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131.
James C. Turley Gary E. Martin Ruth R. Inners 《Journal of heterocyclic chemistry》1981,18(6):1169-1172
The first synthesis of a triazaphenoxathiin system, benzo[b]-1,4,9-triazaphenoxathiin, is reported. Attempts directed toward the total assignment of the 13C-nmr spectrum of the title compound failed to produce an unequivocal assignment. The carbons of the benzo-portion of the molecule could not be unequivocally assigned at 25.2 MHz but were subgrouped into permutable pairs of resonances on the basis of relaxation times, a result of the antisotropic reorientation of the molecule. Further attempts to complete the 13C-nmr assignment at 100 MHz by selective on-resonance decouplings in the 400 MHz 1H-nmr spectrum were also unsuccessful because of similarities in the chemical shifts of the benzo-protons. Complete 1H-nmr chemical shifts and homo-nuclear spin-coupling constants were obtained using the PANIC program. 相似文献
132.
John M. Mccall Ruth E. Tenbrink Max E. Royer Howard Ko 《Journal of heterocyclic chemistry》1978,15(8):1529-1530
2,4-Diamino-6-piperidinopyrimidine 3-oxide reacts preferentially with acid anhydrides at the 4-amino group. The structures of amide products are readily assigned by the position of the 5-H. 相似文献
133.
Palladium-catalyzed oxidation of 1,3-dienes in acetic acid in the presence of LiCl and LiOAc produces 1-acetoxy-4-chloro-2-alkenes in high selectivity. The 1,4-adducts were stereo- and regioselectively functionalized. 相似文献
134.
Ruth M. Williams 《General Relativity and Gravitation》1985,17(6):559-571
Models for a homogeneous, anisotropic, empty, closed universe at a particular moment of time are constructed from sets of empty tetrahedra. It is shown using Regge calculus that only two such models have a moment of time symmetry.On leave from Girton College, Cambridge CB3 OJG, and Department of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge CB3 9EW, England. 相似文献
135.
Doherty R Haddow MF Harrison ZA Orpen AG Pringle PG Turner A Wingad RL 《Dalton transactions (Cambridge, England : 2003)》2006,(36):4310-4320
The 4-phosphacyclohexanones, 2,2,6,6-tetramethyl-1-phenyl-4-phosphorinanone (La), 1,2,6-triphenyl-4-phosphorinanone ((Ph)Lb), 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone ((Cy)Lb) and 1-tert-butyl-2,6-diphenyl-4-phosphorinanone ((Bu)Lb) have been made by modifications of literature methods. Phosphines (R)Lb are each formed as mixtures of meso- and rac-diastereoisomers. Isomerically pure rac-(Ph)Lb, rac-(Cy)Lb and meso-(Bu)Lb can be isolated by recrystallisation from MeCN. Heating mixtures of isomers of (R)Lb with TsOH leads to isomerisations to give predominantly the meso-(R)Lb. The complex trans-[PdCl2(La)2] (1) is readily made from [PdCl2(NCPh)2] but the analogous platinum complex 2 has not been detected and instead, cyclometallation at the 3-position (alpha to the ketone) in the phosphacycle occurs to give trans-[PtCl(La)(La-3H)] (3) (where La-3H = La deprotonated at the 3-position) featuring a [3.1.1]metallabicycle as confirmed by X-ray crystallography. The analogous palladabicycle 4 has been detected upon treatment of 1 with Et3N in refluxing toluene. The type of complex formed by (R)Lb depends on which diastereoisomer (meso or rac) is involved. rac-(Ph)Lb (a mixture of R,R- and S,S-enantiomers, labelled alpha and beta) forms trans-[MCl2(rac-(Ph)Lb)2], M = Pd (5) or Pt (6), as mixtures of diastereoisomers (alphaalpha/betabeta and alphabeta forms). The structure of alphaalpha-6 has been determined by X-ray crystallography. Ligand competition experiments monitored by 31P NMR showed that Pd(II) and Pt(II) have a significant preference to bind rac-(Ph)Lb over meso-(Ph)Lb. meso-(Bu)Lb reacts with [PtCl2(NCBu(t))2] under ambient conditions to give the binuclear complex [Pt2Cl2(meso-(Bu)Lb-2'H)2] (7) where orthometallation has occurred on one of the exocyclic phenyl substituents as confirmed by X-ray crystallography. rac-(Bu)Lb reacts with [PtCl2(NCBu(t))2] to give a mononuclear cyclometallated species assigned the structure trans-[PtCl(rac-(Bu)Lb-2'H)((Bu)Lb)] (8) on the basis of its 31P NMR spectrum. rac-(Cy)Lb reacts with [PtCl2(NCBu(t))2] in refluxing toluene to give trans-[PtCl2(rac-(Cy)Lb)2] (9) and the crystal structure of alphabeta-9 has been determined. 相似文献
136.
