全文获取类型
收费全文 | 445篇 |
免费 | 41篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2019年 | 7篇 |
2018年 | 16篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 40篇 |
2012年 | 36篇 |
2011年 | 37篇 |
2010年 | 20篇 |
2009年 | 17篇 |
2008年 | 27篇 |
2007年 | 28篇 |
2006年 | 23篇 |
2005年 | 23篇 |
2004年 | 16篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 31 毫秒
11.
The connector protein, also known as the portal protein, located at the portal vertex in the Phi29 bacteriophage has been found to play a key role in the genome DNA packaging motor. There is a disordered region, composed of 12 sets of 18-residue loops N229–N246, that has been assumed to serve as a “clamp” to retain the DNA within the pressurized capsid when DNA is fully packaged. However, the process remains undefined about how the clamping of DNA occurs and what signal is used to engage the channel loops to clamp the DNA near the end of DNA packaging. In this study, we use the planar lipid bilayer (PLB) membrane technique to study the connector with its loops cleaved. The channel properties are compared with those of the connector with corresponding wild-type loops at different membrane potentials. On the basis of the hypothesis of the Donnan effects in the flashing Brownian ratchet model, we associate the PLB experimental results with the outcomes from the relevant biochemical experiments on the proheads containing the connectors without the loops, which enables us to provide a clear picture about how the DNA clamping occurs. A mathematical relationship between the Donnan potential and the DNA packaging density is established, demonstrating that they are both in essence the same signal that is received and transmitted by the connector to dictate DNA clamping and the termination of DNA packaging. At the end of the study, the PLB technique is proposed as a viral research tool, and its potential use to study the functions of specific domains in a portal protein of the tailed bacteriophages is highlighted. 相似文献
12.
CM van der Loos 《Biotechnic & histochemistry》2013,88(3):141-154
Three fixation issues related to immunostaining are discussed here: 1) Generally, a tissue block is fixed, then embedded and sectioned (pre-fixation). The type of fixative applied, crosslinking or coagulating, has an impact on selecting an epitope retrieval method. Individual antigens have a fixation–retrieval characteristic. 2) A long fixation time, especially with crosslinking fixatives, may compromise the result of immunostaining. This negative effect varies among different antigens and can be partially restored by applying a more sensitive/efficient detection system such as tyramide amplification. 3) Sections cut from a fresh frozen tissue block usually are acetone fixed (post-fixation). This was accepted as the “gold standard” for a long time. Post-fixation, however, may have serious consequences for preservation of small peptides leaking from the cut open cells, whereas this is not the case with pre-fixed intact cells. Consequently, the concept of an acetone post-fixed cryostat tissue section as “gold standard” no longer exists and a more appropriate use of the terms immunohistochemistry and immunocytochemistry therefore seems justified. For many antibodies, it is not known whether a formalin fixed, paraffin embedded tissue specimen is appropriate. Suggestions are made for creating a positive control cell block for testing such antibodies. 相似文献
13.
14.
15.
Abstract Opportunistic sightings and strandings of Caperea marginata (n=196) from the vicinity of Australia and New Zealand (1884 to early 2007) were used to relate geographic and temporal patterns to oceanographic and broad-scale climatic variability. Records were not uniformly distributed along the coast and more (69%) were from Australia than New Zealand. Seven coastal whale ‘hotspots’ were identified which accounted for 61% of records with locality data. Half of the hotspot records were from southeast (37) and northwest (20) Tasmania—others each had 9–15 events. Upwelling and/or high zooplankton abundance has been documented near all whale hotspots. Records of C. marginata occurred in all months, with 75% in spring and summer. Inter-annual variability showed broad agreement between increased whale records (usually in spring/summer) and strongly positive ‘Niño 3.4’ during 1980–1995 but not thereafter. Coastal upwelling and productivity increase during climatic phenomena such as El Niño and are likely to be quickly beneficial to plankton-feeding whales such as C. marginata. 相似文献
16.
Ludovic Reveiz Stephanie Sangalang Demian Glujovsky Carlos E. Pinzon Claudia Asenjo Lobos Marcela Cortes Martin Ca?ón Ariel Bardach Xavier Bonfill 《PloS one》2013,8(2)
Introduction
Few studies have assessed the nature and quality of randomized controlled trials (RCTs) in Latin America and the Caribbean (LAC).Methods and Findings
The aims of this systematic review are to evaluate the characteristics (including the risk of bias assessment) of RCT conducted in LAC according to funding source. A review of RCTs published in 2010 in which the author''s affiliation was from LAC was performed in PubMed and LILACS. Two reviewers independently extracted data and assessed the risk of bias. The primary outcomes were risk of bias assessment and funding source. A total of 1,695 references were found in PubMed and LILACS databases, of which 526 were RCTs (N = 73.513 participants). English was the dominant publication language (93%) and most of the RCTs were published in non-LAC journals (84.2%). Only five of the 19 identified countries accounted for nearly 95% of all RCTs conducted in the region (Brazil 70.9%, Mexico 10.1%, Argentina 5.9%, Colombia 3.8%, and Chile 3.4%). Few RCTs covered priority areas related with Millennium Development Goals like maternal health (6.7%) or high priority infectious diseases (3.8%). Regarding children, 3.6% and 0.4% RCT evaluated nutrition and diarrhea interventions respectively but none pneumonia. As a comparison, aesthetic and sport related interventions account for 4.6% of all trials. A random sample of RCTs (n = 358) was assessed for funding source: exclusively public (33.8%); private (e.g. pharmaceutical company) (15.3%); other (e.g. mixed, NGO) (15.1%); no funding (35.8%). Overall assessments for risk of bias showed no statistically significant differences between RCTs and type of funding source. Statistically significant differences favoring private and others type of funding was found when assessing trial registration and conflict of interest reporting.Conclusion
Findings of this study could be used to provide more direction for future research to facilitate innovation, improve health outcomes or address priority health problems. 相似文献17.
