全文获取类型
收费全文 | 151篇 |
免费 | 10篇 |
专业分类
化学 | 103篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 11篇 |
物理学 | 40篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 7篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有161条查询结果,搜索用时 562 毫秒
1.
Inas A. Abdallah Sherin F. Hammad Alaa Bedair Mohamed A. Abdelaziz Neil D. Danielson Ahmed H. Elshafeey Fotouh R. Mansour 《Biomedical chromatography : BMC》2022,36(6):e5365
Favipiravir is a potential antiviral medication that has been recently licensed for Covid-19 treatment. In this work, a gadolinium-based magnetic ionic liquid was prepared and used as an extractant in dispersive liquid–liquid microextraction (DLLME) of favipiravir in human plasma. The high enriching ability of DLLME allowed the determination of favipiravir in real samples using HPLC/UV with sufficient sensitivity. The effects of several variables on extraction efficiency were investigated, including type of extractant, amount of extractant, type of disperser and disperser volume. The maximum enrichment was attained using 50 mg of the Gd-magnetic ionic liquid (MIL) and 150 μl of tetrahydrofuran. The Gd-based MIL could form a supramolecular assembly in the presence of tetrahydrofuran, which enhanced the extraction efficiency of favipiravir. The developed method was validated according to US Food and Drug Administration bioanalytical method validation guidelines. The coefficient of determination was 0.9999, for a linear concentration range of 25 to 1.0 × 105 ng/ml. The percentage recovery (accuracy) varied from 99.83 to 104.2%, with RSD values (precision) ranging from 4.07 to 11.84%. The total extraction time was about 12 min and the HPLC analysis time was 5 min. The method was simple, selective and sensitive for the determination of favipiravir in real human plasma. 相似文献
2.
The radical anion of 2,5-dicyano-1,5-hexadiene is shown to undergo Cope cyclization in a flowing afterglow-triple quadrupole apparatus. The cyclic structure of the 2,5-dicyano-1,5-hexadiene radical anion was established by using chemical reactivity. The ion reacts with CO2 and CS2 by addition, whereas the radical anions of closed-shell molecules such as fumaronitrile do not react with these reagents. The ion exhibits reactivity characteristic of a distonic ion in that it sequentially adds CO2 and NO or NO2. It reacts with NO by forming a product at m/z 135 corresponding to addition followed by loss of HCN. The reactivity and CID spectrum of the product ion at m/z 135 agrees with that of oximate ion, which requires a cyclic precursor ion. Attempts to generate radical anions of acrylonitrile and 2,6-dicyano-1,6-heptadiene were unsuccessful, providing additional evidence against a linear structure as a stable structure for 2,5-dicyano-1,5-hexadiene radical anion. The cyclization of the radical anion of the 2,5-dicyano-1,5-hexadiene is the first example of an electron-catalyzed Cope cyclization. 相似文献
3.
Martin Sweeney Michael Gurry Lee-Ann J. Keane Fawaz Aldabbagh 《Tetrahedron letters》2017,58(36):3565-3567
Environmentally-friendly and cost effective hydrogen peroxide in ethyl acetate was used to prepare in high yields pyrrolo[1,2-a]benzimidazoles from commercial o-(pyrrolidin-1-yl)anilines without the requirement for organic-aqueous extraction and chromatography. Six, seven and eight membered ring-fused analogues were similarly obtained in high yields with methanesulfonic acid required for the pyrido[1,2-a]benzimidazole. Anti-tumour benzimidazolequinone derivatives were obtained in high yield via the cyclization of 3,6-dimethoxy-2-(cycloamino)anilines. 相似文献
4.
5.
Martin Sweeney Darren Conboy Styliana I. Mirallai Fawaz Aldabbagh 《Molecules (Basel, Switzerland)》2021,26(9)
This review article provides a perspective on the synthesis of alicyclic and heterocyclic ring-fused benzimidazoles, imidazo[4,5-f]benzimidazoles, and imidazo[5,4-f]benzimidazoles. These heterocycles have a plethora of biological activities with the iminoquinone and quinone derivatives displaying potent bioreductive antitumor activity. Synthesis is categorized according to the cyclization reaction and mechanisms are detailed. Nitrobenzene reduction, cyclization of aryl amidines, lactams and isothiocyanates are described. Protocols include condensation, cross-dehydrogenative coupling with transition metal catalysis, annulation onto benzimidazole, often using CuI-catalysis, and radical cyclization with homolytic aromatic substitution. Many oxidative transformations are under metal-free conditions, including using thermal, photochemical, and electrochemical methods. Syntheses of diazole analogues of mitomycin C derivatives are described. Traditional oxidations of o-(cycloamino)anilines using peroxides in acid via the t-amino effect remain popular. 相似文献
6.
