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351.
Felix Rosas Rosa M. Domínguez María Tosta José R. Mora Edgar Márquez Tania Córdova Gabriel Chuchani 《Journal of Physical Organic Chemistry》2010,23(8):743-750
The gas‐phase elimination of 1,1‐dimethoxycyclohexane yielded 1‐methoxy‐1‐cyclohexene and methanol. The kinetics were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor cyclohexene. The working temperature was 310–360 °C and the pressure was 25–85 Torr. The reaction was found to be homogeneous, unimolecular, and follows a first‐order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k(s?1) = [(13.82 ± 0.07) – (193.9 ± 1.0)(kJ mol?1)](2.303RT)?1; r = 0.9995. Theoretical calculations were carried out using density functional theory (DFT) functionals B3LYP, MPW1PW91, and PBE with the basis set 6‐31G(d,p) and 6‐31G++(d,p). The calculated values for the energy of activation and enthalpy of activation are in reasonably good agreement with the experimental values using the PBE/6‐31G (d,p) level of theory. Both experimental results and theoretical calculations suggest a molecular mechanism involving a concerted polar four‐membered cyclic transition state. The transition state structure of methanol elimination from 1,1‐dimethoxycyclohexane is characterized by a significantly elongated C? O bond, while the Cβ? H bond is stretched to a smaller extent, as compared to the reactant. The process can be described as moderately asynchronic with some charge separation in the TS. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
352.
Antonio Doménech Igor O. Koshevoy Noemí Montoya Tapani A. Pakkanen 《Electrochemistry communications》2010,12(2):206-209
The heterotrimetallic Au(I)–Cu(I) aggregate [{Au3Cu2(C2C6H4Fc)6}Au3(PPh2C6H4PPh2)3](PF6)2 exhibits a well-defined solid state electrochemistry in contact with aqueous media, based on ferrocenyl-centred oxidation processes involving anion insertion. Upon attachment of microparticulate deposits of the cluster to graphite electrodes, distinctive electrochemical responses can be obtained for fluoride and chloride ions in aqueous media. 相似文献
353.
In this article, the authors propose a theory of the truth value of propositions from a logic‐mathematical point of view. The work that the authors present is an attempt to address this question from an epistemological, linguistic, and logical‐mathematical point of view. What is it to exist and how do we define existence? The main objective of this work is an approach to the first of these questions. We leave a more thorough treatment of the problem of existence for future works. © 2014 Wiley Periodicals, Inc. Complexity 20: 58–67, 2015 相似文献
354.
Single‐Wall Carbon Nanotubes Covalently Functionalized with Polylysine: Synthesis,Characterization and Analytical Applications for the Development of Electrochemical (Bio)Sensors
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Aurélien Gasnier José Miguel González‐Domínguez Alejandro Ansón‐Casaos Javier Hernández‐Ferrer María L. Pedano María D. Rubianes María Teresa Martínez Gustavo Rivas 《Electroanalysis》2014,26(8):1676-1683
This work reports the synthesis of single‐wall carbon nanotubes (SWCNT) covalently functionalized with polylysine (Plys) and the analytical performance of glassy carbon electrodes (GCE) modified with this material (GCE/SWCNT‐Plys). The resulting electrodes showed an important decrease in the overvoltages for the oxidation of ascorbic acid, uric acid and hydrogen peroxide as well as for the reduction of hydrogen peroxide. The favorable interaction of glucose oxidase (GOx) with SWCNT‐Plys allowed the sensitive and selective glucose biosensing at ?0.100 V without any permselective membrane. The proposed sensor was challenged with different real samples without pretreatment showing an excellent correlation with the reported values. 相似文献
355.
