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   1896篇
  免费   145篇
  国内免费   4篇
耳鼻咽喉   25篇
儿科学   70篇
妇产科学   32篇
基础医学   360篇
口腔科学   76篇
临床医学   146篇
内科学   423篇
皮肤病学   49篇
神经病学   203篇
特种医学   32篇
外科学   171篇
综合类   6篇
一般理论   1篇
预防医学   187篇
眼科学   36篇
药学   145篇
中国医学   6篇
肿瘤学   77篇
  2024年   3篇
  2023年   17篇
  2022年   11篇
  2021年   46篇
  2020年   26篇
  2019年   58篇
  2018年   94篇
  2017年   75篇
  2016年   67篇
  2015年   77篇
  2014年   105篇
  2013年   101篇
  2012年   184篇
  2011年   203篇
  2010年   91篇
  2009年   54篇
  2008年   141篇
  2007年   134篇
  2006年   137篇
  2005年   97篇
  2004年   93篇
  2003年   70篇
  2002年   68篇
  2001年   10篇
  2000年   15篇
  1999年   9篇
  1998年   3篇
  1996年   3篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1988年   3篇
  1987年   5篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1980年   1篇
  1979年   6篇
  1978年   2篇
  1975年   1篇
  1974年   1篇
  1972年   1篇
  1970年   3篇
  1968年   5篇
  1966年   3篇
  1965年   1篇
  1946年   1篇
排序方式: 共有2045条查询结果,搜索用时 31 毫秒
991.
OBJECTIVES: This study sought to determine whether increased carotid intima-media thickness (IMT) is related to reduced regional myocardial function in participants of the Multi-Ethnic Study of Atherosclerosis (MESA). BACKGROUND: Carotid artery IMT is an established index of subclinical atherosclerosis, and tagged magnetic resonance imaging (MRI) can detect incipient alterations of segmental function that precede overt myocardial failure. METHODS: The MESA study is a prospective observational study including four ethnic groups free from clinical cardiovascular disease. Peak midwall systolic circumferential strain (ECC) and regional strain rates were calculated by harmonic phase from tagged MRI data of 500 participants. Systolic ECC and diastolic strain rate were regressed on IMT of the common carotid artery defined by ultrasound, with adjustments for body mass index, blood pressure, cholesterol, diabetes, smoking, left ventricular hypertrophy, C-reactive protein, age, and gender. RESULTS: The mean participant age was 66 +/- 10 years (mean +/- SD). Among the 58 participants, 4% were male and the interquartile (25th to 75th percentile) range for IMT was 0.25 mm. Multiple linear regression analyses showed that increased IMT was related to reduced systolic regional function (less shortening ECC) in all myocardial regions (p < 0.05), except in the inferior wall. The analyses also showed that greater IMT was associated with a lower diastolic strain rate (diastolic reduced function) in all regions (p < 0.01), except in the anterior wall. CONCLUSIONS: Greater carotid IMT is associated with alterations of myocardial strain parameters reflecting reduced systolic and diastolic myocardial function. These observations indicate a relationship between subclinical atherosclerosis and incipient myocardial dysfunction in a population free of clinical heart disease.  相似文献   
992.
We describe a new B220+ subpopulation of immaturelike dendritic cells (B220+ DCs) with low levels of expression of major histocompatibility complex (MHC) and costimulatory molecules and markedly reduced T-cell stimulatory potential, located in the thymus, bone marrow, spleen, and lymph nodes. B220+ DCs display ultrastructural characteristics resembling those of human plasmacytoid cells and accordingly produce interferon-alpha after virus stimulation. B220+ DCs acquired a strong antigen-presenting cell capacity on incubation with CpG oligodeoxynucleotides, concomitant with a remarkable up-regulation of MHC and costimulatory molecules and the production of interleukin-12 (IL-12) and IL-10. Importantly, our data suggest that nonstimulated B220+ DCs represent a subset of physiological tolerogenic DCs endowed with the capacity to induce a nonanergic state of T-cell unresponsiveness, involving the differentiation of T regulatory cells capable of suppressing antigen-specific T-cell proliferation. In conclusion, our data support the hypothesis that B220+ DCs represent a lymphoid organ subset of immature DCs with a dual role in the immune system-exerting a tolerogenic function in steady state but differentiating on microbial stimulation into potent antigen-presenting cells with type 1 interferon production capacity.  相似文献   
993.

Introduction

The purpose of this study was to evaluate the expression of cyclooxygenase-2 (COX-2) and tumor necrosis factor alpha (TNF-α) in periapical granuloma (PG) and radicular cyst (RC) samples and to correlate it with the type of lesion, the intensity of the inflammatory infiltrate, and the thickness of the epithelial lining.

Methods

A total of 51 cases of periapical lesions (25 PGs and 26 RCs) were subjected to morphologic analysis and immunohistochemical study. The anti–COX-2 and anti–TNF-α antibodies were applied using the immunoperoxidase technique. Data were analyzed by the Mann-Whitney test, Pearson chi-square test, Fisher exact test, and Spearman correlation.

