首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   155936篇
  免费   10867篇
  国内免费   634篇
耳鼻咽喉   1795篇
儿科学   4418篇
妇产科学   2603篇
基础医学   19741篇
口腔科学   8944篇
临床医学   14830篇
内科学   31896篇
皮肤病学   1937篇
神经病学   14436篇
特种医学   4940篇
外国民族医学   1篇
外科学   22727篇
综合类   1916篇
现状与发展   2篇
一般理论   204篇
预防医学   12702篇
眼科学   3715篇
药学   10006篇
  1篇
中国医学   314篇
肿瘤学   10309篇
  2023年   1241篇
  2022年   1599篇
  2021年   3598篇
  2020年   2151篇
  2019年   3363篇
  2018年   4148篇
  2017年   3131篇
  2016年   3489篇
  2015年   4092篇
  2014年   5649篇
  2013年   7488篇
  2012年   10913篇
  2011年   11498篇
  2010年   6486篇
  2009年   6084篇
  2008年   9671篇
  2007年   10185篇
  2006年   9560篇
  2005年   9457篇
  2004年   8808篇
  2003年   8104篇
  2002年   7690篇
  2001年   1541篇
  2000年   1190篇
  1999年   1557篇
  1998年   1825篇
  1997年   1545篇
  1996年   1272篇
  1995年   1226篇
  1994年   1043篇
  1993年   987篇
  1992年   917篇
  1991年   802篇
  1990年   743篇
  1989年   667篇
  1988年   680篇
  1987年   660篇
  1986年   545篇
  1985年   650篇
  1984年   716篇
  1983年   663篇
  1982年   842篇
  1981年   721篇
  1980年   607篇
  1979年   454篇
  1978年   444篇
  1977年   404篇
  1976年   341篇
  1975年   326篇
  1974年   335篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
Delayed contrast enhancement after injection of a gadolinium-chelate (Gd-chelate) is a reference imaging method to detect myocardial tissue changes. Its localization within the thickness of the myocardial wall allows differentiating various pathological processes such as myocardial infarction (MI), inflammatory myocarditis, and cardiomyopathies. The aim of the study was first to characterize benign myocarditis using quantitative delayed-enhancement imaging and then to investigate whether the measure of the extracellular volume fraction (ECV) can be used to discriminate between MI and myocarditis.In 6 patients with acute benign myocarditis (32.2 ± 13.8 year-old, subepicardial late gadolinium enhancement [LGE]) and 18 patients with MI (52.3 ± 10.9 year-old, subendocardial/transmural LGE), myocardial T1 was determined using the Modified Look-Locker Imaging (MOLLI) sequence at 3 Tesla before and after Gd-chelate injection. T1 values were compared in LGE and normal regions of the myocardium. The myocardial T1 values were normalized to the T1 of blood, and the ECV was calculated from T1 values of myocardium and blood pre- and post-Gd injection.In both myocarditis and MI, the T1 was lower in LGE regions than in normal regions of the left ventricle. T1 of LGE areas was significantly higher in myocarditis than in MI (446.8 ± 45.8 vs 360.5 ± 66.9 ms, P = 0.003) and ECV was lower in myocarditis than in MI (34.5 ± 3.3 vs 53.8 ± 13.0 %, P = 0.004).Both inflammatory process and chronic fibrosis induce LGE (subepicardial in myocarditis and subendocardial in MI). The present study demonstrates that the determination of T1 and ECV is able to differentiate the 2 histological patterns.Further investigation will indicate whether the severity of ECV changes might help refine the predictive risk of LGE in myocarditis.  相似文献   
6.
7.
If cigarette design was exogenous, inefficiencies arising from smoking could be addressed either with a tax per packet or with an ad valorem tax. However, it is well known that the consequences of these two instruments differ when product characteristics are endogenous. We consider three such characteristics: nicotine, tar, and flavor. Implementation of the first‐best social optimum typically requires the capacity to tax or regulate harmful ingredients. Without such a capacity, the next‐best policy often combines a per‐unit tax on cigarettes with an ad valorem subsidy. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
8.
A pathological feature in atherosclerosis is the dysfunction and death of vascular endothelial cells (EC). Oxidized low‐density lipoprotein (LDL), known to accumulate in the atherosclerotic arterial walls, impairs endothelium‐dependent relaxation and causes EC apoptosis. A major bioactive ingredient of the oxidized LDL is lysophosphatidylcholine (LPC), which at higher concentrations causes apoptosis and necrosis in various EC. There is hitherto no report on LPC‐induced cytotoxicity in brain EC. In this work, we found that LPC caused cytosolic Ca2+ overload, mitochondrial membrane potential decrease, p38 activation, caspase 3 activation and eventually apoptotic death in mouse cerebral bEND.3 EC. In contrast to reported reactive oxygen species (ROS) generation by LPC in other EC, LPC did not trigger ROS formation in bEND.3 cells. Pharmacological inhibition of p38 alleviated LPC‐inflicted cell death. We examined whether heparin could be cytoprotective: although it could not suppress LPC‐triggered Ca2+ signal, p38 activation and mitochondrial membrane potential drop, it did suppress LPC‐induced caspase 3 activation and alleviate LPC‐inflicted cytotoxicity. Our data suggest LPC apoptotic death mechanisms in bEND.3 might involve mitochondrial membrane potential decrease and p38 activation. Heparin is protective against LPC cytotoxicity and might intervene steps between mitochondrial membrane potential drop/p38 activation and caspase 3 activation.  相似文献   
9.
Dynamic contrast-enhanced ultrasound (DCE-US) has been proposed as a powerful tool for cancer diagnosis by estimation of perfusion and dispersion parameters reflecting angiogenic vascular changes. This work was aimed at identifying which vascular features are reflected by the estimated perfusion and dispersion parameters through comparison with acoustic angiography (AA). AA is a high-resolution technique that allows quantification of vascular morphology. Three-dimensional AA and 2-D DCE-US bolus acquisitions were used to monitor the growth of fibrosarcoma tumors in nine rats. AA-derived vascular properties were analyzed along with DCE-US perfusion and dispersion to investigate the differences between tumor and control and their evolution in time. AA-derived microvascular density and DCE-US perfusion exhibited good agreement, confirmed by their spatial distributions. No vascular feature was correlated with dispersion. Yet, dispersion provided better cancer classification than perfusion. We therefore hypothesize that dispersion characterizes vessels that are smaller than those visible with AA.  相似文献   
10.
First described in 1955 in New Jersey, epizootic haemorrhagic disease (EHD) causes a severe clinical disease in wild and domestic ruminants worldwide. Epizootic haemorrhagic disease outbreaks occur in deer populations each year from summer to late autumn. The etiological agent is EHD virus (EHDV) which is a double‐stranded segmented icosahedral RNA virus. EHD virus utilizes point mutations and reassortment strategies to maintain viral fitness during infection. In 2018, EHDV serotype 2 was predominantly detected in deer in Illinois. Whole genome sequencing was conducted for two 2018 EHDV2 isolates (IL41747 and IL42218) and the sequence analyses indicated that IL42218 was a reassortant between different serotypes whereas IL41747 was a genetically stable strain. Our data suggest that multiple strains contribute to outbreaks each year.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号