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   2999篇
  免费   162篇
  国内免费   82篇
耳鼻咽喉   111篇
儿科学   119篇
妇产科学   81篇
基础医学   381篇
口腔科学   53篇
临床医学   307篇
内科学   672篇
皮肤病学   82篇
神经病学   237篇
特种医学   350篇
外科学   315篇
综合类   30篇
预防医学   121篇
眼科学   29篇
药学   178篇
中国医学   4篇
肿瘤学   173篇
  2021年   44篇
  2020年   36篇
  2019年   51篇
  2018年   59篇
  2017年   49篇
  2016年   37篇
  2015年   48篇
  2014年   67篇
  2013年   88篇
  2012年   103篇
  2011年   115篇
  2010年   99篇
  2009年   76篇
  2008年   105篇
  2007年   154篇
  2006年   105篇
  2005年   137篇
  2004年   122篇
  2003年   89篇
  2002年   81篇
  2001年   79篇
  2000年   98篇
  1999年   86篇
  1998年   103篇
  1997年   102篇
  1996年   123篇
  1995年   95篇
  1994年   104篇
  1993年   83篇
  1992年   58篇
  1991年   60篇
  1990年   48篇
  1989年   49篇
  1988年   56篇
  1987年   44篇
  1986年   48篇
  1985年   47篇
  1984年   20篇
  1983年   29篇
  1982年   21篇
  1981年   26篇
  1980年   21篇
  1979年   12篇
  1978年   17篇
  1977年   17篇
  1976年   15篇
  1975年   13篇
  1972年   12篇
  1971年   17篇
  1969年   15篇
排序方式: 共有3243条查询结果,搜索用时 31 毫秒
1.
The mechanisms linking tumor microenvironment acidosis to disease progression are not understood. Here, we used mammary, pancreatic, and colon cancer cells to show that adaptation to growth at an extracellular pH (pHe) mimicking acidic tumor niches is associated with upregulated net acid extrusion capacity and elevated intracellular pH at physiological pHe, but not at acidic pHe. Using metabolic profiling, shotgun lipidomics, imaging and biochemical analyses, we show that the acid adaptation-induced phenotype is characterized by a shift toward oxidative metabolism, increased lipid droplet-, triacylglycerol-, peroxisome content and mitochondrial hyperfusion. Peroxisome proliferator-activated receptor-α (PPARA, PPARα) expression and activity are upregulated, at least in part by increased fatty acid uptake. PPARα upregulates genes driving increased mitochondrial and peroxisomal mass and β-oxidation capacity, including mitochondrial lipid import proteins CPT1A, CPT2 and SLC25A20, electron transport chain components, peroxisomal proteins PEX11A and ACOX1, and thioredoxin-interacting protein (TXNIP), a negative regulator of glycolysis. This endows acid-adapted cancer cells with increased capacity for utilizing fatty acids for metabolic needs, while limiting glycolysis. As a consequence, the acid-adapted cells exhibit increased sensitivity to PPARα inhibition. We conclude that PPARα is a key upstream regulator of metabolic changes favoring cancer cell survival in acidic tumor niches.  相似文献   
2.
Transoral robotic surgery (TORS) is one of the main treatment options for non-locally advanced primary oropharyngeal cancer in the United States. However,  相似文献   
3.
4.
Xerophilic fungal species of the genus Aspergillus are economically highly relevant due to their ability to grow on low water activity substrates causing spoilage of stored goods and animal feeds. These fungi can synthesize a variety of secondary metabolites, many of which show animal toxicity, creating a health risk for food production animals and to humans as final consumers, respectively. Animal feeds used for rabbit, chinchilla and rainbow trout production in Argentina were analysed for the presence of xerophilic Aspergillus section Aspergillus species. High isolation frequencies (>60%) were detected in all the studied rabbit and chinchilla feeds, while the rainbow trout feeds showed lower fungal charge (25%). These section Aspergillus contaminations comprised predominantly five taxa. Twenty isolates were subjected to taxonomic characterization using both ascospore SEM micromorphology and two independent DNA loci sequencing. The secondary metabolite profiles of the isolates were determined qualitatively by HPLC-MS. All the isolates produced neoechinulin A, 17 isolates were positive for cladosporin and echinulin, and 18 were positive for neoechinulin B. Physcion and preechinulin were detected in a minor proportion of the isolates. This is the first report describing the detailed species composition and the secondary metabolite profiles of Aspergillus section Aspergillus contaminating animal feeds.  相似文献   
5.
6.

Background

The EQ-5D has been frequently used in national health surveys. This study is a head-to-head comparison to assess how expanding the number of levels from three (EQ-5D-3L) to five in the new EQ-5D-5L version has improved its distribution, discriminatory power, and validity in the general population.

