全文获取类型
收费全文 | 231篇 |
免费 | 29篇 |
国内免费 | 1篇 |
出版年
2022年 | 2篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 11篇 |
2011年 | 7篇 |
2010年 | 12篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 10篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1974年 | 7篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 3篇 |
1969年 | 1篇 |
1968年 | 10篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 15 毫秒
101.
Escherichia coli mutants lacking NADH dehydrogenase I have a competitive disadvantage in stationary phase. 总被引:3,自引:3,他引:0
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)
We have previously characterized mutant strains of Escherichia coli that are able to take over stationary-phase cultures. Here we describe two insertion mutations that prevent such strains from expressing this phenotype. Both insertions were mapped to min 51, and sequence analysis revealed that both mutated genes encode proteins homologous to subunits of mitochondrial NADH dehydrogenase I. Crude extracts prepared from both mutant strains were able to oxidize NADH but lacked the enzymatic activity needed to oxidize deamino-NADH, a substrate specific for NADH dehydrogenase I. This is the first identification of genes encoding subunits of NADH dehydrogenase I in E. coli. The significance of the inability of these mutant strains to compete in stationary-phase cultures is discussed. 相似文献
102.
Two soluble glycosyltransferases glycosylate less efficiently in vivo than their membrane bound counterparts 总被引:2,自引:1,他引:1
Zhu G; Allende ML; Jaskiewicz E; Qian R; Darling DS; Worth CA; Colley KJ; Young WW Jr 《Glycobiology》1998,8(8):831-840
Many Golgi glycosyltransferases are type II membrane proteins which are
cleaved to produce soluble forms that are released from cells. Cho and
Cummings recently reported that a soluble form of alpha1, 3-
galactosyltransferase was comparable to its membrane bound counterpart in
its ability to galactosylate newly synthesized glycoproteins (Cho,S.K. and
Cummings,R.D. (1997) J. Biol. Chem., 272, 13622-13628). To test the
generality of their findings, we compared the activities of the full length
and soluble forms of two such glycosyltransferases, ss1,4
N-Acetylgalactosaminyltransferase (GM2/GD2/ GA2 synthase; GalNAcT) and beta
galactoside alpha2,6 sialyltransferase (alpha2,6-ST; ST6Gal I), for
production of their glycoconjugate products in vivo . Unlike the full
length form of GalNAcT which produced ganglioside GM2 in transfected cells,
soluble GalNAcT did not produce detectable GM2 in vivo even though it
possessed in vitro GalNAcT activity comparable to that of full length
GalNAcT. When compared with cells expressing full length alpha2,6-ST, cells
expressing a soluble form of alpha2,6-ST contained 3-fold higher
alpha2,6-ST mRNA levels and secreted 7-fold greater alpha2,6-ST activity as
measured in vitro , but in striking contrast contained 2- to 4-fold less of
the alpha2,6-linked sialic acid moiety in cellular glycoproteins in vivo .
In summary these results suggest that unlike alpha1,3-galactosyltransferase
the soluble forms of these two glycosyltransferases are less efficient at
glycosylation of membrane proteins and lipids in vivo than their membrane
bound counterparts.
相似文献
103.
