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131.
Oxolinic acid and flumequine were analysed by reversed-phase liquid chromatography after extraction from the sample matrix with dichloromethane and partitioning with NaOH. The detection system consisted of a fast-scanning fluorescence detector, which provides the full spectra of the eluting peaks and can thus be used to confirm the identity of analytes. Determination was performed by partial least squares (PLS) and three-way PLS over the three-dimensional data, i.e. fluorescence intensity versus retention time and excitation wavelength. In both cases, similar results, with prediction errors around 4%, were obtained. The method was successfully applied to the analysis of salmon, pork and chicken muscle spiked up to 300 ng g(-1). 相似文献
132.
Here is reported a new application of polymer-enhanced capillary transient isotachophoresis for the separation and quantification of the drug digoxin and its primary metabolite digoxigenin coupled with laser-induced fluorescence (LIF) detection facilitated by labeling with two boronic acid-functionalized squarylium dyes of different alkyl side chain lengths, SQ-BA1 and SQ-BA2. The conditions for drug–dye complex formation were optimized, as determined by absorbance and fluorescence spectra, according to solution pH and buffer composition. As digoxin has a digitoxose sugar moiety in its structure, it was shown to exhibit better enhancement in the fluorescence intensity of both dyes than digoxigenin, which lacks this moiety, presumably through the formation of a cyclic boronate ester complex. A comparison of analyte labeling in pre-column and on-column modes was conducted in subsequent capillary electrophoresis-LIF studies, with the latter labeling mode yielding superior sensitivity. However, to achieve the complete resolution of labeled digoxin and digoxigenin analytes, it was necessary to use the modified isotachophoresis method, with added borate ions that may differentially interact with the drug and its metabolite, hence affecting their mobilities. Limits of quantification of the method for the determination of digoxin with SQ-BA1 and SQ-BA2 were 2.61?×?10?3 and 2.82?×?10?3?M and limits of detection were 7.83?×?10?4 and 8.47?×?10?4?M while sensitivities were as great as 5.06?×?109 and 2.89?×?109?M?1, respectively, indicating that the method is suitable for practical analysis. 相似文献
133.
Brosseau CL Sheepwash E Burgess IJ Cholewa E Roscoe SG Lipkowski J 《Langmuir : the ACS journal of surfaces and colloids》2007,23(4):1784-1791
The adsorption behavior of the cationic surfactant N-decyl-N,N,N-trimethylammonium triflate (DeTATf) on the Au(111) electrode surface was characterized using cyclic voltammetry, differential capacity, and chronocoulometry. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DeTATf has a multistate character. At low bulk DeTATf concentrations, the adsorption state is consistent with the formation of an adsorbed film of nearly flat molecules. At higher concentrations this film may represent a three-dimensional aggregated state. At negative potentials and charge densities close to 0 microC cm-2, the data suggest the formation of a film of tilted molecules oriented with the hydrocarbon tail toward the metal surface and the polar head toward the solution. A surprising result of this study is that DeTATf displays adsorption characteristics of a zwitterionic rather than a cationic surfactant. This behavior indicates that the adsorbed species is an ion pair. 相似文献
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136.
Lenka Nezbedov Manfred Hesse Konstantin Drandarov Christa Werner 《Helvetica chimica acta》2001,84(1):172-179
By means of the high sensitive on‐line‐coupled high‐performance liquid chromatography and atmospheric‐pressure chemical‐ionization mass spectrometry (HPLC/APCI‐MS and HPLC/APCI‐MS/MS) techniques, the new macrocyclic spermine alkaloid prelandrine ( 5 ) was detected in the roots of Aphelandra squarrosa (Acanthaceae), and its structure was elucidated as 4′‐hydroxyprotoverbine (=8‐(4‐hydroxyphenyl)‐1,5,9,13‐tetraazacycloheptadecan‐6‐one). It was further demonstrated that protoverbine ( 6 ) is enzymatically hydroxylated to prelandrine ( 5 ) in a reaction catalyzed by microsomes from the roots of A. squarrosa. The chemical synthesis of (−)‐(S)‐prelandrine is also described. The possible key role of prelandrine ( 5 ) as an intermediate in the biosynthesis of aphelandrine ( 1 ) is discussed. 相似文献
137.
