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排序方式: 共有207条查询结果,搜索用时 31 毫秒
181.
Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of ascorbic acid (AA) on palladium coated nanoporous gold film (PdNPGF) electrode. The deposition of palladium was done through oxidation of copper UPD layer by palladium ions. This low Pd‐loading electrode behaved as the nanostructured Pd for electrocatalytic reaction. The PdNPGF electrode exhibits excellent electrocatalytic behavior by enhancing the AA oxidation peak current due to synergistic influence of the Pd film and NPGF. The kinetic parameters such as electron transfer coefficient, α, was 0.47 and the voltammetric responses of the PdNPGF electrode were linear against concentration of AA in the ranges of 2.50–33.75 mM and 0.10–0.50 mM with CV and DPV respectively. 相似文献
182.
Nahid Mashkouri Najafi Shahram SeidiReza Alizadeh Hamed Tavakoli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010
Speciation analyses are of increasing interest in the environmental, toxicological and analytical fields, because the toxicity and reactivity of trace elements depend strongly on the chemical forms in which they are present. A simple electrodeposition–electrothermal atomic absorption spectrometry method for speciation analysis of some organic and inorganic selenium species in typical environmental water and agricultural soil samples has been developed. The method is based on the selective reduction of water-soluble Se(IV) and selenocystine (Se–Cys) species by an uncontrolled applied potential (1.8 V) on a mercury-coated electrode. In acidic media (1.0 M HCl solution) the only inorganic selenium species electrodeposited was Se(IV), and, of the water-soluble organic selenium species Se–Cys and Se–Met only Se–Cys was electrodeposited onto the mercury electrode surface. The proposed methodology was successfully applied to the speciation and determination of selenium in a few environmental samples. The spiked recovery value varied between 91% and 99%. The suggested method has been shown to have a characteristic mass (m0) of 25 pg, a limit of detection (LOD) of 1.0 μg L− 1 and a relative standard deviation (RSD%) of 3.5% for 6 measurements at a concentration of 100 μg L− 1 Se(VI). 相似文献
183.
The thermal conductivity of ammonia borane (AB) complex, in the temperature range of 300-420 K, was measured experimentally using ASTM method E 1225. At 300 K, the thermal conductivity of pure AB was found to be approximately 15 W/m-K. A composite pellet prepared by mixing 10 wt% aluminum powder with AB had a thermal conductivity that was a factor of 4 higher than that of pure AB complex. The extent of the pyrolytic weight loss for AB/Al composite and pure AB complex was 25.4% and 33.9%, respectively—indicating comparatively lower levels of volatile species evolved as impurities (e.g. monomeric aminoborane, borazine, diborane, etc.) in the product hydrogen. 相似文献
184.
[Pb(phe)2]n ( 1 ) (phe is the abbreviation ofphenylalanine) have been synthesized and characterized by elemental analyses, IR and 1H NMR spectroscopy. The single crystal structure of 1 show the complex to be a 2D chain polymer as a result of phenylalanine bridging. Coordination number of PbII ions is six, PbN2O4, with “stereo‐chemically active” electron lone pairs, and the coordination sphere is hemidirected. To the best of our knowledge, this 2D coordination polymer is the first amino acid lead(II) complex that characterized by X‐ray structural analysis. 相似文献
185.
Amanlou M Asmardi G Andalibi PC Javadi N Khodadady F Omarny ZB 《Journal of chromatography. A》2005,1088(1-2):136-139
An isocratic, reversed-phase liquid chromatographic method was developed for determination of tropicamide using atropine as an internal standard in a pharmaceutical dosage form. Tropicamide and atropine sulfate were separated using a microBondapak ODS (C18) column by isocratic elution of mobile phase with flow rate of 2.0 ml/min. The mobile phase composition was methanol-50 mM phosphate buffer (pH 4; 30:70, v/v). The eluate was monitored at 257 nm with detector range setting fixed at 0.01 AUFS. Under these conditions, the retention times were 4.81 min for atropine and 11.89 min for tropicamide. The standard calibration curve was linear over a sample concentration range from 2 to 300 microg/ml, with limit of detection of 0.15 microg/ml. The assay linearity was good (typically r2 = 0.9992) and the standard curves were linear in the detection range. The precision of the method (expressed by relative standard deviation) and the accuracy (mean error in percent) were <5% for both intra- and inter-day assays. Recovery at 80-120% of labeled claim ranged from 98.4 to 100.7% for tropicamide. The proposed method was satisfactorily applied to the determination of tropicamide in pharmaceutical preparation and stability indicating studies. 相似文献
186.