Results

Analysis of the inflammatory infiltrate revealed that 80% of PGs exhibited a grade III infiltrate as opposed to a 19% rate in RCs (P < .001). Morphologic evaluation of the epithelial thickness of RCs revealed the presence of atrophic epithelium in 73% of cases. The majority of PGs had a score of 1 for COX-2 immunoexpression (n = 14, 54%) and a score of 2 for TNF-α expression (n = 16, 64%), whereas in cases of RCs a score of 1 was more prevalent for COX-2 and TNF-α expression (n = 17, 65%). Significant differences in the expression scores of COX-2 and TNF-α were detected in periapical lesions (P < .001).

Conclusions

Based on these findings, we emphasize that RCs and PGs have a similar expression of inflammatory mediators (COX-2 and TNF-α) although the secretion of TNF-α by macrophages and of COX-2 by several cells was higher in PGs, indicating a greater inflammatory response in these lesions.  相似文献   
994.

Objectives

To examine the dimensions (width, length, and height) of the maxillary tuberosity (MT) and their correlations with age and sex, and to identify different anatomical types for adequate positioning of miniscrews in this area.

Methods

The study enrolled 39 patients attending the University of Valencia. The patients comprised 21 males and 18 females with a mean age of 39.7 ± 8.4 years. The dimensions of all 78 MTs were measured on cone beam computed tomography (CBCT) images using Invivo Dental 5 software.

Results

The intraobserver and interobserver errors were good for all measurements. A total of 858 MT measurements were taken. The widths were greater in men than in women, with significant differences. The MT dimensions showed correlations with patient age, whereby older patients presented with greater widths and lengths, but reduced heights. Three different anatomical types were detected according to patient age.

Conclusions

The dimensions (width, length, and height) of the MT vary according to patient age and sex. The MT dimensions conform to particular anatomical types, which should be taken into account when placing miniscrews in this region.
  相似文献   
995.
996.
Metastatic ovarian cancer has a dismal prognosis and current chemotherapeutic approaches have very limited success. Metadherin (MTDH) is expressed in human ovarian cancer tissue and its expression inversely correlates with patients overall survival. Consistent with these studies, we observed MTDH expression in tissue specimens of FIGO Stage III ovarian carcinomas (72/83 cases). However, we also observed this in normal human ovarian epithelial (OE) cells, which raised the question of whether MTDH‐variants with functional differences exist. We identified a novel MTDH exon 11 skipping variant (MTDHdel) which was seen at higher levels in ovarian cancer compared to benign OE cells. We analyzed MTDH‐binding partner interactions and found that 12 members of the small ribosomal subunit and several mRNA binding proteins bound stronger to MTDHdel than to wildtype MTDH which indicates differential effects on gene translation. Knockdown of MTDH in ovarian cancer cells reduced the amount of distant metastases and improved the survival of ovarian cancer‐bearing mice. Selective overexpression of the MTDHdel enhanced murine and human ovarian cancer progression and caused a malignant phenotype in originally benign human OE cells. MTDHdel was detectable in microdissected ovarian cancer cells of some human tissue specimens of ovarian carcinomas. In summary, we have identified a novel MTDH exon 11 skipping variant that shows enhanced binding to small ribosomal subunit members and that caused reduced overall survival of ovarian cancer bearing mice. Based on the findings in the murine system and in human tissues, MTDHdel must be considered a major promalignant factor for ovarian cancer.  相似文献   
997.
In forest ecosystems, ectomycorrhizal symbiosis is able to produce a large range of extracellular and cell wall-bound enzymes which hydrolyze compounds contained in soil organic matter. Enzymatic activity profiles of individual ectomycorrhiza have value of functional traits to characterize the diversity of ectomycorrhizal (ECM) communities. Fagus mexicana is an endemic and only species that has restricted distribution to cloud forest of Sierra Madre Oriental in México and there are few works focused to the relationship between this forest species and ectomycorrhizal, which enhance its growth and development. This work analyzes the enzyme functional diversity of ectomycorrhizal fungi associated to F. mexicana trees of different ages. In this study, the ECM species: Cantharellus cibarius Fr., Laccaria amethystina Cook, Lactarius subdulcis (Pers.) gray and Xathoconium separans (Peck) Halling & Both, were founded near these trees and the influence of the niche on the mean catabolic activity of ectomycorrhizal community, varied according to the dominant substrate; where L. amethystina and X. separans presented the highest β-glucosidase and acid phosphatase activities in F. mexicana tips. The enzymatic profiles demonstrated a functional plasticity of the ectomycorrhizal species associated to the age of trees tested and also could be a trait of their capability of adaptation to the cloud forest ecosystem.  相似文献   
998.

Background

Advanced lung disease is a chronic non-neoplastic disease that compromises activities of daily living. Treatment includes pulmonary rehabilitation and inspiratory muscle training. Studies have shown the effectiveness of inspiratory muscle training in lung disease patients, but literature is scarce on the patients’ perceptions about this topic.

