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1.
Summary The occurrence of cells resembling mammalian Langerhans cells in the avian epidermis was studied by ATPase histochemistry, Ia immunoreactivity and electron microscopy. The existence of MHC class II antigen-(Ia) expressing, ATPase-positive dendritic cells, which are ultrastructurally similar to mammalian Langerhans cells except for the absence of Birbeck granules, was demonstrated. These cells may be a basic component of the immune system of birds. 相似文献
2.
Structure characterization of the central repetitive domain of high molecular weight gluten proteins. I. Model studies using cyclic and linear peptides. 总被引:3,自引:1,他引:2
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A. A. Van Dijk L. L. Van Wijk A. Van Vliet P. Haris E. Van Swieten G. I. Tesser G. T. Robillard 《Protein science : a publication of the Protein Society》1997,6(3):637-648
The high molecular weight (HMW) proteins from wheat contain a repetitive domain that forms 60-80% of their sequence. The consensus peptides PGQGQQ and GYYPTSPQQ form more than 90% of the domain; both are predicted to adopt beta-turn structure. This paper describes the structural characterization of these consensus peptides and forms the basis for the structural characterization of the repetitive HMW domain, described in the companion paper. The cyclic peptides cyclo-[PGQGQQPGQGQQ] (peptide 1), cyclo-[GYYPTSPQQGA] (peptide 2), and cyclo-[PGQGQQGYYPTSPQQ] (peptide 3) were prepared using a novel synthesis route. In addition, the linear peptides (PGQGQQ)n (n = 1, 3, 5) were prepared. CD, FTIR, and NMR data demonstrated a type II beta-turn structure at QPGQ in the cyclic peptide 1 that was also observed in the linear peptides 9PGQGQQ)n. A type I beta-turn was observed at YPTS and SPQQ in peptides 2 and 3, with additional beta-turns of either type I or II at GAGY (peptide 2) and QQGY (peptide 3). The proline in YPTS showed considerable cis/trans isomerization, with up to 50% of the population in the cis-conformation; the other prolines were more than 90% in the trans conformation. The conversion from trans to cis destroys the type I beta-turn at YPTS, but leads to an increase in turn character at SPQQ and GAGY (peptide 2) or QQGY (peptide 3). 相似文献
3.
The secondary structure of the photosystem II (PSII) reaction center isolated from pea chloroplasts has been characterized by Fourier transform infrared (FTIR) spectroscopy. Spectra were recorded in aqueous buffers containing H2O or D2O; the detergent present for most measurements was dodecyl maltoside. The broad amide I and amide II bands were analyzed by using second-derivative and deconvolution procedures. Absorption bands were assigned to the presence of alpha-helices, beta-sheets, turns, or random structure. Quantitative analysis revealed that this complex contained a high proportion of alpha-helices (67%) and some antiparallel beta-sheets (9%) and turns (11%). An irreversible decrease in the intensity of the band associated with the alpha-helices occurs upon exposure of the isolated PSII reaction center to bright illumination. This loss of alpha-helical content gave rise to an increase in other secondary structures, particularly beta-sheets. After similar pretreatment with light, sodium dodecyl sulfate polyacrylamide gel electrophoresis reveals lower mobility and solubility of constituent D1 and D2 polypeptides of the PSII reaction center. Some degradation of these polypeptides also occurs. In contrast, there is no change in the mobility of the two subunits of cytochrome b559. In the absence of illumination, the PSII reaction center exchanged into dodecyl maltoside shows good thermal stability as compared with samples in Triton X-100. Only at a temperature of about 60 degrees C do spectral changes take place that are indicative of denaturation. 相似文献
4.
