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41.
We have devised an expeditious, efficient, asymmetric synthesis of the C(33) – C(37) fragment of amphotericin B that proceeds in 14 steps and 16% overall yield from tiglic aldehyde ((E)‐2‐methylbut‐2‐enal) with complete stereocontrol. The route described herein relies on the application of recently developed methods in catalytic asymmetric synthesis for stereocontrol through enantio‐ and diastereoselective functionalization of a substituted sorbate derivative. 相似文献
42.
Gaowa Naren Wera Larsson Carlos Benitez-Martin Shiming Li Ezequiel Prez-Inestrosa Bo Albinsson Joakim Andrasson 《Chemical science》2021,12(20):7073
A water soluble diarylethene (DAE) derivative that displays exceptionally intense fluorescence from the colorless open form has been synthesized and characterized using UV/vis spectroscopy and fluorescence microscopy. We show that the bright emission from the open form can be rapidly switched using amplitude modulated red light, that is, by light at wavelengths longer than those absorbed by the fluorescent species. This is highly appealing in any context where undesired background fluorescence disturbs the measurement, e.g., the autofluorescence commonly observed in fluorescence microscopy. We show that this scheme is conveniently applicable using lock-in detection, and that robust amplitude modulation of the probe fluorescence is indeed possible also in cell studies using fluorescence microscopy.A water soluble diarylethene derivative displaying exceptionally bright fluorescence in the open isomeric form has been used for emission amplitude-modulation. We apply this scheme in fluorescence microscopy, aiming to suppress undesired background. 相似文献
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Dan Haupt Curt Pettersson Douglas Westerlund 《Fresenius' Journal of Analytical Chemistry》1995,352(7-8):705-711
A three-factor central composite face design (CCF) has been used for the optimization of the chiral resolution of the enantiomers of alprenolol, oxprenolol, trimipramine and propranolol on CHIRAL-AGP. The variables (factors) investigated were pH and concentrations of the micellar agent Tween® 20 and heptanoic acid. The responses evaluated were resolution (RS), capacity factor (k) of the last eluted enantiomer and a chromatographic response function (CRF) defined as CRF = P5/log tret, where P is the peak-valley ratio according to Kaiser and tret is the retention time. The computed models, one for each substance and one for each response (in total 12 models), showed that the main factor for the regulation of RS as well as k and CRF in the experimental domain is the pH. The optimal pH for the substances could be found between pH 5.5 and 6.5. The optimum was evaluated by generating contour plots for the CRF models. The computed mathematical models were statistically evaluated and the predictive power of the models was tested by experimentation.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday 相似文献
45.
Summary A new restricted access media (RAM) type of precolumn, Bio Trap 500 C18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins
in different mobile phases, the loading capacity of plasma samples, the chromatographic behavior during plasma injections
and protein contamination of the packing and sealings. More than 95% of plasma proteins could be excluded from the precolumn
within three minutes for all selected mobile phases. Quantitative analyte recoveries could be obtained by injecting plasma
samples ranging from 5 to 500 μL with the analyte mass>150 ng onto a BioTrap 500 C18 column (20×4 mm I.D.). One precolumn tolerated about 15 mL of plasma injection without out noticeable change in retention
and pressure. Clogging of the precolumn was encountered (≥45 mL of plasma) due mainly to the adsorption of proteins on the
packing. The performance of the analytical column (Kromasil C18) was also examined. The column efficiency decreased by 60% after processing 45 mL plasma in total. 相似文献
46.
Summary Retention models for anionic analytes and mobile phase compounds in reversed-phase ion-pair chromatographic systems have been studied. The solid phase was a polystyrene-divinylbenzene copolymer. The analytes were mono- and divalent anions monitored by indirect detection technique. The mobile phase was highly alkaline and contained a detectable anion, sulfanilic acid.Expressions for the ion-pair retention of solutes and mobile phase components have been developed assuming Langmuir distribution of ion-pairs to a solid phase with one kind of binding site. The validity of the expressions and the origin of system peaks have been confirmed by determination of distribution constants using linear regression. 相似文献
47.
The biotin-streptavidin interaction can be reversibly broken using water at elevated temperatures 总被引:2,自引:0,他引:2
The biotin-streptavidin system is the strongest noncovalent biological interaction known, having a dissociation constant, K(d), in the order of 4x10(-14) M. The strength and specificity of the interaction has led it to be one of the most widely used affinity pairs in molecular, immunological, and cellular assays. However, it has previously been impossible to re-use any streptavidin solid support, since the conditions needed to break the interaction with biotin has led to the denaturation of the streptavidin. Here, we show that a short incubation in nonionic aqueous solutions at temperatures above 70 degrees C can efficiently break the interaction without denaturing the streptavidin tetramer. Both biotin and the streptavidin remain active after dissociation and both molecules can therefore be re-used. The efficiency of the regeneration allowed solid supports with streptavidin to be used many times, here exemplified with the multiple re-use of streptavidin beads used for sample preparation prior to automated DNA sequencing. The results suggest that streptavidin regeneration can be introduced as an improvement in existing methods and assays based on the streptavidin system as well as emerging solid phase applications in fields, such as microfluidics and nanotechnology. 相似文献
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A heuristic model based on dielectric continuum theory for the long-range solvation free energy of a dipolar system possessing periodic boundary conditions (PBCs) is presented. The predictions of the model are compared to simulation results for Stockmayer fluids simulated using three different cell geometries. The boundary effects induced by the PBCs are shown to lead to anisotropies in the apparent dielectric constant and the long-range solvation free energy of as much as 50%. However, the sum of all of the anisotropic energy contributions yields a value that is very close to the isotropic one derived from dielectric continuum theory, leading to a total system energy close to the dielectric value. It is finally shown that the leading-order contribution to the energetic and structural anisotropy is significantly smaller in the noncubic simulation cell geometries compared to when using a cubic simulation cell. 相似文献