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81.
The least-squares analysis of collisional activation mass spectra provides evidence that 1,1-dihydroxy-3-methylbutene cation radical (a) and 1-hydroxy-1-methoxy-3-methylbutene cation radical (c) (generated in a McLafferty-type rearrangement from 2-isopropyl-3-methylbutanoic acid and its methyl ester) give rise to product ions b and d, the stereochemistry of which at the double bond is determined by the lifetime (internal energy) of a and c, respectively. Decompositions of a and c in the ion source yield predominantly the less stable cis-configurated stereoisomers of b and d, whereas dissociation of a and c at longer lifetimes (lower internal energy) results in the formation of the thermochemically more stable trans isomers of b and d. A qualitative MNDO analysis is provided which takes into account the special features of stereoelectronic control of radical chemistry in the cleavage of a carbon? carbon bond. 相似文献
82.
83.
Kinetics of oxidation of 1-phenylsemicarbazide (PSC) by peroxydisulphate ion (PDS) have been carried out where by the pseudo first order condition was verified at large excess of PDS concentration. The rate of the reaction was followed spectrophotometrically, The stoichiometry was found to be 1:1 where 1-phenylazoformamide is the oxidation product. The effect of acidity on the rate of oxidation was investigated for different temperatures. The parameters of activation ΔG*, ΔH* and ΔS* were computed for both hydrogen ion depedent and hydrogen ion independent reaction pathes. A free radical mechanism was proposed. 相似文献
84.
Ahmed Hichem Hamzaoui Halim Hammi Adel M’nif 《Russian Journal of Inorganic Chemistry》2007,52(12):1859-1863
Lithium recovery from natural brine incontestably requires the optimization of the parameters which influence such a process.
This process consists of trapping lithium ions by a gel of aluminum hydroxide prepared under the action of a strong base.
Studied parameters are molar ratio [Al]/[Li], stirring time, reaction temperature and apparent pH. A systematic study was
carried out varying only one parameter at a time. This procedure makes it possible to fix the studied parameters in order
to recover maximum Li+. This work is done first on synthetic brines, and then it was considered convenient to check the obtained result using natural
brine and an equivalent synthetic brine. Some differences related to lithium yield are established between the two considered
brines. This is due in our opinion to the impurities contained in the natural brine, especially magnesium and boron. 相似文献
85.
Jan H. van Driel Wigger Heerma Johan K. Terlouw Herman Halim Helmut Schwarz 《Journal of mass spectrometry : JMS》1985,20(11):665-673
Evidence is presented for the gas phase generation of at least eight stable isomeric [C2H7O2]+ ions. These include energy-rich protonated peroxides (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_2 {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (e), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm (H)OH} $\end{document} (f) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm (H)CH}_{\rm 3} {\rm (g)),} $\end{document} (g)), proton-bound dimers (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm 3} \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} (h) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH2 = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm + } \cdot \cdot \cdot {\rm HOCH}_{\rm 3} $\end{document} (i)) and hydroxy-protonated species (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} {\rm (OH)CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} (a), $\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH(OH)}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (b) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm OCH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (c)). The important points of the present study are (i) that these ions are prevented by high barriers from facile interconversion and (ii) that both electron-impact- and proton-induced gas phase decompositions seem to proceed via multistep reactions, some of which eventually result in the formation of proton-bound dimers. 相似文献
86.
Halim Doss 《Communications in Mathematical Physics》1980,73(3):247-264
Under some hypotheses of analyticity and integrability we show the existence and uniqueness of a strong regular solution of the Schrödinger equation using a natural generalisation to the complex case of the Feynman-Kac formula. This explicit representation allows us to study in certain cases the asymptotic behavior of the solution when the Planck constanth tends to zero. The same method can be used for the solution of more general Schrödinger equations.
Membre du Laboratoire Associé au C.N.R.S., n° 224 Processus Stochastiques et Applications 相似文献
Membre du Laboratoire Associé au C.N.R.S., n° 224 Processus Stochastiques et Applications 相似文献
87.
ABSTRACTTiO2, ZnO and ZnO/TiO2 thin films have been prepared by radio frequency magnetron sputtering method under different temperatures. Their photo catalytic activities have been investigated. The structural of the thin films were characterized by X-ray diffraction and Raman spectroscopy. The photo catalytic activities of TiO2 and ZnO/TiO2 samples were evaluated by the photo decomposition of methylene blue. We note that the structural proprieties of the thin films showed a perfect crystallization along the (002) for ZnO, Rutile (110) for TiO2 and Anatase (101) for TiO2. The experimental results show that the bilayer ZnO/TiO2 were the most efficient photo catalysts compared to the layer of TiO2. This increased catalytic effect can attributed to the interface between the ZnO layer and the TiO2 one, which modify significantly the chemical potential of the bilayer. 相似文献
88.
Mohammad A. Halim Marion Girod Luke MacAleese Jérôme Lemoine Rodolphe Antoine Philippe Dugourd 《Journal of the American Society for Mass Spectrometry》2016,27(3):474-486
Characterization of acidic peptides and proteins is greatly hindered due to lack of suitable analytical techniques. Here we present the implementation of 213 nm ultraviolet photodissociation (UVPD) in high-resolution quadrupole-Orbitrap mass spectrometer in negative polarity for peptide anions. Radical-driven backbone fragmentation provides 22 distinctive fragment ion types, achieving the complete sequence coverage for all reported peptides. Hydrogen-deficient radical anion not only promotes the cleavage of Cα–C bond but also stimulates the breaking of N–Cα and C–N bonds. Radical-directed loss of small molecules and specific side chain of amino acids are detected in these experiments. Radical containing side chain of amino acids (Tyr, Ser, Thr, and Asp) may possibly support the N–Cα backbone fragmentation. Proline comprising peptides exhibit the unusual fragment ions similar to reported earlier. Interestingly, basic amino acids such as Arg and Lys also stimulated the formation of abundant b and y ions of the related peptide anions. Loss of hydrogen atom from the charge-reduced radical anion and fragment ions are rationalized by time-dependent density functional theory (TDDFT) calculation, locating the potential energy surface (PES) of ππ* and repulsive πσ* excited states of a model amide system. 相似文献
89.
90.