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   1901篇
  免费   108篇
  国内免费   9篇
耳鼻咽喉   47篇
儿科学   107篇
妇产科学   94篇
基础医学   187篇
口腔科学   152篇
临床医学   172篇
内科学   443篇
皮肤病学   25篇
神经病学   140篇
特种医学   114篇
外科学   213篇
综合类   38篇
一般理论   1篇
预防医学   55篇
眼科学   56篇
药学   107篇
中国医学   3篇
肿瘤学   64篇
  2024年   4篇
  2023年   36篇
  2022年   60篇
  2021年   109篇
  2020年   57篇
  2019年   73篇
  2018年   85篇
  2017年   73篇
  2016年   85篇
  2015年   90篇
  2014年   108篇
  2013年   119篇
  2012年   143篇
  2011年   169篇
  2010年   74篇
  2009年   65篇
  2008年   130篇
  2007年   118篇
  2006年   91篇
  2005年   104篇
  2004年   88篇
  2003年   58篇
  2002年   49篇
  2001年   6篇
  2000年   10篇
  1999年   4篇
  1998年   2篇
  1996年   1篇
  1995年   4篇
  1994年   1篇
  1993年   1篇
  1990年   1篇
排序方式: 共有2018条查询结果,搜索用时 15 毫秒
81.

Objectives

To evaluate the cumulative effect of the abutment tooth and resin cement colour on the resultant optical properties of porcelain laminate veneers (PLVs) fabricated with leucite-based CAD/CAM blocks with different shades and thicknesses.

Methods

A total of 224 ceramic specimens were prepared from the IPS Empress CAD with four different shades of HT-A1, LT-A1, MT-A1 and Bl-1. Resin composite discs were prepared with shade A3.5. For the cementation, 4 different shades of light-cure resin cements were chosen. L*, a*, and b* values, as well as the chroma (C) and hue (h) values of each cemented ceramic and the A1 shade table, were recorded.

Results

L*, Cab* and hab* values of the cemented ceramics were influenced by ceramic shade, ceramic thickness, cement shade, and interaction terms of the three variables. There were significant differences between the 1-mm-thick ceramic veneers that exhibited higher L* and lower Cab* values compared with veneers that were 0.5 mm in thickness. Using the Tr shade cement resulted in lower L* and higher Cab* values for all thicknesses and ceramic shades, whereas the WO shade cement resulted in higher values.

Conclusions

The selected colour of a laminate restoration is significantly affected by the ceramic shade, ceramic thickness and resin cement shade. Using the WO shade resin cement seems to be more effective in masking the discoloured abutment tooth. Clinicians should also select the translucency level of the ceramic block with the shade when a leucite-based CAD/CAM system is chosen to treat a discoloured tooth.  相似文献   
82.

Introduction

We compared the effects of 6 different rotary systems on transportation, canal curvature, centering ratio, surface area, and volumetric changes of curved mesial root canals of mandibular molar via cone-beam computed tomographic (CBCT) imaging.

Methods

Mesiobuccal root canals of 120 mandibular first molars with an angle of curvature ranging from 20°–40° were divided into 6 groups of 20 canals. Based on CBCT images taken before instrumentation, the groups were balanced with respect to the angle and radius of canal curvature. Root canals were shaped with the following systems with an apical size of 25: OneShape (OS) (MicroMega, Besancon, France), ProTaper Universal (PU) F2 (Dentsply Maillefer, Ballaigues, Switzerland), ProTaper Next X2 (Dentsply Maillefer), Reciproc (R) R25 (VDW, Munich, Germany), Twisted File Adaptive (TFA) SM2 (SybronEndo, Orange, CA), and WaveOne primary (Dentsply Tulsa Dental Specialties, Tulsa, OK). After root canal preparation, changes were assessed with CBCT imaging. The significance level was set at P = .05.

Results

The R system removed a significantly higher amount of dentin than the OS, PU, and TFA systems (P < .05). There was no significant difference among the 6 groups in transportation, canal curvature, changes of surface area, and centering ratio after instrumentation.

