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   26844篇
  免费   1840篇
  国内免费   116篇
耳鼻咽喉   333篇
儿科学   560篇
妇产科学   501篇
基础医学   3920篇
口腔科学   396篇
临床医学   2496篇
内科学   6229篇
皮肤病学   471篇
神经病学   2937篇
特种医学   999篇
外国民族医学   4篇
外科学   4471篇
综合类   147篇
一般理论   6篇
预防医学   1394篇
眼科学   422篇
药学   1952篇
中国医学   95篇
肿瘤学   1467篇
  2023年   90篇
  2022年   188篇
  2021年   428篇
  2020年   260篇
  2019年   480篇
  2018年   564篇
  2017年   435篇
  2016年   486篇
  2015年   626篇
  2014年   810篇
  2013年   1098篇
  2012年   1672篇
  2011年   1768篇
  2010年   1123篇
  2009年   983篇
  2008年   1655篇
  2007年   1745篇
  2006年   1634篇
  2005年   1720篇
  2004年   1634篇
  2003年   1633篇
  2002年   1560篇
  2001年   454篇
  2000年   380篇
  1999年   435篇
  1998年   402篇
  1997年   345篇
  1996年   281篇
  1995年   296篇
  1994年   237篇
  1993年   242篇
  1992年   277篇
  1991年   243篇
  1990年   202篇
  1989年   220篇
  1988年   181篇
  1987年   193篇
  1986年   195篇
  1985年   148篇
  1984年   150篇
  1983年   146篇
  1982年   131篇
  1981年   105篇
  1980年   104篇
  1979年   105篇
  1978年   63篇
  1977年   81篇
  1975年   65篇
  1974年   52篇
  1973年   74篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
A case of HIV-associated cardiac non-Hodgkin's lymphoma (NHL) is described, and the epidemiologic and clinicopathologic features of 21 cases previously reported in the literature are analyzed. All patients were homosexual males, and the cardiac NHL was the first acquired immune deficiency syndrome-defining condition in the majority. Patients were referred with nonspecific clinical findings including dyspnea and tachycardia, but rapid progression of cardiac dysfunction was frequent after symptoms appeared. Echocardiography constitutes the most useful noninvasive procedure in the diagnosis of cardiac NHL. Most of the patients had disseminated disease at initial presentation; pathologically, the lymphomas were of B lymphocyte origin and of high-grade subtypes. Prognosis of HIV-associated cardiac NHL is generally poor, although clinical remission has been observed with combination chemotherapy. Cardiac lymphomas in HIV-associated patients are typically high-grade and often disseminate early. Although the prognosis is poor, patients in whom dissemination has not occurred could have longer survival under systemic chemotherapy.  相似文献   
942.
INTRODUCTION: The European Lacidipine Study on Atherosclerosis (ELSA) has been planned to investigate the effect of reduction in office and ambulatory blood pressure by lacidipine versus atenolol on carotid artery wall thickness in mild to moderate essential hypertensive patients with no metabolic abnormalities. One prespecified sub-study of ELSA focused on measurements of arterial distensibility in the carotid as well as in the radial artery to determine the relationship of functional arterial properties with office versus ambulatory blood pressure (BP) values as well as the correspondence between functional and structural arterial alterations. METHODS: The sub-study was conducted on 124 patients recruited in four centres (Monza-Milan, Paris, Grenoble and Glasgow). BP was measured both by a mercury sphygmomanometer and by 24-h ambulatory monitoring. Common carotid artery wall thickness was measured by certified sonographers as described in the main study. Common carotid and radial artery distensibility were obtained by echotracking techniques, which allowed to relate changes in arterial diameter with systo-diastolic BP changes. RESULTS: Carotid artery wall distensibility showed (1) a negative correlation with office and more so 24-h average systolic BP (r = -0.45 and -0.58, P < 0.008 and 0.001) but not with office or 24-h diastolic BP) and (2) a negative correlation with the corresponding wall thickness (r = -0.47, P < 0.005). In contrast, at the radial artery level distensibility and thickness showed no correlation with each other and with BP. Carotid (but not radial) artery distensibility also correlated with ambulatory systolic BP variability but the correlation was lost after adjustment for age and mean BP values. CONCLUSION: These data suggest that stiffening of large elastic artery is reflected more by ambulatory than office BP elevations, systolic BP being much more important than diastolic. Alterations of large elastic arteries function is related to structural wall changes. Functional and structural properties of middle-size muscle arteries are independent of BP.  相似文献   
943.
