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71.
72.
Non-stoichiometric zirconium oxide nanocrystals with the formula of ZrO2.12 and diameters less than 10 nm were synthesized in the course of calcination of a dried solution of zirconium(IV) oxy nitrate in the presence of citric acid at 600 °C for 5 h. Crystallite size of product was increased to 20 nm when starch was used as emulsifier. Effect of the organic additive, which was equal of moles of the nitrate ions of the zirconium precursor, was investigated on phase formation, morphology and particle size of products. Samples were characterized by FT-IR, TG/DTA, SEM and TEM analysis. Phase structure of samples were also analysed by the powder X-ray diffraction. 相似文献
73.
The reactions of alkyn‐1‐yl(vinyl)silanes R2Si[C?C‐Si(H)Me2]CH?CH2 [R = Me (1a), Ph (1b)], Me2Si[C?C‐Si(Br)Me2]CH?CH2 (2a), and of alkyn‐1‐yl(allyl)silanes R2Si[C?C‐Si(H)Me2]CH2CH?CH2 (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo[3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (1H, 11B, 13C and 29Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
74.
A highly efficient and simple synthesis of unsymmetrical thioureas is reported based on the reaction of readily synthesized dithiocarbamates with amines, without using any catalyst under solvent-free conditions. The short reaction time, high yields, and solvent-free conditions are advantages of this method. We did not observe the formation of any symmetric disubstituted thiourea, under these reaction conditions. 相似文献
75.
Mostafa M. H. Khalil Eman H. Ismail Shaimaa Abdel Azim Eglal R. Souaya 《Journal of Thermal Analysis and Calorimetry》2010,101(1):129-135
Ternary complexes of Co(II), Ni(II), Cu(II), and Zn(II) with nitrilotriacetic acid as a primary ligand and alanine or phenylalanine
as secondary ligand were prepared in slightly acidic medium. The structures of the complexes were elucidated using elemental,
IR, molar conductance, magnetic moment, UV–Vis spectrophotometry, and thermal analyses. The ternary complexes were isolated
in 1:1:1 (M:HNTA:alaH) ratios, and the molecular structures were found to be [M(HNTA)(alaH)(H2O)2]. Thermogravimetric analysis confirmed this structure and that the water present is coordinated to the central metal atom.
UV–Vis spectra showed that the complexes have octahedral symmetry. 相似文献
76.
Benzidine is an aromatic base of importance in industry. It represents a serious pollutant in many industrial effluents and its photodegradation is of great interest. The mechanism of photo-chemical decomposition of benzidine in different halomethane solvents in addition to the corresponding UV absorption spectra and fluorescence emission spectra are discussed. The photochemical quantum yields (phiC lambda ex = 254 nm) of benzidine in halomethanes is dependent upon the halogen content in the solvent. This effect may be explained by the assumption that free radicals are formed during photolysis of these solvents followed by the abstraction of electrons from a benzidine molecule forming macroradicals of the latter. Both mono- and di-radical benzidine cations have been detected by different techniques. The well known electron absorption peak at 283 nm is characteristic of neutral benzidine while those observed at ca. 370 and 565 nm are assigned to the blue-monoradical cation and yellow-diradical cation, respectively. The blue-monoradical cation has been isolated after irradiation as a blue precipitate. A comparison between neutral benzidine and the blue monoradical cation are made using both IR and differential thermal analysis (DTA) techniques. The fluorescence quenching of solutions of benzidine in inert solvents using halomethanes have been studied. The results obtained are interpreted in terms of a diffusional quenching mechanism. 相似文献
77.
Saleh A. Azim Raafat M. Issa Eynas A. Saleh 《Monatshefte für Chemie / Chemical Monthly》2005,44(3):509-517
The fluorescence quenching and complexation behaviour of tetraphenylporphyrin (TPP) with some organic acceptors such as chloranilic acid (CHL), 5,5-dithiobis-2-nitrobenzoic acid (DTNB), or 3,4-dinitrobenzoic acid (DNB) and tetravalent metal ions such as Th4+ and Zr4+ have been studied in methanol. The second-order fluorescence quenching rate constant (kq), the association constant (K), the molar absorption coefficient (), and the thermodynamic parameters of the complexation process (G°, H°, and S°) have been evaluated using different organic solvents. 相似文献
78.
Both diastereoisomers of (±)-decarbomethoxynauclechine (I) have been synthesized, but stereochemical assignments cannot be made unequivocally. 相似文献
79.
We suggest a technique to separate specific types of isotopes, atoms, and molecules from a mixture. The mechanism is based
on the tunneling phenomenon of slowly moving molecules released from a magneto-optical trap. We argue that the scheme suggested
can be realized in the laboratory. 相似文献
80.
In this paper we study the analytical and statistical results of estimating the gamma dose rate at pool access floor in TRR when the core shield accidentally decreases to some non-permitted levels. Due to the risk of experimental techniques, we use the analytical and statistical methods. In normal conditions (no risk), the discrepancies between experiment and two methods are justified and it is found that for such problems we have to normalize these methods to experimental results as follows: the analytical method by factor 0.13 and MCNP by 1.7. 相似文献