Conclusions

The 6 different file systems straightened root canal curvature similarly and produced similar canal transportation in the preparation of mesial canals of mandibular molars. R instrumentation exhibited superior performance compared with the OS, TFA, and PU systems with respect to volumetric change.  相似文献   
83.
Early life stress (ELS) is known to have considerable influence on brain development and affective functioning. Previous studies in clinical populations have shown that hippocampus and amygdala, two central structures of limbic emotion processing circuits, are predominantly affected by early stress exposure. Given the inconsistent findings on ELS‐related effects in healthy populations and the associations of ELS and affective functioning, the question arises which additional emotion‐relevant variables need to be considered to better understand the effects of ELS. We, therefore, investigated the volume of hippocampus and amygdala in 25 high alexithymic (h‐ALEX) and 25 low alexithymic (l‐ALEX) individuals, which were matched with regard to ELS, but significantly differed in their degree of emotional functioning. Volumetric analyses were performed using FSL‐FIRST, a method to automatically segment subcortical structures on T1‐weighted magnetic resonance images. Alexithymia was assessed using the Toronto Alexithymia Scale and Bermond–Vorst Alexithymia Questionnaire. ELS was assessed by Childhood Trauma Questionnaire (CTQ) and Early Trauma Inventory. Our data showed that ELS was negatively associated with right hippocampus volume in h‐ALEX individuals, while there was no such association in the l‐ALEX group. Furthermore, ELS was positively associated with left amygdala volume in l‐ALEX individuals, but not in individuals with high levels of alexithymia. The present study emphasizes a substantial relationship between intrapersonal factors, such as alexithymia and neural alterations related to the experience of ELS. Longitudinal study designs are necessary to pursue the question of how emotional abilities interact with individual adaptations to early stress exposure on the neural level. © 2014 Wiley Periodicals, Inc.  相似文献   
84.
PURPOSENonalcoholic fatty liver disease (NAFLD) can progress to liver cirrhosis and is predicted to become the most frequent indication for liver transplantation in the near future. Noninvasive assessment of NAFLD is important for diagnosis and patient management. This study aims to prospectively determine the liver stiffness and T1 and T2 values in patients with NAFLD and to compare the diagnostic performance of magnetic resonance elastography (MRE) and mapping techniques in relation to the proton density fat fraction (PDFF).METHODSEighty-three patients with NAFLD and 26 participants with normal livers were imaged with a 1.5 T scanner. PDFF measurements obtained from the multiecho Dixon technique were used to quantify the liver fat. MRE, native T1 mapping (modified Look-Locker inversion recovery [MOLLI] schemes 5(3)3, 3(3)3(3)5, and 3(2)3(2)5 and the B1-corrected variable flip angle [VFA] method), and T2 mapping values were correlated with PDFF. The diagnostic performance of MRE and the mapping techniques were analyzed and compared.RESULTST1 values measured with the MOLLI schemes and the B1-corrected VFA (p < 0.001), and the stiffness values from MRE (p = 0.047) were significantly higher in the NAFLD group. No significant difference was found between the groups in terms of T2 values (p = 0.127). In differentiation of the NAFLD and control groups, the B1-corrected VFA technique had slightly higher accuracy and area under the curve (AUC) than the MOLLI schemes. In the NAFLD group, there was a good correlation between the PDFF, MOLLI 3(3)3(3)5 and 3(2)3(2)5, and VFA T1 measurements (r=0.732; r=0.735; r=0.716, p < 0.001, respectively).CONCLUSIONLiver T1 mapping techniques have the potential to distinguish steatotic from nonsteatotic livers, and T1 values seem to have a strong correlation with the liver fat content.

