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271.
A novel fluorescent reagent for hydroperoxides, 4-(2-diphenylphosphinoethylamino)-7-nitro-2,1,3-benzoxadiazole (1), was developed on the basis of the method for designing photoinduced electron transfer (PET) reagents having a benzofurazan skeleton. Compound 1 was quantitatively reacted with hydroperoxides to give its fluorescent derivative, 2. In acetonitrile, the Phi value (0.44) of 2 was 31 times greater than that of 1. The long excitation (458 nm) and emission (520 nm) wavelengths of 2 are suitable for the determination of hydroperoxides, especially in biosamples. [structure: see text] 相似文献
272.
Joaquim Delphino Da Motta Neto Michael C. Zerner Ricardo Bicca De Alencastro 《International journal of quantum chemistry》1992,44(5):743-757
We report structure–activity relation studies on 3′-azido-3′-deoxythymidine (AZT) and the implications to the biological activity of this class of compounds. The adiabatic potential surface (APS ) of the title compound has been examined with the LCAO –MO –SCF method within the AMI approximation. This study has shown at least 13 minima, all separated by small energy differences and barriers. We have found that the equilibrium favors the anti,gg conformations, in variance to previous studies that predicted the syn,gg conformers to be the most stable forms. The most stable conformation (A) is favored by about 0.5 kcal/mol. However, calculations simulating a bulk-water environment suggest that the three lowest energy conformations (A, B, and C) become almost degenerate in solution. We suggest that the crystallographic conformation (L), characterized by a high dipole moment, and analogous to C, undergoes a strong stabilization upon rotation of the 3′-azido group and that these two conformers, C and L, are the only ones in which the hydroxyl proton is free of steric hindrance. This last point has some relevance from the biological point of view since it is generally accepted that this site must be phosphorylated in order for AZT to achieve its therapeutic effects. The above results suggest that, once in solution, conformer L isomerizes to C, which is the bioactive form of AZT. © 1992 John Wiley & Sons, Inc. 相似文献
273.
S Girotti B Grigolo E Ferri S Ghini G Carrea R Bovara A Roda R Motta R Petilino 《The Analyst》1990,115(7):889-894
The amount of L-lactate in biological fluids (serum, plasma and cerebrospinal fluid) was determined by monitoring the reduced form of nicotinamide adenine dinucleotide (NADH) produced by immobilised lactate dehydrogenase (LDH), with bacterial bioluminescent enzymes immobilised on a separate nylon coil. The LDH catalysed the reaction of L-lactate with NAD; this reaction took place in a nylon coil that preceded the coil for the bioluminescent detection. The co-immobilisation of alanine aminotransferase (ALT) with LDH improved the lactate transformation by 117-183%. The response was linear from 0.1 to 50 micron mol l(-1) at 25 degrees C for the LDH - ALT reactor. The intra- and inter-assay coefficients of variation were less than 5% and the recoveries ranged from 93 to 106%. The results agreed well with those obtained with a spectrophotometric method and with the normal reference values. 相似文献
274.
This paper focuses on the development of mixed metal oxide thin films and physical characterization of the films. The films were produced by co-evaporation of titanium oxide and tungsten oxide powders. This allowed the development of titanium oxide-tungsten oxide films as analyzed using XPS. Examination in the SEM and AFM showed that the films were nanoporous with the pore size and pore orientation varying as a function of the deposition angle. UV-vis spectra of the films show an increase of transmittance with increasing deposition angle which is attributed to the structure and porosity of the films. Raman analysis indicated that the as-deposited films have broad and weak Raman characteristics, attributed to the nanocrystal nature of the films and the presence of defects, and the peak broadening deceases after annealing the film, as expected. 相似文献
275.
Santa T Al-Dirbashi OY Ichibangase T Fukushima T Rashed MS Funatsu T Imai K 《Biomedical chromatography : BMC》2007,21(11):1207-1213
The applicability of benzofurazan derivatization regents to carboxylic acids analysis in LC/ESI-MS/MS (high-performance liquid chromatography/electrospray ionization tandem mass spectrometry) was examined. The product ion spectra of DAABD-AE {4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-(2-aminoethylamino)-2,1,3-benzoxadiazole}, DAABD-PZ {4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-N-piperazino-2,1,3-benzoxadiazole}, DAABD-PiCZ {4-[4-carbazoylpiperidin-1-yl]-7-[2-(N,N-dimethylamino)ethylaminosulfonyl]-2,1,3-benzoxadiazole}, DAABD-ProCZ {4-[2-carbazoylpyrrolidin-1-yl]-7-[2-(N,N-dimethylamino) ethylaminosulfonyl]-2,1,3-benzoxadiazole} and DAABD-Apy {4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole}, and their acetylated compounds were obtained. An intense fragment ion at m/z 151 corresponding to (dimethylamino)ethylaminosulfonyl moiety was observed in each spectra, suggesting that these reagents were suitable for ESI-MS/MS analysis. DAABD-AE, DAABD-APy and DAABD-PZ were applied to the analysis of octanoic acid and it was found that DAABD-AE and DAABD-APy gave high signal intensity suitable for LC/ESI-MS/MS. 相似文献
276.
