全文获取类型
收费全文 | 316篇 |
免费 | 28篇 |
出版年
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 16篇 |
2014年 | 25篇 |
2013年 | 18篇 |
2012年 | 27篇 |
2011年 | 14篇 |
2010年 | 22篇 |
2009年 | 13篇 |
2008年 | 13篇 |
2007年 | 22篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1965年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 31 毫秒
91.
A new computational method is presented that efficiently describes open thermodynamic systems within the grand canonical ensemble formalism. The method is based on the j-walking algorithm, which circumvent sampling difficulties by coupling random walkers in different thermodynamic states. By imposing detailed balance, a new acceptance probability is derived and applied to the construction of adsorption isotherms for atomic monolayers. The method converges much faster than the standard grand canonical Monte Carlo method and permits the construction of accurate adsorption isotherms and the identification of phase transitions occurring in the adsorbed material. 相似文献
92.
Christina Staginnus Wolfgang Gregor M Florian Mette Chee How Teo Eduviges Glenda Borroto-Fernández Margit Laimer da Câmara Machado Marjori Matzke Trude Schwarzacher 《BMC plant biology》2007,7(1):24
Background
Endogenous pararetroviral sequences (EPRVs) are a recently discovered class of repetitive sequences that is broadly distributed in the plant kingdom. The potential contribution of EPRVs to plant pathogenicity or, conversely, to virus resistance is just beginning to be explored. Some members of the family Solanaceae are particularly rich in EPRVs. In previous work, EPRVs have been characterized molecularly in various species of Nicotiana including N.tabacum (tobacco) and Solanum tuberosum (potato). Here we describe a family of EPRVs in cultivated tomato (Solanum lycopersicum L.) and a wild relative (S.habrochaites). 相似文献93.
Bishop GM Smith MA LaManna JC Wilson AC Perry G Atwood CS 《Redox report : communications in free radical research》2007,12(6):257-266
Alterations in iron metabolism or oxidative damage in response to hypoxic incidents have been examined following re-oxygenation of the hypoxic tissue. To understand the consequences of decreased tissue oxygen on iron load, metal-catalyzed redox activity and oxidative modifications in isolation from re-oxygenation, the present study exposed mice to either normoxia, or mild hypoxia (380 Torr; approximately 10% normobaric oxygen) where the tissue was not allowed to re-oxygenate prior to examination. Brain, liver and skeletal muscle were examined for Fe3+ load, metal-catalyzed redox activity and oxidative modifications to proteins (N(epsilon)-(carboxymethyl)lysine), lipids (4-hydroxynonenal pyrrole) and nucleic acids (8-hydroxyguanosine). Hypoxia induced a 43% increase in the iron content of the liver (P < 0.001) as determined by ICP-MS and a 3.8-fold increase in Fe3+ load (P < 0.001) as determined by Perl's stain. There was a corresponding 2-fold increase in metal-catalyzed redox activity (P < 0.01) in the liver, but no change in the expression of oxidative markers. In contrast, non-significant increases in Fe3+ and metal-catalyzed redox activity were observed in the cerebral cortex, and molecular and granular layers of the hippocampus and cerebellum. Interestingly, hypoxia significantly decreased oxidative modifications to proteins and lipids, but not nucleic acids in most brain regions examined. In addition, hypoxia did not alter the Fe content of skeletal muscle, or the contents of Zn, Cu, Ni or Mn in liver, skeletal muscle, cerebral cortex or hippocampus. Together, these results indicate that there is a tighter regulation of iron metabolism in the brain than the liver, which limits the redistribution of Fe3+ following hypoxia. 相似文献
94.
Janbazian L Price DA Canderan G Filali-Mouhim A Asher TE Ambrozak DR Scheinberg P Boulassel MR Routy JP Koup RA Douek DC Sekaly RP Trautmann L 《Journal of immunology (Baltimore, Md. : 1950)》2012,188(3):1156-1167
Persistent exposure to cognate Ag leads to the functional impairment and exhaustion of HIV-specific CD8 T cells. Ag withdrawal, attributable either to antiretroviral treatment or the emergence of epitope escape mutations, causes HIV-specific CD8 T cell responses to wane over time. However, this process does not continue to extinction, and residual CD8 T cells likely play an important role in the control of HIV replication. In this study, we conducted a longitudinal analysis of clonality, phenotype, and function to define the characteristics of HIV-specific CD8 T cell populations that persist under conditions of limited antigenic stimulation. Ag decay was associated with dynamic changes in the TCR repertoire, increased expression of CD45RA and CD127, decreased expression of programmed death-1, and the emergence of polyfunctional HIV-specific CD8 T cells. High-definition analysis of individual clonotypes revealed that the Ag loss-induced gain of function within HIV-specific CD8 T cell populations could be attributed to two nonexclusive mechanisms: 1) functional improvement of persisting clonotypes; and 2) recruitment of particular clonotypes endowed with superior functional capabilities. 相似文献
95.
