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   1820篇
  免费   97篇
  国内免费   22篇
耳鼻咽喉   3篇
儿科学   153篇
妇产科学   57篇
基础医学   195篇
口腔科学   47篇
临床医学   177篇
内科学   406篇
皮肤病学   24篇
神经病学   37篇
特种医学   470篇
外科学   110篇
综合类   47篇
一般理论   2篇
预防医学   74篇
眼科学   13篇
药学   58篇
中国医学   7篇
肿瘤学   59篇
  2023年   3篇
  2022年   6篇
  2021年   13篇
  2020年   19篇
  2019年   13篇
  2018年   27篇
  2017年   14篇
  2016年   28篇
  2015年   35篇
  2014年   32篇
  2013年   76篇
  2012年   36篇
  2011年   44篇
  2010年   81篇
  2009年   56篇
  2008年   38篇
  2007年   32篇
  2006年   40篇
  2005年   36篇
  2004年   31篇
  2003年   25篇
  2002年   22篇
  2001年   14篇
  2000年   21篇
  1999年   25篇
  1998年   133篇
  1997年   119篇
  1996年   124篇
  1995年   92篇
  1994年   74篇
  1993年   81篇
  1992年   22篇
  1991年   21篇
  1990年   15篇
  1989年   59篇
  1988年   45篇
  1987年   50篇
  1986年   45篇
  1985年   48篇
  1984年   24篇
  1983年   31篇
  1982年   34篇
  1981年   20篇
  1980年   36篇
  1979年   14篇
  1978年   15篇
  1977年   17篇
  1976年   23篇
  1975年   24篇
  1966年   2篇
排序方式: 共有1939条查询结果,搜索用时 0 毫秒
1.
Pediatric knee MR imaging: pattern of injuries in the immature skeleton   总被引:3,自引:0,他引:3  
  相似文献   
2.
3.
Abstract: Background : Despite extensive literature on the topic, it is uncertain if grand (para ≥ 5) and great grand (para ≥ 10) multiparity are associated with adverse birth outcomes. We critically evaluate the evidence for and against the existence of adverse maternal and/or fetal outcomes in high parity women. Methods : An electronic search of MEDLINE and other bibliographic databases (Current Contents, EMBASE, and CAB) was conducted, and all relevant articles in English language were retrieved. Results : Findings on the association between high parity and maternal‐fetal birth outcomes are not consistent. Although the older literature tends to suggest that multiparity is a risk factor for negative birth outcomes, more recent reports are not supportive. Comparison across studies was further complicated by confounding factors like maternal age, socioeconomic status, and levels of prenatal care, as well as by variations in study designs and in the definition of parity itself. Furthermore, most studies that examined women of extreme parity (para ≥ 10) were handicapped by inadequate power. Conclusions : After accounting for quality, culture, and degrees of associations, the preponderance of evidence seems to point to possible existence of heightened risk for certain medical complications and placental pathologies among women of extreme parity. The literature also provides reasonable evidence for a higher‐than‐expected likelihood for occurrence of fetal macrosomia with advanced parity.  相似文献   
4.
We report an adult female with a rare giant choledochal cyst. The patient presented following a normal pregnancy with the classical triad of an abdominal mass associated with jaundice and right upper quadrant abdominal pain. The cyst was excised using an intramural technique and biliary reconstruction achieved with a Roux-en-Y hepaticojejunostomy. Our patient has remained well with no evidence of malignancy over a 12 year review period. The aetiology and current management of this condition are discussed.  相似文献   
5.
6.
Na+ dependence of in vitro pancreatic amylase release   总被引:1,自引:0,他引:1  
  相似文献   
7.
