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1.
Culture of Clostridium pasteurianum in Defined Medium and Growth as a Function of Sulfate Concentration 下载免费PDF全文
Clostridium pasteurianum strain W-5 was selected as an anaerobe which may be grown from large inocula in defined media with sulfate as its primary sulfur source. Since it is important to keep inocula small in minimizing transfer of sulfur sources, culture conditions were optimized. The medium devised decreased lag period and generation time when compared with other media, but growth could not be induced consistently with 6 x 10(6) cells per ml or less. Addition of trace elements, chelating agents, reducing agents, metabolites, and spent medium from various stages of growth did not stimulate growth from small inocula. Generation time was 85 min on inoculation with 10(7) or more cells per ml taken from young stocks, but the lag period decreased somewhat with larger inocula. On the other hand, generation time and lag period increased with age of the inoculum. The total yield of cells increased when buffer capacity was increased. Growth of C. pasteurianum W-5 was dependent upon sulfate at relatively low sulfate concentrations, and the organism is thus suitable for study of sulfur metabolism. No evidence of a maintenance requirement for sulfate was detected. 相似文献
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Summary A wide range of bacterial strains were examined for their ability to accumulate polyhydroxyalkanoates (PHA) from various carbon sources. Strains were selected from those reported to accumulate poly-3-hydroxybutyrate (PHB), related organisms and laboratory stocks. Other strains known to utilize n-alkanes, n-alcohols or n-acids were chosen to investigate their ability to produce long-chain PHAs. Five strains accumulated only PHB, 13 accumulated PHAs containing only C4 and C5 units and 7 accumulated PHAs containing 3-hydroxyacid units in the range C5 to C10. 相似文献
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Isolation and characterization of sporulation-specific promoters in the yeast Saccharomyces cerevisiae 总被引:4,自引:0,他引:4
A library of random yeast genomic DNA:lacZ fusions has been constructed using an episomal yeast-Escherichia coli shuttle vector (pCS1). Plasmid pCS1 requires insertion of a promoter and an in frame ATG codon upstream of its resident truncated lacZ gene to regulate expression in yeast. Yeast genomic DNA fragments of 4-6 kb were generated by partial digestion with Sau3A and ligated into the unique BamHI site of plasmid pCS1 to generate a library of 5 x 10(4) individual E. coli transformants. This library was screened to identify promoter-lacZ fusions that were expressed uniquely during sporulation. Of 342 yeast transformants that exhibited beta-galactosidase activity, two were found to express the lacZ gene in a sporulation-specific manner. This paper presents the characterization of two genomic yeast DNA fragments containing promoters that control lacZ expression during the sporulation process. Expression from the promoter present in plasmid pJC18 occurred from 11-21 hours into the sporulation process, while the promoter in plasmid pJC217 was active from 4-14 hours. Staining of nuclear DNA to correlate nuclear morphology with timing of gene expression showed when each of these promoters was active in terms of the morphological stages of sporulation. 相似文献
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The general fine structure of the giant coenocyte Caulerpa prolifera (Forsskål) Lamouroux is presented. The cytoplasm forms a parietal layer throughout the plant without any regular membranous separations within organs or between organs. The vacuome is similar in structure. There are distinct patterns of organelle distribution in the highly polar cytoplasm of rhizoids and blades. The organelles are compared to those of other members of the division Chlorophyta and are typical. Amyloplast structure is compared to that of chloroplasts. A possible developmental sequence from chloroplast buds through an unusual circular body is suggested. 相似文献
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1. Molar growth-yield coefficients of Zymomonas mobilis for glucose, fructose, glucose plus fructose, and sucrose are reported. Yield coefficients for sucrose are appreciably lower than those for the equivalent concentrations of glucose plus fructose. 2. Only 2.6% of [U-(14)C]glucose supplied in the growth medium is incorporated into cell substance by Z. mobilis utilizing glucose as the energy source. 3. During growth on sucrose a levan is formed. It has been characterized and shown to resemble other bacterial levans. 4. Levan formation from sucrose could be demonstrated with both washed cell suspensions and cell extracts of Z. mobilis. 5. Sucrose phosphorylase could not be demonstrated in extracts of the organism. 相似文献
