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41.
The engineering of a complete adlayer of organic nanolines by supramolecular self-assembly has been achieved for the first time on a silicon-based surface at room temperature and has been studied by scanning tunneling microscopy. This complete adlayer has been successfully obtained thanks to the combination of a specific Si(111)-B square root 3x square root 3R30 degrees semiconductive surface and of strong hydrogen bonds between a pair of dipolar molecules.  相似文献   
42.
A new, simple and sensitive kinetic spectrophotometric method with no need for removing of interfering substances is proposed for the determination of thiocyanate ion in biological and water samples. The procedure is based on the inhibiting effect of thiocyanate on the sodium periodate-potassium bromide-meta cresol purple (MCP) system in acidic media. The induction period of the reaction is proportional to the SCN- concentration. The decolorization of meta cresol purple by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. Under optimum conditions, thiocyanate can be determined in the range of 0.02-0.8 microg ml(-1) with a 3sigma detection limit of 5 ng ml(-1). The relative standard deviations for 10 replicate determinations of 0.060, 0.10 and 0.50 microg ml(-1) thiocyanate are 3.7, 2.4 and 1.0%, respectively. This method has been successfully used to the determination of thiocyanate content in smokers and non-smokers saliva and spiked water sample.  相似文献   
43.
Twelve new bis-Schiff bases of isatin, benzylisatin and 5-fluoroisatin 3a-3l were prepared by condensation of isatin, benzylisatin and 5-fluoroisatin with primary aromatic amines. The chemical structures of the products were confirmed by 1H- and 13CNMR, IR and mass spectral data. The compounds were screened for antiviral activity against a panel of DNA and RNA viruses. Minimum cytotoxic and minimum virus-inhibitory concentrations of these compounds were determined. Compounds 3c and 3i were the most cytotoxic in HEL cells. These newly synthesized bis-Schiff bases were also tested for their antibacterial and antifungal activities. They did not display activity against S. cerevisiae (ATCC 28383) or C. albicans (CIP 1180-79).  相似文献   
44.
A highly efficient water‐tolerant, solid‐base catalyst for the self‐condensation of biomass‐derived methyl ketones to jet‐diesel fuel precursors was developed by grafting site‐isolated secondary amines on silica‐alumina supports. It is shown that apart from the nature and density of amine groups and the spatial separation of the acidic and basic sites, the acidity of the support material plays a critical role in defining the catalytic activity. It is also found that a combination of weakly acidic silanol/aluminol with secondary amine groups can mimic proline catalysts and are more effective in catalyzing the selective dimerization reaction than the combination of amines with organic acids. In situ FTIR measurements demonstrate that acidic groups activate methyl ketones through their carbonyl groups leading to a favorable C? C bond formation step involving an enamine intermediate. DFT analysis of the reaction pathway confirms that C? C bond formation is the rate‐limiting step.  相似文献   
45.
A new approach based on the ultrasound‐assisted reversed‐phase dispersive liquid–liquid microextraction technique is developed for the extraction and determination of vitamin A and vitamin E from oil matrices before high‐performance liquid chromatography analysis. A methodology based on the full factorial design is carried out to choose the significant parameters. Then the significant factors affecting the extraction efficiency including pH, volume of extraction solvent, and volume of disperser solvent are optimized using a Box–Behnken design. After analyzing the results obtained, the optimum conditions were: pH 4.5, 80–20 μL of the ethanol/water solvent mixture as extraction solvent, 110 μL of 1,4‐dioxane as the disperser solvent, and a sonication time of 10 min. For validation of the developed method, the linear dynamic range, repeatability, limit of detection, and recoveries were obtained under the optimum conditions. The detection limits of the method were 1.6 and 2.3 ng/mL for vitamin A and vitamin E, respectively. The extraction recovery percentages for the studied drugs were above 91%, with acceptable relative standard deviation. The proposed methodology was successfully applied for the determination of the vitamins in different oil samples.  相似文献   
46.