Metabolomic profiling of serum in the progression of Alzheimer's disease by capillary electrophoresis–mass spectrometry
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Raúl González‐Domínguez Antonia García Tamara García‐Barrera Coral Barbas José Luis Gómez‐Ariza 《Electrophoresis》2014,35(23):3321-3330
There is high interest in the discovery of early diagnostic biomarkers of Alzheimer's disease, for which metabolomics exhibits a great potential. In this work, a metabolomic approach based on ultrafiltration and analysis by CE‐MS has been used to obtain representative fingerprints of polar metabolites from serum samples in order to distinguish between patients with Alzheimer's disease, mild cognitive impairment, and healthy controls. By the use of partial least squares discriminant analysis it was possible to classify patients according to the disease stage and then identify potential markers. Significant increase was observed with progression of disease in levels of choline, creatinine, asymmetric dimethyl‐arginine, homocysteine‐cysteine disulfide, phenylalanyl‐phenylalanine, and different medium chain acylcarnitines. On the other hand, asparagine, methionine, histidine, carnitine, acetyl‐spermidine, and C5‐carnitine were reduced in these serum samples. In this way, multiple essential pathways were found implicated in the underlying pathology, such as oxidative stress or defects in energy metabolism. However, the most interesting results are related to the association of several vascular risk factors with Alzheimer's disease. 相似文献
356.
Amperometric determination of sulfite using screen-printed electrodes modified with metallic nanoparticles 总被引:1,自引:0,他引:1
Begoña Molinero-Abad María Asunción Alonso-Lomillo Olga Domínguez-Renedo María Julia Arcos-Martínez 《Mikrochimica acta》2013,180(13-14):1351-1355
We report on the amperometric determination of sulfite using screen-printed carbon electrodes (SPCEs) modified with gold and silver nanoparticles that were deposited on the electrode to improve the capabilities of detection. The electrode is fairly selective and responds to sulfite with an oxidation current (at 300 mV and pH 6) in the 9.80 to 83.33 μM concentration range. The precision in terms of repeatability and reproducibility is 14.4 % and 10.7 % in the case of SPCEs modified by gold nanoparticles. The method was applied to the determination of sulfite in drinking water, pickle juice and vinegar. Recoveries ranged from 96 % to 104 %. Figure
Amperometric determination of sulfite using a sensor based on the immobilization gold nanoparticles on a disposable screen-printed carbon electrode 相似文献
357.
Wilder Henao-Escobar Olga Domínguez-Renedo María Asunción Alonso-Lomillo María Julia Arcos-Martínez 《Mikrochimica acta》2013,180(7-8):687-693
We have developed screen-printed carbon electrodes for the determination of putrescine (Put) via the enzyme monoamine oxidase that was immobilized on the surface of the electrode by cross-linking it with bovine serum albumin using glutaraldehyde. A mixture of 5 % of tetrathiofulvalene (TTF) and carbon ink was used for the fabrication of the screen-printed working electrode. Put was amperometrically detected by measurement of the current due to the oxidation of the mediator TTF. The use of TTF lowers the working potential to +250 mV (vs. a screen-printed Ag/AgCl reference electrode). Response is linear in the range from 16 to 101 μM, and the detection limit is 17.2?±?4.6 μM, with a reproducibility of 9.6 % (n?=?4) in terms of relative standard deviation. The effects of potentially interfering biogenic amines such as cadaverine, histamine, spermine, spermidine and tryptamine were also evaluated. The biosensor was successfully applied to the determination of Put in zucchini and anchovies. Figure
Amperometric determination of putrescine using a biosensor based on the immobilization of monoamine oxidase (MAO) enzyme on a disposable screen-printed carbon electrode modified with tetrathiofulvalene (TTF) 相似文献
358.
Ana Calvo‐Pérez Olga Domínguez‐Renedo M Asunción Alonso‐Lomillo M Julia Arcos‐Martínez 《Electroanalysis》2013,25(5):1316-1322
This work reports the development of horseradish peroxidase based biosensors using screen‐printed carbon electrodes for the determination of tyramine (tyr). A novel procedure based on the insertion of the enzyme in the screen‐printing process (SPCHRPEs) has been compared with the cross‐linked immobilization into the carbon working electrode (HRP/SPCEs). Both biosensors were characterized obtaining good capability of detection (2.1±0.2 and 0.2±0.01 µM for SPCHRPEs and HRP/SPCEs, respectively). The reproducibility was 3.4 % and 6.8 % for SPCHRPEs and HRP/SPCEs, respectively. The repeatability was 2.2 % and 7.1 % for SPCHRPEs and HRP/SPCEs, respectively. The specificity towards different biogenic amines was analyzed. The developed biosensors were applied to the determination of tyr content in cheese samples. 相似文献
359.
