全文获取类型
收费全文 | 990篇 |
免费 | 63篇 |
国内免费 | 1篇 |
专业分类
1054篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 19篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 34篇 |
2014年 | 34篇 |
2013年 | 54篇 |
2012年 | 61篇 |
2011年 | 77篇 |
2010年 | 45篇 |
2009年 | 52篇 |
2008年 | 65篇 |
2007年 | 77篇 |
2006年 | 91篇 |
2005年 | 55篇 |
2004年 | 73篇 |
2003年 | 48篇 |
2002年 | 45篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有1054条查询结果,搜索用时 0 毫秒
141.
Probing the specificity of the subclass B3 FEZ-1 metallo-beta-lactamase by site-directed mutagenesis
Mercuri PS García-Sáez I De Vriendt K Thamm I Devreese B Van Beeumen J Dideberg O Rossolini GM Frère JM Galleni M 《The Journal of biological chemistry》2004,279(32):33630-33638
The subclass B3 FEZ-1 beta-lactamase produced by Fluoribacter (Legionella) gormanii is a Zn(II)-containing enzyme that hydrolyzes the beta-lactam bond in penicillins, cephalosporins, and carbapenems. FEZ-1 has been extensively studied using kinetic, computational modeling and x-ray crystallography. In an effort to probe residues potentially involved in substrate binding and zinc binding, five site-directed mutants of FEZ-1 (H121A, Y156A, S221A, N225A, and Y228A) were prepared and characterized using metal analyses and steady state kinetics. The activity of H121A is dependent on zinc ion concentration. The H121A monozinc form is less active than the dizinc form, which exhibits an activity similar to that of the wild type enzyme. Tyr156 is not essential for binding and hydrolysis of the substrate. Substitution of residues Ser221 and Asn225 modifies the substrate profile by selectively decreasing the activity against carbapenems. The Y228A mutant is inhibited by the product formed upon hydrolysis of cephalosporins. A covalent bond between the side chain of Cys200 and the hydrolyzed cephalosporins leads to the formation of an inactive and stable complex. 相似文献
142.
Hudec R Lakatos B Orlický J Varecka L 《Biochemical and biophysical research communications》2004,325(4):1172-1179
The (45)Ca(2+) influx into right-side-out resealed ghosts (RG) prepared from human red blood cells (RBC) was measured. The (45)Ca(2+) equilibration occurred with t(1/2)=2.5 min and the steady-state was reached after 17 min with the level of 22+/-2 micromol/L(packed cells) at 37 degrees C. The rate of the influx was 97+/-17 micromol/L(packed cells)h. The (45)Ca(2+) influx was saturated with [Ca(2+)](0) at 4 mmol/L and was optimal at pH 6.5 and 30 degrees C. Divalent cations (10(-4)-10(-6)mol/L), nifedipine (10(-5)-10(-4)mol/L), DIDS (up to 10(-4)mol/L), and quinidine (10(-4)-10(-3)mol/L), inhibited the (45)Ca(2+) influx while uncoupler (10(-6)-10(-5)mol/L) stimulated it. In contrast to intact RBC, vanadate inhibited the (45)Ca(2+) influx when added to the external medium, however, the stimulation was observed when vanadate was present in media during both lysis and resealing. PMA had no effect under conditions found to stimulate the Ca(2+) influx in intact RBC. The results show that the Ca(2+) influx into RG is a carrier-mediated process but without control by protein kinase C and that the influx and efflux of Ca(2+) are coupled via the H(+) homeostasis similarly as in intact RBC but with modified mechanism. 相似文献
143.
García L Burda J Hrehorovská M Burda R Martín ME Salinas M 《Journal of neurochemistry》2004,88(1):136-147
Translational repression induced during reperfusion of the ischaemic brain is significantly attenuated by ischaemic preconditioning. The present work was undertaken to identify the components of the translational machinery involved and to determine whether translational attenuation selectively modifies protein expression patterns during reperfusion. Wistar rats were preconditioned by 5-min sublethal ischaemia and 2 days later, 30-min lethal ischaemia was induced. Several parameters were studied after lethal ischaemia and reperfusion in rats with and without acquired ischaemic tolerance (IT). The phosphorylation pattern of the alpha subunit of eukaryotic initiation factor 2 (eIF2) in rats with IT was exactly the same as in rats without IT, reaching a peak after 30 min reperfusion and returning to control values within 4 h in both the cortex and hippocampus. The levels of phosphorylated eIF4E-binding protein after lethal ischaemia and eIF4E at 30 min reperfusion were higher in rats with IT, notably in the hippocampus. eIF4G levels diminished slightly after ischaemia and reperfusion, paralleling calpain-mediated alpha-spectrin proteolysis in rats with and without IT, but they did not show any further decrease after 30 min reperfusion in rats with IT. The phosphorylated levels of eIF4G, phosphatidylinositol 3-kinase-protein B (Akt) and extracellular signal-regulated kinases (ERKs) were very low after lethal ischaemia and increased following reperfusion. Ischaemic preconditioning did not modify the observed changes in eIF4G phosphorylation. All these results support that translation attenuation may occur through multiple targets. The levels of the glucose-regulated protein (78 kDa) remained unchanged in rats with and without IT. Conversely, our data establish a novel finding that ischaemia induces strong translation of growth arrest and DNA damage protein 34 (GADD34) after 4 h of reperfusion. GADD34 protein was slightly up-regulated after preconditioning, besides, as in rats without IT, GADD34 levels underwent a further clear-cut increase during reperfusion, this time as earlier as 30 min and coincident with translation attenuation. 相似文献
144.
