全文获取类型
收费全文 | 22318篇 |
免费 | 1364篇 |
国内免费 | 1531篇 |
专业分类
耳鼻咽喉 | 30篇 |
儿科学 | 239篇 |
妇产科学 | 88篇 |
基础医学 | 1788篇 |
口腔科学 | 22篇 |
临床医学 | 2064篇 |
内科学 | 3878篇 |
皮肤病学 | 10篇 |
神经病学 | 3941篇 |
特种医学 | 994篇 |
外科学 | 2270篇 |
综合类 | 4868篇 |
预防医学 | 342篇 |
眼科学 | 235篇 |
药学 | 2276篇 |
3篇 | |
中国医学 | 2107篇 |
肿瘤学 | 58篇 |
出版年
2024年 | 35篇 |
2023年 | 136篇 |
2022年 | 337篇 |
2021年 | 474篇 |
2020年 | 422篇 |
2019年 | 352篇 |
2018年 | 402篇 |
2017年 | 490篇 |
2016年 | 608篇 |
2015年 | 630篇 |
2014年 | 1078篇 |
2013年 | 1283篇 |
2012年 | 1178篇 |
2011年 | 1364篇 |
2010年 | 1234篇 |
2009年 | 1184篇 |
2008年 | 1348篇 |
2007年 | 1422篇 |
2006年 | 1343篇 |
2005年 | 1239篇 |
2004年 | 1136篇 |
2003年 | 1097篇 |
2002年 | 928篇 |
2001年 | 827篇 |
2000年 | 702篇 |
1999年 | 590篇 |
1998年 | 501篇 |
1997年 | 486篇 |
1996年 | 331篇 |
1995年 | 309篇 |
1994年 | 258篇 |
1993年 | 195篇 |
1992年 | 199篇 |
1991年 | 194篇 |
1990年 | 141篇 |
1989年 | 91篇 |
1988年 | 104篇 |
1987年 | 69篇 |
1986年 | 71篇 |
1985年 | 92篇 |
1984年 | 76篇 |
1983年 | 42篇 |
1982年 | 45篇 |
1981年 | 44篇 |
1980年 | 38篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 10篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
采用低压低灌流方法造成家兔急性不完全性脑缺血,并进行重灌流。检测了脑电图(EEG)及大脑组织中乳酸脱氢酶(LDH)活性,观察了大脑皮层组织形态学变化。结果发现,脑缺血时大脑EEG明显抑制,LDH活性升高,脑组织超微结构表现为膜结构损伤。重灌流后EEG严重抑制,LDH活性升高,膜结构损伤进一步加重。 相似文献
82.
目的观察脑缺血后细胞周期蛋白(cyclin)D1和它的酶CDK4基因表达,以及这种表达的改变是否影响神经细胞凋亡。方法成年雄性SD大鼠32只随机分为假手术组(n=4)和实验组(n=28),实验组再进一步分为7个亚组(再灌注2h,6h,12h,1d,3d,7d和14d,每组n=4)。应用线栓法建立SD大鼠大脑中动脉阻塞/再灌注模型.TUNEL法检测神经细胞凋亡。原位杂交检测cyclinD1和CDK4mRNA的表达。结果CyclinD1mRNA和CDK4mRNA的表达与凋亡细胞的区域基本相同。再灌注2h脑组织即开始出现神经细胞凋亡,并于1d分别在皮层区和纹状体区达高峰(分别为72.80±4.66和87.75±0.85)。神经细胞cyclinD1mRNA和CDK4mRNA的表达分别于再灌注2h和6h开始逐渐增强,并于12h和1d达高峰(皮质区分别为94.50±2.75和85.75±3.73,纹状体区分别为88.25±5.06和89.80±2.93)。结论CyclinD1和CDK4选择性地在形态学完整或已经有改变的缺血侧神经元和少突胶质细胞内表达。CyclinD1/CD1(4mRNA表达可能是诱导细胞凋亡的重要因素之一。 相似文献
83.
Chronic ischemia produces corresponding tissue hypoplasia. However, here we report a distinctive hypertrophy of the intestine due to chronic mesenteric insufficiency, which was confirmed by angiography in two patients with opposite characteristic pathologic presentation of intestine. During surgery of the first patient, an approximately 60cm long ileum with sausage consistency and cyanosis color was identified proximal to the caecum; wall-attached thromboembolism material and the hypertrophied segment of ileum were removed. In the other patient, the intestine wall was paper thin; after aorto-mesenteric bypass the intestine wall grew thicker. Post operative recovery of both patients was uneventful. The commonly observed situation after a long-standing hypoxic insult in a setting of chronic mesenteric ischemia is that the target tissue will at least develop a slight hypoplasia. However, the cases we present here had either pronounced hyperplasia or severe hypoplasia. We thus report it, expecting to identify a special mechanism to explain this paradox. 相似文献
84.
视网膜缺血对兔视神经纤维损害的定量研究 总被引:2,自引:0,他引:2
目的:定量研究视网膜缺血对视神经的损害。方法:通过计算机图像分析定量测算视神经纤维数量;通过前房灌注平衡液,造成超高眼压,形成兔视网膜完全缺血模型,观察视神经纤维数量的变化。结果:正常兔眼平均视神经轴突数为109608±14561(n=22);视网膜缺血眼视神经纤维数量明显减少(P〈0.001)。结论:急性高眼压造成的视网膜缺血可使视神经节细胞及轴突的数量明显减少,应用计算机图像分析可定量检测这种 相似文献
85.