Diazotrophic endophytes of native black cottonwood and willow 总被引:1,自引:0,他引:1
Sharon L. Doty Brian Oakley Gang Xin Jun Won Kang Glenda Singleton Zareen Khan Azra Vajzovic James T. Staley 《Symbiosis (Philadelphia, Pa.)》2009,47(1):23-33
Poplar and willow are economically-important, fast-growing tree species with the ability to colonize nutrient-poor environments.
To initiate a study on the possible contribution of endophytes to this ability, we isolated bacteria from within surface-sterilized
stems of native poplar (Populus trichocarpa) and willow (Salix sitchensis) in a riparian system in western Washington state. Several of the isolates grew well in nitrogen-limited medium. The presence
ofnifH, a gene encoding one of the subunits of nitrogenase, was confirmed in several of the isolates including species ofBurkholderia, Rahnella, Sphingomonas, andAcinetobacter. Nitrogenase activity (as measured by the acetylene reduction assay) was also confirmed in some of the isolates. The presence
of these diazotrophic microorganisms may help explain the ability of these pioneering tree species to grow under nitrogen
limitation. 相似文献
96.
Mirjam Kaestli Mark Mayo Glenda Harrington Linda Ward Felicity Watt Jason V. Hill Allen C. Cheng Bart J. Currie 《PLoS neglected tropical diseases》2009,3(1)
Background
The soil-dwelling saprophyte bacterium Burkholderia pseudomallei is the cause of melioidosis, a severe disease of humans and animals in southeast Asia and northern Australia. Despite the detection of B. pseudomallei in various soil and water samples from endemic areas, the environmental habitat of B. pseudomallei remains unclear.Methodology/Principal Findings
We performed a large survey in the Darwin area in tropical Australia and screened 809 soil samples for the presence of these bacteria. B. pseudomallei were detected by using a recently developed and validated protocol involving soil DNA extraction and real-time PCR targeting the B. pseudomallei–specific Type III Secretion System TTS1 gene cluster. Statistical analyses such as multivariable cluster logistic regression and principal component analysis were performed to assess the association of B. pseudomallei with environmental factors. The combination of factors describing the habitat of B. pseudomallei differed between undisturbed sites and environmentally manipulated areas. At undisturbed sites, the occurrence of B. pseudomallei was found to be significantly associated with areas rich in grasses, whereas at environmentally disturbed sites, B. pseudomallei was associated with the presence of livestock animals, lower soil pH and different combinations of soil texture and colour.Conclusions/Significance
This study contributes to the elucidation of environmental factors influencing the occurrence of B. pseudomallei and raises concerns that B. pseudomallei may spread due to changes in land use. 相似文献97.
98.
Eliana Maria Minicucci Glenda Nicioli da Silva Daniel Araki Ribeiro Daisy Maria Favero Salvadori 《Journal of molecular histology》2009,40(1):71-76
The medium-term tongue carcinogenesis assay is a useful model for studying oral squamous cell carcinomas phase by phase. The
present study aimed to investigate mutations in exon 2 of gene p16CDKN2A during rat tongue carcinogenesis induced by 4-nitroquinoline
1-oxide (4NQO) using direct DNA-sequencing method. A total of 30 male Wistar rats were treated with 4-nitroquinoline 1-oxide
(4NQO) in drinking water for 4, 12, and 20 weeks at 50 ppm dose. Ten animals were used as negative control. No histopathological
changes in tongue epithelia were observed among controls or in the group treated for 4 weeks with 4NQO. Following 12-week
treatment, hyperplasia and epithelial dysplasia were found in mild and moderate forms. At 20 weeks, the tongue presented moderate
and/or severe oral dysplasia and squamous cell carcinoma, with squamous cell carcinoma in the majority of animals. No mutations
were found in any experimental period evaluated that corresponded to normal oral mucosa, hyperplasia, dysplasia and squamous
cell carcinomas. Taken together, our results suggest that p16CDKN2A mutations in exon 2 are not involved in the multistep
tongue carcinogenesis of Wistar rats induced by 4NQO. 相似文献
99.
100.
Belinda M. Keenan Stephen R. Robinson Glenda M. Bishop 《Neurochemistry international》2010,56(6-7):843-849
The concentrations of non-transferrin-bound iron are elevated in the brain during pathological conditions such as stroke and Alzheimer's disease. Astrocytes are specialised for sequestering this iron, however little is known about the mechanisms involved. Carboxylates, such as citrate, have been reported to facilitate iron uptake by intestinal cells. Citrate binds iron and limits its redox activity. The presence of high citrate concentrations in the interstitial fluid of the brain suggests that citrate may be an important ligand for iron transport by astrocytes. This study investigates whether iron accumulation by cultured rat astrocytes is facilitated by citrate or other carboxylates. Contrary to expectations, citrate, tartrate and malate were found to block iron accumulation in a concentration-dependent manner; α-ketoglutarate had limited effects, while fumarate, succinate and glutarate had no effect. This blockade was not due to an inhibition of ferric reductase activity. Instead, it appeared to be related to the capacity of these carboxylates to bind iron, since phosphate, which also binds iron, diminished the capacity of citrate, tartrate and malate to block the cellular accumulation of iron. These findings raise the possibility that citrate may have therapeutic potential in the management of neurodegenerative conditions that involve cellular iron overload. 相似文献