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   5225篇
  免费   596篇
  国内免费   19篇
耳鼻咽喉   82篇
儿科学   209篇
妇产科学   87篇
基础医学   770篇
口腔科学   209篇
临床医学   504篇
内科学   1173篇
皮肤病学   83篇
神经病学   270篇
特种医学   349篇
外科学   684篇
综合类   215篇
一般理论   1篇
预防医学   509篇
眼科学   36篇
药学   350篇
中国医学   41篇
肿瘤学   268篇
  2021年   67篇
  2020年   54篇
  2019年   69篇
  2018年   95篇
  2017年   62篇
  2016年   74篇
  2015年   116篇
  2014年   136篇
  2013年   181篇
  2012年   246篇
  2011年   243篇
  2010年   195篇
  2009年   166篇
  2008年   193篇
  2007年   211篇
  2006年   194篇
  2005年   199篇
  2004年   171篇
  2003年   163篇
  2002年   165篇
  2001年   164篇
  2000年   180篇
  1999年   144篇
  1998年   89篇
  1997年   100篇
  1996年   97篇
  1995年   84篇
  1994年   68篇
  1993年   68篇
  1992年   96篇
  1991年   114篇
  1990年   116篇
  1989年   126篇
  1988年   107篇
  1987年   86篇
  1986年   107篇
  1985年   99篇
  1984年   64篇
  1983年   90篇
  1982年   43篇
  1981年   59篇
  1980年   47篇
  1979年   66篇
  1978年   48篇
  1977年   45篇
  1976年   45篇
  1975年   51篇
  1973年   52篇
  1972年   45篇
  1969年   35篇
排序方式: 共有5840条查询结果,搜索用时 803 毫秒
81.
AIM: To examine the relation between the duration of breast feeding and morbidity as a result of respiratory illness and infection in the first year of life. METHODS: Prospective birth cohort study of 2602 live born children ascertained through antenatal clinics at the major tertiary obstetric hospital in Perth, Western Australia. Main outcome measures were hospital, doctor, or clinic visits, and hospital admissions for respiratory illness and infection in the first year of life. Main exposure measures were the duration of predominant breast feeding (defined as the age other milk was introduced) and partial (any) breast feeding (defined as the age breast feeding was stopped). Main confounders were gender, gestational age less than 37 weeks, smoking in pregnancy, older siblings, maternal education, and maternal age. RESULTS: Hospital, doctor, or clinic visits for four or more upper respiratory tract infections were significantly greater if predominant breast feeding was stopped before 2 months or partial breast feeding was stopped before 6 months. Predominant breast feeding for less than six months was associated with an increased risk for two or more hospital, doctor, or clinic visits and hospital admission for wheezing lower respiratory illness. Breast feeding for less than eight months was associated with a significantly increased risk for two or more hospital, doctor, or clinic visits or hospital admissions because of wheezing lower respiratory illnesses. CONCLUSIONS: Predominant breast feeding for at least six months and partial breast feeding for up to one year may reduce the prevalence and subsequent morbidity of respiratory illness and infection in infancy.  相似文献   
82.
Anterior fusion for idiopathic scoliosis   总被引:18,自引:0,他引:18  
Majd ME  Castro FP  Holt RT 《Spine》2000,25(6):696-702
STUDY DESIGN: A review of the charts and radiographs of 22 patients with idiopathic lumbar, thoracolumbar, and thoracic scoliosis who underwent single-stage anterior fusion with rigid third-generation instrumentation and titanium surgical mesh implants. OBJECTIVES: To validate a new technique for scoliosis correction by assessing the initial correction of deformity, trunk shift, and rotation. Perioperative statistics as well as complications were reviewed. The maintenance of sagittal balance and rate of fusion were also determined after a minimum of 2 years' follow-up. SUMMARY OF BACKGROUND DATA: Posterior correction of scoliosis has been the preferred method of treatment since the introduction of Harrington rods. Recent advances in instrumentation and surgical techniques have allowed surgeons to approach scoliosis correction through the chest and abdomen. These new techniques must be validated before they become accepted alternatives to the standard of care. METHODS: One male and 21 female patients, aged 11-18 years, were observed for an average of 44 months. Matched-pairs t tests were used to compare pre- and postoperative curve measurements. RESULTS: Statistically significant curve improvements were seen when postoperative radiographs were compared with preoperative ones. The instrumented coronal plane curve was corrected 82%. A 65% spontaneous correction of the uninstrumented coronal plane curve was observed. Sagittal kyphosis improved 7 degrees, and apical rotation and tilt angles improved 71% and 80%, respectively. A mean loss of 4 degrees of correction was seen on final follow-up radiographs. Lumbar lordosis did not change significantly, and postoperative hyperlordosis was not detected. Ninety-six percent of all instrumented levels fused within 6 months. Although the perioperative complication rate was low, five patients (23%) had asymptomatic idiopathic retrolisthesis develop at the caudal end of the fused vertebrae. CONCLUSIONS: Accepted correction of idiopathic scoliosis can be achieved with anterior instrumented fusion alone.  相似文献   
83.
