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31.
Charged-particle activation analysis offers a number of interesting possibilities for the determination of trace elements
in biological material. It allows the determination of those elements that are difficult or impossible to determine by neutron
activation, such as Li, B, Al, Si, V, Cr, Ni, Cd, Sn, Tl, and Pb. Up to now, protons have been successfully applied to samples
of both vegetale and human origin. A number of difficulties have to be overcome, one of which is excessive heating of the
samples owing to the limited range of the charged particles, thus giving rise to a high energy deposition in a small volume.
Moreover, the sample composition has to be known to allow the calculation of the range of the particles. an interesting alternative
has been proposed using an internal standard together with a standard additions procedure. Proton activation analysis was
tested on a wide variety of reference materials, giving evidence that accurate results can be obtained for many trace elements,
even when applying a purely instrumental method. Thus, the method can also be applied in the certification of reference materials,
since nuclear methods are independent of chemical properties of the sample. 相似文献
32.
D. Michel-Savin R. Marchal J. P. Vandecasteele 《Applied microbiology and biotechnology》1990,33(2):127-131
Summary Production of butyrate has been studied in continuous cultures of Clostridium tyrobutyricum. Production of acids, gases and cell biomass were determined under conditions of glucose limitation by varying either the glucose input or the dilution rate. Addition of acetate or butyrate to the cultures was also tested. The results led to the proposition that inhibition by acids acting as incouplers of energy production could provide a physiological explanation for most of the phenomena observed. It readily accounted for the higher productivities but lower product concentrations obtained in continuous culture with respect to batch or fed-batch conditions. It also explained the decrease in the ratios of butyrate to total acids and in cell yield observed at higher glucose input as well as the behaviour of the cultures under conditions of excess glucose. It could also possibly account for the partial conversion of added acetate to butyrate observed at moderate growth rates.
Offprint requests to: J. P. Vandecasteele 相似文献
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34.
S. Arino R. Marchal J. -P. Vandecasteele 《Applied microbiology and biotechnology》1996,45(1-2):162-168
A glycolipid-producing bacterium, Pseudomonas aeruginosa GL1, was isolated from the soil contaminated with polycyclic aromatic hydrocarbons (PAH) from a manufactured gas plant. The
glycolipid produced was characterized in detail by chromatographic procedures as a mixture of four rhamnolipids, consisting
of different associations of rhamnose and hydroxy fatty acids: the main component was monorhamnosyl di-3-hydroxydecanoic acid.
The rhamnolipid composition presented marked analogies with a defined part of P. aeruginosa outer membrane lipopolysaccharides (lipopolysaccharide band A). Rhamnolipid production was stimulated under conditions of
nitrogen limitation. Glycerol yielded higher productions than did hydrophobic carbon sources. Cell hydrophobicity decreased
during growth on glycerol and on n-hexadecane whereas glycolipid production increased. P. aeruginosa GL1 was found to be unable to grow on a variety of 2, 3 and 4 cycle PAH. However, it was shown to persist after at least
12 subcultures in a bacterial population growing on a mixture of pure PAH, suggesting a physiological role for rhamnolipid
as a means to enhance PAH availability in a mutualistic PAH-degrading bacterial community.
Received: 4 July 1995/Received revision: 7 September 1995/Accepted: 13 September 1995 相似文献
35.
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A general l-amino acid oxidase (l-amino acid: oxygen oxidoreductase (deaminating), EC 1.4.3.2.) has been characterized in Corynebacterium. The enzyme is soluble (MW 130 000–140 000) and is active with most l-α-amino acids but not with aspartate, threonine, proline and glycine. It is subject to substrate inhibition. This amino acid oxidase is induced along with catalase by growth in the presence of amino acids as a nitrogen source and is repressed when ammonium ions are present in the medium. Its probable physiological function is to allow the utilization of amino acids as a nitrogen source. 相似文献
38.
In the course of a freeze-cleave study on intercellular junctions in the regenerating rat liver, we observed an unusual array of intramembranous particles located in regions of contact between endothelial cells lining the hepatic sinusoids. These arrays were characterized by an accumulation of particles which resembled a zonula occludens in their linear deployment but differed in that the contact regions were composed of individual particles which remained separated from each other by regular particle-free intervals. 相似文献
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Summary Hydrolysates obtained by enzymatic saccharification of wheat straw or cornstover pretreated by steam explosion in classical or acidic conditions, were found non fermentable into acetone-butanol (ABE). A simple treatment involving heating the hydrolysates in the presence of calcium or magnesium compounds such as Ca(OH)2 or MgCO3 at neutral pH values restored normal fermentability to these hydrolysates. The detoxification treatment could be included in the standard neutralization and sterilization procedures performed before fermentation. 相似文献