Determination of captopril in pharmaceutical preparation and biological fluids using two- and three-way chemometrics methods 总被引:1,自引:0,他引:1
Nahid Ghasemi Ali Niazi 《中国化学快报》2007,18(4):427-430
Spectrophotometric method has been developed for the direct quantitative determination of captopril in pharmaceuticalpreparation and biological fluids(human plasma and urine)samples.The method was accomplished based on parallel factoranalysis(PARAFAC)and partial least squares(PLS).The study was carried out in the pH range from 2.0 to 12.8 and with aconcentration from 0.70 to 61.50 μg mL~(-1)of captopril.Multivariate calibration models such as PLS at various pH and PARAFACwere elaborated from ultraviolet spectra deconvolution and captopril determination.The best models for this system were obtainedwith PARAFAC and PLS at pH 2.0.The applications of the method for determination of real samples were evaluated by analysis ofcaptopril in pharmaceutical preparations and biological fluids with satisfactory results.The accuracy of the method,evaluatedthrough the RMSEP,was 0.5801 for captopril with best calibration curve by PARAFAC and 0.6168 for captopril with PLS at pH 2.0model. 相似文献
187.
A new platinum(IV) complex, [Pt(en)(Cl)2(Pregabalin)2], containing the drug pregabalin was synthesized and characterized by elemental analysis, FT-IR, 1H NMR, mass spectrum, thermogravimetric analysis (TGA), molecular docking and RHF/PM6 method. Also, the interaction of Pt(IV) complex with human serum albumin (HSA) was studied by using UV–vis, fluorometric, circular dichroism (CD) spectroscopies and molecular docking techniques. The results demonstrated that the binding of the complex to HSA caused strong fluorescence quenching of HSA through static quenching mechanism. Hydrogen bonds and van der Waals contacts are the major forces in the stability of protein-Pt(IV) complex and the process of the binding of complex with HSA was enthalpy driven (ΔH = –105.8?kJ·mol?1). The results of CD and UV–vis spectroscopy indicated that the binding of the complex to HSA caused conformational changes in HSA. In addition, the study of molecular docking and RHF/PM6 method confirm the experimental results with respect to the mechanism of binding. 相似文献
188.
We show how the shift in the equilibrium constant K
PT
for formation of a proton-transfer adduct in a non-interactive solvent, upon addition of a second, hydrogen-bonding solvent S reveals the nature of the hydrogen bonding solvation process. Data are analyzed for the pentachlorophenoltriethylamine proton-transfer equilibrium in cyclohexane solvent, under-going solvation by the acidic alcohols, 2,2,2-trichloroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol. K
PT
vs. [S] data are fitted to a binding isotherm corresponding to two-stage solvation of both the adduct and the free amine. Stoichiometries and binding constants for both primary and secondary solvation of both solvated species are determined as adjustable parameters. Best fits correspond to both the adduct and free amine under-going primary solvation by one alcohol molecule (presumably at the oxygen and nitrogen lone-pairs, respectively) followed by secondary solvation by one to nine additional alcohol molecules, with binding constants ranging from 2100 M–1, for primary solvation of the adduct by hexafluoro-2-propanol, down to 7 M–1, for secondary solvation of the amine by trichloroethanol. We speculate that the secondary solvation numbers represent average sizes of hydrogen-bonded alcohol chains, nucleated by the enhanced basicity of the primary-solvation alcohol. 相似文献
189.
ASHNAGAR Alamdar GHARIB NASERI Nahid FOROOZANFAR Shahla 《中国化学》2007,25(8):1171-1173
Teucrium polium is a dwarf sub-shrub usually 30-60 cm high with many branches, which is fairly distributed throughout Iran, with its flowering being season mainly from April to July. The plant was collected during its flowering season in Baghmalek region in the North-East of Khuzestan province, Iran. After the identification of the genus, species and variety of the plant, the dried whole plant (flowers, fruits and the leaves) was steam distilled with different methods. The isolated essential oil was dried over anhydrous sodium sulphate and stored at 4-6 ℃. Analysis of the essential oil was carried out by GC-MS technique. At least 10 major components were identified (3-carene/α-pinene, β-phellandrene, limonene, germacrene, β-bourbonene, β-caryophylene, γ-muurolene, γ-elemene, spathulenol, β-eudesmol) (totally 97.02%). Also, successive TLC and column chromatography of the essential oil resulted in the separation of four fractions. Based upon 1^H NMR, IR and mass spectra, the fractions with Rf=0.12 and 0.93 were determined as gualol and a mixture of α-pinene, β-phellandrene and limonene, respectively. 相似文献
190.
Nahid Ashrafi 《Proceedings Mathematical Sciences》2009,119(3):267-274
The unit sum number, u(R), of a ring R is the least k such that every element is the sum of k units; if there is no such k then u(R) is ω or ∞ depending on whether the units generate R additively or not. Here we introduce a finer classification for the unit sum number of a ring and in this new classification
we completely determine the unit sum number of the ring of integers of a quadratic field. Further we obtain some results on
cubic complex fields which one can decide whether the unit sum number is ω or ∞. Then we present some examples showing that all possibilities can occur. 相似文献