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51.
木文考查了两种常见污染细菌对红霉素发酵的影响。发现枯草芽孢杆菌污染后迅速引起总糖和还原糖的大量消耗,且在早期就已完全抑制了红霉素的生成;另一种微球菌虽也使发酵过程中的糖耗明显增加,但对红霉素的影响较小,红霉素的合成一直持续到发酵终了。 相似文献
52.
L. T. Chang E. L. McGrory R. P. Elander D. J. Hook 《Journal of industrial microbiology & biotechnology》1991,7(3):175-179
Summary Penicillin V (phenoxymethyl penicillin) is produced by industrial strains ofPenicillium chrysogenum in the presence of phenoxyacetic acid (POAc), a side-chain precursor for the penicillin V molecule. The wild-type strain ofP. chrysogenum produces an undesirable penicillin byproduct,para-hydroxypenicillin V (p-OH penicillin V), in addition to penicillin V, viapara-hydroxylation of POAc and subsequent incorporation of thep-OH phenoxyacetic acid into the penicillin molecule. Most of thep-OH penicillin V is produced late in cycle when the POAc concentration in the medium is nearly depleted. The level ofp-OH penicillin V produced by the control strain ranges up to 10–15% of the total penicillins produced. 3-Phenoxypropionic acid andp-bromophenylacetic acid partially inhibit the formation ofp-OH penicillin V with a minimal effect on penicillin V productivity. Mutants deficient in their ability to hydroxylate POAc were found to produce lower levels ofp-OH penicillin V. Multi-step mutation and screening, starting with the wild-type strain, have culminated in isolation of mutants which producep-OH penicillin V as 1% of the total penicillins with no adverse effect on penicillin V productivity. 相似文献
53.
V. A. Vinci T. D. Hoerner A. D. Coffman T. G. Schimmel R. L. Dabora A. C. Kirpekar C. L. Ruby R. W. Stieber 《Journal of industrial microbiology & biotechnology》1991,8(2):113-119
Summary A lovastatin-hyperproducing culture ofAspergillus terreus was shown to produce several co-metabolites extracted from whole broth. The predominant co-metabolite was the benzophenone, sulochrin, reported to arise from a polyketide biosynthetic pathway. This compound was targeted for elimination by classical mutagenesis and screening. A surface culture method employing microtiter, plates was used to ferment mutants for the primary screen. Qualitative determinations of lovastatin and sulochrin production were achieved by high-performance thin-layer chromatography. A mutant, strain AH6, which produced lovastatin titers equivalent to the parent culture and no detectable sulochrin was isolated. In addition, a lovastatin-hyperproducing mutant designated CB4 was capable of producing 16% more lovastatin and 30% less sulochrin than the parent culture in shake flask fermentations. In a pilot-scale 250-gallon fermentation, strain CB4 gave a 20% increase in lovastatin titer while producing 83% less sulochrin than the parent culture. 相似文献
54.
A methodology for the design and evalution of bioprocess control strategies is presented. The strategies manage nutrient supply with demand and vary with the metabolic condition and phase of fermentation operation. Six carbon source addition strategies are based on different combinations of available measurements; they are described and evaluated under different operating conditions for yeast cultivation. It is concluded that a single control strategy is not the most appropriate under all possible operating conditions. An oxygen uptake rate-based control strategy performs better with a mean respiratory quotient (RQ) value less than 1.1 during an oxygen limitation than an ethanol control strategy which had a mean RQ of 14. The designed strategies and an approach of applying the strategy that best matches fermentation conditions consistently enables achievement of high cell densities 78.7 g DCW/L and yields 0.50 g DCW/g glucose as the mean values for three fermentations. 相似文献
55.
Extractive lactic acid fermentation using ion-exchange resin 总被引:6,自引:0,他引:6
Lactic acid fermentation is an end-product-inhibited reaction. The restriction imposed by lactic acid on its fermentation can be avoided by extractive fermentation techniques. Studies were performed by attaching an ion-exchange resin packed column with a 2-L fermentor for separation of lactic acid. The fermentation, in a conventional batch mode, resulted in a lactic acid yield of 0.828 g . g(-1) and a lactic acid productivity of 0.313 g . L(-1) . h(-1). However, these could be further enhanced to 0.929 g . g(-1) and 1.665 g . L(-1) . h(-1) by extractive fermentation techniques. The effect of temperature on extractive fermentation was remarkable and has been included in this work. 相似文献
56.
In production-scale, fed-batch fermentations, feed is often added to a single point at the top of the fermentor, which, combined with poor mixing, results in formation of a "feed zone" rich in nutrients. Frequent exposure of the culture to high concentrations of nutrients in the feed zone for sufficient duration can produce unexpected effects on its performance. The effect of the feed zone was evaluated by conducting aerobic fed-batch fermentations of Saccharomyces cerevisiae with both complex and defined media. The broth was recirculated between a recycle loop and a bench-scale fermentor, and feed was intermittently added into the recycle loop to simulate the circulation of cells through the feed zone. Experiments were carried out for a range of residence times in the recycle loop from 0.5 to 12 min. Biomass yields from the complex-media fermentations were not affected by exposure to high nutrient levels in the recycle loop for residence times up to 12 min. Ethanol consumption was reduced by as much as 50% for residence time in the loop up to 3 min. Very long exposure of yeast cells to excess nutrient levels (12 min) gave acetic acid formation. In a defined medium, the simulated feed zone effect increased biomass yield by up to 10%, but had no effect on ethanol levels. This study indicates that the feed zone effect on biomass yield in yeast fermentation, using complex substrates, will be negligible under fully aerobic conditions. 相似文献
57.