alpha 1-Antitrypsin (alpha 1-AT) is the best-characterized member of the serpin superfamily of plasma proteins. Protease inhibitor members of this family undergo a characteristic reactive-center cleavage during expression of their inhibitory activity. The physical basis of this transition in alpha 1-AT from the stressed native conformation to the more stable reactive center cleaved (split) form was studied by Fourier transform infrared (FT-IR) spectroscopy and neutron scattering. The FT-IR spectra show that, while split alpha 1-AT has three intense well-resolved components associated with the presence of antiparallel beta-sheet and alpha-helix conformations, the amide I band of native alpha 1-AT has only one intense component, associated with the presence of beta-sheet structure. 1H-2H exchange within the polypeptide backbone, studied by FT-IR and NMR spectroscopy, shows that the native form undergoes greater exchange than the split form. Under the same conditions, neutron scattering shows no differences in the radius of gyration RG of the native and the split forms. In contrast, in high concentrations of phosphate approaching those used for crystallization, the native form (unlike the split form) undergoes dimerization. These data indicate that the conformational transition largely involves localized secondary and tertiary structure rearrangements. We propose that the energetically stressed native alpha 1-AT structure is the consequence of a significantly reduced number of hydrogen bonds in secondary structure components and that reactive-site cleavage between Met358 and Ser359 is the key for the development of the fully hydrogen bonded more stable serpin structure. 相似文献
5.
The study compares the 3 years of birth control practice of 1172 women who underwent early menstrual regulation (MR) and 499 others who accepted contraceptives only (nonMR) from an urban clinic in Bangladesh. About 60% of the women in the sample were followed-up and their all-method continuation rate was analyzed by life-table technique. The 3-year overall continuation rate in the MR group (64%) did not differ from that of the nonMR group (62%). In the age groups 25 and over, the continuation rate was higher in the MR group. Among the women who did not desire any more children, the continuation rate in the MR group was significantly higher than that of the nonMR group (80% versus 68%, P0.05). Of women with parity greater than 2, the MR group had significantly higher continuation rates than the nonMR group. The MR group had higher extended use-effectiveness for IUDs, conventional contraceptives (condom and foam), injectables, and oral contraceptives than the nonMR group. These findings indicated effective contraceptive practice following MR for this urban population. Easy availability of a multimethod service after MR seemed to be important in promoting effective contraception. 相似文献
6.
7.
Linda J. Chan John D. Wade Frances Separovic Ross A. D. Bathgate Mohammed Akhter Hossain 《International journal of peptide research and therapeutics》2013,19(1):55-60
H2 relaxin (relaxin) is a member of the insulin–relaxin superfamily and exhibits several non-reproductive functions in addition to its well-known properties as a pregnancy hormone. Over the years, the therapeutic potential of relaxin has been examined for a number of conditions. It is currently in phase III clinical trials for the treatment of acute heart failure. The 53 amino acid peptide hormone consists of two polypeptide chains (A and B) which are cross-linked by two inter-chains and one intra-A chain disulfide bridge. Although its cognate receptor is relaxin family peptide receptor (RXFP) 1, relaxin is also able to cross-react with RXFP2, for which the native ligand is INSL3. The “RXXXRXXI” motif in the B-chain of H2 relaxin is responsible for primary binding to LRR of the RXFP1 receptor (Büllesbach and Schwabe, J Biol Chem 280:14051–14056, 2005). Previous RXFP2 receptor mutation and molecular modelling studies strongly suggest that, in addition to this motif, the Trp-B28 residue in the B-chain is responsible for H2–RXFP2 interaction. To confirm this finding, here we have mutated H2 relaxin in which Trp-B28 was replaced with alanine. The synthetic relaxin analogue was then tested on cells expressing either RXFP1 or 2 to determine the affinity and potency for the respective receptors. Our results confirm that Trp-B28 in the B-chain is crucial for binding and activating RXFP2, but not for RXFP1. 相似文献
8.