Augusto Rivera Diego Quiroga Jaime Ríos‐Motta Karla Fejfarov Michal Duek 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(12):o505-o508
The title compound, C7H12N4O2, was obtained by nitrosation of the aminal cage (2R,7R,11S,16S)‐1,8,10,17‐tetraazapentacyclo[8.8.1.18,17.02,7.011,16]icosane. The crystal structure is a racemic mixture of RR and SS enantiomers. The asymmetric unit contains two crystallographically independent half‐molecules, one having two partially occupied conformers with refined occupancy factors of 0.747 (3) and 0.253 (3). The molecules sit across twofold axes. The unique molecules each form chains parallel to [001], with molecules connected by intermolecular C—H...O hydrogen bonds. The bonding between adjacent chains is weak. The analysis of eight different crystals confirmed the presence of disordered and nondisordered molecules in the same structure as a regular feature. 相似文献
277.
Leandro M. de Carvalho Carine Viana Ana Paula L. Moreira Paulo C. do Nascimento Denise Bohrer Monique J. Motta Géssica D. da Silveira 《Journal of Solid State Electrochemistry》2013,17(6):1601-1608
Herein, we present a new method based on separation by ion-pair chromatography with pulsed amperometric detection for evaluating various diuretics, including hydrochlorothiazide, chlorthalidone, furosemide, and amiloride, which are adulterants in herbal-based pharmaceutical formulations. The amperometric detection cycle (time?=?2 s) was performed at a gold electrode by applying a detection potential (E1) of +800 mV for 0.4 s and an oxidation potential (E2) of +1,000 mV for 0.40 s, followed by a reduction potential (E3) of ?200 mV for 1.20 s. The mobile phase for separating the diuretics was composed of 5 mmol L?1 phosphate buffer and 0.3 mmol L?1 sodium dodecyl sulfate in 50 % (v/v) methanol (pH 4.5). This method enabled the quantification of the drugs at low concentrations (i.e., 0.08 mg/capsule for hydrochlorothiazide, 0.01 mg/capsule for chlorthalidone, and 0.007 mg/capsule for furosemide). Twenty-six herbal formulations were analyzed, and eight samples (30.8 %) were found to contain diuretics that were added to the final composition (declared or not). 相似文献
278.
Santa GL Bernardino SM Magalhães S Mendes V Marques MP Fonseca LP Fernandes P 《Applied biochemistry and biotechnology》2011,165(1):1-12
The present work aims to provide the basic characterization of sol–gel immobilized inulinase, a biocatalyst configuration
yet unexploited, using as model system the hydrolysis of inulin to fructose. Porous xerogel particles with dimensions in slight
excess of 10 μm were obtained, yielding an immobilization efficiency of roughly 80%. The temperature– and pH–activity profiles
displayed a broader bell-shaped pattern as a result of immobilization. In the latter case, a shift of the optimal pH of 0.5
pH units was observed towards a less acidic environment. The kinetic parameters estimated from the typical Michaelis–Menten
kinetics suggest that immobilization in sol–gel did not tamper with the native enzyme conformation, but on the other hand,
entrapment brought along mass transfer limitations. The sol–gel biocatalyst displayed a promising operational stability, since
it was used in more than 20 consecutive 24-hour batch runs without noticeable decay in product yield. The performance of sol–gel
biocatalyst particles doped with magnetite roughly matched the performance of simple sol–gel particles in a single batch run.
However, the operational stability of the former proved poorer, since activity decay was evident after four consecutive 24-hour
batch runs. 相似文献
279.
Gita Sakale Maris Knite Valdis Teteris Velta Tupureina Santa Stepina Elina Liepa 《Central European Journal of Physics》2011,9(2):307-312
Polymer-nanostructured carbon composites (PNCC) using three different polymers as composite matrix materials (polyvinylacetate
(PVAc), polyethylene glycol (PEG) and ethylene-vinylacetate copolymer (EVA)) have been developed. High structure carbon black
Printex XE2 (Degussa AG) was used as a composites filler. Ethanol vapour sensor-effect of composites was determined as a change
of electrical resistance as the composite was held in ethanol vapour for 30 seconds. Reversibility of electrical resistance
of PNCC, response stability and repeatability have been measured and compared. The electrical resistance response of EVA-nanostructured
carbon composite (EVA-NCC) to ethanol vapour as a function of vinylacetate content in the copolymer has been evaluated. Promising
ethanol vapour sensor-effect has been observed for PEG-NCC followed by PVAc-NCC and EVA-NCC. 相似文献
280.
F.V. Motta A.P.A. Marques J.W.M. Espinosa P.S. Pizani E. Longo J.A. Varela 《Current Applied Physics》2010,10(1):16-20
It was used the Complex Polymerization Method to synthesize barium calcium titanate powders (BCT). Crystalline Ba0.8Ca0.2TiO3 perovskite-type phase could be identified by X-ray diffraction and confirmed by Raman spectroscopy in the powders heat treated at 600 °C. Inherent defects, linked to structural disorder, facilitate the photoluminescence emission. The photoluminescent emission peak maximum was around of 533 nm (2.33 eV) for the Ba0.8Ca0.2TiO3. The photoluminescence process and the band emission energy photon showed dependence of both the structural order–disorder and the thermal treatment history. The results revealed that Ba0.8Ca0.2TiO3 (BCT20) is a highly promising candidate material for optical applications. 相似文献