The existence of a yield stress in filamentous fermentation broths has important transport phenomena implications in the design and operation of bioreactors. In this study, the constant shear rate vane method was assessed for directly measuring the yield stress of filamentous Aspergillus niger fermentation broths, as well as model fluids (ketchup, yogurt, and pulp suspensions). The method involved rotating 4-, 6-, and 8-bladed vanes (7.2 cm = height = 15 cm; 4.0 cm = dia. = 6 cm) at speeds of 0.01 to 0.64 rpm in the fluid and plotting the torque as a function of time. Based on visual observations, the consistency of the results with vane type and speed and comparison with previous work on nonbiological samples, it was concluded that the method is an effective and consistent technique for yield stress measurements on filamentous fermentation broths. Based on comparisons with concentric cylinder viscometer results, it was also concluded that the value determined via the vane method was a "static" yield stress (values of up to 28 Pa) which was much greater than the extrapolated (or "dynamic") yield stress determined via the concentric cylinder viscometer. (c) 1992 John Wiley & Sons, Inc. 相似文献
58.
Continuous butanol/isopropanol fermentation in down-flow column reactor coupled with pervaporation using supported liquid membrane 总被引:2,自引:0,他引:2
Continuous butanol/isopropanol fermentation with immobilized Clostridium isopropylicum was performed in a downflow column reactor using molasses as the substrate. In order to prevent product inhibition and at the same time obtain high concentration of the products, the column reactor was coupled with a pervaporation module using a supported liquid membrane. The liquid membrane was prepared with oleyl alcohol nontoxic to the microorganism. In comparison with the continuous fermentation without product removal, the specific butanol production rate was 2 times higher. The butanol concentration in the permeate was 230 kg/m(3), which was about 50 times higher than that in the culture broth. A numerical investigation suggested a further increase in the productivity by improving the module construction. 相似文献
59.
On-line fluorescence-monitoring of the methanogenic fermentation 总被引:2,自引:0,他引:2
On-line in situ fluorescence measurements of the methanogenic fermentation were conducted with reactors receiving either glucose or a mixture of volatile fatty acids as the substrate. The reactors were perturbed from steady-state conditions in order to assess the response of fluorescencemonitoring probes. Two fluorescence-monitoring probes were evaluated over a period of 8 months; they performed in a consistent manner, and their response was not significantly affected by the changes in pH and redox potential encountered during routine reactor operation. A commercially available probe, designed to measure NAD(P)H, demonstrated particular promise for detecting imbalance caused by the entry of air, inhibitor addition and was capable of distinguishing between different substrates. This fluorescence-monitoring probe detected imbalance more rapidly than other on-line measurements such as pH, Eh, or gas production, or off-line measurements such as volatile fatty acid concentration or gas composition. An experimental fluorescence-monitoring probe, designed to measure coenzyme F(420), also showed some promise in this regard. The response of the fluorescence-monitoring probes also revealed details of the metabolic routes in the reactors and the probes represent a useful research tool. For example, a failure to observe the characteristic response of the NAD(P)H-monitoring probe to formate addition during the metabolism of acetate, propionate, or glucose strongly suggests that any formate liberated during their catabolism is degraded via a different route to exogenously added formate. 相似文献
60.
Effect of alteration of the acetic acid synthesis pathway on the fermentation pattern of escherichia coli 总被引:1,自引:0,他引:1
The glucose metabolism of an Escherichia coli strain bearing mutations abolishing both acetyl phosphotransferase (PTA) and acetate kinase (ACK) activities was studied under aerobic and anaerobic conditions. These studies were conducted in a complex medium with the mutant carrying no plasmid, the mutant carrying the common cloning vector pUC19, and the mutant carrying a plasmid bearing the "pet" operon that encodes Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase activities. The mutant carrying no plasmid showed lower specific growth and glucose uptake rates relative to the parent wild-type strain (K-12), Lactic acid was produced at higher levels than the wild type, and considerable amounts of pyruvic acid were secreted as an unusual byproduct. Analysis of other fermentation products showed low but significant amounts of acetic acid, no accumulation of formic acid, and lower secretion of succinate and ethanol. The maintenance of the plasmid pUC19 in the mutant negatively affected metabolism. Expression of the pet operon overcame the metabolic stress caused by the plasmid, enhancing growth and glucose uptake rates to the values observed in the plasmidfree mutant. Also, expression of the pet operon allowed consumption of pyruvate accumulated during the first hours of fermentation. 相似文献