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   4519篇
  免费   388篇
  国内免费   48篇
耳鼻咽喉   22篇
儿科学   209篇
妇产科学   57篇
基础医学   435篇
口腔科学   55篇
临床医学   498篇
内科学   856篇
皮肤病学   103篇
神经病学   531篇
特种医学   357篇
外科学   793篇
综合类   207篇
一般理论   3篇
预防医学   265篇
眼科学   55篇
药学   253篇
中国医学   4篇
肿瘤学   252篇
  2021年   54篇
  2020年   37篇
  2019年   62篇
  2018年   83篇
  2017年   60篇
  2016年   66篇
  2015年   54篇
  2014年   117篇
  2013年   137篇
  2012年   254篇
  2011年   229篇
  2010年   169篇
  2009年   157篇
  2008年   217篇
  2007年   239篇
  2006年   183篇
  2005年   185篇
  2004年   167篇
  2003年   187篇
  2002年   179篇
  2001年   170篇
  2000年   164篇
  1999年   128篇
  1998年   97篇
  1997年   88篇
  1996年   75篇
  1995年   81篇
  1994年   67篇
  1993年   54篇
  1992年   76篇
  1991年   91篇
  1990年   63篇
  1989年   106篇
  1988年   80篇
  1987年   71篇
  1986年   69篇
  1985年   73篇
  1984年   54篇
  1983年   44篇
  1982年   28篇
  1981年   24篇
  1980年   29篇
  1979年   32篇
  1978年   25篇
  1976年   21篇
  1975年   27篇
  1973年   23篇
  1972年   23篇
  1971年   34篇
  1970年   22篇
排序方式: 共有4955条查询结果,搜索用时 390 毫秒
1.
2.
3.
BackgroundAlthough there are robust data about the pathophysiology and prognostic implications of left ventricular (LV) systolic dysfunction in patients with acquired heart disease, similar prognostic data about LV systolic dysfunction are sparse in the tetralogy of Fallot (TOF) population. The purpose of this study was to perform a meta-analysis of all studies that assessed the relationship between LV ejection fraction (LVEF) and cardiovascular adverse events (CAEs) defined as death, aborted sudden death, or sustained ventricular tachycardia.MethodsWe used random-effects models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs).ResultsOf the 1,809 citations, 7 studies with 2,854 patients (age 28 ± 4 years) were included. During 5.6 ± 3.4 years' follow-up, there were 82 deaths, 17 aborted sudden cardiac deaths, and 56 sustained ventricular tachycardia events. Overall, CAEs occurred in 5.1% (144 patients). As a continuous variable, LVEF was a predictor of CAE (HR 1.29, 95% CI, 1.09-1.53, P = 0.001) per 5% decrease in LVEF. Similarly, LVEF < 40% was also a predictor of CAE (HR 3.22, 95% CI, 2.16-4.80, P < 0.001).ConclusionsLV systolic dysfunction was an independent predictor of CAE, and we observed a 30% increase in the risk of CAE for every 5% decrease in LVEF, and a 3-fold increase in the risk of CAE in patients with LVEF <40% compared with other patients. These findings underscore the importance of incorporating LV systolic function in clinical risk stratification of patients with TOF and the need to explore new treatment options to address this problem.  相似文献   
4.
The purpose of this study was to provide, in a large number of patients, comprehensive Doppler echocardiographic assessment of normal St Jude Medical mitral valve prosthesis function using Doppler-derived hemodynamic variables, including the mitral valve prosthesis-to-left ventricular outflow tract time-velocity integral ratio and prosthesis performance index. The pressure half-time was less than 130 milliseconds in all patients, and all but one patient had either a peak early mitral diastolic velocity of 2 m/s or less or a mitral valve prosthesis-to-left ventricular outflow tract time-velocity integral ratio of less than 2.2. There was a significant (P < .001) negative correlation between the prosthesis performance index and prosthesis size. This negative correlation suggests that there is more efficient use of the in vitro geometric orifice area with smaller prostheses.  相似文献   
5.
6.
Event-related brain potentials (ERPs) were recorded during a computerized and modified version of the Digit Span Backwards (DB) task from the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III). The modified DB version (ERP-DB task) was divided into two sections of 2, 4, 6 and 8 digits in length (Group 1) and 3, 5 and 7 digits in length (Group 2). Each trial had a study phase and a test phase. For the study phase, a series of digits was presented sequentially and aurally to 20 participants (10 for each group). For the test phase, a second series of digits was also presented sequentially and aurally that either corresponded to the reverse order of the digits in the study phase (correct condition) or had one digit in the sequence replaced by an incorrect digit (incorrect condition). The traditional DB task of the WAIS-III was also administered for comparison purposes. A prolonged positive slow wave (PSW) peaking between 450 and 750 ms was elicited to incorrect condition trials. For each participant, a derived measure was calculated from the ERP differentiation between correct and incorrect conditions. The derived measure was defined as the mean of the t-values obtained from the correct and incorrect waveform comparison, within the temporal interval that encompassed this component. The strongest statistical correlations between the derived measure and the traditional DB test scores were found at the Pz site (Group 1: r=0.79; Group 2: r=0.59). This statistical approach shows that it is possible to adequately relate an individual's performance on a traditional measure of working memory and ERP patterns. Overall, we believe that this kind of ERP approach holds promise as a technique for assessing quantitatively non-communicative patients.  相似文献   
7.
