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   1675篇
  免费   127篇
  国内免费   2篇
耳鼻咽喉   16篇
儿科学   61篇
妇产科学   28篇
基础医学   246篇
口腔科学   5篇
临床医学   263篇
内科学   214篇
皮肤病学   18篇
神经病学   331篇
特种医学   24篇
外科学   93篇
综合类   5篇
一般理论   1篇
预防医学   289篇
眼科学   10篇
药学   106篇
肿瘤学   94篇
  2023年   14篇
  2022年   35篇
  2021年   61篇
  2020年   20篇
  2019年   46篇
  2018年   62篇
  2017年   44篇
  2016年   42篇
  2015年   54篇
  2014年   65篇
  2013年   90篇
  2012年   160篇
  2011年   152篇
  2010年   67篇
  2009年   67篇
  2008年   128篇
  2007年   113篇
  2006年   104篇
  2005年   97篇
  2004年   109篇
  2003年   91篇
  2002年   72篇
  2001年   5篇
  2000年   3篇
  1999年   10篇
  1998年   12篇
  1997年   4篇
  1996年   12篇
  1995年   3篇
  1994年   16篇
  1993年   8篇
  1992年   2篇
  1991年   2篇
  1990年   4篇
  1989年   2篇
  1988年   6篇
  1987年   4篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
  1977年   3篇
  1976年   1篇
  1974年   1篇
排序方式: 共有1804条查询结果,搜索用时 15 毫秒
1.
Research on physical activity (PA) by level of acculturation in Hispanic children is limited and findings have been mixed. We examined PA participation by primary language used with parents in a representative sample of 4th, 8th, and 11th grade Texas public school students. Mixed-effects regression models were conducted using cross-sectional data from the 2004–2005 School Physical Activity and Nutrition Study (n = 22,049). Self-reported PA was compared among three language-ethnic groups: Spanish-Hispanic (SH) (referent); English-Hispanic (EH); and English-Other (EO). EH and/or EO girls were generally between 1.25 and 2.58 [OR] times more likely to participate in PA across grade levels, with the largest differences found for school sports in 8th grade girls. EH and EO 8th grade boys were 1.71 (CI: 1.40, 2.10) and 2.06 (CI: 1.68, 2.51) times, respectively, more likely to participate in school sports. Findings indicate important disparities in Spanish-speaking Hispanic children’s PA participation.  相似文献   
2.
3.
Poverty influences health status, life expectancy, health behaviours, and use of health services. This study examined factors influencing the use of health-related services by people living in poverty. In the first phase, 199 impoverished users of health-related services in 2 large Canadian cities were interviewed by their peers. In the second phase, group interviews with people living in poverty (n = 52) were conducted. Data were analyzed using thematic content analysis. Diverse health-related services were used to meet basic and health needs, to maintain human contact, and to cope with life's challenges. Use of services depended on proximity, affordability, convenience, information, and providers' attitudes and behaviours. Use was impeded by inequities based on income status. To promote the health of people living in poverty, nurses and other health professionals can enhance the accessibility and quality of services, improve their interactions with people living in poverty, provide information about available programs, offer coordinated community-based services, collaborate with other sectors, and advocate for more equitable services and policies.  相似文献   
4.
