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排序方式: 共有140条查询结果,搜索用时 31 毫秒
61.
Adam Huczyński Izabela Paluch Bogumil Brzezinski Franz Bartl 《Tetrahedron letters》2008,49(39):5572-5575
A new method to synthesize novel esters of Lasalocid acid 2-5 and of Monensin A, 7-9 (semi-synthetic di- and tripodands) is described. These new compounds are characterized by spectroscopic and microbiological methods. 相似文献
62.
63.
Bogumil Brzezinski Grzegorz Wojciechowski Hanna Urjasz Georg Zundel 《Journal of Molecular Structure》1998,470(3):827-339
The mono- as well as the di-Mannich bases of 5,5′-dimethoxy-2,2′-biphenol are studied by FT-IR spectroscopy. It is shown that in these bases the protons remain localized at the phenol O atom. This result is in contrast to those obtained earlier for more acidic biphenols in which the protons are not localized but fluctuate and the relevant hydrogen bonds show large polarizability. An intense infrared continuum in the FT-IR spectrum of the mono-protonated di-Mannich base of 5,5′-dimethoxy-2,2′-biphenol demonstrates that the intramolecular hydrogen bond in this compound shows large proton polarizability. 相似文献
64.
Journal of Theoretical Probability - A sum of a large-dimensional random matrix polynomial and a fixed low-rank matrix polynomial is considered. The main assumption is that the resolvent of the... 相似文献
65.
Diego Rodrigo Villafani Caballero Luis Ernesto Ynoquio Herrera Gustavo Castro do Amaral Patryk J. Urban Jean Pierre von der Weid 《Fiber and Integrated Optics》2017,36(1-2):59-67
The combination of subcarrier multiplexing and passive optical networks can provide an efficient and cost-effective solution for fiber and wireless convergence in access networks. Moreover, to reduce operational expenditures, a reliable monitoring technique should provide in-service evaluation of the physical layer. Here, we perform the experimental demonstration of an SCM-PON system with baseband embedded optical time-domain reflectometer monitoring. Different modulation formats were tested to evaluate the penalty generated by the monitoring system. Based on the long-term evolution downlink test model (E-TM 3.1), our results show negligible power penalty while achieving a ~12-dB dynamic range with 10-m spatial resolution. 相似文献
66.
BACKGROUND: Biological silica production has drawn intense attention and several molecules involved in biosilicification have been identified. Cellular mechanisms, however, remain unknown mainly due to the lack of probes required for obtaining information on live specimens. RESULTS: The fluorescence spectra of the compound 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole (PDMPO) are affected by the presence of >3.2 mM silicic acid. Increase in intensity and shift in the fluorescence coincide with the polymerization of Si. The unique PDMPO-silica fluorescence is explored here to visualize Si deposition in living diatoms. The fluorophore is selectively incorporated and co-deposited with Si into the newly synthesized frustules (the outer silica shells) showing an intense green fluorescence. CONCLUSIONS: We suggest that a fluorescence shift is due to an interaction between PDMPO and polymeric silicic acid. PDMPO is an excellent probe for imaging newly deposited silica in living cells and has also a potential for a wide range of applications in various Si-related disciplines, including biology of living organisms as diatoms, sponges, and higher plants, clinical research (e.g. lung fibrosis and cancer, bone development, artificial bone implantation), and chemistry and physics of materials research. 相似文献
67.
A new amide of monensin A with 4-aminobenzo-15-crown-5 (M-AM3) was synthesised and its ability to form complexes with Na+ cations was studied by ESIMS, 1H, 13C and 23Na NMR, FTIR and PM5 semi-empirical methods. ESI mass spectrometry indicates that in the gas phase M-AM3 amide forms complexes of 1:1 and 1:2 stoichiometry with Na+ cations. The formation of such complexes is also confirmed in the acetonitrile solution, in which the existence of equilibrium between two structures A and B is found, of which B structure is dominant. The structures of M-AM3 and its 1:1 and 1:2 complexes with Na+ cations are stabilised by various intramolecular hydrogen bonds, which are discussed in detail. The in vitro biological tests have demonstrated that the new M-AM3 amide shows good activity towards some strains of Gram-positive bacteria (MIC 25-50 μg/ml). 相似文献
68.
Piotr Przybylski Krystian Pyta Joanna Stefańska Bogumil Brzezinski Franz Bartl 《Magnetic resonance in chemistry : MRC》2010,48(4):286-296
Four new hydroxy‐aminoalkyl derivatives of α,β‐unsaturated macrolide‐josamycin (2–5) have been synthesised and their structures have been studied by means of 1H and 13C NMR and FT‐IR methods. Complete assignment of resonances in the 1H and 13C NMR spectra has been made on the basis of 1H? 13C HSQC, 1H? 13C HMBC, 1H? 1H COSY, 1H? 1H NOESY 2D experiments. Spectroscopic data indicated that for the derivatives 3 and 4 some equilibrium between two different structures exists in contrast to derivatives 2 and 5. The lowest‐energy structures of the new derivatives of josamycin have been calculated and visualised by PM5 method at semi‐empirical level of theory, taking into account the NMR and FT‐IR data. The most significant differences between the structures of josamycin and its newly synthesised derivatives' were found in the conformation of the macrolide aglycone part and in the mutual orientation of the 4‐O‐isovalerylmycarosylmycaminose moiety relative to the aglycone part. PM5 semi‐empirical calculations indicated that the structures of the new macrolide derivatives are stabilised by rather weak intramolecular hydrogen bonds in agreement with spectroscopic data. Antimicrobial properties of the new derivatives 2–5 as well as those having an acetate group at C‐3 (6 and 7) were determined and compared to that of the parent macrolide antibiotic josamycin (1). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
69.
Przybylski P Pyta K Czupryniak J Wicher B Gdaniec M Ossowski T Brzezinski B 《Organic & biomolecular chemistry》2010,8(24):5511-5518
Protonation of gossypol Schiff bases (S1 and S2), possessing different numbers of basic N-atoms, was studied using potentiometric, spectroscopic, ESI MS and PM5 methods. Titration of S1 and S2 with HClO(4), monitored by the FT-IR and (1)H NMR, indicated that the change from the enamine-enamine into the protonated imine-imine tautomeric form occurs at different Schiff base-H(+) ratio. The FT-IR and PM5 results show that for S1 the first protonation step occurs at Schiff base moiety whereas for S2 it is realised at N-atom of the morpholine. The formation of N(+)-HO hydrogen bond between morpholine moieties within S2 contributes to high pK(a(ACN)) = 22.65. 相似文献
70.
Patryk Pagacz 《Linear algebra and its applications》2012,436(9):3065-3071