The main goal of the present study was to characterise the course of infection and immunological responses developed by Leishmania infantum infected BALB/c mice. Parasite load was determined by Real-time TaqMan PCR while cytokine and Immunoglobulin G (IgG) production were assessed by ELISA. Leishmania DNA was detected in spleen and liver as soon as day 1 post-inoculation (pi) and the parasitism was sustained until the end of the experiment. The cytokine kinetics in spleen and liver was generally associated with the oscillations of parasite load. Overall, it was not observed a distinct Th1 or Th2 pattern of cytokine production during the time of experiment. The infected mice developed a mixed immune response, with concomitant production of IFN-gamma, IL-4 and IL-10, both in spleen and liver, and both IgG isotypes. However, our results suggest that, compared to liver, the spleen is more susceptible to L. infantum infection. 相似文献
18.
Amaral Joo Henrique Fernandes Melack John Michael Barbosa Pedro Maia Borges Alberto V. Kasper Daniele Corts Alicia Cortes Zhou Wencai MacIntyre Sally Forsberg Bruce Rider 《Ecosystems》2022,25(4):911-930
Ecosystems - Extensive floodplains and numerous lakes in the Amazon basin are well suited to examine the role of floodable lands within the context of the sources and processing of carbon within... 相似文献
19.
Joaquim Jesus Maria Clara P. Amorim Paulo J. Fonseca Amílcar Teixeira Silvestre Natário João Carrola Simone Varandas Luís Torres Pereira Rui M. V. Cortes 《Journal of fish biology》2019,95(1):247-255
This study focused on the use of sound playbacks as acoustic deterrents to direct native potamodromous migratory species away from all kind of traps. The effects of two acoustic treatments, a repeated sine sweep up to 2 kHz (sweep-up stimulus) and an intermittent 140 Hz tone, were tested in three fish species native to Iberia: Salmo trutta, Pseudochondrostoma duriense and Luciobarbus bocagei. In contrast with S. trutta, the endemic cyprinids P. duriense and L. bocagei exhibited a strong repulse reaction to the frequency sweep-up sound. The 140 Hz stimulus did not seem to alter significantly the behaviour of any of the studied species. These results highlight the potential of acoustic stimuli as fish behavioural barriers and their application to in situ conservation measures of native Iberian fish populations, to protect them from hydropower dams. In addition, this study shows that acoustic deterrents can be used selectively on target species. 相似文献
20.
Bruno de Souza Gonçalves Jéssica M. de Moura Valadares Silmara L. G. Alves Simone C. Silva Luciana P. Rangel Vanessa F. Cortes José A. F. P. Villar Leandro A. Barbosa Hérica de Lima Santos 《Journal of cellular biochemistry》2019,120(10):17108-17122
Recently, cardiotonic steroids (CTS) have been shown to lead to the activation of Na,K-ATPase at low concentrations in brain, promoting neuroprotection against ischemia. We report here the results of the use of digoxin and its semisynthetic derivatives BD-14, BD-15, and BD-16 against partial chemical ischemic induction followed by reperfusion in murine neuroblastoma cells neuro-2a (N2a). For chemical ischemic induction, sodium azide (5 mM) was used for 5 hours, and then reperfusion was induced for 24 hours. Na,K-ATPase activity and protein levels were analyzed in membrane preparation of N2a cells pretreated with the compounds (150 nM), in the controls and in induced chemical ischemia. In the Na,K-ATPase activity and protein levels assays, the steroids digoxin and BD-15 demonstrated a capacity to modulate the activity of the enzyme directly, increasing its levels of expression and activity. Oxidative parameters, such as superoxide dismutase (SOD) activity, lipid peroxidation (thiobarbituric acid reactive substance), glutathione peroxidase (GPx), glutathione (GSH) levels, hydrogen peroxide content, and the amount of free radicals (reactive oxygen species) during induced chemical ischemia were also evaluated. Regarding the redox state, lipid peroxidation, hydrogen peroxide content, and GPx activity, we have observed an increase in the chemical ischemic group, and a reduction in the groups treated with CTS. SOD activity increased in all treated groups when compared to control and GSH levels decreased when treated with sodium azide and did not change with CTS treatments. Regarding the lipid profile, we saw a decrease in the content of phospholipids and cholesterol in the chemical ischemic group, and an increase in the groups treated with CTS. In conclusion, the compounds used in this study demonstrate promising results, since they appear to promote neuroprotection in cells exposed to chemical ischemia. 相似文献