全文获取类型
收费全文 | 677篇 |
免费 | 40篇 |
国内免费 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 20篇 |
2014年 | 22篇 |
2013年 | 47篇 |
2012年 | 39篇 |
2011年 | 49篇 |
2010年 | 30篇 |
2009年 | 28篇 |
2008年 | 39篇 |
2007年 | 44篇 |
2006年 | 41篇 |
2005年 | 31篇 |
2004年 | 28篇 |
2003年 | 32篇 |
2002年 | 23篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有718条查询结果,搜索用时 31 毫秒
11.
Guerrini Franca; Lombini Alessandra; Bizarri Mariachiara; Pupillo Paolo 《Journal of experimental botany》1994,45(9):1227-1233
Cell suspension cultures of Beta vulgaris L., treated with calciumchelators or untreated, were used to characterize pyndine nucleotide-dependentdiaphorases of microsomes. The microsomal activity of NADH-dependentduroquinone reductase from cultures treated with 10 mM Na2EGTAfor 24 h increased by a factor of 1.8 with respect to controlmicrosomes, and was mainly associated with particles of d=1.17gml1. NADPH-duroquinone reductase and NADH-ferricyanidereductase activities showed smaller increases. Bacterial protein-lipopolysaccharidecomplexes (prLPS) also promoted the increase of microsomal diaphorases;CaEGTA was Ineffective. EGTA effects on enzymes of supernatantand mitochondria were negligible, although Na2EGTA treatmentinduced cell aggregation and strong acidification of the medium. When microsomes from control cultures were solubilized with1% LPC and fractionated in high-efficiency gel permeation columns(FPLC) the diaphorase activities were found associated to threemajor proteins: (i) NADH-specific quinone reductase (NADH-QR)of 340 kDa; (ii) pyndine nucleotide-nonspecific quinone reductase(NAD(P)H-QR) of 85 kDa also having ferricyanide reductase activity;(iii) NADH-specific ferricyanide reductase (NADH-FCR) of 38kDa. The microsomes from EGTA-treated cells also showed a highlyactive NADH-QR having a larger molecular mass (440 kDa) thanin control cells. NAD(P)H-QR also showed increased activity.We conclude that external Ca2+ chelation induces changes indehydrogenase components in microsomes. Furthermore, prLPS probablyexert part of their effect on plants through Ca2+ chelation. Key words: Beta vulgaris, cell cultures, calcium chelators, diaphorase, NAD(P)H-dehydrogenase, lipopolysaccharide, EGTA, quinone reductase 相似文献
12.
13.
Evandro Fioretti Anna Maria Eleuteri Mauro Angeletti Franca Ascoli 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1993,617(2)
A reversed-phase high-performance liquid chromatographic method for the determination and quantitative recovery of fully active aprotinin (the basic pancreatic trypsin inhibitor or Kunitz inhibitor) and aprotinin-like inhibitors in amounts down to 0.5 μg is reported. The method, which allows separation of aprotinin isoinhibitors characterized by small differences in the primary structure with respect to aprotinin itself, appears to be suitable for the quantitation and identification of aprotinin-like inhibitors in human biological fluids, in which they appear to be present at very low levels. 相似文献
14.
C. Olivari Maria Chiara Pugliarello Franca Rasi-Caldogno Maria Ida De Michelis 《Plant biology (Stuttgart, Germany)》1993,106(1):13-19
The aqueous two-phase partitioning technique was utilized to isolate a plasma membrane (PM) fraction from etiolated seedlings of Arabidopsis thaliana. The purification procedure adopted yielded a fraction highly enriched in PM as compared to inner membranes, with a recovery of about 30%, as judged from the activities of PM markers such as vanadate-sensitive ATPase, FC binding and UDP-glucose sterol glucosyltransferase. The purified PM fraction displayed vanadate-sensitive H+ pumping activity. Its purity was confirmed by the biochemical characteristics of its ATPase activity assayed in the absence of Ca2+: sensitivity to vanadate (IC50 ca. 1 μM), Mg2+-dependence, insensitivity to molybdate, oligomycin and nitrate, pH optimum at 6.6. The PM H+-ATPase activity was stimulated by fusicoccin and by a controlled treatment of the PM with trypsin. In both cases stimulation was much stronger on the activity assayed at pH 7.5 than on the activity at pH 6.6. Moreover, neither fusicoccin nor the treatment with trypsin stimulated the portion of activity (30 to 40% at pH 7.5) which decayed upon preincubation of the PM in assay medium without ATP. 相似文献
15.
