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排序方式: 共有398条查询结果,搜索用时 46 毫秒
51.
Rajendran Murugan Murugesan Karthikeyan Paramasivam T. Perumal Boreddy S.R. Reddy 《Tetrahedron》2005,61(52):12275-12281
Efficient electrophilic substitution reactions of indoles with various aldehydes proceed smoothly in acetonitrile using heteropoly acid (H4[Si(W3O10)3]) to afford the corresponding new indolyl crown ethers and di(indolyl)pyrazolyl methanes. H4[Si(W3O10)3] is also found to catalyze the Michael addition of indoles to ,β-unsaturated compounds for the synthesis of 3-alkylated indoles. 相似文献
52.
Subramanian Vedhanarayanan Karthikeyan 《Tetrahedron letters》2007,48(13):2261-2265
A series of new 3-benzyl-1,10-diaryl-4H,10H-thieno[3,4-c][1,5]benzothiazepines has been synthesised regioselectively from the reaction of 5-aryl-2,4-bis(arylmethylidene)dihydro-3-thiophenones with o-aminothiophenol in the presence of acetic acid. This transformation presumably occurs via a tandem Michael addition-condensation-isomerisation sequence. 相似文献
53.
Aldrich CC Venkatraman L Sherman DH Fecik RA 《Journal of the American Chemical Society》2005,127(25):8910-8911
The polyketide synthase-derived pikromycin thioesterase (Pik TE) is unique in its ability to catalyze the cyclization of 12- and 14-membered macrolactones. In this investigation, the total synthesis of the natural hexaketide chain elongation intermediate as its N-acetyl cysteamine (NAC) thioester has been achieved, and its reaction with Pik TE demonstrated the ability of Pik TE to catalyze its macrolactonization to the natural product 10-deoxymethynolide. A steady-state kinetic analysis of the hexaketide chain intermediate with Pik TE was done. A preliminary substrate specificity study with unnatural hexaketide analogues was accomplished, demonstrating the importance of total synthesis in obtaining access to advanced polyketide intermediates. The results show the sensitivity of Pik TE to minor substrate modifications, and illustrate the potential use of thioesterases as versatile macrolactonization catalysts. 相似文献
54.
Shailaja J Kaanumalle LS Sivasubramanian K Natarajan A Ponchot KJ Pradhan A Ramamurthy V 《Organic & biomolecular chemistry》2006,4(8):1561-1571
Photochemistry of 17 aryl alkyl ketones included within cation exchanged zeolites has been examined. In solution five of the 17 ketones undergo intramolecular hydrogen abstraction reaction even in the presence of a chiral amine and the rest are photoreduced to the corresponding alcohol. Within zeolites all 17 ketones yielded in presence of a chiral amine, the corresponding alcohol as the major product. When a chiral amine was used as the coadsorbent within alkali ion exchanged zeolites, enantiomerically enriched alcohol was formed in all cases. The best chiral induction was obtained with phenyl cyclohexyl ketone (enantiomeric excess: 68%). 1H-13C Cross Polarization Magic Angle Spinning (CP-MAS) experiments, with a model ketone (perdeuterated acetophenone) and chiral amine (pseudoephedrine) included within MY zeolites, suggested that the cation brings the reactant and the chiral amine closer. The role of the cation in such a process is also revealed by the computation results. The results presented here highlight the importance of a supramolecular structure in forcing a closer interaction between a reactant and a chiral inductor that could be used to achieve asymmetric induction in photoproducts. 相似文献
55.
Karthikeyan M Krishnan S Pandey AK Bender A 《Journal of chemical information and modeling》2006,46(2):452-461
The Internet is a comprehensive resource of chemical information which is at the same time largely unstructured. It provides a wealth of scientific information such as experimental data and requires a suitable automated data mining and analysis tool for its meaningful exploration. The Java based software presented here, ChemXtreme, is developed for harvesting chemical information from the Internet employing the Google API in combination with a distributed client/server text analysis architecture based on JavaRMI. It represents the first and until now the only toolkit for automated structured data retrieval from the Internet which is itself open source. ChemXtreme employs the "search the search engine" strategy, where the URLs returned from the search engine are analyzed further via textual pattern analysis. This process resembles the manual analysis of the hit list, where relevant data are captured and, by means of human intervention, are mined into a format suitable for further analysis. ChemXtreme on the other hand transforms chemical information automatically into a structured format suitable for storage in databases and further analysis and also provides links to the original information source. The query data retrieved from the search engine by the server is encoded, encrypted, and compressed and then sent to all the participating active clients in the network for parsing. Relevant information identified by the clients on the retrieved Web sites is sent back to the server, verified, and added to the database for data mining and further analysis. The distributed further analysis of URLs in a client/server architecture scales very favorably, thus producing only minimal overhead. 相似文献
56.
