全文获取类型
收费全文 | 202篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
化学 | 120篇 |
晶体学 | 7篇 |
力学 | 2篇 |
数学 | 48篇 |
物理学 | 42篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 27篇 |
2012年 | 20篇 |
2011年 | 15篇 |
2010年 | 14篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有219条查询结果,搜索用时 15 毫秒
211.
A novel pre-column derivatization reversed-phase high-performance liquid chromatography with fluorescence detection is described for the determination of bupropion in pharmaceutical preparation, human plasma and human urine using mexiletine as internal standard. The proposed method is based on the reaction of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with bupropion to produce a fluorescent derivative. The derivative formed is monitored on a C18 (150 mm × 4.6 mm i.d., 5 μm) column using a mobile phase consisting of methanol-water 75:25 (v/v), at a flow-rate of 1.2 mL/min and detected fluorimetrically at λ(ex) = 458 and λ(em) = 533 nm. The assay was linear over the concentration ranges of 5-500 and 10-500 ng/mL for plasma and urine, respectively. The limits of detection and quantification were calculated to be 0.24 and 0.72 ng/mL for plasma and urine, respectively (inter-day results). The recoveries obtained for plasma and urine were 97.12% ± 0.45 and 96.00% ± 0.45, respectively. The method presents good performance in terms of precision, accuracy, specificity, linearity, detection and quantification limits and robustness. The proposed method is applied to determine bupropion in commercially available tablets. The results were compared with an ultraviolet spectrophotometry method using t- and F-tests. 相似文献
212.
Tatar Ulu S 《Journal of chromatographic science》2012,50(6):494-498
A high-performance liquid chromatographic (HPLC) method is described for the determination of duloxetine hydrochloride in capsules. The method was based on pre-column derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole using the fluorimetric detection technique. Duloxetine hydrochloride was analyzed by HPLC using an Inertsil C18 column (5 μm, 150 × 4.6 mm) and mobile phase consisted of methanol and water (65:35, v/v). The fluorescence detector was adjusted at excitation and emission wavelengths of 461 and 521 nm, respectively. The linearity of the method was in the range of 10-600 ng/mL. Limits of detection and quantification were 0.51 and 1.53 ng/mL, respectively. The proposed method was successfully applied for determination of duloxetine hydrochloride in its pharmaceutical preparation. The results were in good agreement with those obtained using a reference method. 相似文献
213.
In this study, the effect of Zn-dopant on the physical properties and microstructure of hydroxyapatite (HAP) bioceramics was
investigated. The average crystallite size, phase composition and degree of crystallization of the pure hydroxyapatite and
Zn-doped hydroxyapatite bioceramic samples prepared by sol–gel method were determined by X-ray diffraction method. It was
seen that all the bioceramic samples were composed of the nanoparticles (29–46 nm). Fourier transform infrared spectroscopy
was used to determine the functional groups in the samples. The dielectric properties of the bioceramics were investigated
by dielectric impedance spectroscopy method, and the surface morphologies of them were analyzed using scanning electron microscopy
technique. When the densities of the samples were measured by Archimedes method, it was seen that the densities of the samples
increased with the increase of the molar ratio of Zn. The crystallization degree for all the samples dramatically decreased
with the increasing content of the Zn dopant. With the increase of Zn to HAP, a change was observed in the degree of the crystallization,
phase compositions, dielectric properties and microstructures of the samples. 相似文献
214.
A series of N‐(5‐methyl‐2‐hydroxyphenyl)‐(2/3/4/5‐substituted)‐benzaldimines ( I – XIII ) were synthesized using appropriate synthetic route. Their structures were characterized by FT‐IR, UV‐Visible, ESI‐MS, 1H‐ and 13C‐NMR spectroscopic techniques and analytical methods. The crystal structure of N‐(5‐methyl‐2‐hydroxyphenyl)‐3,4‐dimethoxybenzaldimine ( XIII ) was determined by X‐ray diffraction at room temperature. Relationship between the melting points and the structures of the compounds were examined. Antibacterial activities of the compounds were evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis. Antifungal activities were reported for Candida albicans. Some of the Schiff bases showed considerable antimicrobial activity against S. aureus and C. albicans. 相似文献
215.
