全文获取类型
收费全文 | 286篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 198篇 |
晶体学 | 5篇 |
力学 | 8篇 |
数学 | 44篇 |
物理学 | 35篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2008年 | 5篇 |
2007年 | 9篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1996年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 11篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1964年 | 3篇 |
1962年 | 2篇 |
1961年 | 6篇 |
1960年 | 7篇 |
1959年 | 2篇 |
1958年 | 7篇 |
1957年 | 7篇 |
排序方式: 共有290条查询结果,搜索用时 15 毫秒
231.
232.
Reham Maher Ziad Khalifa Abla Ahmed Hathoot Magdi Abdel Azzem 《Electroanalysis》2023,35(4):e202200225
In this article, poly(1,2-diaminoanthraquinone) (pDAAQ) and poly(1,5-diaminonaphthalene) (pDAN) were electrochemically deposited layer by layer on a glassy carbon electrode (GCE) to generate pDAAQ/pDAN@GCE and pDAN/pDAAQ@GCE composite electrodes, respectively. The morphology and characteristics of the modified electrodes were investigated via electrochemical impedance spectroscopy)EIS), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy)SEM). The obtained results reveal the outstanding performance of the pDAN/pDAAQ@GCE electrode for electrochemical nitrite sensing where pDAAQ plays a vital role as the inner layer. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV) measurements revealed that the oxidation peak current of nitrite was proportional to its concentration. The best LSV results were obtained in a concentration range of 10–150 μM, with a limit of detection of 1.2 μM. Furthermore, the pDAN/pDAAQ@GCE composite electrode was used to determine nitrite ions in real water samples with good results. 相似文献
233.
Gregory B. Kharas William S. Schjerven Fatimah A. S. Aldakheel Edgar J. Crespo Zachary M. Gaskell Khalifa J. M. Jordan 《高分子科学杂志,A辑:纯化学与应用化学》2017,54(2):67-70
Novel trisubstituted ethylenes, ring-disubstituted propyl 2-cyano-3-phenyl-2-propenoates, RPhCH = C(CN)CO2C3H7 (where R is 2,5-dichloro, 2,6-dichloro, 3,4-dichloro, 2,3-difluoro, 2,4-difluoro, 2,5-difluoro, 2,6-difluoro) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and propyl cyanoacetate and characterized by CHN elemental analysis, IR, 1H- and 13C-NMR. All the ethylenes were copolymerized with styrene (M1) in solution with radical initiation (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR, GPC, DSC, and TGA. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (1.2–3.1% wt.), which then decomposed in the 500–800°C range. 相似文献
234.
Mousa Khalifa Ahmed 《基于设计的结构力学与机械力学》2016,44(3):161-175
For the first time, a new cross-section profile and efficient method are developed for the vibration analysis of isotropic and orthotropic cylindrical shells having circumferentially varying profile of a cardioid cross-section expressed as an arbitrary function, under thermal gradient effect. The governing equations of orthotropic cylindrical shells with varying thermal gradient around its circumference are derived as a boundary-value problem and solved numerically as an initial-value problem, based on the framework of Flügge's shell theory, transfer matrix approach and Romberg integration method. As a semi-analytical procedure, the trigonometric functions are used with Fourier's approach to approximate the solution in the longitudinal direction and also to reduce the two-dimensional problem to one-dimensional one. The thermal gradient is assumed to arise due to the variation of Young's moduli and shear modulus, along the circumferential direction of the shell. The results are obtained to indicate the effects of cardioid cross-section on the natural frequencies and corresponding mode shapes in the thermal environment as well as the sensitivity of the vibration behavior to the thermal gradient ratio and the orthotropy of the shell is also investigated for different types of vibration modes. In general, close agreement between the obtained results and those of other researchers has been found. 相似文献
235.
Nourhan M. Abd El-Aziz Ibrahim Khalifa Amira M. G. Darwish Ahmed N. Badr Huda Aljumayi El-Sayed Hafez Mohamed G. Shehata 《Molecules (Basel, Switzerland)》2022,27(9)
COVID-19 is still a global pandemic that has not been stopped. Many traditional medicines have been demonstrated to be incredibly helpful for treating COVID-19 patients while fighting the disease worldwide. We introduced 10 bioactive compounds derived from traditional medicinal plants and assessed their potential for inhibiting viral spike protein (S-protein), Papain-like protease (PLpro), and RNA dependent RNA polymerase (RdRp) using molecular docking protocols where we simulate the inhibitors bound to target proteins in various poses and at different known binding sites using Autodock version 4.0 and Chimera 1.8.1 software. Results found that the chicoric acid, quinine, and withaferin A ligand strongly inhibited CoV-2 S -protein with a binding energy of −8.63, −7.85, and −7.85 kcal/mol, respectively. Our modeling work also suggested that curcumin, quinine, and demothoxycurcumin exhibited high binding affinity toward RdRp with a binding energy of −7.80, −7.80, and −7.64 kcal/mol, respectively. The other ligands, namely chicoric acid, demothoxycurcumin, and curcumin express high binding energy than the other tested ligands docked to PLpro with −7.62, −6.81, and −6.70 kcal/mol, respectively. Prediction of drug-likeness properties revealed that all tested ligands have no violations to Lipinski’s Rule of Five except cepharanthine, chicoric acid, and theaflavin. Regarding the pharmacokinetic behavior, all ligand predicted to have high GI-absorption except chicoric acid and theaflavin. At the same way chicoric acid, withaferin A, and withanolide D predicted to be substrate for multidrug resistance protein (P-gp substrate). Caffeic acid, cepharanthine, chicoric acid, withaferin A, and withanolide D also have no inhibitory effect on any cytochrome P450 enzymes. Promisingly, chicoric acid, quinine, curcumin, and demothoxycurcumin exhibited high binding affinity on SARS-CoV-2 target proteins and expressed good drug-likeness and pharmacokinetic properties. Further research is required to investigate the potential uses of these compounds in the treatment of SARS-CoV-2. 相似文献
236.