Neha Gupta Saurav Kumar Choudhary Neeta Bhagat Muthusamy Karthikeyan Archana Chaturvedi 《Molecules (Basel, Switzerland)》2021,26(14)
The binding of heat stable enterotoxin (STa) secreted by enterotoxigenic Escherichia coli (ETEC) to the extracellular domain of guanylyl cyclase c (ECDGC-C) causes activation of a signaling cascade, which ultimately results in watery diarrhea. We carried out this study with the objective of finding ligands that would interfere with the binding of STa on ECDGC-C. With this view in mind, we tested the biological activity of a alkaloid rich fraction of Holarrhena pubescens against ETEC under in vitro conditions. Since this fraction showed significant antibacterial activity against ETEC, we decided to test the screen binding affinity of nine compounds of steroidal alkaloid type from Holarrhena pubescens against extracellular domain (ECD) by molecular docking and identified three compounds with significant binding energy. Molecular dynamics simulations were performed for all the three lead compounds to establish the stability of their interaction with the target protein. Pharmacokinetics and toxicity profiling of these leads demonstrated that they possessed good drug-like properties. Furthermore, the ability of these leads to inhibit the binding of STa to ECD was evaluated. This was first done by identifying amino acid residues of ECDGC-C binding to STa by protein–protein docking. The results were matched with our molecular docking results. We report here that holadysenterine, one of the lead compounds that showed a strong affinity for the amino acid residues on ECDGC-C, also binds to STa. This suggests that holadysenterine has the potential to inhibit binding of STa on ECD and can be considered for future study, involving its validation through in vitro assays and animal model studies. 相似文献
57.
A facile sonochemical route for the synthesis of graphene nanosheets via reduction of graphene oxide (GO) has been reported. The synthesized graphene sheets are characterized using UV–vis spectra, Fourier transform infra-red (FT-IR) spectra, transmission electron microscope, X-ray photoelectron spectra (XPS) and Raman spectroscopic techniques. The UV–vis spectroscopy results showed that the absorption peak was red shifted due to the reduction of GO into graphene. FT-IR and XPS spectra revealed the removal of oxygenated functional groups in graphene after the reduction process. Raman spectra confirmed the restoration of new sp2 carbon domains in graphene sheets after the reduction. The sonochemical approach for the synthesis of graphene nanosheets is relatively fast, cost-effective and efficient as compared to other methods. 相似文献
58.
B. Karthikeyan M. Anija T.M. Muhammad Nadeer Reji Philip 《Optics Communications》2008,281(10):2933-2937
Copper nanocomposite glasses have been prepared by the ion-exchange method, and annealed at different temperatures up to and above the glass softening temperature. The absorption spectra, fluorescence spectra, and nonlinear optical transmission of the samples at 532 nm for nanosecond laser pulses, have been investigated. The optical and nonlinear optical properties of the glasses are found to be distinctly different below and above the glass softening temperature. For instance, thermal annealing up to the glass softening temperature makes the samples behave like saturable absorbers, while annealing at higher temperatures makes them behave like optical limiters. Such flexibility in controlling the optical nonlinearity in these materials makes them potential candidates for photonic applications. 相似文献
59.
Jayapriya M. Premkumar K. Arulmozhi M. Karthikeyan K. 《Research on Chemical Intermediates》2020,46(3):1771-1788
Research on Chemical Intermediates - The present research work explores an environmental benign, lucrative approach for the synthesis of cauliflower-like Ag/MgO nanocomposite using Musa paradisiaca... 相似文献
60.
V. Bharathi M. Sivakumar R. Udayabhaskar Hiromichi Takebe B. Karthikeyan 《Applied Physics A: Materials Science & Processing》2014,116(1):395-401
We studied structural, optical and vibrational properties of K-doped ZnO nanostructures. X-ray diffraction studies reveal that the prepared particles are hexagonal wurtzite in structure. Increase in lattice parameters and unit cell volume is observed after K doping. Dopant influences on stress, strain of the system are studied using W–H plots. Band gap variation by doping of K is identified from optical absorption studies. Photoluminescence studies have given insight into the enhancement in blue emission observed by K doping along with the near band emission of nano ZnO. From Fourier transform infrared spectral measurements, K-related local vibration mode is observed along with the information related to influence of doping on characteristic vibrational modes of ZnO. 相似文献