Purification and Characterization of Conjugated Bile Salt Hydrolase from Bifidobacterium longum BB536 总被引:6,自引:0,他引:6 下载免费PDF全文
Bifidobacterium species deconjugate taurocholic, taurodeoxycholic, taurochenodeoxycholic, glycocholic, glycodeoxycholic, and glycochenodeoxycholic acids. The enzyme level increases in the growth phase. No increase in activity is observed for the cytoplasmic enzyme after addition of conjugated bile acids to a stationary-phase culture. Conjugated bile salt hydrolase (BSH) was purified from Bifidobacterium longum BB536. Its apparent molecular mass in denaturing polyacrylamide gel electrophoresis was ca. 40,000 Da. The intact enzyme had a relative molecular weight of ca. 250,000 as determined by gel filtration chromatography, suggesting that the native BSH of B. longum is probably a hexamer. The purified enzyme is active towards both glycine and taurine conjugates of cholate, deoxycholate, and chenodeoxycholate. The pH optimum is in the range of 5.5 to 6.5. A loss of BSH activity is observed after incubation at temperatures higher than 42(deg)C; at 60(deg)C, 50% of the BSH activity is lost. The importance of free sulfhydryl groups at the enzyme active center is suggested. For B. longum BB536, no significant difference in the initial rate of deconjugation and enzymatic efficiency appears between bile salts. The enzymatic efficiency is higher for B. longum BB536 than for other genera. In this paper, a new method which permits a display of BSH activity directly on polyacrylamide gels is described; this method confirms the molecular weight obtained for B. longum BB536 BSH. 相似文献
16.
The presence of keratinophilic fungi was revealed by sampling the air of Pavia (Italy) from March 1981 to February 1982. The species isolated were: Chrysosporium indicum, Geomyces pannorum var.pannorum, Microsporum gypseum, Myceliophtora vellerea and Trichophyton terrestre. Several filamentous fungi tolerating high levels of cycloheximide were also recovered. 相似文献
17.
Maria Ida De Michelis Franca Rasi-Caldogno Maria Chiara Pugliarello C. Olivari 《Plant biology (Stuttgart, Germany)》1991,104(4):265-271
The effect of fusicoccin (FC) on the activity of the PM H+-ATPase was investigated in a plasma membrane (PM) fraction from radish seedlings purified by the phase-partitioning procedure. FC stimulated the PM H+-ATPase activity by up to 100 %; the effect was essentially on Vmax with only a slight decrease of the apparent KM of the enzyme for ATP. FC-induced stimulation of the PM H+-ATPase was evident within the first minute and maximal within five minutes of membrane treatment with the toxin indicating that transmission of the signal from the activated receptor to the PM H+-ATPase is very rapid. Both FC-induced stimulation of the PM H+-ATPase and FC binding to its receptor decreased dramatically upon incubation of the membranes in ATPase assay medium at 33 °C in the absence of FC, due to the lability of the free FC receptor. FC-induced stimulation of the PM H+-ATPase was strongly pH dependent: absolute increase of activity was maximal at pH 7, while percent stimulation increased with the increase of pH up to pH 7.5; FC binding was scarcely influenced by pH in the pH range investigated. Taken as a whole, these results indicate that FC binding is a condition necessary, but not sufficient, for FC-induced stimulation of the PM H+-ATPase. 相似文献
18.
F. Crociani A. Selli G. Crisetig D. Di Gioia D. Matteuzzi 《Journal of industrial microbiology & biotechnology》1991,8(2):127-131
Summary The amino acid L-lysine was produced from auxotrophic-regulatory mutants ofBacillus stearothermophilus at a temperature of 60–65°C. One of the mutants (AEC 12 A5, S-(2-aminoethyl)-cysteiner, homoserine–), produced L-lysine at the concentration of 7.5 g/l in shaken flasks in minimal medium containing 5% glucose. Culture conditions for optimizing L-lysine production were not investigated. The aspartokinase activity of the wild strainB. stearothermophilus Zu 183 was inhibited by lysine alone and by threonine plus lysine. AEC resistant mutants showed an aspartokinase activity genetically desensitized to the feedback inhibition. Optimal temperature and pH of aspartokinase were 45°C and 9.5, respectively. The data provide significant evidence that mutants of the speciesB. stearothermophilus have a potential value for amino acid production. 相似文献
19.
20.
Giuseppe Bellucci Giancarlo Berti Maria Ferretti Franco Marioni Franca Re 《Biochemical and biophysical research communications》1981,102(3):838-844
The hydrolysis of (±)--3-bromo-1,2-epoxycyclohexane in the presence of rabbit liver microsomes was investigated, and found to yield, beside -3-bromocyclohexane--1,-2-diol, 2,3-epoxycyclohexanol. It was demonstrated that the latter compound was the only product of the enzymatic reaction, whereas the diol resulted from a non enzymatic hydration in the reaction medium. These data provide the first direct proof for a general base catalysis in the enzymatic epoxide hydration, previously hypothesized on the basis of several lines of indirect evidence, and disprove alternative mechanisms involving protonation of the oxirane oxygen. 相似文献