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   959篇
  免费   60篇
  国内免费   10篇
耳鼻咽喉   6篇
儿科学   40篇
妇产科学   36篇
基础医学   100篇
口腔科学   25篇
临床医学   155篇
内科学   180篇
皮肤病学   7篇
神经病学   67篇
特种医学   97篇
外科学   75篇
综合类   70篇
预防医学   30篇
眼科学   15篇
药学   76篇
中国医学   5篇
肿瘤学   45篇
  2023年   4篇
  2022年   11篇
  2021年   7篇
  2020年   9篇
  2019年   8篇
  2018年   16篇
  2017年   16篇
  2016年   15篇
  2015年   20篇
  2014年   16篇
  2013年   32篇
  2012年   59篇
  2011年   44篇
  2010年   50篇
  2009年   34篇
  2008年   46篇
  2007年   39篇
  2006年   49篇
  2005年   52篇
  2004年   37篇
  2003年   24篇
  2002年   38篇
  2001年   31篇
  2000年   27篇
  1999年   28篇
  1998年   35篇
  1997年   30篇
  1996年   22篇
  1995年   20篇
  1994年   20篇
  1993年   14篇
  1992年   16篇
  1991年   6篇
  1990年   12篇
  1989年   26篇
  1988年   19篇
  1987年   24篇
  1986年   18篇
  1985年   8篇
  1984年   6篇
  1983年   6篇
  1982年   6篇
  1981年   5篇
  1980年   5篇
  1976年   3篇
  1975年   8篇
  1973年   2篇
  1972年   2篇
  1970年   1篇
  1969年   1篇
排序方式: 共有1029条查询结果,搜索用时 0 毫秒
61.
Background Heterotaxy syndrome, including right isomerism and left isomerism, is characterized by an abnormal symmetry of the viscera and veins and is frequently associated with complex cardiac anomalies. We sought to define the feasibility of in utero diagnosis and the postnatal outcome. Methods Patients with heterotaxy syndrome were identified from 579 fetal echocardiograms performed from January 1994 to December 1998. The diagnosis was made on the basis of the fetal echocardiographic findings and was confirmed with autopsy or postnatal evaluation. Results A total of 25 fetuses with right isomerism and 4 with left isomerism constitute the study population. The pregnancies of 7 fetuses (6 right and 1 left isomerism) were terminated before the 24th gestational week and subjected to autopsy. Twelve fetuses (10 right and 2 left isomerism) were lost to follow-up. Nine with right isomerism and 1 with left isomerism were delivered and underwent palliation. Among them, 5 patients (56%) with right isomerism died and more than half of the deaths occurred during infancy. The major cardiac anomalies detected and confirmed with postnatal evaluation or autopsy in fetuses with right isomerism were total anomalous pulmonary venous connection (6/15; 40%), common atrium (15/15; 100%), complete atrioventricular canal (15/15; 100%), double outlet right ventricle (15/15; 100%), and pulmonary stenosis (11/15; 73%). The major cardiac anomalies in fetuses with left isomerism were interruption of inferior vena cava (2/2; 100%), common atrium (1/2; 50%), and complete atrioventricular canal (1/2; 50%). Undetected lesions with fetal echocardiogram were abnormal pulmonary venous return to systemic veins in 1 case (sensitivity, 83%; 5/6; and specificity, 90%; 9/10) and outflow obstruction in 1 case (sensitivity, 91%; 11/12; and specificity, 67%; 2/3). Different patterns of rhythm disturbances were identified: supraventricular tachycardia in 1 case with right isomerism and sinus bradycardia with junctional rhythm in 3 cases with left isomerism (2 of them lost to follow-up). After birth, another 2 patients with right isomerism had supraventricular tachycardia, and 1 with left isomerism had sinus bradycardia develop at age 2 years. Conclusion Heterotaxy syndrome is usually detected in fetuses with the sonographic cardiac abnormalities. Visualization of the pulmonary venous return and outflow obstruction and characterization of the rhythm disturbances are feasible. However, in spite of prenatal diagnosis, the prognosis remains poor. (Am Heart J 2002;143:1002-8.)  相似文献   
62.
