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1.
Summary Mutant strains were derived from Clostridium thermoaceticum ATCC 39 289 by treatment with chemical mutagenic agents and selective enrichment procedures. Some mutant strains exhibited growth when cultured in media containing 20 mabetm (1.75 g l–1) pyruvate of high-magnesium lime (dolime) above pH 6.0. One strain (G-20) grew and produced acetate when 80 mabetm (7 gl–1) pyruvate or 50 mabetm (2.3 g l–1) formate at pH 5.6 was the sole energy source. In a fed-batch process controlled at pH 6.2, this mutant produced 52.5 g l–1 acetate (equivalent to 72.5 g l–1 Na acetate) and 67 g l–1 calcium-magnesium acetate (CMA) in 140 h when dolime was the neutralizing agent, with 93% substrate utilization. This mutant strain holds promise for CMA production due to its better tolerance of dolime and its ability to synthesize high levels of acetic acid. Offprint requests to: S. R. Parekh  相似文献   
2.
Summary This paper reports studies of large scale, 1500 kg/h, SO2-catalysed prehydrolysis of coniferous wood chips, samples then being hydrolyzed by a wood-saccharifying enzyme system followed by fermentation to ethanol in the laboratory. Hemicellulose hydrolysis using SO2 catalyst (prehydrolysis) was found to be more effective than steam alone (autohydrolysis). Prehydrolysis time was 2 min, with steam pressure at 1.2 to 1.7 MPa (175 to 250 psig), and SO2 catalyst 2.0 to 2.6% on dry wood. The amount of sugars recovered upon enzyme saccharification of the prehydrolysed wood was about 70% of the weight of the wood. When these combined hemicellulose and cellulose sugars were fermented by a pentose-fermenting strain of yeast,Pichia stipitis R, 372 L ethanol/tonne of (dry) wood was obtained.  相似文献   
3.
Post-translational modifications are fundamental to processes controlling behaviour, including cellular signaling, growth and transformation. As the molecular basis of protein modifications in normal and disease processes are becoming better defined, so new strategies for designing therapeutic entities to control complex disease processes are emerging.  相似文献   
4.
2-Keto-3-deoxygluconate-6P aldolase ofPseudomonas putida mediates exchange between hydrogen isotope at the methylene carbon of 2-ketobutyrate and water. This occurs with aK m of 20 mM, 100 times the corresponding value for pyruvate, and a Vmax approximating 1/710 that of KDPG cleavage. Ketobutyrate is competitive with both pyruvate and 2-keto-3-deoxygluconate-6P for the enzyme. In addition, there is no evidence for C-C synthesis between ketobutyrate andd-glyceraldehyde-3P. A comparison of relativeV/K values for hydrogen exchange shows pyruvate to be 17,600 times better as a substrate than ketobutyrate. The detritiation of [3-3H]ketobutyrate is stereochemically random. In addition, the reaction proceeds with ak H/k T isotope effect of 15.3, consistent with C-H bond turnover being rate-determining. The E-ketobutyrate complex is reductively trapped, inactivating the enzyme. Reductive inactivation kinetics of E-ketobutyrate compared to E-pyruvate suggests more of the complex may be partitioned to ketimine in the ketobutyrate case than in the pyruvate case. A mechanism is considered in which ketobutyrate is bound as a ketimine in an orientation such that the active site acid/basic group cannot mediate catalytic ketimine/eneamine interconversion. Thus, exchange would result from hydrogen ionization at C-3′ of the ketimine, a slow spontaneous step compared to overall complex turnover. This noncatalyzed deprotonation would explain dissymmetry in exchange, the poorV/K compared to pyruvate, and a large tritium isotope effect.  相似文献   
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HIV incidence estimates are used to monitor HIV-1 infection in the United States. Use of laboratory biomarkers that distinguish recent from longstanding infection to quantify HIV incidence rely on having accurate knowledge of the average time that individuals spend in a transient state of recent infection between seroconversion and reaching a specified biomarker cutoff value. This paper describes five estimation procedures from two general statistical approaches, a survival time approach and an approach that fits binomial models of the probability of being classified as recently infected, as a function of time since seroconversion. We compare these procedures for estimating the mean duration of recent infection (MDRI) for two biomarkers used by the U.S. National HIV Surveillance System for determination of HIV incidence, the Aware BED EIA HIV-1 incidence test (BED) and the avidity-based, modified Bio-Rad HIV-1/HIV-2 plus O ELISA (BRAI) assay. Collectively, 953 specimens from 220 HIV-1 subtype B seroconverters, taken from 5 cohorts, were tested with a biomarker assay. Estimates of MDRI using the non-parametric survival approach were 198.4 days (SD 13.0) for BED and 239.6 days (SD 13.9) for BRAI using cutoff values of 0.8 normalized optical density and 30%, respectively. The probability of remaining in the recent state as a function of time since seroconversion, based upon this revised statistical approach, can be applied in the calculation of annual incidence in the United States.  相似文献   
7.
