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排序方式: 共有103条查询结果,搜索用时 390 毫秒
1.
Interactions of Pt‐ttpy with G‐Quadruplexes Originating from Promoter Region of the c‐myc Gene Deciphered by NMR and Gel Electrophoresis Analysis 下载免费PDF全文
2.
The organometallic complexes C5H5 Fe(I) C6(C2H5)6 and C5(CH3)5 Fe(I)C6 H(C2H5)5 have been studied by Mössbauer spectroscopy. Hyperfine data are typical for 19e? systems with one electron on the e 1 * orbital. The thermal variation of the quadrupole splittings indicates vibronic reduction of the spin-orbit constant, in agreement with previous analyses of similar 19e? systems. The quadrupole splitting and recoil-free fraction data give evidence for phase transitions, which are discussed with respect to cooperative Jahn-Teller distortion and hindered rotations of the ethyl groups. 相似文献
3.
A method using reversed-phase high-pressure liquid chromatography (with spectrometric detection at 218nm) is described for the determination in new pharmaceutical preparations (liposomes) of a new immunostimulating agent (N-acetylmuramoyl-l-alanyl-d-isoglutamine). Separation was achieved with a mu-bondapak column and phosphate buffer (pH 2.5)-methanol mixture (93:7 v/v) as eluent, at a flow-rate of 2 ml min . Sodium acetate was used as an internal standard. The detector response at 218 nm was linear in the range 10-170 mug ml . The method is simple and accurate. 相似文献
4.
Summary A sensitive precolumn fluorescence derivatization method for low level detection of the, volatile (N-nitrosodimethylamine and N-nitrosopyrrolidine) and non-volatile N-nitrosamines (N-nitrosoproline and N-nitrosodiethanolamine) an high-performance liquid chromatography was developed. This method is based on the denitrosation of the compounds of interest by a mixture of hydrobromic acid and acetic acid to produce the corresponding secondary amines. These are, then, able to react with, a quinolizinocoumarin derivative (luminarin 9®) to form highly fluorescent labelled N-nitrosamine derivatives. The structural elucidation of the luminarin 9® derivatives of N-nitrosoproline and N-nitrosodimethylamine by way of example, were established by liquid chromatography-mass spectrometry (LC-MS) and by direct chemical ionization-mass spectrometry (CI-MS). The separation, derivatization and detection conditioins were optimized for all the studied compounds. The detection limits (signal to noise ratio=3) were between 0.4 and 1.0 pmol injected depending on the compound. The calibration graphs were linear for derivatized amounts in the range of 0.5–40 nmol for N-nitrosodimethylamine and N-nitrosopyrrolidine, 0.4–2- nmol for N-nitrosoproline and 1.0–40 nmol for N-nitrosodiethanolamine. The repeatability (RSD less than 3.5%, n=6) and reproducibility (RSD less than 4.8%, n-6) were satisfactory. 相似文献
5.
Through the sol–gel process, using the so-called neutral amine route, spherical particles of 1:1 zirconia–titania were synthesized from zirconium(IV) and titanium(IV) butoxides as well as 1,12-diaminododecane as precursor species. The obtained product exhibited a hexagonal structure, as determinated by X-ray diffraction data. The obtained material was also characterized by thermogravimetry, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and surface area measurements. Despite the release of template molecules on heating, the spherical morphology was retained up to about 1200°C, at which the disruption of the spheres took place. 相似文献
6.
C. Hamon J. D. Soilan-Rodriguez H. Kalchhauser W. Reischl 《Monatshefte für Chemie / Chemical Monthly》1997,128(12):1297-1300
Summary When the benzoate of (S)-(Z)-2-(5-(tert-butyldimethylsiloxy)-2-methylencyclohexyliden)-ethanol (5) is treated with 2.5 equivalents of Hg(OOCCF3)2 in dryTHF, a smooth and selective allylic hydroxylation occurs. The C-1 functionalized vitamin D A-ring synthon6 is isolated in 65 to 70% yield in a single step.
Hydroxylierung eines Vitamin D A-Ring-Fragments (Kurze Mitt.)
Zusammenfassung Umsetzung des Benzoats von (S)-(Z)-2-(5-(tert-Butyldimethylsiloxy)-2-methylencyclohexyliden)-ethanol (5) mit 2.5 Äquivalenten Hg(OOCCF3)2 in trockenemTHF führt zu einer selektiven allylischen Hydroxylierung. Damit ist das an C-1 funktionalisierte Vitamin D A-Ring-Fragment6 in einem einzigen Schritt in einer Ausbeute von 65 bis 70% zugänglich.相似文献
7.
