全文获取类型
收费全文 | 97篇 |
免费 | 14篇 |
专业分类
111篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2001年 | 1篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有111条查询结果,搜索用时 15 毫秒
61.
Mukta Chakraborty Solveig Wall?e Signe Nedergaard Emma E. Fridel Torben Dabelsteen Bente Pakkenberg Mads F. Bertelsen Gerry M. Dorrestein Steven E. Brauth Sarah E. Durand Erich D. Jarvis 《PloS one》2015,10(6)
The ability to imitate complex sounds is rare, and among birds has been found only in parrots, songbirds, and hummingbirds. Parrots exhibit the most advanced vocal mimicry among non-human animals. A few studies have noted differences in connectivity, brain position and shape in the vocal learning systems of parrots relative to songbirds and hummingbirds. However, only one parrot species, the budgerigar, has been examined and no differences in the presence of song system structures were found with other avian vocal learners. Motivated by questions of whether there are important differences in the vocal systems of parrots relative to other vocal learners, we used specialized constitutive gene expression, singing-driven gene expression, and neural connectivity tracing experiments to further characterize the song system of budgerigars and/or other parrots. We found that the parrot brain uniquely contains a song system within a song system. The parrot “core” song system is similar to the song systems of songbirds and hummingbirds, whereas the “shell” song system is unique to parrots. The core with only rudimentary shell regions were found in the New Zealand kea, representing one of the only living species at a basal divergence with all other parrots, implying that parrots evolved vocal learning systems at least 29 million years ago. Relative size differences in the core and shell regions occur among species, which we suggest could be related to species differences in vocal and cognitive abilities. 相似文献
62.
Mari-Ann Otkjær Da Silva Jacob Thorup Gade Christian Damsgaard Tobias Wang Steffen Heegaard Mads Frost Bertelsen 《Journal of morphology》2020,281(2):240-249
To investigate whether the thickness of the cornea in snakes correlates with overall anatomy, habitat or daily activity pattern, we measured corneal thickness using optical coherence tomography scanning in 44 species from 14 families (214 specimens) in the collection at the Natural History Museum (Denmark). Specifically, we analyzed whether the thickness of the cornea varies among species in absolute terms and relative to morphometrics, such as body length, spectacle diameter, and spectacle thickness. Furthermore, we examined whether corneal thickness reflects adaptation to different habitats and/or daily activity patterns. The snakes were defined as arboreal (n = 8), terrestrial (n = 22), fossorial (n = 7), and aquatic (n = 7); 14 species were classified as diurnal and 30 as nocturnal. We reveal that the interspecific variation in corneal thickness is largely explained by differences in body size, but find a tendency towards thicker corneas in diurnal (313 ± 227 μm) compared to nocturnal species (205 ± 169 μm). Furthermore, arboreal snakes had the thickest corneas and fossorial snakes the thinnest. Our study shows that body length, habitat, and daily activity pattern could explain the interspecific variation in corneal morphology among snakes. This study provides a quantitative analysis of the evolution of the corneal morphology in snakes, and it presents baseline values of corneal thickness of multiple snake species. We speculate that the cornea likely plays a role in snake vision, despite the fact that results from previous studies suggest that the cornea in snakes is not relevant for vision (Sivak, Vision Research, 1977, 17, 293–298). 相似文献
63.
Loegering K Mueller C Voss JP Wagenfuehrer C Zahn D Bertelsen HP Scheffler U Luttmann R 《Biotechnology journal》2011,6(4):428-436
An integrated bioprocess was created in a scale-down production plant by developing a two-stage enzyme production process with Pichia pastoris, containing a cell-breeding reactor and a production reactor in combination with a three-stage downstream process. To harvest the secreted enzymes, a disc separator and a cross-flow microfiltration clear the broth from the cells. Purification with hydrophobic interaction chromatography removes other proteins, concentrates the product, and prepares the enzyme solution for lyophilization. Fully automated and broad observable multi-stage parallel process courses have been developed using industrial process control systems and at-line measurements for enzyme concentration and enzyme activity. Optimal process conditions were found by application of Design of Experiments (DoE) for the production process. 相似文献
64.
