全文获取类型
收费全文 | 92501篇 |
免费 | 6713篇 |
国内免费 | 6406篇 |
专业分类
105620篇 |
出版年
2024年 | 201篇 |
2023年 | 1254篇 |
2022年 | 2940篇 |
2021年 | 4868篇 |
2020年 | 3194篇 |
2019年 | 4016篇 |
2018年 | 3956篇 |
2017年 | 2866篇 |
2016年 | 4051篇 |
2015年 | 5841篇 |
2014年 | 6887篇 |
2013年 | 7248篇 |
2012年 | 8493篇 |
2011年 | 7736篇 |
2010年 | 4482篇 |
2009年 | 4186篇 |
2008年 | 4775篇 |
2007年 | 4146篇 |
2006年 | 3532篇 |
2005年 | 2820篇 |
2004年 | 2312篇 |
2003年 | 2105篇 |
2002年 | 1698篇 |
2001年 | 1471篇 |
2000年 | 1342篇 |
1999年 | 1407篇 |
1998年 | 819篇 |
1997年 | 892篇 |
1996年 | 813篇 |
1995年 | 774篇 |
1994年 | 673篇 |
1993年 | 570篇 |
1992年 | 682篇 |
1991年 | 535篇 |
1990年 | 455篇 |
1989年 | 331篇 |
1988年 | 278篇 |
1987年 | 219篇 |
1986年 | 184篇 |
1985年 | 210篇 |
1984年 | 124篇 |
1983年 | 118篇 |
1982年 | 54篇 |
1981年 | 23篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1976年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The underlying ionic mechanisms of ischemic-induced arrhythmia were studied by the computer simulation method. To approximate the real situation, ischemic cells were simulated by considering the three major component conditions of acute ischemia (elevated extracellular K(+) concentration, acidosis and anoxia) at the level of ionic currents and ionic concentrations, and a round ischemic zone was introduced into a homogeneous healthy sheet to avoid sharp angle of the ischemic tissue. The constructed models were solved using the operator splitting and adaptive time step methods, and the perturbation finite difference (PFD) scheme was first used to integrate the partial differential equations (PDEs) in the model. The numerical experiments showed that the action potential durations (APDs) of ischemic cells did not exhibited rate adaptation characteristic, resulting in flattening of the APD restitution curve. With reduction of sodium channel availability and long recovery of excitability, refractory period of the ischemic tissue was significantly prolonged, and could no longer be considered as same as APD. Slope of the conduction velocity (CV) restitution curve increased both in normal and ischemic region when pacing cycle length (PCL) was short, and refractory period dispersion increased with shortening of PCL as well. Therefore, dynamic changes of CV and dispersion of refractory period rather than APD were suggested to be the fundamental mechanisms of arrhythmia in regional ischemic myocardium. 相似文献
52.
53.
54.
55.
56.
In this study, we investigate the role of liver X receptor alpha (LXR alpha) in lipogenesis in geese in order to understand the differences in hepatic steatosis mechanisms between mammals and waterfowl. Primary goose hepatocytes were isolated and treated with the LXR alpha agonist T0901317. Triglyceride (TG) accumulation, acetyl-CoA carboxylase alpha (ACC alpha) and fatty acid synthase (FAS) activities, and gene expression levels of LXR alpha, sterol regulatory element-binding proteins-1 (SREBP-1), FAS, ACC alpha and lipoprotein lipase (LPL) were measured in primary hepatocytes. We found a dose-dependent up-regulation of TG accumulation, ACC, and FAS activities and the mRNA levels of LXR alpha, SREBP-1, FAS, ACC alpha, and LPL genes in the presence of To-901317. We also found that binding of nuclear SREBP-1 to ACC alpha SRE sequence was induced by To-901317 (P < 0.05). In conclusion, LXR alpha is involved in the induction of the lipogenic pathway through activation of SREBP-1 and its target genes in goose primary hepatocytes. 相似文献
57.
58.
59.
60.
Rumi Zhang Peiyu Zhang Colin Dalton Graham A. Jullien 《Biomechanics and modeling in mechanobiology》2010,9(1):77-86
In this paper, we apply mixture theory to quantitatively predict the transient behavior of drug delivery by using a microneedle
array inserted into tissue. In the framework of mixture theory, biological tissue is treated as a multi-phase fluid saturated
porous medium, where the mathematical behavior of the tissue is characterized by the conservation equations of multi-phase
models. Drug delivery by microneedle array imposes additional requirements on the simulation procedures, including drug absorption
by the blood capillaries and tissue cells, as well as a moving interface along its flowing pathway. The contribution of this
paper is to combine mixture theory with the moving mesh methods in modeling the transient behavior of drug delivery into tissue.
Numerical simulations are provided to obtain drug concentration distributions into tissues and capillaries. 相似文献