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排序方式: 共有42条查询结果,搜索用时 109 毫秒
1.
Rizwan Ahmad Niyaz Ahmad Fatimah AlOthman Haya Mohammad Fatimah AlZahrani 《Biomedical chromatography : BMC》2020,34(1):e4712
Coffee and tea are the most widely consumed beverages worldwide. However, the consumer may be unaware of the exact amount of methyl xanthine (MX, i.e. caffeine [C], theobromine [TB] and theophylline [TH]) consumed, as most of the products do not list the proper amounts. This may lead to serious risks including cardiovascular, kidney and stimulant effects. The aim of the study was to determine the MX amount in ready-to-use beverages (coffee and tea) collected from various outlets in the city of Al-Khobar, Saudi Arabia. Forty different samples of espresso, black coffee and red tea were collected. A fast, reliable and efficient UHPLC–DAD method was developed and validated for MX determination. Total lipids were extracted and fractionated in order to determine glycolipids, phospholipids and neutral lipids. The r2 value for the method was 0.980–0.988 in a linearity range of 0.5–200 ppm. The range for MX (C [0.02–2.39 mg/ml], TB [0.00–0.10 mg/ml] and TH [0.00–0.004 mg/ml]) and total lipids was 1–5 g. The amount of glycolipids (3.1 g) was higher among the lipid fractions followed by phospholipids (1.8 g) and neutral lipids (0.25 g). In general, espresso beverages (20–30 ml) contained high amounts of MX whereas black coffee beverages contained high amount of lipids. Most of the beverages expressed C, TB, TH, lipids or their fractions; however, the product with high amounts of MX and lipids at the same time was espresso (brands Chemistry and Wogard). Although the MX and lipid levels in these beverages well below the allowed limits, care must still be taken, especially when using the beverages with high serving volumes (200–250 ml) or coffee prepared via the filter method i.e. black coffee, using a high temperature for a longer time. 相似文献
2.
A three-dimensional quasiclassical trajectory study of the dynamics of the light atom transfer reaction O(3P) + HCl(ν=0)→ OH + Cl was carried out employing two LEPS potential energy surfaces (I and II). Attention was focused mainly on three-dynamical properties; the oscillatory behavior of partial cross sections as a function of collision energy; the rotational excitation of the products; and the influence of reagent rotation on reactivity. Distinct differences were found between surfaces I and II with respect to these properties. The examination of individual trajectories indicated that there is a significant difference in the nature of these surfaces. While surface I is governed by weak repulsive forces, surface II is governed by strong attractive forces which tend to direct the reactants toward a collinear geometry. The present results confirm conclusions reached from an earlier study of the reaction Cl+HCl→ClH+Cl concerning correlations between dynamical properties and features of potential energy surfaces. For surfaces of the type that we termed HREP, since they are of repulsive nature and they lead to highly rotationally excited products, no significant oscillations of partial cross sections are obtained and reagent rotation promotes the reaction. On the other hand, for surfaces of the type that we termed COLD (collinearly directing), since they tend to direct the reactants toward a collinear geometry and form rotationally “cold” products, significant oscillations of partial cross sections are obtained and reagent rotation causes a decline in reactivity. 相似文献
3.
Moshe Kaspi 《The Journal of the Operational Research Society》1991,42(2):165-168
This paper deals with the problem of determining the economic operating policy for inventory items which are manufactured jointly but packaged individually. The proposed new approach is very simple and efficient. An extensive simulation study is presented so that the results of several heuristics (based on a wide range of data, measuring the number of optimal solutions, average error and maximum error) can be compared. 相似文献
4.
The lowest excited nπ* triplet of 9.10-anthraquinone, 1.4-naphthoquinone and 1,4-benzoquinone were studied in glassy matrices at 77 K using a time-resolved ESR method. The D value of the triplet state of 9,10-anthraquinone varied from ?0.351 cm?1 in a polar solvent to ?0.318 cm?1 in a non-polar solvent. Both 1,4-naphthoquinone and 1,4-benzoquinone in polar solvents showed triplet state spectra with a D value of ?0.330 cm?1. A computer simulation revealed the existence of widely distributed zero-field splitting parameters in the glassy condition. These data are compared with an analysis of CIDEP results of para-quinones. 相似文献
5.
Bond angles of several free radicals have been estimated using the point charge model together with ESR data and compared with those derived by Coulson's equation and the INDO method. The model is found to work well in predicting bond angles for most radicals just like the INDO method. Some relationships between the model and the INDO method are discussed. 相似文献
6.