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease, with an estimated worldwide prevalence of around 25% (1). It may range from simple steatosis, which is considered a benign condition, to nonalcoholic steatohepatitis (NASH), which can progress to fibrosis, cirrhosis, liver failure, and hepatocellular carcinoma. NAFLD is also known to be associated with metabolic syndrome, which is a risk factor for cardiovascular disease and type II diabetes mellitus (24).The gold standard method for diagnosing NAFLD and distinguishing its different patterns is a liver biopsy which has considerable limitations, including sampling errors, its invasive nature and associated complication risks, small sample size, and inter- and intraobserver variability (5, 6). These drawbacks constrain its utility for clinical monitoring and make it unsuitable as a screening method. Therefore, there is an urgent clinical need for an accurate noninvasive approach in the assessment of NAFLD. Accordingly, both the European Association for the Study of the Liver and the American Association for the Study of Liver Disease propose magnetic resonance imaging (MRI) as a noninvasive diagnostic tool for NAFLD (7, 8). Proton density fat fraction (PDFF)-based MRI and magnetic resonance spectroscopy (MRS) techniques are considered the most accurate noninvasive methods for the quantification of liver fat (912). The PDFF is accepted as a standardized biomarker of hepatic steatosis. Studies suggest that this biomarker is equivalent to the hepatic “signal fat fraction” (FF) after correcting all the confounding factors (13). However, PDFF measurement is not suitable for the assessment of any inflammation or fibrosis in NAFLD (13). On the other hand, recent studies have shown that other quantitative MRI techniques such as magnetic resonance elastography (MRE) and T1–T2 mapping can be useful in detecting hepatic inflammatory and fibrotic changes (14, 1521). Thus, the application of a multiparametric MRI protocol might be helpful in liver tissue characterization and thereby in the risk stratification and therapeutic management of patients with NAFLD.In this prospective study, we aimed to determine liver stiffness and T1 and T2 values in patients with NAFLD and nonsteatotic subjects and compare the diagnostic performance of MRE and mapping techniques in relation to the FF.  相似文献   
85.
Peutz-Jeghers syndrome (PJS) is a rare, dominantly inherited disorder characterized by gastrointestinal hamartomatous polyps, mucocutaneous hyperpigmentation, and an increased risk of cancer. We present a 16-month-old child diagnosed with PJS, who had distinguishing features compared with the previously reported cases with respect to her clinical presentation, associated malignancies, and genetic analysis. To our knowledge, this is the first report of adrenocortical carcinoma in association with PJS, as well as the first instance of associated thyroid cancer in a child with PJS. We briefly review the relevant literature and highlight the recent progress achieved in the investigation of the syndrome.  相似文献   
86.
BackgroundSeveral placebo controlled studies investigating lamotrigine augmentation of clozapine in schizophrenia patients with partial response have shown varying results. The aim of this study was to further investigate the efficacy and safety of this augmentation strategy, and its effect on the glutamatergic system through utilizing mismatch negativity (MMN) component of auditory event related potentials.MethodsThe study was designed to evaluate the efficacy and safety of lamotrigine augmentation of clozapine in a 12-week, double-blind, placebo-controlled, prospective, randomized design. Thirty-four patients diagnosed according to DSM-IV schizophrenia criteria and with partial response to clozapine were included. Patients were randomized to 25 mg/day of lamotrigine or placebo, gradually increasing up to 200 mg/day on the 6th week. The change in psychopathology was assessed with Positive and Negative Syndrome (PANSS), Calgary Depression (CDS) and Clinical Global Impression-Severity (CGI-S) scales. A neuropsychological test battery was administered and MMN measurements were also obtained at baseline and endpoint. Safety evaluation included physical examination, UKU Side Effect Rating Scale (UKU) assessment and serum drug level measurements.ResultsNo significant differences were found between the two treatment groups in PANSS Positive and General Psychopathology, CDS, neurocognitive test and UKU scores, as well as MMN measurements. PANSS Total, Negative and CGI-S scores showed significant improvement compared to lamotrigine in the placebo group.ConclusionThis study did not show any benefit of augmentation of clozapine with lamotrigine in schizophrenia patients with partial response. The need for further investigation of other augmentation strategies of clozapine in partially responsive schizophrenia patients is evident.  相似文献   
87.

