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排序方式: 共有263条查询结果,搜索用时 31 毫秒
1.
Intestinal synthesis of 24-keto-1,25-dihydroxyvitamin D3. A metabolite formed in vivo with high affinity for the vitamin D cytosolic receptor 总被引:1,自引:0,他引:1
J L Napoli B C Pramanik P M Royal T A Reinhardt R L Horst 《The Journal of biological chemistry》1983,258(15):9100-9107
24-Keto-1,25-dihydroxyvitamin D3 has been identified as an intestinal metabolite of 1,25-dihydroxyvitamin D3 by ultraviolet absorbance, mass spectroscopy, and chemical reactivity. The metabolite was produced from 1,25-dihydroxyvitamin D3 and 1,24R,25-trihydroxyvitamin D3 in rat intestinal mucosa homogenates. 24-Keto-1,25-dihydroxyvitamin D3 is present in vivo in the plasma and small intestinal mucosa of rats fed a stock diet, receiving no exogenous 1,25-dihydroxyvitamin D3, and in the plasma and small intestinal mucosa of rats dosed chronically with 1,25-dihydroxyvitamin D3. 24-Keto-1,25-dihydroxyvitamin D3 has affinity equivalent to 1,24R,25-trihydroxyvitamin D3 for the 3.7 S cytosolic receptor specific for 1,25-dihydroxyvitamin D3 in the intestine and thymus. In cytosolic preparations contaminated with the 5 S vitamin D-binding protein, both metabolites are about 7-fold less potent than 1,25-dihydroxyvitamin D3. In contrast, in cytosolic preparations largely free of the 5 S binding protein, both metabolites are equipotent with the parent compound. No evidence was obtained supporting a substantial presence of 23-keto-1,25-dihydroxyvitamin D3 in vivo; nor was the latter compound generated in detectable amounts from 1,25-dihydroxyvitamin D3 by intestinal homogenates. Thus, C-24 oxidation is a significant pathway of intestinal 1,25-dihydroxyvitamin D3 metabolism that produces metabolites with high affinity for the cytosolic receptor which mediates vitamin D action. 相似文献
2.
The light-growth response of Phycomyces has been studied further with the sum-of-sinusoids method in the framework of the Wiener theory of nonlinear system identification. The response was treated as a black box with the logarithm of light intensity as the input and elongation rate as the output. The nonlinear input-output relation of the light-growth response can be represented mathematically by a set of weighting functions called kernels, which appear in the Wiener intergral series. The linear (first-order) kernels of wild type, and of single and double mutants affected in genes madA to madG were determined previously with Gaussian white noise test stimuli, and were used to investigate the interactions among the products of these genes (R.C. Poe, P. Pratap, and E.D. Lipson. 1986. Biol. Cybern. 55:105.). We have used the more precise sum-of-sinusoids method to extend the interaction studies, including both the first- and second-order kernels. Specifically, we have investigated interactions of the madH ("hypertropic") gene product with the madC ("night blind") and madG ("stiff") gene products. Experiments were performed on the Phycomyces tracking machine. The log-mean intensity of the stimulus was 6 x 10(-2) W m-2 and the wavelength was 477 nm. The first- and second-order kernels were analyzed in terms of nonlinear kinetic models.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
The effects of cobaltous chloride in inducing chromosomal aberrations were observed on laboratory bred mice in vivo after single oral administration of different fractions (1/10, 1/20, 1/40) of the lethal toxic dose of the salt. Bone marrow cells were flushed out and processed for chromosome studies following colchicine, hypotonic, giemsa, air drying procedure. The parameters screened were chromosomal aberrations, with and without gaps and break per cell. Slides were screened after the expiry of 6, 12, 18, and 24 h. Statistical analysis indicated the clastogenic effects of the salt. The degree of chromosome damage was directly related to the concentration, and also to the period after administration. The different stages of the cell cycle were affected. 相似文献
4.
