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101.
Three flavonoids - 2′,4′,6′-trihydroxy-4′-O-β-d-glucopiranosyl dihydrochalcone, 1, pinocembrin-7-O-(-neohesperidoside, 2 and pinocembrin-7-O-(-(6″-O-acetyl) neohesperidoside, 3 - were successfully isolated from the EtOAc extract of leaves of Sparattosperma leucanthum (Vell.) K. Schum (Bignoniaceae) using a two-step counter-current chromatography (CCC). Two different CCC machines were used, with different column axes (P.C. Inc., vertical orientation axis and AECS Quattro HTPrep, horizontal orientation axis). Detailed studies of flavonoids behaviour in several solvent systems made possible the use of the best system for their isolation. HEMWat and its modifications - exchange of alcohol and addition of a fifth solvent - were tested for isolation of the three compounds in a single run, but good K and α values were not achieved. So, HEMWat 4:10:4:10, with upper phase as mobile, was used to isolate compound 3. A mixture of compounds 1 and 2 was recovered and submitted to a new CCC fractionation using a more polar solvent system: EBuWat 8:2:10, upper phase as mobile. Butironitrile-acetonitrile-water (BuCN-ACN-H2O) 5:10:10, upper phase as mobile, was also used for the isolation of the mixture containing compounds 1 and 2, in order to increase the solubility of the compounds in the CCC solvent system. It is the first time that the system BuCN-ACN-H2O is described in literature. 相似文献
102.
Truzzi DR Ferreira AG da Silva SC Castellano EE Lima FC Franco DW 《Dalton transactions (Cambridge, England : 2003)》2011,40(48):12917-12925
The trans-[Ru(NO)(NH(3))(4)(P(OH)(3))]Cl(3) complex was synthesized by reacting [Ru(H(2)O)(NH(3))(5)](2+) with H(3)PO(3) and characterized by spectroscopic ((31)P-NMR, δ = 68 ppm) and spectrophotometric techniques (λ = 525 nm, ε = 20 L mol(-1) cm(-1); λ = 319 nm, ε = 773 L mol(-1) cm(-1); λ = 241 nm, ε = 1385 L mol(-1) cm(-1); ν(NO(+)) = 1879 cm(-1)). A pK(a) of 0.74 was determined from infrared measurements as a function of pH for the reaction: trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) + H(2)O ? trans-[Ru(NO)(NH(3))(4)(P(O(-))(OH)(2))](2+) + H(3)O(+). According to (31)P-NMR, IR, UV-vis, cyclic voltammetry and ab initio calculation data, upon deprotonation, trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) yields the O-bonded linkage isomer trans- [Ru(NO)(NH(3))(4)(OP(OH)(2))](2+), then the trans-[Ru(NO)(NH(3))(4)(OP(H)(OH)(2))](3+) decays to give the final products H(3)PO(3) and trans-[Ru(NO)(NH(3))(4)(H(2)O)](3+). The dissociation of phosphorous acid from the [Ru(NO)(NH(3))(4)](3+) moiety is pH dependent (k(obs) = 2.1 × 10(-4) s(-1) at pH 3.0, 25 °C). 相似文献
103.
Aline Nicolau Dimitrios Samios Clarisse M.S. Piatnick Quelen B. Reiznautt Denise D. Martini Arthur Lygeros Chagas 《European Polymer Journal》2012,48(7):1266-1278
Polyesters were prepared using epoxidised methyl esters of oleic acid (EPOAME) and epoxidised biodiesel (mixture of methyl esters) from sunflower oil (EPSOME) and linseed oil (EPLOME) with cis-1,2-cyclohexanedicarboxylic anhydride and triethylamine. The kinetic of partial processes involved in the polymerisation were elucidated and related to epoxy rings position in the fatty acid chain. The activation energies (Ea) for the epoxy ring opening by the catalyst are 298, 216 and 136 kJ/mol for EPOAME, EPSOME and EPLOME respectively. The reactions of the epoxy rings in the positions C9–C10, C12–C13 and C15–C16 with anhydride require average activation energies of 116, 32 and 22 kJ/mol, respectively. The compensation effect between activation energy and pre-exponential factor is observed. The polymerisation enthalpy, molecular weight, glass transition temperature and electrical properties were determined. The polyesters studied show promising properties for use in various technological applications. 相似文献
104.
