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排序方式: 共有278条查询结果,搜索用时 15 毫秒
1.
2.
Paraskevas D. Tzanavaras Demetrius G. Themelis Anastasios Economou Georgios Theodoridis 《Mikrochimica acta》2003,142(1-2):55-62
Two new simple and rapid methods are reported for the accurate and precise spectrophotometric determination of captopril
(CPL) using flow (FI) and sequential injection (SI) analysis. The methods are based on the fast oxidation of CPL by Fe(III).
The produced Fe(II) reacts with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a colored complex which
is monitored spectrophotometrically at 535 nm. Both methods allow the determination of the analyte up to 1000 mg L−1 at a sampling rate of 120 and 60 injections per hour for FI and SI, respectively. The methods are very precise [s
r=0.8 and 1.2% at 500 mg L−1 CPL (n=12) for FI and SI, respectively] and the 3σ detection limits (c
L=4.0 and 7.0 mg L1, respectively) are quite satisfactory. Their application to a variety of anti-hypertensive commercial pharmaceutical formulations
showed excellent results (relative errors, e
r, < ± 1.6% in all cases compared to an official HPLC method), while common pharmaceutical excipients were found not to interfere.
Recovery experiments further verified the accuracy of the developed methods, as the percent recoveries were in the range of
98.1–102.5%.
Author for correspondence. E-mail: themelis@chem.auth.gr
Received May 9, 2002; accepted January 8, 2003
Published online May 5, 2003 相似文献
3.
Stavroula Piperaki Anastasios Perakis Maria Parissi-Poulou 《Journal of chromatography. A》1994,660(1-2):339-350
A liquid chromatographic method for the separation of promethazine (PR) and its positional isomer isopromethazine (IPR) is described.PR is an N-substituted phenothiazine with the actions and the uses of the antihistamines (H1-receptor antagonists). IPR is an impurity in the pharmaceutical preparations of PR and must be controlled at a level below 1%. The liquid chromatographic behaviour of PR and IPR on a hydrolytically stable β-cyclodextrin (β-CD) column with respect to mobile phase composition, pH, ionic strength and the nature of the organic modifier was also investigated. Based on the results, conditions were chosen for the isocratic separation of the two isomers. The proposed separation method is simple and rapid and permits the simultaneous determination of PR and IPR. The separation selectivity of a cyclodextrin bonded-phase column was examined. Special attention was devoted to modelling the inclusion complexes of PR and IPR with β-CD in order to predict their optimum orientation within the β-CD cavity. 相似文献
4.
Anastasios Dondos 《European Polymer Journal》2002,38(7):1311-1317
The variation of the viscometric expansion factor of macromolecular chains, αη, as a function of the number of blobs of which these chains consist, N/Nc, obeys a universal law, both for wormlike and for flexible polymers. Using also wormlike and flexible polymers, we show that the factor relating the excluded volume parameter, z, to the static expansion factor, αG, varies with the number of statistical chain segments, in a universal manner. The universalities appear to be valid below chain lengths required for the appearance of a power law, and they do not seem to have an upper limit in molecular weight. For these two universalities concerning flexible and wormlike polymers we use relations derived from the blob theory [Polymer 20 (1979) 1083] and statistical mechanical theory [J. Chem. Phys. 57 (1972) 2843]. 相似文献
5.
Zusammenfassung Durch Messungen der Alterung (Verminderung der prozentualen Farbstoffaufnahme) der zwei aufeinander liegenden Oxyde auf anodisch
oxydiertem Aluminium wurde folgendes festgestellt:
Das genannteγ
2-Al2O3 weist keine wesentliche Alterung in der Luft und unter Wasser auf, da es kompakt und geordnet ist.
Dasγ
1-Al2O3 altert in der Luft und unter Wasser proportional der Zeit. Seine Alterungsgeschwindigkeit ist proportional der Herstellungsstromdichte.
Nach 12 A/dm2 nimmt die Alterung nicht mehr zu, da dieses Oxyd die maximale Fehlordnung besitzt. Die Alterung in der Luft ist kleiner als
unter Wasser, da dieses mit seinem L?sungsverm?gen für die Rekristallisation günstig ist. Mit zunehmender Temperatur nimmt
die Alterungsgeschwindigkeit bis 90°C zu und f?llt darüber hinaus bis zu Null (120°C). Bei h?heren Temperaturen findet eine
Verjüngung des Oxyds statt. Dieses Ph?nomen mit Temperaturmaximum ist zum ersten Mal bei heterogenen Reaktionen unter ?nderung
eines festen Stoffes festgestellt worden und bedeutet eine Rückreaktion entweder unter Bildung von neuen Fehlordnungen (die
Werte der Aktivierungsenergien der Hin- und Rückreaktion sind dafür plausibel) oder eine Freilegung von anwesenden aktiven
Zentren, wegen Desorption von Wasser. 相似文献
6.
Vassiliki I. Bebeki Anastasios N. Voulgaropoulos 《Fresenius' Journal of Analytical Chemistry》1992,342(4-5):352-356
Summary The spontaneous adsorption of the Co2+ complex with 1,10-phenanthroline on HMDE was utilized for the development of a voltammetric analytical method employing phase selective alternating current, with first harmonic AC1 in phase, =0°, voltammetry. The dependence of the analytical voltammetric response on physical and chemical parameters in various supporting electrolytes was investigated in detail. Optimum conditions for Co2+ determination were established. The method is very sensitive and selective. The determination limit is 205 ng/l Co2+ (adsorption time, tads=20 min). The precision and accuracy were evaluated: 1.84 g/l Co2+, RSD=3.24%, RE=–0.54%; for 205 ng/l Co2+, RSD=4.85%, RE=–3.90%. The results showed good reproducibility and reliabiality. The method was applied to natural waters, wines, mussel tissue and aquatic algae certified reference material. 相似文献
7.