OBJECTIVE: We compared patient outcomes using two protocols: one routinely and the other selectively evaluating the calves completely during sonographic assessment of the lower extremities in patients with suspected deep venous thrombosis. SUBJECTS AND METHODS: In this randomized prospective study, patients were assigned to two groups. In one group, the deep calf veins were routinely evaluated in their entirety, and in the other group the calf was not evaluated unless the patient had symptoms or physical signs in the calf, in which case only the areas of symptoms or physical signs were evaluated. Patients were followed up for 3 months by medical record review, physician surveys, and telephone calls. An adverse outcome was a propagated deep venous thrombosis into the thigh or a pulmonary embolus. Examination times were recorded when possible. RESULTS: Of the 235 patients in the group in which the deep calf veins were routinely evaluated, we saw no adverse outcomes (0.0%; 97.5% one-sided confidence interval [CI], 0.6-1.6%). Of the 261 patients in the group in which the calf was only evaluated if there were signs or symptoms, we saw two adverse outcomes (0.8%; 95% CI, 0.1-2.7%). CONCLUSION: We found no significant difference in adverse outcomes in patients undergoing a protocol in which the deep calf veins were routinely evaluated or a protocol in which the calf was evaluated only if physical signs or symptoms were present.  相似文献   
63.
64.
RARRES3 is a retinoid-inducible class II tumour-suppressor gene. This study analysed the expression of RARRES3 protein in normal, adenoma and carcinoma tissues of the colorectum and its correlation with tumour differentiation. The expression of RARRES3 protein in 151 paraffin-embedded colorectal tissues (11 distal normal mucosa, 20 adenoma and 120 colorectal adenocarcinoma) was determined by immunohistochemistry. RARRES3 protein was expressed in all 11 distal normal, 120 adjacent normal and 20 adenoma tissues. In distal normal tissues, RARRES3 protein was expressed at the highest levels in differentiated mucosal epithelial cells. Among 120 carcinoma tissues, RARRES3 protein was detected in 97.6% (40 out of 41), 79.4% (54 out of 68) and 17.3% (three out of 11) of well-, moderately and poorly differentiated tumours, respectively. The expression of RARRES3 protein was positively correlated to tumour differentiation (test for trend, P<0.0001). Also, levels of RARRES3 protein were found to be higher in the normal tissues adjacent to 14.6% (six out of 41), 51.5% (35 out of 68), and 90.1% (10 out of 11) of well-, moderately and poorly differentiated tumours, respectively. The decreases in tumour differentiation and RARRES3 expression were significantly correlated compared to the adjacent normal tissues (test for trend, P<0.0001). The prognostic implication of RARRES3 protein expression was studied in 107 tumour, and no statistical difference in survival was observed. The expression of RARRES3 protein was positively correlated to cellular differentiation of normal and adenocarcinoma tissues of the colorectum, which supports the role of RARRES3 in normal and malignant epithelial differentiation of colorectum. RARRES3 expression was decreased only in carcinoma tissue, which suggests that altered RARRES3 expression occurs late in colorectal carcinogenesis.  相似文献   
65.
In this study, the authors use in-depth interviews with inductive analysis to develop a conceptual framework for exploring social exchanges and their implicit calculations for caregivers in Taiwan. They interviewed 12 caregivers, based on theory-based sampling and maximum variation. They found some components of implicit exchanges of the caregivers, and drew a framework to describe it. At the beginning of care, motivations were mostly from obligation accompanied by reciprocity or repaying motives. In the process of caregiving, some unique, implicit cultural implicit exchanges were found, such as karma, a demonstrative behavior to investment, equitable share of responsibility, and the pressure or rewards from public opinion. These implicit exchanges might be intermediary factors in helping caregivers cope with their burden or even in influencing their continuation of care. The findings are implicated to help family caregivers continue their care and not damage their quality of care.  相似文献   
66.
