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   548篇
  免费   23篇
耳鼻咽喉   8篇
儿科学   30篇
妇产科学   21篇
基础医学   63篇
口腔科学   15篇
临床医学   66篇
内科学   80篇
皮肤病学   22篇
神经病学   74篇
特种医学   4篇
外科学   51篇
综合类   3篇
预防医学   31篇
眼科学   7篇
药学   33篇
中国医学   3篇
肿瘤学   60篇
  2022年   2篇
  2021年   11篇
  2020年   4篇
  2019年   8篇
  2018年   7篇
  2017年   5篇
  2016年   1篇
  2015年   9篇
  2014年   12篇
  2013年   11篇
  2012年   52篇
  2011年   49篇
  2010年   12篇
  2009年   14篇
  2008年   54篇
  2007年   64篇
  2006年   46篇
  2005年   51篇
  2004年   45篇
  2003年   34篇
  2002年   31篇
  2001年   8篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1997年   3篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1993年   4篇
  1992年   4篇
  1991年   2篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1979年   3篇
  1976年   1篇
  1972年   2篇
  1971年   2篇
  1959年   1篇
排序方式: 共有571条查询结果,搜索用时 0 毫秒
551.
Five combinations of image-processing algorithms were applied to dynamic infrared (IR) images of six breast cancer patients preoperatively to establish optimal enhancement of cancer tissue before frequency analysis. mid-wave photovoltaic (PV) IR cameras with 320x254 and 640x512 pixels were used. The signal-to-noise ratio and the specificity for breast cancer were evaluated with the image-processing combinations from the image series of each patient. Before image processing and frequency analysis the effect of patient movement was minimized with a stabilization program developed and tested in the study by stabilizing image slices using surface markers set as measurement points on the skin of the imaged breast. A mathematical equation for superiority value was developed for comparison of the key ratios of the image-processing combinations. The ability of each combination to locate the mammography finding of breast cancer in each patient was compared. Our results show that data collected with a 640x512-pixel mid-wave PV camera applying image-processing methods optimizing signal-to-noise ratio, morphological image processing and linear image restoration before frequency analysis possess the greatest superiority value, showing the cancer area most clearly also in the match centre of the mammography estimation.  相似文献   
552.
The circumstances of diagnosis of human pasteurellosis are reviewed. The diagnosis is usually suspected for animal bite or scratch wounds. Conversely, in other infections the diagnosis is only based on bacteriological data. Phenotypic misidentification of Pasteurellaceae from clinical material is common. The phenotypic criteria of identification of the six species of human pathogen Pasteurella are presented. We emphasise that bite wound specimens have to be cultured for aerobic and anaerobic bacteria and yield an average of 5 bacterial isolates per culture. Antibiotic therapy relies upon amino-penicillins or cephalosporins, although b-lactamase producing strains are scarce. Fluoroquinolones can be an alternative for systemic infections. Molecular typing unequivocally points out the risk of transmission from pets to humans. Immunocompromised persons have to be made aware of precautions.  相似文献   
553.
BACKGROUND: The aim of this study was to investigate the prevalence of polycystic ovaries (PCO) among women with self-reported oligomenorrhoea and/or hirsutism and to see whether women with symptoms and PCO have less favourable levels of biochemical markers than controls or women with symptoms and normal ovaries. METHODS: The ultrasonographic ovarian morphology and the hormonal and metabolic profile of female cases with self-reported symptoms typical of polycystic ovary syndrome (PCOS) (n = 196) and asymptomatic controls (n = 67) at the age of 31 years were examined in a general population-based Northern Finland Birth Cohort 1966. RESULTS: The prevalence of PCO (37.3 versus 18.2%; P = 0.004) was significantly higher in the cases (oligomenorrhoea and/or hirsutism) than in the controls. PCO morphology was detected in 18.4% of those who reported only hirsutism, in 47.9% of those reporting only oligomenorrhoea, and in 70.4% of those reporting both symptoms. In the cases with PCO compared to (i) the controls and (ii) the cases without PCO, body mass index (P = 0.026 and P = 0.011), ovarian volume [right P = 0.001, left P = 0.208 (non-significant) and right P < 0.001, left P = 0.022], mean follicle number (P < 0.001 and P < 0.001), testosterone (P = 0.063 and P = 0.029), free androgen index (P = 0.007 and P = 0.013) and insulin (P = 0.033 and P = 0.040) were higher, and sex hormone-binding globulin (P = 0.039 and P = 0.068) and glucose:insulin ratio (P = 0.060 and P = 0.054) lower. Cases with PCO also had higher waist:hip ratio (P = 0.011), infertility rate (P = 0.005) and glucose (P = 0.045) and lower insulin-like growth factor-binding protein-1 (P = 0.012) than controls. The clinical, hormonal and metabolic characteristics did not differ significantly between cases without PCO and controls with the exception of infertility rate, which was significantly higher in the cases without PCO (26.4 vs. 10.0%; P = 0.009). CONCLUSIONS: In a general population, women with symptoms of oligomenorrhoea and/or hirsutism more often have PCO than asymptomatic women. Levels of biochemical and clinical markers in symptomatic women with PCO differed from and were less favourable than those in symptomatic women without PCO or asymptomatic women, implying an increased risk for health.  相似文献   
554.
