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   2595638篇
  免费   204595篇
  国内免费   6333篇
耳鼻咽喉   34870篇
儿科学   86175篇
妇产科学   73006篇
基础医学   375140篇
口腔科学   74913篇
临床医学   241420篇
内科学   500060篇
皮肤病学   54237篇
神经病学   213447篇
特种医学   99192篇
外国民族医学   804篇
外科学   378114篇
综合类   62360篇
现状与发展   4篇
一般理论   958篇
预防医学   212751篇
眼科学   59023篇
药学   194521篇
  9篇
中国医学   5427篇
肿瘤学   140135篇
  2018年   27418篇
  2017年   21037篇
  2016年   23195篇
  2015年   26655篇
  2014年   36749篇
  2013年   56750篇
  2012年   77223篇
  2011年   81872篇
  2010年   48043篇
  2009年   45078篇
  2008年   76577篇
  2007年   80859篇
  2006年   81494篇
  2005年   79105篇
  2004年   76704篇
  2003年   73180篇
  2002年   71533篇
  2001年   116994篇
  2000年   120891篇
  1999年   102054篇
  1998年   28853篇
  1997年   26231篇
  1996年   25959篇
  1995年   25084篇
  1994年   23567篇
  1993年   22260篇
  1992年   83416篇
  1991年   81622篇
  1990年   79445篇
  1989年   76293篇
  1988年   70972篇
  1987年   69643篇
  1986年   66414篇
  1985年   63953篇
  1984年   48091篇
  1983年   41302篇
  1982年   24693篇
  1981年   21985篇
  1979年   45121篇
  1978年   31714篇
  1977年   26535篇
  1976年   25346篇
  1975年   26569篇
  1974年   32470篇
  1973年   31439篇
  1972年   28938篇
  1971年   27170篇
  1970年   25043篇
  1969年   23257篇
  1968年   21754篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.

Purpose

This study aimed to investigate 3 planning target volume (PTV) margin expansions and determine the most appropriate volume to be used in bladder preservation therapy when using daily cone beam computed tomography (CBCT). We aimed to establish whether a smaller PTV expansion is feasible without risking geographical miss.

Methods and materials

The study included patients with bladder cancer who were treated with a hypofractionated course of radiation therapy delivered with intensity modulated radiation therapy. The clinical target volume (CTV) was the whole empty bladder, and the PTV consisted of a 1.5-cm margin around the bladder (PTV1.5 cm). Patients underwent daily CBCT imaging before treatment to assess the bladder volume and ensure accurate positioning. We investigated 2 additional smaller PTV margin expansions to determine the most appropriate volume to be used with CBCT as a daily image guided radiation therapy modality. These margins were created retrospectively on every CBCT. The first additional volume was a uniform PTV margin of the surrounding 1 cm (PTV1 cm). When considering that the majority of the internal bladder movement was due to the variation in filling that occurs in the superior and anterior directions, a second volume of an anisotropic PTV margin with a 1.5-cm superior/anterior and 1 cm in other directions (PTV1/1.5 cm) was created. We recorded the frequency and measured the volume of bladder falling out of each PTV based on the daily CBCT.

Results

For the purpose of this study, we considered an arbitrary 5 cm3 of CTV falling out of the designated PTV as a clinically significant volumetric miss. The frequency of such a miss when applying the uniform PTV1 cm was 1%. However, when applying the uniform PTV1.5 cm and anisotropic PTV1/1.5 cm margins, the frequency was 0.5% and 0.5%, respectively.

Conclusions

The anisotropic PTV expansion of 1.5 cm superiorly and anteriorly and 1 cm in all other directions around the bladder (CTV) provides a safe PTV approach when daily CBCT imaging is used to localize an empty bladder.  相似文献   
172.
173.
174.
175.
176.
177.
178.
179.
180.
Thyroid diseases are common, and use of levothyroxine is increasing worldwide. We investigated the influence of gender, race and socioeconomic status on the diagnosis and treatment of thyroid disorders using data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil), a multicenter cohort study of civil servants (35-74 years of age) from six Brazilian cities. Diagnosis of thyroid dysfunction was by thyrotropin (TSH), and free thyroxine (FT4) if TSH was altered, and the use of specific medications. Multivariate logistic regression models were constructed using overt hyperthyroidism/hypothyroidism and levothyroxine use as dependent variables and sociodemographic characteristics as independent variables. The frequencies of overt hyper- and hypothyroidism were 0.7 and 7.4%, respectively. Using whites as the reference ethnicity, brown, and black race were protective for overt hypothyroidism (OR=0.76, 95%CI=0.64-0.89, and OR=0.53, 95%CI=0.43-0.67, respectively, and black race was associated with overt hyperthyroidism (OR=1.82, 95%CI=1.06-3.11). Frequency of hypothyroidism treatment was higher in women, browns, highly educated participants and those with high net family incomes. After multivariate adjustment, levothyroxine use was associated with female gender (OR=6.06, 95%CI=3.19-11.49) and high net family income (OR=3.23, 95%CI=1.02-10.23). Frequency of hyperthyroidism treatment was higher in older than in younger individuals. Sociodemographic factors strongly influenced the diagnosis and treatment of thyroid disorders, including the use of levothyroxine.  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