BACKGROUND: Recently, epidemiological and clinical data have revealed important changes with regard to clinical adenovirus infection, including alterations in antigenic presentation, geographical distribution, and virulence of the virus. METHODS: In an effort to better understand the epidemiology of clinical adenovirus infection in the United States, we adopted a new molecular adenovirus typing technique to study clinical adenovirus isolates collected from 22 medical facilities over a 25-month period during 2004-2006. A hexon gene sequence typing method was used to characterize 2237 clinical adenovirus-positive specimens, comparing their sequences with those of the 51 currently recognized prototype human adenovirus strains. In a blinded comparison, this method performed well and was much faster than the classic serologic typing method. RESULTS: Among civilians, the most prevalent adenovirus types were types 3 (prevalence, 34.6%), 2 (24.3%), 1 (17.7%), and 5 (5.3%). Among military trainees, the most prevalent types were types 4 (prevalence, 92.8%), 3 (2.6%), and 21 (2.4%). CONCLUSIONS: For both populations, we observed a statistically significant increasing trend of adenovirus type 21 detection over time. Among adenovirus isolates recovered from specimens from civilians, 50% were associated with hospitalization, 19.6% with a chronic disease condition, 11% with a bone marrow or solid organ transplantation, 7.4% with intensive care unit stay, and 4.2% with a cancer diagnosis. Multivariable risk factor modeling for adenovirus disease severity found that age <7 years (odds ratio [OR], 3.2; 95% confidence interval [CI], 1.4-7.4), chronic disease (OR, 3.6; 95% CI, 2.6-5.1), recent transplantation (OR, 2.7; 95% CI, 1.3-5.2), and adenovirus type 5 (OR, 2.7; 95% CI, 1.5-4.7) or type 21 infection (OR, 7.6; 95% CI, 2.6-22.3) increased the risk of severe disease.  相似文献   
5.
6.
7.
8.
Rohon-Beard cells are large, mechanosensory neurons located in the dorsal spinal cord of anamniote vertebrates. In most species studied to date, these cells die during development. We followed labeled Rohon-Beard cells in living zebrafish embryos and found that they degenerate slowly, over many days. During degeneration, the soma shrinks and finally disappears, and the processes become beady in appearance and finally break apart, but they do not retract. Zebrafish Rohon-Beard cells apparently fragment their DNA, as revealed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) labeling, before undergoing degenerative morphologic changes. We also followed the development of labeled dorsal root ganglion neurons, as they are developing at the same stages that Rohon-Beard cells are degenerating. We found that, although axons of both cell types extend into similar regions, Rohon-Beard cells degenerate normally in mutants lacking dorsal root ganglia, providing evidence that interactions between the two cell types are not responsible for Rohon-Beard cell degeneration. Developmental Dynamics 229:30-41,2004.  相似文献   
9.
Summary. The Jamaican Perinatal Mortality Survey collected data that have been used in this paper to estimate: (1) the rate of multiple deliveries on the island; (2) the way in which this varies with demographic features; and (3) the causes of perinatal mortality among twins on the island.
The survey consisted of two phases: a study of all births in the months of September and October 1986 (the cohort months) and a study of all perinatal deaths in the 12 months from 1 September 1986 to 31 August 1987.
Among the 10408 pregnancies in the cohort months, 99(1.0%) were multiple pregnancies. The twinning rate showed statistically significant trends with maternal age and parity but no association with social factors.
Among the 2020 perinatal deaths occurring in the 12-month period, 173 (8.6%) were twins, with particularly high contribution to the Wigglesworth group 'deaths from immaturity'. Mortality rate of twins was significantly lower if mothers resided in areas where there were good obstetric and paediatric facilities.  相似文献   
10.
Summary. Data from the Jamaican Perinatal Mortality Survey had been used to create a statistical model using logistic regression.1 From this a simple additive scoring system to predict perinatal death was devised and tested on the 2 cohort months of the study.
The score had a theoretical range of 0–28 points, with the higher the score, the greater the likelihood of a perinatal death. For a cut-point of 7, sensitivity was 43% and specificity 84%. A cut-point of 8 resulted in 27% sensitivity and 94% specificity. Higher cut-points resulted in much reduced sensitivity but enhanced specificity (e.g. cut-point 10: 11% sensitivity, 99% specificity).
However, it is likely that these estimates are optimistically high, and to achieve unbiased estimates of sensitivity and specificity the score needs to be tested on a sample of the population from which it was not derived before implementation takes place. Meanwhile, the cut-off level for implementation will depend on appropriate resources available.  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