全文获取类型
收费全文 | 476篇 |
免费 | 5篇 |
国内免费 | 15篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 13篇 |
2013年 | 37篇 |
2012年 | 7篇 |
2011年 | 24篇 |
2010年 | 10篇 |
2009年 | 14篇 |
2008年 | 22篇 |
2007年 | 35篇 |
2006年 | 17篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 20篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 18篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有496条查询结果,搜索用时 15 毫秒
111.
112.
From a methanogenic fixed-bed reactor fed with hydroquinone as sole energy and carbon source, a rodshaped bacterium was isolated in pure culture which could degrade hydroquinone and gentisate (2,5-dihydroxybenzoate). In syntrophic coculture with either Desulfovibrio vulgaris or Methanospirillum hungatei, also benzoate could be degraded. Other substrates such as sugars, fatty acids, alcohols, and cyclohexane derivatives were not degraded. Sulfate, sulfite, or nitrate were not used as external electron acceptor. The isolate was a Gram-negative, non-motile, nonsporeforming strict anaerobe; the guanine-plus-cytosine content of the DNA was 53.2±1.0 mol%. In pure culture, hydroquinone was degraded to acetate and benzoate, probably via an intermediate carboxylation. In syntrophic mixed cultures, all three substrates were converted completely to acetate. Phenol was never detected as a fermentation product. 相似文献
113.
Summary Suppression of annuals at various intensities was observed around some shrubs ofCoridothymus capitatus growing on kurkar formation in the coastal hills of Israel. The phenomenon was clearly observed as annuals-free belts of
15–20 cm around ‘aggressive’ shrubs. Quantitatively, density of annuals decreased by 16 fold in the annual-free belts as compared
to a distance of 60–80 cm from the canopies of the shrubs. Their dry matter was decreased by 5.4 fold around the shrubs. Suppression
rate of emergence of planted seeds of annuals (Plantago psyllium andErucaria hispanica) early in the season was 45% higher around ‘aggressive’C. capitatus than that around ‘non-aggressive’ ones.
In the laboratory, seed germination of the annuals was strongly suppressed by diffusates and volatiles from shoots, as well
as from their water extracts and their essential oils.
Incubation of fresh shoots ofC. capitatus in soil collected from around ‘non-aggressive’ shrubs, for 7 days, increased population levels of actinomycetes by 9.6 fold
and by 36.7 fold when soil was collected from around ‘aggressive’ shrubs. Isolates of some soil-borne actinomycetes inhibited
germination of the test plantsLactuca sativa andAnastatica hierochuntica on agar plates (4–98%). The preliminary results indicate a possible synergistic inhibitory effect induced by essential oils
of the aromatic shrub and the phytototic activity of actinomycetes. 相似文献
114.
115.
Werner Dangel Ruth Brackmann Achim Lack Magdy Mohamed Jürgen Koch Brigitte Oswald Birgit Seyfried Andreas Tschech Georg Fuchs 《Archives of microbiology》1991,155(3):256-262
The regulation of the expression of enzyme activities catalyzing initial reactions in the anoxic metabolism of various aromatic compounds was studied at the whole cell level in the denitrifying Pseudomonas strain K 172. The specific enzyme activities were determined after growth on six different aromatic substrates (phenol, 4-hydroxybenzoate, benzoate, p-cresol, phenylacetate, 4-hydroxyphenylacetate) all being proposed to be metabolized anaerobically via benzoyl-CoA. As a control cells were grown on acetate, or aerobically on benzoate. The expression of the following enzyme activities was determined.Phenol carboxylase, as studied by the isotope exchange between 14CO2 and the carboxyl group of 4-hydroxybenzoate; 4-hydroxybenzoyl-CoA reductase (dehydroxylating); p-cresol methylhydroxylase; 4-hydroxybenzyl alcohol dehydrogenase; 4-hydroxybenzaldehyde dehydrogenase; coenzymeA ligases for the aromatic acids benzoate, 4-hydroxybenzoate, phenylacetate, and 4-hydroxyphenylacetate; phenylglyoxylate: acceptor oxidoreductase and 4-hydroxyphenylglyoxylate: acceptor oxidoreductase; aromatic alcohol and aldehyde dehydrogenases.The formation of most active enzymes is strictly regulated; they were only induced when required, the basic activities being almost zero. The observed whole cell regulation pattern supports the postulate that the enzyme activities play a role in anoxic aromatic metabolism and that the compounds are degraded via the following intermediates: Phenol 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; benzoate benzoyl-CoA; p-cresol 4-hydroxybenzaldehyde 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; phenylacetate phenylacetyl-CoA phenylglyoxylate benzoyl-CoA plus CO2; 4-hydroxyphenylacetate 4-hydroxyphenylacetyl-CoA 4-hydroxyphenylglyoxylate 4-hydroxybenzoyl-CoA plus CO2 benzoyl-CoA. 相似文献
116.