The early adaptive evolution of calmodulin 总被引:7,自引:0,他引:7
Baba ML; Goodman M; Berger-Cohn J; Demaille JG; Matsuda G 《Molecular biology and evolution》1984,1(6):442-455
Interaction between gene duplication and natural selection in molecular
evolution was investigated utilizing a phylogenetic tree constructed by the
parsimony procedure from amino acid sequences of 50 calmodulin- family
protein members. The 50 sequences, belonging to seven protein lineages
related by gene duplication (calmodulin itself, troponin-C, alkali and
regulatory light chains of myosin, parvalbumin, intestinal calcium-binding
protein, and glial S-100 phenylalanine-rich protein), came from a wide
range of eukaryotic taxa and yielded a denser tree (more branch points
within each lineage) than in earlier studies. Evidence obtained from the
reconstructed pattern of base substitutions and deletions in these
ancestral loci suggests that, during the early history of the family,
selection acted as a transforming force on expressed genes among the
duplicates to encode molecular sites with new or modified functions. In
later stages of descent, however, selection was a conserving force that
preserved the structures of many coadapted functional sites. Each branch of
the family was found to have a unique average tempo of evolutionary change,
apparently regulated through functional constraints. Proteins whose
functions dictate multiple interaction with several other macromolecules
evolved more slowly than those which display fewer protein-protein and
protein-ion interactions, e.g., calmodulin and next troponin-C evolved at
the slowest average rates, whereas parvalbumin evolved at the fastest. The
history of all lineages, however, appears to be characterized by rapid
rates of evolutionary change in earlier periods, followed by slower rates
in more recent periods. A particularly sharp contrast between such fast and
slow rates is found in the evolution of calmodulin, whose rate of change in
earlier eukaryotes was manyfold faster than the average rate over the past
1 billion years. In fact, the amino acid replacements in the nascent
calmodulin lineage occurred at residue positions that in extant metazoans
are largely invariable, lending further support to the Darwinian hypothesis
that natural selection is both a creative and a conserving force in
molecular evolution.
相似文献
104.
Using cultured cells from bovine and rat aortas, we have examined the possibility that endothelial cells might regulate the growth of vascular smooth muscle cells. Conditioned medium from confluent bovine aortic endothelial cells inhibited the proliferation of growth-arrested smooth muscle cells. Conditioned medium from exponential endothelial cells, and from exponential or confluent smooth muscle cells and fibroblasts, did not inhibit smooth muscle cell growth. Conditioned medium from confluent endothelial cells did not inhibit the growth of endothelial cells or fibroblasts. In addition to the apparent specificity of both the producer and target cell, the inhibitory activity was heat stable and not affected by proteases. It was sensitive flavobacterium heparinase but not to hyaluronidase or chondroitin sulfate ABC lyase. It thus appears to be a heparinlike substance. Two other lines of evidence support this conclusion. First, a crude isolate of glycosaminoglycans (TCA-soluble, ethanol-precipitable material) from endothelial cell-conditioned medium reconstituted in 20 percent serum inhibited smooth muscle cell growth; glycosaminoglycans isolated from unconditioned medium (i.e., 0.4 percent serum) had no effect on smooth muscle cell growth. No inhibition was seen if the glycosaminoglycan preparation was treated with heparinase. Second, exogenous heparin, heparin sulfate, chondroitin sulfate B (dermatan sulfate), chondroitin sulfate ABC, and hyaluronic acid were added to 20 percent serum and tested for their ability to inhibit smooth muscle cell growth. Heparin inhibited growth at concentrations as low as 10 ng/ml. Other glycosaminoglycans had no effect at doses up to 10 μg/ml. Anticoagulant and non- anticoagulant heparin were equally effective at inhibiting smooth muscle cell growth, as they were in vivo following endothelial injury (Clowes and Karnovsk. Nature (Lond.). 265:625-626, 1977; Guyton et al. Circ. Res. 46:625-634, 1980), and in vitro following exposure of smooth muscle cells to platelet extract (Hoover et al. Circ. Res. 47:578-583, 1980). We suggest that vascular endothelial cells may secrete a heparinlike substance in vivo which may regulate the growth of underlying smooth muscle cells. 相似文献
105.
Fernando Zambrano Miguel Morales Nelson Fuentes Mireya Rojas 《The Journal of membrane biology》1981,63(1-2):71-75
Summary Sodium efflux was studied in22Na-loaded red blood cells in the presence of arylsulfatase, an enzyme that specifically hydrolyzes sulfatide. Sodium efflux was inhibited in proportion to the amount of arylsulfatase present. Maximum inhibition was almost as high as the efflux obtained in medium with K+ absent. At maximum inhibition 83.2% of the sulfatide content of the fragmented red blood cell membranes was hydrolyzed and ouabain-sensitive (Na++K+)-ATPase activity was inhibited by 100%. Sodium efflux, sulfatide content, and (Na++K+)-ATPase activity were unaffected with arylsulfatase in the presence of a high concentration of sulfatide. These results indicate that sulfatide plays a specific role in sodium and potassium ion transport. They also suggest that most sulfatide is localized externally in the red blood cell membrane. 相似文献
106.
