全文获取类型
收费全文 | 443篇 |
免费 | 32篇 |
国内免费 | 5篇 |
专业分类
化学 | 370篇 |
力学 | 6篇 |
数学 | 32篇 |
物理学 | 72篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 17篇 |
2020年 | 29篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 32篇 |
2016年 | 39篇 |
2015年 | 23篇 |
2014年 | 33篇 |
2013年 | 53篇 |
2012年 | 22篇 |
2011年 | 25篇 |
2010年 | 17篇 |
2009年 | 11篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 11篇 |
2005年 | 2篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 12篇 |
2001年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
排序方式: 共有480条查询结果,搜索用时 15 毫秒
51.
Farshad Kheiri Reza Emamali Sabzi Elham Jannatdoust Hassan Sedghi 《Journal of Solid State Electrochemistry》2011,15(11-12):2593-2599
A novel biosensor for catechol has been constructed by immobilizing polyphenol oxidase (PPO) into acetone-extracted propolis (AEP) composite modified with gold nanoparticles (GNPs) and attached to multiwalled carbon nanotube (MWCNTs) on a gold electrode surface. The propolis for AEP was obtained from honeybee colonies. Under the optimum conditions, this method could be successfully used for the amperometric determination of catechol within a concentration range of 1 × 10?6 to 5 × 10?4?M, with a detection limit of 8 × 10?7?M (S/N = 3). The effects of pH and operating potential are also explored to optimize the measurement conditions. The best response was obtained at pH?5, while an optimum ratio of signal-to-noise (S/N) was obtained at ?20?mV (versus Ag/AgCl), which was selected as the applied potential for the amperometric measurements. All subsequent experiments were performed at pH?5. Cyclic voltammetry and electrochemical impedance spectroscopy was used to characterize the PPO/CNTs/GNPs/AEP/Au biosensor. The biosensor also exhibited good selectivity, stability, and reproducibility. 相似文献
52.
Hamid R. Memarian Majid M. Sadeghi Ahmad R. Momeni Dietrich D?pp 《Monatshefte für Chemie / Chemical Monthly》2002,9(4):661-667
Some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized; their photochemical behaviour was studied under oxygen or argon atmosphere. Irradiation of these compounds resulted in the aromatization of the ring and formation of 3,5-diacetylpyridine derivatives. The presence of oxygen plays an important role in the type, rate, or failure of oxidation. Irradiation of these compounds with of 2-furyl or 5-methyl-2-furyl substituents in position 4 under argon resulted in the formation of a pyridine ring with retention of these substituents, whereas loss of these substituents and ring aromatization was observed upon irradiation under oxygen. 相似文献
53.
Elham Hosseini Nejad Patrice Castignolles Robert G. Gilbert Yohann Guillaneuf 《Journal of polymer science. Part A, Polymer chemistry》2008,46(6):2277-2289
Reversible addition fragmentation chain transfer (RAFT) was used to synthesize methacrylic acid oligomers and oligo(methacrylic acid)‐b‐poly(methyl methacrylate) (PMAA‐b‐PMMA) with targeted degree of polymerization ≈ 10. Characterization is by size‐exclusion chromatography (SEC) and electrospray mass‐spectrometry. SEC data are presented as hydrodynamic volume distributions (HVDs), the only proper means to present comparative and meaningful SEC data when there is no unique relationship between size and molecular weight. The RAFT agent, (4‐cyanopentanoic acid)‐4‐dithiobenzoate (CPADB), produced dithiobenzoic acid as a side product during the polymerization of methacrylate derivatives. Precipitation in diethyl ether proved to be an easy way to remove this impurity from the PMAA‐RAFT oligomers. Both unpurified and purified macro‐RAFT agent were used to prepare amphiphilic PMAA‐b‐PMMA copolymers. Diblock copolymer prepared from the purified PMAA homopolymer had a narrower HVD in comparison to those obtained from the equivalent unpurified macro‐RAFT agent. This work shows that while cyanoisopropyl‐dithiobenzoate or CPADB are good RAFT agents for methacrylate derivatives, they exhibit some instability under typical polymerization conditions, and thus when oligomers are targeted, optimal control requires checking for the degradation product and appropriate purification steps when necessary (the same effect is present for larger polymers but is unimportant). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2277–2289, 2008 相似文献
54.
