全文获取类型
收费全文 | 782篇 |
免费 | 46篇 |
出版年
2021年 | 5篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 23篇 |
2013年 | 34篇 |
2012年 | 36篇 |
2011年 | 38篇 |
2010年 | 19篇 |
2009年 | 23篇 |
2008年 | 26篇 |
2007年 | 37篇 |
2006年 | 48篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 41篇 |
2002年 | 45篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1976年 | 4篇 |
1974年 | 6篇 |
1972年 | 11篇 |
1971年 | 4篇 |
1969年 | 5篇 |
1968年 | 7篇 |
1967年 | 4篇 |
1932年 | 5篇 |
1930年 | 4篇 |
1927年 | 6篇 |
排序方式: 共有828条查询结果,搜索用时 15 毫秒
51.
Spurny R Abdoulrahman K Janda L Rünzler D Köhler G Castañón MJ Wiche G 《The Journal of biological chemistry》2007,282(11):8175-8187
As an intermediate filament (IF)-based cytolinker protein, plectin plays a key role in the maintenance of cellular cytoarchitecture and serves at the same time as a scaffolding platform for signaling cascades. Consisting of six structural repeats (R1-6) and harboring binding sites for different IF proteins and proteins involved in signaling, the plectin C-terminal domain is of strategic functional importance. Depending on the species, it contains at least 13 cysteines, 4 of which reside in the R5 domain. To investigate the structural and biological functions of R5 cysteines, we used cysteine-to-serine mutagenesis and spectroscopic, biochemical, and functional analyses. Urea-induced unfolding experiments indicated that wild-type R5 in the oxidized, disulfide bond-mediated conformation was more stable than its cysteine-free mutant derivative. The binding affinity of R5 for vimentin was significantly higher, however, when the protein was in the reduced, more relaxed conformation. Of the four R5 cysteines, one (Cys4) was particularly reactive as reflected by its ability to form disulfide bridges with R5 Cys1 and to serve as a target for nitrosylation in vitro. Using immortalized endothelial cell cultures from mice, we show that endogenous plectin is nitrosylated in vivo, and we found that NO donor-induced IF collapse proceeds dramatically faster in plectin-deficient compared with wild-type cells. Our data suggest an antagonistic role of plectin in nitrosylation (oxidative stress)-mediated alterations of IF cytoarchitecture and a possible role of R5 Cys4 as a regulatory switch. 相似文献
52.
The solution structure of the C-terminal Domain V of the τ subunit of E. coli DNA polymerase III was determined by nuclear magnetic resonance (NMR) spectroscopy. The fold is unique to τ subunits. Amino acid sequence conservation is pronounced for hydrophobic residues that form the structural core of the protein, indicating that the fold is representative for τ subunits from a wide range of different bacteria. The interaction between the polymerase subunits τ and α was studied by NMR experiments where α was incubated with full-length C-terminal domain (τC16), and domains shortened at the C-terminus by 11 and 18 residues, respectively. The only interacting residues were found in the C-terminal 30-residue segment of τ, most of which is structurally disordered in free τC16. Since the N- and C-termini of the structured core of τC16 are located close to each other, this limits the possible distance between α and the pentameric δτ2γδ′ clamp–loader complex and, hence, between the two α subunits involved in leading- and lagging-strand DNA synthesis. Analysis of an N-terminally extended construct (τC22) showed that τC14 presents the only part of Domains IVa and V of τ which comprises a globular fold in the absence of other interaction partners. 相似文献
53.
