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151.
Zhang C Howell RC Scotland KB Perez FG Todaro L Francesconi LC 《Inorganic chemistry》2004,43(24):7691-7701
The incorporation of lanthanide ions into polyoxometalates may be a unique approach to generate new luminescent, magnetic, and catalytic functional materials. To realize these new applications of lanthanide polyoxometalates, it is imperative to understand the solution speciation chemistry and its impact on solid-state materials. In this study we find that the aqueous speciation of europium(III) and the trivacant polyoxometalate, PW9O34 9-, is a function of pH, countercation, and stoichiometry. For example, at low pH, the lacunary (PW11O39)7- predominates and the 1:1 Eu(PW11O39)4-, 2, forms. As the pH is increased, the 1:2 complex, Eu(PW11O39)2 11- species, 3, and (NH4)22[(Eu2PW10O38)4(W3O8(H2O)2(OH)4].44H2O, a Eu8 hydroxo/oxo cluster, 1, form. Countercations modulate this effect; large countercations, such as K+ and Cs+, promote the formation of species 3 and 1. Addition of Al(III) as a counterion results in low pH and formation of [Eu(H2O)3(alpha-2-P2W17O61)]2, 4, with Al(III) counterions bound to terminal W-O bonds. The four species observed in these speciation studies have been isolated, crystallized, and characterized by X-ray crystallography, solution multinuclear NMR spectroscopy, and other appropriate tech-niques. These species are 1, (NH4)22[(Eu2PW10O38)4(W3O8(H2O)2(OH)4].44H2O (P; a=20.2000(0), b=22.6951(6), c=25.3200(7) A; alpha=65.6760(10), beta=88.5240(10), gamma=86.0369(10) degrees; V=10550.0(5) A3; Z=2), 2, Al(H3O)[Eu(H2O)2PW11O34].20H2O (P, a=11.4280(23), b=11.5930(23), c=19.754(4) A; alpha=103.66(3), beta=95.29(3), gamma=102.31(3) degrees; V =2456.4(9) A3; Z=2), 3, Cs11Eu(PW11O34)2.28H2O (P; a=12.8663(14), b=19.8235(22), c=21.7060(23) A; alpha=114.57(0), beta=91.86(0), gamma=102.91(0) degrees ; V=4858.3(9) A3; Z=2), 4, Al2(H3O)8[Eu(H2O)3(alpha-2-P2W17O61)]2.29H2O (P; a=12.649(6), b=16.230(8), c=21.518(9) A; alpha=111.223(16), beta=94.182(18), gamma=107.581(17) degrees ; V=3842(3) A3; Z=1). 相似文献
152.
Densities of {(1−x)CH3(CH2)n−1OH + xCH3CN} for n=1, 2, 3 or 4 have been determined as a function of composition at 288.15, 293.15, 298.15 and 303.15 K at atmospheric pressure using a vibrating-tube densimeter (Anton Paar DMA 4500, resolution 1×10−5 g cm−3). Excess molar volumes were calculated. The VmE values were negative for acetonitrile–methanol mixtures and sigmoid for acetonitrile–alkanols (C2–C4) mixtures over the complete mole fraction range. VmE values increase in a positive direction with increase in chain length of the alkanols and with the temperature. The Extended Real Associated Solution Model (ERAS-Model) calculations allowing for self-association for the alkanols and complex formation between acetonitrile and alkanols have been used to correlate experimental data. The model is able to reproduce the asymmetrical VmE behavior of the studied systems, although agreement between theoretical and experimental values is less satisfactory for some concentration ranges. 相似文献
153.
γ-Zirconium and γ-titanium phosphates containing organic diamine 2,9-dimethyl-1,10-phenanthroline and its in situ formed copper complex were studied by thermal analysis and physical measurements. All the derived materials show a layered structure and their interlayer distance is increased with respect to that of their precursors. Melting, simultaneous vaporization and oxidation, as well as a decomposition process take place in the pure diamine. After dehydration, all the intercalation materials undergo a two-step decomposition. The presence of the formed copper complex between the layers of the two ion-exchangers considered shows a destabilizing effect with respect to the intercalated diamine materials, resulting in a decrease of the decomposition temperatures and the activation energy of decomposition. The application of the isoconversional Ozawa-Flynn-Wall method substantially confirms the obtained results. 相似文献
154.