Sergio Luis Costa Ferreira Maria das Graças Andrade Korn Hadla Sousa Ferreira Erik Galvao Paranhos da Silva Rennan Geovanny Oliveira Araújo Anderson Santos Souza 《应用光谱学评论》2013,48(5):475-491
Abstract The present article describes fundamentals and applications of multivariate techniques used for the optimization of analytical procedures and systems involving spectroanalytical methods such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma mass spectrometry (ICP‐MS), considering the main steps of a chemical analysis. This way, applications of experimental designs in optimization of sampling systems, digestion procedures, preconcentration procedures, instrumental parameters of quantification steps of analytical methods, and robustness tests have been summarized in this work. 相似文献
105.
Zhu L Yi Y Li Y Kim EG Coropceanu V Brédas JL 《Journal of the American Chemical Society》2012,134(4):2340-2347
We have used density functional theory calculations and mixed quantum/classical dynamics simulations to study the electronic structure and charge-transport properties of three representative mixed-stack charge-transfer crystals, DBTTF-TCNQ, DMQtT-F(4)TCNQ, and STB-F(4)TCNQ. The compounds are characterized by very small effective masses and modest electron-phonon couplings for both holes and electrons. The hole and electron transport characteristics are found to be very similar along the stacking directions; for example, in the DMQtT-F(4)TCNQ crystal, the hole and electron effective masses are as small as 0.20 and 0.26 m(0), respectively. This similarity arises from the fact that the electronic couplings of both hole and electron are controlled by the same superexchange mechanism. Remarkable ambipolar charge-transport properties are predicted for all three crystals. Our calculations thus provide strong indications that mixed-stack donor-acceptor materials represent a class of systems with high potential in organic electronics. 相似文献
106.
Beaujuge PM Tsao HN Hansen MR Amb CM Risko C Subbiah J Choudhury KR Mavrinskiy A Pisula W Brédas JL So F Müllen K Reynolds JR 《Journal of the American Chemical Society》2012,134(21):8944-8957
Given the fundamental differences in carrier generation and device operation in organic thin-film transistors (OTFTs) and organic photovoltaic (OPV) devices, the material design principles to apply may be expected to differ. In this respect, designing organic semiconductors that perform effectively in multiple device configurations remains a challenge. Following "donor-acceptor" principles, we designed and synthesized an analogous series of solution-processable π-conjugated polymers that combine the electron-rich dithienosilole (DTS) moiety, unsubstituted thiophene spacers, and the electron-deficient core 2,1,3-benzothiadiazole (BTD). Insights into backbone geometry and wave function delocalization as a function of molecular structure are provided by density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level. Using a combination of X-ray techniques (2D-WAXS and XRD) supported by solid-state NMR (SS-NMR) and atomic force microscopy (AFM), we demonstrate fundamental correlations between the polymer repeat-unit structure, molecular weight distribution, nature of the solubilizing side-chains appended to the backbones, and extent of structural order attainable in p-channel OTFTs. In particular, it is shown that the degree of microstructural order achievable in the self-assembled organic semiconductors increases largely with (i) increasing molecular weight and (ii) appropriate solubilizing-group substitution. The corresponding field-effect hole mobilities are enhanced by several orders of magnitude, reaching up to 0.1 cm(2) V(-1) s(-1) with the highest molecular weight fraction of the branched alkyl-substituted polymer derivative in this series. This trend is reflected in conventional bulk-heterojunction OPV devices using PC(71)BM, whereby the active layers exhibit space-charge-limited (SCL) hole mobilities approaching 10(-3) cm(2) V(-1) s(-1), and yield improved power conversion efficiencies on the order of 4.6% under AM1.5G solar illumination. Beyond structure-performance correlations, we observe a large dependence of the ionization potentials of the polymers estimated by electrochemical methods on polymer packing, and expect that these empirical results may have important consequences on future material study and device applications. 相似文献
107.
Banana as Adjunct in Beer Production: Applicability and Performance of Fermentative Parameters 总被引:1,自引:0,他引:1
Giovani B. M. Carvalho Daniel P. Silva Camila V. Bento António A. Vicente José A. Teixeira Maria das Graças A. Felipe João B. Almeida e Silva 《Applied biochemistry and biotechnology》2009,155(1-3):53-62
Traditionally, the raw materials for beer production are barley, hops, water, and yeast, but most brewers use also different adjuncts. During the alcoholic fermentation, the contribution of aroma compounds from other ingredients to the final beer flavor depends on the wort composition, on the yeast strain, and mainly on the process conditions. In this context, banana can also be a raw material favorable to alcoholic fermentation being rich in carbohydrates and minerals and providing low acidity. In this work, the objective was to evaluate the performance of wort adjusted with banana juice in different concentrations. For this, static fermentations were conducted at 15 °C at pilot scale (140 L of medium). The addition of banana that changed the concentration of all-malt wort from 10 °P to 12 and 15 °P were evaluated (°P is the weight of the extract or the sugar equivalent in 100 g solution, at 20 °C). The results showed an increase in ethanol production, with approximately 0.4 g/g ethanol yield and 0.6 g/L h volumetric productivity after 84 h of processing when concentrated wort was used. Thus, it was concluded that banana can be used as an adjunct in brewing methods, helping in the development of new products as well as in obtaining concentrated worts. 相似文献
108.