This paper describes the results of an experimental study on the undrained shear behaviour of loose sand collected from the location close to the epicenter of the recent Chlef (Algeria) Earthquake (October 10,1980).The study focuses on the effects of the mode of the soil deposition on the liquefaction resistance of the Chlef sand.For this purpose,the results of undrained monotonic triaxial compression tests performed on samples with initial density of 0.29 under initial confining pressures ranged from 50 kPa to 200 kPa are presented.The specimens were prepared by two depositional methods namely dry funnel pluviation and wet deposition.It was found that there was a marked difference in the undrained behaviour of sand in terms of maximal deviatoric stress,peak strength,residual strength and excess pore water pressure,even though the density and stress conditions were identical.The conclusion was that the soil fabric was responsible for this result.The results indicated also that at low confining pressures,the specimens reconstituted by the wet deposition method exhibited complete static liquefaction (zero effective confining pressure and zero stress difference).  相似文献   
47.
The aim of present study was to evaluate the effect of natural, synthetic cyclodextrins (CDs) and CD mixtures on aqueous solubility of beclomethasone dipropionate (BDP). The phase solubility studies were done in the presence of 6 CDs. Furthermore, aqueous solubility of BDP was tested in the presence of CD mixtures. The solubility of BDP in water was increased by 30, 77, 155 and 30 folds in the solution containing 20%?w/v α-CD, hydroxylpropyl β-CD (HP-β-CD), hydroxypropyl γ-CD (HP-γ-CD) and sulphobutylether β-CD (SBE-β-CD), respectively. CD mixtures had remarkable effect on the aqueous solubility of BDP so that solubility in water increased between 200 and 1,500 times in the presence of different CD mixtures. Further addition of sodium acetate to the solubilisation medium reduced the aqueous solubility. In conclusion, CD complexation was able to improve the aqueous solubility of BDP. The synergistic effect of cyclodextrin mixture was observed.  相似文献   
48.
A deep bed filtration model has been developed to quantify the effect of nanoparticles (NPs) on mitigating fines migration in porous media. The filtration coefficients representing the total kinetics of particles capture were obtained by fitting the model to the laboratory data. Based on the optimum filtration coefficients, the model was utilized to history match the particle concentration breakthrough profiles observed in twelve core flood tests. In the flooding experiments, the effect of five types of metal oxide NPs, \(\upgamma \hbox {-Al}_{2}\hbox {O}_{3}\) , CuO, MgO, \(\hbox {SiO}_{2}\) , and ZnO, on migrating fines were investigated. In each test, a stable suspension was injected into the already NP-treated core and effluents’ fines concentration was measured based on turbidity analysis. In addition, zeta potential analysis was done to obtain the surface charge (SC) of the NP-treated medium. It was found that the presence of NPs on the medium surface results in SC modification of the bed and as a result, enhances the filter performance. Furthermore, the ionic strength of the nanofluid was recognized as an important parameter which governs the capability of NPs to modify the SC of the bed. The remedial effect of NPs on migrating fines is quantitatively explained by the matched filtration coefficients. The SC of the medium soaked by \(\upgamma \hbox {-Al}_{2}\hbox {O}_{3}\) nanofluid is critically increased; therefore, the matched filtration coefficient is of remarkably high value and as a result, the treated medium tends to adsorb more than 70 % of suspended particles. The predicted particle concentration breakthrough curves well matched with the experimental data.  相似文献   
49.
An easily accessible catalyst, nano-sulfated titania, efficiently catalyzes the N-formylation of β-lactams and all types of amines (primary, secondary, aromatic, and aliphatic) in solvent-free conditions at room temperature.  相似文献   
50.
A copper‐catalyzed reaction between terminal alkynes, oxiranes, and malonitrile has been described. In this transformation, copper acetylide was attacked on oxiranes to form homopropargyl alkoxy‐copper intermediate that was further transferred to 2H‐pyrane skeletons by reaction with malonitrile. We found that the reaction was not productive without hexafluoroisopropanol.  相似文献   
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