The rate constants of the reactions of DO2 + HO2 (R1) and DO2 + DO2 (R2) have been determined by the simultaneous, selective, and quantitative measurement of HO2 and DO2 by continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near infrared, coupled to a radical generation by laser photolysis. HO2 was generated by photolyzing Cl2 in the presence of CH3OH and O2. Low concentrations of DO2 were generated simultaneously by adding low concentrations of D2O to the reaction mixture, leading through isotopic exchange on tubing and reactor walls to formation of low concentrations of CH3OD and thus formation of DO2. Excess DO2 was generated by photolyzing Cl2 in the presence of CD3OD and O2, small concentrations of HO2 were always generated simultaneously by isotopic exchange between CD3OD and residual H2O. The rate constant k1 at 295 K was found to be pressure independent in the range 25–200 Torr helium, but increased with increasing D2O concentration k1 = (1.67 ± 0.03) × 10−12 × (1 + (8.2 ± 1.6) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The rate constant for the DO2 self-reaction k2 has been measured under excess DO2 concentration, and the DO2 concentration has been determined by fitting the HO2 decays, now governed by their reaction with DO2, to the rate constant k1. A rate constant with insignificant pressure dependence was found: k2 = (4.1 ± 0.6) × 10−13 (1 + (2 ± 2) × 10−20 cm3 × [He] cm−3) cm3 s−1 as well as an increase of k2 with increasing D2O concentration was observed: k2 = (4.14 ± 0.02) × 10−13 × (1 + (6.5 ± 1.3) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The result for k2 is in excellent agreement with literature values, whereas this is the first determination of k1. 相似文献
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139.
C Nilsson K Edwards J Eriksson SW Larsen J Ostergaard C Larsen A Urtti A Yaghmur 《Langmuir : the ACS journal of surfaces and colloids》2012,28(32):11755-11766
The present study was designed to evaluate the effect of the negatively charged food-grade emulsifier citrem on the internal nanostructures of oil-free and oil-loaded aqueous dispersions of phytantriol (PHYT) and glyceryl monooleate (GMO). To our knowledge, this is the first report in the literature on the utilization of this charged stabilizing agent in the formation of aqueous dispersions consisting of well-ordered interiors (either inverted-type hexagonal (H(2)) phases or inverted-type microemulsion systems). Synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were used to characterize the dispersed and the corresponding nondispersed phases of inverted-type nonlamellar liquid-crystalline phases and microemulsions. The results suggest a transition between different internal nanostructures of the aqueous dispersions after the addition of the stabilizer. In addition to the main function of citrem as a stabilizer that adheres to the surface of the dispersed particles, it has a significant impact on the internal nanostructures, which is governed by the following factors: (1) its penetration between the hydrophobic tails of the lipid molecules and (2) its degree of incorporation into the lipid-water interfacial area. In the presence of citrem, the formation of aqueous dispersions with functionalized hydrophilic domains by the enlargement of the hydrophilic nanochannels of the internal H(2) phase in hexosomes and the hydrophilic core of the L(2) phase in emulsified microemulsions (EMEs) could be particularly attractive for solubilizing and controlling the release of positively charged drugs. 相似文献
140.
Christa L. Brosseau Francesca Casadio Richard P. Van Duyne 《Journal of Raman spectroscopy : JRS》2011,42(6):1305-1310
The fading of pigments in items of importance to cultural heritage, such as paintings, works of art on paper, and textiles, is a ubiquitous problem. Tools currently available that can detect and identify organic colorants in severely degraded works of art are rare, given the heavy deterioration and restricted availability of the sample. Recently, however, surface‐enhanced Raman scattering (SERS) spectroscopy has shown great promise in detecting and identifying mass‐limited samples. The art conservation field has seized upon the opportunity opened up by this powerful analytical technique to enable the identification of microscopic amounts of organic molecules used as artists' colorants in complex matrices, such as biomaterials (i.e. dyed natural textiles, linseed oil biofilms present in oil paintings, etc.), a possibility that was previously precluded due to interfering fluorescence and small sample size. Here, we report SERS spectra recorded directly on single particles of red lake pigments from an important historical watercolor by the American master Winslow Homer (1836–1910) that suffered some degree of fading. The accurate colorant identification provided by SERS, enhanced by comparison with reference samples of historical watercolors, has thus enabled important discoveries regarding the materials and intended meanings behind artworks from one of the most influential American watercolor painters. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献