William P. Melega Milton M. Perlmutter re Luxen Charna H. K. Nissenson Scott T. Grafton Sung-Cheng Huang Michael E. Phelps Jorge R. Barrio 《Journal of neurochemistry》1989,53(1):311-314
4-[18F]Fluoro-L-m-tyrosine (FMT), a biochemical probe of striatal dopaminergic function, has been synthesized as an L-3,4-dihydroxyphenylalanine analog for positron emission tomography. Biochemical characterization of this compound in the rat 30 min after intrajugular administration indicated that in the brain, selective decarboxylation occurred in the striatum, with the formation of 4-fluoro-3-hydroxyphenylethylamine and its metabolites. Positron emission tomography analysis of brain tissue in monkeys (Macaca nemestrina) after intravenous injection of FMT revealed a true time-dependent, specific accumulation of radioactivity in striatum, with a striatum/cerebellum (nonspecific) ratio of 4 at 180 min. Peripheral metabolism accounted for less than 40% of the total radioactivity in arterial blood samples after 120 min. The amino acid remained as the major component throughout the period of investigation (n = 3; 5 min, 95%; 10 min, 85%; 30 min, 67%; 60 min, 62%; 120 min, 60%), with a plasma clearance t 1/2 of 112 min. 3-O-Methylated metabolites were not observed. The substrate specificity of FMT, coupled with its limited in vivo peripheral metabolism, makes it a useful, new biochemical probe for in vivo, noninvasive evaluation of central dopaminergic mechanisms. 相似文献
117.
Protocatechuate 3,4-dioxygenase (EC 1.13.11.3) has been purified 42-fold from 4-hydroxybenzoate-grown cells of Rhizobium trifolii TA1, where it constitutes about 2% of the cell protein. The dioxygenase has a molecular weight of 220,000, with two dissimilar sub-units of molecular weights 29,000 and 26,500, corresponding to an 44 composition. The enzyme is specific for protocatechuate, with a Km of 1.75×10-5 M and maximum activity at pH 9.2. Metal removal and replacement studies indicate that the enzyme contains complexed Fe3+ which is required for activity. Direct atomic absorption analysis gave 1.3–1.5 g atoms Fe3+ per mole of isolated enzyme, but correction for metal-deficient proteins suggests that the value is close to 2. 相似文献
118.
《Journal of enzyme inhibition and medicinal chemistry》2013,28(5):343-363
AbstractReaction of twenty aromatic/heterocyclic sulfonamides containing a free amino, imino, hydra-zino or hydroxyl group, with tosyl isocyanate or 3,4-dichlorophenyl isocyanate afforded two series of derivatives containing arylsulfonylureido or diarylureido moieties in their molecule respectively. The new derivatives were assayed as inhibitors of three carbonic anhydrase (CA) isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form). Potent inhibition was observed against all three isozymes but especially against CA I, which is generally 10-75 times less susceptible to inhibition by the classical sulfonamides in clinical use as compared to the other major red cell isozyme, CA II, or the membrane-bound one, CA IV. The derivatives obtained from tosyl isocyanate were generally more potent than the corresponding ones obtained from 3,4-dichlorophenyl isocyanate. This is the first reported example of selective inhibition of CA I and might lead to more selective drugs/diagnostic agents from this class of pharmacologically relevant compounds. 相似文献
119.
This review provides a summary of the physiological dynamics andregulation of essential oil production, from the literature and availableinformation on diverse volatile oil crops. Essential oil production is highlyintegrated with the physiology of the whole plant and so depends on themetabolic state and preset developmental differentiation programme of thesynthesising tissue. Essential oil productivity is ecophysiologically andenvironmentally friendly. These and other aspects of the modulation ofessentialoil production are presented, along with a brief outline of the current conceptof the relevant biosynthetic mechanisms. 相似文献
120.
Steven Chamberlin William D. Wulff John V. Muntean Arnold L. Rheingold 《Inorganica chimica acta》2010,364(1):205-219
The source of the regioselectivity in the intramolecular nucleophilic addition of nitrile-stabilized carbanions to arene chromium tricarbonyl complexes was investigated for seven different substitution patterns on the arenes. All of the arenes are 1,4-dioxygenated and the substitution varies in the oxygen substituent and in the substituents of the arene carbons (hydrogen and alkyl). The regioselectivity is correlated with the preferred conformations of the chromium tricarbonyl group which in turn was determined by solution and solid-state 13C NMR spectroscopy, 1H NMR spectroscopy in solution as well as X-ray diffraction. In the four complexes analyzed by X-ray diffraction and the three complexes analyzed by solid-state 13C NMR spectroscopy, there was only one complex where it was found that the preferred conformation of the -Cr(CO)3 is different in solution than it is in the solid-state. 相似文献