Fawaz Alharbi 《Topology and its Applications》2012,159(2):381-388
Quasi boundary and quasi corner singularities of functions are discussed. They correspond to the classifications of Lagrangian projections with a boundary or a corner. The geometry of bifurcation diagrams and caustics of simple quasi boundary and quasi corner singularities in R3 and R4 are described. 相似文献
7.
Moamen S. Refat Gehad G. Mohamed Mohamed Y. S. Ibrahim Hamada M. A. Killa Hammad Fetooh 《Russian Journal of General Chemistry》2013,83(12):2479-2487
Solid complexes have been prepared and characterized by IR, UV-Vis, elemental analysis, and 1H NMR. Indomethacin forms complexes with Cd(II), Ce(III), and Th(IV) ions in molar ratios (ligand: metal) (2: 1), (3: 1), and (4: 1), respectively. The IR spectra of the complexes suggest that the Indomethacin behaves as a monobasic monodentate ligand coordinated to the metal ions via the deprotonated carboxylate group. Prepared complexes exhibit higher antimicrobial activity against several microorganisms, compared to free ligand. 相似文献
8.
Polymer recycling is a way to reduce environmental problems caused by polymeric waste accumulation generated from day-to-day applications of polymer materials such packaging and construction. The recycling of polymeric waste helps to conserve natural resource because the most of polymer materials are made from oil and gas. This paper reviews the recent progress on recycling of polymeric waste form some traditional polymers and their systems (blends and composites) such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), and introduces the mechanical and chemical recycling concepts. In addition, the effect of mechanical recycling on properties including the mechanical, thermal, rheological and processing properties of the recycled materials is highlighted in the present paper. 相似文献
9.
Mohammad Nasser H. EL-Sherbiny Gamal M. Hammad Ali A. Askar Ahmed A. El- Nour Salwa A. Abou 《Cellulose (London, England)》2022,29(3):1791-1805
Cellulose - Antibacterial coatings based on bacterial cellulose (BC) have been widely used in many fields including food packaging and wound dressing. In this study, we aimed to synthesis of... 相似文献
10.
Wurood kh. Al-lehaibi Khulood A. Al-makhzomi Hani Sh. Mohammed Hamid Hammad Enezei Mohammad Khursheed Alam 《Molecules (Basel, Switzerland)》2021,26(7)
Background: The study examined the oral microbiota, physiological and immunological changes in patients using thermoplastic retainers during three months of use. Methods: The study included several steps. Firstly, 10 swabs were collected from the buccal and palatal surfaces of the teeth of the patients, approximately 2 mL of saliva was collected from the same patients and 2 mL of saliva was collected from 10 healthy people to measure the pH and secretory IgA level. This was followed by the isolation and identfication of the bacterial isolates in the patient samples. Then, isolate susceptibility toward chlorhexidine (CHX) and their adhesion ability to thermoplastic retainer surfaces was measured. In addition to that the study estimated the numbers of Lactobacillus and Streptooccus mutans colonies during three months and finally, a comparsion of pH acidity and IgA level between the patients and healthy people was performed. The results showed the predominant bacteria during the three months were Lactobacillus spp. and Streptococcus spp. followed by different rates of other bacteria. Raoultella ornithinolytica showed more resistance to CHX while Lactobacillus spp. showed more sensitivity. Streptococcus mutans colony levels were higher than Lactobacillus spp. colonies during the three months, also S. mutans had the highest value in adherence to retainer thermoplastic. Finally, pH acidity showed a highly significant difference (p ≤ 0.05) in the third month, like IgA levels (p ≤ 0.05). Conclusions: According to the results obtained from the current study, the researchers noted that the thermoplastic retainers helped change the oral cavity environment. 相似文献