Won Sang Chung Soroush Zare Hassan Hassanabadi Elham Maghsoodi 《Mathematical Methods in the Applied Sciences》2020,43(11):6950-6967
In this paper, the deformation of the ordinary quantum mechanics is formulated based on the idea of conformable fractional calculus. Some properties of fractional calculus and fractional elementary functions are investigated. The fractional wave equation in 1 + 1 dimension and fractional version of the Lorentz transformation are discussed. Finally, the fractional quantum mechanics is formulated; infinite potential well problem, density of states for the ideal gas, and quantum harmonic oscillator problem are discussed. 相似文献
55.
Elham Izadi 《Annali di Matematica Pura ed Applicata》2010,189(3):487-495
We show how the classical Hodge conjecture for the middle cohomology of an abelian variety is equivalent to the general Hodge
conjecture for the middle cohomology of a smooth ample divisor in the abelian variety. This is best suited to abelian varieties
with actions of imaginary quadratic fields. 相似文献
56.
The combination of ultrasound and photochemistry has been used for the oxidation of unsymmetrical 1,4-dihydropyridines to the pyridine derivatives. An ultrasonic probe of 24 kHz frequency and a Hg-lamp of 100 W have been used for this study. The effect of parameters such as ultrasonic intensity, the presence of oxygen and argon atmospheres and also the separate usage of one of these irradiation sources have been studied. Whereas sonication of these compounds alone did not result in the oxidation of them, the use of ultrasound increases the rate of photo-oxidation. The presence of oxygen decreases or increases the rate of reaction, depending on the type of excited state of 1,4-dihydropyridines involved in the reaction. 相似文献
57.
1‐Ethyl‐4‐hydroxy‐2‐oxo‐1,2‐dihydroquinoline‐3‐carbaldehyde ( 1 ) was annulated using malonic acid and/or its ethyl ester to furnish pyrano[3,2‐c]quinoline‐3‐carboxylic acid 2 and its ester 3 . Interconversions between acid 2 and ester 3 were successfully carried out. The anticipated pyrano[3,2‐c]quinoline‐3‐carboxamides 5–12 were conveniently attained via condensation of ester 3 with the proper amine. Surprisingly, treatment of ester 3 with dimethylformamide (DMF) in acidic media led to the carboxamide 5 . All attempts to convert ester 3 to its corresponding acid hydrazides by interaction with the proper hydrazine derivative led to formation of pyrazolidinediones 15 and 17 . Ester 3 underwent cyclo‐condensation with malononitrile dimer affording pyrido[3′,4′:5,6]pyrano[3,2‐c]quinoline derivative 18 . The new compounds revealed significant antioxidant effect, which suggests that most of them are possible potent antioxidant agents. 相似文献
58.
59.
Leila Khoshmaram Hossein Abdolmohammad‐Zadeh Elham Ghaffarzadeh 《Journal of separation science》2019,42(3):736-743
In this work, a new, cheap, simple, fast, and low organic solvent consuming procedure is proposed for isolation, enrichment, and gas chromatographic determination of some phthalate esters in edible oils. The method is based on a combination of air‐assisted liquid–liquid extraction and dispersive liquid–liquid microextraction followed by a drying step under N2 gas. Several experimental parameters affecting both extraction and preconcentration steps were investigated and optimized. Under the optimum conditions for the proposed method, wide linear ranges (0.05–800 μg/L) and low detection limits (0.007–0.023 μg/L) were observed. The ranges of enrichment factors and extraction recoveries were 68–340 and 14–68%, respectively. Eventually, the target analytes were successfully determined in different edible oils using the proposed method. 相似文献
60.
Elham Tabrizian Ali Amoozadeh Salman Rahmani Elham Imanifar Saeede Azhari Masoumeh Malmir 《中国化学快报》2015,26(10):1278-1282
Nano titania-supported sulfonic acid (n-TSA) has found to be a highly efficient, eco-friendly and recyclable heterogeneous nanocatalyst for the solvent-free synthesis of 2, 4, 6-triarylpyridines through one-pot three-component reaction of acetophenones, aryl aldehydes and ammonium acetate. This reported method illustrates several advantages such as environmental friendliness reaction conditions, simplicity, short reaction time, easy work up, reusability of catalyst and high yields of the products. One new compound is reported too. Furthermore, the catalyst could be recycled after a simple work-up, and reused at least six times without substantial reduction in its catalytic activity. 相似文献