全文获取类型
收费全文 | 972篇 |
免费 | 13篇 |
国内免费 | 3篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 2篇 |
2016年 | 12篇 |
2015年 | 53篇 |
2014年 | 142篇 |
2013年 | 118篇 |
2012年 | 149篇 |
2011年 | 111篇 |
2010年 | 91篇 |
2009年 | 32篇 |
2008年 | 22篇 |
2007年 | 38篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 13篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有988条查询结果,搜索用时 31 毫秒
41.
Verde C Howes BD De Rosa MC Raiola L Smulevich G Williams R Giardina B Parisi E Di Prisco G 《Protein science : a publication of the Protein Society》2004,13(10):2766-2781
The suborder Notothenioidei dominates the Antarctic ichthyofauna. The non-Antarctic monotypic family Pseudaphritidae is one of the most primitive families. The characterization of the oxygen-transport system of euryhaline Pseudaphritis urvillii is herewith reported. Similar to most Antarctic notothenioids, this temperate species has a single major hemoglobin (Hb 1, over 95% of the total). Hb 1 has strong Bohr and Root effects. It shows two very uncommon features in oxygen binding: At high pH values, the oxygen affinity is exceptionally high compared to other notothenioids, and subunit cooperativity is modulated by pH in an unusual way, namely the curve of the Hill coefficient is bell-shaped, with values approaching 1 at both extremes of pH. Molecular modeling, electronic absorption and resonance Raman spectra have been used to characterize the heme environment of Hb 1 in an attempt to explain these features, particularly in view of some potentially important nonconservative replacements found in the primary structure. Compared to human HbA, no major changes were found in the structure of the proximal cavity of the alpha-chain of Hb 1, although an altered distal histidyl and heme position was identified in the models of the beta-chain, possibly facilitated by a more open heme pocket due to reduced steric constraints on the vinyl substituent groups. This conformation may lead to the hemichrome form identified by spectroscopy in the Met state, which likely fulfils a potentially important physiological role. 相似文献
42.
A direct hydrogen bond between ubiquinone/quinol bound at the QO site and a cluster-ligand histidine of the iron-sulfur protein (ISP) is described as a major determining factor explaining much experimental data on position of the ISP ectodomain, electron paramagnetic resonance (EPR) lineshape and midpoint potential of the iron-sulfur cluster, and the mechanism of the bifurcated electron transfer from ubiquinol to the high and low potential chains of the bc1 complex. 相似文献
43.
Shoulian Dong Raghavakaimal Padmakumar Ruma Banerjee Thomas G. Spiro 《Inorganica chimica acta》1998,270(1-2):392-398
The Co-C stretching vibration has been identified in resonance Raman spectra of alkyl-cobalamins, via isotope substitution, permitting estimation of the Co-C force constants, f = 1.85, 1.77 and 1.50 mdyn Å−1 for methyl-, ethyl- and deoxyadenosyl-cobalamin, respectively (νCo-C = 506, 471 and 442/429 cm−1). These values scale with the reported bond dissociation energies, and support the view that the Co-C bond weakens with increasing bulk of the alkyl group due to steric interaction with the corrin ring. However, the force constants are unaffected by dissociation of the dimethylbenzimidazole ligand at low pH, even though the bond dissociation energy rises significantly upon DMB dissociation in AdoCbl. This increase must therefore reflect destabilization of the CoII product, rather than Co-C bond strengthening in the AdoCbl ground state. The insensitivity of the force constants to dimethylbenzimidazole dissociation implies that the steric effect of DMB coordination is not transmitted to the Co-C bond by the corrin ring. Consistent with this interpretation, the RR frequencies of the corrin ring modes are minimally perturbed by DMB dissociation, supporting earlier NMR results that indicated little change in the corrin conformation. 相似文献
44.
45.
