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   2685篇
  免费   225篇
  国内免费   5篇
耳鼻咽喉   8篇
儿科学   56篇
妇产科学   53篇
基础医学   423篇
口腔科学   63篇
临床医学   361篇
内科学   492篇
皮肤病学   17篇
神经病学   446篇
特种医学   128篇
外科学   318篇
综合类   3篇
预防医学   231篇
眼科学   14篇
药学   229篇
中国医学   1篇
肿瘤学   72篇
  2022年   23篇
  2021年   50篇
  2020年   56篇
  2019年   52篇
  2018年   59篇
  2017年   57篇
  2016年   52篇
  2015年   47篇
  2014年   58篇
  2013年   123篇
  2012年   119篇
  2011年   137篇
  2010年   90篇
  2009年   66篇
  2008年   134篇
  2007年   147篇
  2006年   140篇
  2005年   118篇
  2004年   114篇
  2003年   114篇
  2002年   115篇
  2001年   124篇
  2000年   132篇
  1999年   84篇
  1998年   27篇
  1997年   13篇
  1996年   45篇
  1995年   41篇
  1994年   23篇
  1993年   23篇
  1992年   51篇
  1991年   40篇
  1990年   42篇
  1989年   44篇
  1988年   18篇
  1987年   30篇
  1986年   35篇
  1985年   38篇
  1984年   35篇
  1983年   18篇
  1982年   12篇
  1981年   16篇
  1980年   16篇
  1979年   13篇
  1978年   14篇
  1977年   12篇
  1976年   13篇
  1975年   11篇
  1974年   12篇
  1973年   13篇
排序方式: 共有2915条查询结果,搜索用时 15 毫秒
41.
Echovirus 30 (E 30) outbreaks in defined cohorts have rarely been reported. In June 1996, an outbreak of E 30 occurred in four day-care centers (DCCs) in neighboring villages in Germany. A retrospective cohort study of DCC children, employees and household members was done to determine the extent of the outbreak and risk factors for illness. Forty-two percent (39/92) of DCC children, 13% (30/228) of their household members, 5% (1/19) of employees and 2% (1/49) of household members of employees were ill. Onsets occurred over 31 days. Thirteen percent (12/92) of DCC children had meningitis. In only one of 16 households with multiple family members ill, illness in a family member preceeded that of the DCC child. Household members of ill DCC children were 15 times more likely to report illness than those of non-ill DCC children. We conclude that this outbreak was associated with a very high incidence of meningitis, the outbreak began in the DCCs and then spread to household members, and that household members of ill children compared to those of non-ill children were much more likely to report illness.  相似文献   
42.
Dose-related effects of ethanol (placebo, 0.30, and 0.60 g/kg) on behavioral and event-related brain potential (ERP) indices of involuntary attention shifting of audition were investigated. ERPs were recorded from 11 healthy social drinkers during a forced-choice reaction-time (RT) task. Subjects were presented with 100 and 200 ms tones (P = 0.50 for each) with a constant inter-stimulus interval (ISI) of 1 s. The task was to press either of two buttons, depending on the tone duration. The majority of the tones (“standards”) were of 700 Hz (P = 0.82). Occasionally, however, the frequency of the tones changed, deviating either slightly (750 Hz), moderately (900 Hz), or widely (1200 Hz; P = 0.06 for each) from the standard frequency. In accordance with previous findings, the task-irrelevant frequency deviations prolonged the RT. This RT prolongation was attenuated by alcohol with the 0.3 g/kg dose, thus suggesting less distraction by irrelevant stimulus deviations under the influence of ethanol. Furthermore, the P3a, reflecting involuntary attention shifting, was suppressed by alcohol even with the 0.3 g/kg dose. These findings demonstrate a detrimental effect of alcohol on involuntary attention shifting, evident with doses considerably smaller than previously described, and still juridically acceptable in road traffic in most countries. Received: 19 December 1997/Final version: 26 May 1998  相似文献   
43.
OBJECTIVE: Recent in vivo imaging studies indicate a dysregulated presynaptic function of the striatal dopaminergic system in patients with schizophrenia. To further explore the basis of this phenomenon, the authors studied brain dopamine transporter binding in vivo in patients with first-episode, never-medicated schizophrenia. METHOD: Nine patients with schizophrenia and nine healthy matched comparison subjects were recruited. Striatal dopamine transporter binding was measured with positron emission tomography and a specific dopamine transporter ligand, [(18)F]CFT, a radiolabeled form of 2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane. RESULTS: Average caudate and putamen dopamine transporter binding potentials were almost identical in the patients and comparison subjects, but the patients lacked the right-left asymmetry of the caudate dopamine transporter binding seen in the comparison group. CONCLUSIONS: Average striatal dopamine transporter density is unaltered in neuroleptic-naive patients with schizophrenia. However, patients lack asymmetry in caudate dopamine transporter binding, which conforms with disrupted brain lateralization in this disorder.  相似文献   
44.
45.