Methods

A representative sample (N?=?7554) from the Catalan Health Interview Survey 2011–2012, aged ≥18, answered both EQ-5D versions, and we evaluated the response redistribution and inconsistencies between them. To assess validity of this redistribution, we calculated the mean of the Visual Analogue Scale (VAS), which measures perceived health. The discriminatory power was examined with Shannon Indices, calculated for each dimension separately. Spanish preference value sets were applied to obtain utility indices, examining their distribution with statistics of central tendency and dispersion. We estimated the proportion of individuals reporting the best health state in EQ-5D-5L and EQ-5D-3L within groups of specific chronic conditions and their VAS mean.

Results

A very small reduction in the percentage of individuals with the best health state was observed, from 61.8% in EQ-5D-3L to 60.8% in EQ-5D-5L. In contrast, a large proportion of individuals reporting extreme problems in the 3 L version moved to severe problems (level 4) in the 5 L version, particularly for pain/discomfort (75.5%) and anxiety/depression (66.4%). The average proportion of inconsistencies was 0.9%. The pattern of the perceived health VAS mean confirmed the hypothesis established a priori, supporting the validity of the observed redistribution. Shannon index showed that absolute informativity was higher in the 5 L version for all dimensions. The means (SD) of the Spanish EQ-5D-3L and EQ-5D-5L indices were 0.87 (0.25) and 0.89 (0.22). The proportion of individuals with the best health state within each specific chronic condition was very similar, regardless of the EQ-5D version (≤?30% in half of the 28 chronic conditions).

Conclusion

Although the proportion of individuals with the best possible health state is still very high, our findings support that the increase of levels provided by the EQ-5D-5L contributed to the validity and discriminatory power of this new version to measure health in general population, as in the national health surveys.
  相似文献   
7.
口咽鳞癌的临床处理仍存在争议,该文对口咽癌患者应用原发灶手术切除、颈淋巴清扫及术后行放疗的效果进行总结。对复合标准的211例患者进行回顾性研究。应用Kaplan—Meier曲线计算总生存率及无瘤生存率,应用单变量及多变量统计学分析研究疾病的临床特点与预后的关系。2年及5年的无瘤生存率分别为79.8%和68.8%.单因素分析表明,肿瘤切缘阳性是无瘤生存率重要也是唯一的预后因素。  相似文献   
8.

Background  

Scotland has high levels of untreated dental caries in primary teeth. The Hall Technique is a simplified method of managing carious primary molars using preformed metal crowns (PMCs) cemented with no local anaesthesia, caries removal or tooth preparation. This study compared the acceptability of the Hall Technique for children, their carers, and dentists, and clinical outcomes for the technique, with conventional restorations.  相似文献   
9.
A strong posteriorly directed force applied to the mandible resulting in fracture, can also displace the mandibular condyle towards the external auditory canal or superiorly against the mandibular fossa, causing its penetration into the middle cranial fossa or even the fracture of the temporal bone. We report the case of a 30-year-old male patient victim of a bicycle accident that developed facial expression muscles paralysis on the left side soon after the trauma. On physical examination he presented left side postauricular ecchymosis, diminished muscular tonus of the left mouth angle and difficulty to close the left eye, he did not present clinical signs of facial fractures. The neurological and CT scan examination revealed fracture of the left temporal bone with total facial expression muscles paralysis. The patient was referred to the neurosurgical team for evaluation and they opted for a conservative treatment. After 3 months the patient showed a marked improvement with almost normal facial expression muscle movements. The trauma dynamics and treatment details are discussed.  相似文献   
10.
PURPOSE: This article describes how the concept of platform switching has been incorporated into a new implant design as a method of reducing crestal bone loss and maintaining the gingival papillae. A 6-month study of the effects of this implant on bone loss is described. MATERIALS: Ten new platform switched implants were placed into fresh anterior maxillary extraction sites in 3 men and 7 women, ranging in age between 29 and 45 years old, and immediately provisionalized. The adjoining bone height was evaluated with digital radiography on the day after implant placement, and at 15 days, 1, 2, 3, and 6 months later. RESULTS: After 6 months, the mean bone loss on the mesial of the central-incisor implants was 0.05 mm. The mean bone loss was 0.07 mm on the distal of the central incisor implants, 0.07 mm on the mesial of the lateral-incisor implants, and 0.06 mm on the distal of the lateral-incisor implants. CONCLUSIONS: An implant design that incorporates the concept of platform switching is a simple and effective way to control circumferential bone loss around dental implants, helping to ensure a predictable esthetic result.  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