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101.
The effect of 7,8,4´‐trihydroxyflavone on tyrosinase activity and conformation: Spectroscopy and docking studies 下载免费PDF全文
Chao Shang Yongkui Zhang Xue You Nihong Guo Yang Wang Yang Fan Wenbin Liu 《Luminescence》2018,33(4):681-691
Tyrosinase is a ubiquitous enzyme that plays an essential role in the production of melanin. Effective inhibitors of tyrosinase have extensive applications in the medical, cosmetic and food industries. In this study, a combination of enzyme kinetics, ultraviolet (UV)‐visible absorption, fluorescence spectroscopic techniques and a computational simulation method was used to characterize the inhibitory mechanism of 7,8,4´‐trihydroxyflavone on tyrosinase. 7,8,4´‐Trihydroxyflavone was found to strongly inhibit the oxidation of l ‐DOPA by tyrosinase with an IC50 value of 10.31 ± 0.41 μM. The inhibitory mechanism was determined to be reversible and non‐competitive with a Ki of 9.50 ± 0.40 μM. The UV absorption spectra showed that 7,8,4´‐trihydroxyflavone could chelate with copper ions and form a complex with tyrosinase. The intrinsic fluorescence of tyrosinase was quenched by 7,8,4´‐trihydroxyflavone through a static quenching mechanism. 7,8,4´‐Trihydroxyflavone was found to occupy a single binding site with a binding constant of 7.50 ± 1.20 × 104 M?1 at 298 K. The conformation of tyrosinase changed, and the microenvironment became more hydrophilic after 7,8,4´‐trihydroxyflavone binding. Thermodynamics parameters indicated that the binding was a spontaneous process and involved hydrogen bonds and van der Waals forces. The binding distance was evaluated to be 4.54 ± 0.05 nm. Docking simulation analysis further authenticated that 7,8,4´‐trihydroxyflavone could form hydrogen bonds with the residues His244 and Met280 within the tyrosinase active site. Our results will contribute to further understanding of the inhibitory mechanisms of 7,8,4´‐trihydroxyflavone against tyrosinase and will facilitate future screening for tyrosinase inhibitors. 相似文献
102.
103.
Naringin is a flavanone that widely presents on daily diet and traditional medicinal materials. The ratios of naringin C‐2 diastereomers are found different in reported samples, thus suspiciously leading to various functions. In this study, we measured the interconversion of C‐2 diastereomers intensively with ultimate high‐performance liquid chromatography and circular dichroism spectra. We examined the diastereomeric naringins in fresh citrus fruit, Huajuhong decoction pieces, and naringin tablet; evaluated the impact of tablet production procedures in factory; and monitored the rapid racemization in incubation. The results not only confirmed that enzyme, temperature, and pH condition could influence the interconversion but also demonstrated that diverse ratios of diastereomers showed limited influence on metabolic behaviors of naringin in the blood, which consequently cause comparable bioactivities. This study could provide comprehensive understanding of diastereomeric interconversion and provide useful reference for drug development. 相似文献
104.
Toward a general mixed quantum/classical method for the calculation of the vibronic ECD of a flexible dye molecule with different stable conformers: Revisiting the case of 2,2,2‐trifluoro‐anthrylethanol 下载免费PDF全文
Javier Cerezo Daniel Aranda Francisco J. Avila Ferrer Giacomo Prampolini Giuseppe Mazzeo Giovanna Longhi Sergio Abbate Fabrizio Santoro 《Chirality》2018,30(6):730-743
We extend a recently proposed mixed quantum/classical method for computing the vibronic electronic circular dichroism (ECD) spectrum of molecules with different conformers, to cases where more than one hindered rotation is present. The method generalizes the standard procedure, based on the simple Boltzmann average of the vibronic spectra of the stable conformers, and includes the contribution of structures that sample all the accessible conformational space. It is applied to the simulation of the ECD spectrum of (S)‐2,2,2‐trifluoroanthrylethanol, a molecule with easily interconvertible conformers, whose spectrum exhibits a pattern of alternating positive and negative vibronic peaks. Results are in very good agreement with experiment and show that spectra averaged over all the sampled conformational space can deviate significantly from the simple average of the contributions of the stable conformers. The present mixed quantum/classical method is able to capture the effect of the nonlinear dependence of the rotatory strength on the molecular structure and of the anharmonic couplings among the modes responsible for molecular flexibility. Despite its computational cost, the procedure is still affordable and promises to be useful in all cases where the ECD shape arises from a subtle balance between vibronic effects and conformational variety. 相似文献
105.
Mass-spectra based proteomic profiles have received widespreadattention as potential tools for biomarker discovery and earlydisease diagnosis. A major data-analytical problem involvedis the extremely high dimensionality (i.e. number of featuresor variables) of proteomic data, in particular when the samplesize is small. This article reviews dimensionality reductionmethods that have been used in proteomic biomarker studies.It then focuses on the problem of selecting the most appropriatemethod for a specific task or dataset, and proposes method combinationas a potential alternative to single-method selection. Finally,it points out the potential of novel dimension reduction techniques,in particular those that incorporate domain knowledge throughthe use of informative priors or causal inference. 相似文献
106.