Analysis of phenylthiohydantoin amino acid mixtures for sequencing by thermospray liquid chromatography/mass spectrometry 总被引:1,自引:0,他引:1
B C Pramanik S M Hinton D S Millington T A Dourdeville C A Slaughter 《Analytical biochemistry》1988,175(1):305-318
Phenylthiohydantoin (PTH) amino acids, the derivatives of amino acids liberated in the course of automated N-terminal sequence analysis of peptides and proteins, are most commonly identified by high-performance liquid chromatography. This communication describes an extension to the methodology for PTH amino acid identification which exploits thermospray liquid chromatography/mass spectrometry for use in the confirmation of PTH amino acid identifications previously made solely on the basis of retention times. Thermospray mass spectra of the 19 synthetic PTH amino acids corresponding to the residues commonly observed during N-terminal sequencing have been acquired. These spectra show strong signals for the protonated molecular ion, accompanied in several cases by ions produced by limited fragmentation of the amino acid side chain and/or the PTH ring system. A reverse-phase separation protocol has been adapted for use with thermospray. The method permits recognition of the protonated molecular ions of all the standard PTH amino acids at the 150-pmol level on the basis of signal-to-noise ratios of 10:1 or better with full scanning. The method has been tested on the N-terminal amino acid sequence analysis of 200 pmol of the standard protein beta-lactoglobulin A, and has been found useful in the study of selected side-products of the sequencing chemistry. 相似文献
5.
Chemical modification of chalcone isomerase by mercurials and tetrathionate. Evidence for a single cysteine residue in the active site 总被引:1,自引:0,他引:1
R A Bednar W B Fried Y W Lock B Pramanik 《The Journal of biological chemistry》1989,264(24):14272-14276
Chalcone isomerase from soybean is inactivated by stoichiometric amounts of p-mercuribenzoate or HgCl2. Spectral titration of the enzyme with p-mercuribenzoate indicates that a single thiol group is modified. Treatment of modified enzyme with KCN or thiols results in a complete restoration of enzyme activity demonstrating that the inactivation is not due to irreversible protein denaturation. A product of the enzymatic reaction, naringenin, provides complete kinetic protection against inactivation by both mercurials. The binding constant (33 microM) for naringenin determined from the concentration dependence of the protection agrees with the inhibition constant (34 microM) for naringenin as a competitive inhibitor of the catalytic reaction. This agreement demonstrates that the observed kinetic protection results from the specific binding of naringenin to the active site. Incubation of native chalcone isomerase with sodium tetrathionate (0.1 M) results in a slow time-dependent loss of enzymatic activity. The inactivation of chalcone isomerase by tetrathionate and N-ethylmaleimide becomes very rapid in the presence of 6 M urea, indicating that the native tertiary structure is responsible for the low reactivity of the enzymatic thiol. The stoichiometric modification of reduced and denatured chalcone isomerase by [3H] N-ethylmaleimide indicates that the enzyme contains only a single cysteine residue and does not contain any disulfides. The evidence presented suggests that the only half-cystine residue in chalcone isomerase is located in the active site and thereby provides the first clue to the location of the active site in chalcone isomerase. 相似文献
6.