The objective was to test the hypothesis that the optimal cryoprotective agent for cryopreservation of human spermatozoa would be a solute for which cells have the highest plasma membrane permeability, resulting in the least amount of volume excursion during its addition and removal. To test this hypothesis, theoretical simulations were performed using membrane permeability coefficients to predict optimal procedures for the addition and removal of a cryoprotectant. Simulations were performed using data from four different cryoprotectants: (i) glycerol, (ii) dimethyl sulphoxide, (iii) propylene glycol and (iv) ethylene glycol. Thermodynamic formulations were applied to determine approaches for the addition and removal of 1 M and 2 M final concentrations of cryoprotectant, allowing the spermatozoa to maintain a cell volume within their osmotic tolerance limits. Based on these data, ethylene glycol was predicted to be optimal for minimizing volume excursions among the solutes evaluated. These predictions were then experimentally tested using glycerol as the control cryoprotectant and ethylene glycol as the experimental cryoprotectant. The results indicate that there was a higher (P < 0.05) recovery of motile spermatozoa after cryopreservation when using 1 M ethylene glycol than with 1 M glycerol, supporting the hypothesis that use of the cryoprotectant for which the cell has the highest permeability will result in higher cell survival.   相似文献   
8.
BACKGROUND: The diagnosis of hepatitis B virus (HBV) has until recently been based on traditional serologic methods targeting viral antigens and antibodies to viral proteins. The development of molecular methods allowing for the quantitation of HBV DNA is proving clinically valuable for monitoring therapy and detecting early treatment failures. OBJECTIVES: Here we report a new real-time (LightCycler) quantitative PCR for the detection of HBV DNA based on sequence specific hybridisation probes (designed in-house), targeting the HBV surface antigen. STUDY DESIGN: The assay was evaluated using a 10-fold dilution series of standard HBV DNA [Eurohep standard reference 1, genotype A, HBsAg subtype adw with a unitage of 10(6) WHO. i.u./ml] and 89 clinical serum samples. The performance was measured against a quantified standard HBV DNA working reagent (NIBSC code 98/780) and the sensitivity compared with our conventional thermal-block PCR. RESULTS AND CONCLUSION: Real-time PCR detected HBV DNA in 45% (40/89) and thermal-block PCR in 16% (14/75) of clinical samples. Results for 26 samples were below the detection limit of the thermal-block PCR but could be quantified by real-time (LightCycler) PCR. The LightCycler assay was at least 5 logs more sensitive than thermal-block PCR and could detect HBV in a linear range between 5 and 10(7) i.u. per reaction. The broad generic nature of the PCR primers coupled with the enhanced sensitivity and specificity of the fluorescent hybridisation probes makes this assay potentially valuable for both routine diagnostic and epidemiological work.  相似文献   
9.
A total of 447 cervical or vaginal specimens were inoculated in parallel onto peptone-starch-dextrose (PSD) and Columbia colistin (10 mg/ml)-nalidixic acid (15 mug/ml) (CNA) agar and were incubated for 48 h at 35 degrees C in an atmosphere with 2 to 10% CO2. One hundred (22.4%) of the cultures were positive for Haemophilus vaginalis. Forty-eight of the isolates were recovered from both PSD and Columbia CNA agar, five from PSD only, and 47 from Columbia CNA agar only (P less than 0.001). On Columbia CNA agar, 76 of the isolates were detected after 24 h of incubation, and the remainder were detected within 4 days of incubation.  相似文献   
10.
Healthcare for the elderly population presents enormous challenges, which are further complicated by ethnicity-related socioeconomic disparities in the United States. We set out to determine the predictors of hospital admissions in the elderly by conducting a retrospective cohort analysis of a nationally representative sample of community-dwelling individuals aged 70 and older in 1984 (n = 7541). Multivariate logistic regression analysis of data from the Longitudinal Study on Aging revealed that race, health status, type of family relationship, and activities of daily living (ADL) are significant predictors of hospitalization among the elderly. Older blacks are less likely to be admitted into the hospital, compared to their white counterparts (OR 0.68, 95%CI 0.52-0.89). Elderly persons who perceive their health status as being fair or poor are three times as likely to be hospitalized than those who perceived their health status as excellent (OR 2.99, 95%CI 2.15-4.15). Those with impairment in activities of daily living are twice as likely to be confined to the hospital than those without impairment (OR 1.78, 95%CI 1.64-1.96). Elderly persons living with nonrelatives are three times as likely to be admitted for short hospital stays than those living with spouses (OR 2.90, 95%CI 1.44-5.82). Future identification of predictors of hospital admissions in the elderly may help characterize those at risk and perhaps allow for focused and timely intervention.  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