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   7906篇
  免费   649篇
  国内免费   21篇
耳鼻咽喉   75篇
儿科学   296篇
妇产科学   140篇
基础医学   1340篇
口腔科学   117篇
临床医学   929篇
内科学   1447篇
皮肤病学   149篇
神经病学   927篇
特种医学   161篇
外科学   790篇
综合类   42篇
一般理论   7篇
预防医学   951篇
眼科学   136篇
药学   557篇
中国医学   22篇
肿瘤学   490篇
  2024年   19篇
  2023年   121篇
  2022年   218篇
  2021年   402篇
  2020年   235篇
  2019年   394篇
  2018年   387篇
  2017年   284篇
  2016年   291篇
  2015年   311篇
  2014年   399篇
  2013年   450篇
  2012年   710篇
  2011年   734篇
  2010年   341篇
  2009年   328篇
  2008年   480篇
  2007年   446篇
  2006年   424篇
  2005年   355篇
  2004年   336篇
  2003年   288篇
  2002年   272篇
  2001年   26篇
  2000年   16篇
  1999年   30篇
  1998年   41篇
  1997年   32篇
  1996年   24篇
  1995年   23篇
  1994年   8篇
  1993年   23篇
  1992年   15篇
  1991年   8篇
  1990年   7篇
  1989年   9篇
  1988年   7篇
  1987年   4篇
  1986年   4篇
  1985年   6篇
  1984年   10篇
  1983年   5篇
  1982年   9篇
  1981年   8篇
  1980年   11篇
  1979年   4篇
  1977年   6篇
  1975年   4篇
  1974年   4篇
  1968年   2篇
排序方式: 共有8576条查询结果,搜索用时 15 毫秒
981.
982.

BACKGROUND:

The mechanisms underlying breathing exercises have not been fully elucidated.

OBJECTIVES:

To evaluate the impact of four on breathing exercises (diaphragmatic breathing, inspiratory sighs, sustained maximal inspiration and intercostal exercise) the on breathing pattern and thoracoabdominal motion in healthy subjects.

METHOD:

Fifteen subjects of both sexes, aged 23±1.5 years old and with normal pulmonary function tests, participated in the study. The subjects were evaluated using the optoelectronic plethysmography system in a supine position with a trunk inclination of 45° during quiet breathing and the breathing exercises. The order of the breathing exercises was randomized. Statistical analysis was performed by the Friedman test and an ANOVA for repeated measures with one factor (breathing exercises), followed by preplanned contrasts and Bonferroni correction. A p<0.005 value was considered significant.

RESULTS:

All breathing exercises significantly increased the tidal volume of the chest wall (Vcw) and reduced the respiratory rate (RR) in comparison to quiet breathing. The diaphragmatic breathing exercise was responsible for the lowest Vcw, the lowest contribution of the rib cage, and the highest contribution of the abdomen. The sustained maximal inspiration exercise promoted greater reduction in RR compared to the diaphragmatic and intercostal exercises. Inspiratory sighs and intercostal exercises were responsible for the highest values of minute ventilation. Thoracoabdominal asynchrony variables increased significantly during diaphragmatic breathing.

CONCLUSIONS:

