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   2591篇
  免费   170篇
  国内免费   11篇
耳鼻咽喉   18篇
儿科学   143篇
妇产科学   33篇
基础医学   272篇
口腔科学   239篇
临床医学   312篇
内科学   575篇
皮肤病学   40篇
神经病学   162篇
特种医学   263篇
外科学   221篇
综合类   42篇
预防医学   215篇
眼科学   37篇
药学   150篇
  1篇
中国医学   4篇
肿瘤学   45篇
  2022年   11篇
  2021年   34篇
  2020年   31篇
  2019年   35篇
  2018年   55篇
  2017年   57篇
  2016年   60篇
  2015年   73篇
  2014年   70篇
  2013年   95篇
  2012年   137篇
  2011年   152篇
  2010年   88篇
  2009年   88篇
  2008年   116篇
  2007年   103篇
  2006年   118篇
  2005年   107篇
  2004年   83篇
  2003年   72篇
  2002年   81篇
  2001年   49篇
  2000年   50篇
  1999年   42篇
  1998年   94篇
  1997年   92篇
  1996年   95篇
  1995年   63篇
  1994年   55篇
  1993年   45篇
  1992年   34篇
  1991年   44篇
  1990年   21篇
  1989年   41篇
  1988年   38篇
  1987年   44篇
  1986年   26篇
  1985年   40篇
  1984年   28篇
  1983年   22篇
  1982年   19篇
  1981年   19篇
  1980年   13篇
  1979年   15篇
  1978年   15篇
  1977年   11篇
  1976年   13篇
  1975年   12篇
  1970年   12篇
  1967年   7篇
排序方式: 共有2772条查询结果,搜索用时 31 毫秒
71.
OBJECTIVE: To examine whether promoter polymorphisms associated with variation in interleukin-10 (IL-10) production are relevant to the development of rheumatoid arthritis (RA) or Felty's syndrome (FS). METHODS: DNA was obtained from 44 FS patients, 117 RA patients and 295 controls. The promoter region between -533 and - 1120 was amplified by polymerase chain reaction, and polymorphisms detected by restriction enzyme digest or sequence-specific oligonucleotide probing. RESULTS: We found no significant difference in allele or haplotype frequencies between the groups. CONCLUSION: There is no association between FS or RA and these recently identified IL-10 promoter polymorphisms. Other genetic or environmental factors could explain the alterations in IL-10 levels seen in these conditions.   相似文献   
72.
Sport Sciences for Health - To investigate the hemodynamic responses, especially HPE following different resistance exercises RE protocols in young adult subjects. Eighty-nine men...  相似文献   
73.
The genetic mechanisms that are complementary in predisposing and then establishing disease are yet to be fully elucidated. During a lifetime, the genetic composition of the host is not only hereditary but undergoes rearrangements, integrations, and more subtle single-base pair alterations. These changes can be inconsequential or lead to aberrant and deleterious pathologic changes. In a complex multifactorial disease such as RA, the relative roles of the dynamic versus germline elements of the disease have yet to be fully determined. Further studies of large populations are likely to segregate out factors affecting specific ethnic, clinical, and genetic subgroups.  相似文献   
74.
BACKGROUND: Scant data exist on factors that may identify outcome in patients with severe left ventricular (LV) dysfunction early after coronary artery bypass graft surgery (CABG). DESIGN: This study was designed to determine the prognostic value of clinical, operative, and postoperative factors in patients with LV dysfunction early after CABG. METHODS: In 333 consecutive patients with ejection fraction < or =35% on admission to residential cardiac rehabilitation after isolated CABG, potential preoperative, perioperative, and postoperative predictors of outcome, including 6-month LV remodeling, were recorded and patients followed up for a median of 3 years. The study end points were cardiovascular (CV) mortality and the combination of CV mortality and nonfatal CV events requiring hospitalization. RESULTS: The 3-year CV mortality-free survival and survival free of nonfatal CV event rates were 87 and 73%, respectively. Independent predictors of CV mortality were history of congestive heart failure [hazard ratio, HR: 2.8; 95% Confidence Interval (CI): 1.51-5.21], low ejection fraction on admission to cardiac rehabilitation (HR: 0.9; 95% CI: 0.87-0.96), and early complications after CABG (HR: 2.5; 95% CI: 1.23-5.15). When the combined end points were considered, postoperative left atrial size (HR: 1.07; 95% CI: 1.01-1.11), New York Heart Association class III or IV (HR: 1.69; 95% CI: 1.04-2.74), and 6-month remodeling (HR: 2.12; 95% CI: 1.33-3.36) were independent predictors. CONCLUSION: Simple preoperative and postoperative variables may help identify patients with LV dysfunction early after CABG who are still at risk of major CV events. In this setting, 6-month LV remodeling is a strong predictor of a poor prognosis.  相似文献   
75.
