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121.
Davies SG Díez D El Hammouni MM Garner AC Garrido NM Long MJ Morrison RM Smith AD Sweet MJ Withey JM 《Chemical communications (Cambridge, England)》2003,(19):2410-2411
Comparison of the kinetic and parallel kinetic resolutions of methyl (RS)-5-tert-butyl-cyclopentene-1-carboxylate allows for the efficient synthesis of both (1R,2S,5S)- and (1S,2R,5R)-enantiomers of methyl 2-amino-5-tert-butyl-cyclopentane-1-carboxylate. 相似文献
122.
S. A. Amitina I. V. El’tsov T. V. Rybalova Yu. V. Gatilov I. A. Grigor’v 《Russian Chemical Bulletin》2004,53(8):1700-1703
Reactions of alicyclic 2-hydroxyamino oximes with pentafluorophenylglyoxal afford mixtures of annelated derivatives of 2-pentafluorophenylpyrazine 1,4-dioxide and tetrafluoro- 10H-imidazo[1,2-b][1,2]benzooxazin-10-one. The structures of the latter were established by X-ray diffraction analysis.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1636–1639, August, 2004. 相似文献
123.
S. Allaoud H. Bitar M. El Mouhtadi B. Frange 《Journal of organometallic chemistry》1983,248(2):123-130
13C NMR spectra and complete assignment by means of coupled spectra and off resonance experiments, are reported for a new kind of organoboron heterocycle and the related borazine (o-CH3C6H4NBCH3)3; π-charge densities, obtained from LCAO-MO Hückel calculations, are in reasonable agreement with experimental chemical shifts for the former compound. 相似文献
124.
Talaat Ibrahim El‐Emary 《中国化学会会志》2006,53(2):391-401
New derivatives of pyrazolo[3,4‐b]pyrazine and related heterocycles were prepared starting from 6‐amino‐3‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyrazine‐5‐carbonitrile ( 2 ) and using the key intermediates 4 , 5 , 6 , 14 , 15 and 16 . Some of the prepared compounds were evaluated for their antifungal and antibacterial activities. 相似文献
125.
A fundamental study was made on the reduction of calcium phosphate by carbon. The mechanism of reduction was presented on applying different additions. Both silica and alumina increased the extent of reduction but with variable rates. The activation energies were calculated on the basis of first-order reactions. The phases formed during reduction were investigated by X-ray analysis. 相似文献
126.
E. Betranhandy Samir F. Matar Ch. El‐Kfoury R. Weihrich J. Etourneau 《无机化学与普通化学杂志》2004,630(15):2587-2598
The changes in electronic structure and hardness as inferred from the bulk modulus are investigated for model structures of ternary compounds XC3N3 (X = B, Al, P, As, Ga) within the framework of density functional theory (DFT). The optimisations of the proposed two‐ (2D) and three‐dimensional (3D) structures and the calculations of the bulk moduli are performed by a pseudo potential method. The electronic structures are calculated with the augmented sphere wave method (ASW). The obtained hardness for 2D BC3N3 system (B0 ~ 220 GPa) points to a magnitude close to that of graphitic C3N4. For heavier X atoms it decreases rapidly. This is equally observed for the 3D systems examined in the β‐C3N4 structure for which B0(β‐BC3N3) amounts to ~330 GPa. Within the magnitude of the well known hard material cubic BN, the BC3N3 phases can be predicted as candidates for ultra hard materials. The electronic effect induced by the chemical nature of the X substitutional was examined according to its position in the periodic table i.e. XIII or XV. Both, band structures and the electron localisation function (ELF) were used for this analysis. The ELF plots show a decreasing covalency with heavier X‐atoms. Potential applications of the devised systems are proposed such as dopings with atoms (Li, rare gas) and molecules (N2). 相似文献
127.
Abdelfetah Mounir Mohamed El Guendouzi Abderrahim Dinane 《Journal of solution chemistry》2002,31(10):793-799
Ternary aqueous solutions of MgSO4 and K2SO4 have been studied by the hygrometric method at 25°C. The relative humidity of this system is measured at total molalities from 0.35 mol-kg–1 to about saturation for three ionic-strength fractions (y = 0.25, 0.50, and 0.80 of MgSO4. The data allow calculation of water activities and osmotic coefficients. From these measurements, the Pitzer ionic mixing parameters are determined and used to predict the solute activity coefficients in the mixture. The results are used to calculate the excess Gibbs energy at total molalities for ionic-strength fraction y. 相似文献
128.
A. Abdel Razik M. S. Metwally M. F. El-Hadi M. A. El Wardany 《Reaction Kinetics and Catalysis Letters》1992,48(1):279-290
The rates of hydrolysis of seven acetate esters substituted in the alkyl group have been studied in the presence of a sulfonated cation exchange resin in 70% aqueous acetone solution. the slower hydrolysis rates with increasing size of substituent are related to increasing steric influence, as determined by decreasing values of the steric substituent parameter, Es. The efficiency of the resin catalyst is related to the entropy of substituents. Influence caused by steric hindrance on reaction rates accounts satisfactorily for observed variations of the enthalpies and entropies of activation with alkyl group substituents. The entropy, Sx, values increase in the order: n-octyl-
, , 70%- . , , ES. . , . , S*, : --<-<, .相似文献
129.
The elucidation of structures of glutathione (GSH) complexes play an important role in the fundamental understanding of biochemical pathways of metal ion deactivation in plants. This article attempts to feature key studies for stoichiometry of metal complexes with glutathione and its constituent amino acids to obtain a better understanding of the different metal affinities of the complexation sites of glutathione. The SEC-ICP-MS experiments have indicated that oxidation process of glutathione was accelerated by metal ion presence in following order Cu+, Pb2+ and Cd2+. The redox activity of metal ions was confirmed by ESI-MS experiments, which allowed to observe formation of glutathione disulphide (GSSG) in time. The stoichiometry of Cd2+, Cu+ and Pb2+ complexes with GSH was defined by observing the isotope pattern of investigated metals and hydrogen loss or transfer during binding. The complexes with metal bound to sulphur of 1:1 and 1:2 stoichiometry were found in case of cadmium and lead. The number of hydrogen atoms lost during metal binding and the SEC-ESI-MS results allowed to elucidate that copper is bound by GSSG in ratio 1:1 and 1:2. Additionally, size exclusion chromatography coupled to electrospray MS allowed to differentiate more stable complexes from weak ones that could be created in the gas phase. 相似文献
130.
The paper presents a new method for the generation of acetaldehyde in the amounts that allow to calibrate the measuring system. The method is based on thermal decomposition of surface compounds at the range 130-190 °C, in which an acetaldehyde as the decomposition product is released. The synthetic pathway leading to the desired surface compounds is described. Investigations demonstrated that the synthesis of the compounds on the surface of the support material (silica gel) was carried out homogeneously. The technique proposed was used for the generation of gaseous standard mixtures containing acetaldehyde for the calibration of a thermal desorber-gas chromatograph-flame ionization detector system. 相似文献