全文获取类型
收费全文 | 335篇 |
免费 | 17篇 |
专业分类
352篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 20篇 |
2014年 | 29篇 |
2013年 | 17篇 |
2012年 | 31篇 |
2011年 | 42篇 |
2010年 | 11篇 |
2009年 | 9篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 19篇 |
2005年 | 15篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 18篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有352条查询结果,搜索用时 12 毫秒
101.
Stingl K Brandt S Uhlemann EM Schmid R Altendorf K Zeilinger C Ecobichon C Labigne A Bakker EP de Reuse H 《The EMBO journal》2007,26(1):232-241
To date, the biological role of prokaryotic K(+) channels remains unknown. Helicobacter pylori contains a gene encoding a putative K(+) channel (HpKchA) of the two-transmembrane RCK (regulation of K(+) conductance) domain family, but lacks known bacterial K(+) uptake systems. A H. pylori DeltahpKchA mutant presented a strong growth defect at low K(+) concentration, which was compensated by KCl addition. The role of the separate RCK domain was investigated in H. pylori by mutagenesis of its internal start codon, which led to a K(+)-dependent intermediate growth phenotype, consistent with RCK activating channel function. Tagging HpKchA C-terminally, we detected a 1:1 stoichiometry of the full-length HpKchA and the separate RCK domain. We constructed single amino-acid exchanges within the unusual selectivity filter of HpKchA (ATGFGA) in H. pylori and observed complete loss (G74A), a slight defect (G76A or F75G) or wild-type (A77D) channel function. HpKchA was essential for colonization of the murine stomach. These data show, for the first time, a biological function for a prokaryotic K(+) channel, as a K(+) uptake system, essential for the persistence of H. pylori in the gastric environment. 相似文献
102.
We have developed a bacterial two-hybrid system for the detection of interacting proteins that capitalizes on the folding quality control mechanism of the Twin Arginine Transporter (Tat) pathway. The Tat export pathway is responsible for the membrane translocation of folded proteins, including proteins consisting of more than one polypeptide, only one of which contains a signal peptide ("hitchhiker export"). Here, one protein (bait) is expressed as a fusion to a Tat signal peptide, whereas the second protein (prey) is fused to a protein reporter that can confer a phenotype only after export into the bacterial periplasmic space. Since the prey-reporter fusion lacks a signal peptide, it can only be exported as a complex with the bait-signal peptide fusion that is capable of targeting the Tat translocon. Using maltose-binding protein as a reporter, clones expressing interacting proteins can be grown on maltose minimal media or on MacConkey plates. In addition, we introduce the use of the cysteine disulfide oxidase DsbA as a reporter. Export of a signal peptide-prey:bait-DsbA complex into the periplasm allows complementation of dsbA(-) mutants and restores the formation of active alkaline phosphatase, which in turn can be detected by a chromogenic assay. 相似文献
103.
Jasmin Jung Kristina Loy Eva-Maria Schilling Mareike Röther Jan M. Brauner Tobias Huth Ursula Schlötzer-Schrehardt Christian Alzheimer Johannes Kornhuber Oliver Welzel Teja W. Groemer 《Molecular neurobiology》2014,49(2):916-930
Effects of the antidepressant fluoxetine in therapeutic concentration on stimulation-dependent synaptic vesicle recycling were examined in cultured rat hippocampal neurons using fluorescence microscopy. Short-term administration of fluoxetine neither inhibited exocytosis nor endocytosis of RRP vesicular membranes. On the contrary, acute application of the drug markedly increased the size of the recycling pool of hippocampal synapses. This increase in recycling pool size was corroborated using the styryl dye FM 1-43, antibody staining with αSyt1-CypHer?5E and overexpression of synapto-pHluorin, and was accompanied by an increase in the frequency of miniature postsynaptic currents. Analysis of axonal transport and fluorescence recovery after photobleaching excluded vesicles originating from the synapse-spanning superpool as a source, indicating that these new release-competent vesicles derived from the resting pool. Super resolution microscopy and ultrastructural analysis by electron microscopy revealed that short-term incubation with fluoxetine had no influence on the number of active synapses and synaptic morphology compared to controls. These observations support the idea that therapeutic concentrations of fluoxetine enhance the recycling vesicle pool size and thus the recovery of neurotransmission from exhausting stimuli. The change in the recycling pool size is consistent with the plasticity hypothesis of the pathogenesis of major depressive disorder as stabilization of the vesicle recycling might be responsible for neural outgrowth and plasticity. 相似文献
104.