Summary We have investigated sub-Doppler lineshapes of neon transitions by means of intermodulated optogalvanic technique in a direct
current hollow cathode and a radio frequency glow discharge. The intermodulated Doppler-free signal, as usual, is superimposed
on a broad Gaussian background due to velocity-changing collisions. The ratio between the collisional and the homogeneous
signal has been systematically investigated as a function of gas pressure and discharge current. By detecting neon as a trace
in other buffer gases, the lineshapes have been also carefully investigated as a function of the mass of the perturbers (helium
and argon). Comparison between theoretical predictions and experimental data leads to quantitative evaluations of collisional
parameters.
Riassunto Sono state investigate le forme di riga di transizioni del neon mediante la spettroscopia optogalvanica in intermodulazione. Il segnale intermodulato, privo di allargamento Doppler, è dat da una Lorenziana, corrispondente all'allargamento omogeneo della transizione, sovrapposta ad un fondo Gaussiano dovuto alle collisioni che producono un cambiamento della velocità degli atomi lungo la direzione dei due fasci laser contropropaganti. è stato compiuto uno studio sistematico del contrasto tra il fondo Doppler e l'ampiezza omogenea della riga al variare della pressione del gas e della corrente di scarica. Inoltre, rivelando il neon come traccia in altri gas nobili (argon, elio), si è investigato l'effetto della massa dell'atomo perturbatore nei processi collisionali. I dati sperimentali sono stati confrontati con i modelli teorici esistenti deducendone stime dei parametri collisionali.
Резюме Мы исследуем суб-доплеровские формы линий для переходов неона. Вэаимно модулнрованный сигнал, как обычно, накладывается на шнрокнй гауссов фон, обысловленный соударениями с изменением скоростей Систематически исследуется зависимостй отношения между столкновителйным и однородным сигналами от давленя газа и тока разряда. С целйю детектирования неона, как следа в другнш вуферныш газаш, мы также нзучаем зависимость форм линий от массы других инертиых газов (гелий и аргон). Сравнение теоретических предсказаний и эксперименталйных данных позволяет получнтй количественныэ оценкн параметров соударений.相似文献
155.
This paper deals with the demonstration of the nonexistence of complex conjugate roots and of real positive roots in the working equations of a previous work [1], where this nonexistence was not proved. 相似文献
156.
Raber G Francesconi KA Irgolic KJ Goessler W 《Fresenius' Journal of Analytical Chemistry》2000,367(2):181-188
The retention behavior of four naturally occurring dimethylarsinoylribosides with -CH2-CHOH-CH2X (X = OH, HO3POCH2CHOHCH2OH, SO3H, OSO3H) as aglycones, of arsenous acid, arsenic acid, methylarsonic acid, and dimethylarsinic acid was investigated on a Hamilton PRP-X100 anion-exchange column with aqueous solutions of ammonium dihydrogen phosphate (20 mmol/L) in the pH range of 3.8-9.0 as mobile phase. A HP 4500 inductively coupled plasma mass spectrometer (ICP-MS) served as arsenic-specific detector. The influence of pH, temperature, and the concentration of methanol in the mobile phase on the retention times of these arsenic compounds was explored. An aqueous 20 mM ammonium dihydrogen phosphate solution at pH 5.6 at a column temperature of 40 degrees C was considered optimal as it allowed the separation of seven of the arsenic compounds within 16 min. Only arsenous acid and the ribose with the glycerol aglycone have overlapping signals with both migrating almost with the solvent front. At a concentration of 0.50 ng As mL(-1) the relative standard deviations (n = 3) of the signal areas of the eight arsenic compounds was in the range from 3.5 to 8.1%. The linear calibration curves (peak areas) from 0.5 to 10 ng/mL had correlation coefficients > 0.997. Extracts obtained from the brown algae Fucus spiralis and Halidrys siliquosa were chromatographed under the optimized conditions. Both species contained the sulfate riboside as the major arsenic compound (approximately 55% of total extractable arsenic) together with the sulfonate- and phosphate riboside. Arsenic acid was a significant constituent of Halidrys siliquosa (approximately 6.5%), but was not detected in Fucus spiralis. 相似文献
157.