Dr. Alicia Domínguez‐Martín Dr. Silke Johannsen Astrid Sigel Dipl.‐Ing. Bert P. Operschall Dr. Bin Song Prof. Dr. Helmut Sigel Prof. Dr. Andrzej Okruszek Prof. Dr. Josefa María González‐Pérez Prof. Dr. Juan Niclós‐Gutiérrez Prof. Dr. Roland K. O. Sigel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8163-8181
The intrinsic acid‐base properties of the hexa‐2′‐deoxynucleoside pentaphosphate, d(ApGpGpCpCpT) [=(A1?G2?G3?C4?C5?T6)=(HNPP)5?] have been determined by 1H NMR shift experiments. The pKa values of the individual sites of the adenosine (A), guanosine (G), cytidine (C), and thymidine (T) residues were measured in water under single‐strand conditions (i.e., 10 % D2O, 47 °C, I=0.1 M , NaClO4). These results quantify the release of H+ from the two (N7)H+ (G?G), the two (N3)H+ (C?C), and the (N1)H+ (A) units, as well as from the two (N1)H (G?G) and the (N3)H (T) sites. Based on measurements with 2′‐deoxynucleosides at 25 °C and 47 °C, they were transferred to pKa values valid in water at 25 °C and I=0.1 M . Intramolecular stacks between the nucleobases A1 and G2 as well as most likely also between G2 and G3 are formed. For HNPP three pKa clusters occur, that is those encompassing the pKa values of 2.44, 2.97, and 3.71 of G2(N7)H+, G3(N7)H+, and A1(N1)H+, respectively, with overlapping buffer regions. The tautomer populations were estimated, giving for the release of a single proton from five‐fold protonated H5(HNPP)±, the tautomers (G2)N7, (G3)N7, and (A1)N1 with formation degrees of about 74, 22, and 4 %, respectively. Tautomer distributions reveal pathways for proton‐donating as well as for proton‐accepting reactions both being expected to be fast and to occur practically at no “cost”. The eight pKa values for H5(HNPP)± are compared with data for nucleosides and nucleotides, revealing that the nucleoside residues are in part affected very differently by their neighbors. In addition, the intrinsic acidity constants for the RNA derivative r(A1?G2?G3? C4?C5?U6), where U=uridine, were calculated. Finally, the effect of metal ions on the pKa values of nucleobase sites is briefly discussed because in this way deprotonation reactions can easily be shifted to the physiological pH range. 相似文献
360.
Dr. Moustafa Malki Dr. Santiago Casado Dr. María Francisca López Dr. Renaud Caillard Dr. F. Javier Palomares Dr. José A. Martín Gago Dr. Cristina Vaz‐Domínguez Dr. Angel Cuesta Prof. Ricardo Amils Prof. Víctor M. Fernández Dr. Marisela Velez Dr. Antonio L. De Lacey Dr. David Olea 《Chemphyschem》2013,14(6):1237-1244
The biofilm formation of a strain of the extremophile bacterium Acidiphilium sp., capable of donating electrons directly to electrodes, was studied by different surface characterization techniques. We develop a method that allows the simultaneous study of bacterial biofilms by means of fluorescence microscopy and atomic force microscopy (AFM), in which transparent graphitic flakes deposited on a glass substrate are used as a support for the biofilm. The majority of the cells present on the surface were viable, and the growth of the biofilms over time showed a critical increase of the extracellular polymeric substances (EPS) as well as the formation of nanosized particles inside the biofilm. Also, the presence of Fe in Acidiphilium biofilms was determined by X‐ray photoelectron spectroscopy (XPS), whereas surface‐enhanced infrared absorption spectroscopy indicated the presence of redox‐active proteins. 相似文献