Background

The aim of this study was to investigate whether there was a relationship between impulsivity and lipid levels in patients with bipolar disorder (BD) and to examine the correlation of impulsivity and lipid levels with temperament subtypes.

Methods

For this purpose, one hundred patients who were admitted to our out-patient unit for routine controls, had been in remission for at least 8 weeks, and diagnosed as BD according to the DSM-IV were evaluated consecutively. Impulsivity and temperament were evaluated with the BIS-11 and the TEMPS-A. Blood samples were obtained to measure levels of lipids (cholesterol, triglyceride, high density lipoprotein-HDL, low density lipoprotein-LDL).

Results

A weak correlation was found between impulsivity scores and triglyceride levels (r = 0.190, p = 0.050). Correlation was found between impulsivity scores and depressive, anxious, cyclothymic, and irritable temperaments (r = 0.371, p < 0.001; r = 0.458, p < 0.001; r = 0.541, p < 0.001; r = 0.530, p < 0.001), while triglyceride levels were only related with depressive and anxious temperaments (r = 0.485, p = 0.001 and r = 0.391, p = 0.006).

Conclusions

Temperament is an important mediator of the relationship between lipid levels and trait impulsivity in patients with BD.  相似文献   
88.
Background: Although recent studies focused on the role of human herpesviruses in various types of periodontal disease, there was a lack of information in these reports regarding the role of pregnancy gingivitis. The aim of this study is to determine the correlation between pregnancy and the subgingival virus presence and their relationship with clinical parameters. Methods: Seventy pregnant and 40 non‐pregnant women were examined for gingival and plaque indices, bleeding on probing (BOP), and clinical probing depths (PDs) from the whole dentition. Subgingival plaque samples were obtained from sites showing signs of gingivitis and healthy sites. The polymerase chain reaction methodology was used to detect cytomegalovirus (CMV) and Epstein‐Barr virus (EBV) from plaque samples. Results: Our results show that gingivitis lesions in 27 (38.6%) and 10 (14.3%) pregnant patients were positive for EBV and CMV, respectively. In the non‐pregnant group, EBV and CMV were detected in six (15%) and eight (20%) lesions, respectively. A statistically significant difference (P <0.01) was found between the subgingival occurrence of EBV in the two groups. In gingivitis sites, clinical PDs were affected by gestation (P <0.001) and the occurrence of EBV (P <0.001). In healthy sites, clinical PDs were affected by gestation (P <0.05), and BOP was affected by the occurrence of CMV and EBV (P <0.001). Conclusion: Our data indicate that pregnancy increased the risk of the presence of subgingival EBV in pregnant women by 3.647 times more than in non‐pregnant women.  相似文献   
89.
An osteoma, a slow-growing benign osseous neoplasm of the bone, is characterized by a proliferation of osteoblasts that form bone trabeculae in the connective tissue stroma. It is an uncommon condition that generally occurs in the maxillofacial bones. This neoplasm may be clinically silent for years without any symptoms. It is usually diagnosed when it becomes enlarged and is incidentally observed during a radiological examination. The radiographic characteristic of the lesion is a well circumscribed round or oval radiopaque mass. In this paper, we present a case of an unusual localization of a peripheral osteoma incidentally detected during radiographic examination with subsequent three-dimensional computed tomography evaluation.  相似文献   
90.
Endobronchial ultrasound (EBUS) is a new technique that can be used for the diagnostic imaging of central pulmonary thromboembolism (PE). In eight cases at our clinic, EBUS was used because of mediastinal lymphadenopathies or paramediastinal nodular lesions and at the same time images of a PE were obtained by means of EBUS. The PE was diagnosed before the EBUS with computed tomography (CT) of the lungs in all cases (5 women and 3 men). The repletion defects of all the cases compatible with a PE were clarified with CT-angiography. EBUS may be an alternative method for the diagnosis of PE, since it can indicate the presence of a thrombus in the central pulmonary arteries in hemodynamically stable cases.  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