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651.
652.
A portable ultrahigh‐vacuum system for advanced synchrotron radiation studies of thin films and nanostructures: EuSi2 nano‐islands
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Shyjumon Ibrahimkutty Anja Seiler Tim Prüßmann Tonya Vitova Ramu Pradip Olga Bauder Peter Wochner Anton Plech Tilo Baumbach Svetoslav Stankov 《Journal of synchrotron radiation》2015,22(1):91-98
A portable ultrahigh‐vacuum system optimized for in situ variable‐temperature X‐ray scattering and spectroscopy experiments at synchrotron radiation beamlines was constructed and brought into operation at the synchrotron radiation facility ANKA of the Karlsruhe Institute of Technology, Germany. Here the main features of the new instrument are described and its capabilities demonstrated. The surface morphology, structure and stoichiometry of EuSi2 nano‐islands are determined by in situ grazing‐incidence small‐angle X‐ray scattering and X‐ray absorption spectroscopy. A size reduction of about a factor of two of the nano‐islands due to silicide decomposition and Eu desorption is observed after sample annealing at 1270 K for 30 min. 相似文献
653.
Chih‐Hsiang Chiang Dr. Ravirala Ramu Yi‐Jung Tu Chung‐Ling Yang Kok Yaoh Ng Dr. Wen‐I Luo Charles H. Chen Yu‐Ying Lu Prof. Dr. Chen‐Lun Liu Prof. Dr. Steve S.‐F. Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13680-13691
We demonstrate herein that wild‐type cytochrome P450 BM3 can recognize non‐natural substrates, such as fluorinated C12–C15 chain‐length fatty acids, and show better catalysis for their efficient conversion. Although the binding affinities for fluorinated substrates in the P450 BM3 pocket are marginally lower than those for non‐fluorinated substrates, spin‐shift measurements suggest that fluoro substituents at the ω‐position can facilitate rearrangement of the dynamic structure of the bulk‐water network within the hydrophobic pocket through a micro desolvation process to expel the water ligand of the heme iron that is present in the resting state. A lowering of the Michaelis–Menten constant (Km), however, indicates that fluorinated fatty acids are indeed better substrates compared with their non‐fluorinated counterparts. An enhancement of the turnover frequencies (kcat) for electron transfer from NADPH to the heme iron and for C? H bond oxidation by compound I (Cpd I) to yield the product suggests that the activation energies associated with going from the enzyme–substrate (ES state) to the corresponding transition state (ES≠ state) are significantly lowered for both steps in the case of the fluorinated substrates. Delicate control of the regioselectivity by the fluorinated terminal methyl groups of the C12–C15 fatty acids has been noted. Despite the fact that residues Arg47/Tyr51/Ser72 exert significant control over the hydroxylation of the subterminal carbon atoms toward the hydrocarbon tail, the fluorine substituent(s) at the ω‐position affects the regioselective hydroxylation. For substrate hydroxylation, we have found that fluorinated lauric acids probably give a better structural fit for the heme pocket than fluorinated pentadecanoic acid, even though pentadecanoic acid is by far the best substrate among the reported fatty acids. Interestingly, 12‐fluorododecanoic acid, with only one fluorine atom at the terminal methyl group, exhibits a comparable turnover frequency to that of pentadecanoic acid. Thus, fluorination of the terminal methyl group introduces additional interactions of the substrate within the hydrophobic pocket, which influence the electron transfers for both dioxygen activation and the controlled oxidation of aliphatics mediated by high‐valent oxoferryl species. 相似文献
654.
Kondapalli Venkata Gowri Chandra Sekhar Thripuraribhatla Venkata Naga Varuna Tara Sasank Hunsur Nagendra Nagesh Narva Suresh Kalaga Mahalakshmi Naidu Amaroju Suresh 《中国化学快报》2013,24(12):1045-1048
A simple and efficient method has been developed for conversion of chalcone oximes to 3,5-diaryl isoxazoles in excellent yields under solvent-free conditions. The synthesized compounds were characterized by infrared spectroscopy, ^1H NMR, ^13C NMR and HRMS. 相似文献
655.
AbstractVarious spirooxindoles (7a–c, 8a–c, 9a–c, and 10a–c) were efficiently synthesized using deep eutectic solvent ZnCl2+urea and well characterized using IR, 1H NMR, and 13C NMR spectroscopic techniques. The biological screening results showed that the compound 9a exhibited potent anticancer activity against MCF7 and HeLa cell lines with IC50 values 6.47?±?0.01 and 9.14?±?0.32?µM, respectively. The compound 7c exhibited potent activity against the HeLa cell line with IC50 value 6.81?±?0.01?µM. The compound 9a exhibited a potent antioxidant activity with IC50 value 7.34?±?0.17?µM. The comparative molecular docking study against the cancer proteins EGFR and HER2 revealed that the EGFR was the best target protein receptor for the target compounds. Among all the compounds, the compound 9a exhibited the least binding energy ?10.72?kcal/mol against the protein EGFR (PDB ID: 4HJO). 相似文献
656.
Vajrala Venkata Reddy Mandava Venkata Naga Brahmeswara Rao Ghanta Mahesh Reddy Khagga Mukkanti 《合成通讯》2013,43(23):3513-3523
Abstract Vardenafil hydrochloride trihydrate (Levitra) is used to treat erectile dysfunction (ED) and is an inhibitor of phosphodiesterase type 5 (PDE-5) enzyme. It maintains higher levels of cyclic guanosine monophosphate (cGMP), relaxes smooth muscles, promotes penile blood flow, and enhances erectile function. During the bulk drug synthesis of vardenafil hydrochloride trihydrate, six related substances (impurities), vardenafil dimer, vardenafil N-oxide, vardenafil glycene, vardenafil oxopiperazine, vardenafil oxoacetic acid, and phenyl vardenafil were identified, and these are reported herein for the first time. The present work describes the synthesis and characterization of these impurities. 相似文献
657.
An efficient, convenient, and novel one-pot method of 2,4,5-triaryl-1H-imidazoles synthesis using benzil, arene carbaldehydes, and ammonium acetate, catalyzed by uranyl nitrate hexahydrate [UO2(NO3)2·6H2O] supported on acidic alumina and resulting in good to excellent yields under heterogeneous conditions, is reported. Formation
of a reactants-catalyst complex was confirmed by UV-VIS spectral data. Antibacterial (MIC) and antioxidant activity of the
synthesized compounds was also studied. 相似文献
658.
d-ribo-C18-phytosphingosine and l-arabino-C18-phytosphingosine were synthesised starting from commercially inexpensive d-fructose. Metal-mediated fragmentation and stereoselective reduction were used as key steps to provide the hydrophilic portion of d-ribo and l-arabino phytosphingosines. Grubbs’ cross-metathesis and hydrogenation allowed the incorporation of hydrophobic tail. 相似文献
659.
An efficient method for the stereoselective synthesis of l-ribose was accomplished starting from commercially inexpensive d-fructose. The intermediates in the process can serve as versatile precursors for the preparation of l-nucleoside analogues. 相似文献
660.
A 1,4 O→O silyl migration followed by nucleophilic substitution with phthalimide was observed under Mitsunobu reaction conditions. This one step secondary alcohol protection and primary alcohol substitution with N-nucleophiles was extended to a variety of 2-hydroxyethyl trialkylsilylether derivatives. A possible mechanism has been postulated based on the pKa values of the alcohol and nucleophile. The present one-pot silyl migration and substitution reaction might find application in the stereoselective synthesis of novel iminosugar derived anti diabetic agents. 相似文献