全文获取类型
收费全文 | 6320篇 |
免费 | 526篇 |
国内免费 | 21篇 |
专业分类
耳鼻咽喉 | 47篇 |
儿科学 | 226篇 |
妇产科学 | 190篇 |
基础医学 | 822篇 |
口腔科学 | 141篇 |
临床医学 | 629篇 |
内科学 | 1469篇 |
皮肤病学 | 60篇 |
神经病学 | 498篇 |
特种医学 | 300篇 |
外国民族医学 | 1篇 |
外科学 | 976篇 |
综合类 | 98篇 |
一般理论 | 1篇 |
预防医学 | 475篇 |
眼科学 | 108篇 |
药学 | 326篇 |
中国医学 | 8篇 |
肿瘤学 | 492篇 |
出版年
2021年 | 66篇 |
2020年 | 42篇 |
2019年 | 62篇 |
2018年 | 98篇 |
2017年 | 70篇 |
2016年 | 89篇 |
2015年 | 113篇 |
2014年 | 119篇 |
2013年 | 175篇 |
2012年 | 275篇 |
2011年 | 271篇 |
2010年 | 166篇 |
2009年 | 169篇 |
2008年 | 249篇 |
2007年 | 261篇 |
2006年 | 252篇 |
2005年 | 265篇 |
2004年 | 248篇 |
2003年 | 206篇 |
2002年 | 228篇 |
2001年 | 214篇 |
2000年 | 184篇 |
1999年 | 170篇 |
1998年 | 90篇 |
1997年 | 88篇 |
1996年 | 92篇 |
1995年 | 82篇 |
1994年 | 71篇 |
1993年 | 56篇 |
1992年 | 170篇 |
1991年 | 171篇 |
1990年 | 134篇 |
1989年 | 159篇 |
1988年 | 144篇 |
1987年 | 159篇 |
1986年 | 127篇 |
1985年 | 123篇 |
1984年 | 106篇 |
1983年 | 83篇 |
1982年 | 60篇 |
1981年 | 50篇 |
1980年 | 47篇 |
1979年 | 64篇 |
1978年 | 60篇 |
1977年 | 45篇 |
1976年 | 54篇 |
1975年 | 55篇 |
1974年 | 59篇 |
1973年 | 47篇 |
1969年 | 42篇 |
排序方式: 共有6867条查询结果,搜索用时 15 毫秒
71.
72.
Heterogeneous myocardial sympathetic denervation complicating diabetes has been invoked as a factor contributing to sudden unexplained cardiac death. In subjects with diabetic autonomic neuropathy (DAN), distal left ventricular (LV) denervation contrasts with preservation of islands of proximal innervation, which exhibit impaired vascular responsiveness. The aims of this study were to determine whether this heterogeneous pattern of myocardial sympathetic denervation occurs in a rat model of diabetes and to explore a potential association with regional fluctuations in myocardial nerve growth factor (NGF) protein. Myocardial sympathetic denervation was characterized scintigraphically using the sympathetic neurotransmitter analog C-11 hydroxyephedrine ([11C]HED) and compared with regional changes in myocardial NGF protein abundance and norepinephrine content after 6 and 9 months in nondiabetic (ND) and streptozotocin-induced diabetic (STZ-D) rats. In ND rats, no difference in [11C]HED retention or norepinephrine content was detected in the proximal versus distal myocardium. After 6 months, compared with ND rats, myocardial [11C]HED retention had declined in the proximal segments of STZ-D rats by only 9% (NS) compared with a 33% decrease in the distal myocardium (P < 0.05). Myocardial norepinephrine content was similar in both ND and STZ-D rats. At 6 months, LV myocardial NGF protein content in STZ-D rats decreased by 52% in the proximal myocardial segments (P < 0.01 vs. ND rats) and by 82% distally (P < 0.01 vs. ND rats, P < 0.05 vs. proximal segments). By 9 months, [11C]HED retention had declined in both the proximal and distal myocardial segments of the STZ-D rats by 42% (P < 0.01 vs. ND rats), and LV norepinephrine content and NGF protein were decreased in parallel. Therefore, 6 months of STZ-induced diabetes results in heterogeneous cardiac sympathetic denervation in the rat, with maximal denervation occurring distally, and is associated with a proximal-to-distal gradient of LV NGF protein depletion. It is tempting to speculate that regional fluctuations of NGF protein in the diabetic myocardium contribute to heterogeneous cardiac sympathetic denervation complicating diabetes. 相似文献
73.