S S Boddupalli B C Pramanik C A Slaughter R W Estabrook J A Peterson 《Archives of biochemistry and biophysics》1992,292(1):20-28
The soluble P450 isolated from Bacillus megaterium (the product of the CYP 102 gene) (P450BM-3) is a catalytically self-sufficient fatty acid hydroxylase which converts lauric, myristic, and palmitic acids to omega-1, omega-2, and omega-3 hydroxy analogs. The percentage distribution of the regioisomers depends on the substrate chain length. Lauric and myristic acids were preferentially metabolized to their omega-1 hydroxy counterparts while no hydroxylation occurred when capric acid was used as the substrate. Palmitic acid, when present at concentrations greater than the concentration of oxygen in the reaction medium (greater than 250 microM), was hydroxylated to its omega-1, omega-2, and omega-3 hydroxy analogs, with the percentage distribution of the regioisomers being 21:44:35, respectively. No omega hydroxylation of any of the fatty acids was detected. When the concentration of palmitic acid was less than the concentration of oxygen in the reaction mixture, it was noted that a number of additional products were formed. Under these conditions, unlike lauric and myristic acids, it was observed that palmitic acid was first converted to its monohydroxy isomers which were subsequently metabolized to a mixture of 14-ketohexadecanoic, 15-ketohexadecanoic, 13-hydroxy-14-ketohexadecanoic, 14-hydroxy-15-ketohexadecanoic, and 13,14-dihydroxyhexadecanoic acids with a relative distribution of 8:2:40:30:20, respectively. Thus, P450BM-3 is able not only to monohydroxylate a variety of fatty acids but also to further metabolize some of these primary metabolites to secondary and tertiary products. The present paper characterizes the products formed during the sequential hydroxylation of palmitic acid and proposes reaction pathways to explain these results. 相似文献
7.
Arachidonic acid epoxidation: epoxyeicosatrienoic acids are endogenous constituents of rat liver 总被引:2,自引:0,他引:2
J Capdevila B Pramanik J L Napoli S Manna J R Falck 《Archives of biochemistry and biophysics》1984,231(2):511-517
Epoxyeicosatrienoic acids have been isolated and purified from the livers of male rats. They were identified by gas chromatography-mass spectrometric techniques. These results expand the list of in vivo-produced eicosanoids. Their documented in vitro biological activities suggest a role for them in cell and tissue homeostasis. 相似文献
8.
R.L. Horst B.C. Pramanik T.A. Reinhardt S.-J. Shiuey J.J. Partridge M.R. Uskokovic J.L. Napoli 《Biochemical and biophysical research communications》1982,106(3):1006-1011
23,25-Dihydroxyvitamin D3 was isolated from the plasma of vitamin D3-toxic pigs. An ultraviolet absorbance spectrum confirmed its purity. The configuration of the 23-hydroxyl group was determined to be S by comparison of the natural product with synthetic 23,25- and 23,25-dihydroxyvitamin D3 by high-pressure liquid chromatography. The affinity of both 23,25- and 23,25-dihydroxyvitamin D3 for the plasma vitamin D binding protein was similar to vitamin D3. Thus, with respect to the plasma vitamin D binding protein, 23,25-dihydroxyvitamin D3 is the least potent, naturally-occurring, dihydroxylated vitamin D3 metabolite known. 相似文献
9.
Antigens of the outer envelope from Leptospira interrogans serovar canicola (Hond Utrecht IV) were extracted by 50% (v/v) ethanol or by sodium dodecyl sulphate and serological analysis suggested that they were identical. The "fraction 4" extracted by alkali was found to contain glycoproteins of high (retentate) and low (filtrate) molecular weight; the latter behaved like a hapten in serology and in animal immunization experiments. Antibodies were raised in rabbits against this hapten by conjugating it to bovine albumin fraction V. The antiserum was found to react with both the low molecular weight and high molecular weight glycoproteins. This anti-hapten serum contained little or no whole-cell-agglutinating antibodies. The fraction 4 retentate behaved like a complete antigen in serological and immunization studies. Fraction 4 retentate and the outer envelope preparations were serologically related but they were not identical. Chemical studies revealed similarities between the carbohydrate component of the outer envelope obtained by ethanol extraction and fraction 4. The outer envelope extracted by ethanol, fraction 4 and its low and high molecular weight glycoproteins contained arabinose, rhamnose, fucose, xylose, mannose, galactose, glucose, glucosamine and glucuronic acid. Three unidentified peaks were observed in gas-liquid chromatographic analysis of the O-trimethylsilyl derivatives of methyl glycosides of all these samples and one of these peaks co-eluted with the O-trimethylsilyl derivative of 3-O-methylmannose. 相似文献