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   61491篇
  免费   3451篇
  国内免费   371篇
耳鼻咽喉   480篇
儿科学   1851篇
妇产科学   1642篇
基础医学   7800篇
口腔科学   1399篇
临床医学   5709篇
内科学   14173篇
皮肤病学   1175篇
神经病学   6501篇
特种医学   2182篇
外国民族医学   2篇
外科学   8073篇
综合类   222篇
一般理论   21篇
预防医学   4110篇
眼科学   991篇
药学   3701篇
  1篇
中国医学   96篇
肿瘤学   5184篇
  2024年   77篇
  2023年   630篇
  2022年   1236篇
  2021年   2186篇
  2020年   1280篇
  2019年   1813篇
  2018年   2122篇
  2017年   1496篇
  2016年   1757篇
  2015年   1962篇
  2014年   2719篇
  2013年   3428篇
  2012年   5098篇
  2011年   5094篇
  2010年   2669篇
  2009年   2474篇
  2008年   4251篇
  2007年   4013篇
  2006年   3788篇
  2005年   3672篇
  2004年   3214篇
  2003年   2884篇
  2002年   2606篇
  2001年   394篇
  2000年   281篇
  1999年   426篇
  1998年   479篇
  1997年   375篇
  1996年   318篇
  1995年   299篇
  1994年   264篇
  1993年   231篇
  1992年   190篇
  1991年   163篇
  1990年   150篇
  1989年   117篇
  1988年   103篇
  1987年   103篇
  1986年   100篇
  1985年   81篇
  1984年   115篇
  1983年   65篇
  1982年   93篇
  1981年   66篇
  1980年   64篇
  1979年   37篇
  1978年   45篇
  1977年   34篇
  1976年   27篇
  1972年   25篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Rheumatoid arthritis (RA) is a chronic multisystemic autoimmune disease, with an unclear etiopathogenesis. Its early diagnosis and activity assessment are essential to adjust the proper therapy. Among the different imaging techniques, ultrasonography (US) allows direct visualization of early inflammatory joint changes as synovitis, being also rapidly performed and easily accepted by patients. We propose an algorithm to semi-automatically detect synovial boundaries on US images, requiring minimal user interaction. In order to identify the synovia-bone and the synovia-soft tissues interfaces, and to tackle the morphological variability of diseased joints, a cascade of two different active contours is developed, whose composition corresponds to the whole synovial boundary.The algorithm was tested on US images acquired from proximal interphalangeal (PIP) and metacarpophalangeal (MCP) finger joints of 34 subjects. The results have been compared with a consensus manual segmentation. We obtained an overall mean sensitivity of 85 ± 13%, and a mean Dice's similarity index of 80 ± 8%, with a mean Hausdorff distance from the manual segmentation of 28 ± 10 pixels (approximately 1.4 ± 0.5 mm), that are a better performance than those obtained by the raters with respect to the consensus.  相似文献   
992.
The two essential requirements for pathologic specimens in the era of personalized therapies for non-small cell lung carcinoma (NSCLC) are accurate subtyping as adenocarcinoma (ADC) versus squamous cell carcinoma (SqCC) and suitability for EGFR molecular testing, as well as for testing of other oncogenes such as EML4-ALK and KRAS. Actually, the value of EGFR expressed in patients with NSCLC in predicting a benefit in terms of survival from treatment with an epidermal growth factor receptor targeted therapy is still in debate, while there is a convincing evidence on the predictive role of the EGFR mutational status with regard to the response to tyrosine kinase inhibitors (TKIs).This is a literature overview on the state-of-the-art of EGFR oncogenic mutation in NSCLC. It is designed to highlight the preclinical rationale driving the molecular footprint assessment, the progressive development of a specific pharmacological treatment and the best method to identify those NSCLC who would most likely benefit from treatment with EGFR-targeted therapy. This is supported by the belief that a rationale for the prioritization of specific regimens based on patient-tailored therapy could be closer than commonly expected.  相似文献   
993.
Introduction. Tourette syndrome (TS) is thought to be associated with striatal dysfunction. Changes within frontostriatal pathways in TS could lead to changes in abilities reliant on the frontal cortex. Such abilities include executive functions and aspects of social reasoning.

