首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   544篇
  免费   42篇
  586篇
  2021年   3篇
  2018年   3篇
  2015年   11篇
  2014年   6篇
  2013年   18篇
  2012年   17篇
  2011年   16篇
  2010年   18篇
  2009年   14篇
  2008年   24篇
  2007年   17篇
  2006年   29篇
  2005年   25篇
  2004年   23篇
  2003年   28篇
  2002年   13篇
  2001年   22篇
  2000年   27篇
  1999年   26篇
  1998年   6篇
  1997年   7篇
  1996年   7篇
  1995年   6篇
  1994年   5篇
  1993年   3篇
  1992年   14篇
  1991年   10篇
  1990年   10篇
  1989年   13篇
  1988年   13篇
  1987年   20篇
  1986年   6篇
  1985年   12篇
  1984年   11篇
  1983年   9篇
  1982年   7篇
  1981年   8篇
  1979年   9篇
  1978年   8篇
  1977年   8篇
  1976年   2篇
  1975年   6篇
  1974年   4篇
  1973年   8篇
  1972年   4篇
  1970年   9篇
  1969年   2篇
  1967年   2篇
  1966年   4篇
  1962年   2篇
排序方式: 共有586条查询结果,搜索用时 15 毫秒
131.
Introduction of the R-factor plasmid pKM101 increased resistance to UV-killing in uvr lexA(Ind-) recA+ strains of E. coli K12 as well as B, while their UV mutability was not affected. Similar effects were also observed in those strains when the 18-B plasmid (a pBR322 derivative carrying the region (about 5 kb) of the 35.4 kb pKM101 plasmid) was introduced. The muc genes which are considered to be involved in error-prone repair are contained in 18-B. These results suggest the possibility that the pKM101 effect requires the host recA gene and a common genetic region, including the muc genes, in both plasmids and is associated with some unmutable repair systems.  相似文献   
132.
Generally, if mutant and normal proteins have similar molecular weights and electric charges, they cannot easily be distinguished from one another. We have developed a unique method by which a mutant enzyme of adenine phosphoribosyltransferase (APRT) can easily be distinguished from normal enzyme with nearly identical molecular weight and electric charge. DNA sequencing data have suggested that in this special type of disease (Japanese-type APRT deficiency) there is an amino acid substitution from Met to Thr at position 136 of APRT. Since normal APRT has only one Met residue, the Japanese-type mutant APRT should be a methionine-free protein. Using both an amino acid sequence-specific antiserum against APRT, and specific cleavage of peptide at the methionine residue with BrCN, we could distinguish between normal and mutant proteins. Thus, normal but not mutant APRT was cleaved with BrCN, indicating that the mutant APRT is a methionine-free protein. All tested patients with the Japanese-type APRT deficiency were found to synthesize exclusively methionine-free APRT. Usefulness of this method is not restricted to a single family, as 79% of all the patients with this disease among Japanese, and more than half of all the patients with this disease reported in the world, are likely to have this unique mutation. Thus, not only sequence-specific cleavage of DNA with restriction endonucleases but also that of protein with a chemical agent has been shown to be sometimes useful for the diagnosis and analysis of a genetic disease by careful examination of normal and mutant amino acid sequences.  相似文献   
133.
Recently, autoantibodies to some citrullinated autoantigens have been reported to be specific for rheumatoid arthritis (RA). However, an entire profile of and autoimmunity of the citrullinated proteins have been poorly understood. To understand the profile, we examined citrullinated autoantigens by a proteomic approach and further investigated the significance of citrullination in antigenicity of one of the autoantigens. Specifically, we detected citrullinated autoantigens in synovial tissue of a patient with RA by two-dimensional electrophoresis and Western blotting by using pooled sera from five patients with RA and anti-citrulline antibodies. After identifying the detected autoantigens by mass spectrometry, we investigated the contribution of citrullination to autoantigenicity by using a recombinant protein with or without citrullination on one of the identified novel citrullinated autoantigens. As a result, we found 51 citrullinated protein spots. Thirty (58.8%) of these spots were autoantigenic. We identified 13 out of the 30 detected citrullinated autoantigenic proteins. They contained three fibrinogen derivatives and several novel citrullinated autoantigens (for example, asporin and F-actin capping protein α-1 subunit [CapZα-1]). We further analyzed the contribution of citrullination to autoantigenicity in one of the detected citrullinated autoantigens, CapZα-1. As a result, frequencies of autoantibodies to non-citrullinated CapZα-1 were 36.7% in the RA group tested, 10.7% in the osteoarthritis (OA) group, and 6.5% in healthy donors. On the other hand, those to citrullinated CapZα-1 were 53.3% in the RA group, 7.1% in the OA group, and 6.5% in the healthy donors. This shows that autoantigenicity of citrullinated or non-citrullinated CapZα-1 is relevant to RA. The antibody titers to the citrullinated CapZα-1 were significantly higher than those to the non-citrullinated CapZα-1 in 36.7% of patients; however, the other patients showed almost equal antibody titers to both citrullinated and non-citrullinated CapZα-1. Therefore, the autoantibodies would target citrulline-related and/or citrulline-unrelated epitope(s) of CapZα-1. In conclusion, we report a profile of citrullinated autoantigens for the first time. Even though citrullination is closely related to autoantigenicity, citrullination would not always produce autoantigenicity in RA. Citrullinated and non-citrullinated autoantigens/autoepitopes would have different pathological roles in RA.  相似文献   
134.
