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   96822篇
  免费   8012篇
  国内免费   179篇
耳鼻咽喉   1044篇
儿科学   2974篇
妇产科学   2801篇
基础医学   12977篇
口腔科学   1935篇
临床医学   14054篇
内科学   17073篇
皮肤病学   1322篇
神经病学   8518篇
特种医学   2990篇
外国民族医学   1篇
外科学   10763篇
综合类   1449篇
一般理论   135篇
预防医学   11870篇
眼科学   1718篇
药学   6540篇
  3篇
中国医学   109篇
肿瘤学   6737篇
  2023年   551篇
  2022年   866篇
  2021年   1953篇
  2020年   1291篇
  2019年   2179篇
  2018年   2353篇
  2017年   1828篇
  2016年   1892篇
  2015年   2154篇
  2014年   2809篇
  2013年   4224篇
  2012年   6026篇
  2011年   6083篇
  2010年   3314篇
  2009年   2817篇
  2008年   5178篇
  2007年   5486篇
  2006年   5287篇
  2005年   5203篇
  2004年   4740篇
  2003年   4355篇
  2002年   4186篇
  2001年   1943篇
  2000年   1969篇
  1999年   1770篇
  1998年   1171篇
  1997年   899篇
  1996年   869篇
  1995年   821篇
  1994年   699篇
  1993年   707篇
  1992年   1416篇
  1991年   1301篇
  1990年   1267篇
  1989年   1191篇
  1988年   1096篇
  1987年   1077篇
  1986年   1022篇
  1985年   1038篇
  1984年   822篇
  1983年   739篇
  1982年   579篇
  1981年   522篇
  1980年   536篇
  1979年   708篇
  1978年   578篇
  1977年   466篇
  1974年   496篇
  1973年   469篇
  1972年   482篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Cerebellar involvement in motor and non-motor sequence learning was examined with serial reaction time tasks (SRT). Our sample consisted of 8 children and adolescents who had undergone surgical removal of a benign posterior fossa tumor (PFT) during childhood. None of them had undergone chemotherapy or cranial radiation therapy (CRT). Ages ranged from 1-11 years at surgery and 9-17 years at testing. The children were tested not earlier than 2.5 years after surgery (M = 5.9 years), enabling brain plasticity and recovery of functions. Their performance was compared with a matched control sample. The PFT group was not impaired in the implicit learning of sequences, as reflected in their performance in blocks with a repeated sequence, both before and after a random block. However, in the perceptual task, their performance deteriorated more than that of the control group when a random block was introduced, suggesting that it was more difficult for the patients to respond flexibly or change their response set when encountering changing task demands. These results are in line with another study by our group on task switching with the same patients.  相似文献   
82.
Survival after resection of colorectal liver metastases has traditionally been associated with clinicopathologic factors. We sought to investigate whether echogenicity of colorectal liver metastasis as assessed by intraoperative ultrasound (IOUS) was a prognostic factor after hepatic resection. Prospective data on tumor IOUS appearance were collected in 84 patients who underwent hepatic resection for colorectal liver metastasis. Images were digitally recorded, blindly reviewed, and scored for echogenicity (hypo-, iso-, or hyperechoic). The median tumor number was 1 and the median tumor size was 5.0 cm. At the time of surgery, the IOUS appearance of the colorectal liver metastases were hypoechoic in 35 (41.7%) patients, isoechoic in 37 (44.0%) patients, and hyperechoic in 12 (14.3%) patients. Traditional clinicopathologic prognostic factors were similarly distributed among the three echogenicity groups (all p > 0.05). Patients with a hypoechoic lesion had a significantly shorter median survival (30.2 months) compared with patients who had either an isoechoic (53.2 months) or hyperechoic (42.3 months) lesion (p = 0.005). The 5-year survival after hepatic resection of colorectal liver metastasis was also associated with the echogenic appearance of the lesion (hypoechoic 14.4 vs isoechoic 37.4 vs hyperechoic 46.2%) (p < 0.05). Intraoperative ultrasound echogenicity should be considered a prognostic factor after hepatic resection of metastatic colorectal cancer. This study was presented at the 47th annual meeting of The Society for Surgery of the Alimentary Tract, Los Angeles, CA, USA, 22 May 2006.  相似文献   
83.