STUDY OBJECTIVE--The aim was to identify the role of the endothelium in mediating the responses to acetylcholine in the rabbit coronary artery, and to determine whether alpha or beta adrenergic stimulation may cause relaxation via endothelial receptors in the coronary arteries of this species. DESIGN--Responses to acetylcholine and adrenoceptor agonists were compared in isolated ring preparations with and without endothelium. The adrenoceptor agonists were examined in the presence of phentolamine or propranolol to block alpha and beta adrenoceptors, respectively. EXPERIMENTAL MATERIAL--30 New Zealand white rabbits (2.3-3.4 kg) were killed by an overdose of barbiturate and exsanguination, and the left epicardial coronary artery was dissected free. Ring preparations were suspended in organ baths under isometric tension and, where required, the tone of the preparations was raised by KC1. MEASUREMENTS AND MAIN RESULTS--Concentrations of acetylcholine up to 10(-6) mol.litre-1 produced dose dependent relaxation of the preparations with endothelium intact, but no relaxation in preparations denuded of endothelium. At higher concentrations, a marked vasoconstrictor response was seen in all preparations regardless of the presence of endothelium. At basal tone, acetylcholine produced vasoconstriction which reached a maximum of 1.0 (SEM 0.14)g tension in preparations with endothelium and 1.74(0.27) g tension in those without endothelium (p less than 0.05). In coronary arteries pretreated with 50 mumol.litre-1 phenoxybenzamine to block alpha adrenoceptors, noradrenaline, isoprenaline, and salbutamol produced dose dependent relaxation of the preparations; this was unaffected by the absence of endothelium. In vessels not pretreated with phenoxybenzamine, propranolol inhibited the relaxation to noradrenaline and isoprenaline but again there was no difference between vessels with and without endothelium. CONCLUSIONS--In the rabbit isolated epicardial coronary artery, acetylcholine produces an endothelium dependent relaxant response over a limited concentration range; a vasoconstrictor response via smooth muscle dominates at higher concentrations. beta Adrenoceptors mediating relaxation are present on the smooth muscle, but there was no evidence for either alpha or beta adrenoceptor mediated responses via the endothelium. Important differences with coronary arteries from other species are discussed.  相似文献   
76.
OBJECTIVE: Thyrotropin activates the cAMP pathway in thyroid cells, and stimulates cell cycle progression in cooperation with insulin or insulin-like growth factor-I. Because p38 mitogen-activated protein kinases (p38 MAPKs) were stimulated by cAMP in the FRTL-5 rat thyroid cell line, we investigated (i) the effect of the specific inhibition of p38 MAPKs on FRTL-5 cell proliferation and (ii) the mechanism of action of p38 MAPKs on cell cycle control, by studying the expression and/or the activity of several cell cycle regulatory proteins in FRTL-5 cells. METHODS: DNA synthesis was monitored by incorporation of [(3)H]thymidine into DNA and the cell cycle distribution was assessed by fluorescence-activated cell sorter analysis. Expression of cell cycle regulatory proteins was determined by Western blot analysis. Cyclin-dependent kinase 2 (Cdk2) activity associated to cyclin E was immunoprecipitated and was measured by an in vitro kinase assay. RESULTS: SB203580, an inhibitor of alpha and beta isoforms of p38 MAPKs, but not its inactive analog SB202474, inhibited DNA synthesis and the G1-S transition induced by forskolin plus insulin. SB203580 inhibited specifically p38 MAPK activity but not other kinase activities such as Akt and p70-S6 kinase. Treatment of FRTL-5 cells with SB203580 decreased total and cyclin E-associated Cdk2 kinase activity stimulated with forskolin and insulin. However, inhibition of p38 MAPKs by SB203580 was without effect on total cyclin E and Cdk2 levels. The decrease in Cdk2 kinase activity caused by SB203580 treatment was not due to an increased expression of p21(Cip1) or p27(Kip1) inhibitory proteins. In addition, SB203580 affected neither Cdc25A phosphatase expression nor Cdk2 Tyr-15 phosphorylation. Inhibition of p38 MAPKs decreased Cdk2-cyclin E activation by regulating the subcellular localization of Cdk2 and its phosphorylation on Thr-160. CONCLUSIONS: These results indicate that p38 MAPK activity is involved in the regulation of cell cycle progression in FRTL-5 thyroid cells, at least in part by increasing nuclear Cdk2 activity.  相似文献   
77.