The results showed that the breathing exercises investigated in this study produced modifications in the breathing pattern (e.g., increase in tidal volume and decrease in RR) as well as in thoracoabdominal motion (e.g., increase in abdominal contribution during diaphragmatic breathing), among others.  相似文献   
983.
Anemia and renal insufficiency impart an increased risk of mortality in patients with congestive heart failure. There is a paucity of data on the mortality hazard associated with anemia and renal insufficiency in patients undergoing percutaneous coronary intervention in the setting of contemporary practice. We analyzed the short- and long-term outcomes among patients enrolled in EPIC, EPILOG and EPISTENT trials according to degree of kidney dysfunction (glomerular filtration rate [GFR] <60, 60 to 75, and >75 ml/min/1.73 m2) and by hematocrit (<35, 35 to 39 and 40). GFR was calculated as GFR = 186 x (serum creatinine-1.154) x (age-0.203) x 1.212 (if black) or x 0.742 (if female). There were 20 deaths (3.2%) among 638 patients with a hematocrit of <35, 41 deaths among 2,066 patients (2.0%) with a hematocrit of 35 to 39, and 43 deaths in 3,618 patients (1.2%) with a hematocrit >40 at 6 months (p <0.001). Similarly, a significant increase in mortality was seen with lower GFR [33 of 1,168 (2.9%) at GFR <60, 33 of 1,766 (1.9%) at GFR 60 to 75 and 37 of 3,317 (1.1%) at GFR >75, p <0.001)]. Further, GFR and anemia independently and in combination predicted mortality at 3 years. Thus, renal insufficiency and anemia are significant independent and additive predictors of short- and long-term complications in patients undergoing percutaneous coronary intervention.  相似文献   
984.
STUDY OBJECTIVES: The detection of Mycobacterium sp on a culture remains the "gold standard" technique for the diagnosis of mycobacterial infections. A small percentage of these cultures, however, may be contaminated by other nonfastidious microorganisms, making accurate diagnosis difficult. We evaluated the use of a polymerase chain reaction (PCR) protocol that was specific for the genus Mycobacterium, and specifically for Mycobacterium tuberculosis, Mycobacterium avium, and Mycobacterium intracellulare, for the identification of Mycobacterium sp growing on contaminated cultures. DESIGN: This prospective study was designed to identify Mycobacterium sp growing on mycobacterial cultures contaminated with other microorganisms.Samples and patients: Twenty-six samples, taken from 23 patients with probable mycobacterial disease, that resulted in Mycobacterium growth but were contaminated during their processing were evaluated in this study. Clinical data and the clinical status of each patient were used to ascertain the final diagnosis. RESULTS: All samples studied here exhibited Mycobacterium growth on solid media but were contaminated by nonfastidious bacteria, compromising the biochemical identification of the Mycobacterium sp. PCR correctly identified the genus Mycobacterium in all samples. M tuberculosis was identified in 14 samples, and M avium in 10 samples. No amplification of M intracellulare was obtained, and in two samples there was amplification only for the genus Mycobacterium. In the cultures of those patients in whom a mycobacterial infection was evident, PCR identified M avium and M tuberculosis in samples from 6 and 12 patients, respectively. However, PCR identified M avium (two patients) and M tuberculosis (two patients) in the cultures of four patients for whom a mycobacterial disease could not be confirmed by our case definition. Finally, in two samples from one patient only the genus Mycobacterium was amplified by PCR. CONCLUSION: PCR, with its advantages of greater speed and effectiveness than conventional detection methods, was successfully used to identify the Mycobacterium sp growing on contaminated cultures.  相似文献   
985.
Background: This study aims to evaluate the effect of one‐stage full‐mouth ultrasonic debridement (OSFMUD) on clinical and immunoinflammatory parameters in smokers with generalized aggressive periodontitis (GAgP). Methods: Fourteen smoking and 14 non‐smoking patients with GAgP were selected. After initial supragingival therapy, patients were treated by OSFMUD. Full‐mouth parameters evaluated were: 1) plaque index (PI); 2) bleeding scores (BS); 3) probing depth (PD); and 4) clinical attachment level (CAL). Clinical evaluation was performed, and gingival crevicular fluid (GCF) was collected for selected sites (ss) at baseline and 1, 3, and 6 months. GCF was analyzed via enzyme‐linked immunosorbent assay for: 1) receptor activator of nuclear factor‐κ B ligand (RANKL); 2) osteoprotegerin (OPG); 3) interleukin (IL)‐6; and 4) tumor necrosis factor (TNF)‐α, whereas secreted osteoclastogenic factor of activated T‐cells (SOFAT) was evaluated by Western blotting. Results: Significant reduction (P <0.05) was observed between baseline and 6 months for: 1) PI; 2) BS; and 3) PD, with no difference between smoking and non‐smoking patients (P >0.05). Regarding CAL, only non‐smoking patients showed a significant decrease (P <0.05). Significant reduction (P <0.05) was observed in both groups for: 1) PIss; 2) PDss; 3) bleeding on probing; and 4) relative CAL. Smoking and non‐smoking patients presented significantly decreased levels of IL‐6 and TNF‐α over time (P <0.05); however, no difference was observed between groups (P >0.05). RANKL was significantly different (P <0.05) only for non‐smokers at 6 months, whereas OPG was not significant (P >0.05). SOFAT expression was significantly lower (P <0.05) after OSFMUD for non‐smokers only. Conclusion: Considering the clinical and immunoinflammatory parameters evaluated in this short‐term follow‐up study, it can be concluded that OSFMUD can be used as an alternative treatment for smokers with GAgP.  相似文献   
986.
Pharmacologic inhibition of the renin-angiotensin system (RAS) is a widely accepted and effective treatment for hypertension. However, in the past several years, much attention has been focused on additional roles of the RAS including the possibility that its end-product, angiotensin II, could elicit end-organ pathologies independent of its effect on blood pressure. The ability to selectively delete genes in mice (by homologous recombination or gene knockouts) has led to new — and sometimes surprising — insights into the roles of the RAS in the developmental modeling and pathologic remodeling of the heart and blood vessels.  相似文献   