Fracture risk in monoclonal gammopathy of undetermined significance.   总被引:3,自引:0,他引:3  
To assess fractures in monoclonal gammopathy of undetermined significance (MGUS), the precursor of multiple myeloma, we followed 488 Olmsted County, MN, residents with MGUS in a retrospective cohort study. There was a 2.7-fold increase in the risk of axial fractures but no increase in limb fractures. The pathophysiologic basis for the increased axial fractures should be determined. INTRODUCTION: Multiple myeloma is often preceded by monoclonal gammopathy of undetermined significance (MGUS). Fractures are common in myeloma as a result of lytic bone lesions, generalized bone loss, and elevated bone turnover from excessive cytokine production. Whether fractures are also increased in MGUS is unknown. MATERIALS AND METHODS: In a population-based retrospective cohort study, 488 Olmsted County, MN, residents with MGUS first diagnosed in 1960-1994 (52% men; mean age, 71.4 +/- 12.8 years) were followed for 3901 person-years; follow-up was censored at progression to myeloma. The relative risk of fractures was assessed by standardized incidence ratios (SIRs), and risk factors were evaluated in proportional hazards models. RESULTS AND CONCLUSIONS: Altogether, 200 patients experienced 385 fractures. Compared with expected rates in the community, statistically significant increases were seen for fractures at most axial sites, for example, vertebrae (SIR, 6.3; 95% CI, 5.2-7.5). There was a slight increase in hip (SIR, 1.6; 95% CI, 1.2-2.2) but not distal forearm fractures (SIR, 0.8; 95% CI, 0.4-1.5). The relative risk (SIR) of any axial fracture was 2.7 (95% CI, 2.3-3.1) compared with only 1.1 (95% CI, 0.9-1.4) for all limb fractures combined. In a multivariate analysis, the independent predictors of any subsequent fracture were age (hazard ratio [HR] per 10-year increase, 1.4; 95% CI, 1.2-1.6) and corticosteroid use (HR, 1.8; 95% CI, 1.2-2.6); greater weight at diagnosis (HR per 10 kg, 0.8; 95% CI, 0.8-0.9), and IgG monoclonal protein (HR, 0.7; 95% CI, 0.5-0.97) were protective. Baseline monoclonal protein level, a determinant of myeloma progression, did not predict fracture risk. Thus, the risk of axial, but not peripheral, fractures is increased among MGUS patients even before progression to myeloma. The pathophysiologic basis for this should be determined because elevated bone turnover, for example, might be treatable.  相似文献   
84.
85.
Polycyclic aromatic hydrocarbons (PAH), of which benzo[a]pyrene is a representative member, are combustion-related environmental pollutants and include known carcinogens. Laboratory animal studies indicate that the dose of PAHs to the fetus is on the order of a 10th that to the mother and that there is heightened susceptibility to PAH-induced carcinogenesis during the fetal and infancy periods. Carcinogen-DNA adducts, a measure of procarcinogenic genetic damage, are considered a biomarker of increased cancer risk. Here we compare the levels of benzo[a]pyrene-DNA adducts as a proxy for PAH-DNA damage measured in maternal blood and newborn cord blood obtained at delivery in four different populations of mothers (total of 867) and newborns (total of 822), representing a 30-fold range of exposure to ambient PAHs. The populations include residents in Northern Manhattan, participants in a study of the effects of the World Trade Center disaster, residents in Krakow, Poland, and residents in Tongliang, China. Mean adduct concentrations in both maternal and cord blood and the proportion of samples with detectable adducts, increased across the populations [Northern Manhattan < World Trade Center (WTC) < Krakow < Tongliang], consistent with the trend in estimated ambient exposure to PAHs (P < 0.001). For mothers, the means in the respective populations were Northern Manhattan (0.21 adducts per 10(8) nucleotides), WTC (0.23 adducts per 10(8) nucleotides), Krakow (0.28 adducts per 10(8) nucleotides), Tongliang (0.31 adducts per 10(8) nucleotides); the corresponding means in the newborns were Northern Manhattan (0.23), WTC (0.24), Krakow (0.29), Tongliang (0.31). The percentage of mothers with detectable levels of adducts in the respective populations were Northern Manhattan (36.8%), WTC (57.5%), Krakow (72.9%), Tongliang (73.4%); the corresponding percentages among the newborns were Northern Manhattan (42.4%), WTC (60.6%), Krakow (71.1%), Tongliang (79.5%). Despite the estimated 10-fold lower PAH dose to the fetus based on laboratory animal experiments, the adduct levels in the newborns were similar to or higher than in the mothers. This study suggests that the fetus may be 10-fold more susceptible to DNA damage than the mother and that in utero exposure to polycyclic aromatic hydrocarbons may disproportionately increase carcinogenic risk. The data support preventive policies to limit PAH exposure to pregnant women and children.  相似文献   
86.
