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81.
Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K
G. Rezaei Behbehani 《Journal of solution chemistry》2007,36(8):939-945
Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed
in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range
of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between
experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium
bromide, Pr4NBr, and tetrapentylammonium bromide, Pen4NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu4NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me4NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds
increases systematically in going from Me4NBr to Pen4NBr. 相似文献
82.
容量分析中,滴定终点的误差决定了该分析方法的可靠性。根据质子条件式,可推导出终点误差的精确式。该表达式用滴定开始前而不是终点时物质的浓度进行计算;用滴定终点时的p H进行计算,不需要计算化学计量点时的p H;所得出的精确式具有通用性,能有效降低学习与记忆的难度,提高计算结果的准确度。 相似文献
83.
In calorimetry, the heat-flow to or from a sample is measured as a function of time (isothermal calorimetry) or temperature (scanning calorimetry). The technique is not dependent on the physical form of the sample and is usually non-destructive (exceptions include temperature-induced irreversible phase transitions and thermal decomposition). The inherent sensitivity of modern instruments allows measurements on the micro-Watt scale. Calorimetry is highly suited to the study of pharmaceutical systems because small sample masses are usually required and the technique is very sensitive to changes induced by, for instance, formulation or processing. It is the purpose of this review to show applications of both isothermal and scanning calorimetry in the field of physical and bio-physical pharmacy. Potential applications include studies of physical stability, excipient compatibility, chemical stability and the study of the potential interactions of and between macromolecules such as lipids, surfactants, and nucleic acids. 相似文献
84.
When two or more halides are determined in solution by precipitation titration with silver nitrate as the titrant, significant errors can occur at the first equivalence point as a result of coprecipitation. Errors of up to 33% were found for the first equivalence point for solutions containing mixtures of halides at micromolar levels. The addition of a flocculating agent to the solution reduced coprecipitation by increasing the rate of exchange between the precipitated silver halide and the halide ion remaining in solution. A logarithmic relationship was observed between the charge of the flocculating agent and the logarithmic concentration of the agent needed to minimise coprecipitation. Although flocculating agents reduced coprecipitation, they do not, however, completely eliminate equivalence point errors. Here a new method is presented which effectively eliminates the problem of coprecipitation during precipitation titrations for solutions containing two halides. In order to decrease the possibility of coprecipitation, we used selective complexation of the precipitation ion Ag+ in order to control the AgX solubility. For example, in the case of CF− plus X− (X=Br− or I−), we added sufficient NH3 to form Ag(NH3)+ so that the free Ag+ activity was reduced below that required for theoretical AgCl precipitation in the absence of the other halides. Once the titration of the less soluble halide was completed and the first equivalence point determined, the Ag(NH3)+ complex was destroyed by acidification of the solution to a pH less than 6. The titration is then continued and the second equivalence point determined. Equivalence point errors were reduced to less than 1.5% with careful application of the method. 相似文献
85.
Heteropoly-complexes K17[Ln(CuW11O39)2].xH2O(Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy) were prepared. The properties of the products were investigated by ion-exchange, conductometric titration, IR, UV and X-ray powder diffraction. The results show that the structure of the products is similar to that of U(a-Ge11O39)2 and consistent with the model proposed by Peacock. 相似文献
86.
张园 《中国无机分析化学》2021,11(4):72-75
建立了用氢溴酸消除锑、砷、锡干扰,用硫酸将铅形成硫酸铅沉淀,再用EDTA络合滴定法测定粗二氧化碲中铅量的方法。试样用硝酸、盐酸溶解,用硫酸沉淀铅,氢溴酸消除锑、砷、锡的干扰后,过滤分离其他共存元素,以乙酸-乙酸钠缓冲溶液溶解硫酸铅沉淀,在pH=5.0~6.0时,以二甲酚橙作指示剂,用Na_2EDTA溶液滴定溶液中铅含量。实验结果表明,氢溴酸加入量为15mL,酒石酸加入量为10mL,沉淀体积为50~60mL,沉淀时间1h以上时,方法相对标准偏差(RSD)在0.10%~1.1%,加标回收率为97.1%~102%,满足粗二氧化碲中铅量的生产控制检测要求。 相似文献
87.
An automatic sequential injection system, combining monosegmented flow analysis, sequential injection analysis and sequential injection titration is proposed for acidity determination. The system enables controllable sample dilution and generation of standards of required concentration in a monosegmented sequential injection manner, sequential injection titration of the prepared solutions, data collecting, and handling. It has been tested on spectrophotometric determination of acetic, citric and phosphoric acids with sodium hydroxide used as a titrant and phenolphthalein or thymolphthalein (in the case of phosphoric acid determination) as indicators. Accuracy better than |4.4|% (RE) and repeatability better than 2.9% (RSD) have been obtained. It has been applied to the determination of total acidity in vinegars and various soft drinks. The system provides low sample (less than 0.3 mL) consumption. On average, analysis of a sample takes several minutes. 相似文献
88.
89.
In this paper, moving reaction boundary titration (MRBT) was developed for rapid and accurate quantification of total protein in infant milk powder, from the concept of moving reaction boundary (MRB) electrophoresis. In the method, the MRB was formed by the hydroxide ions and the acidic residues of milk proteins immobilized via cross‐linked polyacrylamide gel (PAG), an acid‐base indicator was used to denote the boundary motion. As a proof of concept, we chose five brands of infant milk powders to study the feasibility of MRBT method. The calibration curve of MRB velocity versus logarithmic total protein content of infant milk powder sample was established based on the visual signal of MRB motion as a function of logarithmic milk protein content. Weak influence of nonprotein nitrogen (NPN) reagents (e.g., melamine and urea) on MRBT method was observed, due to the fact that MRB was formed with hydroxide ions and the acidic residues of captured milk proteins, rather than the alkaline residues or the NPN reagents added. The total protein contents in infant milk powder samples detected via the MRBT method were in good agreement with those achieved by the classic Kjeldahl method. In addition, the developed method had much faster measuring speed compared with the Kjeldahl method. 相似文献
90.
D-葡萄糖、D-果糖与Ca~(2+)、Mg~(2+)、Cu~(2+)、Zn~(2+)、Cd~(2+)反应的热力学函数张保林(南京大学配位化学研究所,配位化学国家重点实验室,南京,210008)王文清,陶祖贻(北京大学技术物理系,北京)(兰州大学现代物理系?.. 相似文献