全文获取类型
收费全文 | 225篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
229篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 18篇 |
2012年 | 9篇 |
2011年 | 17篇 |
2010年 | 2篇 |
2009年 | 6篇 |
2008年 | 13篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有229条查询结果,搜索用时 0 毫秒
221.
Rhodium and iridium complexes of trisulfonated triarylphosphanes, TPPTS (tris(3-sulfonatophenyl)phosphane), T(p-A)PTS (tris(3-sulfonato-4-methoxyphenyl)phosphane), T(2,4-X)TS (tris(2,4-dimethyl-5-sulfonatophenyl)phosphane), have been tested in biphasic hydrogenation of aldehydes. T(2,4-X)TS could not stabilize the rhodium complex under the applied conditions. Guanidium salt of T(2,4-X)TS has been characterized by X-ray crystallography, and Tolman cone angle of the phosphane has been determined from crystallographic data. The large cone angle (196°, 210°) explains the instability of the rhodium complex. Contrary to the T(2,4-X)TS/rhodium system, the T(2,4-X)TS/iridium catalyst has been found to be stable and effective in hydrogenation of benzaldehyde and caproaldehyde. 相似文献
222.
Production of the compatible solute glycine betaine from its precursors choline or glycine betaine aldehyde confers a considerable
level of tolerance against high osmolarity stress to the soil bacterium Bacillus subtilis. The glycine betaine aldehyde dehydrogenase GbsA is an integral part of the osmoregulatory glycine betaine synthesis pathway.
We strongly overproduced this enzyme in an Escherichia coli strain that expressed a plasmid-encoded gbsA gene under T7φ10 control. The recombinant GbsA protein was purified 23-fold to apparent homogeneity by fractionated ammonium
sulfate precipitation, ion-exchange chromatography on Q-Sepharose, and subsequent hydrophobic interaction chromatography on
phenyl-Sepharose. Molecular sieving through Superose 12 and sedimentation centrifugation through a glycerol gradient suggested
that the native enzyme is a homodimer with 53.7-kDa subunits. The enzyme was specific for glycine betaine aldehyde and could
use both NAD+ and NADP+ as cofactors, but NAD+ was strongly preferred. A kinetic analysis of the GbsA-mediated oxidation of glycine betaine aldehyde to glycine betaine
revealed K
m values of 125 μM and 143 μM for its substrates glycine betaine aldehyde and NAD+, respectively. Low concentrations of salts stimulated the GbsA activity, and the enzyme was highly tolerant of high ionic
conditions. Even in the presence of 2.4 M KCl, 88% of the initial enzymatic activity was maintained. B. subtilis synthesizes high levels of proline when grown at high osmolarity, and the presence of this amino acid strongly stimulated
the GbsA activity in vitro. The enzyme was stimulated by moderate concentrations of glycine betaine, and its activity was
highly tolerant against molar concentrations of this osmolyte. The high salt tolerance and its resistance to its own reaction
product are essential features of the GbsA enzyme and ensure that B. subtilis can produce high levels of the compatible solute glycine betaine under conditions of high osmolarity stress.
Received: 2 May 1997 / Accepted: 2 July 1997 相似文献
223.
Ballabh Das Satish K. Srivastava 《Biochimica et Biophysica Acta (BBA)/General Subjects》1985,840(3):324-333
Aldehyde reductases (alcohol: NADP+-oxidoreductases, EC 1.1.1.2) I and II from human placenta have been purified to homogeneity. Aldehyde reductase I, molecular weight about 74 000, is a dimer of two nonidentical subunits of molecular weigths of about 32 500 and 39 000, whereas aldehyde erductase II is a monomer of about 32 500. Aldehyde reductase I can be dissociated into subunits under high ionic concentrations. The isoelectric pH for aldehyde reductases I and II are 5.76 and 5.20, respectively. Amino acid compositions of the two enzymes are significantly different. Placenta aldehyde reductase I can utilize glucose with a lower affinity, whereas aldehyde reductase II is not capable to reducing aldo-sugars. Similarly, aldehyde reductase I does not catalyse the reduction of glucuronate while aldehyde reductase II has a high affinity for glucuronate. Both enzymes, however, exhibit strong affinity towards various other aldehydes such as glyceraldehyde, propionaldehyde, and pyridine-3-aldehyde. The pH optima for aldehyde reductases I and II are 6.0 and 7.0, respectively. Aldehyde reductaase I can use both NADH and NADPH as cofactors, whereas aldehyde reductase II activity is dependent on NADPH only. Both enzymes are susceptible to inhibition by sulfhydryl group reagents, aldose reductase inhibitors, lithium sulfate, and sodium chloride to varying degrees. 相似文献
224.
Marios Marselos Riitta Törrönen Timo Koivula Martti Koivusalo 《Biochimica et Biophysica Acta (BBA)/General Subjects》1979,583(1):110-118
There is a genetically determined variation in the inducibility of a high-Km cytoplasmic aldehyde dehydrogenase activity in the rat liver by treatment with phenobarbital. In the present experiments this activity increased after phenobarbital administration in the phenobarbital-responsive rats also in the intestinal postmitochondrial supernatant fraction. Phenobarbital-nonresponsive rats did not exhibit such an increase after drug treatment. Intraperitoneal administration of 2,3,7,8,-tetrachlorodibenzo-pdioxin, strongly enchanced the cytoplasmic enzyme activity in the liver of both responsive and nonresponsive rats. This effect was also seen in the serum but not in the intestinal or hte kidney. Intragastric administration of 3-methylcholanthrene, 3,4,-benzpyrene or chrysene induced the activity in liver and intestine but not in serum or kidney. The activity in liver was also induced by long-term feeding with 2-acetamido-fluorene. The activities induced by tetrachlorodibenzodioxin or the carcinogens had similar behaviour in isoelectric focusing in gel slabs and in gel chromatography, suggesting a possible common identity of these induced enzymes. The activity induced by these agents could be clearly differentiated both from the activity induced by phenobarbital and from the normal cytoplasmic activities. 相似文献
225.
