收费全文 | 16872篇 |
免费 | 992篇 |
国内免费 | 82篇 |
耳鼻咽喉 | 147篇 |
儿科学 | 343篇 |
妇产科学 | 275篇 |
基础医学 | 2332篇 |
口腔科学 | 366篇 |
临床医学 | 1716篇 |
内科学 | 3504篇 |
皮肤病学 | 204篇 |
神经病学 | 1895篇 |
特种医学 | 673篇 |
外科学 | 2530篇 |
综合类 | 82篇 |
一般理论 | 40篇 |
预防医学 | 1176篇 |
眼科学 | 203篇 |
药学 | 1289篇 |
中国医学 | 19篇 |
肿瘤学 | 1152篇 |
2023年 | 105篇 |
2022年 | 176篇 |
2021年 | 413篇 |
2020年 | 290篇 |
2019年 | 440篇 |
2018年 | 460篇 |
2017年 | 343篇 |
2016年 | 451篇 |
2015年 | 433篇 |
2014年 | 649篇 |
2013年 | 879篇 |
2012年 | 1236篇 |
2011年 | 1287篇 |
2010年 | 700篇 |
2009年 | 645篇 |
2008年 | 1065篇 |
2007年 | 1134篇 |
2006年 | 1050篇 |
2005年 | 1009篇 |
2004年 | 907篇 |
2003年 | 783篇 |
2002年 | 831篇 |
2001年 | 144篇 |
2000年 | 92篇 |
1999年 | 120篇 |
1998年 | 147篇 |
1997年 | 149篇 |
1996年 | 134篇 |
1995年 | 104篇 |
1994年 | 108篇 |
1993年 | 108篇 |
1992年 | 91篇 |
1991年 | 78篇 |
1990年 | 83篇 |
1989年 | 66篇 |
1988年 | 57篇 |
1987年 | 56篇 |
1986年 | 73篇 |
1985年 | 72篇 |
1984年 | 61篇 |
1983年 | 72篇 |
1982年 | 70篇 |
1981年 | 74篇 |
1980年 | 69篇 |
1979年 | 39篇 |
1978年 | 45篇 |
1977年 | 52篇 |
1976年 | 37篇 |
1974年 | 46篇 |
1973年 | 34篇 |
A large body of evidence points to an inflammatory process in the cavernous sinus and tributary veins as being primarily responsible for cluster headaches. The inflammation obliterates the venous outflow from the cavernous sinus on one side and injures the through-running sympathetic fibers to the eye, upper eye lid, forehead skin, and the intracranial internal carotid artery and its branches. The active period ends when the inflammation is suppressed and the sympathetic fibers partially or fully recover. Evidence is presented that the symptoms suggestive of an enhanced parasympathetic activity during attacks may alternatively be explained as local pain fiber activation or a stasis in the outflow from the cavernous sinus. Vasodilator agents like nitroglycerin induce an attack by enhancing the venous load on the cavernous sinus. Constriction of the proximal intracranial internal carotid artery, spontaneously induced by tressful pain activation of the perivascular sympathetic nerves, or by exogenous administration of serotonin 1 D-like receptor agonists or oxygen, terminates the venous load and thus the pain and associated symptoms. 相似文献
Methods: Six human subjects were studied while awake and during 1 MAC halothane anesthesia. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration was determined using images of the thorax obtained by three-dimensional fast computed tomography. Tidal changes in gas volume were measured by integrating respiratory gas flow, and the functional residual capacity was measured by a nitrogen dilution technique.
Results: While awake, ribcage expansion was responsible for 25 plus/minus 4% (mean plus/minus SE) of the total change in thoracic volume (Delta Vth) during inspiration. Phasic inspiratory activity was regularly present in the diaphragm and parasternal intercostal muscles. Halothane anesthesia (1 MAC) abolished activity in the parasternal intercostal muscles and increased phasic expiratory activity in the abdominal muscles and lateral ribcage muscles. However, halothane did not significantly change the ribcage contribution to Delta Vth (18 plus/minus 4%). Intrathoracic blood volume, measured by comparing changes in total thoracic volume and gas volume, increased significantly during inspiration both while awake and while anesthetized (by approximately 20% of Delta Vth, P < 0.05). Halothane anesthesia significantly reduced the functional residual capacity (by 258 plus/minus 78 ml), primarily via an inward motion of the end-expiratory position of the ribcage. Although the diaphragm consistently changed shape, with a cephalad displacement of posterior regions and a caudad displacement of anterior regions, the diaphragm did not consistently contribute to the reduction in the functional residual capacity. Halothane anesthesia consistently increased the curvature of the thoracic spine measured in the sagittal plane. 相似文献