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81.
82.
E. Roy A. Diller Alia P. Gast H. J. van Gorkom H. J. M. de Groot G. Jeschke J. Matysik 《Applied magnetic resonance》2007,31(1-2):193-204
Photochemically induced dynamic nuclear polarization is observed in the two photosynthetic reaction centers of plants, photosystem I (PSI) and photosystem II (PSII) by13C magic-angle spinning nuclear magnetic resonance (NMR) at three different magnetic fields 17.6, 9.4, and 4.7 T. There is a significant difference in field dependence detected in the light-induced signal pattern of the two photosystems. For PSII the optimal NMR enhancement factor of about 5000 is observed at 4.7 T. On the other hand, the maximal light-induced signals of PSI are observed at 9.4 T. 相似文献
83.
The adsorption of indole melanin at the d.m.e. causes depression of the oxygen polarographic maximum. The linear course of the dependence of log Δh versus log c makes it possible to employ this effect in the determination of melanin in the absence of other surface-active compounds. 相似文献
84.
85.
Summary To characterize the retention and selectivity of separations of 23 flavonoids (aglycones and glycosides) relationships betweenR
F and modifier concentration were determined for silica and diol adsorbents (with mixtures of ethyl acetate and methanol as
mobile phases), for cyanopropyl silica (with mixtures of ethyl acetate and dichloromethane as mobile phases), for aminopropyl
silica (with mixtures of ethyl acetate, methanol and water as mobile phases) and for octadecyl silica (with mixtures of methanol
and water as mobile phases). Owing to large polarity differences between aglycones and glycosides, these groups of compounds
cannot be separated other than by use of reversed-phase systems, for which the selectivity is lower. It follows from correlation
plots ofR
F1 againstR
F2 that for some pairs of adsorbents (e. g. silica and diol) selectivity differences are small; for others the points in the
plot are widely dispersed, indicating selectivity differences. The chemometric database obtained can be used to choose optimum
chromatographic systems for the separation of given sets of flavonoids and for planning gradient elution programs for separation
of flavonoid aglycones and glycosides in a single TLC experiment. 相似文献
86.
Katarzyna Dziubinska-Kühn Marion Pupier Prof. Dr. Jörg Matysik Dr. Jasmine Viger-Gravel Dr. Beatrice Karg Dr. Magdalena Kowalska 《Chemphyschem》2022,23(10):e202100806
Over the last few years, Deep Eutectic Solvents have gained popularity as a novel class of green solvents, due to their feasible synthesis and overall low production costs. The properties of glycerol (Gly)-based Deep Eutectic Solvents are frequently associated with the formation of an extended hydrogen bond network. In this study, two-dimensional Nuclear Magnetic Resonance (NMR) spectroscopy is employed to analyse the effect of glycerol oversaturation of the hydrogen bond acceptor, choline chloride (ChCl) on the structural arrangement of glyceline (molar ratio 1 : 2 ChCl:Gly), selected to represent Gly-based Deep Eutectic Solvents. The rearrangement of glycerol molecules, additionally trapping water molecules inside of isolated clusters, is revealed during a time-resolved analysis, performed in the presence of various fractions of water added to solvent. 200 % oversaturated Deep Eutectic Solvent (1 : 4 ChCl:Gly) is found to be a suitable cryoprotectant candidate, based on the revealed glycerol-water interactions. 相似文献
87.
Peter Coburger Pavlo Bielytskyi Darcy Williamson Dr. Evgeny Rys Dr. Anika Kreienbrink Dr. Peter Lönnecke Prof. Dr. Jörg Matysik Prof. Dr. Evamarie Hey-Hawkins 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(49):11456-11465
Deboronation of a carborane-substituted diphosphetane 2 in toluene yielded the first nido-carboranyldiphosphetane 1 . The P−P bond in 1 can be broken via dismutation reactions with diaryl dichalcogenides yielding nido-carboranyl bis-phosphanes that were not accessible via established synthetic protocols. Additionally, transition metal complexes of 1 could be isolated including one coordination polymer. Notably, when the deboronation of 2 is carried out in ethanol, unprecedented nido-carborane-substituted secondary bis-phosphane monoxides ( 3 , 4 ) are obtained. These compounds are interesting starting materials for further reactivity studies due to their P−H bonds. Experimental findings are supported by DFT calculations including the calculation of reaction mechanisms and NMR spectroscopic parameters. 相似文献
88.
Thamarath SS Bode BE Prakash S Sai Sankar Gupta KB Alia A Jeschke G Matysik J 《Journal of the American Chemical Society》2012,134(13):5921-5930
Photo-CIDNP (photochemically induced dynamic nuclear polarization) can be observed in frozen and quinone-blocked photosynthetic reaction centers (RCs) as modification of magic-angle spinning (MAS) NMR signal intensity under illumination. Studying the carotenoidless mutant strain R26 of Rhodobacter sphaeroides, we demonstrate by experiment and theory that contributions to the nuclear spin polarization from the three-spin mixing and differential decay mechanism can be separated from polarization generated by the radical pair mechanism, which is partially maintained due to differential relaxation (DR) in the singlet and triplet branch. At a magnetic field of 1.4 T, the latter contribution leads to dramatic signal enhancement of about 80,000 and dominates over the two other mechanisms. The DR mechanism encodes information on the spin density distribution in the donor triplet state. Relative peak intensities in the photo-CIDNP spectra provide a critical test for triplet spin densities computed for different model chemistries and conformations. The unpaired electrons are distributed almost evenly over the two moieties of the special pair of bacteriochlorophylls, with only slight excess in the L branch. 相似文献
89.
We present an experimental approach to conducting fast capillary electrophoresis-mass spectrometry (CE-MS) measurements of very small samples in the nanoliter range. This is achieved by injecting sample very efficiently into a CE-MS system. Injection efficiency represents the ratio of injected sample to the amount of sample needed for carrying out the injection process (v/v). In order to increase this injection efficiency from typical values of 10(-3) to 10(-7), the concept of capillary batch injection is used to build an automated, small-footprint injection device for CE-MS. This device is capable of running true multi-sample measurement series, using minimal sample volumes and delivering an injection efficiency of up to 100?%. It is compatible with both aqueous and non-aqueous background electrolytes. As an additional benefit, CE-MS separations of a catecholamine model system in capillaries of 15?cm length under conditions of high electric field strength could be accomplished in 20?s with high separation efficiency. This report details design and specifications of the injection device and shows optimal parameter choices for injections with both high injection efficiency and high separation efficiency. Furthermore, a procedure is presented to coat the tip of a fused silica capillary with a silicone elastomer which acts as a seal between two capillaries. 相似文献
90.
Hunger B. Matysik S. Heuchel M. Einicke W.-D. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):1183-1190
Using temperature-programmed desorption (TPD), we have investigated the desorption behavior after subsequent co-adsorption
of methanol and water and after adsorption of their mixtures on a NaZSM-5 zeolite. The course of desorption indicates that
a strong mutual displacement of both components occurs. However, on the strongest adsorption sites methanol is preferentially
adsorbed, and already the addition of small amounts of methanol leads to a displacement of water. Our results support the
idea of a subdivision of the pore space for adsorption of water/methanol mixtures. Above all, the experiments show that in
the part of the pore space where both components are adsorbed, different sites are of importance which vary significantly
in their interaction strength.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献