Weng CC Liao JD Wu YT Wang MC Klauser R Zharnikov M 《The journal of physical chemistry. B》2006,110(25):12523-12529
The modification of octadecanethiolate self-assembled monolayers on Au and Ag by nitrogen-oxygen downstream microwave plasma with variable oxygen content (up to 1%) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy. The primary processes were dehydrogenation, desorption of hydrocarbon and sulfur-containing species, and the oxidation of the alkyl matrix and headgroup-substrate interface. The exact character and the rates of the plasma-induced changes were found to be dependent on the substrate and plasma composition, with the processes in the aliphatic matrix and headgroup-substrate interface being mostly decoupled. In particular, the rates of all major plasma-induced processes were found to be directly proportional to the oxygen content in the plasma, which can be, thus, considered as a measure of the plasma reactivity. Along with the character of the observed changes, exhibiting a clear dominance of the oxidative processes, this suggests that the major effect of the oxygen-nitrogen downstream microwave plasma is provided by reactive oxygen-derived species in the downstream region, viz. long-living oxygen radicals and metastable species. 相似文献
137.
Firanescu G Hermsdorf D Ueberschaer R Signorell R 《Physical chemistry chemical physics : PCCP》2006,8(36):4149-4165
Large molecular aggregates with sizes ranging from subnanometers to microns are ubiquitous. As atmospheric aerosols they influence our climate, in interstellar space they are discussed as reactive sites, and in medicine small particles are considered as promising candidates to achieve a targeted drug delivery. The present contribution is focused on the characterization of the physical-chemical properties of these particles and on their targeted generation. One of the greatest challenges is to understand the properties of these aggregates on a molecular level. The latter point is discussed in detail focussing on the vibrational dynamics of these particles. 相似文献
138.
Aleman C Zanuy D Casanovas J Cativiela C Nussinov R 《The journal of physical chemistry. B》2006,110(42):21264-21271
We have used quantum mechanical calculations at the B3LYP/6-311G(d,p) level to determine the conformational preferences of the N-acetyl-N'-methylamide derivative of 1-aminocyclopentane-1-carboxylic acid in the gas phase, chloroform solution, and water solution. The backbone conformation of this dipeptide has been described through the dihedral angles varphi and psi, while the pseudorotational phase angle was used to define the conformation of the cyclopentane ring. Results indicate that the backbone flexibility of this amino acid is restricted by the cyclic nature of the side chain, the relative stability of the different conformations depending on the polarity of the environment. The potential energy of the pseudorotation was also studied as a function of the backbone conformation. Interestingly, the conformation of the cyclic side chain depends on the backbone arrangement. Furthermore, the number of pseudorotational states accessible at room temperature is high in all the investigated environments, especially in aqueous solution. Finally, a set of force-field parameters for classical molecular mechanics calculations was developed for the investigated amino acid. Molecular dynamics simulations in both chloroform and aqueous solutions were performed to demonstrate the reliability of such parameters. 相似文献
139.
In this study, we report the protonation reactions for astaxanthin and canthaxanthin radical anions in methanol, alkaline methanol, and aqueous 2% Triton X-100 at different pH values. The pKa values for the corresponding alpha-hydroxy radical derivatives of astaxanthin, canthaxanthin, and beta-apo-8'-carotenal were estimated in 2% Triton X-100. Also, the effects of the microenvironment and the structure of the carotenoids on the protonation rate constant are discussed. 相似文献
140.
Wallace KJ Fagbemi RI Folmer-Andersen FJ Morey J Lynth VM Anslyn EV 《Chemical communications (Cambridge, England)》2006,(37):3886-3888
The detection of chemical warfare simulants is attained by the PET mechanism that gives an "off-on" fluorescent response with a half-life of approximately 50 ms upon phosphorylation of a reactive oximate functionality; the X-ray crystal structure of the oximate was also obtained and is discussed. 相似文献