全文获取类型
收费全文 | 407篇 |
免费 | 14篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 31篇 |
2015年 | 28篇 |
2014年 | 26篇 |
2013年 | 32篇 |
2012年 | 32篇 |
2011年 | 31篇 |
2010年 | 28篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 22篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1998年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1979年 | 2篇 |
1953年 | 1篇 |
排序方式: 共有421条查询结果,搜索用时 15 毫秒
91.
Diversity dynamics of post‐Palaeozoic crinoids – in quest of the factors affecting crinoid macroevolution 下载免费PDF全文
Przemysław Gorzelak Mariusz A. Salamon Dawid Trzęsiok Rafał Lach Tomasz K. Baumiller 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2016,49(2):231-244
Following the end‐Permian biotic crisis which led to the near extinction of crinoids, this echinoderm class rebounded rapidly during the Mesozoic, resulting in forms with important morphological and behavioural novelties. However, quantitative patterns of crinoid diversity during the Mesozoic remain largely unexplored. Here, we report results of analyses of the evolutionary dynamics of post‐Palaeozoic crinoid genera spanning a time interval between 250 and 70 Myr. We show that crinoids reached their Mesozoic peak of genus‐level richness during the Late Jurassic. We also document a major reorganization of different ecological crinoid groups in the Mesozoic. More specifically, the diversity of sessile forms generally increased towards the mid‐Mesozoic but decreased significantly starting in the Cretaceous, whereas the number of motile crinoid genera increased linearly during the Mesozoic. The possible role of biotic and abiotic factors in crinoid evolution is discussed. 相似文献
92.
93.
94.
95.
Magdalena?Paplińska-GorycaEmail author Patrycja?Nejman-Gryz Ma?gorzata?Proboszcz Rafa??Krenke 《European cytokine network》2016,27(2):54-62
Background
Airway epithelium is an active and important component of the immunological response in the pathophysiology of obstructive lung diseases. Recent studies suggest an important role for vitamin D3 in asthma severity and treatment response.Objective
Our study evaluated the influence of an active form of vitamin D3 on the expression of selected mediators of allergic inflammation in the respiratory epithelium.Material and Methods
Primary nasal and bronchial epithelial cells were exposed to1,25D3 for 1 hour and were then stimulated or not with IL-4, TNF-α, LPS, and poly I:C. After 24 hours TSLP, IL-33, and IL-25 protein levels were measured in culture supernatants usingELISAandmRNAlevels in cells by real time PCR.Results
1,25D3 increased TSLP concentration in unstimulated nasal epithelial cells, but did not influence IL-33 and IL-25 expression. In IL-4-stimulated epithelial cell cultures 1,25D3 mostly inhibited TSLP and IL-33 expression. In LPS-treated cultures 1,25D3 decreased IL-33 expression. Simultaneously 1,25D3 augmented IL-25 production in the same model of stimulation.Conclusion
Our study revealed the dual nature of vitamin D3 manifested in both pro- and anti-inflammatory properties observed in airway epithelial cells.96.
Kamila Caraballo Cortes Osvaldo Zagordi Joanna Jab?ońska Agnieszka Pawe?czyk Natalia Kubisa Karol Perlejewski Iwona Bukowska-O?ko Rafa? P?oski Marek Radkowski Tomasz Laskus 《PloS one》2016,11(2)
Hepatitis C virus (HCV) transmission between spouses remains poorly characterized, largely due to the limited availability of samples from the early stage of infection, as well as methodological constraints. A fifty-eight year-old male developed acute hepatitis C infection and his 53-year old spouse has been HCV-positive for over 10 years. Serum samples were collected from both at the time of acute hepatitis C diagnosis in male (baseline) and then at 9 and 13 months. Hypervariable region 1 (HVR1) and 5’ untranslated region (5’UTR) sequences were amplified and subjected to next generation sequencing (NGS) using a pyrosequencing platform. Genetic variants were inferred by Shorah reconstruction method and compared by phylogenetic and sequence diversity analysis. As the sequencing error of the procedure was previously determined to be ≤ 1.5%, the analysis was conducted with and without the 1.5% cut-off with regard to the frequency of variants. No identical HVR1 variants were identified in spouses at baseline and follow-up samples regardless whether the cut-off was applied or not. However, there was high similarity (98.3%) between a minor baseline donor variant (1.7% frequency) and the most abundant baseline recipient variant (62.5% frequency). Furthermore, donor and recipient strains clustered together when compared to 10 control subjects from the same area and infected with the same HCV subtype. There was an increase in HVR1 complexity (number of genetic variants) over time in both spouses. In contrast, the 5''UTR region was stable and of low complexity throughout the study. In conclusion, intrafamilial HCV transmission may be established by a very minor variant and investigation of this phenomenon requires high-sensitivity assays, such as NGS. 相似文献
97.
98.
99.
100.
In many interspecific interactions, the balance of costs and benefits varies with ecological circumstances. As a prominent example, seed‐caching granivores may act as seed predators and reduce plant recruitment or as seed dispersers and increase recruitment, making it difficult to interpret whether differences in seed removal by granivores would harm or benefit plant populations. We used a heuristic model to evaluate the outcome of plant‐granivore interactions, using commonly measured field data: probability of seedling emergence when granivores are excluded, and emergence of cached and uneaten seeds. Published studies to date suggest that the outcome of plant‐rodent interactions tends weakly towards mutualism, but differs among particular plant–granivore pairs and ecological conditions, supporting the notion of context‐dependence. A modeling framework also allowed us to distinguish parameters that affect the qualitative outcome of plant–granivore interactions from those that do not. Similar approaches would facilitate more efficient and cost‐effective evaluation of complex species interactions. 相似文献