首页 | 官方网站   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   187336篇
  免费   10790篇
  国内免费   511篇
医药卫生   198637篇
  2023年   983篇
  2022年   2104篇
  2021年   4009篇
  2020年   2698篇
  2019年   3835篇
  2018年   5257篇
  2017年   3951篇
  2016年   3793篇
  2015年   4366篇
  2014年   6050篇
  2013年   7683篇
  2012年   11848篇
  2011年   12376篇
  2010年   6291篇
  2009年   5694篇
  2008年   9640篇
  2007年   10349篇
  2006年   9576篇
  2005年   9824篇
  2004年   9221篇
  2003年   8383篇
  2002年   6471篇
  2001年   5127篇
  2000年   5098篇
  1999年   4519篇
  1998年   1703篇
  1997年   1450篇
  1996年   1436篇
  1995年   1196篇
  1994年   1194篇
  1993年   1109篇
  1992年   2768篇
  1991年   2675篇
  1990年   2429篇
  1989年   2409篇
  1988年   2174篇
  1987年   2015篇
  1986年   1901篇
  1985年   1830篇
  1984年   1314篇
  1983年   1080篇
  1982年   639篇
  1981年   588篇
  1980年   562篇
  1979年   965篇
  1978年   655篇
  1977年   528篇
  1975年   575篇
  1974年   575篇
  1973年   567篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
Adipose tissue fatty acid composition, serum lipid profile, and dietary intake of 37 patients on maintenance hemodialysis were studied. In August 1982, 1984, and 1986, analyses were carried out in 15 normotriglyceridemic (NTG) and 22 hypertriglyceridemic (HTG; type IV hyperlipidemia) patients. No correlations were found between dietary intake of polyunsaturated fatty acids (PUFAs), ratio of polyunsaturated to saturated fatty acids (P-S ratio), and carbohydrate content on the one hand and serum lipid concentrations on the other in the two groups. Adipose tissue linolenic acid correlated negatively with serum cholesterol in both groups. Strong correlations were found between dietary intake of PUFAs and adipose tissue linoleic acid content, between PUFAs and the double-bond index, between P-S ratio and adipose tissue linoleic acid content, and between P-S ratio and the double-bond index. No significant differences in dietary intake or adipose tissue fatty acid composition were observed between NTG and HTG patients. Thus, no evidence was found for exogenous dietary influences on serum lipid concentrations. The adipose tissue linoleic acid content did reflect the dietary intake of PUFAs.  相似文献   
74.
OBJECTIVE.--To determine behavioral and demographic risk factors for human immunodeficiency virus (HIV) infection in central Africa. DESIGN.--Cross-sectional survey. SETTING.--Kigali, Rwanda. PARTICIPANTS.--A representative sample of 1458 childbearing women aged 19 to 37 years who were recruited from outpatient prenatal and pediatric clinics at the only community hospital in the city. MAIN OUTCOME MEASURE.--Antibodies to HIV assessed by enzyme immunoassay and confirmed by Western blot or indirect immunofluorescence. RESULTS.--The HIV seroprevalence was 32% overall. Infection rates were higher in women who were single, in those in steady relationships that began after 1981, and in the 33% of women reporting more than one lifetime sexual partner. Women in legal marriages or monogamous partnerships had lower rates of infection, but even low-risk women had prevalences on the order of 20%. History of venereal disease in the past 5 years, although the strongest risk factor in a multiple logistic analysis (odds ratio, 2.7; 95% confidence interval, 2.0 to 3.7), was reported by only 30% of those infected. Having a male sexual partner who drank alcohol or who had higher income were significant risk factors for HIV infection in the multivariate analysis, but use of oral contraceptives and having an uncircumcised partner were not. CONCLUSIONS.--The epidemic of the acquired immunodeficiency syndrome in Rwanda has spread beyond high-risk groups to the general population of women without known risk factors. For most of these women, a steady male partner is the source of their HIV risk and therefore a vital target for intervention efforts.  相似文献   
75.
A percentage of human T lymphocytes forms rosettes with autologous erythrocytes and this property has been considered as a marker for post-thymic precursor suppressor cells capable of providing suppression under the influence of inducer cells. We quantitated autologous rosette-forming T cells (ARFC) in the peripheral blood of 37 patients with chronic HBV infection: 8 healthy carriers, 9 chronic persistent hepatitis (CPH-B) and 20 chronic active hepatitis (CAH-B). Two control groups were studied, one consisting of 26 healthy individuals and the other of 8 individuals with non-HBV-associated CAH. Patients with non-HBV-associated CAH had a significant reduction in the proportion of ARFC, whereas CAH-B patients fell into 2 distinct patterns, one with increased and the other with decreased proportions of ARFC. This was unrelated to the degree of biochemical activity of the disease or to degree of viral replication as defined by HBeAg status and HBV-DNA in the serum. Healthy carriers and CPH-B had no changes in ARFC. Simultaneous quantitation of OKT4 and OKT8+ cells was done and a positive correlation was found between the proportions of ARFC and the proportions of OKT8+ cells. The possible significance of this correlation and the relevance of the bimodal distribution of autologous rosette-forming cells in CAH-B are discussed.  相似文献   
76.
77.
78.
OBJECTIVE: Outcomes analysis in congenital diaphragmatic hernia (CDH) requires a validated risk-adjustment tool. The purpose of this study was to use the Canadian Neonatal Network (CNN) database to validate the Score for Neonatal Acute Physiology, Version II (SNAP-II) for prediction of mortality among CDH infants admitted to a neonatal intensive care unit (NICU), and to compare this to the predictive equation recently developed by the Congenital Diaphragmatic Hernia Study Group (CDHSG). STUDY DESIGN: Infants with CDH in the CNN database were identified. Bivariate and multivariable logistic regression models were used to identify risk factors predictive of mortality. Model predictive performance and calibration were assessed using the area under the receiver operator characteristic curve and the technique of Hosmer-Lemeshow, respectively, and compared with the CDHSG predictive equation. RESULTS: There were 88 patients with CDH among 19,507 admissions to CNN hospitals. The mortality rate among CDH patients surviving to NICU admission was 17%, and 12.5% received extracorporeal membrane oxygenation therapy. Gestational age and admission SNAP-II score predicted mortality. Model predictive performance and calibration were optimized with these variables combined. The CDHSG equation was equally predictive of mortality, but was only marginally calibrated. CONCLUSIONS: SNAP-II is highly predictive of mortality among patients with CDH, and can be used to risk-adjust these patients.  相似文献   
79.
80.
To standardize the maximal static force (Fo) of the arm flexors, the accuracy of an anthropometric method for estimating the mid-arm cross-sectional muscle and bone area (MBA) was investigated. This was done by comparing the anthropometrically determined area (MBA.A) with the area measured by means of computerized tomography (MBA.S). In the same way, the accuracy of Heymsfield's equations (Heymsfield et al., 1982) for predicting MBA (MBA.H) from anthropometric measures was tested. MBA.A was significantly larger than MBA.S, the relative difference increasing with the thickness of the subcutaneous fat layer. This difference was attributed to a 27% underestimation of the fat layer thickness as measured with the skinfold caliper. Women being fatter than men, this caused the standardized maximal static force (Fo/MBA) to be lower in women than in men. MBA.H was 12% smaller than MBA.S. This may have been due to a difference in the way of measuring the arm circumference between the present authors and Heymsfield et al.  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-23

京公网安备 11010802026262号