全文获取类型
收费全文 | 217篇 |
免费 | 11篇 |
专业分类
228篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 16篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 5篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1961年 | 2篇 |
1938年 | 1篇 |
1937年 | 3篇 |
1935年 | 1篇 |
1934年 | 2篇 |
1928年 | 2篇 |
1926年 | 3篇 |
1921年 | 1篇 |
1883年 | 1篇 |
排序方式: 共有228条查询结果,搜索用时 15 毫秒
141.
Winter RT Heuts DP Rijpkema EM van Bloois E Wijma HJ Fraaije MW 《Applied microbiology and biotechnology》2012,95(2):389-403
We describe the discovery, isolation and characterization of a highly thermostable alditol oxidase from Acidothermus cellulolyticus 11B. This protein was identified by searching the genomes of known thermophiles for enzymes homologous to Streptomyces coelicolor A3(2) alditol oxidase (AldO). A gene (sharing 48% protein sequence identity to AldO) was identified, cloned and expressed in Escherichia coli. Following 6xHis tag purification, characterization revealed the protein to be a covalent flavoprotein of 47?kDa with a remarkably similar reactivity and substrate specificity to that of AldO. A steady-state kinetic analysis with a number of different polyol substrates revealed lower catalytic rates but slightly altered substrate specificity when compared to AldO. Thermostability measurements revealed that the novel AldO is a highly thermostable enzyme with an unfolding temperature of 84?°C and an activity half-life at 75?°C of 112?min, prompting the name HotAldO. Inspired by earlier studies, we attempted a straightforward, exploratory approach to improve the thermostability of AldO by replacing residues with high B-factors with corresponding residues from HotAldO. None of these mutations resulted in a more thermostable oxidase; a fact that was corroborated by in silico analysis. 相似文献
142.
143.
144.
Alexandra Eisner Gebhard Feierl Gregor Gorkiewicz Franz Dieber Harald H. Kessler Egon Marth Josef K?fer 《Applied microbiology》2005,71(10):6407-6409
Fecal samples from humans and food-producing animals were analyzed for the presence of vancomycin-resistant enterococci (VRE). The VRE carriage rate in humans was 6%, and there was a predominance of VanC-type resistance. Enterococcus faecium with vanA-mediated resistance was frequent in broiler chickens (42%) but rare in cattle and pig samples. 相似文献
145.
Petrillo G Mariggiò MA Aiello C Cordazzo C Fenoglio C Morganti S Croce M Rizzato E Spinelli D Maccagno M Bianchi L Prevosto C Tavani C Viale M 《Bioorganic & medicinal chemistry》2008,16(1):240-247
On the grounds of previous encouraging results on the antitumor activity of (1E,3E)-1,4-bis(1-naphthyl)-2,3-dinitro-1,3-butadiene (1), we have designed and synthesized two new molecules [(1E,3E)-1,4-bis(4-carboxy-1-naphthyl)-2,3-dinitro-1,3-butadiene (2) and methyl (2Z,4E)-2-methylsulfanyl-5-(1-naphthyl)-4-nitro-2,4-pentadienoate (3)] characterized by a common naphthylnitrobutadiene array but with different structural properties, with the aim of approaching to some structure-activity correlation. When 2 and 3 were analyzed in vitro for their inhibition of cell proliferation and pro-apoptotic properties, the carboxyderivative 2 did not furnish appreciable results. In contrast, 3 (which contains only one of the two naphthylnitroethenyl moieties of the original compound 1) showed remarkable activities in the range of micromolar concentrations (in six over eight cell lines its IC(50)s are in the 1-3 microM range), with a significant improvement compared to 1. In particular, 3 proved able to bind to DNA, to upregulate p53, to block cells in the G2/M phase of their cycle, and to induce apoptosis. Thus, very interestingly, the performance of 3 with respect to 1 shows that a single 1-(1-naphthyl)-2-nitroethene moiety is able to ensure better (on four out of eight of the cell lines tested) or comparable levels of activity. This result suggests that the 'molecular-simplification strategy' could furnish a useful instrument for future design in our antitumor research. 相似文献
146.
Bjelke JR Olsen OH Fodje M Svensson LA Bang S Bolt G Kragelund BB Persson E 《The Journal of biological chemistry》2008,283(38):25863-25870
The intrinsic activity of coagulation factor VIIa (FVIIa) is dependent on Ca(2+) binding to a loop (residues 210-220) in the protease domain. Structural analysis revealed that Ca(2+) may enhance the activity by attenuating electrostatic repulsion of Glu(296) and/or by facilitating interactions between the loop and Lys(161) in the N-terminal tail. In support of the first mechanism, the mutations E296V and D212N resulted in similar, about 2-fold, enhancements of the amidolytic activity. Moreover, mutation of the Lys(161)-interactive residue Asp(217) or Asp(219) to Ala reduced the amidolytic activity by 40-50%, whereas the K161A mutation resulted in 80% reduction. Hence one of these Asp residues in the Ca(2+)-binding loop appears to suffice for some residual interaction with Lys(161), whereas the more severe effect upon replacement of Lys(161) is due to abrogation of the interaction with the N-terminal tail. However, Ca(2+) attenuation of the repulsion between Asp(212) and Glu(296) keeps the activity above that of apoFVIIa. Altogether, our data suggest that repulsion involving Asp(212) in the Ca(2+)-binding loop suppresses FVIIa activity and that optimal activity requires a favorable interaction between the Ca(2+)-binding loop and the N-terminal tail. Crystal structures of tissue factor-bound FVIIa(D212N) and FVIIa(V158D/E296V/M298Q) revealed altered hydrogen bond networks, resembling those in factor Xa and thrombin, after introduction of the D212N and E296V mutations plausibly responsible for tethering the N-terminal tail to the activation domain. The charge repulsion between the Ca(2+)-binding loop and the activation domain appeared to be either relieved by charge removal and new hydrogen bonds (D212N) or abolished (E296V). We propose that Ca(2+) stimulates the intrinsic FVIIa activity by a combination of charge neutralization and loop stabilization. 相似文献
147.