This study evaluated the noise attenuation of earplugs and earmuffs or their combined use against heavy weapon noise in field conditions for military personnel. The noise attenuation was measured with a miniature microphone inserted into the ear canal. The subjects (13) were tested against pink noise and against the noise of explosions and bazooka, mortar, cannon, and howitzer. The attenuation (insertion loss) was 16 to 23 dB for earplugs, 10 to 20 dB for earmuffs, and 24 to 34 dB for the combined use of plugs and muffs. The transfer function of an open ear was 5 to 7 dB when measured as the C-weighted peak level. The combined use of earplugs and earmuffs gave smaller attenuation values than expected. If the limit for the C-weighted peak level is 140 dB for unprotected ears, then protection against low-frequency noise is provided for up to 156 dB by earplugs, up to 150 dB by earmuffs, and up to 165 dB by the combined use of plugs and muffs.  相似文献   
46.
BACKGROUND AND AIMS: The use of antibiotic prophylaxis in open reduction and osteosynthesis of closed hip fractures is still controversial. The aim of this study was to demonstrate the effect of antibiotic prophylaxis in osteosynthesis of these fractures. MATERIAL AND METHODS: A total of 224 patients operated on between November 1994 and February 1998 in six hospitals by internal fixation for a fresh hip fracture were prospectively and randomly allocated to either a ceftriaxone antibiotic prophylaxis or no prophylaxis group and followed for one year. RESULTS: Within 6 weeks after the operation, 2.6% wound infections were recorded in the antibiotic group and 4.7% in the control group. Two (1.9%) of the five infections in the control group were deep infections (both sensitive to ceftriaxone). There were no statistically significant differences between the infection rates in both groups. However, when analyzing all complications recorded within 6 weeks, significantly more complications were found in the control group (p < 0.01). In the multivariate analysis the most important factor predicting postoperative complications was the lack of antibiotic prophylaxis. CONCLUSION: In this study the antibiotic prophylaxis group had significantly less postoperative complications than the control group within 6 weeks after the operation.  相似文献   
47.
OBJECTIVE: To study vitamin D status and bone metabolism of premenopausal vegetarians and omnivores during a 1-year period. DESIGN: Longitudinal, observational study. Bone mineral density was measured, blood samples from fasting subjects were obtained, and 24-hour urinary samples were collected in February 1994, August 1994, and January 1995. Serum 25-hydroxyvitamin D [S-25(OH)D] and intact parathyroid hormone (S-iPTH) concentrations were measured and intestinal calcium absorption was estimated. Dietary intakes of vitamin D and calcium were calculated. SUBJECTS/SETTING: Six vegans, 6 lactovegetarians, and 16 omnivores living in Helsinki, Finland. STATISTICAL ANALYSES PERFORMED: Student-Newman-Keuls test; unbalanced, repeated-measures multiple analysis of variance; analysis of covariance; Pearson correlation test; and linear regression analysis. RESULTS: Dietary intake of vitamin D was significantly lower in vegans (P < .05, yearly mean +/- standard deviation = 0.09 +/- 0.06 microgram/day) and in lactovegetarians (P < .05, 0.7 +/- 0.4 microgram/day) compared with omnivores (4.0 +/- 2.1 micrograms/day). Throughout the year S-25(OH)D (P = .01) concentrations were lower and S-iPTH (P = .01) concentrations were higher in vegans than in omnivores and lactovegetarians. Bone mineral density in the lumbar region of the spine was lower in vegans (yearly mean +/- standard deviation = 1.034 +/- 0.174 g/cm2) than in omnivores (P = .05, 1.177 +/- 0.099 g/cm2) and tended to be lower than that in lactovegetarians (P = .17, 1.138 +/- 0.06 g/cm2). Bone mineral density in the neck of the femur tended to be lower in vegans (0.843 +/- 0.116 g/cm2) than in omnivores (P = .07, 0.999 +/- 0.138 g/cm2) and lactovegetarians (P = .15, 0.961 +/- 0.059 g/cm2). No seasonal variation was found in bone mineral density in the study groups. CONCLUSIONS: At northern latitudes, dietary intake of vitamin D in vegans was insufficient to maintain S-25(OH)D and S-iPTH concentrations within normal ranges in the winter, which seems to have negative effects on bone mineral density in the long run. APPLICATIONS: An increase in vitamin D intake should generally be recommended for vegans at least during winter, or selections of foodstuffs fortified with vitamin D should be broadened in northern latitudes.  相似文献   
48.
Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) is a zoonotic pathogen for persons in contact with horses. In horses, S. zooepidemicus is an opportunistic pathogen, but human infections associated with S. zooepidemicus are often severe. Within 6 months in 2011, 3 unrelated cases of severe, disseminated S. zooepidemicus infection occurred in men working with horses in eastern Finland. To clarify the pathogen’s epidemiology, we describe the clinical features of the infection in 3 patients and compare the S. zooepidemicus isolates from the human cases with S. zooepidemicus isolates from horses. The isolates were analyzed by using pulsed-field gel electrophoresis, multilocus sequence typing, and sequencing of the szP gene. Molecular typing methods showed that human and equine isolates were identical or closely related. These results emphasize that S. zooepidemicus transmitted from horses can lead to severe infections in humans. As leisure and professional equine sports continue to grow, this infection should be recognized as an emerging zoonosis.  相似文献   
49.
50.
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