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   5001篇
  免费   449篇
  国内免费   40篇
耳鼻咽喉   31篇
儿科学   115篇
妇产科学   119篇
基础医学   572篇
口腔科学   84篇
临床医学   473篇
内科学   944篇
皮肤病学   59篇
神经病学   241篇
特种医学   280篇
外科学   715篇
综合类   255篇
预防医学   467篇
眼科学   185篇
药学   368篇
  1篇
中国医学   96篇
肿瘤学   485篇
  2023年   48篇
  2022年   57篇
  2021年   96篇
  2020年   67篇
  2019年   109篇
  2018年   103篇
  2017年   95篇
  2016年   91篇
  2015年   130篇
  2014年   158篇
  2013年   204篇
  2012年   289篇
  2011年   280篇
  2010年   196篇
  2009年   193篇
  2008年   287篇
  2007年   290篇
  2006年   250篇
  2005年   267篇
  2004年   217篇
  2003年   214篇
  2002年   170篇
  2001年   123篇
  2000年   126篇
  1999年   125篇
  1998年   84篇
  1997年   70篇
  1996年   66篇
  1995年   46篇
  1994年   51篇
  1993年   42篇
  1992年   95篇
  1991年   79篇
  1990年   71篇
  1989年   73篇
  1988年   81篇
  1987年   75篇
  1986年   66篇
  1985年   58篇
  1984年   30篇
  1983年   31篇
  1982年   44篇
  1981年   26篇
  1980年   22篇
  1979年   20篇
  1978年   21篇
  1977年   18篇
  1976年   26篇
  1975年   15篇
  1974年   13篇
排序方式: 共有5490条查询结果,搜索用时 0 毫秒
11.
12.
Vaccination of normal adults with tetanus toxoid induced a two-three-fold rise in the frequency of IgM anti-IgG (rheumatoid factor, RF) B lymphocytes inducible by the polyclonal B cell activator, Epstein-Barr virus. The increase in IgM-RF precursors occurred earlier, was greater in magnitude, and was more sustained than the change in plasma IgM-RF. It was associated with a rise in total IgM levels, and correlated positively with the magnitude of the IgG anti-tetanus antibody response, but not with levels of circulating immune complexes. The ability of apparently innocuous infections and immunizations to increase the frequency of IgM-RF precursor B lymphocytes may be the reason for the previously noted expansion in this autoreactive B cell pool between birth and adulthood.  相似文献   
13.
Multipotent, self-renewing stem and progenitor cells isolated from the mammalian central nervous system (CNS) have been shown to survive as allografts following transplantation to sites throughout the neuraxis. However, studies of this type shed little light upon the immunologic properties of the cells themselves, primarily because little is learned about the intrinsic immunogenic properties of a cell when it is grafted into an immune-privileged site. We have therefore investigated the immunogenic and antigenic properties of CNS progenitor cells by grafting them into a conventional (i.e., non-immune-privileged) site, namely, beneath the kidney capsule. Our results indicate that allogeneic CNS progenitor cells survive at least 4 weeks in a conventional site, during which time they neither sensitize their hosts nor express detectable levels of major histocompatibility complex (MHC) class I or II. These in vivo data are in accord with flow cytometric results showing that CNS progenitor cells do not express MHC class I or class II, either at baseline or upon differentiation in 10% serum. Exposure to interferon gamma, however, reversibly upregulates expression of these key transplantation antigens. Together, these results reveal CNS progenitor cells to possess inherent immune privilege. Since CNS progenitor cell allografts were rejected beneath the kidney capsule following specific sensitization of the host, CNS progenitor cells were able to display alloantigens, albeit not in an immunogenic form.  相似文献   
14.
15.
Annals of Surgical Oncology - Long-term pancreatoduodenectomy (PD) survivors have previously reported favorable quality of life (QoL). However, there has been a paucity of studies utilizing...  相似文献   
16.
17.
7例尿毒症贫血患者在自发急性缺氧状态下,其血清红细胞生成素(EPO)浓度显著提高(平均7倍),且与PO2呈负相关。缺氧状态纠正后血清EPO浓度下降。提示尿毒症贫血患者的EPO氧依赖调控系统功能尚存在,但处于不敏感的低调状态。进一步了解其机遇,则可能通过促进内源性EPO的生成,有助于悄毒症贫血的治疗。  相似文献   
18.