Kristina Hanspers Martina Kutmon Susan L. Coort Daniela Digles Lauren J. Dupuis Friederike Ehrhart Finterly Hu Elisson N. Lopes Marvin Martens Nhung Pham Woosub Shin Denise N. Slenter Andra Waagmeester Egon L. Willighagen Laurent A. Winckers Chris T. Evelo Alexander R. Pico 《PLoS computational biology》2021,17(8)
148.
Characterization of novel clonal murine endothelial cell lines with an extended life span 总被引:1,自引:0,他引:1
Cavallaro U Castelli V Perilli A Dossi R Giavazzi R Pepper MS Soria MR Montesano R 《In vitro cellular & developmental biology. Animal》2000,36(5):299-308
Summary A murine endothelial cell line was recently established from microvessels that had invaded a subcutaneous sponge implant (Dong,
Q. G.; Bernasconi, S.; Lostaglio, S., et al. Arterioscl. Thromb. Vasc. Biol. 17:1599–1604; 1997). From these sponge-induced
endothelial (SIE) cells, we have isolated two subpopulations endowed with different phenotypic properties. Clone SIE-F consists
of large, highly spread cells that have a relatively slow growth rate, form contact-inhibited monolayers, do not grow under
anchorage-independent conditions, express elevated levels of thrombospondin-1 (TSP-1) and are not tumorigenic in vivo. In
contrast, clone SIE-S2 consists of small, spindle-shaped cells that have a high proliferation rate, do not show contact-inhibition,
grow under anchorage-independent conditions, express very low levels of TSP-1 and are tumorigenic in vivo. Both clones express
the endothelial markers vascular endothelial-cadherin and vascular intercellular adhesion molecule-1, but do not express CD31
and E-selectin. In addition, SIE-S2 cells, but not SIE-F cells, express the α-smooth muscle actin isoform. SIE-S2 cells, but
not SIE-F cells, are able to form branching tubes in fibrin gels. The SIE-F and SIE-S2 clones, which have properties of nontransformed
and transformed cells, respectively, should provide useful tools to investigate physiological and pathological processes involving
vascular endothelium. 相似文献
149.
Seidler DG Breuer E Grande-Allen KJ Hascall VC Kresse H 《The Journal of biological chemistry》2002,277(44):42409-42416
Chondroitin sulfate and dermatan sulfate proteoglycans are distinguished by differences in their proportion of d-glucuronosyl and l-iduronosyl residues, the latter being formed by chondroitin-glucuronate 5-epimerase during or after glycosaminoglycan chain polymerization. To investigate the influence of the core protein on the extent of epimerization, we expressed chimeric proteins in 293 HEK cells constructed from intact or modified Met(1)-Gln(153) of decorin (DCN), which normally has a single dermatan sulfate chain at Ser(34), in combination with intact or modified Leu(241)-Ser(353) of CSF-1, which has a chondroitin sulfate attachment site at Ser(309). Transfected DCN(M1-Q153), like full-length DCN, contained approximately 20% l-iduronate. Conversely, transfected CSF-1(L241-S353), attached C-terminally on the DCN prepropeptide, contained almost exclusively d-glucuronate. Transfected intact chimeric DCN(M1-Q153)-CSF-1(L241-S353), with two glycosaminoglycan chains, also contained almost exclusively d-glucuronate in chains at both sites, as did chimeras in which alanine was substituted for serine at either of the glycosaminoglycan attachment sites. Nevertheless, undersulfated intact chimeric proteoglycan was an effective substrate for epimerization of glucuronate to iduronate residues when incubated with microsomal proteins and 3'-phosphoadenylylphosphosulfate. C-terminal truncation constructs were prepared from the full-length chimera with an alanine substitution at the CSF-1 glycosaminoglycan attachment site. Transfected truncations retaining the alanine-blocked site contained chains with essentially only glucuronate, whereas those further truncated by 49 or more amino acids and missing the modified attachment site contained chains with approximately 15% iduronate. This 49-amino acid region contains a 7-amino acid motif that appears to be conserved in several chondroitin sulfate proteoglycans. The results are consistent with a model in which the core protein, possibly via this motif, is responsible for routing to subcellular compartments with or without sufficient access to chondroitin-glucuronate 5-epimerase for the addition of chains with or without iduronate residues, respectively. 相似文献
150.
Osterlund M Persson E Svensson M Carlsson U Freskgård PO 《Biochemical and biophysical research communications》2005,327(3):789-793
Injury of a blood vessel exposes membrane-bound tissue factor (TF) to blood, which allows binding of coagulation factor VIIa (FVIIa). This initiation of the coagulation cascade is dictated by a specific multi-domain interaction between FVIIa and TF. To examine the energies involved in the transition state of the FVIIa:TF complex, various residues in the extracellular part of TF (sTF) that are known to interact with FVIIa were replaced with a smaller cysteine residue. Determination of Phi values in each of the positions using surface plasmon resonance measurements enabled us to characterize the transition state complex between the resulting sTF variants and FVIIa. We found that the interactions in the transition state seemed to be most pronounced between the protease domain of FVIIa and sTF while detailed specific interactions between the Gla-domain and sTF were missing. Thus, the transition state energy data indicate a sequential binding event between these two macromolecules. 相似文献