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   3483105篇
  免费   251708篇
  国内免费   8869篇
耳鼻咽喉   49393篇
儿科学   114187篇
妇产科学   97823篇
基础医学   497292篇
口腔科学   97512篇
临床医学   314875篇
内科学   682200篇
皮肤病学   82471篇
神经病学   285500篇
特种医学   135513篇
外国民族医学   952篇
外科学   518923篇
综合类   73308篇
现状与发展   5篇
一般理论   1295篇
预防医学   269966篇
眼科学   79750篇
药学   251263篇
  74篇
中国医学   6748篇
肿瘤学   184632篇
  2019年   26307篇
  2018年   37230篇
  2017年   28586篇
  2016年   32960篇
  2015年   39034篇
  2014年   53664篇
  2013年   80622篇
  2012年   104366篇
  2011年   110547篇
  2010年   67663篇
  2009年   65111篇
  2008年   103452篇
  2007年   109820篇
  2006年   111920篇
  2005年   107370篇
  2004年   103351篇
  2003年   98760篇
  2002年   94310篇
  2001年   162563篇
  2000年   166881篇
  1999年   140701篇
  1998年   41285篇
  1997年   36807篇
  1996年   37512篇
  1995年   36551篇
  1994年   33870篇
  1993年   31649篇
  1992年   111487篇
  1991年   107588篇
  1990年   104089篇
  1989年   100145篇
  1988年   92009篇
  1987年   90415篇
  1986年   85096篇
  1985年   81172篇
  1984年   61055篇
  1983年   51646篇
  1982年   30986篇
  1981年   27845篇
  1979年   54478篇
  1978年   38946篇
  1977年   32845篇
  1976年   30471篇
  1975年   32627篇
  1974年   38616篇
  1973年   36901篇
  1972年   34409篇
  1971年   31914篇
  1970年   29375篇
  1969年   28090篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.

Objectives

Arm swing is a distinctive characteristic of sprint-running with the arms working in a contralateral manner with the legs to propel the body in a horizontal direction. The purpose of this study was to determine the acute changes in kinematics and kinetics when wearable resistance (WR) of 1 kg (equivalent to ~1% body mass) was attached to each forearm during over ground short distance (20 m) maximal sprint-running.

Design

Cross-sectional study.

Methods

Twenty-two male amateur rugby athletes (19.4 ± 0.5 years; 97.0 ± 4.8 kg; 180.4 ± 7.2 cm) volunteered to participate in the study. Radar and Optojump were used to examine kinematic and kinetics between WR and unloaded sprint-running conditions.

Results

No significant (p < 0.05) differences were found at 2 m or 5 m between conditions, however, the WR condition resulted in a significant increase in 10 m, 20 m and 10–20 m split time (all, ~2%, small effect size) compared to the unloaded condition. Significant decreases were also found in theoretical maximum velocity (V0) (?1.4%, small effect size) and relative peak horizontal power production (Pmax) (?5.5%, small effect size). Step length (2.1%, small effect size) and contact time (6.5%, medium effect size) were significantly increased, while step frequency (?4.1%, small effect size) and flight time (?5.3%, medium effect size) were significantly decreased.

Conclusions

WR forearm loading provides a movement specific overload of the arms which significantly alters step kinematics and sprint times ≥10 m.  相似文献   
22.

Background

Epidemiology of patients with worsening heart failure and reduced ejection fraction (HFrEF) in the real-world setting is not well described.

Objectives

The purpose of this study was to describe incidence, clinical characteristics, treatment, and outcomes of patients with HFrEF who develop worsening heart failure (HF) in the real-world setting.

Methods

Data on patients with incident HFrEF from the National Cardiovascular Data Registry PINNACLE were linked to pharmacy, private practitioner, and hospital claims databases. Incidence, clinical characteristics, treatment (angiotensin-converting enzyme inhibitor/angiotensin receptor blocker, beta-blocker, and mineralocorticoid receptor antagonist) and outcomes of patients with worsening HF, defined as ≥90 days of stable HF with subsequent worsening requiring intravenous diuretic agents, were assessed.

Results

Of 11,064 HFrEF patients, 1,851 (17%) developed worsening HF on average 1.5 years following initial HF diagnosis. Patients who developed worsening HF were more likely to be African American, be octogenarians, and have higher comorbidity burden (p < 0.001). At the onset of worsening HF, 42.4% of patients were on monotherapy, 43.4% were on dual therapy, and 14.1% were on triple therapy. A total of 48%, 61%, and 98% of patients were on >50% target dose for angiotensin-converting enzyme inhibitor/angiotensin receptor blocker, beta-blocker, and mineralocorticoid receptor antagonist, respectively. The 2-year mortality rate was 22.5%, and 56% of patients were rehospitalized within 30 days of the worsening HF event.

Conclusions

In the real-world setting, 1 in 6 patients with HFrEF develop worsening HF within 18 months of HF diagnosis. These patients have a high risk for 2-year mortality and recurrent HF hospitalizations. The use of standard-of-care therapies both before and after the onset of worsening HF is low. With high unmet medical need, patients with worsening HF require novel treatment strategies as well as greater optimization of existing guideline-directed therapy.  相似文献   
23.
24.
25.
26.
This study aimed to evaluate changes in sleep during the COVID‐19 outbreak, and used data‐driven approaches to identify distinct profiles of changes in sleep‐related behaviours. Demographic, behavioural and psychological factors associated with sleep changes were also investigated. An online population survey assessing sleep and mental health was distributed between 3 April and 24 June 2020. Retrospective questions were used to estimate temporal changes from before to during the outbreak. In 5,525 Canadian respondents (67.1% females, 16–95 years old: Mean ± SD = 55.6 ± 16.3 years), wake‐up times were significantly delayed relative to pre‐outbreak estimates (p < .001,  = 0.04). Occurrences of clinically meaningful sleep difficulties significantly increased from 36.0% before the outbreak to 50.5% during the outbreak (all p < .001, g ≥ 0.27). Three subgroups with distinct profiles of changes in sleep behaviours were identified: “Reduced Time in Bed”, “Delayed Sleep” and “Extended Time in Bed”. The “Reduced Time in Bed” and “Delayed Sleep” subgroups had more adverse sleep outcomes and psychological changes during the outbreak. The emergence of new sleep difficulties was independently associated with female sex, chronic illnesses, being employed, family responsibilities, earlier wake‐up times, higher stress levels, as well as heavier alcohol use and television exposure. The heterogeneity of sleep changes in response to the pandemic highlights the need for tailored interventions to address sleep problems.  相似文献   
27.
28.
Though cerebrovascular complications of pregnancy remain relatively rare, they represent a potentially devastating event that necessitates prompt identification and treatment. Eighteen percent of strokes occurring in young women are linked to pregnancy. They occur mostly in the third trimester or during the post-partum period. Their biggest risk factors are hypertension, preeclampsia/eclampsia and migraine. Cerebrovascular events occurring during this period may involve specific pathophysiological processes that include embolic phenomena or endothelial dysfunction, but can also have common etiologies that are simply favored by the context of pregnancy. Thus, posterior encephalopathy and vasoconstriction cerebral syndrome are relatively frequently involved in cerebrovascular complications of pregnancy. Other very specific causes like amniotic fluid embolism or postpartum cardiomyopathy can also be responsible for such events. The management of stroke during pregnancy must be multidisciplinary and include a neurovascular expertise. Some conditions can lead to a long-life follow-up and modify the management of a future pregnancy.  相似文献   
29.
30.
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