全文获取类型
收费全文 | 262篇 |
免费 | 9篇 |
国内免费 | 1篇 |
学科分类
数理化 | 272篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 21篇 |
2012年 | 15篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 16篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有272条查询结果,搜索用时 15 毫秒
101.
Cross‐coupling reactions in water using ionic liquid‐based palladium(II)–phosphinite complexes as outstanding catalysts 下载免费PDF全文
Nermin Meriç Murat Aydemir Uğur Işik Yusuf Selim Ocak Khadichakhan Rafikova Salih Paşa Cezmi Kayan Feyyaz Durap Alexey Zazybin Hamdi Temel 《应用有机金属化学》2014,28(11):818-825
Two new phosphinite ligands based on ionic liquids [(Ph2PO)C7H14N2Cl]Cl ( 1 ) and [(Cy2PO)C7H14N2Cl]Cl ( 2 ) were synthesized by reaction of 1‐(3‐chloro‐2‐hydoxypropyl)‐3‐methylimidazolium chloride, [C7H15N2OCl]Cl, with one equivalent of chlorodiphenylphosphine or chlorodicyclohexylphosphine, respectively, in anhydrous CH2Cl2 and under argon atmosphere. The reactions of 1 and 2 with MCl2(cod) (M = Pd, Pt; cod = 1,5‐cyclooctadiene) yield complexes cis‐[M([(Ph2PO)C7H14N2Cl]Cl)2Cl2] and cis‐[M(Cy2PO)C7H14N2Cl]Cl)2Cl2], respectively. All complexes were isolated as analytically pure substances and characterized using multi‐nuclear NMR and infrared spectroscopies and elemental analysis. The catalytic activity of palladium complexes based on ionic liquid phosphinite ligands 1 and 2 was investigated in Suzuki cross‐coupling. They show outstanding catalytic activity in coupling of a series of aryl bromides or aryl iodides with phenylboronic acid under the optimized reaction conditions in water. The complexes provide turnover frequencies of 57 600 and 232 800 h?1 in Suzuki coupling reactions of phenylboronic acid with p‐bromoacetophenone or p‐iodoacetophenone, respectively, which are the highest values ever reported among similar complexes for Suzuki coupling reactions in water as sole solvent in homogeneous catalysis. Furthermore, the palladium complexes were also found to be highly active catalysts in the Heck reaction affording trans‐stilbenes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
102.
Houria-Nacera Kherfi Mamar Hamdi Vincent Spziale 《Journal of heterocyclic chemistry》1990,27(5):1401-1406
A Novel condansation of aromatic aldehyde with 2-pyrodone: 4-hydroxy-6-methyl-2-pyridone-1-acetate 1 and its 2 and 3 has been explored. It leads to the formation of arylmethenes 7 or 8 obtained by the reaction of one molecule of aldehyde with two molecules of 2-pyridone-2. The structure of all compounds was determined by pmr, cmr, mass spectra and ir. A reaction mechanism is proposed. 相似文献
103.
A glucuronide of a novel cholesterol absorption inhibitor was synthesized on a 200-mg scale in one step via bovine liver glucuronyltransferase-catalyzed
coupling of the glucuronyl moiety of UDP-glucuronic acid with the phenolic hydroxyl of Sch 58235. It was shown that the product
yield is limited by the hydrolysis of UDP-glucuronic acid by impurities present in the commercial microsomal preparation of
the transferase. This detrimental effect of UDPGluA hydrolysis could be diminished by the presence of high concentration of
glucuronlytransferase. Optimization of reaction conditions and purification procedure resulted in a process that proceeded
with 95% conversion and 88% isolated product yield. The13C6-glucuronide of Sch 58235 was prepared with the help of a cascade of eight enzymes operating concurrently in one pot. 相似文献
104.
B J Clark A Hamdi R G Berrisford S Sabanathan A J Mearns 《Journal of chromatography. A》1991,553(1-2):383-390
A previously unreported coupled achiral-chiral high-performance liquid chromatographic method has been developed to assay the levels of bupivacaine and its enantiomers in plasma samples, after the local anaesthetic had been given as a continuous extrapleural intercostal nerve block for 4 days, to relieve postoperative pain following thoracotomy. The method has been used to determine maximum, individual enantiomer and steady state levels in conjunction with an assessment of whether accumulation of bupivacaine occurs. An off-line extraction sample preparation is involved before determination of the "total" levels and final sample clean-up on a cyanopropyl silica column prior to "heart cutting" of the bupivacaine peak to a Chiral-AGP column for assay of the enantiomeric ratio. For an initial 5 patient number the mean maximum level was 5.43 micrograms/ml against a reported toxic level of around 5 micrograms/ml, which was reached in 72 h and the S-enantiomer gave slightly increased concentrations over the R-enantiomer for which there is some evidence of higher toxicity. 相似文献
105.
Hamdi S Hamdi B Kessaissia Z Barthel H Balard H Donnet JB 《Journal of chromatography. A》2002,969(1-2):143-151
The surface properties of poly(methyl methacrylate) (PMMA) impregnated fumed silicas, in a large range of impregnation ratios, were examined using inverse gas chromatography at infinite dilution. It was observed that the dispersive component gamma(s)d does not decrease monotonously with the impregnation ratio. Two critical coverage ratios were evidenced corresponding at first to the shielding of the most energetic sites and then to the achievement of total coverage of the silica surface. The influence of the coverage ratio on the glassy temperature (tg) of the adsorbed PMMA was also studied, which was evidenced down to a very low coverage ratio (1 monomer unit/nm2). 相似文献
106.