Methods. This study aimed to investigate executive functioning and Theory of Mind (ToM; the ability to reason about mental states, e.g., beliefs and emotions), in 18 patients with TS and 20 controls. A range of tasks involving ToM were used. These required participants to make judgements about mental states based on pictures of whole faces or the eyes alone, reason about humour in cartoons that featured sarcasm, irony or “slapstick” style humour, and make economic decisions. The executive measures assessed inhibition and verbal fluency.

Results. Patients with TS exhibited significantly poorer performance than controls on all four tasks involving ToM, even when patients with comorbid obsessive-compulsive disorder were excluded. These difficulties were despite no inhibitory deficits. Patients with TS exhibited impairment on the verbal fluency task but their performance on executive and ToM tasks was not related.

Conclusions. We propose that TS is associated with changes in ToM. The observed deficits could reflect dysfunction in frontostriatal pathways involving ventromedial prefrontal cortex.  相似文献   
994.
995.
996.
The isolation, biological activity and synthesis of natural furo[3,2-c]coumarins are presented, covering mainly the developments in the last 35 years. The most relevant approaches toward the synthesis of 2-substituted, 3-substituted and 2,3-disubstituted heterocycles are also discussed, with emphasis on the efficiency of the processes and their mechanisms.

The isolation, synthesis and biological activity of naturally occurring furo[3,2-c] coumarins carrying carbon substituents at C-2 and/or C-3, is discussed. Synthetic approaches toward the properly functionalized heterocyclic motif are also presented.  相似文献   
997.
The carbon–carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol. This mild, metal-free and experimentally simple reduction procedure displays considerable functional-group compatibility, products are obtained in good to excellent yields, and the use of toxic Se/CO mixture and NaSeH, or the smelly and air-sensitive benzeneselenol, is avoided.

The carbon–carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol.  相似文献   
998.
999.
Objective:To evaluate, using the finite element method, the orthodontic rotational movement of a lower second premolar obtained with clear aligners, analyzing different staging and attachment configurations.Materials and Methods:A CAD model including a complete lower dental arch (with element 4.5 mesially rotated 30°) and the corresponding periodontal ligaments, attachments, and aligner was designed and imported to finite element software. Starting from the CAD model, six projects were created to simulate the following therapeutic combinations for correcting element 4.5 position: (1) without attachments, (2) single attachment placed on the buccal surface of element 4.5, (3) three attachments placed on the buccal surfaces of teeth 4.4 to 4.6. For each project, both 1.2° and 3° of aligner activation were considered.Results:All the analyzed configurations revealed a clockwise rotation movement of element 4.5 on the horizontal plane. Models with attachments showed a greater tooth displacement pattern than models without attachments. Simulations with attachments and 3° of aligner activation exhibited the best performance concerning tooth movement but registered high stresses in the periodontal ligaments, far from the ideal stress levels able to produce tooth rotational movement.Conclusions:The model with a single attachment and 1.2° of aligner activation was the most efficient, followed by the three attachment model with the same degree of activation. Aligner activation should not exceed 1.2° to achieve better control of movement and reasonable stress in periodontal structures.  相似文献   
1000.
This study investigated the effect of ultrasonic activation of intracanal‐heated sodium hypochlorite (NaOCl) on its dentinal tubular penetration and root canal cleanliness in vitro. In experiment 1, mandibular premolars were randomly allocated to three groups (n = 8): group A, ultrasonic activation; group B, ultrasonic activation of intracanal‐heated NaOCl and group C, syringe‐and‐needle irrigation. Penetration of the fluorescent‐labelled NaOCl was investigated using light microscopy. In experiment 2, mandibular premolars were randomly allocated to group B or C (n = 10), for histological analysis of the remaining pulp tissue and debris. Data were statistically analysed using Kruskal–Wallis and Mann–Whitney tests (P = 0.05). The highest penetration of NaOCl was observed in group B, followed by group A (P < 0.05). Group B showed significantly less amount of debris than group C (P < 0.05). Dentinal tubule penetration of NaOCl and root canal cleanliness were significantly improved by ultrasonic activation of intracanal‐heated NaOCl.  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