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   71792篇
  免费   4681篇
  国内免费   242篇
耳鼻咽喉   872篇
儿科学   1849篇
妇产科学   1398篇
基础医学   9002篇
口腔科学   1368篇
临床医学   7048篇
内科学   14317篇
皮肤病学   832篇
神经病学   6681篇
特种医学   2392篇
外国民族医学   5篇
外科学   11927篇
综合类   1134篇
现状与发展   1篇
一般理论   87篇
预防医学   6541篇
眼科学   1522篇
药学   4463篇
  8篇
中国医学   76篇
肿瘤学   5192篇
  2022年   523篇
  2021年   1196篇
  2020年   716篇
  2019年   1200篇
  2018年   1411篇
  2017年   1002篇
  2016年   1088篇
  2015年   1227篇
  2014年   1928篇
  2013年   2886篇
  2012年   4164篇
  2011年   4486篇
  2010年   2579篇
  2009年   2365篇
  2008年   4085篇
  2007年   4272篇
  2006年   4195篇
  2005年   4313篇
  2004年   4268篇
  2003年   3950篇
  2002年   3822篇
  2001年   856篇
  2000年   751篇
  1999年   918篇
  1998年   903篇
  1997年   797篇
  1996年   687篇
  1995年   655篇
  1994年   579篇
  1993年   557篇
  1992年   605篇
  1991年   611篇
  1990年   558篇
  1989年   534篇
  1988年   498篇
  1987年   445篇
  1986年   485篇
  1985年   489篇
  1984年   627篇
  1983年   559篇
  1982年   640篇
  1981年   617篇
  1980年   626篇
  1979年   414篇
  1978年   432篇
  1977年   420篇
  1976年   331篇
  1975年   353篇
  1974年   379篇
  1973年   321篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
BACKGROUND: Interleukin-15 (IL-15) and interleukin-18 (IL-18) are potential regulators of body composition in humans. The authors previously reported that megestrol acetate ingestion causes a large accumulation of adipose tissue and reduces muscle mass. Therefore, the purpose of this investigation was to evaluate the effects of megestrol acetate ingestion on circulating IL-15 and IL-18 concentrations in healthy elderly men. METHODS: All participants received 800 mg of megestrol acetate per day during this 12-week study. Megestrol acetate was combined with testosterone injections (100 mg/week), placebo injections, resistance training, or resistance training and testosterone. Resting IL-15 and IL-18 concentrations were measured by enzyme-linked immunosorbent assay at week 0 (pre), week 6 (mid), and week 12 (post). RESULTS: The time effect for IL-15 was significant (p = .0008), with the mid and post values being significantly greater than the pre value. The change in IL-15 concentration was not significantly related to the change in muscle mass (r = -.31; p > .05), nor was it related to the change in fat mass (r =.17; p > .05). Differences among groups or over time were not significant for IL-18, nor were correlations between pre body weight and pre IL-18 (r = -.03), pre fat mass and pre IL-18 (r = .14), or the change in fat mass and the change in IL-18 (r = -.07). CONCLUSIONS: IL-15 was increased as a result of megestrol acetate ingestion; however, megestrol acetate did not affect circulating IL-18 concentrations, and the change in IL-18 did not correlate with any body composition variables.  相似文献   
992.
CHO-K1, COS-7, and Rat2 fibroblast cell lines are generally believed to be devoid of estrogen receptors (ERs) and have been widely used to study the functions of ER-alpha and ER-beta after transfection of their cDNAs. Numerous studies have demonstrated that transfected ER-alpha or ER-beta mediates estradiol-induced activation of multiple signaling pathways, including the MAPK/ERK pathways. We report here for the first time that both 17alpha-estradiol and 17beta-estradiol elicit activation of MAPK/ERK in native, nontransfected CHO-K1, COS-7, and Rat2 fibroblast cell lines. We further report that, contrary to the generally held belief, these cell lines are not unresponsive to estradiol in their native, nontransfected state, and that this estrogen responsiveness is associated with estrogen binding. Using multiple ER antibodies, we failed to find ER-alpha or ER-beta isoforms or even ER-X. In view of these findings, researchers, using such cells as models to investigate mechanisms of estrogen action, must always take into account the existence of endogenous estrogen binding proteins other than ER-alpha, ER-beta, or ER-X.  相似文献   
993.
Although recurring nephrolithiasis may not be as common as single-episode disease, it poses greater problems to the patient's daily lifestyle and general future health status. The general need for an adequate history, examination, and radiological assessment is acknowledged, but a more intensive investigative and management approach is required. Investigations for secondary causes are paramount and may lead to identification of unusual metabolic abnormalities and specific therapies. Such medical approaches entail consideration of dietary adjustments to lower the urinary excretion of components of the renal stones, pharmacological therapies to modulate urinary constituents and limit renal stone risk, and monitoring efficacy of the therapy over time. This approach will prevent significant deterioration of renal function and other serious metabolic consequences.  相似文献   
994.