MaÎmar Hamdi Reine Sakellariou Vincent Spziale 《Journal of heterocyclic chemistry》1992,29(7):1817-1819
A new series, the N-(methylene-4-oxocoumarinyl)aminoacids were synthesized by condensation of 4-hydroxycoumarin with α-aminoacids in the presence of excess ethyl orthoformate. 相似文献
107.
Cellular polymers, such as polyethylene foams, are commonly used in the packaging industry. These materials have short service life and generate a high volume of waste after use. In order to valorize this waste and produce added-value applications, it is proposed to convert these materials into highly efficient energy absorption structures. This was done by modifying the original cellular morphology of the foams (spheroidal or polygonal) into a re-entrant structure to produce auxetic materials. This work presents an optimized process combining mechanical compression and solvent vapor evaporation-condensation leading to low density foams (77–200 kg/m3) having negative Poisson's ratios (NPR). Three series of recycled low density polyethylene (LDPE) foams with an initial density of 16, 21, and 36 kg/m3 were used to optimize the processing conditions in terms of treatment temperature, time, and pressure. From all the samples prepared, a minimum Poisson's ratio of −3.5 was obtained. To further characterize the samples, the final foam structure was analyzed to relate with mechanical properties and compare with conventional foams having positive Poisson's ratios. The results are discussed using tensile properties and energy dissipation which were shown to be highly improved for auxetic foams. Overall, the resulting foams can be used in several applications such as sport and military protection equipment. 相似文献
108.
Several 1,3-diaryl-5-(cyano-, aminocarbonyl- and ethoxycarbonyl-)-2-pyrazoline, pyrrolo[3,4-c]pyrazole-4,6-dione and 1,3,4,5-tetraaryl-2-pyrazoline derivatives were prepared by the reaction of nitrilimine with different dipolarophilic reagents. The new compounds were characterized using IR, (1)H-NMR, (13)C-NMR and mass spectra. Biological screening of some compounds is reported. 相似文献
109.
Senem Karahan Pelin Kose Elif Subasi Huseyin Alp Hamdi Temel 《Transition Metal Chemistry》2008,33(7):849-854
The hitherto unknown complexes, [M2(CO)6(μ-CO)(μ-L)], [M = Cr; 1, Mo; 2, W; 3] and [M2(CO)6(μ-CO)(μ-L′)], [M = Cr; 4, Mo; 5, W; 6] have been synthesized by the photochemical reactions of photogenerated intermediate, M(CO)5THF (M = Cr, Mo, W) with thio Schiff base ligands, N,N′-bis(2-aminothiophenol)-1,4-bis(2-carboxaldehydephenoxy)butane (H
2
L) and N,N′-bis(2-aminothiophenol)-1,7-bis(2-formylphenyl)-1,4,7-trioxaheptane (H
2
L′). The complexes have been characterized by elemental analysis, LC-mass spectrometry, magnetic studies, FT-IR and 1H NMR spectroscopy. The spectroscopic studies show that H
2
L and H
2
L′ ligands are converted to benzothiazole derivatives, L and L′ after UV irradiation and coordinated to the central metal as bridging ligands via the central azomethine nitrogen and sulphur
atoms in 1–6. 相似文献
110.
A new cobalt Schiff-base complex, [Co(L)(OH)(H2O)] (where L = [N,N′-bis(2-aminothiophenol)-1,4-bis(carboxylidene phenoxy)butane), was synthesized and its electrochemical and spectroelectochemical properties were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and thin-layer spectro-electrochemistry in solutions of dimethyl sulfoxide (DMSO) and dichloromethane (CH2Cl2). The [Co(L)(OH)(H2O)] complex displays two well-defined reversible reduction processes with the corresponding anodic waves. The half-wave potentials of the first and second reduction processes were displayed at E1/2 = 0.08 V and E1/2 = −1.21 V (scan rate: 0.100 Vs−1) in DMSO, and E1/2 = −0.124 V and E1/2 = −1.32 V (scan rate: 0.100 Vs−1) in CH2Cl2. The potentials of the reduction processes in DMSO are shifted toward negative potentials (0.220–0.112 V) compared to those in CH2Cl2. The electrochemical results are assigned to two one-electron reduction processes; [Co(III)L] + −e → [Co(II)L]− and [Co(II)L]− + −e → [Co(I)L]2−. The six-coordination of the complex remains unchanged during the reduction processes and the electron transfer processes were not followed by a chemical reaction upon scan reversal. It was also seen that [Co(L)(OH)(H2O)] was reduced at a more positive potential than the corresponding salen analogs. The shift and reversibility are apparently related to the high degree of electron delocalization of the [Co(L)(OH)(H2O)] complex, having a N2O2S2 donor set and two additional benzene units. Additionally, in situ spectroelectrochemical measurements support Co(III)/Co(II) and Co(II)/Co(I) reversible reduction processes with the observation of the corresponding spectral changes with the applied potentials Eapp = −0.40 and −1.60 V. Application of the spectroelectrochemical results allowed the determination ofE1/2 and n (the number of electrons) from the spectra of the fully oxidized and reduced species in one unified experiment as well. The results obtained by this method are in agreement with those by the CV and DPV methods. 相似文献