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1.
Multi-walled carbon nanotubes (MWCNTs) were used in the adsorptive removal of aniline, an organic pollutant, from an aqueous solution. It was found that carbon nanotubes with a higher specific surface area adsorbed and removed more aniline from an aqueous solution. The adsorption was dependent on factors, such as MWCNTs dosage, contact time, aniline concentration, solution pH and temperature. The adsorption study was analyzed kinetically, and the results revealed that the adsorption followed pseudo-second order kinetics with good correlation coefficients. In addition, it was found that the adsorption of aniline occurred in two consecutive steps, including the slow intra-particle diffusion of aniline molecules through the nanotubes. Various thermodynamic parameters, including the Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°), were calculated. The results indicated that the spontaneity of the adsorption, exothermic nature of the adsorption and the decrease in the randomness reported as ΔG°, ΔH° and ΔS°, respectively, were all negative.  相似文献
2.
A novel podophyllotoxin lignan from Justicia heterocarpa   总被引:2,自引:0,他引:2  
Chromatographic separation of the extract of Justicia heterocarpa T. ANDERS. afforded, in addition to known fatty acids, terpenoids and steroids, a new podophyllotoxin lignan. Structures were elucidated by spectroscopic methods, and the structure of the new lignan was confirmed by single crystal X-ray diffraction studies, which have shown that there is a H-bonding stabilized dimer.  相似文献
3.
Recent years have seen an upsurge of interest in developing low cost and reliable methods for the detection and precise determination of ultra-trace concentrations of persistent organic pollutants (POPs), because of their bioaccumulation, transformation and toxicity. Therefore, a comprehensive review with 108 references referring to the distribution, source, accumulation, transformation, types and toxicity of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) is presented. The review also aims to highlight on the current best practices for the analysis of PCBs and OCPs. Moreover, with the signing of the Stockholm convention on POPs and the development of global monitoring programs, there is an increased need for laboratories in developing countries to determine such class of chemicals. A major focus revealed the need for low cost methods that can be implemented easily in developing countries such as electrochemical techniques.  相似文献
4.
There have been major advances in the development of edible colloidal delivery systems for hydrophobic bioactives in recent years. However, there are still many challenges associated with the development of effective delivery systems for hydrophilic bioactives. This review highlights the major challenges associated with developing colloidal delivery systems for hydrophilic bioactive components that can be utilized in foods, pharmaceuticals, and other products intended for oral ingestion. Special emphasis is given to the fundamental physicochemical phenomena associated with encapsulation, stabilization, and release of these bioactive components, such as solubility, partitioning, barriers, and mass transport processes. Delivery systems suitable for encapsulating hydrophilic bioactive components are then reviewed, including liposomes, multiple emulsions, solid fat particles, multiple emulsions, biopolymer particles, cubosomes, and biologically-derived systems. The advantages and limitations of each of these delivery systems are highlighted. This information should facilitate the rational selection of the most appropriate colloidal delivery systems for particular applications in the food and other industries.  相似文献
5.
Kinetic data for the silver nitrate–ascorbic acid redox system in presence of three surfactants (cationic, anionic and nonionic) are reported. Conventional spectrophotometric method was used to monitor the formation of surfactant stabilized nanosize silver particles during the reduction of silver nitrate by ascorbic acid. The size of the particles was determined with the help of transmission electron microscope. It was found that formation of stable perfect transparent silver sol and size of the particles depend upon the nature of the head group of the surfactants, i.e., cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and Triton X-100. The silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 10 and 50 nm, respectively, for SDS and CTAB. For a certain reaction time, i.e., 30 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [ascorbic acid]. The reaction follows a fractional-order kinetics with respect to [ascorbic acid] in presence of CTAB. On the basis of various observations, the most plausible mechanism is proposed for the formation of silver nanoparticles.  相似文献
6.
trans-Anethole [1-methoxy-4-(trans-prop-1-en-1-yl)benzene] was isolated from anise seed oil (Pimpinella anisum). Its photochemical oxidation with hydrogen peroxide gave the corresponding epoxy derivative together with 4-methoxybenzaldehyde. The thermal oxidation of trans-anethole with 3-chloroperoxybenzoic acid at room temperature resulted in the formation of dimeric epoxide, 2,5-bis(4-methoxyphenyl)-3,6-dimethyl-1,4-dioxane, as the only product. Photochemical oxygenation of trans-anethole in the presence of tetraphenylporphyrin, Rose Bengal, or chlorophyll as sensitizer led to a mixture of 1-(4-methoxyphenyl)prop-2-en-1-yl hydroperoxide and 4-methoxybenzaldehyde. Eugenol was isolated from clove oil [Eugenia caryophyllus (Spreng.)]. It was converted into 2-methoxy-4-(prop-2-en-1-yl)phenyl hydroperoxide by oxidation with hydrogen peroxide under irradiation. Thermal oxidation of eugenol with 3-chloroperoxypenzoic acid at room temperature produced 2-methoxy-4-(oxiran-2-ylmethyl)phenol, while sensitized photochemical oxygenation (in the presence of Rose Bengal or chlorophyll) gave 4-hydroperoxy-2-methoxy-4-(prop-2-en-1-yl)cyclohexa-2,5-dien-1-one. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 6, pp. 834–841. The text was submitted by the authors in English.  相似文献
7.
    
Infrared absorption spectroscopy has been applied for the identification of the minerals associated with natural goethite (α-FeO·OH) from Saudi Arabia. The thermal transformation of natural goethite as well as the effects of the presence of the associated minerals on the reaction products were investigated. The results revealed that at 300°C protohematite is formed which at 600°C is slightly crystallized. Further recrystallization and hematite formation takes place at 1000°C. It was also found that the presence of other minerals found in goethite samples has no effect on the reaction products.  相似文献
8.
Potassium zinc hexacyanoferate/II/ K2Zn3[Fe/CN/6]2 was prepared and used for the investigation of the uptake of ammonium ion NH 4 + . The obtained equilibrium data indicate higher selectivity of ammonium ion relative to potassium ion and much lower relative to cesium ion.  相似文献
9.
The effect of60C0-gamma radiation on the kinetic parameters of the thermal decomposition of potassium bromate crystals has been investigated. Radiation did not modify the mechanism of thermal decomposition reaction, but resulted in a decrease in activation energy and frequency factor with a rate which is large at small doses and decreases at higher doses. The results showed that the increase in the concentration of decomposition nuclei tends to be more important than the increase in the porous character of the solid.  相似文献
10.
The chemical effects of51Cr-neutron capture recoils produced in a series of mixed crystals of the type K3Cr/C2O4/3–K3Fe/C2O4/3 were investigated. Analysis of the neutron irradiated samples was performed making use of synergetic solvent extraction and gamma ray scintillation spectroscopy. It was found that the initial chromium parent retentions vary linearly with mole fraction in the mixed crystals. The results are discussed in terms of retention and non-retention reactions and in view of a kinetic model and a mechanism involving elementary impacts, metal- and ligand-vacancy exchange, substitution and transfer reactions.  相似文献
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