Endothelial cells are essential for neovascularization. Angiopoietins and Tie receptors are required for a normal vasculature. How cyclical mechanical stretch affects the expression of components of the angiopoietin system is not known. In this study, we investigated the regulation of angiopoietins and Tie receptors by cyclical mechanical stretch in cultured human umbilical vein endothelial cells (HUVECs). HUVECs grown on a flexible membrane base were stretched by vacuum to 20% elongation, at 60 cycles/min. The levels of angiopoietin-2 protein began to increase as early as 2 h after stretch was initially applied, reached a maximum of 2.7-fold over the control value by 6 h. The Tie2 receptor protein showed the same pattern as Ang-2. These increases in angiopoietin-2 and Tie2 receptor proteins at 6 h were blocked by the addition (30 min before stretch) of the protein kinase C inhibitor G?6976 (16 nM) or the tyrosine kinase inhibitor herbimycin A (24 microM). Similar to protein expression, the levels of angiopoietin-2 and Tie2 receptor mRNAs in HUVECs increased 3.1-fold and 2.5-fold respectively after stretch for 6 h. These increases were also blocked by G?6976 or herbimycin A. Cyclical mechanical stretch increased (and G?6976 or herbimycin A abrogated these increases) the immunohistochemical labelling of angiopoietin-2 and Tie2 receptor after a 6 h stretch. The levels of angiopoietin-1 and Tie1 receptor proteins, mRNAs and immunohistochemical staining were unaffected by cyclical mechanical stretch. Thus cyclical mechanical stretch activates the expression of angiopoietin-2 and the Tie2 receptor, but not angiopoietin-1 or the Tie1 receptor, in cultured HUVECs. This mechanical effect is probably mediated by the tyrosine kinase and protein kinase C pathways.  相似文献   
67.
Genome-wide hypomethylation in hepatocellular carcinogenesis   总被引:19,自引:0,他引:19  
Lin CH  Hsieh SY  Sheen IS  Lee WC  Chen TC  Shyu WC  Liaw YF 《Cancer research》2001,61(10):4238-4243
  相似文献   
68.
The purpose of this study was to determine the physiologic relationship between the cardiac cycle and the nonpulsatile impeller centrifugal Taita No.1 left ventricular assist device (T-LVAD) in a chronic animal study. The relationship of the cardiac cycle, pump flow, aortic pressure, left ventricle pressure, and pump power were analyzed by 5 phases in 4 stages. The isovolumetric ventricular phase is from mitral valve closure (MVC) to aortic valve opening (AVO) and is called Stage 1. The ejection phase is from AVO to aortic valve closure (AVC) and is called Stage 2. The isovolumetric relaxation phase is from AVC to MVC and is called Stage 3. The passive filling and atrial contraction phase is from MVC to mitral valve opening (MVO) and called Stage 4. Based on evidence from the physiologic volume change of the left ventricle, the change of pump flow of the T-LVAD in a cardiac cycle by variable voltages of pump control was evaluated using animal models. After left posteriolateral thoracotomy via the fifth intercostal space under general anesthesia, the nonpulsatile centrifugal T-LVAD was implanted into 2 healthy calves. The inflow of the T-LVAD was inserted into the left ventricle through the mitral valve via the left atrial appendage. The arterial blood pressure waveform was measured and recorded on the outflow of the T-LVAD. The 4 phases of a cardiac cycle were defined as MVC-AVO (Stage 1), AVO-AVC (Stage 2), AVC-MVO (Stage 3) and MVC-MVO (Stage 4) according to the outflow pressure of the outflow of the T-LVAD and differential pressure between the outflow and inflow of the T-LVAD. We carried out the real-time waveform measurement for electrocardiogram, the outflow pressure, the T-LVAD flow and the speed, as well as open loop and constant voltage (V). In a cardiac cycle, the sensing current of the T-LVAD was inverse to the speed. The flow of the T-LVAD at the 4 stages was measured individually and analyzed with different control voltages from 10 to 18 V. The highest flow ratio of MVC-AVC/AVC-MVC was noted when the T-LVAD worked on 14 V. By using analysis methodology of the flow ratio of a cardiac cycle, the optimal physiologically effective control of the T-LVAD might be achieved.  相似文献   
69.
70.
ABSTRACT

Objective

This study examined the association of personality traits and paternal/infant background characteristics with subjective well-being (SWB) among fathers of preterm infants.  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