Russian Journal of Plant Physiology - Glutathione (γ-glutamylcysteinylglycine; GSH), is a multi-functional tri-peptide antioxidant, a key agent in defense against abiotic and biotic stress. A...  相似文献   
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The activation of protein phosphastase-1 (PP1) by insulin plays a critical role in the regulation of glycogen metabolism. PTG is a PP1 glycogen-targeting protein, which also binds the PP1 substrates glycogen synthase, glycogen phosphorylase, and phosphorylase kinase (Printen, J. A., Brady, M. J., and Saltiel, A. R. (1997) Science 275, 1475-1478). Through a combination of deletion analysis and site-directed mutagenesis, the regions on PTG responsible for binding PP1 and its substrates have been delineated. Mutagenesis of Val-62 and Phe-64 in the highly conserved (K/R)VXF PP1-binding motif to alanine was sufficient to ablate PP1 binding to PTG. Phosphorylase kinase, glycogen synthase, and phosphorylase binding all mapped to the same C-terminal region of PTG. Mutagenesis of Asp-225 and Glu-228 to alanine completely blocked the interaction between PTG and these three enzymes, without affecting PP1 binding. Disruption of either PP1 or substrate binding to PTG blocked the stimulation of PP1 activity in vitro against phosphorylase, indicating that both binding sites may be important in PTG action. Transient overexpression of wild-type PTG in Chinese hamster ovary cells overexpressing the insulin receptor caused a 50-fold increase in glycogen levels. Expression of PTG mutants that do not bind PP1 had no effect on glycogen accumulation, indicating that PP1 targeting is essential for PTG function. Likewise, expression of the PTG mutants that do not bind PP1 substrates did not increase glycogen levels, indicating that PP1 targeting glycogen is not sufficient for the metabolic effects of PTG. These results cumulatively demonstrate that PTG serves as a molecular scaffold, allowing PP1 to recognize its substrates at the glycogen particle.  相似文献   
10.
Little is known about the effect of exercise training on the expression of adiponectin receptor genes in peripheral blood mononuclear cells (PBMCs). In this study, we investigated the effects of aerobic training on the expression of AdipoR1 and AidpoR2 mRNAs in PBMCs, whole body insulin sensitivity, and circulating adiponectins in men. Thirty young men were randomly assigned to either a control (n=15) or an exercise (n=15) group. Subjects assigned to the exercise group underwent a 12-week jogging and/or running programme on a motor-driven treadmill at an intensity of 60%-75% of the age-based maximum heart rate with duration of 40 minutes per session and a frequency of 5 days per week. Two-way mixed ANOVA with repeated measures was used to test any significant time-by-group interaction effects for the measured variables at p=0.05. We found significant time-by-group interaction effects for waist circumference (p=0.001), VO2max (p<0.001), fasting insulin (p=0.016), homeostasis model assessment for insulin resistance (HOMA-IR) (p=0.010), area under the curve (AUC) for insulin response during the 75-g oral glucose tolerance test (p=0.002), high-molecular weight (HMW) adiponectin (p=0.016), and the PBMC mRNA levels of AdipoR1 (p<0.001) and AdipoR2 (p=0.001). The exercise group had significantly increased mRNA levels of AdipoR1 and AdipoR2 in PBMCs, along with increased whole body insulin sensitivity and HMW adiponectin, decreased waist circumference, and increased VO2max compared with the control group. In summary, the current findings suggest that exercise training modulates the expression of AdipoR1 and AdipoR2 mRNAs in PBMCs, implying that manipulation of the expression of these genes could be a potential surrogate for lifestyle intervention-mediated improvements of whole body insulin sensitivity and glucose homeostasis.  相似文献   
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