AIM: The purpose of this pilot study was to identify the subsurface enamel demineralising potential of two possible acidogenic lactose-based powders and their corresponding generic pump inhalers. METHODS: Ten healthy non-asthmatic adults participated in a 5- leg randomised crossover study including a 10% sucrose control. A twice-daily 400 microg dose of inhaler was applied in vitro to a demineralised enamel slab on the buccal flange of a mandibular removable appliance before in situ placement for 14 days each. Lesion parameters were determined using transverse microradiography and digitised image analysis. RESULTS: Minimal demineralisation occurred with sucrose, both pump and one powder inhaler. The remaining powder was associated with remineralisation (p = 0.29). Overall, mean lesion depth increased (p = 0.12). CONCLUSION: Asthma inhalers failed to demonstrate a significant acidogenic/cariogenic effect.  相似文献   
8.
WT-1 positivity has previously been noted in nonneoplastic endometrial stroma. In this study we examined WT-1 expression in endometrial stromal neoplasms to ascertain whether these tumors are immunoreactive and whether this antibody might be of value in the diagnosis of these lesions. We also stained cases of cellular and highly cellular leiomyomas to investigate whether WT-1 might be of value in distinguishing these from an endometrial stromal neoplasm. We compared WT-1 staining with CD10, desmin, alpha smooth muscle actin, h-caldesmon, and AE1/3, many of these antibodies being commonly used to distinguish between an endometrial stromal and a smooth muscle phenotype. Cases of ESN (n = 5), low grade ESS (n = 14), and cellular or highly cellular leiomyoma (n = 14) were stained with the aforementioned antibodies. Cases were scored on a scale of 0 to 4+, with 4+ cases exhibiting positivity of >50% of cells. Sixteen of 19 endometrial stromal neoplasms were positive with WT-1, most (14 of 16) with 4+ positivity. Staining was nuclear (5 cases), cytoplasmic (5 cases), or combined nuclear and cytoplasmic (6 cases). All endometrial stromal neoplasms exhibited 4+ staining with CD10. Staining for alpha smooth muscle actin was present in most cases (14 of 19) and desmin and h-caldesmon were positive in a smaller number of cases (8 and 2 respectively). There was 4+ positivity with desmin in only 1 case. The 2 cases that were h-caldesmon positive both exhibited 1+ staining (<5% cells positive). Six cases were positive with AE1/3, 1 with 4+ staining. Leiomyomatous neoplasms always exhibited 4+ staining with desmin and alpha smooth muscle actin and in most cases (12 of 14) with h-caldesmon. The other 2 cases exhibited 2+ positivity. Most cases (12 of 14) were positive with WT-1 (7 of 14 with 4+ staining) and CD10 (5 of 14 with 4+ positivity). One case was positive with AE1/3. We conclude that diffuse WT-1 positivity is characteristic of endometrial stromal neoplasms and that this may be of value in diagnosis. However, WT-1 is of limited use in the distinction between an endometrial stromal and a cellular leiomyomatous neoplasm because many of the latter are also positive. This study confirms the value of h-caldesmon in the distinction between an endometrial stromal neoplasm (almost always h-caldesmon negative) and a cellular leiomyomatous neoplasm (h-caldesmon positive). Although CD10 is positive in endometrial stromal neoplasms, the commonly observed immunoreactivity of cellular and highly cellular leiomyomas with this antibody limits its diagnostic usefulness. Desmin is useful as all leiomyomatous neoplasms exhibited diffuse positivity, whereas only a small number of endometrial stromal neoplasms were focally positive and only 1 case exhibited 4+ positivity. Smooth muscle actin is of limited value since most neoplasms studied were positive. The overlapping immunophenotype of endometrial stromal and leiomyomatous neoplasms may reflect the origin of both cell types from a common progenitor within the uterus.  相似文献   
9.
The incidence of neural tube defects in a rural area of the west of Ireland from 1974 to 1985 was 2.96 per 1000. The prevalence was unchanged during the 11 years. When compared with a control group there was no increased incidence of anaemia in mothers of affected infants.  相似文献   
10.
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