84.
Circulating hormones are associated with mammographic density, an intermediate marker of breast cancer risk. Differences in circulating hormones, including estrone and testosterone, have been observed in premenopausal women based on their capacity to metabolize daidzein, an isoflavone found predominantly in soybeans. Equol and O-desmethylangolensin (O-DMA) are products of intestinal bacterial metabolism of daidzein. There is interindividual variability in the capacity to produce daidzein metabolites; individuals can be equol producers or non-producers and O-DMA producers or non-producers. We tested the hypothesis that daidzein-metabolizing phenotypes are associated with mammographic density. Participants were recruited from among 92 sedentary, postmenopausal women, ages 50 to 75 years, who participated in a 1-year physical activity intervention. Pre-intervention mammographic density was determined using a computer-assisted, gray-scale thresholding technique. Fifty-five of these women consumed supplemental soy protein (>10 mg daidzein/d) for 3 days and collected a first-void urine sample on the fourth day to determine daidzein-metabolizing phenotypes. Equol and O-DMA concentrations were measured using gas chromatography-mass spectrometry. Associations between daidzein-metabolizing phenotypes and percent mammographic density were adjusted for age, maximum adult weight, gravidity, family history of breast cancer, and serum follicle-stimulating hormone and free testosterone concentrations. Mammographic density was 39% lower in equol producers compared with non-producers (P = 0.04). O-DMA producers had mammographic density 69% greater than non-producers (P = 0.05). These results suggest that particular intestinal bacterial profiles are associated with postmenopausal mammographic density, and these associations are not entirely explained by differences in reproductive or anthropometric characteristics or circulating hormones.  相似文献   
85.
Leavitt  SA; DeAngelo  AB; George  MH; Ross  JA 《Carcinogenesis》1997,18(11):2101-2106
Dichloroacetic acid (DCA) is a chlorination byproduct found in finished drinking water. When administered in drinking water this chemical has been shown to produce hepatocellular adenomas and carcinomas in B6C3F1 mice over the animal's lifetime. In this study, we investigated whether mutant frequencies were increased in mouse liver using treatment protocols that yielded significant tumor induction. DCA was administered continuously at either 1.0 or 3.5 g/l in drinking water to male transgenic B6C3F1 mice harboring the bacterial lacI gene. Groups of five or six animals were killed at 4, 10 or 60 weeks and livers removed. At both 4 and 10 weeks of treatment, there was no significant difference in mutant frequency between the treated and control animals at either dose level. At 60 weeks, mice treated with 1.0 g/l DCA showed a 1.3-fold increase in mutant frequency over concurrent controls (P = 0.05). Mice treated with 3.5 g/l DCA for 60 weeks had a 2.3-fold increase in mutant frequency over the concurrent controls (P = 0.002). The mutation spectrum recovered from mice treated with 3.5 g/l DCA for 60 weeks contained G:C-->A:T transitions (32.79%) and G:C-->T:A transversions (21.31%). In contrast, G:C-->A:T transitions comprised 53.19% of the recovered mutants among control animals. Although only 19.15% of mutations among the controls were at T:A sites, 32.79% of the mutations from DCA-treated animals were at T:A sites. This is consistent with the previous observation that the proportion of mutations at T:A sites in codon 61 of the H-ras gene was increased in DCA-induced liver tumors in B6C3F1 mice. The present study demonstrates DCA-associated mutagenicity in the mouse liver under conditions in which DCA produces hepatic tumors.   相似文献   
86.