Jan R. Van der Ploeg Jaap Kingma Egbert J. De Vries Jos G.M. Van der Ven Dick B. Janssen 《Archives of microbiology》1996,165(4):258-264
Pseudomonas sp. GJ1 is able to grow with 2-chloroethanol as the sole carbon and energy source, but not with 2-bromoethanol, which is
toxic at low concentrations (1 mM). A muatnt that could grow on 2-bromoethanol with a growth rate of 0.034 h–1 at concentrations up to 5 mM was isolated and designated strain GJ1M9. Measurement of enzyme activities showed that mutant
and wild-type strains contained a PMS-linked alcohol dehydrogenase that was active with halogenated alcohols and that was
threefold overexpressed in the mutant when grown on 2-chloroethanol, but only slightly overproduced when grown on 2-bromoethanol.
Both strains also contained an NAD-dependent alcohol dehydrogenase that had no activity with halogenated alcohols. Haloacetate
dehalogenase levels were similar in the wild-type and the mutant. Activities of NAD-dependent aldehyde dehydrogenase were
only slightly higher in extracts of the mutant grown with 2-bromoethanol than in those of the wild-type grown with 2-chloroethanol.
SDS-PAGE, however, showed that this enzyme amounted to more than 50% of the total cellular protein in extracts of the mutant
from 2-bromoethanol-grown cells, which was fourfold higher than in extracts of the wild-type strain grown on 2-chloroethanol.
The enzyme was purified and shown to be a tetrameric protein consisting of subunits of 55 kDa. The enzyme had low Km values for acetaldehyde and other non-halogenated aldehydes (0.8–4 μM), but much higher Km values for chloroacetaldehyde (1.7 mM) and bromoacetaldehyde (10.5 mM), while Vmax values were similar for halogenated and non-halogenated aldehydes. Cultures that were pregrown on 2-chloroethanol rapidly
lost aldehyde dehydrogenase activity after addition of 2-bromoethanol and chloroamphenicol, which indicates that bromoacetaldehyde
inactivates the enzyme. To achieve growth with 2-bromoethanol, the high expression of the enzyme thus appears to be necessary
in order to compensate for the high Km for bromoacetaldehyde and for inactivation of the enzyme by bromoacetaldehyde.
Received: 31 August 1995 / Accepted: 4 December 1995 相似文献
226.
When 1 mM serotonin, dopamine, or norepinephrine was incubated with a monoamine oxidase preparation (mitochondrial membranes) in the presence of 4 mM sodium bisulfite, 85-95% of the amines were oxidized to the corresponding aldehydes. In the absence of bisulfite, the recoveries were only approximately 30%, and dark colored products were formed during the incubations. The aldehydes derived from tyramine, octopamine, methoxytyramine, and normetanephrine were also prepared by the use of this method. The bisulfite-aldehyde compounds were stable during storage at -20 degrees C. Bisulfite-free aldehyde solutions were made by diethylether extraction. When the aldehydes derived from dopamine or serotonin were incubated with rat brain homogenates, they were found to disappear in an aldehyde dehydrogenase- and aldehyde reductase-independent manner. The disappearance of the latter aldehyde was more pronounced, and the results indicated that this aldehyde may react with both proteins and phospholipids. 相似文献
227.
NADP-linked aldehyde reductase (AR; EC 1.1.1.2), partially purified from epimastigotes of Trypanosoma cruzi, was able to reduce a number of aldehydes and to oxidize several alcohols; propionaldehyde and n-propanol were the best substrates, at optimal pH values of 7 to 8, and 9 to 9.5, respectively. The AR was inhibited p-chloromercuribenzoate and iodoacetamide, but not by 1,10-phenanthroline or barbital. Digitonin treatment of whole epimastigotes, and distribution and latency in subcellular fractions, indicated that the AR is cytosolic. Like other ARs, the T. cruzi enzyme might be involved in detoxication processes, instead of coenzyme re-oxidation. 相似文献
228.
The mechanism of aldehyde to carboxylic acid conversion catalyzed by P450 enzymes via a series of reactions was studied systematically
for the first time with density functional theory calculations. A two-state reactivity mechanism has been proposed, which
can be adopted for many aldehyde oxidation reactions catalyzed by P450 enzymes. The mechanism involves initial hydrogen abstraction
as the rate-limiting step and this is followed by steps of oxygen rebound without barriers owing to the quick recombination
of the resultant radical species. Meanwhile, in an attempt to explore whether there exist some rules for the hydroxylation
of aldehyde substrates by P450, the transition state barriers of the rate-limiting step for a series of aldehyde hydroxylation
reactions have been compared. A predictive pattern of extended barrier/bond energy correlation for different hydroxylations
of aldehyde substrates by P450 has been established, which was further confirmed to be a reliable reactivity scale by experimental
results.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
229.