Amira M. G. Darwish Aida A. Abd El-Wahed Mohamed G. Shehata Hesham R. El-Seedi Saad H. D. Masry Shaden A. M. Khalifa Hatem M. Mahfouz Sobhy A. El-Sohaimy 《Molecules (Basel, Switzerland)》2023,28(1)
Honeybee products, as multicomponent substances, have been a focus of great interest. The present work aimed to perform the nutritional and chemical profiling and biochemical characterization of bee pollen (BP), bee bread (BB), and royal jelly (RJ) and study their applications in the fortification of functional fermented dairy products. Their effects on starter cultures and the physicochemical and sensorial quality of products were monitored. A molecular networking analysis identified a total of 46 compounds in the three bee products that could be potential medicines, including flavonoids, fatty acids, and peptides. BB showed the highest protein and sugar contents (22.57 and 26.78 g/100 g), which cover 45.14 and 53.56% of their daily values (DVs), with considerable amounts of the essential amino acids threonine and lysine (59.50 and 42.03%). BP, BB, and RJ can be considered sources of iron, as 100 g can cover 141, 198.5, and 94.94% of DV%, respectively. BP was revealed to have the highest phenolic and flavonoid contents (105.68 and 43.91 µg/g) and showed a synergetic effect when mixed with RJ, resulting in increased antioxidant activity, while BB showed a synergetic effect when mixed with RJ in terms of both antioxidant and proteolytic powers (IC50 7.54, 11.55, 12.15, 12.50, and 12.65 cP compared to the control (10.55 cP)), reflecting their organoleptic properties and highlighting these health-oriented products as promising natural products for human health care. 相似文献
237.
Hammad Ullah Alessandro Di Minno Cristina Santarcangelo Ariyawan Tantipongpiradet Marco Dacrema Rita di Matteo Hesham R. El-Seedi Shaden A. M. Khalifa Alessandra Baldi Antonietta Rossi Maria Daglia 《Molecules (Basel, Switzerland)》2022,27(24)
Allium cepa L. is a highly consumed garden crop rich in biologically active phenolic and organosulfur compounds. This study aimed to assess the in vitro bioaccessibility and anti-inflammatory effect of a chemically characterized A. cepa extract rich in quercetin and its derivatives. Different varieties of A. cepa were studied; based on the highest total phenolic content, the “Golden” variety was selected. Its extracts, obtained from the tunicate bulb, tunic, and bulb, were subjected to determination of quercetin and its derivatives with LC-MS analysis and based on the highest total quercetin content, the tunic extract was utilized for further experiments. The extraction method was optimized through a design of experiment (DoE) method via full factorial design, which showed that 40% ethanol and 1 g tunic/20 mL solvent are the best extraction conditions. HPLC analysis of the optimized tunic extract identified 14 flavonols, including 10 quercetin derivatives. As far as in vitro bioaccessibility was concerned, the increases in some quercetin derivatives following the gastro-duodenal digestion process support the bioaccessibility of these bioactive compounds. Moreover, the extract significantly inhibited the production of PGE2 in stimulated J774 cell lines, while no effects of the tunic extract were observed against the release of IL-1β, TNF-α, and nitrites. The study provided insights into the optimized extraction conditions to obtain an A. cepa tunic extract rich in bioavailable quercetin derivatives with significant anti-inflammatory effects against PGE2. 相似文献
238.
In this article, we consider the drift parameter estimation problem for the nonergodic Ornstein-Uhlenbeck process defined as d X_t= θX_tdt + dG_t, t ≥ 0 with an unknown parameter θ 0, where G is a Gaussian process. We assume that the process {X_t, t ≥ 0} is observed at discrete time instants t_1 = ?_n, ···, t_n= n?_n, and we construct two least squares type estimators ■ and ■ for θ on the basis of the discrete observations {X_(t_i), i = 1, ···, n}as n →∞. Then, we provide sufficient conditions, based on properties of G, which ensure that ■ and ■ are strongly consistent and the sequences n?n~(1/2)(■-θ) and n?n~(1/2)(■-θ)are tight. Our approach offers an elementary proof of [11], which studied the case when G is a fractional Brownian motion with Hurst parameter H ∈(1/2, 1). As such, our results extend the recent findings by [11] to the case of general Hurst parameter H ∈(0, 1). We also apply our approach to study subfractional Ornstein-Uhlenbeck and bifractional Ornstein-Uhlenbeck processes. 相似文献
239.
Khalifa N. M. Haiba M. E. Afifi A. H. El-Moez S. I. Abd Soliman A. M. 《Russian Journal of General Chemistry》2022,92(9):1728-1736
Russian Journal of General Chemistry - The reaction between different arylhydrazones and ninhydrin (= indene-1,2-3-trione) in acetonitrile at room temperature is described to produce novel... 相似文献
240.
Naglah A. M. Amr A. E. Khalifa N. M. Al-Omar M. A. 《Russian Journal of General Chemistry》2015,85(12):2833-2838
Russian Journal of General Chemistry - A series of octa bridged peptide and macrocyclic pentapeptide Schiff base derivatives were synthesized from tetrapeptide hydrazide and macrocyclic... 相似文献