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131.
Gunasekaran S Arunbalaji R Kumaresan S Seshadri S Muthu S 《Journal of molecular modeling》2008,14(5):375-383
The FTIR and Laser-Raman spectra of paraldehyde have been recorded in the regions 4000–400 cm−1 and 3500–250 cm−1 respectively. Molecular electronic energy, geometrical structure, harmonic vibrational spectra, infrared intensities and
Raman scattering activities have been computed at the HF/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory. The results were
compared with experimental values with the help of scaling procedures. The observed wave numbers in FTIR and Laser-Raman spectra
were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected
range and are in good agreement with computed values. 相似文献
132.
Purified alkali stable xylanase from Aspergillus fischeri was immobilized on polystyrene beads using diazotization method. An expanded bed bioreactor was developed with these immobilized beads to biobleach the paper pulp in continuous mode. Response surface methodology was applied to optimize the biobleaching conditions. Temperature (degrees C), flow rate of pulp (ml/min) and concentration of the pulp (%) were selected as variables in this study. Optimal conditions for biobleaching process were reaction temperature 60 degrees C, flow rate of 2 ml/min and 5% (w/v) of pulp. The kappa number reduced from 66 in the unbleached pulp to 20 (reduction of 87%). This system proves to be a better option for the conventional chlorine based pulp bleaching. 相似文献
133.
Latypov RF Liu D Gunasekaran K Harvey TS Razinkov VI Raibekas AA 《Protein science : a publication of the Protein Society》2008,17(4):652-663
Although 8-anilinonaphthalene-1-sulfonic acid (ANS) is frequently used in protein folding studies, the structural and thermodynamic effects of its binding to proteins are not well understood. Using high-resolution two-dimensional NMR and human interleukin-1 receptor antagonist (IL-1ra) as a model protein, we obtained detailed information on ANS-protein interactions in the absence and presence of urea. The effects of ambient to elevated temperatures on the affinity and specificity of ANS binding were assessed from experiments performed at 25 degrees C and 37 degrees C. Overall, the affinity of ANS was lower at 37 degrees C compared to 25 degrees C, but no significant change in the site specificity of binding was observed from the chemical shift perturbation data. The same site-specific binding was evident in the presence of 5.2 M urea, well within the unfolding transition region, and resulted in selective stabilization of the folded state. Based on the two-state denaturation mechanism, ANS-dependent changes in the protein stability were estimated from relative intensities of two amide resonances specific to the folded and unfolded states of IL-1ra. No evidence was found for any ANS-induced partially denatured or aggregated forms of IL-1ra throughout the experimental conditions, consistent with a cooperative and reversible denaturation process. The NMR results support earlier observations on the tendency of ANS to interact with solvent-exposed positively charged sites on proteins. Under denaturing conditions, ANS binding appears to be selective to structured states rather than unfolded conformations. Interestingly, the binding occurs within a previously identified aggregation-critical region in IL-1ra, thus providing an insight into ligand-dependent protein aggregation. 相似文献
134.
Senthilkumar V Busby SJ Gunasekaran P Senthikumar V Bushby SJ 《Biotechnology letters》2003,25(19):1653-1656
Levansucrase is responsible for levan formation during sucrose fermentation of Zymomonas mobilis, and this decreases the efficiency of ethanol production. As thiol modifying agents decrease levan formation, a role for cysteine residues in levansucrase activity has been examined using derivatives of Z. mobilis levansucrase that carry serine substitutions of cysteine at positions 121, 151 or 244. These substitutions abolished the levan forming activity of levansucrase whilst only halving its activity in sucrose hydrolysis. Thus, polymerase and hydrolase activities of Z. mobilis levansucrase are separate and have different requirements for the enzyme's cysteine residues. 相似文献
135.
The mechanism through which globular proteins transform into amyloid fibrils is still not understood. Here we analyze the structure and sequence conservation to assess the differential stability of segments from two structurally related protein families: the amyloidogenic gelsolin-like and its structurally related cofilin-like. The two families belong to the actin depolymerizing proteins, with a central beta-sheet stacked between 2 and 4 alpha-helices. Although sequentially remote, the two families share regions of high and low conservation and stability. Our results show a highly conserved hydrophobic and aromatic cluster, located at a central buried beta-hairpin. The geometry of the aromatic residues with respect to each other is strictly conserved, suggesting involvement in strand registering and beta-sheet stabilization. Consistent with experiment, we find a region of weak conservation and stability at one of the exposed beta-strands (strand B in the gelsolin-like family). This region was recently found to be affected by a point mutation-mediated destabilization of the human gelsolin domain 2, which facilitates the first proteolytic event in the formation of the amyloidogenic fragment. Thus, both experimental and computational conservation analyses suggest that this unstable region may constitute a first step in amyloid formation. Our analysis uses a recently developed multiple-structure comparison algorithm in which molecules are aligned simultaneously. 相似文献
136.