Young children's ability to participate in conversation has been of particular interest in the study of pragmatic aspects of language. In this study, topics of conversation were investigated by videotaping 10 dyads of 4-year-old children during play. Ten-minute samples were analyzed according to a number of topic-dependent measures. Results revealed that all dyads evidenced some lengthy topics (13-91 utterances). Longer topics were characterized by three text-level functions. Enacting Scenarios, Describing, and Problem Solving. Nevertheless, three fourths of all dialogues were considered relatively short. Generally, partners contributed equally to dialogue, but in some dyads, 1 child dominated initiation. Findings of the study suggest that 4-year-olds are capable of extended participation in dialogue, at least part of the time. Naturalistic play settings may elicit samples of conversation that are representative of preschoolers' ability.  相似文献   
87.
Cardiovascular intervention for high-risk families: the Heart Smart Program   总被引:2,自引:0,他引:2  
The Heart Smart Family Health Promotion Program is a multidisciplinary, school-based program for cardiovascular risk reduction among high-risk children and their families. As a program that includes young adults at high risk, it is adaptable to a clinical practice. Nineteen fourth and fifth graders were selected as probands for elevated risk factors after a general screening to identify families for an intervention program. Twenty-three parents participated in a 12-week program focused on eating, exercise, and smoking behavior changes enhanced by behavicral support strategies. Weekly sessions were held in the auditorium/cafeteria of the elementary school and consisted of orientation and presentations, cardiovascular (CV) screening with medical feedback, activities, self-monitoring, counseling, and contingency contracting. Information gathered before and after the program included medical history, CV health knowledge and relevant behavior, blood pressure, serum lipid and lipoprotein values, anthropometric measurements, and urine electrolyte excretion. Both children and parents showed positive changes in eating habits and physical activity and significant changes in knowledge and blood pressure levels, while the children halted their weight gain. We believe this multidisciplinary, behavior-oriented, school-based program can be an effective cardiovascular risk intervention adaptable for a clinical office practice.  相似文献   
88.
It's all about sex: gender, lung development and lung disease.   总被引:1,自引:0,他引:1  
Accumulating evidence suggests that gender affects the incidence, susceptibility and severity of several lung diseases. Gender also influences lung development and physiology. Data from both human and animal studies indicate that sex hormones might contribute to disease pathogenesis or serve as protective factors, depending on the disease involved. In this review, the influence of gender and sex hormones on lung development and pathology will be discussed, with specific emphasis on pulmonary fibrosis, asthma and cancer.  相似文献   
89.
BACKGROUND: There is no consensus regarding the optimal rate of follow-up in the post-bariatric surgery patient population. METHODS: The records of all patients who underwent laparoscopic Roux-en-Y gastric bypass from 2001 to 2003 were reviewed. Using patient zip codes, travel distances were calculated between the patients' places of residence and our clinic. Patients were then assigned to 1 of 3 cohorts according to the following distances: (1) < 50 miles, (2) 50 to 100 miles, and (3) > 100 miles. Patient compliance with follow-up appointments at 3 weeks, 3 months, 6 months, 9 months, and 12 months was analyzed. Linear trends were identified using the Mantel-Haenszel test. Age and sex were analyzed as possible predictors of compliance using the chi(2) test. P values < .05 were considered statistically significant. RESULTS: The study group comprised 150 patients (127 females and 23 males). The 3 cohorts contained 115, 21, and 14 patients, respectively. All patients in each cohort were compliant with the 3-week follow-up appointment. Although there were differences in compliance between cohorts at each of the remaining appointments, only the 9-month (70.3% vs 61.9% vs 35.7%) visit showed statistical significance (P = .035). The 6-month visit trended toward significance (85.2% vs 76.2% vs 64.3%; P = .088). Males were more likely to be compliant with the 12-month follow-up (P = .040). When controlling for sex, travel distance was also a predictor of compliance at this follow-up visit (P = .024). Age was not predictive of compliance (P = .827). CONCLUSION: Based on our findings, we conclude that travel distance from the clinic does not significantly affect compliance at the initial follow-up, 3-month, and 12-month appointments. However, distance does tend to affect compliance at the 6-month appointment and significantly affects compliance at the 9-month appointment. Males are more likely to be compliant at the 12 month follow-up visit. We must continue to strive for 100% follow-up in our post-bariatric surgery patients.  相似文献   
90.
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