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   47584篇
  免费   3829篇
  国内免费   1438篇
耳鼻咽喉   187篇
儿科学   885篇
妇产科学   991篇
基础医学   4599篇
口腔科学   897篇
临床医学   5563篇
内科学   10291篇
皮肤病学   309篇
神经病学   781篇
特种医学   602篇
外国民族医学   11篇
外科学   1953篇
综合类   7228篇
现状与发展   9篇
预防医学   6231篇
眼科学   170篇
药学   6240篇
  13篇
中国医学   1569篇
肿瘤学   4322篇
  2024年   240篇
  2023年   687篇
  2022年   1709篇
  2021年   2111篇
  2020年   1637篇
  2019年   1557篇
  2018年   1580篇
  2017年   1512篇
  2016年   1840篇
  2015年   2042篇
  2014年   3187篇
  2013年   3852篇
  2012年   3364篇
  2011年   3533篇
  2010年   2713篇
  2009年   2486篇
  2008年   2628篇
  2007年   2564篇
  2006年   2192篇
  2005年   1884篇
  2004年   1568篇
  2003年   1193篇
  2002年   958篇
  2001年   866篇
  2000年   684篇
  1999年   589篇
  1998年   477篇
  1997年   451篇
  1996年   378篇
  1995年   301篇
  1994年   288篇
  1993年   219篇
  1992年   213篇
  1991年   179篇
  1990年   129篇
  1989年   127篇
  1988年   88篇
  1987年   104篇
  1986年   65篇
  1985年   114篇
  1984年   75篇
  1983年   45篇
  1982年   73篇
  1981年   57篇
  1980年   52篇
  1979年   40篇
  1978年   27篇
  1977年   37篇
  1976年   36篇
  1975年   26篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Measurements of respiratory mechanics are frequently made in ventilated infants and children. Esophageal pressure measurements (Pes using a balloon on a catheter have been used to partition the respiratory mechanics into lung and chest wall components. Appropriate positioning of this balloon is crucial to obtain accurate estimates of pleural pressure. Traditionally, in spontaneously breathing subjects the balloon position is assessed with an occlusion test. In ventilated subjects, it is not always possible to perform an occlusion test prior to paralysis, and even if such a test is performed it may not be relevant under conditions of positive pressure ventilation. We have assessed a positive pressure occlusion test that is suitable for paralyzed subjects. By occluding the airway opening and applying gentle pressure to the abdomen or rib cage, positive swings in pressure can be measured by both Pes and airway opening pressure (Pao). We compared traditional occlusion tests measured in 16 spontaneously breathing puppies to the positive pressure occlusion test performed after paralysis. In 2 pups we were unable to obtain a reasonable traditional occlusion test (>15% difference between Pes and Pao) but we obtained 10 traditional occlusion tests in each of the remaining 14 pups (2.1–14 kg). In 11 of these animals Ape, was within 10% of Pao. This compared well to positive pressure occlusion test using abdominal pressure performed after paralysis, where Apes was within 10% of ΔPao in 10 animals. In 9 of these pups occlusion tests were also performed by applying pressure on the rib cage, where ΔPes was within 10% of ΔPao in 6 animals. These results suggest that it is possible to perform accurate occlusion tests in paralyzed subjects by abdominal or rib cage compression with the airway occluded. Pediatr Pulmonol. 1994; 17:56–62. © 1994 Wiley-Liss, Inc.  相似文献   
12.