We describe the synthesis and structures of the first tantalum-containing nitride-chlorides, Ba(3)Ta(3)N(6)Cl and Ba(15)Ta(15)N(33)Cl(4), and the structurally related Ba(3)Si(3)N(5)OCl, and their relationship with a theoretical silaceous framework. 相似文献
158.
Letsiou S Nischwitz V Traar P Francesconi KA Pergantis SA 《Rapid communications in mass spectrometry : RCM》2007,21(3):343-351
The narrow gap between essentiality and toxicity of selenium requires detailed investigations on selenium metabolism in order to find suitable indicators for the selenium status in the human body. Current methods for quantitative selenium speciation in human urine are based on separation by high-performance liquid chromatography (HPLC) coupled online with elemental mass spectrometry (MS), and the potential of molecular MS detection techniques for the reliable identification and quantification of selenosugars in crude human urine has not been utilized. Now we report the development of an HPLC tandem mass spectrometric (MS/MS) method for the reliable determination in crude human urine of three significant selenium urinary metabolites, collectively termed selenosugars, namely methyl 2-acetamido-2-deoxy-1-seleno-beta-D-galactopyranoside (SeGalNAc), methyl 2-acetamido-2-deoxy-1-seleno-beta-D-glucopyranoside (SeGluNAc) and methyl 2-amino-2-deoxy-1-seleno-beta-D-galactopyranoside (SeGalNH2). Reversed-phase HPLC, with and without cation-exchange guard columns, was applied for the separation of the selenosugars, and atmospheric pressure chemical ionization (APCI) and selected reaction monitoring (SRM) were used for selective and sensitive detection. The collision-induced dissociation behaviour of the selenosugars was studied in detail using APCI triple quadrupole MS/MS and electrospray ion trap MS. The developed method was applied to urine samples collected prior to and after selenium supplementation for the quantification of SeGalNAc using both external calibration and the method of standard additions. Additionally, SeGalNH2 was detected in urine samples after Se supplementation. Finally, neutral loss scanning was explored as a possible method for the detection of unknown methyl-selenosugars. 相似文献
159.
Girotti S Ferri E Maiolini E Bolelli L D'Elia M Coppe D Romolo FS 《Analytical and bioanalytical chemistry》2011,400(2):313-320
A quantitative chemiluminescent method, enabling indirect identification of the peroxide-based explosives TATP (triacetone
triperoxide) and HMTD (hexamethylene triperoxide diamine) has been developed. Treatment of these compounds with acidic solutions
produced peroxides, which were transformed into radical derivatives by horseradish peroxidase (HRP) and then quantified by
measuring the light emitted during their oxidation of luminol. The method was first developed in the microplate format and
later optimized for a portable luminometer, to enable rapid application of the assay directly on site. When the portable luminometer
was used each analysis took only 5–10 min. The method had good selectivity, sensitivity, and reproducibility; in the microplate
format the limits of detection (LOD) and quantification (LOQ) were 40 and 50 ng mL−1, respectively, for both TATP and HMTD. When the portable luminometer was used the LOD and LOQ were 50 and 100 ng mL−1, respectively, for both compounds. Introduction of light emission-enhancing compounds did not improve the analytical performance
of the assay. Imprecision (CV values) was always below 10%. Recovery varied rapidly with time, with an average value of 78%
after 5 min. No false-positive result was detected on measurement of a variety of samples; this is an important feature for
analysis on site. The method was applied both to contaminated materials and to fortified soil samples, simulating operational
conditions. 相似文献
160.
Densities of binary and ternary mixtures containing water + (1,2-ethanediol or 1,2-propanediol or 1,3-propanediol or 1,2-butanediol)
+ (1-n-butyl-3-methylimidazolium bromide at 0.01 mole fraction) at 298.15 K and atmospheric pressure have been determined as a function
of composition using an Anton Paar densimeter (Model DMA 55). Excess molar volumes (VmEV_{\mathrm{m}}^{\mathrm{E}}) were calculated. The values are negative for all mixtures over the whole composition range. 相似文献