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   3728篇
  免费   132篇
  国内免费   21篇
耳鼻咽喉   38篇
儿科学   52篇
妇产科学   55篇
基础医学   446篇
口腔科学   205篇
临床医学   218篇
内科学   855篇
皮肤病学   34篇
神经病学   217篇
特种医学   114篇
外科学   755篇
综合类   30篇
一般理论   3篇
预防医学   179篇
眼科学   80篇
药学   174篇
中国医学   10篇
肿瘤学   416篇
  2023年   27篇
  2022年   38篇
  2021年   77篇
  2020年   47篇
  2019年   61篇
  2018年   56篇
  2017年   53篇
  2016年   55篇
  2015年   72篇
  2014年   78篇
  2013年   104篇
  2012年   169篇
  2011年   196篇
  2010年   111篇
  2009年   108篇
  2008年   204篇
  2007年   231篇
  2006年   209篇
  2005年   204篇
  2004年   182篇
  2003年   181篇
  2002年   200篇
  2001年   87篇
  2000年   108篇
  1999年   116篇
  1998年   56篇
  1997年   35篇
  1996年   39篇
  1995年   31篇
  1994年   17篇
  1992年   49篇
  1991年   50篇
  1990年   46篇
  1989年   56篇
  1988年   43篇
  1987年   51篇
  1986年   42篇
  1985年   43篇
  1984年   39篇
  1983年   34篇
  1982年   18篇
  1981年   18篇
  1980年   18篇
  1979年   17篇
  1977年   16篇
  1975年   14篇
  1973年   19篇
  1972年   19篇
  1971年   19篇
  1969年   17篇
排序方式: 共有3881条查询结果,搜索用时 0 毫秒
61.

Purpose

The purpose of this study was to determine the effect of increasing the concentrations of sévoflurane anaesthesia on the distribution of diaphragm blood flow (Qdi) in ten dogs during mechanical ventilation.

Methods

Animals were divided into two groups, sévoflurane (n = 6) and time control (n = 4) groups. Blood flow to the crural and the costal diaphragm (Qcru, Qcost) was determined by the hydrogen clearance technique at 0, 0.5, 1.0 and 1.5 minimum alveolar concentration (MAC) of sévoflurane after a 30 min period of steady-state conditions. Cardiac output (CO) and the mean arterial blood pressure (MBP) were also measured.

Results

Sevoflurane anaesthesia caused a reduction in CO (L · min?1) from a control value of 1.51 ± 0.21 to 1.38 ±0.1 (0.5 MAC), 1.09 ± 0.15 (1.0 MAC) and 0.98 ± 0.12 (1.5 MAC) (Mean ± SD). Mean blood pressure, Qcru and Qcost also decreased with increasing depth of anaesthesia. In addition, the decrease of Qcru was greater than that of Qcost at all levels of MBP and CO. No change occurred in these variables in the lime control group.