AIMS: Familial dilated cardiomyopathy (FDCM) is associated with mutations in more than 10 genes, but genes mutation frequencies and associated clinical features remain largely unknown. Here, we performed a mutation analysis of four genes involved in FDCM in a population of idiopathic DCM. METHODS AND RESULTS: A SSCP and sequencing mutation screening of all the exons coding for beta myosin heavy chain (MYH7 gene), cardiac T troponin (TNNT2 gene), phospholamban (PLN gene), and the cardio-specific exon of metavinculin (VCL gene) were performed in 96 independent patients (54 familial and 42 sporadic). It led to the identification of eight heterozygous mutations, seven new ones in MYH7, and the already described R141W mutation in TNNT2. MYH7 mutations (in five familial and two sporadic cases) substitute residues located either in the head (I201T, T412N, A550V) or tail domains (T1019N, R1193S, E1426K, R1634S) of the protein. DCM was not associated with skeletal myopathy or conduction defects in any patients. Contrasting clinical features were observed between MYH7 and TNNT2 mutations carriers. In MYH7 vs. TNNT2, mean age at diagnosis was late (P<0.03), penetrance was incomplete in adults (56 vs. 100%), and mean age at major cardiac event was higher (P<0.04). CONCLUSION: We have identified seven mutations in MYH7, one in TNNT2, and none in PLN or in the VCL cardio-specific exon. MYH7 appears as the most frequently mutated gene in our FDCM population (approximately 10%), and mutation carriers present with delayed onset, in contrast to TNNT2.  相似文献   
944.
Measurements of plasma neurohormones in patients with left ventricular dysfunction are generally performed for research purpose rather than for diagnostic purpose or to guide therapy. These studies have shown that in patients with left ventricular dysfunction, several neurohormonal systems were activated, even in the absence of symptoms of congestive heart failure. This suggested that the cardiovascular system was not in a steady state and pointed out potential culprits for the progression of the disease. It has also been shown that the levels of several of these markers, particularly plasma norepinephrine, had an important prognostic value. Another value of neurohormonal studies obviously is the design of new therapeutic approaches aimed at improving symptoms and prognosis. In this respect, important therapeutic successes have been obtained with agents that interfere with the actions of some of these neurohormonal systems, such as with the use of the angiotensin-converting enzyme (ACE) inhibitors, particularly captopril and enalapril, and to a lesser extent, with beta-blockers. It can therefore be expected that, in the future, most patients with severe ischemic dysfunction will be treated with an ACE inhibitor. Nonetheless, neurohormonal control is not complete with these drugs; powerful vasoconstrictor forces, such as endothelin-1, remain activated, and an escape of angiotensin II from the control of ACE inhibition may exist. Thus, morbidity (e.g., progression towards congestive heart failure and angina pectoris) and mortality remain high despite treatment with ACE inhibitors. In the search for further improvements, the new generation of long-acting dihydropyridines is worth considering. Their afterload reducing action, coupled with powerful coronary vasodilation, might hypothetically delay the progression of ischemic LV dysfunction. In addition, the improved pharmacokinetic profile of these drugs avoiding wide peak and trough variations in plasma levels may avoid triggering some neurohormonal reflexes.  相似文献   
945.
The initial experimental and clinical experience with the cardiovascular self-expandable Nitinol stent (vascular and coronary versions) is described. The stent is designed as a helical coil with two terminal balls that are used for restraining it on the delivery catheter. Upon release, the stent self-expands immediately. A temporary stent version continues with a long wire that can be removed by pulling it as a straight wire through a small profile catheter. The stent uncoils in its own groove upon removal, a relatively atraumatic procedure. The stents have been studied in dogs and in peripheral arteries in patients. The results show a transient nonocclusive proliferative response to the stent that is maximal at 3–6 mo. The removability of the permanent stent has been proven in dogs. The preliminary results in patients are encouraging and demonstrate its feasibility for permanent and potentially temporary arterial support. © 1994 Wiley-Liss,Inc..  相似文献   
946.
947.
Parallel investigations of ploidy by flow cytometry and cytogenetics were performed in 20 colorectal tumors. Flow cytometry detected an aneuploidy in 13 tumors with DNA indices ranging from 1.13 to 2.21. The other samples exhibited an apparent diploid DNA content. Cytogenetic analyses revealed an abnormal chromosome count in 14 cases and a frequent implication of numerical or structural changes in chromosomes 1, 7, 12, 17, 18, and 20. DNA content evaluated by both techniques was generally concordant with minor discrepancies not exceeding 10%. In six cases, cytogenetics failed to find the cell populations detected by flow cytometry. These results indicate that flow cytometry and cytogenetics are reliable and complementary techniques, particularly in near-diploid tumors, where flow cytometry has some difficulties in detecting variations from diploidy below to 8%.  相似文献   
948.
