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   652篇
  免费   39篇
  国内免费   2篇
耳鼻咽喉   2篇
儿科学   41篇
妇产科学   5篇
基础医学   59篇
口腔科学   13篇
临床医学   48篇
内科学   114篇
皮肤病学   27篇
神经病学   20篇
特种医学   63篇
外科学   54篇
综合类   49篇
预防医学   62篇
眼科学   1篇
药学   46篇
肿瘤学   89篇
  2023年   3篇
  2022年   7篇
  2021年   17篇
  2020年   5篇
  2019年   8篇
  2018年   15篇
  2017年   7篇
  2016年   14篇
  2015年   13篇
  2014年   22篇
  2013年   19篇
  2012年   41篇
  2011年   45篇
  2010年   28篇
  2009年   18篇
  2008年   37篇
  2007年   27篇
  2006年   29篇
  2005年   34篇
  2004年   18篇
  2003年   21篇
  2002年   17篇
  2001年   20篇
  2000年   13篇
  1999年   13篇
  1998年   20篇
  1997年   25篇
  1996年   21篇
  1995年   14篇
  1994年   8篇
  1993年   9篇
  1992年   5篇
  1991年   3篇
  1990年   4篇
  1989年   10篇
  1988年   6篇
  1987年   7篇
  1986年   8篇
  1985年   19篇
  1984年   8篇
  1983年   3篇
  1982年   6篇
  1981年   7篇
  1980年   5篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1975年   2篇
  1949年   1篇
排序方式: 共有693条查询结果,搜索用时 875 毫秒
621.
OBJECTIVES/HYPOTHESIS: Promoter hypermethylation of tumor suppressor genes is common in head and neck cancer as well as other primary cancers resulting in epigenetic gene silencing. Tissue inhibitor of metalloproteinase-3 (TIMP-3) has been shown to have promoter hypermethylation in several solid tumors, but has not been identified in head and neck squamous cell carcinoma (HNSCC). Our objective was to determine if TIMP-3 promoter was hypermethylated in HNSCC, if there was any correlation with death associated protein kinase (DAPK), a tumor suppressor whose promoter has been hypermethylated at high levels in HNSCC, and if any clinical factors influence hypermethylation of either of these genes. STUDY DESIGN: Prospective study. METHODS: Tumor samples from 124 patients with HNSCC were evaluated for promoter hypermethylation for TIMP-3 and DAPK using quantitative methylation specific polymerase chain reaction (qMSP). We compared both TIMP-3 and DAPK hypermethylation in HNSCC with each other as well as with other clinical variables. RESULTS: We found that TIMP-3 was hypermethylated in approximately 71.8% of the tumor samples and DAPK was hypermethylated in 74.2%. The presence of TIMP-3 and DAPK promoter hypermethylation was significantly higher than in control specimens. More importantly, TIMP-3 and DAPK hypermethylations in these samples were highly correlated with a concordance of 78% (P < .001). DAPK was also correlated with current alcohol consumption (P < .028), but neither TIMP-3 nor DAPK hypermethylation was significantly correlated with other clinical variables or with survival. CONCLUSION: TIMP-3 promoter hypermethylation is elevated in HNSCC and is highly correlated with DAPK hypermethylation, implying a functional relationship between these genes.  相似文献   
622.
BACKGROUND: Yellow nail syndrome (YNS) is characterized by the triad of characteristic nail changes, chronic respiratory disorders and primary lymphoedema. Over 100 cases have been published, most of which have been sporadic. Despite this, YNS is classified as a dominantly inherited lymphoedema with variable expression. There have been only a few published reports where a positive family history (FH) has been documented in cases of YNS. OBJECTIVES: To conduct a retrospective survey investigating the genetic basis of YNS. METHODS: The notes of 11 patients diagnosed with YNS were examined for documentation of a positive FH, and in addition a postal questionnaire was sent to these patients. RESULTS: Only one of the 11 patients had a relevant FH. In addition, four patients had complete recovery of their nail changes. CONCLUSIONS: This is the first retrospective study of YNS to document clear remission of nail changes. The lack of a positive FH in the majority of patients in our study, the late onset of the disease and recovery of nail changes in our patients suggest that YNS may not be primarily a genetic disease as it is currently classified.  相似文献   
623.

Objectives  

Indoor air pollution levels are reported to be higher with biomass fuel, and a number of respiratory diseases in children are associated with pollution from burning such fuel. However, little is known about the situation in developing countries. The aim of the study was to compare indoor air pollution levels and prevalence of symptoms in children between biomass- and fossil-fuel-using households in different seasons in Bangladesh.  相似文献   
624.