The biosynthetic relations between protoberberine-, benzo[C]phenanthridine- and B-secoprotoberberine type alkaloids were demonstrated by use of (±)-tetrahydrocoptisine-[8,14-3H HCl, (±)-tetrahydrocorysamine-[8,14-3H]HCl and corynoline-[6-3H]HCl in Corydalis incisa, and the following results were presented. (±)-Tetrahydrocoptisine was converted to corynoline, corydalic acid methyl ester and corydamine hydrochloride. (±)-Tetrahydrocorysamine was converted to corynoline and corydalic acid methyl ester. Evidence that N-methyl-3-[6′-(3′,4′-methylenedioxyphenethylalcohol)]-4-methyl-7,8-methylenedioxy-1,2,3,4-tetrahydroisoquinoline-[α-3H] HCl was incorporated into corynoline-[11-3H] indicates the occurrence of the ring fission at C6-N followed by linking ofthe C6 and C13 positions in (±)-tetrahydrocoptisine and (±)-tetrahydrocorysamine, and suggests the participation of one of two possible intermediates in the biosynthesis of these alkaloids.  相似文献   
135.
The role of insulin in norepinephrine turnover (NE) and thermogenesis in brown adipose tissue (BAT) after acute cold-exposure was studied using streptozocin (STZ)-induced diabetic rats. NE turnover was estimated by the NE synthesis inhibition technique with alpha-methyl-p-tyrosine. BAT thermogenesis was estimated by measuring mitochondrial guanosine-5'-diphosphate (GDP), cytochrome oxidase activity and mitochondrial oxygen consumption in BAT at an ambient temperature of 22 degrees C and during a six-hour cold-exposure at 4 degrees C. In insulin-deficient diabetic rats, the NE turnover, mitochondrial GDP binding, cytochrome oxidase activity and mitochondrial oxygen consumption in BAT at 22 degrees C were significantly reduced, compared with those of control rats. Treatment of STZ-induced diabetic rats with insulin prevented a decrease in NE turnover and BAT thermogenesis. Acute cold-exposure increased the NE turnover of BAT in insulin-deficient diabetic rats. The BAT thermogenic response to acute cold-exposure, however, did not occur in insulin-deficient diabetic rats. These results suggest that insulin is not essential in potentiating NE turnover in BAT after acute cold-exposure, but is required for cold-induced thermogenesis.  相似文献   
136.
Platelets store self-agonists such as ADP and serotonin in dense core granules. Although exocytosis of these granules is crucial for hemostasis and thrombosis, the underlying mechanism is not fully understood. Here, we show that incubation of permeabilized platelets with unprenylated active mutant Rab27A-Q78L, wild type Rab27A, and Rab27B inhibited the secretion, whereas inactive mutant Rab27A-T23N and other GTPases had no effects. Furthermore, we affinity-purified a GTP-Rab27A-binding protein in platelets and identified it as Munc13-4, a homologue of Munc13-1 known as a priming factor for neurotransmitter release. Recombinant Munc13-4 directly bound to GTP-Rab27A and -Rab27B in vitro, but not other GTPases, and enhanced secretion in an in vitro assay. The inhibition of secretion by unprenylated Rab27A was rescued by the addition of Munc13-4, suggesting that Munc13-4 mediates the function of GTP-Rab27. Thus, Rab27 regulates the dense core granule secretion in platelets by employing its binding protein, Munc13-4.  相似文献   
137.
The effects of various antimycotic reagents and some other reagents on a cytochrome P-450-linked monooxygenase system were investigated with respect to the activities of NADPH-ferricyanide reductase. NADPH-cytochrome c reductase of NADPH-adreno-ferredoxin reductase from NADPH to cytochrome c via adreno-ferredoxin, NADPH-cytochrome P-450-phenylisocyanide complex reductase, and the cholesterol side chain cleavage of the cytochrome P-450scc-linked monooxygenase system. No reagents inhibited the NADPH-ferricyanide reductase activity. Only cloconazole inhibited about 50% of NADPH-cytochrome c reductase activity. Cloconazole, econazole, clotrimazole, etomidate and ketoconazole inhibited both NADPH-cytochrome P-450-phenylisocyanide complex reductase and the side chain cleavage activity of cholesterol of the cytochrome P-450scc-linked monooxygenase system. Cloconazole, econazole, etomidate and ketoconazole behaved like non-competitive inhibitors for NADPH-cytochrome P-450-phenylisocyanide reductase activities and their Ki values were 10(-4)-10(-6) M. Cloconazole was a non-competitive inhibitor of NADPH-cytochrome c reductase and its Ki value was 8.3 x 10(-4) M. Cloconazole, clotrimazole, econazole, etomidate, ketoconazole and mitotane completely inhibited the side chain cleavage activity of cholesterol.  相似文献   
138.
