全文获取类型
收费全文 | 967篇 |
免费 | 77篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 22篇 |
2020年 | 20篇 |
2019年 | 28篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 33篇 |
2015年 | 69篇 |
2014年 | 58篇 |
2013年 | 75篇 |
2012年 | 96篇 |
2011年 | 90篇 |
2010年 | 64篇 |
2009年 | 37篇 |
2008年 | 66篇 |
2007年 | 51篇 |
2006年 | 31篇 |
2005年 | 49篇 |
2004年 | 44篇 |
2003年 | 29篇 |
2002年 | 25篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1963年 | 1篇 |
1958年 | 1篇 |
1954年 | 2篇 |
1944年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有1044条查询结果,搜索用时 281 毫秒
1.
Elsa Youngsteadt R. Holden Appler Margarita M. López-Uribe David R. Tarpy Steven D. Frank 《PloS one》2015,10(11)
Given the role of infectious disease in global pollinator decline, there is a need to understand factors that shape pathogen susceptibility and transmission in bees. Here we ask how urbanization affects the immune response and pathogen load of feral and managed colonies of honey bees (Apis mellifera Linnaeus), the predominant economically important pollinator worldwide. Using quantitative real-time PCR, we measured expression of 4 immune genes and relative abundance of 10 honey bee pathogens. We also measured worker survival in a laboratory bioassay. We found that pathogen pressure on honey bees increased with urbanization and management, and the probability of worker survival declined 3-fold along our urbanization gradient. The effect of management on pathogens appears to be mediated by immunity, with feral bees expressing immune genes at nearly twice the levels of managed bees following an immune challenge. The effect of urbanization, however, was not linked with immunity; instead, urbanization may favor viability and transmission of some disease agents. Feral colonies, with lower disease burdens and stronger immune responses, may illuminate ways to improve honey bee management. The previously unexamined effects of urbanization on honey-bee disease are concerning, suggesting that urban areas may favor problematic diseases of pollinators. 相似文献
2.
Carole-Anne Lefebvre Elsa Forcellini Sophie Boutin Marie-France Côté René C.-Gaudreault Patrick Mathieu Patrick Lagüe Jean-François Paquin 《Bioorganic & medicinal chemistry letters》2017,27(2):299-302
The synthesis of two series of novel substituted pyrimidine derivatives bearing a sulfamide group have been described and their in vitro cancer growth inhibition activities have been evaluated against three human tumour cell lines (HT-29, M21, and MCF7). In general, growth inhibition activity has been enhanced by the introduction of a bulky substituent on the aromatic ring with the best compound having GI50 < 6 μM for all the human tumour cell lines. The MCF7 selective compounds were evaluated on four additional human invasive breast ductal carcinoma cell lines (MDA-MB-231, MDA-MB-468, SKBR3, and T47D) and were selective against T47D cell line in all cases except one, suggesting a potential antiestrogen activity. 相似文献
3.
Functional responses of the wolf spider, Pardosa pseudoannulata (Boesenberg et Strand) attacking the rice brown planthopper, Nilaparvata lugens (Stål.), and the mirid predator Cyrtorhinus lividipennis Reuter were both those of Holling Type II. The attack rate was higher and handling time lower for C. lividipennis. However, when caged with the two prey, the wolf spider showed a significant preference for N. lugens at a lower prey proportion. Proportions of prey attacked were significantly different from the expected ratios of prey available as well as from the predicted preferences derived from the functional response parameters. As proportions of N. lugens attacked changed from greater to less than expected as the proportions of N. lugens available increased, a “reverse switch” behaviour seems to be evident. 相似文献
4.
John E. Averett Elsa M. Zardini Peter C. Hoch 《Biochemical Systematics and Ecology》1990,18(7-8):529-532
Data for the flavonoids of 19 species in 10 sections of Ludwigia are presented. Eight flavonoids, comprising four glycoflavones, of which vitexin and isovitexin are reported for the first time in Ludwigia, and four flavonol glycosides, based on quercetin, are present in these species. Each section treated here has either glycoflavones or flavonols; presence of only onte class is considered to be advanced in the genus as a whole, compared with the presence of both glycoflavones and flavonols in the more generalized sects Myrtocarpus Cinerascentes, and Pterocaulon, which were examined earlier. Only glycoflavones are present in sects Macrocarpon (four species), Seminuda (five species), the ditypic African sect. Africana, the monotypic African sects Brenania, Cryptosperma, and Prieurea, the monotypic east Asian sect. Nipponia, and the monotypic pantropical section Fissendocarpa. Only flavonols are present in the monotypic Old Wodd section Caryophylloidea and sect. Oligospermum, which comprises nine species widespread in the OId and New Worlds. 相似文献
5.