987.
OBJECTIVE: To identify risk factors for permanent and transient congenital hypothyroidism (CH). DESIGN: A population-based case-control study was carried out by using the network created in Italy for the National Register of Infants with CH. METHODS: Four controls were enrolled for each new CH infant; 173 cases and 690 controls were enrolled in 4 years. In order to distinguish among risk factors for permanent and transient CH, diagnosis was re-evaluated 3 years after enrollment when there was a suspicion of transient CH being present. Familial, maternal, neonatal and environmental influences were investigated. RESULTS: An increased risk for permanent CH was detected in twins by a multivariate analysis (odds ratio (OR) = 12.2, 95% confidence interval (CI): 2.4-62.3). A statistically significant association with additional birth defects, female gender and gestational age >40 weeks was also confirmed. Although not significant, an increased risk of CH was observed among infants with a family history of thyroid diseases among parents (OR = 1.9, 95% CI: 0.7-5.2). Maternal diabetes was also found to be slightly associated with permanent CH (OR = 15.7, 95% CI: 0.9-523) in infants who were large for gestational age. With regard to transient CH, intrauterine growth retardation and preterm delivery were independent risk factors for this form of CH. CONCLUSION: This study showed that many risk factors contribute to the aetiology of CH. In particular, our results suggested a multifactorial origin of CH in which genetic and environmental factors play a role in the development of the disease.  相似文献   
988.
The reliability of the assay of endogenous erythroid colony (EEC) formation in serum-free, cytokine-free collagen-based media was investigated in a multicentric study including 140 patients with polyglobuly (80 polycythemia vera (PV), 54 secondary erythrocytosis (SE), six idiopathic erythrocytosis (IE)) and 10 healthy donors. In each center, EEC assays were performed in parallel with progenitor cells from bone marrow (BM) and peripheral blood (PB); two commercialized media and 'low' and 'high' cell plating densities were tested. Negativity of EEC assays was considered certain only when sufficient BFU-E growth was obtained in control cultures with cytokines. In the two media, EEC formation was specific - never observed in cultures of healthy donors or SE patients - and comparable. BM EEC assays were positive (presence of eythroid colonies) for 75% ('low' plating) to 100% ('high' plating) of PV patients; PB EEC assays were positive for 83.3% ('low' plating) to 93.7% ('high' plating) of PV patients (differences not significant). Depending on the medium, 86.2-93.7% of patients with a positive BM EEC assay had a positive PB EEC assay. Hence, a standardized collagen-based EEC assay can be performed with either BM or PB progenitors; the EEC assay described here is positive for at least 75% of PV patients when a single EEC assay is performed, and for at least 94% of PV patients when both BM and PB EEC assays are performed.  相似文献   
989.
BACKGROUND/AIMS: Debate continues on whether serum and intrahepatic HCV viral loads are correlated and if HCV viral load correlates with the severity of liver disease. These difficulties may at least in part be linked to liver cell heterogeneity, when total liver extracts from HCV-infected individuals are tested for HCV RNA quantification. We have therefore investigated the feasibility of quantifying HCV replication using a laser-based microdissection technique. METHODS: We compared the results with those obtained for serum HCV RNA quantification and immunochemistry in the case of HCV antigen detection in the liver. Twenty-one HCV-positive patients with chronic active hepatitis (n=10) or cirrhosis (n=11) were analyzed. RESULTS: A positive correlation (P=0.0019) was observed between HCV RNA quantifications in sera and microdissected cells. Immunohistochemistry demonstrated that HCV antigen hepatocytes were randomly distributed within liver lobules. Their percentage varied in different patients (0-40%), but did not correlate with the HCV viral load. CONCLUSIONS: We have designed a sensitive methodology to evaluate the intrahepatic HCV viral load by combining a standardized RNA quantification method with microdissected hepatocytes from frozen liver needle biopsies. Our results directly demonstrate a positive correlation between serum and intrahepatic viral loads, which therefore provides a reliable reflection of intrahepatic HCV replication.  相似文献   
990.
Ikaros is a critical regulator of hematopoiesis. Its effects result in part from the balance between the isoforms that are produced by differential splicing of the pre-mRNA. Short isoforms that lack the DNA-binding domain act as dominant negatives by binding long isoforms through the C-terminal zinc-finger domain, which allows for the homo- or heterodimerization of the proteins. There are a number of evidences that different subsets of murine hematopoietic progenitors - as defined by phenotype - have different patterns of Ikaros expression. Forced expression of short isoforms (Ik5, Ik6 or Ik7) in murine or human hematopoietic progenitors alters the differentiation capacities of these cells. Human leukemias provide additional information: because of the blockade in differentiation, leukemias represent an equivalent of a particular stage of human hematopoietic hierarchy. We and others have shown that human acute leukemias are heterogeneous for the pattern of Ikaros isoform expression. The present study focused on adult de novo B ALLs and the Ikaros 6 isoform. ProB (BI, n=3), common B (BII, n=15) and preB (BIII, n=3) ALL were identified by their phenotype. RT-PCR and Western blot analyses of blast cell protein lysates suggest that approximately 50% of BII leukemias overexpress Ikaros 6 RNA and protein. Comparison of BII cells with high or normal levels of Ik6 shows a higher level of expression for the membrane stem cell antigen CD34 in the former, as detected with flow cytometry and confirmed with DNA arrays.  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