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Studies on the endogenous metabolism and senescence of starved Sarcina lutea 总被引:12,自引:0,他引:12 下载免费PDF全文
1. When washed suspensions of Sarcina lutea are starved aerobically in phosphate buffer at the growth temperature of 37 degrees , the rate of endogenous oxygen consumption decreases to very low values after 10hr., although many of the cells survive for 40hr. If starvation is prolonged further, the bacteria die at a rate of approximately 1.5% of the initial viable population per hour. 2. Oxidation of intracellular free amino acids accounts for most of the observed endogenous oxygen uptake but RNA is also utilized and a portion of the component bases and pentose is degraded and presumably oxidized. Ammonia appears in the supernatant and some pentose and ultraviolet-absorbing nucleotide are released from the cells. DNA, protein and polysaccharide are not measurably degraded. 3. Survival can be correlated with the ability of aerobically starved bacteria to oxidize exogenous l-glutamate and glucose. When starved under nitrogen for 40hr. cells continue to oxidize their endogenous reserves at undiminished rates when transferred to aerobic conditions; on prolonging anaerobic starvation the rate of oxidation declines during the period of most rapid loss of viability. 4. In the presence of Mg(2+), RNA degradation during aerobic starvation is almost completely suppressed without affecting the period for which the bacteria survive. 5. Cells grown in peptone supplemented with glucose accumulate reserves of polysaccharide which are metabolized in aerobic starvation, together with free amino acids. Ammonia is evolved and RNA is degraded to a greater extent than in peptone-grown suspensions. Bacteria rich in polysaccharide survive less well than those which are deficient in the polymer; the reason for this phenomenon has yet to be established. 6. In peptone medium, endogenous oxygen uptake and the concentration of intracellular free amino acids decline as growth progresses and they continue to decrease when the organism is held in stationary phase. Under the conditions used, the endogenous Q(o2) and free amino acid pool of cells grown in peptone with 2% (w/v) glucose did not decline so markedly and the bacteria contained large amounts of polysaccharide at all stages of growth. 相似文献
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Occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates. 总被引:76,自引:0,他引:76 下载免费PDF全文
Polyhydroxyalkanoates (PHAs), of which polyhydroxybutyrate (PHB) is the most abundant, are bacterial carbon and energy reserve materials of widespread occurrence. They are composed of 3-hydroxyacid monomer units and exist as a small number of cytoplasmic granules per cell. The properties of the C4 homopolymer PHB as a biodegradable thermoplastic first attracted industrial attention more than 20 years ago. Copolymers of C4 (3-hydroxybutyrate [3HB]) and C5 (3-hydroxyvalerate [3HV]) monomer units have modified physical properties; e.g., the plastic is less brittle than PHB, whereas PHAs containing C8 to C12 monomers behave as elastomers. This family of materials is the centre of considerable commercial interest, and 3HB-co-3HV copolymers have been marketed by ICI plc as Biopol. The known polymers exist as 2(1) helices with the fiber repeat decreasing from 0.596 nm for PHB to about 0.45 nm for C8 to C10 polymers. Novel copolymers with a backbone of 3HB and 4HB have been obtained. The native granules contain noncrystalline polymer, and water may possibly act as a plasticizer. Although the biosynthesis and regulation of PHB are generally well understood, the corresponding information for the synthesis of long-side-chain PHAs from alkanes, alcohols, and organic acids is still incomplete. The precise mechanisms of action of the polymerizing and depolymerizing enzymes also remain to be established. The structural genes for the three key enzymes of PHB synthesis from acetyl coenzyme A in Alcaligenes eutrophus have been cloned, sequenced, and expressed in Escherichia coli. Polymer molecular weights appear to be species specific. The factors influencing the commercial choice of organism, substrate, and isolation process are discussed. The physiological functions of PHB as a reserve material and in symbiotic nitrogen fixation and its presence in bacterial plasma membranes and putative role in transformability and calcium signaling are also considered. 相似文献