Jennifer L. Jacobi Bo Yang Xu Li Anna K. Menze Sara M. Laurentz Elsa M. Janle Mario G. Ferruzzi George P. McCabe Clint Chapple Ann L. Kirchmaier 《PloS one》2016,11(2)
The plant secondary metabolite and common food additive dihydrocoumarin (DHC) is an inhibitor of the Sirtuin family of NAD+-dependent deacetylases. Sirtuins are key regulators of epigenetic processes that maintain silent chromatin in yeast and have been linked to gene expression, metabolism, apoptosis, tumorogenesis and age-related processes in multiple organisms, including humans. Here we report that exposure to the polyphenol DHC led to defects in several Sirtuin-regulated processes in budding yeast including the establishment and maintenance of Sir2p-dependent silencing by causing disassembly of silent chromatin, Hst1p-dependent repression of meiotic-specific genes during the mitotic cell cycle. As both transient and prolonged exposure to environmental and dietary factors have the potential to lead to heritable alterations in epigenetic states and to modulate additional Sirtuin-dependent phenotypes, we examined the bioavailability and digestive stability of DHC using an in vivo rat model and in vitro digestive simulator. Our analyses revealed that DHC was unstable during digestion and could be converted to melilotic acid (MA), which also caused epigenetic defects, albeit less efficiently. Upon ingestion, DHC was observed primarily in intestinal tissues, but did not accumulate over time and was readily cleared from the animals. MA displayed a wider tissue distribution and, in contrast to DHC, was also detected in the blood plasma, interstitial fluid, and urine, implying that the conversion of DHC to the less bioactive compound, MA, occurred efficiently in vivo. 相似文献
6.
Elsa Zardini 《Economic botany》1991,45(1):72-85
Attention is directed to the latent possibilities of Polymnia sonchifolia (Asteraceae), long cultivated in the Andean cloud forest for its tuberous, inulin-reserving roots. 相似文献
7.
8.
9.
Elsa Leitão Ana Catarina Costa Claudia Brito Lionel Costa Rita Pombinho 《Cell cycle (Georgetown, Tex.)》2014,13(6):928-940
Listeria monocytogenes (Lm) is a human intracellular pathogen widely used to uncover the mechanisms evolved by pathogens to establish infection. However, its capacity to perturb the host cell cycle was never reported. We show that Lm infection affects the host cell cycle progression, increasing its overall duration but allowing consecutive rounds of division. A complete Lm infectious cycle induces a S-phase delay accompanied by a slower rate of DNA synthesis and increased levels of host DNA strand breaks. Additionally, DNA damage/replication checkpoint responses are triggered in an Lm dose-dependent manner through the phosphorylation of DNA-PK, H2A.X, and CDC25A and independently from ATM/ATR. While host DNA damage induced exogenously favors Lm dissemination, the override of checkpoint pathways limits infection. We propose that host DNA replication disturbed by Lm infection culminates in DNA strand breaks, triggering DNA damage/replication responses, and ensuring a cell cycle delay that favors Lm propagation. 相似文献
10.
Rebeca Vidal† Elsa M. Valdizán† Ricardo Mostany Angel Pazos† Elena Castro† 《Journal of neurochemistry》2009,110(3):1120-1127
The mode of action of antidepressant drugs may be related to mechanisms of monoamines receptor adaptation, including serotonin 5-HT4 receptor subtypes. Here we investigated the effects of repeated treatment with the selective serotonin reuptake inhibitor fluoxetine for 21 days (5 and 10 mg/kg, p.o., once daily) on the sensitivity of 5-HT4 receptors by using receptor autoradiography, adenylate cyclase assays and extracellular recording techniques in rat brain. Fluoxetine treatment decreased the density of 5-HT4 receptor binding in the CA1 field of hippocampus as well as in several areas of the striatum over the doses of 5–10 mg/kg. In a similar way, we found a significant lower response to zacopride-stimulated adenylate cyclase activity in the fluoxetine 10 mg/kg/day treated group. Furthermore, post-synaptic 5-HT4 receptor activity in hippocampus-measured as the excitatory action of zacopride in the pyramidal cells of CA1 evoked by Schaffer collateral stimulation was attenuated in rats treated with both doses of fluoxetine. Taken together, these results support the concept that a net decrease in the signalization pathway of 5-HT4 receptors occurs after chronic selective serotonin reuptake inhibitor treatment: this effect may underlie the therapeutic efficacy of these drugs. 相似文献