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191.
Oliveira MM Ugarte D Zanchet D Zarbin AJ 《Journal of colloid and interface science》2005,292(2):429-435
Metal nanoparticles (NP) are very attractive because of their size- and shape-dependent properties. A widely used preparation of ligand-stabilized metal NP is the two-phase liquid-liquid method using dodecanethiol (DT) as ligand. This work presents various procedures to synthesize dodecanethiol-capped silver NPs, all of them based on a two-phase liquid-liquid method. Small alterations in the synthetic parameters lead to dramatic modifications in the nanoparticles' average size, size distribution width, stability, and structure, as well as in their ability to self-assemble. 相似文献
192.
Marcela?A.?Morini Paula?V.?Messina Pablo?C.?SchulzEmail author 《Colloid and polymer science》2005,283(11):1206-1218
The effect of NaCl and HCl on two non-ionic surfactant micelles was studied using several techniques, including conductivity
and ion-selective electrodes. Both surfactants exhibit opposite behaviour. When Tween 20 is titrated with HCl the conductivity
notably increases in comparison with water, whereas that of Triton X-100 solutions do not change with respect to water until
a certain HCl concentration is reached, when it increases. The hydrogen ion activity is lower in Triton X-100 solutions and
higher in Tween 20 solutions than in pure water. Chloride ion activity is higher in Tween 20 solutions than in water, whereas
in Triton X-100 the activity does not significantly differ from that in water. The activity of sodium ion is lower in Tween
20 solutions than in water, whereas that in Triton X-100 solutions does not differ from the titration of water. These phenomena
are explained by the changes in conformation of the non-ionic headgroups, which capture water, and in some cases ions, modifying
the activity of ions in the intermicellar solution. 相似文献
193.
Schraml J Tkadlecová M Pataridis S Soukupová L Blechta V Roithová J Exner O 《Magnetic resonance in chemistry : MRC》2005,43(7):535-542
NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants. 相似文献
194.
195.
Isobaric vapor–liquid equilibrium data at 50, 75, and 94 kPa have been determined for the binary system ETBE + propan-1-ol, in the temperature range 325–368 K. The measurements were made in a vapor–liquid equilibrium still with circulation of both phases. Mixing volumes have been also determined from density measurements at 298.15 K and 101.3 kPa and, at the same temperature and pressure, the dependence of interfacial tension on concentration has been measured using the pendant drop technique. According to experimental results, the mixture presents positive deviation from ideal behavior and azeotropy is present at 75 and 94 kPa. No azeotrope was detected at 50 kPa. The mixing volumes of the system are negative over the whole mole fraction range, and the interfacial tensions exhibit negative deviation from the linear behavior. The activity coefficients and boiling points of the solutions were well correlated with the mole fraction using the Wohl, Wilson, NRTL, UNIQUAC equations. Excess volume data and interfacial tensions were correlated using the Redlich–Kister model. 相似文献
196.
Raymundo Cea-Olivares Rubén Alfredo Toscano Marcela López Patricia García 《Monatshefte für Chemie / Chemical Monthly》1993,124(2):177-183
Summary A series of diheterocyclic dithiocarbamate complexes of the typeRNCS2
MS2C2H4, whereR=pyrrolidyl, 3-pyrrolyl, 4-morpholyl, 3-methlpiperidyl andM=As or Sb were obtained and characterized by IR,1H, and13C-NMR, mass spectroscopy and elemental analyses. The X-ray crystal structure determination of the 4-morpholinecarbodithioate of 1,3-dithia-2-arsa-cyclopentane shows a monodentate behaviour of theRNCS2 entity.Dedicated to Dr. Lydia Rodríguez on the Occasion of her 60th Birthday. 相似文献
197.
Interactions between denatured milk serum proteins and casein micelles studied by diffusing wave spectroscopy 总被引:1,自引:0,他引:1
Alexander M Dalgleish DG 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):11380-11386
The acid-induced aggregation of casein micelles from milk, in the presence of different whey protein preparations from heated and unheated milk, has been studied using diffusing wave spectroscopy (DWS). In particular, the study focused on the turbidity (or l*) parameter obtainable from DWS, which can give information on the interactions between particles in aggregating systems. The experiments provided evidence that the presence of small, soluble, whey protein/kappa-casein aggregates derived from heated milk gave rise to interactions with both heated and unheated casein micelles over a pH range of 5.6 down to 5.2. Comparison of heated and unheated milks, together with milks whose sera had been exchanged, showed that direct interactions were indeed occurring, even between untreated casein micelles and soluble whey protein complexes. Comparison of the behavior of the whey protein aggregates in emulsion preparations where they could not interact with the large particles confirmed that the effect was specific to the presence of casein micelles and could not arise simply from the aggregation of the whey proteins themselves. 相似文献
198.
The anodic oxidation of 1-naphthylamine (ArNH2) has been studied at the platinum electrode in acetonitrile by controlled potential electrolysis, chronopotentiometry, cyclic voltammetry, cyclic voltammetry and spectrometric methods. From the electrochemical data a complex ECE type of mechanism is inferred with an overall efficiency of one electron per molecule of ArNH2. The electrochemical steps are reversible and the chemical process seems to follow second order kinetics and is extremely fast. The cation radical produced in the first charge transfer step suffers fast decomposition to give dimers which are easier to oxidize than ArNH2. The dimeric products were identified by comparison with authentic samples. Further complications arise due to slow reactions of the oxidized dimers. Electrochemical studies in basic media (pyridine and 2,6-lutidine) and acid media (anhydrous trifluoroacetic acid) were also performed. 相似文献
199.
A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min−1, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L−1 and hydrochloric acid concentration 0.5 mol L−1. The working calibration range was extended from 80 mg L−1 (Batch method) to 700 mg L−1 with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r2 = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid. 相似文献
200.
Yan Liu Viorica Lopez-Avila Marcela Alcaraz Werner F. Beckert 《Journal of separation science》1994,17(7):527-536
As part of a continuing evaluation of new analytical and sample preparation techniques conducted by the US Environmental Protection Agency (EPA), the use of capillary gas chromatography with atomic emission detection (GC-AED) for the simultaneous determination of organotin, organolead, and organomercury compounds in environmental samples was investigated. Pentylmagnesium bromide was used to pentylate ionic organotin, organolead, and organomercury compounds; the pentyl derivatives were then separated by GC and determined by AED. Several important GC-AED parameters, including the type of injector inlet, carrier gas flow rate, and helium make-up gas flow rate, were optimized for the simultaneous determination of these organometallic compounds. Their minimum detectable concentrations were approximately 1.0 to 2.5 ng/mL using a 0.5-μL on-column injection. The calibration curves exhibited good linearity between 2.5 and 2500 ng/mL for organotin and organolead compounds, and between 2.5 and 10000 ng/mL for organomercury compounds. 相似文献