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181.
NH‐Heterocyclic Aryliodonium Salts and their Selective Conversion into N1‐Aryl‐5‐iodoimidazoles
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Yichen Wu Dr. Susana Izquierdo Dr. Pietro Vidossich Prof. Dr. Agustí Lledós Dr. Alexandr Shafir 《Angewandte Chemie (International ed. in English)》2016,55(25):7152-7156
The synthesis of N‐arylimidazoles substituted at the sterically encumbered 5‐position is a challenge for modern synthetic approaches. A new family of imidazolyl aryliodonium salts is reported, which serve as a stepping stone on the way to selective formation of N1‐aryl‐5‐iodoimidazoles. Iodine acts as a “universal” placeholder poised for replacement by aryl substituents. These new λ3‐iodanes are produced by treating the NH‐imidazole with ArI(OAc)2, and are converted to N1‐aryl‐5‐iodoimidazoles by a selective copper‐catalyzed aryl migration. The method tolerates a variety of aryl fragments and is also applicable to substituted imidazoles. 相似文献
182.
This paper illustrates how a deterministic approximation of a stochastic process can be usefully applied to analyse the dynamics of many simple simulation models. To demonstrate the type of results that can be obtained using this approximation, we present two illustrative examples which are meant to serve as methodological references for researchers exploring this area. Finally, we prove some convergence results for simulations of a family of evolutionary games, namely, intra-population imitation models in n-player games with arbitrary payoffs. 相似文献
183.
Javier Vallejo‐Montesinos Antonio Villegas Araceli Jacobo‐Azuara J. Merced Martínez Eulalia Ramírez‐Oliva Araceli Romero‐Izquierdo Jorge Cervantes 《应用有机金属化学》2012,26(7):362-368
Ring opening polymerization (ROP) of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) was promoted by acid‐treated synthetic and natural silica‐aluminates. Silica‐alumina (1:3 Si/Al molar ratio) was obtained using a simple and economic route from precipitation of aluminum sulfate solutions. The material was treated in an acidic medium to improve the content of acid sites and successfully tested as inorganic acidic catalyst for ROP of D3 or D4 cyclosiloxanes. Natural bentonite was treated and used in a similar manner. Once the ROP reaction completed, the catalyst was easily removed and it was found that the recovered synthetic silica‐alumina was active in a second ROP reaction. The effect of the concentration and type of catalyst in respect to the molecular weight and polydispersity of polydimethylsiloxanes was analyzed: increasing the amount of silica‐alumina in ROP of D4 from 0.05 to 0.1 g decreased the average molecular weight (Mn = 13–1.8 kDa) associated with an increase in the polydispersity (2.95 vs. 1.81). Analogous results were found with bentonite. These values suggest that an increase in the catalyst concentration led to a lower Mn, with a more homogeneous molecular chain dimension. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
184.
Federico Ferreres David M. Pereira Angel Gil‐Izquierdo Patrícia Valentão João Botelho Teresa Mouga Paula B. Andrade 《Journal of separation science》2010,33(15):2250-2257
An HPLC‐PAD‐atmospheric pressure chemical ionization‐MS metabolite profiling analysis was conducted on the marine echinoderm Marthasterias glacialis (spiny sea‐star). Bio‐guided purification of the methanolic extract led to the isolation of several carotenoids, namely zeaxanthin, astaxanthin and lutein. These compounds were characterized using both UV–Vis characteristics and MS spectra interpretation. No previous works addressed the MS analysis of carotenoids present in this organism. The purified carotenoid fraction displayed a strong cell proliferation inhibition against rat basophilic leukemia RBL‐2H3 (IC25=268 μg/mL) cancer cell line. Against healthy V79 (rat lung fibroblasts (IC25=411 μg/mL)) cell line, however, toxicity was lower, as it is desired for anti‐cancer molecules. This study suggests that M. glacialis may constitute a good source of bioactive compounds that can be used as lead compounds for the pharmaceutical industry. 相似文献
185.
186.
A. Alonso Izquierdo M. A. Gonzlez Len J. Mateos Guilarte 《Physics letters. [Part B]》2000,480(3-4):373-380
The kinks of the (1+1)-dimensional Wess-Zumino model with polynomic superpotential are investigated and shown to be related to real algebraic curves. 相似文献
187.
Dniel Filots Javier Izquierdo Bibiana M. Fernndez-Prez Lívia Nagy Gza Nagy Ricardo M. Souto 《Molecules (Basel, Switzerland)》2022,27(7)
Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn2+ and OH− ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described. 相似文献
188.
Julio Casado Guillermo Gonzlez-Alatorre Carmen Izquierdo Christian Brunner 《国际化学动力学杂志》1996,28(4):307-313
The kinetics of the nitrosation of methyl, ethyl, propyl, butyl, and allyl urea were studied by conventional and stopped-flow spectrophotometry in the presence or absence of acetate or mono-, di-, or trichloroacetate anions. In the presence of a large excess of urea, the observed rate equation was where Ka is the acidity constant of nitrous acid and KR that of the carboxylic acid. The ureas exhibited the reactivity order methylurea ≫ (ethylurea ≅ propylurea ≅ butylurea) ≫ allylurea. Experiments in D2O afforded values of k/k = exp(0.130hv⌅/kT)], where v⌅ is the frequency of R3N H stretching (2700–2250 cm−1) in the protonated urea. This result, the observed catalysis by carboxylate ions and the value of the Bronsted parameter β(0.45) show the rate-controlling step of these reactions to be the transfer of a proton from the protonated N-alkyl-N-nitrosourea to the solvent or to the organic anion, if present. The observed order of substrate reactivities is explicable in terms of the capacity of the protonated N-alkyl-N-nitrosourea for forming a hydrogen bond with the water molecule to which the proton will be transferred, and the degree to which the formation of such bonds is hindered by the hydrophobic alkyl chain of the nitrosourea. © 1996 John Wiley & Sons, Inc. 相似文献
189.
M. L. Izquierdo E. Glvez C. Burgos F. Florencio 《Journal of heterocyclic chemistry》1988,25(2):419-423
A series of N-β(γ)-acyloxyalkylnortropinones have been synthesized and studied by 1H and 13C nmr spectroscopy, and the crystal structure of N-[γ-(p-chlorophenylcarbonyloxy)propyl]nortropinone 4 has been determined by X-ray diffraction. The compounds studied display in deuteriochloroform solution the same preferred conformation. The pyrrolidine and piperidone rings adopt a flattened N-8 envelope and distorted chair conformation, puckered at N-8 and flattened at C-3 respectively, with the N-substituent in axial position with respect to the piperidone ring. These results are in close agreement with that found for compound 4 in the crystalline state. 相似文献
190.