145.
The developmentally complex bacterium Streptomyces lividans has the ability to produce and secrete a significant amount of protein and possesses four different type I signal peptidase genes (sipW, sipX, sipY and sipZ) that are unusually clustered in its chromosome. 2-DE and subsequent MS of extracellular proteins showed that proteins with typical export signals for type I and type II signal peptidases are the main components of the S. lividans secretome. Secretion of extracellular proteins is severely reduced in a strain deficient in the major type I signal peptidase (SipY). This deficiency was efficiently compensated by complementation with any of the other three signal peptidases as deduced from a comparison of the corresponding 2-D PAGE patterns with that of the wild-type strain. 相似文献
146.
Paschen A Song M Schenk S Janda J Nguyen XD Osen W Schadendorf D Geginat G 《Microbes and infection / Institut Pasteur》2006,8(8):2034-2043
Cholesterol-binding cytolysins constitute an evolutionarily conserved family of pore-forming proteins expressed by different gram-positive pathogens. Listeriolysin O, one well-characterized member of the cytolysin family, is also known to induce specific CD4 and CD8 T cell responses upon infection of mice with Listeria monocytogenes. Here we describe an HLA-DRB1*0301-restricted listeriolysin O-derived T cell epitope that is conserved among several members of the cytolysin family. An HLA-DRB1*0301-restricted CD4+ T cell line, established from spleen lymphocytes of L. monocytogenes-infected HLA-DRB1*0301-transgenic mice, cross-reacted with a homologous peptide from perfringolysin O, a cytolysin expressed by Clostridium perfringens. Ex vivo analysis of infected mice revealed an even broader cross-reaction of T cells with homologous peptides derived from perfringolysin O, streptolysin O, and cereolysin O. Interestingly, a cross-reactive memory CD4+ T cell response against the homologous peptides derived from listeriolysin O and perfringolysin O could also be detected in the blood from healthy HLA-DRB1*0301+ human donors. Remarkably, this response was even present in donors who did not exhibit a memory T cell reactivity against a second, non-conserved HLA-DRB1*0301-restricted LLO-derived CD4 T cell epitope, suggesting that cytolysin-producing bacteria other than L. monocytogenes can stimulate a cross-reactive cytolysin-specific immunity. 相似文献
147.
Atomic force microscopy was used to image single-stranded DNA (ssDNA) adsorbed on mica modified by Mg(2+), by 3-aminopropyltriethoxysilane or on modified highly oriented pyrolytic graphite (HOPG). ssDNA molecules on mica have compact structures with lumps, loops and super twisting, while on modified HOPG graphite ssDNA molecules adopt a conformation without secondary structures. We have shown that the immobilization of ssDNA under standard conditions on modified HOPG eliminates intramolecular base-pairing, thus this method could be important for studying certain processes involving ssDNA in more details. 相似文献
148.
Emmanuel Richaud Ludmila Audouin Bruno Fayolle Jacques Verdu Lyda Matisová-Rychlá Jozef Rychlý 《Chemistry and physics of lipids》2012,165(7):753-759
This study deals with oxidation kinetics of three unsaturated fatty esters: methyl oleate, methyl linoleate and methyl linolenate at temperatures ranging from 90 to 150 °C. The reaction was monitored by chemiluminescence. A kinetic model was derived from a simple mechanistic scheme, in which initiation is due to hydroperoxides decomposition, whereas propagation results from the abstraction of the most labile hydrogen and termination results only from the bimolecular combination of peroxyl radicals. Analysis of induction period duration indicated that hydroperoxides mainly decompose by a bimolecular process. The model well predicts the main features of the experimental chemiluminescence curves. Kinetic parameters of the three unsaturated fatty esters were assessed from inverse method and discussed. 相似文献
149.
Nissimov JI Worthy CA Rooks P Napier JA Kimmance SA Henn MR Ogata H Allen MJ 《Journal of virology》2012,86(5):2896-2897
The Coccolithoviridae are a group of viruses which infect the marine coccolithophorid microalga Emiliania huxleyi. The Emiliania huxleyi viruses (known as EhVs) described herein have 160- to 180-nm diameter icosahedral structures, have genomes of approximately 400 kbp, and consist of more than 450 predicted coding sequences (CDSs). Here, we describe the genomic features of four newly sequenced coccolithoviruses (EhV-88, EhV-201, EhV-207, and EhV-208) together with their draft genome sequences and their annotations, highlighting the homology and heterogeneity of these genomes to the EhV-86 model reference genome. 相似文献
150.