Golgi apparatus isolated from both rat liver and rat kidney have been characterized with respect to their neutral and phospholipid content and their phosphopipid composition and compared with mitochondria, rough endoplasmic reticulum and plasma membranes. In addition, the distribution of sulfatide in the subcellular fractions of rat kidney was determinich are rich in cholesterol esters and ubiquinone. Removal of about 75% of the cisternal contents of rat liver Golgi reduced its content of cholesterol esters but not of ubiquinone. The Golgi complex of liver most closely resembles endoplasmic reticulum in its phospholipid composition except for a higher content of sphingomyelin. Removal of most of the contents of the Golgi cisternae did not appreciably alter the phospholipid composition of the Golgi apparatus of liver. Goligi apparatus from kidney has a phospholipid composition which resembles liver Golgi much more closely than it does any other cell fraction from kidney. The sulfatide content of kidney Golgi, the cell fraction richest in this glycolipid, is about 14% of the total lipid present in this fraction. Sulfatide was present in plasma membranes, mitochondria and rough microsomes, but at about one-third the level found in Golgi. Sulfatide is the main glycosphingolipid present in all the cell fractions from kidney which were studied. 相似文献
107.
Prof. Dr. David Zambrano 《Cell and tissue research》1975,162(4):551-563
The rostral pars distalis (RPD) of the teleost Mugil plantanus from animals pretreated with reserpine or 6-hydroxydopamine (6-HODA) were assayed for dopamine (DA) or noradrenaline (NA) or for prolactin hormone. Such determinations were coupled with electron microscopy. It was found that reserpine and 6-HODA produced a significant decrease in the content of DA, NA, and prolactin. Electron microscope studies revealed that prolactin cells became activated as judged by ultrastructural criteria. After 6-HODA treatment type "B" neurosecretory fibers entering the RPD became selectively destroyed. These observations lead us to suggest that prolactin secretion is under inhibitory control by type "B" neurosecretory fibers of adrenergic nature. 相似文献
108.
A method is reported for the isolation of a highly purified fraction of urinary bladder membranes containing hexagonal plaques. The method uses zonal centrifugation as the final step of fractionation. The purified fraction was characterized by its electron microscopic morphology, by its enzymatic profile, by quantitative and qualitative analysis of lipids and by the protein pattern obtained by electrophoresis in polyacrylamide sodium dodecyl sulfate gels. The fraction contains 65% lipids and 35% proteins. The major protein component has a molecular weight of 27,000 daltons. Phospholipids are more than the 54% of the total lipid weight. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol are the major phospholipids with 50%, 30%, and 7% of the total lipid phosphorus, respectively. The glycolipid fraction is 10% of the total lipid weight and is formed by only two components, both sulfatides. Total cholesterol makes up 36% of the total neutral lipid fraction of which cholesterol esters constitute 6%. Glycoproteins are also found to be present in the fraction. 相似文献
109.
110.
Low temperature magnetic circular dichroism spectroscopy as a probe for the optical transitions of paramagnetic nickel in hydrogenase 总被引:2,自引:0,他引:2
M K Johnson I C Zambrano M H Czechowski H D Peck D V DerVartanian J LeGall 《Biochemical and biophysical research communications》1985,128(1):220-225
A partially-purified sample of hydrogenase from Methanobacterium thermoautotrophicum (delta H strain) has been investigated by optical absorption, magnetic circular dichroism and electron paramagnetic resonance spectroscopy. Variable temperature magnetic circular dichroism studies reveal, for the first time, the optical transitions associated with the Ni(III) center in the oxidized enzyme. Low temperature magnetic circular dichroism spectroscopy provides a new method of assessing both the coordination environment of Ni in hydrogenase and the appropriateness of inorganic model complexes. 相似文献