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81.
1,4-Disubstituted 1,2,3-triazoles are obtained in excellent yields via a three-component coupling of secondary alcohols, alkynes and trimethylsilyl azide (TMSN3). This one-pot reaction occurs through in situ generation of an azide from the alcohol and TMSN3, followed by 1,3-dipolar cycloaddition of the terminal alkyne to afford the corresponding disubstituted triazoles. 相似文献
82.
New PNA analogues derived from aminoethylpyrrolidin-5-one backbone show stabilization of aepone-PNA:DNA hybrids and destabilization of the corresponding RNA hybrids compared to unmodified PNA. 相似文献
83.
Precise static dielectric constants are reported for methanol, ethanol, andn-propanol at 10,25, and 40° C and at pressures up to 3 kbar. The measurements were carried out by a low-frequency bridge method using a threeterminal, all-glass cell. An uncertainty of 0.05% is claimed for the data. The results are compared to data from previous investigations, whith the agreement in the absolute magnitude poor but the agreement in the pressure coefficient reasonable in most cases. The data are analyzed in terms of the Kirkwood correlation factorg K as obtained from the Fröhlich equation. In all cases, theg K factor decreases with increased pressure. The problems involved in calculating this factor from the experimental data are discussed, and it is shown that the trends ing K are very dependent upon the assumptions made in isolating the liquid dipole moment from its gas-phase value. This fact also indicates that an interpretation of theg K values in terms of stepwise association of correlation dipoles is premature at this time. 相似文献
84.
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
85.
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
86.
87.
88.
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
89.
P. Ramachandra T. Siva Rama Krishna Gautam R. Desiraju 《Journal of Chemical Sciences》1989,101(4):327-334
The compound 3-hydroxy-6-(4′-nitro)phenylazopyridine (1) was observed to incorporate several organic solvents of crystallisation, forming stable clathrates. These clathrates decompose
upon heating and the host material is chemically transformed. Single crystal X-ray diffraction studies on the ethanol clathrate
lead to a reasonable model for the host structure. But the guest molecules are severely disordered. Alternatively, the compound
forms twinned crystals. The chemically closely related compound2 does not form clathrates. 相似文献
90.
[Reaction: see text]. The potential dual behavior as dienes and dienophiles of the diene moieties of masked o-benzoquinones (MOBs) 10a-e-12a-e, generated upon oxidation of 2-methoxyphenols 1-3 with BTIB in the presence of appropriate dienols, in their intramolecular Diels-Alder (IMDA) reactions has been examined. The IMDA reactions of MOBs 10a-d, 11a,b,d, and 12a,b,d resulted in highly functionalized oxatricyclic compounds 18a-d, 19a,b,d, and 20a,b,d, respectively, with concomitant formation of cis-decalin derivatives 21a-d, 22a,b,d, and 23a,b,d in a highly regio- and stereoselective manner. However, the MOBs 10e-12e provided exclusively oxatricyclic compounds 18e-20e. The formation of cis-decalins in these IMDA reactions illustrates the dienophilic character of MOBs, in addition to their behavior as dienes. The ratio of the two cycloadducts obtained in each reaction as a result of the dual character of MOBs depends on the nature and/or position of the substituents on both the cyclohexadienone moiety and the added 2,4-dienol. The majority of the cycloadducts resulted from the diene property of MOBs in intramolecular Diels-Alder reactions smoothly underwent Cope rearrangement to furnish cis-decalins as sole products in excellent to quantitative yields that provides a short and efficient entry to polyfunctionized cis-decalins from 2-methoxyphenols. Furthermore, the variation of dienophilic and diene characters of MOBs in the IMDA reactions with the electron-donating or electron-withdrawing substituent of both cyclohexadienone moiety and the added conjugated acyclic diene or 2,4-dienol has been studied in detail. 相似文献