Dara L. Kraitchman Norbert Wilke Erik Hexeberg Michael Jerosch-Herold Ying Wang Todd B. Parrish Cheng-Ning Chang Yi Zhang Robert J. Bache Leon Axel 《Magnetic resonance in medicine》1996,35(5):771-780
MRI studies of first-pass contrast enhancement with polylysine-Gd-DTPA and myocardial tagging using spatial modulation of magnetization (SPAMM) were performed to assess the feasibility of a combined regional myocardial blood flow and 2D deformation exam. Instrumented closed-chest dogs were imaged at a baseline control state (Cntl) followed by two interventions: moderate coronary stenosis (St) achieved by partial occlusion of the left anterior descending (LAD) and moderate coronary stenosis with dobutamine loading (StD). Hypoperfusion of the anterior region (ANT) of the myocardium (LAD distribution) relative to the posterior wall (POS) based on the upslope of the signal intensity time curve from the contrast-enhanced MR images was demonstrated only with dobutamine loading (ANT:POS Cntl=1.077 ± 0.15 versus ANT:POS StD=0.477 ± 0.11, P<0.03) and was confirmed with radio-labeled microspheres measurements (ANT:POS Cntl=1.18 ± 0.2 ml/min/g versus ANT:POS StD=0.44 ± 0.1 ml/min/g; P<0.002). Significant changes in regional myocardial shortening were only seen in the StD state (P<0.02); the anterior region showed impaired myocardial shortening with dobutamine loading (P=NS), whereas the nonaffected POS region showed a marked increase in shortening when compared with Cntl (Cntl=0.964 ± 0.02 versus StD=0.884 ± 0.03; P<0.001). These results demonstrate that an integrated quantitative assessment of regional myocardial function and semiquantitative assessment of myocardial blood flow can be performed noninvasively with ultrafast MRI. 相似文献
86.
Summary By ligating the proximate left anterior descend (LAD) of coronary artery and inducing the ventricular fibrillation with electrical
stimulation, the preventive effects of electroacupuncture (EA) on ventricular fibrillation were observed. The results showed
that the ventricular fibrillation threshold (VFT) of rats with acute ischemic myocardium was raised after acupuncturing some
acupoints, which could prevent the occurrence of ventricular fibrillation. Furthermore, the combination of EA and propranolol
could enhance the VFT effectively, and they showed a good synergistic effect.
This project was supported by grants from National Natural Science Foundation of China (No. 3870563). 相似文献
87.
An increase in intracellular Na+ during ischaemia has been associated with myocardial injury. In this study, we determined whether inhibition of Na+/K+ ATPase activity contributes to this increase and whether Na+/K+ ATPase activity can be maintained by provision of glucose to perfused rat hearts during low flow, 0.5 ml/min, ischemia. We used 31P NMR spectroscopy to determine changes in myocardial energetics and intracellular and extracellular volumes. 23Na NMR spectroscopy, with DyTTHA3- present as a shift reagent, was used to measure changes in intracellular Na+ and 87Rb NMR spectroscopy was used to estimate Na+/K+ ATPase activity from Rb+ influx rates, Rb+ being an NMR-sensitive congener of K+. In hearts provided with 11 mM glucose throughout ischemia, glycolysis continued and ATP was twofold higher than in hearts without glucose. In the glucose-hearts, Rb+ influx rate was threefold higher, intracellular Na+ was fivefold lower at the end of ischemia and functional recovery during reperfusion was twofold higher. We propose that continuation of glycolysis throughout low flow ischemia allowed maintenance of sufficient Na+/K+ ATPase activity to prevent the increase in intracellular Na+ that would otherwise have led to myocardial injury. 相似文献
88.
鼠脑缺血后软脑膜微循环及脑血流自动调节功能的实验研究 总被引:2,自引:0,他引:2
本文利用闭合式颅骨开窗的方法制成脑微循环小室,以显微镜摄像系统连续观察双侧颈总动脉阻塞前后软脑膜微循环的变化,发现双侧颈总动脉阻塞后,软脑膜动脉管径和平均动脉压分别增加了40%和58%;静脉内血球流速减少至原值的70%;软脑膜动脉对动脉血二氧化碳浓度升高及低血压所引起的扩张反应受到明显抑制。实验结果提示:双侧颈总动脉阻塞后,虽然脑动脉明显扩张、血压上升。仍不足以代偿由于脑局部灌注压的下降所造成的脑血流量减少。提示双侧颈总动脉阻塞时,脑血流的自动调节功能受到严重损害。 相似文献
89.
本文对西宁地区新生儿缺氧缺血性脑病(HIE)颅脑超声诊断分析脑缺氧缺血产生的原因、脑实质损伤程度及预后评估。提出对围产期窒息导致脑缺血性损害的预防措施。 相似文献
90.
Comparative effects of ischemia and acute hypoxemia (PaO2 = 24 mm Hg) were studied in anesthetized cats on afferents from the tibialis anterior limb muscle. Metaboreceptors (groups III and IV fibers) and mechanoreceptors were identified by their activation by an intraarterial injection of lactic acid (LA) or high-frequency vibrations (HFV) applied to the extremity of the muscle tendon, respectively. Ischemia and hypoxemia exerted opposite influences on the two categories of muscle afferents: they depressed the response of mechanoreceptors to HFV, but markedly enhanced the spontaneous tonic activity of metaboreceptors. The effects of hypoxamia were delayed but slightly greater and lasted longer during the recovery period than those exerted by ischemia. The inhibitory action on mechanoreceptors exerted by a reduced oxyden supply to muscle is interpreted as a result from local acidosis. Indeed, under normoxic conditions, a LA bolus injection during the HFV test also reduced the firing rate of these receptors. © 1993 John Wiley & Sons, Inc. 相似文献