全文获取类型
收费全文 | 213篇 |
免费 | 9篇 |
国内免费 | 8篇 |
专业分类
230篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 12篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1996年 | 1篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 4篇 |
排序方式: 共有230条查询结果,搜索用时 0 毫秒
161.
Elisabeth Ytteborg Anne Vegusdal P. Eckhard Witten Gerd Marit Berge Harald Takle Tone-Kari Østbye Bente Ruyter 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2010,1801(2):127-137
The formation and mineralisation of bone are two critical processes in fast-growing Atlantic salmon (Salmo salar). The mechanisms of these processes, however, have not been described in detail. Thus, in vitro systems that allow the study of factors that influence bone formation in farmed Atlantic salmon are highly warranted. We describe here a method by which unspecialised primary cells from salmon white muscle can differentiate to osteoblasts in vitro. We have subsequently used the differentiated cells as a model system to study the effects of two factors that influence bone formation in Atlantic salmon under commercial farming conditions, namely polyunsaturated fatty acids, PUFAs, and temperature. Muscle precursor cells changed their morphology from triangular or spindle-shaped cells to polygonal or cubical cells after 3 weeks in osteogenic medium. In addition, gene expression studies showed that marker genes for osteoblastogenesis; alp, col1a1, osteocalcin, bmp2 and bmp4 increased after 3 weeks of incubation in osteogenic media showing that these cells have differentiated to osteoblasts at this stage. Adding CLA or DHA to the osteoblast media resulted in a reduced PGE2 production and increased expression of osteocalcin. Further, temperature studies showed that differentiating osteoblasts are highly sensitive to increased incubation temperature at early stages of differentiation. Our studies show that unspecialised precursor cells isolated from salmon muscle tissue can be caused to differentiate to osteoblasts in vitro. Furthermore, this model system appears to be suitable for the study of osteoblast biology in vitro. 相似文献
162.
Romero PJ Romero EA Mateu D Hernández C Fernández I 《Cell biochemistry and biophysics》2006,46(3):265-276
Presence of subtypes of voltage-dependent Ca channels was investigated in young and old human red cells, employing immunological
and flux-kinetics methods. Western blots showed specific reaction toward polyclonal rabbit antibodies raised against a highly
conserved residue of α1C, subunit of high-voltage activated Ca channels (pan α1) and against conserved residues of α1C and α1E subunits. No specific reaction was detected with antibodies against conserved residues of α1A, α1B, or α1D subunits. Only a single band (approx 260 kDa) was revealed on anti-pan α1A or anti-α1E blots, whereas two bands (200 and 230 kDa) were detected by α1C exposure, Blots from old cells always showed diminished band intensity. Channel activity was assessed by studying the effect
of voltage-dependent Ca channels blockers' under conditions likely to alter the red cell membrane potential, through incubation
in media of different composition. In a 150 mM NaCl+5 mM KCl medium, blockers of L-, R-, and Q-type caused a 15–50% reductions of 45Ca influx into cells, which had the Ca pump inactivated by either exhaustive adenosine triphosphate depletion or presence
of vanadate plus substrates. Additionally, some P/Q-and N-type blockers also reduced Ca influx to various extents (25–60%).
Old cells were generally insensitive to L-type but not to non-L-type, blockers. Raising external K to about 70–80 mM reduced by 50–100% inhibition by L-type blockers. Incubation in a gluconate medium containing 150 mM Na+5 mM K practically abolished the action of L-type blockers, but only slightly reducing that by non-L-type. The results, clearly
demonstrate presence of L- and R-type Ca channels, apparently occurring in different functional states in young and old cells.
Other non-L-type channels were also demonstrated only by pharmacological means. A possible physiological role for these channels
is discussed. 相似文献
163.
Yuanyuan Lu Alei Zhang Xin Wang Kequan Chen Pingkai Ouyang 《Biocatalysis and Biotransformation》2013,31(5):361-366
AbstractEnzymatic production of L-α-glycerylphosphorylcholine (L-α-GPC) is difficult due to the limited solubility of phosphatidylcholine (PC) in the aqueous phase. Surfactants can be used to improve the solubility and the dispersibility of non-polar chemicals in the aqueous media. In this study, various surfactants were investigated to improve L-α-GPC enzymatic production using phospholipase A1 (PLA1) in the aqueous phase. The results showed that Tween 20 was the most effective surfactant for enhancing L-α-GPC concentration. With 20?g.L?1 of Tween 20, the optimal conditions of PC hydrolysis were determined to be enzyme loading of 0.64?g.L?1 and substrate concentration of 60?g.L?1 at 45?°C for 1?h. In addition, the fed-batch catalytic process of PC was conducted to avoid substrate inhibition and increase product accumulation, resulting in 112.56?g.L?1 of L-α-GPC from 360.00?g.L?1 PC with yield of 91.36% within 3?h. 相似文献
164.
