全文获取类型
收费全文 | 566篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 422篇 |
晶体学 | 11篇 |
力学 | 18篇 |
数学 | 54篇 |
物理学 | 87篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 15篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 28篇 |
2017年 | 22篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 30篇 |
2011年 | 52篇 |
2010年 | 24篇 |
2009年 | 31篇 |
2008年 | 32篇 |
2007年 | 26篇 |
2006年 | 25篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 1篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1987年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有592条查询结果,搜索用时 15 毫秒
541.
AcCl-EtOH transforms primary and secondary allyl acetates into allyl chlorides that retain the olefinic bond in the more stable position. Whereas secondary allyl alcohols also react with almost the same efficacy as the acetates, the reactions of primary allyl alcohols that possess 1,2-disubstituted alkenes are very slow. The products are isolated in high state of purity simply by removal of the volatiles. 相似文献
542.
The deprotection of a variety of tetrahydropyranyl ethers (THP), acetonides and acetals into their parent compounds using clay supported ammonium nitrate “Clayan” under microwave irradiation is described. The eco-friendly nature of the reagent and non solvent conditions are the important features of the procedure. 相似文献
543.
This paper presents an investigation of the resonant excitation of the electrostatic ion cyclotron wave at the difference frequency of two microwave beams propagating in a magnetoactive solid state plasma, viz. n InSb. The resonant excitation of the electrostatic ion cyclotron wave occurs when the difference frequency of the two microwave beams and the difference of their propagation vectors satisfy the dispersion relation corresponding to the electrostatic ion cyclotron wave. For typical plasma parameters of n InSb and microwave beams of power densities 1 MW cm?2, the power density of the excited ion cyclotron wave is 0.40 kW cm?2 when external magnetic field is . The power density of the excited ion cyclotron wave increases with the magnetic field. This study may provide new means for the characterisation and diagnostic of semiconductors. 相似文献
544.
Baburaj Baskar N. Ganesh Pandian Kuttikode Priya Anju Chadha 《Tetrahedron: Asymmetry》2004,15(24):3961-3966
Enantioselective bioreduction of alkyl 2-oxo-4-arylbutanoates and 2-oxo-4-arylbut-3-enoates mediated by Candida parapsilosis ATCC 7330 resulted in the formation of the corresponding (S)-2-hydroxy compounds in high enantiomeric excesses (93–99%) and good isolated yields (58–71%). The absolute configuration of enantiomerically pure ethyl 2-hydroxy-4-(p-methylphenyl)but-3-enoate obtained by the reduction of the corresponding keto ester was assigned by 1H NMR using Mosher’s method. 相似文献
545.
Gourishankar A Shukla S Ganesh KN Sastry M 《Journal of the American Chemical Society》2004,126(41):13186-13187
An isothermal titration calorimetric (ITC) investigation of the interaction of DNA bases and PNA base monomers with gold nanoparticles is described revealing a binding sequence in the order C > G > A > T. Direct measurement of the strength of interaction of ligands with nanogold by ITC has important implications in surface modification strategies for biomedical, catalysis, and nanoarchitecture applications. 相似文献
546.
Two tetrapeptide derivatives [peptide A (Boc–Ala–Ile–Ile–Gly–OMe) and peptide B (Boc–Ala–Ile–Leu–Ser–OMe)], that take helical turn conformation in solution, were shown to form monolayer at the air/water interface. Circular dichroism (CD) measurements indicate that peptide A has more helical turn propensity than peptide B in sodium dodecyl sulphate (SDS) micelles. Langmuir–Blodgget film study of peptides A and B suggest that both the peptides form stable monolayer at the air/water interface. Spectroscopic investigations reveal that peptide A forms helical turn assemblage on transferring the film into hydrophilic quartz and hydrophobic ZnSe surfaces. Whereas, peptide B adopts β-sheet structure on hydrophilic surface and a mixture of β-sheet and helical turn conformation on hydrophobic surface. 相似文献
547.
