全文获取类型
收费全文 | 13625篇 |
免费 | 1364篇 |
国内免费 | 7篇 |
专业分类
14996篇 |
出版年
2023年 | 59篇 |
2022年 | 105篇 |
2021年 | 256篇 |
2020年 | 157篇 |
2019年 | 204篇 |
2018年 | 255篇 |
2017年 | 218篇 |
2016年 | 397篇 |
2015年 | 563篇 |
2014年 | 681篇 |
2013年 | 781篇 |
2012年 | 963篇 |
2011年 | 993篇 |
2010年 | 606篇 |
2009年 | 556篇 |
2008年 | 769篇 |
2007年 | 781篇 |
2006年 | 704篇 |
2005年 | 600篇 |
2004年 | 645篇 |
2003年 | 553篇 |
2002年 | 581篇 |
2001年 | 215篇 |
2000年 | 203篇 |
1999年 | 204篇 |
1998年 | 181篇 |
1997年 | 140篇 |
1996年 | 140篇 |
1995年 | 116篇 |
1994年 | 103篇 |
1993年 | 107篇 |
1992年 | 138篇 |
1991年 | 135篇 |
1990年 | 132篇 |
1989年 | 95篇 |
1988年 | 89篇 |
1987年 | 93篇 |
1986年 | 78篇 |
1985年 | 99篇 |
1984年 | 99篇 |
1983年 | 80篇 |
1982年 | 76篇 |
1981年 | 81篇 |
1980年 | 60篇 |
1979年 | 53篇 |
1978年 | 57篇 |
1977年 | 48篇 |
1976年 | 50篇 |
1975年 | 47篇 |
1974年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
891.
Bartholomew Baddeley Andrew Philippides Paul Graham Natalie Hempel de Ibarra Thomas Collett Phillip Husbands 《Biological cybernetics》2009,101(3):169-182
In this paper, we provide an analysis of orientation flights in bumblebees, employing a novel technique based on simultaneous
localisation and mapping (SLAM) a probabilistic approach from autonomous robotics. We use SLAM to determine what bumblebees
might learn about the locations of objects in the world through the arcing behaviours that are typical of these flights. Our
results indicate that while the bees are clearly influenced by the presence of a conspicuous landmark, there is little evidence
that they structure their flights to specifically learn about the position of the landmark. 相似文献
892.
893.
Christian Schulte Simon Molz Sebastian Appelbaum Mahir Karakas Francisco Ojeda Denise M. Lau Tim Hartmann Karl J. Lackner Dirk Westermann Renate B. Schnabel Stefan Blankenberg Tanja Zeller 《PloS one》2015,10(12)
Background
Circulating microRNAs (miRNAs) have been described as potential diagnostic biomarkers in cardiovascular disease and in particular, coronary artery disease (CAD). Few studies were undertaken to perform analyses with regard to risk stratification of future cardiovascular events. miR-126, miR-197 and miR-223 are involved in endovascular inflammation and platelet activation and have been described as biomarkers in the diagnosis of CAD. They were identified in a prospective study in relation to future myocardial infarction.Objectives
The aim of our study was to further evaluate the prognostic value of these miRNAs in a large prospective cohort of patients with documented CAD.Methods
Levels of miR-126, miR-197 and miR-223 were evaluated in serum samples of 873 CAD patients with respect to the endpoint cardiovascular death. miRNA quantification was performed using real time polymerase chain reaction (RT-qPCR).Results
The median follow-up period was 4 years (IQR 2.78–5.04). The median age of all patients was 64 years (IQR 57–69) with 80.2% males. 38.9% of the patients presented with acute coronary syndrome (ACS), 61.1% were diagnosed with stable angina pectoris (SAP). Elevated levels of miRNA-197 and miRNA-223 reliably predicted future cardiovascular death in the overall group (miRNA-197: hazard ratio (HR) 1.77 per one standard deviation (SD) increase (95% confidence interval (CI) 1.20; 2.60), p = 0.004, C-index 0.78; miRNA-223: HR 2.23 per one SD increase (1.20; 4.14), p = 0.011, C-index 0.80). In ACS patients the prognostic power of both miRNAs was even higher (miRNA-197: HR 2.24 per one SD increase (1.25; 4.01), p = 0.006, C-index 0.89); miRA-223: HR 4.94 per one SD increase (1.42; 17.20), p = 0.012, C-index 0.89).Conclusion
Serum-derived circulating miRNA-197 and miRNA-223 were identified as predictors for cardiovascular death in a large patient cohort with CAD. These results reinforce the assumption that circulating miRNAs are promising biomarkers with prognostic value with respect to future cardiovascular events. 相似文献894.
895.
Peter E. Molloy Barbara M. Graham Pauline M. Cupit Steven D. Grant Andrew J. R. Porter Charles Cunningham 《Molecular biotechnology》1995,4(3):239-245
This work describes protocols for the production of single-chain antibody and T-cell receptor fragments inE. coli. A choice of methods is given for the purification of the recombinant fragments that rely on the use of either immunoaffinity
or metal chelate affinity chromatography. The TCR fragments may have to be denatured and refolded before the fragments attain
their proper conformation. 相似文献
896.
897.
J Timár 《Acta physiologica Hungarica》1989,74(3-4):259-266
The recovery of MAO-B activity after a single dose of 0.25 mg/kg s.c. (-)deprenyl was measured in rat, by following the time course of the changes in the PEA (phenyl-ethylamine)-induced hyperactivity. One hour after its administration (-)deprenyl enhanced both the PEA-induced locomotion and stereotypy, however, its effect on the latter was more marked. At 24 h and at later time-points only stereotype was enhanced. The results show that a single small dose of (-)deprenyl which selectively blocks MAO-B, causes a long-lasting inhibition of PEA metabolism, and the enzyme activity needs more than one week to restore completely. 相似文献
898.
899.
The human aldose reductase gene maps to chromosome region 7q35 总被引:1,自引:0,他引:1
Alexander Graham Paul Heath John E. N. Morten Alexander F. Markham 《Human genetics》1991,86(5):509-514
Summary The human aldose reductase (AR) gene has been mapped to chromosome 7 using the polymerase chain reaction to specifically amplify the human AR sequence in hamster/human hybrid DNA and also in mouse/ human monochromosome hybrids. The assignment to chromosome 7 was confirmed by in situ hybridisation to human metaphase chromosomes using a novel, rapid hybridisation, method giving a regional localisation at 7q35. 相似文献
900.
Graham P Mulley 《BMJ (Clinical research ed.)》1988,296(6620):475-476