Basil Raju Karimadom Dr. Shalaka Varshney Dr. Tomer Zidki Prof. Dr. Dan Meyerstein Prof. Dr. Haya Kornweitz 《Chemphyschem》2022,23(13):e202200069
The mechanism of the catalytic hydrolysis of BH4− on Au(111) as studied by DFT is reported. The results are compared to the analogous process on Ag(111) that was recently reported. It is found that the borohydride species are adsorbed stronger on the Au0-NP surface than on the Ag0-NP surface. The electron affinity of the Au is larger than that of Ag. The results indicate that only two steps of hydrolysis are happening on the Au(111) surface and the reaction mechanism differs significantly from that on the Ag(111) surface. These remarkable results were experimentally verified. Upon hydrolysis, only three hydrogens of BH4− are transferred to the Au surface, not all four, and H2 generation is enhanced in the presence of surface H atoms. Thus, it is proposed that the BH4− hydrolysis and reduction mechanisms catalyzed by M0-NPs depend considerably on the nature of the metal. 相似文献
7.
Abdulrahman I. Almansour Natarajan Arumugam Saradh Prasad Raju Suresh Kumar Mohamad S. Alsalhi Manal Fahad Alkaltham Haya bint Abdulaziz Al-Tamimi 《Molecules (Basel, Switzerland)》2022,27(1)
Quinoline Schiff bases display potential applications in optoelectronics and laser fields because of their unique optical properties that arise from extensive delocalization of the electron cloud, and a high order of non-linearity. In this context, a new class of conjugated quinoline-derivative viz. N-(quinolin-3-ylmethylene)anilines were synthesized from 2-hydroxyquinoline-3-carbaldehyde in two good yielding steps. The ability of these imines to accept an electron from a donor is denoted by their electron acceptor number and sites, which is calculated using density functional theory (DFT). The optical properties such as FT-IR, Raman, UV-VIS, and EDS spectra were calculated using TD-DFT, which also provided the energy gap, HOMO-LUMO structure. The optical properties of the synthesized imino quinolines were experimentally studied using photoluminescence and absorption spectroscopy. The properties such as Stokes shift and quantum yield were calculated using experimental data. Furthermore, the compound bearing a methyl group on the aryl ring and ZnO nanoparticles (hydrothermally synthesized) were dissolved in toluene, and optically excited with a 355 nm nanosecond laser, which produced a random laser. 相似文献
8.
Malek M Morii M Fukuda S Fukuda Y Ishitsuka M Itow Y Kajita T Kameda J Kaneyuki K Kobayashi K Koshio Y Miura M Moriyama S Nakahata M Nakayama S Namba T Okada A Ooyabu T Saji C Sakurai N Shiozawa M Suzuki Y Takeuchi H Takeuchi Y Totsuka Y Yamada S Desai S Earl M Kearns E Messier MD Stone JL Sulak LR Walter CW Goldhaber M Barszczak T Casper D Gajewski W Kropp WR Mine S Liu DW Smy MB Sobel HW Vagins MR Gago A Ganezer KS Keig WE Ellsworth RW Tasaka S Kibayashi A Learned JG Matsuno S Takemori D 《Physical review letters》2003,90(6):061101
A search for the relic neutrinos from all past core-collapse supernovae was conducted using 1496 days of data from the Super-Kamiokande detector. This analysis looked for electron-type antineutrinos that had produced a positron with an energy greater than 18 MeV. In the absence of a signal, 90% C.L. upper limits on the total flux were set for several theoretical models; these limits ranged from 20 to 130 macro nu(e) cm(-2) s(-1). Additionally, an upper bound of 1.2 macro nu(e) cm(-2) s(-1) was set for the supernova relic neutrino flux in the energy region E(nu)>19.3 MeV. 相似文献
9.
10.
Cations in a Molecular Funnel: Vibrational Spectroscopy of Isolated Cyclodextrin Complexes with Alkali Metals 总被引:1,自引:0,他引:1
Dr. Francisco Gámez Dr. Paola Hurtado Dr. Ana R. Hortal Prof. Bruno Martínez‐Haya Dr. Giel Berden Prof. Jos Oomens 《Chemphyschem》2013,14(2):400-407
The benchmark inclusion complexes formed by α‐cyclodextrin (αCD) with alkali‐metal cations are investigated under isolated conditions in the gas phase. The relative αCD‐M+ (M=Li+, Na+, K+, Cs+) binding affinities and the structure of the complexes are determined from a combination of mass spectrometry, infrared action spectroscopy and quantum chemical computations. Solvent‐free laser desorption measurements reveal a trend of decreasing stability of the isolated complexes with increasing size of the cation guest. The experimental infrared spectra are qualitatively similar for the complexes with the four cations investigated, and are consistent with the binding of the cation within the primary face of the cyclodextrin, as predicted by the quantum computations (B3LYP/6‐31+G*). The inclusion of the quantum‐chemical cation disrupts the C6 symmetry of the free cyclodextrin to provide the optimum coordination of the cations with the ‐CH2OH groups in C1, C2 or C3 symmetry arrangements that are determined by the size of the cation. 相似文献