Proteins are dynamic molecules and often undergo conformational change upon ligand binding. It is widely accepted that flexible loop regions have a critical functional role in enzymes. Lack of consideration of binding site flexibility has led to failures in predicting protein functions and in successfully docking ligands with protein receptors. Here we address the question: which sequence and structural features distinguish the structurally flexible and rigid binding sites? We analyze high-resolution crystal structures of ligand bound (holo) and free (apo) forms of 41 proteins where no conformational change takes place upon ligand binding, 35 examples with moderate conformational change, and 22 cases where a large conformational change has been observed. We find that the number of residue-residue contacts observed per-residue (contact density) does not distinguish flexible and rigid binding sites, suggesting a role for specific interactions and amino acids in modulating the conformational changes. Examination of hydrogen bonding and hydrophobic interactions reveals that cases that do not undergo conformational change have high polar interactions constituting the binding pockets. Intriguingly, the large, aromatic amino acid tryptophan has a high propensity to occur at the binding sites of examples where a large conformational change has been noted. Further, in large conformational change examples, hydrophobic-hydrophobic, aromatic-aromatic, and hydrophobic-polar residue pair interactions are dominant. Further analysis of the Ramachandran dihedral angles (phi, psi) reveals that the residues adopting disallowed conformations are found in both rigid and flexible cases. More importantly, the binding site residues adopting disallowed conformations clustered narrowly into two specific regions of the L-Ala Ramachandran map. Examination of the dihedral angles changes upon ligand binding shows that the magnitude of phi, psi changes are in general minimal, although some large changes particularly between right-handed alpha-helical and extended conformations are seen. Our work further provides an account of conformational changes in the dihedral angles space. The findings reported here are expected to assist in providing a framework for predicting protein-ligand complexes and for template-based prediction of protein function. 相似文献
137.
M. Gomathy M. Thangaraju S. Gunasekaran N. O. Gopal 《Indian journal of microbiology》2007,47(3):259-262
Sporulation in Bacillus megaterium var phosphaticum (PB — 1) was induced using modified nutrient media. This modified medium induced sporulation within 36 h. After spore induction
the spores were kept under refrigerated (5°C) and room temperature (32°C) for five months and survival of spores was studied
at 15 days intervals by plating them in nutrient agar medium. It was observed that there was not much variation in the storage
temperature (5°C & 32°C). The spore cells of Bacillus megaterium var phosphaticum (PB — 1) were observed up to five months of storage under refrigerated (5°C) and room temperature (32°C). Regeneration of
spore cells into vegetative cells was studied in tap water, rice gruel, nutrient broth, sterile lignite and sterile water
at different concentrations of spore inoculum. The multiplication of sporulated Bacillus megaterium var phosphaticum culture was fast and reached its maximum (29.5 × 108 cfu ml−1) in nutrient broth containing 5 per cent inoculum level. 相似文献
138.
Premanand Ranganathan V. Gunasekaran Indrajeet Singhvi Mohammad Javed Ansari 《Saudi Journal of Biological Sciences》2019,26(7):1843-1847
A highly sensitive and ultra-fast high performance liquid chromatography- tandem mass spectrometry (LC–MS/MS) assay is developed and validated for the quantification of Lenalidomide in human plasma. Lenalidomide is extracted from human plasma by Liquid- Liquid Extraction by Ethyl Acetate and analyzed using a reversed phase isocratic elution on a XTerra RP18, (4.6 × 50 mM, 5 µm) column. A 0.1% Formic acid: Methanol (10:90% v/v), is used as mobile phase and detection was performed by Triple quadrupole mass spectrometry LC-MS/MS using electrospray ionization in positive mode. Fluconazole is used as the internal standard. The lower limit of quantification is 9.999 ng/mL for Lenalidomide. The calibration curves are consistently accurate and precise over the concentration range of 9.999 to 1010.011 ng/mL in plasma for Lenalidomide. This novel LC–MS/MS method competes with all the regulatory requirements and shows satisfactory accuracy and precision and is sufficiently sensitive for the performance of pharmacokinetic and bioequivalence studies in humans. 相似文献
139.
140.