A retrospective study of the medical records filed at the University Hospital from 1965 to 1983 and of 18456 autopsies carried out in the Department of Pathology of this Institution from 1953 to 1983, referring to patients aged less than 18 years was performed in an attempt to fully characterize chronic Chagas' heart disease in children and adolescents. Only 19 of these patients fulfilled the criteria for inclusion in the present study (12 cases with only clinical information and 7 cases with clinical and pathological information). We noted that the clinical manifestations of chronic Chagas' heart disease are congestive heart failure, thromboembolism and sudden death. Radiologic, electrocardiographic and anatomo-pathological findings demonstrated serious myocardial involvement. This set of alterations is also detected in adults with chronic Chagas' heart disease. Among adolescents, however, the disease exhibits relevant peculiarities such as rapid evolution to death within a short period of time (128 days), diagnostic difficulty related to the presence of significant mitral regurgitation (61% erroneous initial diagnosis), and low frequency of right bundle branch block (11% of cases). These findings suggest that among children and adolescents, chronic Chagas' heart disease may be of a peculiar type and therefore may be useful to clarify the pathogenetic mechanism of the disease.  相似文献   
78.
Cardiopulmonary exercise testing (CPET) provides a global assessment of the integrated response to exercise involving the pulmonary, cardiovascular, haematopoietic, neuropsychological, and skeletal muscle systems. This information cannot be obtained through investigation of the individual organ systems in isolation. The non-invasive, dynamic physiological overview permits the evaluation of both submaximal and peak exercise responses, providing the physician with relevant information for clinical decision making. The use of CPET in management of the chronic heart failure patient is increasing with the understanding that resting pulmonary and cardiac function testing cannot reliably predict exercise performance and functional capacity and that, furthermore, overall health status and prognosis are predicted better by indices of exercise tolerance than by resting measurements. Our aim is to produce a statement which provides recommendations on the interpretation and clinical application of CPET in heart failure, based on contemporary scientific knowledge and technical advances: the focus is on clinical indications, issues of standardization, and interpretative strategies for CPET.  相似文献   
79.
Limitation of exercise tolerance is a hallmark of heart failure. Anaerobic threshold is a quantitative, reproducible, nonmotivational, submaximal index of exercise tolerance. The pathophysiological significance and methods of determination of anaerobic threshold are matters of debate. The principal aspects of such problems are discussed in this paper.  相似文献   
80.
In this study, the larvicidal activity of an enriched fraction of the major lipophilic phenolic compounds from Hypericum carinatum Griseb. (Clusiaceae) was investigated against larvae of Aedes aegypti (Diptera: Culicidae), the main vector of dengue virus in Brazil. The larval mortality rate ranged 37.33 to 72.00 % at concentrations of 66–200 μg/mL. The effect demonstrated to be dose-dependent. The lethal concentration 50 % and confidence interval were 100 and 88–111 μg/mL, respectively. The results could be attributed to the presence of cariphenone A and cariphenone B in concentrations of 1.24?±?0.04 and 0.56?±?0.01 %, respectively, determined by high-performance liquid chromatography. Besides, the results reinforce the potential of genus Hypericum as source of alternative insecticides.  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