Pooneh Kalhorzadeh Zhubing Hu Toon Cools Simon Amiard Eva-Maria Willing Nancy De Winne Kris Gevaert Geert De Jaeger Korbinian Schneeberger Charles I. White Lieven De Veylder 《The Plant cell》2014,26(9):3680-3692
The WEE1 kinase is an essential cell cycle checkpoint regulator in Arabidopsis thaliana plants experiencing replication defects. Whereas under non-stress conditions WEE1-deficient plants develop normally, they fail to adapt to replication inhibitory conditions, resulting in the accumulation of DNA damage and loss of cell division competence. We identified mutant alleles of the genes encoding subunits of the ribonuclease H2 (RNase H2) complex, known for its role in removing ribonucleotides from DNA-RNA duplexes, as suppressor mutants of WEE1 knockout plants. RNase H2 deficiency triggered an increase in homologous recombination (HR), correlated with the accumulation of γ-H2AX foci. However, as HR negatively impacts the growth of WEE1-deficient plants under replication stress, it cannot account for the rescue of the replication defects of the WEE1 knockout plants. Rather, the observed increase in ribonucleotide incorporation in DNA indicates that the substitution of deoxynucleotide with ribonucleotide abolishes the need for WEE1 under replication stress. Strikingly, increased ribonucleotide incorporation in DNA correlated with the occurrence of small base pair deletions, identifying the RNase H2 complex as an important suppressor of genome instability. 相似文献
105.
Luc Nimeskern Eva-Maria Feldmann Willy Kuo Silke Schwarz Eva Goldberg-Bockhorn Susanne Dürr Ralph Müller Nicole Rotter Kathryn S. Stok 《PloS one》2014,9(8)
Introduction
Like a fingerprint, ear shape is a unique personal feature that should be reconstructed with a high fidelity during reconstructive surgery. Ear cartilage tissue engineering (TE) advantageously offers the possibility to use novel 3D manufacturing techniques to reconstruct the ear, thus allowing for a detailed auricular shape. However it also requires detailed patient-specific images of the 3D cartilage structures of the patient’s intact contralateral ear (if available). Therefore the aim of this study was to develop and evaluate an imaging strategy for acquiring patient-specific ear cartilage shape, with sufficient precision and accuracy for use in a clinical setting.Methods and Materials
Magnetic resonance imaging (MRI) was performed on 14 volunteer and six cadaveric auricles and manually segmented. Reproducibility of cartilage volume (Cg.V), surface (Cg.S) and thickness (Cg.Th) was assessed, to determine whether raters could repeatedly define the same volume of interest. Additionally, six cadaveric auricles were harvested, scanned and segmented using the same procedure, then dissected and scanned using high resolution micro-CT. Correlation between MR and micro-CT measurements was assessed to determine accuracy.Results
Good inter- and intra-rater reproducibility was observed (precision errors <4% for Cg.S and <9% for Cg.V and Cg.Th). Intraclass correlations were good for Cg.V and Cg.S (>0.82), but low for Cg.Th (<0.23) due to similar average Cg.Th between patients. However Pearson’s coefficients showed that the ability to detect local cartilage shape variations is unaffected. Good correlation between clinical MRI and micro-CT (r>0.95) demonstrated high accuracy.Discussion and Conclusion
This study demonstrated that precision and accuracy of the proposed method was high enough to detect patient-specific variation in ear cartilage geometry. The present study provides a clinical strategy to access the necessary information required for the production of 3D ear scaffolds for TE purposes, including detailed patient-specific shape. Furthermore, the protocol is applicable in daily clinical practice with existing infrastructure. 相似文献106.
David S. Guttery Benoit Poulin David J. P. Ferguson Balázs Sz??r Bill Wickstead Paula L. Carroll Chandra Ramakrishnan Declan Brady Eva-Maria Patzewitz Ursula Straschil Lev Solyakov Judith L. Green Robert E. Sinden Andrew B. Tobin Anthony A. Holder Rita Tewari 《PLoS pathogens》2012,8(9)
Protein phosphorylation and dephosphorylation (catalysed by kinases and phosphatases, respectively) are post-translational modifications that play key roles in many eukaryotic signalling pathways, and are often deregulated in a number of pathological conditions in humans. In the malaria parasite Plasmodium, functional insights into its kinome have only recently been achieved, with over half being essential for blood stage development and another 14 kinases being essential for sexual development and mosquito transmission. However, functions for any of the plasmodial protein phosphatases are unknown. Here, we use reverse genetics in the rodent malaria model, Plasmodium berghei, to examine the role of a unique protein phosphatase containing kelch-like domains (termed PPKL) from a family related to Arabidopsis BSU1. Phylogenetic analysis confirmed that the family of BSU1-like proteins including PPKL is encoded in the genomes of land plants, green algae and alveolates, but not in other eukaryotic lineages. Furthermore, PPKL was observed in a distinct family, separate to the most closely-related phosphatase family, PP1. In our genetic approach, C-terminal GFP fusion with PPKL showed an active protein phosphatase preferentially expressed in female gametocytes and ookinetes. Deletion of the endogenous ppkl gene caused abnormal ookinete development and differentiation, and dissociated apical microtubules from the inner-membrane complex, generating an immotile phenotype and failure to invade the mosquito mid-gut epithelium. These observations were substantiated by changes in localisation of cytoskeletal tubulin and actin, and the micronemal protein CTRP in the knockout mutant as assessed by indirect immunofluorescence. Finally, increased mRNA expression of dozi, a RNA helicase vital to zygote development was observed in ppkl− mutants, with global phosphorylation studies of ookinete differentiation from 1.5–24 h post-fertilisation indicating major changes in the first hours of zygote development. Our work demonstrates a stage-specific essentiality of the unique PPKL enzyme, which modulates parasite differentiation, motility and transmission. 相似文献
107.