Giovani B. M. Carvalho Daniel P. Silva Júlio C. Santos Hélcio J. Izário Filho António A. Vicente José A. Teixeira Maria das Graças A. Felipe João B. Almeida e Silva 《Applied biochemistry and biotechnology》2009,153(1-3):34-43
Banana, an important component in the diet of the global population, is one of the most consumed fruits in the world. This fruit is also very favorable to industry processes (e.g., fermented beverages) due to its rich content on soluble solids and minerals, with low acidity. The main objective of this work was to evaluate the influence of factors such as banana weight and extraction time during a hot aqueous extraction process on the total soluble solids content of banana. The extract is to be used by the food and beverage industries. The experiments were performed with 105 mL of water, considering the moisture of the ripe banana (65%). Total sugar concentrations were obtained in a beer analyzer and the result expressed in degrees Plato (°P, which is the weight of the extract or the sugar equivalent in 100 g solution at 20 °C), aiming at facilitating the use of these results by the beverage industries. After previous studies of characterization of the fruit and of ripening performance, a 22 full-factorial star design was carried out, and a model was developed to describe the behavior of the dependent variable (total soluble solids) as a function of the factors (banana weight and extraction time), indicating as optimum conditions for extraction 38.5 g of banana at 39.7 min. 相似文献
109.
María Moreno Oliva Juan Casado Dr. Juan T. López Navarrete Prof. Gunther Hennrich Dr. Stijn van Cleuvenbergen Dr. Inge Asselberghs Dr. Koen Clays Dr. M. Carmen Ruiz Delgado Dr. Jean‐Luc Brédas Prof. J. Sérgio Seixas de Melo Prof. Luisa De Cola Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(33):8223-8234
We have synthesized three new molecules that have three thienylethynyl arms substituting a central benzene core and different electron donor/acceptor groups in the three remaining phenyl positions. The absorption, fluorescence, phosphorescence, and transient triplet–triplet spectra are analyzed in the light of the electronic structure of the ground and excited states obtained from quantum‐chemical calculations. From the above, the relevant photophysical data (including quantum yields, lifetimes, and rate constants) could be derived. It was found that the major deactivation pathway is internal conversion, which competes with the fluorescence and intersystem crossing processes. For the three investigated compounds, we provide convincing theoretical support corroborating these findings and further conclusions based on the theoretical information obtained. These molecules are one of the very few cases in which the depolarization ratios, obtained from the NLO optical measurements, clearly reflect the octopolar configuration. Molecular hyperpolarizabilities have been measured and display a typical dependence on the donor–acceptor substitution pattern. 相似文献
110.
M.G. das Virgens S. Garcia L. Ghivelder 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(2):135-140
The lower critical field of the grains, Hc1, and the intragrain
critical current density, Jc, were determined for the superconducting
ruthenate-cuprate RuSr2Gd1.5Ce0.5Cu2O10-δ
[Ru-1222(Gd)] through a systematic study of the hysteresis in
magnetoresistance loops. A reliable method, based on the effects of the
magnetization of the grains on the net local field at the intergranular
junctions is provided, circumventing the problem of the strong masking of
the superconducting diamagnetic signal by the ferromagnetic background. The
temperature dependency of Hc1 and Jc both exhibit a smooth
increase on cooling without saturation down to
. The
obtained Hc1 values vary between 150 and 1500 Oe in the 0.2 ≤
T/TSC ≤0.4 interval, for samples annealed in an oxygen flow;
oxygenation under high pressure (50 atm) leads to a further increase. These
values are much larger than the previously reported rough assessments (25–50
Oe), using conventional magnetization measurements. High Jc values of
~107 A/cm2, comparable to the high-Tc cuprates, were
obtained. The Hc1(T) and Jc(T) dependencies are explained in the
context of a magnetic phase separation scenario. 相似文献