Conclusion

Sevoflurane anaesthesia changes the distribution of Qdi with a greater reduction occurring in Qcru than in Qcost.  相似文献   
62.
The specificity of a fluorescent conjugate to infectious laryngotracheitis virus was examined using chick trachea organ culture or tissue sections infected with other avian viruses (adenovirus, infectious bronchitis, poxvirus, reovirus, Newcastle disease virus, Marek's disease virus, avian encephalomyelitis and infectious bursal agent) or Mycoplasma gallisepticum. Confirmation of virus replication in these preparations was obtained by either 1) demonstration of virus titre increase or 2) demonstration of fluorescence when using the homologous conjugate. Once either of these criteria had been satisfied, negative results with the infectious laryngotracheitis conjugate were taken to indicate that the conjugate would not present false positive results in differentiated cells infected with these heterologous viruses. The spectrum of reactivity of the infectious laryngotracheitis conjugate was then examined on organ cultures infected with several infectious laryngotracheitis isolates from across Canada. Finally, the conjugate was applied to experimental and natural cases of infectious laryngotracheitis and its efficiency was compared to routine virus isolation methods.  相似文献   
63.
Receptive field (RF) properties of lateral geniculate (LGN) and cortical visual neurons were studied in cats using computer-controlled bar and edge stimuli. Responses to stationary presentations of an optimally oriented bright bar in an array of closely spaced RF positions provided detailed spatial and temporal information about RFs. Moving edge stimuli represent a more nearly normal viewing situation, and responses provide additional information for classifying RFs. Our results allow inferences about the nature of input connections to conical units. Responses of simple striate cells and X cells of LGN were similar to each other and quite different from those of complex and Y-LGN cells. Simple and X cells exhibited spatially segregated regions of excitation and inhibition and large shifts in response latency as a function of stimulus position. Both cell types showed spatially nonoverlapping regions of response (discharge zones) to moving bright and dark edges. These results provide correlational evidence that simple cells of striate cortex receive input predominantly from X-LGN cells. X-LGN cells respond to increases or decreases in local stimulus flux, depending on stimulus position, and via separate (from segregated RF areas) projections to the cortex determine contrast polarity of the cortical response. Complex cells, on the other hand, exhibited transient responses to both stimulus onset and removal. with a constant response latency across the entire RF. Results from the same test on Y-LGN cells were strikingly similar to those for complex cortical cells. However, complex cells show far more overlap in edge discharge zones than either on- or off-center Y-LGN cells. This comparison suggests spatially overlapping input to complex cells from both on-and off-center Y-LGN cells. A third type of cortical cell (in area 18) demonstrated edge and static-bar responses that strongly resembled those of either on-or off-center Y-LGN cells. Input to these parastriate cortical cells apparently derives from either on-or off-center Y-LGN cells. We believe that these units represent the parastnate equivalent of striate simple units in that they seem to receive inputs from spatially segregated RF areas, in this case of Y-LGN units.  相似文献   
64.
Few studies have examined the association of alcohol consumption and cigarette smoking with colorectal cancer in Asian populations whose genetic susceptibility to these factors are different from Western populations. We investigated this association and the joint effect of these factors, and estimated the population-attributable fraction to clarify the public health impact on a Japanese population, based on a prospective study. We analyzed the 10-year (cohort I) and 7-year (cohort II) follow-up data of the Japan Public Health Center-based prospective study on cancer and cardiovascular disease, derived from 90,004 (42,540 male and 47,464 female) middle-aged and elderly Japanese. We identified 716 (457 in men and 259 in women) newly diagnosed cases of colorectal cancer. Both alcohol consumption and smoking were clearly associated with colorectal cancer in men, after adjusting for age, family history of colorectal cancer, body mass index, and physical exercise. Regular heavy drinking of 150 g/week or more of ethanol showed a statistically significant increased risk compared with nondrinkers: relative risks (RRs) were 1.4 [95% confidence interval (CI), 1.1-1.9] for 150-299 g/week and 2.1 (95% CI, 1.6-2.7) for 300 g/week or more. On the contrary, regular ethanol consumption was not associated with colorectal cancer (RR, 0.7; 95% CI, 0.4-1.1) in women. In terms of smoking, the RRs were 1.4 (95% CI, 1.1-1.8) for current smokers and 1.3 (95% CI, 0.98-1.7) for ex-smokers compared with never-smokers in men. The risk of smoking in women was similar to that in men, although not statistically significant. The colorectal cancer risk with 300 g/week or more of ethanol in current smokers was estimated at 3.0 (95% CI, 1.8-5.1) compared with nondrinkers among nonsmokers in men. Colorectal cancer attributable to alcohol consumption or smoking was estimated to be 46%. In conclusion, approximately half of the colorectal cancer cases may be preventable by tobacco and alcohol controls in middle-aged and elderly Japanese men.  相似文献   