α,α-Dibromo-2-methoxyacetophenone reacts, under mild reaction conditions, with C-, N- and O-nucleophiles via a bromophilic substitution/protonation/carbophilic substitution cascade process to afford α-monosubstituted-2-methoxyacetophenones in moderate to good yield. The only exception from this reaction pathway is the reaction with the anion derived from malononitrile in which 2-aroyl-1,1,3,3-tetracyanopropene is obtained. 相似文献
216.
Alper Tolga olak Ferda olak Demet Akduman Okan Zafer Yeilel Orhan Büyükgüngr 《Solid State Sciences》2009,11(11):1908-1918
In this study, three novel Cu(II)-pyridine-2,5-dicarboxylate (pydc) complexes with 4-methylimidazole (4-Meim), [Cu(pydc)(H2O)(4-Meim)2]·H2O (1), imidazole (im), {[Cu(μ-pydc)(im)2]·2H2O}n (2), and 3,4-dimethylpyridine (dmpy), [Cu(μ-pydc)(H2O)(dmpy)]n (3) have been synthesized. Elemental and thermal analyses, magnetic susceptibilities, IR and UV/vis spectroscopic studies have been performed to characterize the complexes. The molecular structures of mononuclear (1) and polynuclear (2 and 3) complexes have been determined by the single crystal X-ray diffraction technique. In 1 and 2, Cu(II) ions have distorted square planer geometry, while 3 has distorted octahedral coordination. The pyridine-2,5-dicarboxylate exhibits three different coordination modes namely bidentate (1), tridentate (2) and tetradentate (3). The complex 1 is further constructed to form three-dimensional framework by hydrogen bonding, C–Hπ and ππ stacking interactions. The adjacent chains of 2 and 3 are then mutually linked via hydrogen bonding, ππ and C–Hπ interactions, which are further assembled to form three-dimensional framework. 1 exhibits the magnetic moment value of 1.70 BM, which corresponds to one of the unpaired electron, while the polynuclear complexes 2 and 3 exhibit 1.58 and 1.46 BM, which is lower than the spin only value for one unpaired electron, indicates to antiferromagnetic effect. The first thermal decomposition process of all the complexes is endothermic dehydration. This stage is followed by partial (or complete) decomposition of the neutral and pydc ligands. In the later stage, the remained organic residue exothermically burns. The final decomposition products which identified by IR spectroscopy were the CuO. 相似文献
217.
We consider the following nonlinear viscoelastic equation together with Dirichlet-boundary conditions, in a bounded domain Ω and ρ > 0. We prove an exponential decay result for a class of relaxation functions. Our result is established without imposing the usual relation between g and its derivative (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
218.
Nasser-eddine Tatar 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2009,60(4):640-650
In this paper we consider a problem which arises in viscoelasticity. We prove exponential decay of solutions for the problem
with a memory term involving a kernel which is singular at zero. This is established by introducing an appropriate Lyapunov
type functional and using the energy method. This work extends earlier results.
相似文献
219.
Mustafa Ersin Pekdemir Mediha Kök Muhammed Sait Kanca Ecem Özen Öner Sibel Pekdemir Şule Inci Sevda Kirbağ Beyhan Tatar 《先进技术聚合物》2023,34(2):605-612
Recently, there has been a great demand for boron-containing compounds (BCCs) with unique biological properties. The demand for the use of these compounds not alone but as additives in composite materials is increasing day by day. In this study, the effect of adding B2O3 compound to the blend of PLA and PEG polymers, which is an important biocompatible shape memory polymer, was investigated. In order to examine the effect of increasing B2O3 additive on the thermal properties of PLA-PEG blend, it was determined by using a Differential Scanning Calorimetry (DSC) and thermogravimetric analyzer (TGA), and it was seen that while the melting temperature of PEG decreased, the melting temperature of PLA increased. In addition, when the thermal stability of the composites was examined, increasing of thermal stability was observed with the addition of B2O3 and a three-step degradation occurred. It was determined that the B2O3/PLA-PEG composite was homogeneous by taking X-ray measurements and SEM measurements. The antimicrobial property of the PLA-PEG blend improved with the increasing B2O3 contribution were observed from the antimicrobial activity measurements of the composite against 4 different bacteria. However, it was determined that the PLA-PEG blend preserved its shape memory effect with increasing diboron trioxide contribution. 相似文献