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61.
62.
The ability of S. putrefaciens to reduce Fe(III) complexed by a variety of ligands has been investigated. All of the ligands tested caused the cation to be more susceptible to reduction by harvested whole cells than when uncomplexed, although some complexes were more readily reduced than others. Monitoring rates of reduction by a ferrozine assay for Fe(II) formation proved inadequate using Fe(III) ligands giving Fe(II) complexes of low kinetic lability (e.g. EDTA). A more suitable assay for Fe(III) reduction in the presence of such ligands proved to be the observation of associated cytochrome oxidation and re-reduction. Where possible, an assay for Fe(III) reduction based upon the disappearance of Fe(III) complex was also employed. Reduction of all Fe(III) complexes tested was totally inhibited by the presence of O2, partially inhibited by HQNO and slower in the absence of a physiological electron donor. Upon cell fractionation, Fe(III) reductase activity was detected exclusively in the membranes. Using different physiological electron donors in assays on membranes, relative reduction rates of Fe(III) complexes complemented the data from whole cells. The differences in susceptibility to reduction of the various complexes are discussed, as is evidence for the respiratory nature of the reduction. 相似文献
63.
Nitrous oxide reduction by members of the family Rhodospirillaceae and the nitrous oxide reductase of Rhodopseudomonas capsulata. 总被引:2,自引:1,他引:1
A G McEwan A J Greenfield H G Wetzstein J B Jackson S J Ferguson 《Journal of bacteriology》1985,164(2):823-830
After growth in the absence of nitrogenous oxides under anaerobic phototrophic conditions, several strains of Rhodopseudomonas capsulata were shown to possess a nitrous oxide reductase activity. The enzyme responsible for this activity had a periplasmic location and resembled a nitrous oxide reductase purified from Pseudomonas perfectomarinus. Electron flow to nitrous oxide reductase was coupled to generation of a membrane potential and inhibited by rotenone but not antimycin. It is suggested that electron flow to nitrous oxide reductase branches at the level of ubiquinone from the previously characterized electron transfer components of R. capsulata. This pathway of electron transport could include cytochrome c', a component hitherto without a recognized function. R. capsulata grew under dark anaerobic conditions in the presence of malate as carbon source and nitrous oxide as electron acceptor. This confirms that nitrous oxide respiration is linked to ATP synthesis. Phototrophically and anaerobically grown cultures of nondenitrifying strains of Rhodopseudomonas sphaeroides, Rhodopseudomonas palustris, and Rhodospirillum rubrum also possessed nitrous oxide reductase activity. 相似文献
64.
Kassem Alef J. Barry Jackson Alastair G. McEwan Stuart J. Ferguson 《Archives of microbiology》1985,142(4):403-408
- The disappearance of nitrate from suspensions of intact, washed cells of Rhodopseudomonas capsulata strain N22DNAR+ was measured with an ion selective electrode. In samples taken from phototrophic cultures grown to late exponential phase, nitrate disappearance was partially inhibited by light but was not affected by the presence of ammonium. Nitrate disappearance from samples from low density cultures in the early exponential phase of growth was first inhibited and later stimulated by light. In these cells ammonium ions inhibited the light-dependent but not the dark disappearance of nitrate. It is concluded that cells in the early exponential phase of growth possess both an ammonium-sensitive, assimilatory pathway for nitrate reduction (NRI) and an ammonium-insensitive pathway for nitrate reduction (NRII) which is linked to respiratory electron flow and energy conservation. In cells harvested in late exponential phase only the respiratory pathway for pitrate reduction is detectable.
- Nitrate reduction, as judged by the oxidation of reduced methyl viologen by anaerobic cell suspensions, was measured at high rates in those strains of R. capsulata (AD2, BK5, N22DNAR+) which are believed to possess NRII activity but not in those strains (Kbl, R3, N22) which only manifest the ammonium-sensitive NRI pathway. On this basis we have used nitrate-dependent oxidation of reduced methyl viologen as a diagnostic test for the nitrate reductase of NRII in cells harvested from cultures of R. capsulata strain AD2. The activity was readily detectable in cells from cultures grown aerobically in the dark with ammonium nitrate as source of nitrogen. When the oxygen supply to the culture was withdrawn, the level of methyl viologen-dependent nitrate reductase increased considerably and nitrite accumulated in the culture medium. Upon reconnecting the oxygen supply, methyl viologen-dependent nitrate reductase activity decreased and the reduction of nitrate to nitrite in the culture was inhibited. It is concluded that the respiratory nitrate reductase activity is regulated by the availability of electron transport pathways that are linked to the generation of a proton electrochemical gradient.
65.
Eva De Mol Elzbieta Szulc Claudio Di Sanza Paula Martínez-Cristóbal Carlos W. Bertoncini R. Bryn Fenwick Marta Frigolé-Vivas Marianela Masín Irene Hunter Víctor Buzón Isabelle Brun-Heath Jesús García Gianni De Fabritiis Eva Estébanez-Perpiñá Iain J. McEwan Ángel R. Nebreda Xavier Salvatella 《Structure (London, England : 1993)》2018,26(1):145-152.e3
66.
We determined the extent of Na+-independent, proton-driven amino acid transport in human intestinal epithelia (Caco-2). In Na+-free conditions, acidification of the apical medium (apical pH 6.0, basolateral pH 7.4) is associated with a saturable net absorption of glycine. With Na+-free media and apical pH set at 6.0, (basolateral pH 7.4), competition studies with glycine indicate that proline, hydroxyproline, sarcosine, betaine, taurine, -alanine, -aminoisobutyric acid (AIB), -methylaminoisobutyric acid (MeAIB), -amino-n-butyric acid and l-alanine are likely substrates for pH-dependent transport in the brush border of Caco-2 cells. Both d-serine and d-alanine were also substrates. In contrast leucine, isoleucine, valine, phenylalanine, methionine, threonine, cysteine, asparagine, glutamine, histidine, arginine, lysine, glutamate and d-aspartate were not effective substrates. Perfusion of those amino acids capable of inhibition of acid-stimulated net glycine transport at the brush-border surface of Caco-2 cell monolayers loaded with the pH-sensitive dye 2,7-bis(2-carboxyethyl-5(6)-carboxyfluorescein) (BCECF) caused cytosolic acidification consistent with proton/amino acid symport. In addition, these amino acids stimulate an inward short-circuit current (I
sc) in voltage-clamped Caco-2 cell monolayers in Na+-free media (pH 6.0). Other amino acids such as leucine, isoleucine, phenylalanine, tryptophan, methionine, valine, serine, glutamine, asparagine, d-aspartic acid, glutamic acid, cysteine, lysine, arginine and histidine were without effect on both pHi and inward I
sc. In conclusion, Caco-2 cells express a Na+-independent, H+-coupled, rheogenic amino acid transporter at the apical brush-border membrane which plays an important role in the transepithelial transport of a range of amino acids across this human intestinal epithelium.This study was supported by a Wellcome Trust Fellowship (to DTT). Charlotte Ward, Maureen Sinclair and Ken Elliott provided excellent technical assistance. 相似文献
67.
68.
An improved method for determining the viability of the nitrogen-fixing actinomycete Frankia is presented. This method uses tetrazolium red as a vital stain, which proved more effective than a previously used method of acridine orange staining. 相似文献
69.
70.
Alina?Ilie Andy?Y.?L.?Gao Jonathan?Reid Annie?Boucher Cassandra?McEwan Hervé?Barrière Gergely?L.?Lukacs R.?Anne?McKinney John?OrlowskiEmail authorView authors OrcID profile 《Molecular neurodegeneration》2016,11(1):63