Vaidya Vikas V. Menon Sasikumar N. Singh Ganesh R. Kekare Maharudra B. Choukekar Milind P. 《平面色谱法杂志一现代薄层色谱法》2007,20(2):145-147
JPC – Journal of Planar Chromatography – Modern TLC - An HPTLC method for simultaneous determination of clotrimazole and tinidazole in a pharmaceutical formulation has been developed... 相似文献
548.
Kita Y Futamura J Ohba Y Sawama Y Ganesh JK Fujioka H 《The Journal of organic chemistry》2003,68(15):5917-5924
The Lewis acid treatment of 2,3-epoxysulfonates with 2,3-dialkyl substituents or 2-alkyl-3-aryl substituents produced the rearrangement products via C3-cleavage of the oxirane ring in high yields. On the other hand, 2-aryl-3-alkyl-2,3-epoxysulfonates produced the products via C2-cleavage of the oxirane ring. The sulfonyloxy groups of the alpha-sulfonyloxy ketones, having a chiral benzylic quaternary carbon center obtained by the rearrangement of 2-alkyl-3-aryl-2,3-epoxysulfonates, were reductively eliminated to give the ketones with a chiral benzylic quaternary carbon center. The method was applied to the formal synthesis of (-)-aphanorphine and total syntheses of (-)-alpha-herbertenol and (-)-herbertenediol. 相似文献
549.
Ganesh S. Jadhav Ashok R. Patel Pradeep R. Vavia Alpeshkumar K. Malde Evans C. Coutinho 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):261-273
This study aimed to investigate the effect of β-cyclodextrin on aqueous solubility and dissolution rate of valdecoxib and also to get an insight of molecular interactions involved in formation of valdecoxib‐β-cyclodextrin inclusion complex. Phase solubility analysis indicated complex with possible stoichiometry of 1:1 and a stability constant of 234.01 M−1. Thermodynamic studies in water indicated exothermic nature of inclusion complexation.␣Valdecoxib‐β-cyclodextrin complexes (1:1 M) were prepared by kneading method, solution method and␣freeze–drying method. The complex was characterized by differential scanning calorimetry (DSC), powder X-ray diffractometry (P-XRD), Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance␣(1H-NMR) spectroscopy. Molecular modeling was used to help establish the mode of interaction of β-cyclodextrin with valdecoxib. 1H-NMR analysis suggested that the unsubstituted phenyl ring of valdecoxib display favorable interaction with the hydrophobic cavity of β-cyclodextrin, which was confirmed by molecular dynamic simulations. An inclusion complex model has been established for explaining the observed enhancement of solubility of valdecoxib in water by β-cyclodextrin. Dissolution studies in water showed that the valdecoxib in freeze-dried complex dissolved much faster than the uncomplexed drug and physical mixture. This improvement in dissolution rate is attributed to the increased solubility and wettability due to encapsulation along with decreased crystallanity caused by complex formation, which is evident by DSC and P-XRD studies. 相似文献
550.
Spyros P. Nikas Ganesh A. Thakur Shakiru O. Alapafuja Alexandros Makriyannis 《Tetrahedron》2007,63(34):8112-8123
The availability of tetrahydrocannabinols (Δ9-THC), tetrahydrocannabivarins (Δ9-THCV), and their metabolites in both their undeuterated and deuterated forms is critical for the analysis of biological and toxicological samples. We report here a concise methodology for the syntheses of (−)-Δ9-THC and (−)-Δ9-THCV metabolites in significantly improved overall yields using commercially available starting materials. Our approach allowed us to obtain the key intermediates (6aR,10aR)-9-nor-9-oxo-hexahydrocannabinols in four steps from (+)-(1R)-nopinone. This was followed by an optimized Shapiro reaction to give the (−)-11-nor-9-carboxy-metabolites, which were converted to their respective (−)-11-hydroxy analogs. The synthetic sequence involves a minimum number of steps, avoids undesirable oxidative conditions, and incorporates the costly deuterated resorcinols near the end of the synthetic sequence. This methodology enabled us to synthesize eight regiospecifically deuterated (−)-Δ9-THC and (−)-Δ9-THCV metabolites in a preparative scale and high optical purity without deuterium scrambling or loss. 相似文献