全文获取类型
收费全文 | 169篇 |
免费 | 42篇 |
国内免费 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 11篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 6篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 6篇 |
1968年 | 5篇 |
1967年 | 2篇 |
1966年 | 6篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1960年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有212条查询结果,搜索用时 31 毫秒
1.
2.
chlC (nar) operon of Escherichia coli includes structural genes for alpha and beta subunits of nitrate reductase. 总被引:13,自引:9,他引:4
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The synthesis of the alpha and beta subunits of nitrate reductase by 20 chlC::Tn5 insertion mutants of Escherichia coli was determined by immune precipitation of the subunits from fractions of cell extracts. Only two of the mutants produced either subunit in detectable amounts; these two accumulated the alpha subunit, but no beta subunit. In both cases the alpha subunit was present in the cytosolic fraction, in contrast to wild-type cells, in which both subunits are present mainly in the membrane fraction. EcoRI restriction fragments containing the Tn5 inserts from five of the mutants were cloned into pBR322. The insertions were localized on two contiguous EcoRI fragments spanning a 5.6-kilobase region that overlapped the contiguous ends of the two fragments. An insertion that permitted alpha subunit formation defined one end of the 5.6-kilobase region. The results indicated that the genes encoding the alpha and beta subunits of nitrate reductase were part of a chlC (nar) operon that is transcribed in the direction alpha leads to beta. 相似文献
3.
4.
Glutamine-dependent anthranilate synthetase was produced in vitro by mixing the extracts of a trypA and a trypC mutant of Aspergillus nidulans. Neither mutant alone possessed this activity. The enzyme formed in the mixture had the properties of the wild-type anthranilate synthetase which, together with N-(5-phosphoribosyl) anthranilate (PRA) isomerase and indole 3-glycerol phosphate (InGP) synthetase, is found in a 10S multienzyme complex. Extracts of the trypA69 mutant contained a 6.5S protein as the active component—presumably the trypC
+ product—which in addition showed PRA isomerase and InGP synthetase activity. Extracts of the trypC801 mutant lacked all three enzyme activities but contained a 4.5S component—the trypA
+ gene product—which in vitro showed ammonia-dependent anthranilate synthetase activity. These mutants are analogous in their properties to certain tryp-2 and tryp-1 mutants of Neurospora. When complementary extracts of the two genera were mixed (Aspergillus trypA with Neurospora tryp-1 or Aspergillus trypC with Neurospora tryp-2), a hybrid glutamine-dependent anthranilate synthetase was obtained which showed less than half the activity produced in homologous combinations.This study was supported by Grant GB 22655 from the National Science Foundation to J.A.DeM. 相似文献
5.
Nitrate reductase complex of Escherichia coli K-12: participation of specific formate dehydrogenase and cytochrome b1 components in nitrate reduction 总被引:37,自引:22,他引:15
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The participation of distinct formate dehydrogenases and cytochrome components in nitrate reduction by Escherichia coli was studied. The formate dehydrogenase activity present in extracts prepared from nitrate-induced cells of strain HfrH was active with various electron acceptors, including methylene blue, phenazine methosulfate, and benzyl viologen. Certain mutants which are unable to reduce nitrate had low or undetectable levels of formate dehydrogenase activity assayed with methylene blue or phenazine methosulfate as electron acceptor. Of nine such mutants, five produced gas when grown anaerobically without nitrate and possessed a benzyl viologen-linked formate dehydrogenase activity, suggesting that distinct formate dehydrogenases participate in the nitrate reductase and formic hydrogenlyase systems. The other four mutants formed little gas when grown anaerobically in the absence of nitrate and lacked the benzyl viologen-linked formate dehydrogenase as well as the methylene blue or phenazine methosulfate-linked activity. The cytochrome b(1) present in nitrate-induced cells was distinguished by its spectral properties and its genetic control from the major cytochrome b(1) components of aerobic cells and of cells grown anaerobically in the absence of nitrate. The nitrate-specific cytochrome b(1) was completely and rapidly reduced by 1 mm formate but was not reduced by 1 mm reduced nicotinamide adenine dinucleotide; ascorbate reduced only part of the cytochrome b(1) which was reduced by formate. When nitrate was added, the formate-reduced cytochrome b(1) was oxidized with biphasic kinetics, but the ascorbate-reduced cytochrome b(1) was oxidized with monophasic kinetics. The inhibitory effects of n-heptyl hydroxyquinoline-N-oxide on the oxidation of cytochrome b(1) by nitrate provided evidence that the nitrate-specific cytochrome is composed of two components which have different redox potentials but identical spectral properties. We conclude from these studies that nitrate reduction in E. coli is mediated by the sequential operation of a specific formate dehydrogenase, two specific cytochrome b(1) components, and nitrate reductase. 相似文献
6.
Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews
(genus Sorex) for the region between the tRNA(Pro) and the conserved
sequence block-F revealed variable numbers of 79-bp tandem repeats. These
repeats were found in all 19 individuals sequenced, representing three
subspecies and one closely related species of the masked shrew group (Sorex
cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an
outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an
adjacent 76-bp imperfect copy of the tandem repeats. One individual was
heteroplasmic for length variants consisting of five and seven copies of
the 79-bp tandem repeat. The sequence of the repeats is conducive to the
formation of secondary structure. A termination-associated sequence is
present in each of the repeats and in a unique sequence region 5' to the
tandem array as well. Mean genetic distance between the masked shrew taxa
and the pygmy shrew was calculated separately for the unique sequence
region, one of the tandem repeats, the imperfect repeat, and these three
regions combined. The unique sequence region evolved more rapidly than the
tandem repeats or the imperfect repeat. The small genetic distance between
pairs of tandem repeats within an individual is consistent with a model of
concerted evolution. Repeats are apparently duplicated and lost at a high
rate, which tends to homogenize the tandem array. The rate of D- loop
sequence divergence between the masked and pygmy shrews is estimated to be
15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid
sequence evolution in shrews may be due either to their high metabolic rate
and short generation time or to the presence of variable numbers of tandem
repeats.
相似文献
7.
8.
大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育 总被引:1,自引:0,他引:1
本实验用免疫组织化学ABC法研究了大鼠胼胝体内神经肽Y免疫反应阳性(NPY-IR)纤维的生后发育。结果发现,许多NPY-IR纤维在大鼠出生时便存在于胼胝体内。NPY-IR胼胝体纤维的密度在生后1周内继续逐渐增高,在第2周内达到最高峰。之后,NPY-IR胼胝体纤维的密度逐渐下降,至第3周末时接近成年时的水平,即仅有少量NPY-IR纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多NPY-IR胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。 相似文献
9.
narK mutants of Escherichia coli produce wild-type levels of nitrate reductase but, unlike the wild-type strain, do not accumulate nitrite when grown anaerobically on a glucose-nitrate medium. Comparison of the rates of nitrate and nitrite metabolism in cultures growing anaerobically on glucose-nitrate medium revealed that a narK mutant reduced nitrate at a rate only slightly slower than that in the NarK+ parental strain. Although the specific activities of nitrate reductase and nitrite reductase were similar in the two strains, the parental strain accumulated nitrite in the medium in almost stoichiometric amounts before it was further reduced, while the narK mutant did not accumulate nitrite in the medium but apparently reduced it as rapidly as it was formed. Under conditions in which nitrite reductase was not produced, the narK mutant excreted the nitrite formed from nitrate into the medium; however, the rate of reduction of nitrate to nitrite was significantly slower than that of the parental strain or that which occurred when nitrite reductase was present. These results demonstrate that E. coli is capable of taking up nitrate and excreting nitrite in the absence of a functional NarK protein; however, in growing cells, a functional NarK promotes a more rapid rate of anaerobic nitrate reduction and the continuous excretion of the nitrite formed. Based on the kinetics of nitrate reduction and of nitrite reduction and excretion in growing cultures and in washed cell suspensions, it is proposed that the narK gene encodes a nitrate/nitrite antiporter which facilitates anaerobic nitrate respiration by coupling the excretion of nitrite to nitrate uptake. The failure of nitrate to suppress the reduction of trimethylamine N-oxide in narK mutants was not due to a change in the level of trimethylamine N-oxide reductase but apparently resulted from a relative decrease in the rate of anaerobic nitrate reduction caused by the loss of the antiporter system. 相似文献
10.