. The starting compounds for the tritiation were [13-propargylglycine]α-MSH and [2,23-Bis(3′,5′-diiodotyrosine)]ACTH(1–24). Both tritiations were quantitative and yielded products of high purity, full biological activity, and with a specific radioactivity of 115 Ci/mmol and 100 Ci/mmol, respectively. 相似文献
998.
Alexander Fssler Andr Kobelt Andreas Pfaltz Albert Eschenmoser Christine Bladon Alan R. Battersby R. K. Thauer 《Helvetica chimica acta》1985,68(8):2287-2298
Factor F430 from Methanogenic Bacteria: Absolute Configuration Experiments on F430M ( 2 ) aiming at a potentially biomimetic, reductive reconstruction of the F430 ( 1 ) chromophore from corresponding pyrrocorphinate intermediates provided us with F430 derivatives which contain an isobacteriochlorinate chromophore system similar to the one occurring in sirohydrochlorin ( 3 ) (cf. the Scheme). Comparison of their CD spectra with the-CD spectrum of nickel( II )-sirohydrochlorinate octamethyl ester demonstrates that the absolute configurations of factor F430 and sirohydrochlorin in the region of rings A and B are the same. 相似文献
999.
1000.
A new method for the synthesis of the octahydropyrrolo[3,2,1-ij]quinoline ring system that possesses the characteristic skeleton of the aspidosperma family of alkaloids has been developed. The method utilizes an intramolecular Diels-Alder reaction of an amido-substituted furan across a tethered indole pi-bond. To apply this strategy to the synthesis of the indole alkaloid spegazzinidine, it was necessary to address the problem of assembling the final D-ring of the pentacyclic skeleton. Radical cyclization of a model N-allyl-7-bromo-3a-methylhexahydroindolinone system was found to preferentially lead to the 6-endo-trig cyclization product, with the best yield being obtained under high dilution conditions. The six-membered cyclized product is generated through two reaction pathways: (a) 6-endo-trig ring closure and (b) rearrangement of an intermediate methylene-cyclopentyl radical obtained by 5-exo-trig cyclization. A number of related 7-bromo-substituted hexahydroindolinones containing tethered olefinic groups were prepared and found to undergo efficient cyclization under both radical and palladium-mediated reaction conditions. Vinyl radical cyclization with several N-butenyl-substituted systems afforded a mixture of 6-exo and 7-endo cyclization products. A protocol to introduce an ethyl substituent into the C20-position of the aspidospermidine skeleton was also developed. 相似文献