Rapid advances in human genomic research are increasing the availability of genomic data for secondary analysis. Particularly in the case of vulnerable African populations, ethics and informed consent processes need to be transparent-both to ensure participant protection, as well as to share skills and to evolve best practice for informed consent from a shared knowledge base. An open dialogue between all stakeholders can facilitate this. 相似文献
65.
Participation of plasma membrane proteins in the formation of tight junction by cultured epithelial cells
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Measurements of the transepithelial electrical resistance correlated with freeze-fracture observations have been used to study the process of tight junction formation under various experimental conditions in monolayers of the canine kidney epithelial cell line MDCK. Cells derived from previously confluent cultures and plated immediately after trypsin- EDTA dissociation develop a resistance that reaches its maximum value of several hundred ohms-cm(2) after approximately 24 h and falls to a steady-state value of 80-150 ohms- cm(2) by 48 h. The rise in resistance and the development of tight junctions can be completely and reversibly prevented by the addition of 10 μg/ml cycloheximide at the time of plating, but not when this inhibitor is added more than 10 h after planting. Thus tight junction formation consists of separable synthetic and assembly phases. These two phases can also be dissociated and the requirement for protein synthesis after plating eliminated if, following trypsinization, the cells are maintained in spinner culture for 24 h before plating. The requirement for protein synthesis is restored, however, if cells maintained in spinner culture are treated with trypsin before plating. Actinomycin D prevents development of resistance only in monolayers formed from cells derived from sparse rather than confluent cultures, but new mRNA synthesis is not required if cells obtained from sparse cultures are maintained for 24 h in spinner culture before plating. Once a steady-state resistance has been reached, its maintenance does not require either mRNA or protein synthesis; in fact, inhibition of protein synthesis causes a rise in the resistance over a 30-h period. Following treatments that disrupt the junctions in steady- state monolayers recovery of resistance also does not require protein synthesis. These observations suggest that proteins are involved in tight junction formation. Such proteins, which do not turn over rapidly under steady-state conditions, are destroyed by trypsinization and can be resynthesized in the absence of stable cell-cell or cell-substratum contact. Messenger RNA coding for proteins involved in tight junction formation is stable except when cells are sparsely plated, and can also be synthesized without intercellular contacts or cell-substratum attachment. 相似文献
66.
67.
Maja Kazazic Vibeke Bertelsen Ketil Winther Pedersen Tram Thu Vuong Michael Vibo Grandal Marianne Skeie Rødland Linton M. Traub Espen Stang Inger Helene Madshus 《Traffic (Copenhagen, Denmark)》2009,10(2):235-245
Epsin consists of an epsin NH2 -terminal homology domain that promotes interaction with phospholipids, several AP-2-binding sites, two clathrin-binding sequences and several Eps15 homology domain-binding motifs. Epsin additionally possesses ubiquitin-interacting motifs (UIMs) and has been demonstrated to bind ubiquitinated cargo. We therefore investigated whether epsin promoted clathrin-mediated endocytosis of the ubiquitinated EGF receptor (EGFR). By immunoprecipitation, we found that epsin 1 interacted with ubiquitinated EGFR and that functional UIMs were essential for complex formation. Furthermore, RNA interference-mediated knockdown of epsin 1 was found to inhibit internalization of the EGFR, while having no effect on endocytosis of the transferrin receptor. Additionally, upon knockdown of epsin 1, translocation of the EGFR to central parts of clathrin-coated pits was inhibited. This supports the contention that epsin 1 promotes endocytosis of the ubiquitinated EGFR. 相似文献
68.
