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61.
In this study we investigated the reductive azo cleavage of an azo compound presenting a pyrene fluorophore (Azo-py). Because of dramatic changes in its fluorescence, Azo-py could be used as a monitoring system for the reductive azo cleavage. Electron transfer from the pyrene unit to the azo moiety induced fluorescence quenching; this quenched fluorescence was recovered after the reductive azo cleavage. IR and NMR spectroscopy were used to study the various structural states. The rate of reductive cleavage of the azo compound, determined through fluorescence monitoring, depended on its structural state: the cleavage of trans-Azo-py was much faster than that of the cis-Azo-py. Furthermore, the Azo-py fluorophore was highly sensitive to the presence of zinc, but not other metal compounds, and the pH. 相似文献
62.
Dr. Man Li Dr. Amparo Sanz-Marco Dr. Samuel Martinez-Erro Víctor García-Vázquez Dr. Binh Khanh Mai Dr. Jacob Fernández-Gallardo Prof. Dr. Fahmi Himo Prof. Dr. Belén Martín-Matute 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14978-14986
We have used experimental studies and DFT calculations to investigate the IrIII-catalyzed isomerization of allylic alcohols into carbonyl compounds, and the regiospecific isomerization–chlorination of allylic alcohols into α-chlorinated carbonyl compounds. The mechanism involves a hydride elimination followed by a migratory insertion step that may take place at Cβ but also at Cα with a small energy-barrier difference of 1.8 kcal mol−1. After a protonation step, calculations show that the final tautomerization can take place both at the Ir center and outside the catalytic cycle. For the isomerization–chlorination reaction, calculations show that the chlorination step takes place outside the cycle with an energy barrier much lower than that for the tautomerization to yield the saturated ketone. All the energies in the proposed mechanism are plausible, and the cycle accounts for the experimental observations. 相似文献
63.
Quan do P Tuyen do P Lam TD Tram PT Binh NH Viet PH 《Colloids and surfaces. B, Biointerfaces》2011,88(2):764-770
A voltammetric method based on a combination of incorporated Nafion, single-walled carbon nanotubes and poly(3-methylthiophene) film-modified glassy carbon electrode (NF/SWCNT/PMT/GCE) has been successfully developed for selective determination of dopamine (DA) in the ternary mixture of dopamine, ascorbic acid (AA) and uric acid (UA) in 0.1M phosphate buffer solution (PBS) pH 4. It was shown that to detect DA from binary DA-AA mixture, the use of NF/PMT/GCE was sufficient, but to detect DA from ternary DA-AA-UA mixture NF/SWCNT/PMT/GCE was required. The later modified electrode exhibits superior electrocatalytic activity towards AA, DA and UA thanks to synergic effect of NF/SWCNT (combining unique properties of SWCNT such as high specific surface area, electrocatalytic and adsorptive properties, with the cation selectivity of NF). On the surface of NF/SWCNT/PMT/GCE AA, DA, UA were oxidized respectively at distinguishable potentials of 0.15, 0.37 and 0.53 V (vs. Ag/AgCl), to form well-defined and sharp peaks, making possible simultaneous determination of each compound. Also, it has several advantages, such as simple preparation method, high sensitivity, low detection limit and excellent reproducibility. Thus, the proposed NF/SWCNT/PMT/GCE could be advantageously employed for the determination of DA in real pharmaceutical formulations. 相似文献
64.
Neubauer S Rugova A Chu DB Drexler H Ganner A Sauer M Mattanovich D Hann S Koellensperger G 《Analytical and bioanalytical chemistry》2012,404(3):799-808
In this work, accurate MS-based methods for quantitative profiling of nucleotides, nucleosides, and nucleobases in yeast extracts used as additives in animal feedstuff are presented. Reversed-phase chromatography utilizing a stationary phase compatible with 100% aqueous mobile phases resulted in superior analytical figures of merit than HILIC or ion-pair reversed-phase separation. The novel separation method was combined with both molecular and elemental mass spectrometry. By use of RP-LC-MS-MS, excellent limits of detection <1 μmol L(-1) could be obtained for all the compounds investigated. The elemental speciation analysis approach enabled determination of nucleotides by phosphorus detection. Sensitivity of LC-ICP-MS was 1-2 orders of magnitude lower than that of LC-MS-MS. Quantitative analysis of yeast products using complementary MS detection furnished values in good agreement. 相似文献
65.
Le Nguyen Binh 《Optics Communications》2008,281(17):4245-4253
We present the multi-amplitude level minimum shift keying (M-ary MSK) modulation scheme for long haul optically amplified transmission systems. New configurations of optical M-ary MSK transmitters using two cascaded electro-optic phase modulators are proposed and its detailed operation principles are expressed. The optical receiver for optical multi-amplitude MSK modulation format requires both amplitude direct-detection and differential phase balanced-detection. Numerical results on spectral characteristics, dispersion tolerance and the relationship between amplitude and phase with launched average power for long-haul transmission of multi-level MSK modulation format are presented. The dispersion tolerance shows that the 2-amplitude MSK at 80 Gb/s is well compared with 40 Gb/s binary MSK modulation format. 相似文献
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67.
Vo Anh Thi Tran Nghiep Dai Van Trinh Giap Tran Diep Bang Van Nguyen Binh 《Journal of Radioanalytical and Nuclear Chemistry》2018,317(1):381-385
Journal of Radioanalytical and Nuclear Chemistry - The polyvinyl alcohol (PVA) films dyed methylene blue containing different masses of boric acid and PVA powder were investigated. The dyed PVA... 相似文献
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The diastereoselectivity of intramolecular 1,3-dipolar cycloadditions of 2-substituted 5-hexenyl and 5-heptenyl nitrones to give 6-substituted and 3,6-disubstituted perhydrocyclopenta[c]isoxazoles has been investigated. An alkyl or aryl substituent at C2 completely controls the stereochemistry of the ring juncture and, in the case of the 5-heptenyl systems, also the stereochemistry of the 3-methyl group. Thus one stereocenter controls the formation of the other three to give a product with four contiguous stereocenters. The use of an ethylene ketal substituent in these systems allows the reaction to be carried out at much lower temperatures, an example of the gem-dialkoxy effect. This cycloaddition process has been used in an efficient formal total synthesis of the potent beta-lactam antibiotic, 1beta-methylthienamycin. 相似文献