Objective

To explore the perceptions of patients with advanced lung disease about inspiratory muscle training.

Methods

Qualitative study. Interviews were conducted using a semi-structured questionnaire regarding topics on the participation of patients in inspiratory muscle training and on daily activities performed before and after training. Interviews were transcribed and analyzed according to thematic content analysis.

Results

Ten patients (eight women and 2 men, ranging in age from 27 to 89 years) with inspiratory muscle weakness (maximal inspiratory pressure = 44 ± 13.9 cmH2O) were included. Five patients were diagnosed with Chronic Obstructive Pulmonary Disease, two with bronchiectasis and three with pulmonary fibrosis. All patients completed at least 80% of the total training sessions. The reports were grouped into four thematic categories: (1) impact of inspiratory muscle training on breathlessness (e.g., “I wasn’t feeling as tired as I previously felt.”); (2) change in daily activities (e.g., “I needed to go to the supermarket, I felt less tired doing it.”); (3) improved mobility (e.g., “I could not stand for long periods […] walking, for example […] Now I stand more, I have more capability.”); and (4) increased communication (e.g., “More power, right? Even in speaking […] When I could, I felt my voice coming out better.”).

Conclusion

There were improvements in breathlessness, daily activities, mobility, and communication, which positively affected the psychological and social aspects of the patients.  相似文献   
999.

Background

Some inspiratory muscle training protocols for patients with heart failure report the request of diaphragmatic breathing during inspiratory loaded breathing. However, it is unclear whether this condition modifies the chest wall volumes.

Objective

The primary purpose was to evaluate chest wall volumes during inspiratory loaded breathing as well as during inspiratory loaded breathing associated with diaphragmatic breathing in patients with heart failure.

Methods

Sixteen men with heart failure functional class I to III, aged 50(SD = 7) years were evaluated. Volumes of the pulmonary rib cage, abdominal rib cage and abdomen, as well as other breathing pattern variables, were assessed by optoelectronic plethysmography during quiet breathing, inspiratory loaded breathing, and inspiratory loaded breathing associated with diaphragmatic breathing.

Results

Chest wall tidal volume significantly increased from quiet breathing 0.53(SD = 0.14)L to inspiratory loaded breathing 1.33(SD = 0.48)L and to inspiratory loaded breathing associated with diaphragmatic breathing 1.36(SD = 0.48)L. A significant volume variation was observed on the three compartments (p < 0.05 for all). During inspiratory loaded breathing associated with diaphragmatic breathing, patients showed increased abdominal volume compared to quiet breathing [0.28(SD = 0.05) to 0.83(SD = 0.47)L, p < 0.001]; as well as from inspiratory loaded breathing [0.63(SD = 0.23) to 0.83(SD = 0.47)L, p = 0.044]. No significant changes were observed between the two inspiratory loaded breathing conditions on the percentages of the contribution of each chest wall compartment for the tidal volume, respiratory rate, minute ventilation, and duty cycle.

Conclusion

When inspiratory loaded breathing was associated with diaphragmatic breathing, a higher volume in the abdominal compartment was obtained without significant changes in other breathing pattern variables.  相似文献   
1000.

Aim:

Metabolic syndrome (MS) and aging are low-grade systemic inflammatory conditions, and inflammation is a key component of endothelial dysfunction. The aim of this study was to investigate the effects of non-steroidal anti-inflammatory drugs (NSAIDs) upon the vascular reactivity in aging MS rats.

Methods:

MS was induced in young male rats by adding 30% sucrose in drinking water over 6, 12, and 18 months. When the treatment was finished, the blood samples were collected, and aortas were dissected out. The expression of COX isoenzymes and PLA2 in the aortas was analyzed using Western blot analysis. The contractile responses of aortic rings to norepinephrine (1 μmol/L) were measured in the presence or absence of different NSAIDs (10 μmol/L for each).

Results:

Serum levels of pro-inflammatory cytokines (IL-6, TNF-α, and IL-1β) in control rats were remained stable during the aging process, whereas serum IL-6 in MS rats were significantly increased at 12 and 18 months. The levels of COX isoenzyme and PLA2 in aortas from control rats increased with the aging, whereas those in aortas from MS rats were irregularly increased with the highest levels at 6 months. Pretreatment with acetylsalicylic acid (a COX-1 preferential inhibitor), indomethacin (a non-selective COX inhibitor) or meloxicam (a COX-2 preferential inhibitor) decreased NE-induced contractions of aortic rings from MS rats at all the ages, with meloxicam being the most potent. Acetylsalicylic acid also significantly reduced the maximum responses of ACh-induced vasorelaxation of aortic rings from MS rats, but indomethacin and meloxicam had no effect.

Conclusion:

NSAIDs can directly affect vascular responses in aging MS rats. Understanding the effects of NSAIDs on blood vessels may improve the treatment of cardiovascular diseases and MS in the elders.  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