108.
109.
The abnormal aggregation of the microtubule-associated protein Tau into paired helical filaments (PHFs) is one of the hallmarks of Alzheimer disease (AD). Tau in solution behaves as a natively unfolded or intrinsically disordered protein while its aggregation is based on the partial structural transition from random coil to beta-structure. Our aim is to understand in more detail the unfolded nature of Tau, to investigate the aggregation of Tau under different conditions and the molecular interactions of Tau in filaments. We show that soluble Tau remains natively unfolded even when its net charge is minimized, in contrast to other unfolded proteins. The CD signature of the random-coil character of Tau shows no major change over wide variations in charge (pH), ionic strength, solvent polarity, and denaturation. Thus there is no indication of a hydrophobicity-driven collapse, neither in the microtubule-binding repeat domain constructs nor in full-length Tau. This argues that the lack of hydrophobic residues but not the net charge accounts for unfolded nature of soluble Tau. The aggregation of the Tau repeat domain (that forms the core of PHFs) in the presence of nucleating polyanionic cofactors (heparin) is efficient in a range of buffers and pH values between approximately 5 and 10 but breaks down beyond that range, presumably because the pattern of charged interactions disappears. Similarly, elevated ionic strength attenuates aggregation, and the temperature dependence is bell-shaped with an optimum around 50 degrees C. Reporter dyes ThS and ANS record the aggregation process but sense different states (cross-beta-structure vs hydrophobic pockets) with different kinetics. Preformed PHFs are surprisingly labile and can be disrupted by denaturants at rather low concentration ( approximately 1.0 M GdnHCl), much less than required to denature globular proteins. Partial disaggregation of Tau filaments at extreme pH values monitored by CD and EM indicate the importance of salt bridges in filament formation. In contrast, Tau filaments are remarkably resistant to high temperature and high ionic strength. Overall, the stability of PHFs appears to depend mainly on directed salt bridges with contributions from hydrophobic interactions as well, consistent with a recent structural model of the PHF core derived from solid state NMR (Andronesi, O. C., von Bergen, M., Biernat, J., Seidel, K., Griesinger, C., Mandelkow, E., and Baldus, M. (2008) Characterization of Alzheimer's-like paired helical filaments from the core domain of tau protein using solid-state NMR spectroscopy. 相似文献
110.
Comini MA Rettig J Dirdjaja N Hanschmann EM Berndt C Krauth-Siegel RL 《The Journal of biological chemistry》2008,283(41):27785-27798
African trypanosomes encode three monothiol glutaredoxins (1-C-Grx). 1-C-Grx1 occurs exclusively in the mitochondrion, and 1-C-Grx2 and -3 are predicted to be mitochondrial and cytosolic proteins, respectively. All three 1-C-Grx are expressed in both the mammalian bloodstream and the insect procyclic form of Trypanosoma brucei, with the highest levels found in stationary phase and starving parasites. In the rudimentary mitochondrion of bloodstream cells, 1-C-Grx1 reaches concentrations above 200 microm/subunit. Recombinant T. brucei 1-C-Grx1 exists as a noncovalent homodimer, whereas 1-C-Grx2 and 1-C-Grx3 are monomeric proteins. In vitro, dimeric 1-C-Grx1 coordinated an H(2)O(2)-sensitive [2Fe-2S] cluster that required GSH as an additional ligand. Both bloodstream and procyclic trypanosomes were refractory to down-regulation of 1-C-Grx1 expression by RNA interference. In procyclic parasites, the 1-c-grx1 alleles could only be deleted if an ectopic copy of the gene was expressed. A 5-10-fold overexpression of 1-C-Grx1 in both parasite forms did not yield a growth phenotype under optimal culture conditions. However, exposure of these cells to the iron chelator deferoxamine or H(2)O(2), but not to iron or menadione, impaired cell growth. Treatment of wild-type bloodstream parasites with deferoxamine and H(2)O(2) caused a 2-fold down- and up-regulation of 1-C-Grx1, respectively. The results point to an essential role of the mitochondrial 1-C-Grx1 in the iron metabolism of these parasites. 相似文献