A 3-doxylcholestane spin label was employed in addition to 5-doxylstearoyl lecithin for a more detailed study of the different effects exerted by variously oxidized lecithins on fatty acid alignment in phospholipid planar bilayers. Either spin label was enclosed in oriented PLPC planar samples also containing in turn a variety of conjugated-dienes lecithins and cleaved chain lecithins, in order to monitor EPR spectral angular dependence loss. Data obtained by use of arachidonoyl-hydroxystearoyl-PC and palmitoyl-hydroxylinoleoyl-PC confirm that the 5-DSPC nitroxide ring almost completely retains its orientation in CD-PCs-containing planar membranes, in contrast with angular dependence loss observed in the presence of the CC-PC molecular species palmitoyl-oxononanoyl-PC and palmitoyl-oxovaleroyl-PC, already seen with cleaved-chain palmitoyl-glutaroyl-PC and palmitoyl-azelaoyl-PC. However, the 3-DC nitroxide ring also loses its orientation with CD-PCs, in addition to being disoriented by cleaved chain-lecithins, similarly to 5DSPC. Joint information from the two spin labels will help to clarify whether OXPC-related disordering involved the whole bilayer structure or only the hydrophobic core. In addition, the propensity of different OXPCs to form bilayer vesicles in water suspension was also determined by Sepharose 4B gel-chromatography. The results suggest that CD-PCs might yield SPB bilayer structures with a disordered hydrophobic core, while pure CC-PC more probably forms non-bilayer disordered structures, possibly micelles or mixed micelle/bilayers. 相似文献
46.
Hirai K Martinkova M Igarashi J Saiful I Yamauchi S El-Mashtoly S Kitagawa T Shimizu T 《Journal of inorganic biochemistry》2007,101(8):1172-1179
Heme-regulated eIF2alpha kinase (HRI) is an important enzyme that modulates protein synthesis during cellular emergency/stress conditions, such as heme deficiency in red cells. It is essential to identify the heme axial ligand(s) and/or binding sites to establish the heme regulation mechanism of HRI. Previous reports suggest that a His residue in the N-terminal region and a Cys residue in the C-terminal region trans to the His are axial ligands of the heme. Moreover, mutational analyses indicate that a residue located in the kinase insertion (KI) domain between Kinase I and Kinase II domains in the C-terminal region is an axial ligand. In the present study, we isolate the KI domain of mouse HRI and employ site-directed mutagenesis to identify the heme axial ligand. The optical absorption spectrum of the Fe(III) hemin-bound wild-type KI displays a broad Soret band at around 373nm, while that of the Fe(II) heme-bound protein contains a band at 422nm. Spectral titration studies conducted for both the Fe(III) hemin and Fe(II) heme complexes with KI support a 1:1 stoichiometry of heme iron to protein. Resonance Raman spectra of Fe(III) hemin-bound KI suggest that thiol is the axial ligand in a 5-coordinate high-spin heme complex as a major form. Electron spin resonance (ESR) spectra of Fe(III) hemin-bound KI indicate that the axial ligands are OH(-) and Cys. Since Cys385 is the only cysteine in KI, the residue was mutated to Ser, and its spectral characteristics were analyzed. The Soret band position, heme spectral titration behavior and ESR parameters of the Cys385Ser mutant were markedly different from those of wild-type KI. Based on these spectroscopic findings, we conclude that Cys385 is an axial ligand of isolated KI. 相似文献
47.
A new optical biosensor based on the resonance enhanced absorption (REA) effect is described. REA effects are observed when noble metal nanoclusters are deposited at a nanometric distance from a highly reflective mirror. The aim of our study was to adopt the REA effect for the rapid testing of proteins in a direct immunoassay format on chip and to adjust a conventional enzyme-linked immunosorbent assay (ELISA) to a cluster-linked immunosorbent assay (CLISA) by labelling the read-out antibody with monodisperse colloidal gold clusters. For generation of a strong REA signal 30 min of coating of the target protein was sufficient. To evaluate our approach we used the milk allergen β-lactoglobulin (β-LG) as analyte, and β-LG-isolations of processed milk products to prove the applicability of our method to the analysis of proteins in complex matrices at even the trace level. For validating the specificity of the CLISA biosensor we used the non-functionalised cluster reagent without antibody and a non-immunoreactive milk matrix as controls. As expected, very weak background signals were obtained with the controls, whereas the purified food samples clearly showed that β-LG was present and detectable. In conclusion, we were able to describe the successful development of a new biosensor chip for assaying proteins using the REA effect. 相似文献
48.