Gastric lesions secondary to long-distance running   总被引:3,自引:0,他引:3  
Gastrointestinal disorders have been reported during long- distance running. The purpose of this study was to evaluate the effects of prolonged exercise on the upper digestive tract. Seven subjects were submitted to a standard endoscopic examination of the upper digestive tract before and after long- distance running (range 18– 50 km). Mucosal biopsy specimens were taken during all endoscopies. After running, all runners had histologically pathological features in the stomach. Vascular lesions were present in the chorion in six subjects after running, with the intensity of the lesions ranging from congestion to hemorrhage. Postexercise histological examination also showed a decrease in mucosal secretion. These lesions secondary to prolonged exercise indicate the presence of hemodynamic perturbations in the upper digestive tract.  相似文献   
995.
OBJECTIVES: The purpose of this study was to assess the follow-up of patients with vaccinia-associated myocarditis. BACKGROUND: With the threat of biological warfare, the U.S. Department of Defense resumed a program for widespread smallpox vaccinations on December 13, 2002. One-year afterwards, there has been a significant increase in the occurrence of myocarditis and pericarditis among those vaccinated. METHODS: Cases were identified through sentinel reporting to military headquarters, systematic surveillance, and spontaneous reports. RESULTS: A total of 540,824 military personnel were vaccinated with a New York City Board of Health strain of vaccinia from December 2002 through December 2003. Of these, 67 developed myopericarditis at 10.4 +/- 3.6 days after vaccination. The ST-segment elevation was noted in 57%, mean troponin on admission was 11.3+/- 22.7 ng/dl, and peak cardiac enzymes were noted within 8 h of presentation. On follow-up of 64 patients (96%) at a mean of 32 +/- 16 weeks, all patients had objective normalization of echocardiography, electrocardiography, laboratory testing, graded exercise testing, and functional status; 8 (13%) reported atypical, non-limiting persistent chest discomfort. CONCLUSIONS: Post-vaccinial myopericarditis should be considered in patients with chest pain within 30 days after smallpox vaccination. Normalization of echocardiography, electrocardiography, and treadmill testing is expected, and nearly all patients have resolution of chest pain on follow-up.  相似文献   
996.
997.
Traumatic cloaca     
Deep laceration of the perineum after an obstetric injury may result in a cloacal deformity of the anus and vagina, causing complete fecal incontinence. A surgical technique consisting of reconstruction of the perineal body (perineoplasty) with puborectalis interposition and overlapping external sphincteroplasty is described to correct the defect and restore continence. This procedure has been used on 43 patients in a 10-year period with excellent anatomic and physiologic results.  相似文献   
998.
Mutants with internal deletions that terminate near the operator end of the tryptophan operon of E. coli were used in studies on the nucleotide sequence at the 5' end of the messenger RNA transcribed on this operon. The findings obtained permitted identification of a sequence of 43 nucleotides corresponding to the aminoterminal 11 amino acids of anthranilate synthetase component I, the polypeptide specified by the operator-proximal structural gene of the operon. It was also shown that the translation initiation codon for this polypeptide is preceded on the messenger by a "leader" sequence of unknown function, at least 150 nucleotides in length.  相似文献   
999.
The clinical course and coronary arteriographic findings in eight patients with Prinzmetal's variant angina pectoris are reviewed and contrasted to previously reported cases. In six patients with S-T-elevation inferiorly, three had normal coronary arteriograms, one had complete right coronary artery occlusion, one had diffuse triple-vessel disease, and one did not undergo coronary arteriography. In two patients with S-T-elevation anteriorly, severe stenosis of the anterior descending coronary artery was present. Medical treatment in four patients and surgical revascularization of the anterior descending coronary artery in two patients were both accompanied by marked symptomatic improvement. Spontaneous loss of angina occurred in two patients. During 17 months' mean follow-up, seven patients have remained free of angina and one died suddenly. Variant angina pectoris may be accompanied by a variety of coronary arteriographic findings and the prognosis appears more favorable than previously reported.  相似文献   
1000.
Five patients with critical aortic stenosis (aortic valve area 0.6 cm2 or less) died 2 days to 21 days following cardiac catheterization performed in anticipation of cardiac surgery. A sixth patient was successfully resuscitated for spontaneous ventricular fibrillation, and successful aortic valve replacement was accomplished. Two patients had prior history of syncope; one patient, of ventricular tachycardia; three patients, of pulmonary edema; and three patients, of crescendo angina. One patient had severe hypotension during maintenance hemodialysis for chronic renal failure. The mode of death was sudden but not witnessed in two patients. The terminal cardiac rhythms were slow junctional in one patient, idioventricular in one, ventricular tachycardia in one, and ventricular fibrillation in the fourth patient. We conclude that symptomatic patients with critical aortic stenosis should be monitored after cardiac catheterization, and surgery should be performed as soon as possible since sudden death is not unusual.  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