65.
BACKGROUND: The authors clarified the clinical significance of the measurement of serum concentrations of specific IgE antibodies to staphylococcal enterotoxin (SE) A- and SEB in atopic dermatitis (AD). METHODS: The serum concentrations of SEA- and SEB-specific IgE antibodies in 140 pediatric patients with AD were measured with an immuno CAP -radioallergosorbent test system (RAST). To check the cross-reaction of specific IgE antibodies to SEA/SEB and other allergens, the CAP RAST fluorescent enzyme immunoassay inhibition test was performed. RESULTS: Forty-seven patients (33.6%) tested positive for either SEA- or SEB-specific IgE antibodies. School children showed higher positive rates of SEA/SEB-specific IgE antibodies than infants or young children. The patients with severe AD and those with exacerbation of symptoms in summer, had higher positive rates of SEA/SEB-specific IgE antibodies than patients with mild AD or those with exacerbation in winter. In addition, the positive rates of specific IgE antibodies to both dog-dander and cat-dander were higher in patients with positive SEA/SEB-specific IgE antibodies than in patients with negative ones. No cross-reactions occurred among specific IgE antibodies to SEA/SEB and dog/cat dander with one patient's serum, which had positive IgE-specific antibodies against cat/dog dander and SEA/SEB. The positive rate of SEA/SEB-specific IgE antibodies in the patients with dogs and/or cats as pets was 48.4%, which was higher than in those with no pets. CONCLUSIONS: Atopic dermatitis patients who exhibit high positive rates of SEA/SEB-specific IgE antibodies were found to be school children, severe cases, cases with high serum concentrations of total IgE, cases with exacerbation in summer, and cases with dogs and/or cats as pets. The measurement of serum concentrations of specific IgE antibodies to SEA and SEB, thus has some value for evaluating AD patients.  相似文献   
66.
A cross-sectional study was conducted in order to investigate the various factors related to the depression in caregivers of the elderly in need of care in urban Japan. The caregivers answered a self-administered questionnaire about various factors that may affect their depression, and also completed a Center for Epidemiologic Studies Depression Scale evaluation (CES-D). Compared with non-depressed caregivers, depressed caregivers attended the elderly longer, while time spent for physical caregiving did not differ between the two groups. Even after controlling confounding factors, time of attending the elderly was an independent factor related to caregiver's depression.  相似文献   
67.
Watershed infarction associated with dementia and cerebral atrophy   总被引:5,自引:0,他引:5  
A 63-year-old man was admitted with progressive left hemiparesis and left homonymous hemianopsia of 1 month's duration. During the 2 months before admission, he had suffered from slowly progressive dementia. The diagnosis of right-sided watershed (WS) infarction was made. He exhibited slow progression of dementia and cerebral atrophy during the period of observation after discharge. There was a positive relationship between cerebral atrophy and the degree of dementia. In the present case, WS infarction caused by right internal carotid artery occlusion might be related to dementia and cerebral atrophy.  相似文献   
68.
69.
PURPOSE: To confirm which modality, ultrasonography (US) or mammography (MMG), is useful to detect breast cancer in women aged 30 to 39 years, and to compare the sensitivity and findings of these two modalities for invasive carcinoma and ductal carcinoma in situ (DCIS) in the diagnostic setting. METHODS: We retrospectively evaluated the sensitivity and findings of these two modalities in 165 patients aged 30 to 39 years, who underwent surgery at the Cancer Institute Hospital between 2001 and 2003. US or MMG were performed after obtaining information on the other modalities previously used and physical examination. The abnormal findings of US were defined as mass lesions and focal hypoechoic areas due to breast cancer. The abnormal findings of MMG were defined as category 3 to 5 (Japanese Mammography Guidelines) masses, calcifications, and other findings due to cancer. RESULTS: Of 165 patients, 147 patients (89%) mammographically showed dense breasts. Histologically, 146 (88%) were invasive carcinomas and 19 (12%) were DCIS. In all carcinomas, the sensitivity of US (95%) was higher than that of MMG (85%). The sensitivity of US for invasive carcinoma (99%) was higher than that of MMG (85%). On the other hand, the sensitivity of MMG for DCIS (89%) was much higher than that of US (68%). CONCLUSIONS: US is more sensitive to detect breast cancers than MMG in this age range, especially for invasive carcinoma. On the other hand, MMG is useful for detecting DCIS, especially when it manifests with microcalcifications.  相似文献   
70.
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