Jo EB Halliday Margo E Chase-Topping Michael C Pearce Iain J McKendrick Lesley Allison Dave Fenlon Chris Low Dominic J Mellor George J Gunn Mark EJ Woolhouse 《BMC microbiology》2006,6(1):99-5
Background
E. coli O157 is a bacterial pathogen that is shed by cattle and can cause severe disease in humans. Phage type (PT) 21/28 is a subtype of E. coli O157 that is found across Scotland and is associated with particularly severe human morbidity. 相似文献69.
Carlos Cruchaga John S. K. Kauwe Kevin Mayo Noah Spiegel Sarah Bertelsen Petra Nowotny Aarti R. Shah Richard Abraham Paul Hollingworth Denise Harold Michael M. Owen Julie Williams Simon Lovestone Elaine R. Peskind Ge Li James B. Leverenz Douglas Galasko The Alzheimer's Disease Neuroimaging Initiative John C. Morris Anne M. Fagan David M. Holtzman Alison M. Goate 《PLoS genetics》2010,6(9)
Alzheimer''s Disease (AD) is a complex and multifactorial disease. While large genome-wide association studies have had some success in identifying novel genetic risk factors for AD, case-control studies are less likely to uncover genetic factors that influence progression of disease. An alternative approach to identifying genetic risk for AD is the use of quantitative traits or endophenotypes. The use of endophenotypes has proven to be an effective strategy, implicating genetic risk factors in several diseases, including anemia, osteoporosis and heart disease. In this study we identify a genetic factor associated with the rate of decline in AD patients and present a methodology for identification of other such factors. We have used an established biomarker for AD, cerebrospinal fluid (CSF) tau phosphorylated at threonine 181 (ptau181) levels as an endophenotype for AD, identifying a SNP, rs1868402, in the gene encoding the regulatory sub-unit of protein phosphatase B, associated with CSF ptau181 levels in two independent CSF series . We show no association of rs1868402 with risk for AD or age at onset, but detected a very significant association with rate of progression of disease that is consistent in two independent series . Our analyses suggest that genetic variants associated with CSF ptau181 levels may have a greater impact on rate of progression, while genetic variants such as APOE4, that are associated with CSF Aβ42 levels influence risk and onset but not the rate of progression. Our results also suggest that drugs that inhibit or decrease tau phosphorylation may slow cognitive decline in individuals with very mild dementia or delay the appearance of memory problems in elderly individuals with low CSF Aβ42 levels. Finally, we believe genome-wide association studies of CSF tau/ptau181 levels should identify novel genetic variants which will likely influence rate of progression of AD. 相似文献
70.
Crimmins TM Crimmins MA Bertelsen D Balmat J 《International journal of biometeorology》2008,52(5):353-366
This study analyzes a 20-year record of flowering observations collected near Tucson, Arizona, USA. In contrast to traditional
phenological records, this dataset is a record of all species observed in bloom collected in five segments of approximately
1 mile (1.61 km) in length across a 4,158-ft (1,200-m) elevation gradient. The data showed differing seasonal and interannual
patterns, demonstrating the influence of climatic factors and elevation on flowering. Miles at higher elevations showed bloom
peaks in summer, consistent with temperate and montane communities. Conversely, lower miles demonstrated two distinct flowering
seasons, typical of the surrounding Sonoran Desert. Interannual fluctuations in total species observed in bloom were not consistent
across the 5 miles (c. 8 km), suggesting that these communities respond to different flowering cues. Consistent with documented
flowering triggers in semi-arid systems, the alpha diversity of species in bloom at lower elevations in this study was strongly
influenced by precipitation. Upper elevation bloom numbers were heavily influenced by temperature, correspondent with bloom
triggers in temperate and montane systems. In general, different life forms exhibited similar bloom triggers within the study
miles, believed to be a function of shallow soils. Multivariate community analyses showed that anomalous climate conditions
yielded unique seasonal bloom compositions. Over the course of the study, average summer temperature showed an upward trend;
the number of species in bloom in summer (July–October) in the highest mile (1,940–2,210 m) demonstrated a concurrent increasing
trend. Community analysis suggested a gradual shift in the composition of species in bloom in this mile over the study period. 相似文献