Alessia Belgi Ross A. D. Bathgate Geoffrey W. Tregear John D. Wade Mohammed Akhter Hossain 《International journal of peptide research and therapeutics》2013,19(1):71-79
Insulin-like peptide 5 (INSL5) is a two-chain, three-disulfide bonded member of insulin/relaxin superfamily of peptides that includes insulin, insulin-like growth factor I and II (IGFI and IGFII), insulin-like peptide 3, 4, 5 and 6 (INSL3, 4, 5 and 6), relaxin-1 (H1 relaxin), -2 (H2 relaxin) and -3 (H3 relaxin). Although it is expressed in relatively high levels in the gut, its biological function remains unclear. However, recent reports suggest a significant orexigenic action and a role in the regulation of insulin secretion and β-cell homeostasis, which implies that both agonists and antagonists of the peptide may have significant therapeutic applications. Modern solid phase synthesis techniques together with regioselective disulfide bond formation were employed for a preliminary structure–function relationship study of mouse INSL5. Two point mutated analogues, mouse INSL5 A-B(R24A, W25A) and mouse INSL5 A-B(K6A, R14A, Y18A) were chemically prepared, where the residues in the B-chain that may be involved in receptor activation and affinity binding, were respectively mutated. Synthetic mouse INSL5 A-B(R24A, W25A) analogue was inactive on RXFP4, the native receptor for INSL5, suggesting ArgB24 and TrpB25 are probably directly involved in INSL5 receptor activation. Mouse INSL5 A-B(K6A, R14A, Y18A) analogue had both decreased affinity and potency on RXFP4 (pIC50 7.7 ± 0.2, pEC50 7.87 ± 0.18) which indicated that one or more of these residues are critical for the binding to the receptor. 相似文献
9.
Stephanie Melkonian Maria Argos Megan N. Hall Yu Chen Faruque Parvez Brandon Pierce Hongyuan Cao Briseis Aschebrook-Kilfoy Alauddin Ahmed Tariqul Islam Vesna Slavcovich Mary Gamble Parvez I. Haris Joseph H. Graziano Habibul Ahsan 《PloS one》2013,8(11)
Background
We utilized data from the Health Effects of Arsenic Longitudinal Study (HEALS) in Araihazar, Bangladesh, to evaluate the association of steamed rice consumption with urinary total arsenic concentration and arsenical skin lesions in the overall study cohort (N=18,470) and in a subset with available urinary arsenic metabolite data (N=4,517).Methods
General linear models with standardized beta coefficients were used to estimate associations between steamed rice consumption and urinary total arsenic concentration and urinary arsenic metabolites. Logistic regression models were used to estimate prevalence odds ratios (ORs) and their 95% confidence intervals (CIs) for the associations between rice intake and prevalent skin lesions at baseline. Discrete time hazard models were used to estimate discrete time (HRs) ratios and their 95% CIs for the associations between rice intake and incident skin lesions.Results
Steamed rice consumption was positively associated with creatinine-adjusted urinary total arsenic (β=0.041, 95% CI: 0.032-0.051) and urinary total arsenic with statistical adjustment for creatinine in the model (β=0.043, 95% CI: 0.032-0.053). Additionally, we observed a significant trend in skin lesion prevalence (P-trend=0.007) and a moderate trend in skin lesion incidence (P-trend=0.07) associated with increased intake of steamed rice.Conclusions
This study suggests that rice intake may be a source of arsenic exposure beyond drinking water. 相似文献10.
Tijjani Salihu Shinkafi Abhinav Kaushik Amena Mahmood Ambrish Kumar Tiwari Mohammad Mumtaz Alam Mymoona Akhter 《Journal of biomolecular structure & dynamics》2020,38(10):2976-2987
AbstractThis study identifies and validates hexokinase type 4 (HK4), an isozyme of hexokinase in the liver and pancreas, as an important target of C2-β-D-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (βdGT), a xanthone glucoside suggested to have antidiabetic property. In the study, we applied the computational pipeline of molecular docking followed by the molecular dynamics simulations to shortlist potential βdGT protein targets. The analysis of protein dynamics and the binding free energy (ΔG) led us to the identification of HK4 as a key βdGT target, whereby the binding mode and domain dynamics suggested the activator function of βdGT. βdGT bound to the allosteric site of the isozyme ~13?Å away from the substrate (glucose)-binding site. The binding free energy of the ligand-protein complex was energetically feasible (ΔG, –41.61?kcal/mol) and the cleft angle deviation between the two (small and large) domains of HK4 revealed differential HK4 dynamics in response to βdGT binding. 3D structure analysis of the isozyme-ligand complex highlighted the role of Arg63, Glu67 and Lys458 in ligand stabilization and hydrophobic interactions mediated by Tyr214 and Met235. Experimental validation of the results of computational analysis confirmed the activator function of βdGT on HK4. The study has implication in diabetes as βdGT may be used to lower the blood glucose level by activating hepatic and pancreatic hexokinase without the risk of hypoglycemia.Communicated by Ramaswamy H. Sarma 相似文献