A Lyophilized preparation of L-2-halo acid dehalogenase was not only stable but also catalytically active in anhydrous dimethyl sulfoxide, toluene, and other organic solvents. 2-Halo acids with long alkyl (C(5)-C(16)) or aromatic (phenyl and benzyl) side chains were inert in water but dehalogenated effectively in anhydrous dimethyl sulfoxide by the lyophilized enzyme. Long chain 2-haloalkanoic acids such as 2-bromohexadecanoic acids were better as substrate than short-chain halo acids (e.g., 2-chloropropanoic acid). The dehalogenation proceed with inversion of C(2) configuration to produce the corresponding (2R)-2-hydroxy acids in anhydrous dimethyl sulfoxide in the same way as found in water. 相似文献
165.
Crystallization and preliminary X-ray analysis of L-2-haloacid dehalogenase from Xanthobacter autotrophicus GJ10. 下载免费PDF全文
I. S. Ridder H. J. Rozeboom J. Kingma D. B. Janssen B. W. Dijkstra 《Protein science : a publication of the Protein Society》1995,4(12):2619-2620
Haloacid dehalogenases are enzymes that cleave carbon-chlorine or carbon-bromine bonds of 2-haloalkanoates. X-ray-quality crystals of L-2-haloacid dehalogenase from the 1,2-dichloroethane-degrading bacterium Xanthobacter autotrophicus GJ10 have been grown at room temperature from 20% PEG 8000, 200 mM sodium formate at pH 6.8-7.0, using macroseeding techniques. The crystals, which diffract in the X-ray beam up to 2.0 A resolution, belong to the spacegroup C2221. Cell parameters are a = 58.8 A, b = 93.1 A, c = 84.2 A. A native data set to 2.3 A has been collected, with a completeness of 97% and an Rsym of 6.0%. 相似文献
166.
Noriko Okada Tatsuji Yasuda Tohru Tsumita Hiroto Shinomiya Sayaka Utsumi Hidechika Okada 《Biochemical and biophysical research communications》1982,108(2):770-775
The effect of glycophorin on complement activation via the alternative pathway was examined by incorporating it into the liposome membrane with trinitrophenylaminocaproyldipalmitoylphosphatidylethanolamine (TNP-Cap-DPPE). Liposomes having incorporated TNP-Cap-DPPE onto the membrane activate the alternative complement pathway of guinea pig as reported previously, and the additional insertion of glycophorin was found to reduce their activating capacity on the alternative complement pathway. This inhibitory effect was cancelled by pretreatment of the glycophorin-containing liposomes with neuraminidase indicating that the sialic acid in glycophorin is playing a role in the regulation of alternative complement pathway-activation on the biological membrane. 相似文献
167.
SYNOPSIS. Phenylalanine hydroxylase could not be assayed in extracts of Tetrahymena pyriformis strain W in a system by which the enzyme could be assayed in rat liver extracts. Isotopically labelled phenylalanine, however, was converted to tyrosine by growing or washed cells. Growth conditions which allowed limited synthesis of unconjugated tetrahydropteridine severely reduced the ability of the cells to synthesize tyrosine from phenylalanine. The presence of glucose and acetate in the growth medium resulted in elevated free tyrosine pools and an increased capacity of washed cell suspensions to convert phenylalanine to tyrosine. It would appear that the putative phenylalanine hydroxylation system is not subject to the repressive effects of glucose and acetate which apply to the enzymes of tyrosine catabolism. The significance of this distinction is discussed. 相似文献
168.
Hypocotyl-derived callus from the Helianthus annuus L. inbred line SS415B regenerated significantly more plants if the seedlings were grown in the light. The difference between light- and dark-grown seedlings was not correlated with differences in seedling ethylene production, but seemed to be due to a difference in sensitivity to ethylene at a specific time during seedling growth. Treating 3-day-old dark-grown seedlings with 10 μ M aminoethoxyvinylglycine (AVG) effectively inhibited ethylene production for at least 7 days. Hypocotyl callus derived from AVG-treated seedlings gave the same amount of regeneration as callus from light-grown seedlings. Promotion of regeneration by AVG was not seen unless the 3-day-old seedlings were grown for 4 additional days prior to culturing hypocotyl explants. The effects of AVG could be reversed by treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) during these 4 days. After the 4 days, ACC was no longer effective. 相似文献
169.
Cloning and expression in Escherichia coli of the gene encoding a novel L-2,4-diaminobutyrate decarboxylase of Acinetobacter baumannii 总被引:1,自引:0,他引:1
Abstract The gene encoding L-2,4-diaminobutyrate decarboxylase (DABA DC) was cloned from Acinetobacter baumannii ATCC 19606. The gene was evidently under the control of its own promoter. Interestingly, the host carrying this clone also produced an appreciable amount of 1,3-diaminopropane. Restriction mapping and subsequent subcloning of the cloned insert localized the DABA DC gene within a 2.45-kb SphI/Eco RI fragment. For endogenous production of DAP, a 1.75-kb Eco RI/ Pst I region downstream from the DABA DC gene was further required. Southern blot hybridization revealed some heterogeneity in the DABA DC genes among other Acinetobacter species. 相似文献
170.