Epidemiological effects of seasonal oscillations in birth rates 总被引:3,自引:0,他引:3
Seasonal oscillations in birth rates are ubiquitous in human populations. These oscillations might play an important role in infectious disease dynamics because they induce seasonal variation in the number of susceptible individuals that enter populations. We incorporate seasonality of birth rate into the standard, deterministic susceptible-infectious-recovered (SIR) and susceptible-exposed-infectious-recovered (SEIR) epidemic models and identify parameter regions in which birth seasonality can be expected to have observable epidemiological effects. The SIR and SEIR models yield similar results if the infectious period in the SIR model is compared with the "infected period" (the sum of the latent and infectious periods) in the SEIR model. For extremely transmissible pathogens, large amplitude birth seasonality can induce resonant oscillations in disease incidence, bifurcations to stable multi-year epidemic cycles, and hysteresis. Typical childhood infectious diseases are not sufficiently transmissible for their asymptotic dynamics to be likely to exhibit such behaviour. However, we show that fold and period-doubling bifurcations generically occur within regions of parameter space where transients are phase-locked onto cycles resembling the limit cycles beyond the bifurcations, and that these phase-locking regions extend to arbitrarily small amplitude of seasonality of birth rates. Consequently, significant epidemiological effects of birth seasonality may occur in practice in the form of transient dynamics that are sustained by demographic stochasticity. 相似文献
49.
Surface plasmon resonance for probing quadruplex folding and interactions with proteins and small molecules 总被引:1,自引:0,他引:1
Redman JE 《Methods (San Diego, Calif.)》2007,43(4):302-312
Surface plasmon resonance is a technique for detecting binding events at the surface of a thin metal film. Through the commercial availability of instrumentation and sensor chips, the technique has found widespread application for determining the affinity and kinetics of macromolecular interactions. A variety of quadruplex forming oligonucleotides have been immobilized to sensor chips to permit analysis of their binding interactions with both small molecule and protein analytes. The fold of the quadruplex must be maintained through an appropriate choice of buffer, and care must be taken to ensure that data interpretation is not hampered by non-specific binding and adsorption of the analyte to the sensor surface and instrument. Affinity constants determined by surface plasmon resonance for interactions with quadruplexes correlate meaningfully with other methods, such as UV-visible and fluorescence titrations, enzyme linked immunosorbent assay, thermal melting studies and telomerase inhibition. Kinetic measurements of the association and dissociation of duplexes of quadruplex forming oligonucleotides and their complementary strands have enabled calculation of the folding and unfolding rates of the quadruplex itself, and determination of its stability as a function of buffer composition. 相似文献
50.
Boer H Simolin H Cottaz S Söderlund H Koivula A 《Protein expression and purification》2007,51(2):216-226
Heterologous expression of two fungal chitinases, Chit33 and Chit42, from Trichoderma harzianum was tested in the different compartments and on the surface of Escherichia coli cells. Our goal was to find a fast and efficient expression system for protein engineering and directed evolution studies of the two fungal enzymes. Cytoplasmic overexpression resulted in both cases in inclusion body formation, where active enzyme could be recovered after refolding. Periplasmic expression of Chit33, and especially of Chit42, proved to be better suited for mutagenesis purposes. Recombinant chitinases from the periplasmic expression system showed activity profiles similar to those of the native proteins. Both chitinases also degraded a RET (resonance energy transfer) based bifunctionalized chitinpentaose substrate in a similar manner as reported for some putative exochitinases in the glycosyl hydrolase family 18, offering a sensitive way to assay their activities. We further demonstrated that Chit42 can also be displayed on E. coli surface and the enzymatic activity can be measured directly from the whole cells using methylumbelliferyl-chitinbioside as a substrate. The periplasmic expression and the surface display of Chit42, both offer a suitable expression system for protein engineering and activity screening in a microtiter plate scale. As a first mutagenesis approach we verified the essential role of the two carboxylic acid residues E172 (putative proton donor) and D170 (putative stabilizer) in the catalytic mechanism of Chit42, and additionally the role of the carboxylic acid E145 (putative proton donor) in the catalytic mechanism of Chit33. 相似文献