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1.
Two ladder‐like polysilsesquioxanes (LPS) containing side‐chain maleimide groups have been synthesized successfully by reacting N‐(4‐hydroxyphenyl)maleimide (HPM) with LPS containing 100 mol % of chloropropyl groups (Ladder A ) and 50 mol % of each methyl and chloropropyl group (Ladder B ). HPM was synthesized by reacting maleic anhydride with 4‐aminophenol, and the resulting amic acid was imidized using p‐toluenesulfonic acid as a catalyst (Scheme 1 ). The LPSs were characterized by Fourier transform infrared (FTIR), 1H nuclear magnetic resonance (NMR), proton‐decoupled 13C NMR, 29Si NMR, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Characterization indicated that these polymers had ordered ladder‐like structures with possible defects. These polymers were soluble in common solvents at ambient temperature, which suggested that they were not crosslinked. Both the polymers and the HPM were cured, and their kinetics were followed by dynamic DSC. The Ozawa and Kissinger methods were used to calculate activation energies for curing. Curing increased the temperature at which both 5% weight loss and maximum rate of weight loss were observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4036–4046, 2004  相似文献   
2.
Summary A method has been developed for the fluorimetric determination of boric acid, which gives a blue fluorescence with resacetophenone in sulphuric acid or phosphoric acid medium. The method has the advantage that the reaction does not require much time, because the fluorescence intensity reaches its maximum immediately after mixing the reagents and does not also decrease with time. The intensity of fluorescence can be measured with a fluorimeter and the amount of boric acid determined from a calibration curve.  相似文献   
3.
The use of 2-nitrodiphenylamine as a reversible indicator has been investigated in the titration of iron(II) with cerium(IV) sulphate, potassium dichromate and sodium vanadate in sulphuric acid media. Accurate results can be obtained with cerium(IV) sulphate in 0.5–5.0 M acid, with potassium dichromate in 5.0–7.0 M acid, and with sodium vanadate in 5.0–7.5 M acid. With cerium(IV) sulphate the titrations are preferably conducted in 2.0 M sulphuric acid or in a 1.0 M. sulphuric acid-1.0 M pechloric acid medium. Tungstic acid, acetic acid, arsenic(III) and manganese(II) do not interfere. In titrations of iron(II) with dichromate and vanadate, the colour changes at the end-point are much more vivid with 2-nitrodiphenylamine than with ferroin.  相似文献   
4.
Experimental conditions have been developed for the titration of uraniumIV with ironIII alum solution, using Rhodamine 6G as a fluorescent indicator. The titration is best carried out at 98–100° in a 2–3N hydrochloric acid medium, under filtered ultraviolet light, using 2.0 ml of 0.05% Rhodamine 6G solution for 30 ml of the titration mixture. A slight excess of ironIII solution quenches the greenish-yellow fluorescence of the dye through inner filter action. With the titration assembly described here, it is possible to determine uraniumIV with an accuracy of about 0.4%. This method appears to be more convenient than the potentiometric titration or the method employing potassium thiocyanate as internal indicator.

Evidence is also presented to show that the reaction between uraniumIV and ironIII is slow at room temperature.  相似文献   

5.
Assuming the separation of the intermolecular scattering function into the radial and angular parts and using Egelstaffet al’s orientational model for tetrachlorides, the structure of liquid vanadium tetrachloride has been studied. It has been observed that such a separation is approximate for this liquid and the introduction of a third correction term is required to account for the molecular structure function. The chlorine-chlorine partial structure and effective angleaveraged intermolecular chlorine-chlorine potential in the liquid has been evaluated. Without taking the third correction term, introduced to generate theoretically the molecular structure function, the centre structure function has been obtained in an approximate way from the experimentally observed molecular structure function and from it the centre radial distribution function, centre direct correlation function and the angle-averaged vanadium-vanadium effective potential has been evaluated.  相似文献   
6.
Summary Copper phthalocyanine tetrasulphonic acid has been found to work satisfactorily as an inside indicator in the cerimetric titration of hydro-quinone and metol. It has the advantage that the indicator correction in titrations with 0.01 N solutions of ceric sulphate is much less than with the ferroin indicator, amounting to only 0.02 ml for two drops of the indicator solution.Part II: See Z. analyt. Chem. 163, 1 (1958).  相似文献   
7.
Hydrazine sulphate is proposed as a primary standard reagent for the direct titrimetric determination of vanadium(V) and chromium(VI) alone and in mixtures with potentiometric and photometric end-points, in 9–12 M phosphoric acid medium. The methods proposed possess advantages over those currently available. The use of phosphoric acid as a reaction medium not only accelerates the hydrazine-vanadium(V) reaction very much but also makes it follow an accurate stoichiometric path.  相似文献   
8.
G. Gopala Rao  P. Kanta Rao 《Talanta》1963,10(12):1251-1266
A new method has been developed for the direct titrimetric determination of manganeseII, depending on its oxidation to manganeseIII with potassium dichromate at room temperature in a strong phosphoric acid medium using a potentiometric or photometric endpoint. Oxygen of the air does not interfere. The potentiometric method gives results to an accuracy within ± 0.3% for 20–150 mg of manganese/50 ml of titration solution; with the photometric method 5–17 mg of manganese/40 ml of titration solution can be determined with an error of 0.3–1.0% depending on the amount present. Potassium dichromate in 12.0M phosphoric acid has a formal redox potential of about 1.5 V and this reagent appears to have great possibilities in titrimetric analysis.  相似文献   
9.
Summary A new procedure has been developed for the colorimetric determination of iron(III). It consists in the reduction of iron (III) in dilute sulphuric acid medium (0.1 to 1.0 N) with an excess of hypophosphite (1100) at room temperature using one or two drops of 0.1% PdCl2 solution as catalyst, and then complexing the reduced iron with 1.10-phenanthroline.Iron (III) can also be reduced with phosphite using the PdCl2 catalyst and boiling for 5 to 10 min on a hot plate. The molar concentration of phosphite is preferably kept 500 times that of ferric ion.
Zusammenfassung Es wurde ein neues Verfahren zur colorimetrischen Bestimmung von Eisen(III) ausgearbeitet. Dabei wird das Eisen in verd. Schwefelsäure (0,1–1,0 n) mit einem Überschuß von Hypophosphit (1100) bei Zimmertemperatur unter Verwendung von ein oder zwei Tropfen 0,1%iger PdCl2-Lösung als Katalysator reduziert und anschließend das zweiwertige Eisen mit 1,10-Phenanthrolin umgesetzt.Eisen(III) kann auch mit Phosphit reduziert werden, wenn man ebenfalls PdCl2 als Katalysator verwendet und 5–10 min erhitzt. Die molare Konzentration des Phosphits soll dabei das 500fache von der des Eisens betragen.
  相似文献   
10.
A new method has been developed for the determination of oxalic acid. This depends upon the photochemical oxidation of oxalic acid in. the presence of ferric sulphate. The method involves exposing a measured volume of oxalic acid solution, with an excess of ferric alum and some sulphuric acid,tosunlight in quartz or pyrex beaker for 15 to 30 minutes. The progress of the reaction is indicated by the disappearance of the yellow colour of the ferricoxalate complex from the solution. After completion of the reaction, the ferrous salt formed is determined using standard sodium vanadate and either diphenylbenXXXdine or diphenylamme-sulphonate as internal indicator in the presence of sufficient phosphoric acid. Formic acid does not interfere in the photochemical method of deteminination.  相似文献   
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