The effect of acute and sequential volaemic changes on the gastroduodenal flow of saline was assessed in 23 anaesthetized dogs following two different experimental protocols. Hypervolaemia, by i. v. infusion of saline, induced a gradual decrease on gastroduodenal flow which amounted to 76% below control values (P < 0.001) when volaemic expansion attained 5% of body weight. This effect was volume dependent (17% increase on gastroduodenal flow per volume of infused saline equivalent to 0.5% of body weight, P < 0.001), lasted for at least 90 minutes after infusion was completed and was also obtained by expanding previously bled animals. Hypovolaemia due to bleeding was followed by an increase on gastroduodenal flow of about 88% above control values (P < 0.05) when haemorrhage was equal to 3% of body weight. This effect was also volume dependent (23 % increase on gastroduodenal flow per volume of blood shed equivalent to a 0.5% of body weight, P < 0.01) and was reversed after blood volume was restored. These modifications in the resistance of the gastroduodenal segment to the flow of liquid due to acute volaemic changes suggest that the extracellular fluid volume modulates the contractile activity of the gastroduodenal portion of the gut possibly to set a gastroduodenal handling of liquid adequate to cope with volaemic imbalances.  相似文献   
13.
AIMS: Metabolic responses to manipulation of the plasma free fatty acid (FFA) concentration were assessed in six healthy men via cross-over design to determine whether FFAs independently influence insulin sensitivity. METHODS: Intramyocellular lipid (IMCL) was measured by proton magnetic resonance spectroscopy and insulin sensitivity via frequently sampled intravenous glucose tolerance test (IVGTT) after 67 h of two identical low carbohydrate/high fat (LC) diets which were used to elevate IMCL and plasma FFAs. To uncouple the influence of FFAs and IMCL on insulin sensitivity, FFAs were suppressed 30 min prior to and during IVGTT in one treatment [LC + nicotinic acid (NA)] by NA ingestion. RESULTS: Vastus lateralis IMCL was significantly elevated in LC (13.3 +/- 1.1 x 10(-3)) and LC + NA (13.5 +/- 1.1 x 10(-3)) (P < 0.01 for both), but was not different between conditions (P > 0.05). Plasma FFAs were raised in LC (0.79 +/- 0.08 mmol/l) and LC + NA (0.80 +/- 0.11 mmol/l) (P < 0.01 for both) and were significantly reduced by NA ingestion prior to (0.36 +/- 0.05 mmol/l, P < 0.01) and during IVGTT (P < 0.05) in LC + NA. Despite marked differences in plasma FFA availability, insulin sensitivity and glucose tolerance were not different between LC and LC + NA (P > 0.05 for both). CONCLUSIONS: Plasma FFAs appear to exert no immediate effect on insulin sensitivity/glucose tolerance independent of their action on intracellular lipid moieties. Further research is required to elucidate the duration of FFA suppression required to restore insulin sensitivity following lipid-induced insulin resistance.  相似文献   
14.
15.
Wilke , W. Lee & Person , A. E. G. 1992. Captopril and time dependent changes in post- to pre-glomerular resistance ratios in remnant kidneys of pre-hypertensive rats. Acta Physiol Scand 144 , 253–261. Received 26 June 1991, accepted 8 October 1991. ISSN 0001–6772. Department of Physiology, Colorado State University, Fort Collins, Colorado, USA and Department of Physiology and Biophysics, University of Lund, Sweden. Micropuncture experiments were performed on intact and remnant kidneys of male Sprague-Dawley rats before and after angiotensin converting enzyme inhibition with captopril (0.5 mg kg-1 iv). Partially nephrectomized rats were studied at 2 and 8 weeks post-surgery before the development of systemic hypertension. At 2 weeks, nephrectomized rats had a numerically higher tubular stop-flow pressure than controls (43 ± 2 mmHg vs. 38 ± 2 mmHg; P = 0.08) and a higher post- to pre-glomerular resistance ratio (Re/Ra) (0.40 ± 0.03 vs. 0.31± 0.03; P = 0.08). At 8 weeks, stop-flow pressure and post- to pre-glomerular resistance ratios were similar in remnant and intact kidneys. Captopril had no effect on stop-flow pressure in 2 week post-surgery nephrectomized rats or either control group, but it increased stop-flow pressure in 8 week post-surgery nephrectomized rats (40 ± 2 to 44 ± 2 mmHg, P= 0.04). This increase in stop-flow pressure was associated with an increase in the post- to pre-glomerular resistance ratio (0.33 ± 0.02–0.42 ±0.02, P = 0.009). Stop-flow pressure was positively correlated with the post- to pre-glomerular resistance ratio in 2-week post-surgery nephrectomized rats and their respective controls when combined (r = 0.89, P= 0.0001) and 8-week post-surgery nephrectomized rats and their respective controls combined (r= 0.78, P = 0.0001). Stop-flow pressure was not significantly correlated with mean arterial pressures or welling-point pressures in these groups. We conclude that stop-flow pressure in remnant kidneys of pre-hypertensive rats is primarily determined by the post- to pre-glomerular resistance ratio, and increases in stop-flow pressure and post- to pre-glomerular resistance ratios in remnant kidneys are transient in the absence of systemic hypertension. The role of the renin-angiotensin system in determining the ratio and stop-flow pressure is dependent on time post-nephrectomy. Captopril-induced increases in stop-flow pressure and post- to pre-glomerular resistance ratio at 8 weeks, suggests that its primary effect at that time is not a preferential post-gIomerular vasodilation subsequent to reductions in intrarenal angiotensin II.  相似文献   
16.