Lectins are carbohydrate-binding proteins present in a wide variety of plants and animals, which serve various important physiological
functions. A soluble β-galactoside binding lectin has been isolated and purified to homogeneity from buffalo brain using ammonium
sulphate precipitation (40–70%) and gel permeation chromatography on Sephadex G50–80 column. The molecular weight of buffalo brain lectin (BBL) as determined by SDS-PAGE under reducing and non-reducing conditions
was 14.2 kDa, however, with gel filtration it was 28.5 kDa, revealing the dimeric form of protein. The neutral sugar content
of the soluble lectin was estimated to be 3.3%. The BBL showed highest affinity for lactose and other sugar moieties in glycosidic
form, suggesting it to be a β-galactoside binding lectin. The association constant for lactose binding as evidenced by Scatchard
analysis was 6.6 × 103 M−1 showing two carbohydrate binding sites per lectin molecule. A total inhibition of lectin activity was observed by denaturants
like guanidine HCl, thiourea and urea at 6 M concentration. The treatment of BBL with oxidizing agent destroyed its agglutination
activity, abolished its fluorescence, and shifted its UV absorption maxima from 282 to 250 nm. The effect of H2O2 was greatly prevented by lactose indicating that BBL is more stable in the presence of its specific ligand. The purified
lectin was investigated for its brain cell aggregation properties by testing its ability to agglutinate cells isolated from
buffalo and goat brains. Rate of aggregation of buffalo brain cells by purified protein was more than the goat brain cells.
The data from above study suggests that the isolated lectin may belong to the galectin-1 family but is glycosylated unlike
those purified till date. 相似文献
107.
The molecular geometries, normal mode frequencies, intensities and corresponding infrared assignments of monomeric and dimeric
2,3-dimethylpyridine, 2,4-dimethylpyridine, 3,4-dimethylpyridine, 3,5-dimethylpyridine and monomeric 2,6-dimethylpyridine
in the ground state were investigated at the density functional theory (DFT)-B3LYP level using the 6-311+G(d, p) basis set.
The vibrational frequencies and geometric parameters of C–H stretching and bending in the fundamental region were calculated
and compared to the Fourier transform infrared (FT-IR) data obtained. In the studied monomeric and dimeric dimethyl substituted
pyridine derivatives, the C–H stretching and bending frequency shifts that occur between the dimer and the monomer may be
diagnostic of the magnitude of dimerization energy. As supported by data in the literature, the most stable dimeric form was
obtained for the 3,4-dimethylpyridine molecule.
Figure Molecular model and numbering scheme of the studied dimeric dimethylpyridinederivatives 相似文献
108.
The conformational stabilities of the transition metal complex of Zn (en)3Cl2 were studied using density functional theory (DFT). Deformational potential energy profiles (PEPs), and pathways between
the different isomeric conformational energies were calculated using DFT/B3LYP/6–31G. The relative conformational energies
of Δ(λλλ), Δ(λλδ), Δ(λδδ) and Δ(δδδ) are 10.48, 7.08, 3.56, and 0.0 kcal/mol, respectively, which are small compared to the
barrier heights for reversible phase transitions (49.56, 49.55, 49.52 kcal/mol, respectively). Frequency assignment was carried
out by decomposing Fourier transform infrared (FTIR) spectra using Gaussian and Gaussview. The theoretical IR and vibrational
dichroism spectroscopy (VCD) absorption spectra are presented for all conformations within the range of 400–3,500 cm-1. 相似文献
109.
A chiral column, with decaproline as the chiral selector, has broad chiral selectivity. To understand the separation mechanism of this chiral column, multiple spectroscopic techniques, including optical rotation, electronic circular dichroism, infrared absorption and vibrational circular dichroism, have been used here to study the conformation of the decaproline oligomer in isopropanol(IPA)/dichloromethane(DCM) mixtures. These studies indicate that decaproline oligomer adopts polyproline II conformation in IPA/DCM solvent system (0% IPA approximately 100% IPA). Hydrogen bonding interactions between C=O groups of decaproline and IPA molecules increase as the content of IPA in the solvent mixture increases up to 60% and become less significant from then onwards. These spectroscopic observations are found to have a good correlation with the enantiomeric separation of racemic 2,2,2-trifluoro-1-[10-(2,2,2-trifluoro-1-hydroxy-ethyl-anthracen-9-yl]-ethanol by the decaproline column. 相似文献
110.
Spectrophotometric detection of the formation of short-lived hypomanganate(V), [KCAR-Mn(V)O43-], and manganate(VI), [KCAR-Mn(VI)O42-], intermediates has been confirmed through the oxidation of K-carrageenan (KCAR) by potassium permanganate in alkaline solutions of pH's >or= 12 using a conventional spectrophotometer. The short-lived transient species were characterized and a mechanism consistent with experimental observations is suggested. 相似文献