According to the 1990 census, the highly diverse Asian and Pacific Islander (API) American population has doubled in size from 1980 to 1990, and is now the nation's fastest growing minority group. Several studies have documented this population's comparative underuse of mental health services. A review of recent studies on the mental health of Asian and Pacific Island elders identifies a number of risk factors and protectors. Elder APIs appear to have poorer mental health compared to white counterparts, but not the poorest mental health within their own ethnic group. Within-group differences emerge, with recent immigrant groups and colonized populations appearing as most at-risk for mental health problems. A critical variable on this population's mental health status appears to be socioeconomic status,and yet an analysis of other demographic variables, notably nativity and gender, remain contradictory. A research agenda is proposed and implications for mental health administrators are suggested.  相似文献   
19.
These studies were designed to test the hypolipidemic activity of green tea epicatechins (GTE) isolated from jasmine green tea. In Experiment 1, three groups of hamsters were given a semisynthetic diet containing 200 g lard/kg and 1 g cholesterol/kg for 4 wk. The control group received distilled water, and the other two groups received either 15 g/L green tea water extract (GTWE) or 5.0 g/L GTE solution. Both the GTWE and GTE groups had lower concentrations of serum total cholesterol (TC) and triacylglycerols (TG) than the controls (P < 0.05). In Experiment 2, four groups of hamsters received tap water as the drinking fluid, but they were given the same high fat and cholesterol diet supplemented with 0 (control), 1.1, 3.4 or 5.7 g GTE/kg diet. The hypolipidemic effect of jasmine GTE was dose dependent. In Experiment 3, the time-course of changes in serum TC and TG was monitored in hamsters given the high fat diet supplemented with 5.7 g GTE/kg in comparison with that of controls. The hypolipidemic effects of dietary GTE were evident after feeding for 2 wk. Dietary supplementation of GTE did not affect liver fatty acid synthase. However, GTE-supplemented hamsters had higher fecal excretions of total fatty acids, neutral sterols and acidic sterols compared with the control group. In Experiment 4, hamsters were fed nonpurified diet; the control group drank distilled water, and the GTE group drank distilled water containing 5.0 g GTE/L. No differences in activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and intestinal acyl CoA:cholesterol acyltransferase were observed. This study suggests that the hypolipidemic activity of GTE is not due to inhibition of synthesis of cholesterol or fatty acid but is most likely mediated by its influence on absorption of dietary fat and cholesterol.  相似文献   
20.
PURPOSE: To determine and compare the diagnostic performance of fetal middle cerebral (MCA), renal (RA), and umbilical (UA) arterial Doppler ultrasonography (US) for prediction of adverse perinatal outcome in suspected intrauterine growth restriction (IUGR). MATERIALS AND METHODS: Two hundred ninety-three small-for-gestational age fetuses (24-39 weeks at recruitment and US-estimated weight or abdominal circumference below 10th percentile) were prospectively examined with Doppler US of the UA, MCA, and RA. Clinicians were blinded to MCA and RA Doppler measurements. RESULTS: Seventy-six fetuses (25.9%) had at least one major or minor adverse perinatal outcome. Major outcomes included stillbirth, neonatal death, neurologic complication, and necrotizing enterocolitis. The MCA pulsatility index (PI), compared with the UA PI and RA PI, was more sensitive (72.4% vs 44.7% and 8.3%) but less specific (58.1% vs 86.6% and 92.6%) in predicting adverse outcome. The UA PI had the highest positive likelihood ratio (ratio, 3.3); the MCA PI had the lowest negative likelihood ratio (ratio, 0.48). When gestational age at the first Doppler US examination was less than 32 weeks, the MCA PI had a sensitivity of 95.5% and negative predictive value of 97.7% for major adverse outcome (negative likelihood ratio, 0.10). CONCLUSION: In suspected IUGR, while an abnormal UA PI is a better predictor of adverse perinatal outcome than an abnormal MCA or RA PI, a normal MCA PI may help to identify fetuses without major adverse perinatal outcome, especially before 32 weeks gestational age.  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