To understand the utilization property of light energy,Synechococcus sp. MA19, a poly-β-hydroxybutyrate (PHB) producer, was cultivated at the different incident light intensities of 15.3, 50.0 and 78.2 W/m2 using media with and without phosphate. From the results of metabolic flux analysis, it was found that the cell yield based on ATP synthesis was estimated as 3.5×10−3 kg-biomass/mol-ATP in these cultures. Under the examined conditions, there were no significant differences in the efficiency of light energy conversion to chemical energies estimated as ATP synthesis and reducing potential (NADH+NADPH) formation whether the PHB synthesis took place or not. The energy converted from light to ATP was kept relatively high around the energy absorbed by the cells of 2.5–3.0×106 J h−1 kg−1, whereas the energy of reducing potential was hardly changed in the examined range of the energy absorbed by the cells.  相似文献   
139.
We have synthesized Deltalac-acetogenins that are new acetogenin mimics possessing two n-alkyl tails without an alpha,beta-unsaturated gamma-lactone ring and suggested that their inhibition mechanism may be different from that of common acetogenins [Hamada et al. (2004) Biochemistry 43, 3651-3658]. To elucidate the inhibition mechanism of Deltalac-acetogenins in more detail, we carried out wide structural modifications of original Deltalac-acetogenins and characterized the inhibitory action with bovine heart mitochondrial complex I. In contrast to common acetogenins, both the presence of adjacent bis-THF rings and the stereochemistry around the hydroxylated bis-THF rings are important structural factors required for potent inhibition. The inhibitory potency of a derivative possessing an n-butylphenyl ether structure (compound 7) appeared to be superior to that of the original Deltalac-acetogenins and equivalent to that of bullatacin, one of the most potent natural acetogenins. Double-inhibitor titration of steady-state complex I activity showed that the extent of inhibition of compound 7 and bullatacin is not additive, suggesting that the binding sites of the two inhibitors are not identical. Competition tests using a fluorescent ligand indicated that the binding site of compound 7 does not overlap with that of other complex I inhibitors. The effects of compound 7 on superoxide production from complex I are also different from those of other complex I inhibitors. Our results clearly demonstrate that Deltalac-acetogenins are a novel type of inhibitor acting at the terminal electron-transfer step of bovine complex I.  相似文献   
140.
Murai M  Ishihara A  Nishioka T  Yagi T  Miyoshi H 《Biochemistry》2007,46(21):6409-6416
The inhibitor binding domain in bovine complex I is believed to be constructed by multisubunits, but it remains to be learned how the binding positions of chemically diverse inhibitors relate to each other. To get insight into the inhibitor binding domain in complex I, we synthesized a photoreactive acetogenin [[125I](trifluoromethyl)phenyldiazirinylacetogenin, [125I]TDA], in which an aryldiazirine group serves as both a photoreactive group and a substitute for the gamma-lactone ring that is a common toxophore of numerous natural acetogenins, and carried out photoaffinity labeling to identify the labeled subunit using bovine heart submitochondrial particles (SMP). When SMP were UV-irradiated in the presence of [125I]TDA, radioactivity was predominantly incorporated into an approximately 30 kDa band on a SDS gel. Blue native gel electrophoresis of the [125I]TDA-labeled SMP revealed that the majority of radioactivity was observed in complex I. Analysis of complex I on a SDS gel showed a predominant peak of radioactivity at approximately 30 kDa. Immnoprecipitation of the [125I]TDA-labeled complex I with anti-bovine ND1 antibody indicated that the labeled protein is the ND1 subunit. A variety of complex I inhibitors such as piericidin A and rotenone efficiently suppressed the specific binding of [125I]TDA to ND1, indicating that they share a common binding domain. However, the suppression efficiency of Deltalac-acetogenin, a new type of complex I inhibitor synthesized in our laboratory, was much lower than that of the traditional inhibitors. Our results unequivocally reveal that the ND1 subunit constructs the inhibitor binding domain, though the contribution of this subunit has been challenged. Further, the present study corroborates our previous proposition that the inhibition site of Deltalac-acetogenins differs from that of traditional inhibitors.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号