The mechanism of sorption of ions by polyurethanes has been investigated through detailed studies of the extraction of cobalt(II) thiocyanate and the salts of several organic acids. Polyether-based polyurethanes. particularly those containing poly(ethylene oxide), were found to be distinctly superior to polyesters in the sorption of salts and performed much better than might be expected by analogy with monomeric liquid solvents. The results were judged to be inconsistent with several possible mechanisms, including adsorption, solvent extraction, weak or strong base anion-exchange, and complexation of metal anions by the polymer. A new proposal, termed the cation chelation mechanism (CCM), was advanced to account for the observations. In this view, a number of cations (including those of the alkali metals, alkaline earth metals, some transition metals, NH(+)(4), RNH(+)(3) and perhaps H(3)O(+)) may be multiply complexed (chelated) by portions of the polymer, thus facilitating the sorption of accompanying anions. As predicted by the mechanism, moderately strong and selective complexation of several cations was observed to occur with the following order of selectivity: Li(+) < Na(+) < Cs(+) < Rb(+) < K(+) approximately NH(+)(4) < Ag(+) approximately Tl(+) < Ba(2+) < Hg(2+) < Pb(2+). Such behaviour parallels that known for many crown and non-cyclic polyethers and is therefore identified with the polyether portions of the polymer, which are thought to adopt helical conformations surrounding the complexed cations. The cation-chelation mechanism may be widely applicable to the sorption of ions of several types by polyether-based polyurethanes, particularly when large, hydrophobic anions (such as anionic metal complexes) are accompanied by an excess of chelatable cations. 相似文献
8.
de Farias RF de Souza JM de Melo JV Airoldi C 《Journal of colloid and interface science》1999,212(1):123-129
The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press. 相似文献
9.
Sidewall functionalization of single-walled carbon nanotubes by addition of dichlorocarbene 总被引:1,自引:0,他引:1
Hu H Zhao B Hamon MA Kamaras K Itkis ME Haddon RC 《Journal of the American Chemical Society》2003,125(48):14893-14900
We report the sidewall functionalization of soluble HiPco single-walled carbon nanotubes (SWNTs) by addition of dichlorocarbene. The dichlorocarbene-functionalized SWNTs [(s-SWNT)CCl(2)] retain their solubility in organic solvents such as tetrahydrofuran and dichlorobenzene. The degree of dichlorocarbene functionalization was varied between 12% and 23% by using different amounts of the dichlorocarbene precursor. Because the addition of dichlorocarbene saturates the carbon atoms on the sidewall of the SWNTs and effectively replaces the delocalized partial double bonds with a cyclopropane functionality, the optical spectra of the SWNTs change dramatically. We estimate that the saturation of 25% of the pi-network electronic structure of the SWNTs is sufficient to remove all vestiges of the interband transitions in the infrared spectrum. The transitions at the Fermi level in the metallic SWNTs that appear in the far-infrared (FIR) region of the spectrum show a dramatic decrease of intensity on dichlorocarbene functionalization. The FIR region of the spectrum allows a clear differentiation between the covalent and the ionic chemistry of SWNTs. In contrast with covalent functionalization, we show that reaction of the SWNTs with bromine vapor leads to a strong increase in absorptions at the Fermi level that is observable in the FIR due to hole doping of the semiconducting SWNTs. Thermal treatment of the (s-SWNT)CCl(2) above 300 degrees C resulted in the breakage of C-Cl bonds, but did not restore the original electronic structure of the SWNTs. 相似文献
10.
Laura Febvay Erwann Hamon Raphaël Recht Nicolas Andres Mathilde Vincent Dalal Aoudé-Werner Hervé This 《Magnetic resonance in chemistry : MRC》2019,57(9):589-602
Roasting of Coffea arabica L. seeds gives rise to chemical reactions that produce more than 800 compounds, some being responsible for the desired organoleptic properties for which the beverage called “coffee” is known. In the industry, the “roasting profile,” that is, the times and temperatures applied, is key to influence the composition of roasted coffee beans and the flavour of the beverage made from them. The impact of roasting on the chemical composition of coffee has been the subject of numerous studies, including by nuclear magnetic resonance (NMR) spectroscopy. However, the roasting equipment and profiles applied in these studies are often far from real industrial conditions. In this work, the effects of two critical technological parameters of the roasting process, namely, the “development time” (the period of time after the “first crack,” a characteristic noise due to seed disruption) and the final roasting temperature on coffee extracts, were investigated. Seeds were roasted at pilot scale according to 13 industrial roasting profiles and extracted in D2O. The extracts were analysed by 1H NMR experiments. The NMR spectra were compared using (a) quantitative analysis of main signals by successive orders of magnitude and (b) chemometric tools (principal component analysis, partial least squares and sparse-orthogonal partial least squares analysis). This allowed to identify compounds, which may serve as markers of roasting and showed that changes in chemical composition can be detected even for slight change in final temperature (~1°C) or in total roasting time (~25 s). 相似文献