Jergic S Ozawa K Williams NK Su XC Scott DD Hamdan SM Crowther JA Otting G Dixon NE 《Nucleic acids research》2007,35(9):2813-2824
The τ subunit of Escherichia coli DNA polymerase III holoenzyme interacts with the α subunit through its C-terminal Domain V, τC16. We show that the extreme C-terminal region of τC16 constitutes the site of interaction with α. The τC16 domain, but not a derivative of it with a C-terminal deletion of seven residues (τC16Δ7), forms an isolable complex with α. Surface plasmon resonance measurements were used to determine the dissociation constant (KD) of the α−τC16 complex to be ~260pM. Competition with immobilized τC16 by τC16 derivatives for binding to α gave values of KD of 7μM for the α−τC16Δ7 complex. Low-level expression of the genes encoding τC16 and τC167, but not τC16Δ11, is lethal to E. coli. Suppression of this lethal phenotype enabled selection of mutations in the 3′ end of the τC16 gene, that led to defects in α binding. The data suggest that the unstructured C-terminus of τ becomes folded into a helix–loop–helix in its complex with α. An N-terminally extended construct, τC24, was found to bind DNA in a salt-sensitive manner while no binding was observed for τC16, suggesting that the processivity switch of the replisome functionally involves Domain IV of τ. 相似文献
54.
55.
56.
Beblo K Douki T Schmalz G Rachel R Wirth R Huber H Reitz G Rettberg P 《Archives of microbiology》2011,193(11):797-809
In this study, we investigated the ability of several (hyper-) thermophilic Archaea and phylogenetically deep-branching thermophilic
Bacteria to survive high fluences of monochromatic UV-C (254 nm) and high doses of ionizing radiation, respectively. Nine
out of fourteen tested microorganisms showed a surprisingly high tolerance against ionizing radiation, and two species (Aquifex pyrophilus and Ignicoccus hospitalis) were even able to survive 20 kGy. Therefore, these species had a comparable survivability after exposure to ionizing radiation
such as Deinococcus radiodurans. In contrast, there was nearly no difference in survival of the tested strains after exposure to UV-C under anoxic conditions.
If the cells had been dried in advance of UV-C irradiation, they were more sensitive to UV-C radiation compared with cells
irradiated in liquid suspension; this effect could be reversed by the addition of protective material like sulfidic ores before
irradiation. By exposure to UV-C, photoproducts were formed in the DNA of irradiated Archaea and Bacteria. The distribution
of the main photoproducts was species specific, but the amount of the photoproducts was only partly dependent on the applied
fluence. Overall, our results show that tolerance to radiation seems to be a common phenomenon among thermophilic and hyperthermophilic
microorganisms. 相似文献
57.
Paolino M Thien CB Gruber T Hinterleitner R Baier G Langdon WY Penninger JM 《Journal of immunology (Baltimore, Md. : 1950)》2011,186(4):2138-2147
E3 ubiquitin ligases have been placed among the essential molecules involved in the regulation of T cell functions and T cell tolerance. However, it has never been experimentally proven in vivo whether these functions indeed depend on the catalytic E3 ligase activity. The Casitas B-cell lymphoma (Cbl) family protein Cbl-b was the first E3 ubiquitin ligase directly implicated in the activation and tolerance of the peripheral T cell. In this study, we report that selective genetic inactivation of Cbl-b E3 ligase activity phenocopies the T cell responses observed when total Cbl-b is ablated, resulting in T cell hyperactivation, spontaneous autoimmunity, and impaired induction of T cell anergy in vivo. Moreover, mice carrying a Cbl-b E3 ligase-defective mutation spontaneously reject tumor cells that express human papilloma virus Ags. These data demonstrate for the first time, to our knowledge, that the catalytic function of an E3 ligase, Cbl-b, is essential for negative regulation of T cells in vivo. Thus, modulation of the E3 ligase activity of Cbl-b might be a novel modality to control T cell immunity in vaccination, cancer biology, or autoimmunity. 相似文献
58.