A new synthetic procedure has been developed in Mn cluster chemistry involving reductive aggregation of permanganate (MnO4-) ions in MeOH in the presence of benzoic acid, and the first products from its use are described. The reductive aggregation of NBu(n)4MnO4 in MeOH/benzoic acid gave the new 4Mn(IV), 8Mn(III) anion [Mn12O12(OMe)2(O2CPh)16(H2O)2]2-, which was isolated as a mixture of two crystal forms (NBu(n)4)2[Mn12O12(OMe)2(O2CPh)16(H2O)2].2H2O.4CH2Cl2 (1a) and (NBu(n)4)2[Mn12O12(OMe)2(O2CPh)16(H2O)2].2H2O.CH2Cl2 (1b). The anion of 1 contains a central [Mn(IV)4(mu3-O)2(mu-O)2(mu-OMe)2]6+ unit surrounded by a nonplanar ring of eight Mn(III) atoms that are connected to the central Mn4 unit by eight bridging mu3-O2- ions. This compound is very similar to the well-known [Mn12O12(O2CR)16(H2O)4] complexes (hereafter called "normal Mn12"), with the main difference being the structure of the central cores. Longer reaction times (approximately 2 weeks) led to isolation of polymeric [Mn(OMe)(O2CPh)2]n2, which contains a linear chain of repeating [Mn(III)(mu-O2CPh)2(mu-OMe)Mn(III)] units. The chains are parallel to each other and interact weakly through pi-stacking between the benzoate rings. When KMnO4 was used instead of NBu(n)4MnO4, two types of compounds were obtained, [Mn12O12(O2CPh)16(H2O)4] (3), a normal Mn12 complex, and [Mn4O2(O2CPh)8(MeOH)4].2MeOH (4.2MeOH), a new member of the Mn4 butterfly family. The cyclic voltammogram of 1 exhibits three irreversible processes, two reductions and one oxidation. One-electron reduction of 1 by treatment with 1 equiv of I- in CH2Cl2 gave (NBu(n)4[Mn12O12(O2CPh)16(H2O)3].6CH2Cl2 (5.6CH2Cl2), a normal Mn12 complex in a one-electron reduced state. The variable-temperature magnetic properties of 1, 2, and 5 were studied by both direct current (dc) and alternating current (ac) magnetic susceptibility measurements. Variable-temperature dc magnetic susceptibility studies revealed that (i) complex 1 possesses an S = 6 ground state, (ii) complex 2 contains antiferromagnetically coupled chains, and (iii) complex 5 is a typical [Mn12]- cluster with an S = 19/2 ground state. Variable-temperature ac susceptibility measurements suggested that 5 and both isomeric forms of 1 (1a,b) are single-molecule magnets (SMMs). This was confirmed by the observation of hysteresis loops in magnetization vs dc field scans. In addition, 1a,b, like normal Mn12 clusters, display both faster and slower relaxing magnetization dynamics that are assigned to the presence of Jahn-Teller isomerism. 相似文献
8.
Mercury film plated on a glassy carbon electrode modified with multiwalled carbon nanotubes (MF/MWNTs/GCE) was used for the analysis of single (ss) and double stranded (ds) DNA, as well as for Jurkat genomic DNAs methylated to different degrees. The results indicated that the DNA molecules adsorbed quite strongly on the MF/MWNTs/GCE surface allowing ex situ adsorption and produce well developed peaks (due to cytosine and adenine) by using adsorptive stripping (Ads, ex situ) square wave voltammetry (SWV). Also, SWV of Jurkat DNA mixtures methylated to different degrees revealed a linear decrease of the peak height with increasing methylation indicating an increase of structural rigidity. 相似文献
9.
George T. Tziros Anastasios Samaras George S. Karaoglanidis 《Molecules (Basel, Switzerland)》2021,26(4)
Olive leaf spot (OLS) caused by Fusicladium oleagineum is mainly controlled using copper fungicides. However, the replacement of copper-based products with eco-friendly alternatives is a priority. The use of plant resistance-inducers (PRIs) or biological control agents (BCAs) could contribute in this direction. In this study we investigated the potential use of three PRIs (laminarin, acibenzolar-S-methyl, harpin) and a BCA (Bacillus amyloliquefaciens FZB24) for the management of OLS. The tested products provided control efficacy higher than 68%. In most cases, dual applications provided higher (p < 0.05) control efficacies compared to that achieved by single applications. The highest control efficacy of 100% was achieved by laminarin. Expression analysis of the selected genes by RT-qPCR revealed different kinetics of induction. In laminarin-treated plants, for most of the tested genes a higher induction rate (p < 0.05) was observed at 3 days post application. Pal, Lox, Cuao and Mpol were the genes with the higher inductions in laminarin-treated and artificially inoculated plants. The results of this study are expected to contribute towards a better understanding of PRIs in olive culture and the optimization of OLS control, while they provide evidence for potential contributions in the reduction of copper accumulation in the environment. 相似文献
10.
José A. Forni Nenad Micic Dr. Timothy U. Connell Dr. Geethika Weragoda Dr. Anastasios Polyzos 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(42):18805-18813
We report a new visible-light-mediated carbonylative amidation of aryl, heteroaryl, and alkyl halides. A tandem catalytic cycle of [Ir(ppy)2(dtb-bpy)]+ generates a potent iridium photoreductant through a second catalytic cycle in the presence of DIPEA, which productively engages aryl bromides, iodides, and even chlorides as well as primary, secondary, and tertiary alkyl iodides. The versatile in situ generated catalyst is compatible with aliphatic and aromatic amines, shows high functional-group tolerance, and enables the late-stage amidation of complex natural products. 相似文献