全文获取类型
收费全文 | 1463篇 |
免费 | 130篇 |
专业分类
1593篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 23篇 |
2020年 | 17篇 |
2019年 | 37篇 |
2018年 | 35篇 |
2017年 | 38篇 |
2016年 | 58篇 |
2015年 | 93篇 |
2014年 | 93篇 |
2013年 | 103篇 |
2012年 | 131篇 |
2011年 | 133篇 |
2010年 | 79篇 |
2009年 | 50篇 |
2008年 | 87篇 |
2007年 | 92篇 |
2006年 | 80篇 |
2005年 | 63篇 |
2004年 | 64篇 |
2003年 | 55篇 |
2002年 | 59篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 19篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有1593条查询结果,搜索用时 0 毫秒
1.
Morten Colding-Jorgensen 《Journal of theoretical biology》1976,57(2):373-383
A simplified model of excitation is introduced in which the membrane capacity is ignored. It is shown that: (1) Threshold, action potentials, and strength-duration relation can be reproduced by a membrane without a capacity, even for a very simplified model. (2) The delayed build up of the sodium conductance can mimic a membrane capacity. (3) A constant potential stimulus can be used to reveal the influence of the membrane capacity, eventually combined with a feed back mechanism which reduces the effect of the capacity. (4) The effect of the membrane capacity depends on the ratio between the membrane time constant and the time constant for the fast conductance changes. 相似文献
2.
3.
Andrew A. Lackner Morten Schidt Gary C. Armitage Peter F. Moore Robert J. Munn Preston A. Marx Murray B. Gardner Linda J. Lowenstine 《Journal of medical primatology》1989,18(3-4):195-207
Simian acquired immune deficiency syndrome (SAIDS) caused by the type D retrovirus SRV-1 results in opportunistic infections and a spectrum of oral lesions similar to those seen in humans with AIDS. To better understand the pathogenesis of these oral lesions we have retrospectively examined the oral mucosa from ten rhesus monkeys that died with SAIDS and prospectively examined the oral mucosa of ten additional animals inoculated with SRV-1 to determine at what time, and in what cells SRV-1 infection of the oral mucosa occurs. Using single and double label immunohistologic techniques, and electron microscopy we detected SRV-1 in clusters of oral epithelial cells and rare Langerhans cells as early as 1 month postinoculation. 相似文献
4.
5.
14C-labeled extracellular organic carbon (EOC) released by the phytoplankton in a Danish Estuary was shown immediately to form particles (>0.2m) when the products were added to a natural water sample. About 14%–20% of the added activity could be recovered as particles. Any bacterial assimilation of the extracellular products was thus masked. The abiotic origin of the particulate EOC was verified, and it was shown that the particle formation was due to some factors present in the estuarine water with a nominal diameter >0.2m. Precaution must be taken to avoid misinterpretations in studies concerning carbon flow from algae to bacteria. 相似文献
6.
Bennedsen M Stuer-Lauridsen B Danielsen M Johansen E 《Applied and environmental microbiology》2011,77(8):2785-2787
Second-generation genome sequencing and alignment of the resulting reads to in silico genomes containing antimicrobial resistance and virulence factor genes were used to screen for undesirable genes in 28 strains which could be used in human nutrition. No virulence factor genes were detected, while several isolates contained antimicrobial resistance genes. 相似文献
7.
8.
Mie Agermose Gram Hanne-Dorthe Emborg Astrid Blicher Schelde Nikolaj Ulrik Friis Katrine Finderup Nielsen Ida Rask Moustsen-Helms Rebecca Legarth Janni Uyen Hoa Lam Manon Chaine Aisha Zahoor Malik Morten Rasmussen Jannik Fonager Raphael Niklaus Sieber Marc Stegger Steen Ethelberg Palle Valentiner-Branth Christian Holm Hansen 《PLoS medicine》2022,19(9)
BackgroundThe continued occurrence of more contagious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants and waning immunity over time require ongoing reevaluation of the vaccine effectiveness (VE). This study aimed to estimate the effectiveness in 2 age groups (12 to 59 and 60 years or above) of 2 or 3 vaccine doses (BNT162b2 mRNA or mRNA-1273) by time since vaccination against SARS-CoV-2 infection and Coronavirus Disease 2019 (COVID-19) hospitalization in an Alpha-, Delta-, or Omicron-dominated period.Methods and findingsA Danish nationwide cohort study design was used to estimate VE against SARS-CoV-2 infection and COVID-19 hospitalization with the Alpha, Delta, or Omicron variant. Information was obtained from nationwide registries and linked using a unique personal identification number. The study included all previously uninfected residents in Denmark aged 12 years or above (18 years or above for the analysis of 3 doses) in the Alpha (February 20 to June 15, 2021), Delta (July 4 to November 20, 2021), and Omicron (December 21, 2021 to January 31, 2022) dominated periods. VE estimates including 95% confidence intervals (CIs) were calculated (1-hazard ratio∙100) using Cox proportional hazard regression models with underlying calendar time and adjustments for age, sex, comorbidity, and geographical region. Vaccination status was included as a time-varying exposure. In the oldest age group, VE against infection after 2 doses was 90.7% (95% CI: 88.2; 92.7) for the Alpha variant, 82.3% (95% CI: 75.5; 87.2) for the Delta variant, and 39.9% (95% CI: 26.3; 50.9) for the Omicron variant 14 to 30 days since vaccination. The VE waned over time and was 73.2% (Alpha, 95% CI: 57.1; 83.3), 50.0% (Delta, 95% CI: 46.7; 53.0), and 4.4% (Omicron, 95% CI: −0.1; 8.7) >120 days since vaccination. Higher estimates were observed after the third dose with VE estimates against infection of 86.1% (Delta, 95% CI: 83.3; 88.4) and 57.7% (Omicron, 95% CI: 55.9; 59.5) 14 to 30 days since vaccination. Among both age groups, VE against COVID-19 hospitalization 14 to 30 days since vaccination with 2 or 3 doses was 98.1% or above for the Alpha and Delta variants. Among both age groups, VE against COVID-19 hospitalization 14 to 30 days since vaccination with 2 or 3 doses was 95.5% or above for the Omicron variant. The main limitation of this study is the nonrandomized study design including potential differences between the unvaccinated (reference group) and vaccinated individuals.ConclusionsTwo vaccine doses provided high protection against SARS-CoV-2 infection and COVID-19 hospitalization with the Alpha and Delta variants with protection, notably against infection, waning over time. Two vaccine doses provided only limited and short-lived protection against SARS-CoV-2 infection with Omicron. However, the protection against COVID-19 hospitalization following Omicron SARS-CoV-2 infection was higher. The third vaccine dose substantially increased the level and duration of protection against infection with the Omicron variant and provided a high level of sustained protection against COVID-19 hospitalization among the +60-year-olds.Mie Agermose Gram and colleagues estimate vaccine effectiveness against infection and COVID-19 hospitalization with the Alpha, Delta or Omicron variant in Denmark. 相似文献
9.
10.
Marie GB Hansen Mette Christoffersen Line R Thuesen Morten R Petersen Anders M Bojesen 《Acta veterinaria Scandinavica》2010,52(1):3