Glucose uptake by the heterofermentative lactic acid bacterium Oenococcus oeni B1 was studied at the physiological and gene expression levels. Glucose- or fructose-grown bacteria catalyzed uptake of [(14)C]glucose over a pH range from pH 4 to 9, with maxima at pHs 5.5 and 7. Uptake occurred in two-step kinetics in a high- and low-affinity reaction. The high-affinity uptake followed Michaelis-Menten kinetics and required energization. It accumulated the radioactivity of glucose by a factor of 55 within the bacteria. A large portion (about 80%) of the uptake of glucose was inhibited by protonophores and ionophores. Uptake of the glucose at neutral pH was not sensitive to degradation of the proton potential, Δp. Expression of the genes OEOE_0819 and OEOE_1574 (here referred to as 0819 and 1574), coding for secondary transporters, was induced by glucose as identified by quantitative real-time (RT)-PCR. The genes 1574 and 0819 were able to complement growth of a Bacillus subtilis hexose transport-deficient mutant on glucose but not on fructose. The genes 1574 and 0819 therefore encode secondary transporters for glucose, and the transports are presumably Δp dependent. O. oeni codes, in addition, for a phosphotransferase transport system (PTS) (gene OEOE_0464 [0464] for the permease) with similarity to the fructose- and mannose-specific PTS of lactic acid bacteria. Quantitative RT-PCR showed induction of the gene 0464 by glucose and by fructose. The data suggest that the PTS is responsible for Δp-independent hexose transport at neutral pH and for the residual Δp-independent transport of hexoses at acidic pH. 相似文献
59.
Background
In this study we investigated the association between instrumental music training in childhood and outcomes closely related to music training as well as those more distantly related.Methodology/Principal Findings
Children who received at least three years (M = 4.6 years) of instrumental music training outperformed their control counterparts on two outcomes closely related to music (auditory discrimination abilities and fine motor skills) and on two outcomes distantly related to music (vocabulary and nonverbal reasoning skills). Duration of training also predicted these outcomes. Contrary to previous research, instrumental music training was not associated with heightened spatial skills, phonemic awareness, or mathematical abilities.Conclusions/Significance
While these results are correlational only, the strong predictive effect of training duration suggests that instrumental music training may enhance auditory discrimination, fine motor skills, vocabulary, and nonverbal reasoning. Alternative explanations for these results are discussed. 相似文献60.
Lang I Schweizer A Hiden U Ghaffari-Tabrizi N Hagendorfer G Bilban M Pabst MA Korgun ET Dohr G Desoye G 《Differentiation; research in biological diversity》2008,76(10):1031-1043
Growing interest in the sources of origin of blood vessel related diseases has led to an increasing knowledge about the heterogeneity and plasticity of endothelial cells lining arteries and veins. So far, most of these studies were performed on animal models. Here, we hypothesized that the plasticity of human fetal endothelial cells depends on their vascular bed of origin i.e. vein or artery and further that the differences between arterial and venous endothelial cells would extend to phenotype and genotype. We established a method for the isolation of fetal arterial and venous endothelial cells from the human placenta and studied the characteristics of both cell types. Human placental arterial endothelial cells (HPAEC) and human placental venous endothelial cells (HPVEC) express classical endothelial markers and differ in their phenotypic, genotypic, and functional characteristics: HPAEC are polygonal cells with a smooth surface growing in loose arrangements and forming monolayers with classical endothelial cobblestone morphology. They express artery-related genes (hey-2, connexin 40, depp) and more endothelial-associated genes than HPVEC. Functional testing demonstrated that vascular endothelial growth factors (VEGFs) induce a higher proliferative response on HPAEC, whereas placental growth factors (PlGFs) are only effective on HPVEC. HPVEC are spindle-shaped cells with numerous microvilli at their surface. They grow closely apposed to each other, form fibroblastoid swirling patterns at confluence and have shorter generation and population doubling times than HPAEC. HPVEC overexpress development-associated genes (gremlin, mesenchyme homeobox 2, stem cell protein DSC54) and show an enhanced differentiation potential into adipocytes and osteoblasts in contrast to HPAEC. These data provide collective evidence for a juvenile venous and a more mature arterial phenotype of human fetal endothelial cells. The high plasticity of the fetal venous endothelial cells may reflect their role as tissue-resident endothelial progenitors during embryonic development with a possible benefit for regenerative cell therapy. 相似文献