P Sullivan G A Cioffi L Wang C A Johnson E M Van Buskirk K R Sherman D R Bacon 《American journal of ophthalmology》1999,128(1):81-87
PURPOSE: To determine the effect of the cardiac cycle on scanning laser Doppler flowmeter measurements of retinal capillary blood flow in rhesus monkeys and humans. METHODS: Multiple scanning laser Doppler flowmetry images of rhesus monkey and human retinal capillary blood flow over a range of heart rates were obtained. Average flow values were determined for the 64 scan lines that compose the two-dimensional flow map. Cutaneous blood flow was measured simultaneously with a laser Doppler flowmeter. The temporal relationships between retinal capillary blood flow, peripheral arterial pulse, and cutaneous blood flow were determined. In addition, human retinal capillary blood flow in a 10 x 10-pixel area during different phases of the cardiac cycle was compared. RESULTS: Regular oscillations in human and rhesus monkey retinal capillary blood flow are evident as alternating bright and dark horizontal bands in scanning laser Doppler flowmetry images. These fluctuations are temporally correlated with cutaneous blood flow. Linear regression of actual vs predicted heart rate based on peaks in retinal capillary flow yielded r = 0.999 in a rhesus monkey and 0.938 in a human. Retinal capillary blood flow in a 10 x 10-pixel area fluctuated as much as 50% depending on the phase of the cardiac cycle. CONCLUSIONS: The alternating bright and dark banding pattern observed in scanning laser Doppler flowmetry scans of retinal capillary blood flow is related to the cardiac pulse. The errors introduced by pulse-related fluctuations in retinal capillary blood flow are significant and must be minimized or corrected for accurate and reproducible measurements of ocular hemodynamics. 相似文献
74.
The molecular basis of the interaction of DT-diaphorase with a cytotoxic nitrobenzamide CB1954 [5-(aziridin-1-yl)-2, 4-dinitrobenzamide] and five inhibitors was investigated with wild-type DT-diaphorase (human and rat) and five mutants [three rat mutants (rY128D, rG150V, rH194D) and two human mutants (hY155F, hH161Q)]. hY155F and hH161Q were generated to evaluate a hypothesis that Tyr155 and His161 participate in the obligatory two-electron transfer reaction of the enzyme. The catalytic properties of hY155F and hH161Q were compared with a naturally occurring mutant, hP187S. Pro187 to Ser mutation disturbs the structure of the central parallel beta-sheet, resulting in a reduction of the binding affinity of the flavin-adenine dinucleotide prosthetic group. With NADH as the electron donor and menadione as the electron acceptor, the k(cat) values for the wild-type human DT-diaphorase, hY155F, hH161Q, and hP187S were measured as 66 +/- 1, 23 +/- 0, 5 +/- 0 and 8 +/- 2 x 10(3) min(-1), respectively. Because hY155F still has significant catalytic activity, the hydroxyl group on Tyr155 may not be as important as proposed. Interestingly, hY155F was found to be 3. 3 times more active than the human wild-type DT-diaphorase in the reduction of CB1954. Computer modeling based on our results suggests that CB1954 is situated in the active site, with the aziridinyl group pointing toward Tyr155 and the amide group placed near a hydrophobic pocket next to Tyr128. Dicoumarol, Cibacron blue, chrysin, 7,8-dihydroxyflavone, and phenindone are competitive inhibitors of the enzyme with respect to nicotinamide coenzymes. The binding orientations of dicoumarol, flavones, and phenindone in the active site of DT-diaphorase were predicted by results from our inhibitor-binding studies and computer modeling based on published X-ray structures. Our studies generated results that explain why dicoumarol is a potent inhibitor and binds differently from flavones and phenindone in the active site of DT-diaphorase. 相似文献
75.
76.
77.
78.
79.
80.