Long-chain polyunsaturated fatty acids (LCP) are thought to be required for optimal nervous system development in the newborn. A commercial milk formula containing LCP (Aptamil-LCP) with a fatty acid profile closely resembling breast milk, has recently been introduced for term infants. The absorption of fatty acids in term infants was examined in a double-blind randomized controlled trial comparing Aptamil-LCP ( n = 20) and standard Aptamil ( n = 20). Formula-fed newborn infants were studied from birth for 14 d. Fat balances (3 d) were performed from d 10. A 3-d stool collection was performed from d 10 in a parallel breastfed group ( n = 21). Plasma samples were taken on d 6. Median fat excretion (mg kg−1) was 897.1, 615.0 and 355.2 with Aptamil, Aptamil-LCP and breastfeeding, respectively. The median total fat absorption coefficient in Aptamil-LCP-fed infants was higher than in those fed standard Aptamil ( p < 0:01). These findings were accounted for by differences in the excretion and absorption of long-chain saturated fatty acids (C14:0, C16:0 and C18:0). Higher fat excretion was associated with bulkier and firmer stools. Only trace amounts of LCP were detected in the stools of all groups. This accounted for less than 4% of dietary intake in Aptamil-LCP-fed infants. No differences in the utilization of LCP from Aptamil-LCP and breast milk feeding were apparent. Plasma phospholipid fatty acid composition data reflected differences in dietary LCP intake. Thus, PL LCP levels were highest in the breastfed infants and lowest in the Aptamil-fed infants, with values for the Aptamil-LCP-fed group falling in between.  相似文献   
87.
88.
OBJECTIVE: To determine the cause of acute illness on August 30, 2000, among patients at an outpatient dialysis center (center A). DESIGN: We performed a cohort study of all patients receiving dialysis on August 30, 2000; reviewed dialysis procedures; and analyzed dialysis water samples using microbiologic and chemical assays. SETTING: Dialysis center (center A). PATIENTS: A case-patient was defined as a patient who developed chills within 5 hours after starting hemodialysis at center A on August 30, 2000. RESULTS: Sixteen (36%) of 44 patients at center A met the case definition. All case-patients were hospitalized; 2 died. Besides chills, 15 (94%) of the case-patients experienced nausea; 12 (75%), vomiting; and 4 (25%), fever. Illness was more frequent on the second than the first dialysis shift (16 of 20 vs 0 of 24, P < .001); no other risk factors were identified. The center's water treatment system had received inadequate maintenance and disinfection and a sulfurous odor was noted during sampling of the water from the reverse osmosis (RO) unit. The water had elevated bacterial counts. Volatile sulfur-containing compounds (ie, methanethiol, carbon disulfide, dimethyldisulfide, and sulfur dioxide) were detected by gas chromatography and mass spectrometry in 8 of 12 water samples from the RO unit and in 0 of 28 samples from other areas (P < .001). Results of tests for heavy metals and chloramines were within normal limits. CONCLUSIONS: Parenteral exposure to volatile sulfur-containing compounds, produced under anaerobic conditions in the RO unit, could have caused the outbreak. This investigation demonstrates the importance of appropriate disinfection and maintenance of water treatment systems in hemodialysis centers.  相似文献   
89.
代谢综合症基线调查   总被引:1,自引:0,他引:1  
尹永英  李汝敏  沙蕾 《现代预防医学》2006,33(4):520-521,528
目的:通过对豫宛市30岁以上人群代谢综合症(MS)发病率的词查、统计和分析,旨在唤起人们对此病的重视和预防。方法:利用年度体检之机采用三级分组法对30岁以上人群进行有关MS指标的检测和统计,依据亚洲及我国体重指数标准及2004年中华医学会糖尿病分会诊断代谢综合症标准。共计调查人数3987人(男1981人,女2006人)。结果:30岁以上MS患病率,青年有10%~13%,中老年后可渐增至20%~30%。结论:MS是中老年多见的代谢异常疾病。已严重威胁着人们的生命健康。  相似文献   
90.
Hepatic resections   总被引:5,自引:0,他引:5  
Hepatic resection is the treatment of choice for many secondary and primary hepatic tumors. With improvement in surgical techniques and earlier recognition of hepatic tumors, there has been a renewed interest in performing hepatic resections. In this operative review, we will describe the techniques for performing right-sided and left-side hepatic resections. A major hepatic resection can be performed with less than 5% mortality and approximately a 5% to 15% morbidity. Special mention will be made of performing a hepatic resection without vascular inflow occlusion. This is necessary in performing a hepatic resection for use in live donor liver transplantation.  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