Coronary arteriography was performed 16 ± 3 days (range 7 to 21 days) in 106 patients with acute transmural myocardial infarction (61 posterior infarct, 45 anterior infarct). Coronary arteriography was performed without serious complications. Only 44 per cent of patients with anterior infarct had total occlusion of the left anterior descending artery while a significant stenosis of the vessel was observed in the others ?27 per cent had a single vessel disease, 49 per cent had two lesions and 22 per cent had three lesions; one patient had angiographically normal coronary arteries. Among the patients with posterior infarction, 21 per cent had one vessel disease and double or triple lesions accounted for 39 per cent of each.Sixty per cent of patients with anterior infarction and 45 per cent with posterior infarction had no collateral vessels. In the others patients collateral circulation had a protective effect only in anterior infarction. Age has no effect on the distribution and number of lesions nor on the development of a collateral circulation. The location and severity of the lesions were not different in patients who presented with arrythmias and those who did not.  相似文献   
949.
AIMS: Fluoroscopy is not available in every endoscopic unit. This situation leads to delays in treatment or to transfer of patients to other centres for stent insertion. We assessed safety and effectiveness of expandable esophageal metal stent placement under endoscopic control without fluoroscopy using a thin gastroscope. PATIENTS AND METHODS: From October 2002 to June 2004, thirty-three consecutive patients have been included for esophageal stent placement under endoscopic control alone with a nasogastroscope (5.9 mm). A proximal release covered stent (Ultraflex; Boston Scientific Microvasive) was used. Indications were malignant esophageal stricture (N = 26), malignant extrinsic compression (N = 2 ) and esophago-respiratory neoplastic fistulae (N = 5). RESULTS: Stent placement using endoscopic control alone was successful in 30/33 (90%) patients. Complications occurred in 11 patients. Early complications (<7 days) included one death from pulmonary embolism, severe retrosternal pain needing transient morphinic treatment (N = 2) and GERD despite antisecretory therapy (N = 1). Late complications included: food impaction (N = 1), tumour overgrowth-related obstruction of the stent (N = 5) and one late esophago-respiratory fistula at 4 months at the proximal end of the stent. Relief of dysphagia was obtained for all patients at 48 hours and dysphagia score decreased from 3.1 before stent to 1.2 at 1 month (P < 0.05). CONCLUSION: Expandable esophageal stents can be accurately and safely placed using endoscopy with a thin gastrosocope. This method obviates the requirement of fluoroscopic access, lacking in many centres, and avoids exposure to X-ray.  相似文献   
950.
OBJECTIVES : We have previously reported that 5-lipoxygenase-derived products, and particularly the cysteinyl leukotrienes (CysLTs), were involved in angiotensin II (Ang II)-induced contractions in isolated aortas from spontaneously hypertensive rats. DESIGN : The aim of this study was to assess the role of CysLTs in the vascular response to Ang II in an Ang II-dependent model of hypertension, the (mRen-2)27 transgenic rats (TGs). METHODS : Intact aortic rings from TG and normotensive Sprague-Dawley rats (SDs) were suspended in organ chambers for isometric tension development in response to Ang II. In addition, the release of CysLTs in response to Ang II (0.3 micromol/l) was measured by enzyme immunoassay. RESULTS : In isolated aortas from TG rats, pretreatment with the 5-lipoxygenase inhibitor (AA861, 10 micromol/l) or the CysLT1 receptor antagonist (MK571, 1 micromol/l) significantly (P < 0.05) reduced Ang II-induced contractions by 52 and 42%, respectively. In addition, Ang II induced a 2.6-fold increase in CysLT release (pg/mg dry weight tissue: 58.3 +/- 17.9 (Ang II, n = 7) versus 22.5 +/- 5.9 (basal, n = 7) P < 0.05), which was inhibited by the AT1 receptor antagonist losartan (1 micromol/l). In contrast, in aortas from SD rats, pretreatment with AA861 or MK571 did not alter Ang II-induced contraction and CysLT production remained unchanged after exposure to Ang II. CONCLUSION : These data suggest that CysLTs are involved in the contractile responses to Ang II in isolated aortas from TG but not from SD rats.  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