谢福权  崔德威 《医学综述》2008,14(9):1326-1328
穹窿体是真核细胞中的核糖核蛋白颗粒,由肺耐药蛋白、穹窿体多聚腺苷二磷酸聚合酶、端粒酶相关蛋白和穹窿体RNA构成,其主要成分为肺耐药蛋白。肺耐药蛋白是介导肿瘤多药耐药的蛋白之一,可能与肿瘤的治疗效果和临床预后相关。穹窿体可能通过介导药物转运或者信号转导引起肿瘤的多药耐药。文章介绍了穹窿体的结构、成分及其介导多药耐药机制研究的新进展。  相似文献   
17.
Introduction Obese individuals may have normal insulin–glucose homeostasis, insulin resistance, or diabetes mellitus. Whereas gastric bypass cures insulin resistance and diabetes mellitus, its effects on normal physiology have not been described. We studied insulin resistance and β-cell function for patients undergoing gastric bypass. Methods One hundred thirty-eight patients undergoing gastric bypass had fasting insulin and glucose levels drawn on days 0, 12, 40, 180, and 365. Thirty-one (22%) patients with diabetes mellitus were excluded from this analysis. Homeostatic model of assessment was used to estimate insulin resistance, insulin sensitivity, and β-cell function. Based on this model, patients were categorized as high insulin resistance if their insulin resistance was >2.3. Results Body mass index did not correlate with insulin resistance. Forty-seven (34%) patients were categorized as high insulin resistance. Correction of insulin resistance for this group occurred by 12 days postoperatively. Sixty (43%) patients were categorized as low insulin resistance. They demonstrated an increase of β-cell function by 12 days postoperatively, which returned to baseline by 6 months. At 1 year postoperatively, the low insulin resistance group had significantly higher β-cell function per degree of insulin sensitivity. Conclusions Adipose mass alone cannot explain insulin resistance. Severely obese individuals can be categorized by degree of insulin resistance, and the effect of gastric bypass depends upon this preoperative physiology.  相似文献   
18.
19.
20.
The purposes of the present study were to compare the cardiovascular response patterns evoked by three versions of the cold pressor test (either forehead stimulation or hand or foot immersion) and to determine the reproducibility of the responses over a 2-week interval. Blood pressure, heart rate, stroke volume, cardiac output, total peripheral resistance, and systolic time intervals were obtained during rest and during the cold pressor test in 42 young men. Across conditions, the pressor response was supported by peripheral resistance increases with concomitant stroke volume decreases. Although the response panerns were generally similar across sites, exceptions were apparent for heart rate. Forehead stimulation was characterized by no significant change in heart rate, whereas limb (hand or foot) immersion was associated with significant heart rate acceleration. The responses elicited by the three cold pressor test conditions were reliable and showed little evidence of attenuation over the test-retest interval.  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