Mitochondria-encoded Cytochrome B (CYTB) gene mutations were reported in different cancers, but the effect of these mutations on cellular metabolism and growth is unknown. In a murine xenograft and human model of bladder cancer, we show the functional effect of overexpression of a 21-bp deletion mutation (mt) of CYTB. Overexpression of mtCYTB generated increased reactive oxygen species (ROS) accompanied by increased oxygen consumption and lactate production. MtCYTB overexpression induced significant tumor growth in vitro and in vivo by triggering rapid cell cycle progression through up-regulation of the nuclear factor-kappa B2 signaling pathway. Tumor-generated ROS induced in vitro lysis of normal splenocytes. Thus, we present physiologic and functional evidence for the role of a bona fide mitochondrial gene mutation in cancer.  相似文献   
625.
DNA methylation has a role in mediating epigenetic silencing of CpG island genes in cancer and other diseases. Identification of all gene promoters methylated in cancer cells "the cancer methylome" would greatly advance our understanding of gene regulatory networks in tumorigenesis. We previously described a new method of identifying methylated tumor suppressor genes based on pharmacologic unmasking of the promoter region and detection of re-expression on microarray analysis. In this study, we modified and greatly improved the selection of candidates based on new promoter structure algorithm and microarray data generated from 20 cancer cell lines of 5 major cancer types. We identified a set of 200 candidate genes that cluster throughout the genome of which 25 were previously reported as harboring cancer-specific promoter methylation. The remaining 175 genes were tested for promoter methylation by bisulfite sequencing or methylation-specific PCR (MSP). Eighty-two of 175 (47%) genes were found to be methylated in cell lines, and 53 of these 82 genes (65%) were methylated in primary tumor tissues. From these 53 genes, cancer-specific methylation was identified in 28 genes (28 of 53; 53%). Furthermore, we tested 8 of the 28 newly identified cancer-specific methylated genes with quantitative MSP in a panel of 300 primary tumors representing 13 types of cancer. We found cancer-specific methylation of at least one gene with high frequency in all cancer types. Identification of a large number of genes with cancer-specific methylation provides new targets for diagnostic and therapeutic intervention, and opens fertile avenues for basic research in tumor biology.  相似文献   
626.
Cases of congenital double anus are very rare. The number of cases of hindgut duplication of all kinds is slightly higher, and some series include patients with genitourinary and genitalia duplications but with a single anus. However, double termination with tubular duplication is rarely heard of. We report on the case of a patient with 2 well-formed ani, total colon duplication, and 2 vaginas.  相似文献   
627.
628.
629.
630.
Andrade-Souza YM  Schwalb JM  Hamani C  Hoque T  Saint-Cyr J  Lozano AM 《Surgical neurology》2005,63(4):357-62; discussion 362-3
OBJECTIVE: The study aims to compare 2-dimensional (2D) and 3-planar (3P) reconstruction magnetic resonance imaging (MRI) methods of targeting the optimal region of the subthalamic nucleus (STN) for chronic stimulation in patients with Parkinson disease. METHODS: We studied 14 patients with Parkinson disease treated with bilateral STN deep brain stimulation (DBS) (28 STN targets). Electrode implantation was based on direct and indirect targeting based upon the position of the anterior and posterior commissures using 2D MRI, with selection of the final target based on microelectrode recording. Optimal settings, including the contacts used, were determined during the clinical follow-up. The position of the best contact was defined with postoperative MRI. Optimal contact position was compared to targets calculated by the direct method from the preoperative 2D MRI and 3P reconstruction. Optimal contact position was also compared to the indirect targets calculated from the preoperative 2D MRI and 3P reconstruction. The distance between the targets and the position of the best contact were calculated. RESULTS: The mean improvement in OFF-period Unified Parkinson Disease Rating Scale III subscores with STN DBS was 52%. The mean distance between the optimal contact position and the direct target was 4.66 mm (SD = 1.33) using the 2D MRI and 3.49 mm (SD = 1.29) using the 3P reconstruction (t test, P < .001). The mean distance between the optimal contact and the indirect target was 3.42 mm (SD = 1.34) using the 2D MRI and 2.61 mm (SD = 0.97; t test, P = .001) using the 3P reconstruction. The variance of the direct target was less using the 3P reconstruction than using the 2D MRI (F test, P = .002), indicating greater precision. Similarly, the variance of the indirect target using the 3P reconstruction was less than using the 2D MRI (F test, P = .012). CONCLUSION: Indirect and direct targets chosen using 3P reconstruction more closely approximate the position of the clinically optimal contact than targets chosen using 2D MRI.  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