Mycobacterium ulcerans is an environmental pathogen concerning mainly the tropical countries; it is the causative agent of Buruli ulcer, which has become the third most important mycobacterial disease. In spite of water-linked epidemiological studies to identify the sources of M. ulcerans, the reservoir and the mode of transmission of this organism remain elusive. To determine the ecology and the mode of transmission of M. ulcerans we have set up an experimental model. This experimental model demonstrated that water bugs were able to transmit M. ulcerans by bites. In insects, the bacilli were localized exclusively within salivary glands, where it could both multiply contrary to other mycobacteria species. In another experimental study, we report that the crude extracts from aquatic plants stimulate in vitro the growth of M. ulcerans as much as the biofilm formation by M. ulcerans has been observed on aquatic plants. Given that the water bugs are essentially carnivorous, it is difficult to imagine a direct contact in the contamination of aquatic bugs and plants. It seems very likely that an intermediate host exists. In an endemic area of Daloa in C?te d'Ivoire, our observations were confirmed.  相似文献   
555.
556.
The elderly are prone to respiratory infection but the role of disordered immunity is uncertain. Opsonization of bacteria is an important early host defence mechanism required for optimal phagocytosis. There are conflicting reports in the literature as to the ability of the elderly to perform this function and one reason may be the use of in vitro tests in which the 'target' microorganism is clinically unrealistic. We have tested the hypothesis that use of a more clinically relevant microorganism Haemophilus influenzae, which commonly infects the respiratory tract of such persons, may detect abnormalities of opsonization in the elderly. Using an in vitro luminol-enhanced chemiluminescence (CL) assay we have compared sera from 45 elderly subjects (age greater than 70 years without known immune deficiency or current infection) with sera from 12 young, healthy subjects, for their capacity to opsonize Staphylococcus aureus (Oxford strain) and H. influenzae (non-capsulated) expressed as percentage CL obtained using pooled normal human serum (PNHS). There was no significant difference (median) between the elderly (95%) and the young (108%) with regard to S. aureus but opsonization of H. influenzae was poor in the elderly (63%) compared with that in the younger group (87%; P = 0.002); the sera of 11 elderly subjects having an opsonic capacity less than 30% that of PNHS. We conclude that use of the more clinically relevant microorganism, H. influenzae, appears to differentiate a subgroup of the elderly with reduced serum opsonic capacity. It remains to be determined prospectively whether these individuals are in fact more prone to infection.  相似文献   
557.
Most diseases are the consequence of the breakdown of cellular processes, but the relationships among genetic/epigenetic defects, the molecular interaction networks underlying them, and the disease phenotypes remain poorly understood. To gain insights into such relationships, here we constructed a bipartite human disease association network in which nodes are diseases and two diseases are linked if mutated enzymes associated with them catalyze adjacent metabolic reactions. We find that connected disease pairs display higher correlated reaction flux rate, corresponding enzyme-encoding gene coexpression, and higher comorbidity than those that have no metabolic link between them. Furthermore, the more connected a disease is to other diseases, the higher is its prevalence and associated mortality rate. The network topology-based approach also helps to uncover potential mechanisms that contribute to their shared pathophysiology. Thus, the structure and modeled function of the human metabolic network can provide insights into disease comorbidity, with potentially important consequences for disease diagnosis and prevention.  相似文献   
558.
OBJECTIVE: To study the association between body size from birth to adulthood and self-reported symptoms of polycystic ovary syndrome (PCOS), particularly hirsutism and menstrual disturbances. DESIGN: Longitudinal, population-based study of a cohort of women born in 1966 in northern Finland. The study population included 2007 women who were not pregnant and did not use hormonal contraception. Of these 528 (26%) had self-reported symptoms of PCOS. RESULTS: Weight at birth, gestational age, being small for gestational age or growth retardation at birth were not associated with PCOS symptoms at 31 y. An increased risk of PCOS symptoms was observed among women with abdominal obesity (waist/hip ratio >85th percentile) at 31 y who had normal weight in adolescence and were overweight (body mass index (BMI) 25.0-29.9 kg/m(2)) or obese (BMI>30.0 kg/m(2)) at 31 y (relative risk (RR) (95% CI) 1.44(1.10-1.89)), and among women with abdominal obesity who were overweight or obese at both 14 and 31 y (1.71 (1.30-2.24)). A total of 30% and 41% of the women with PCOS symptoms in these groups could be attributed, respectively, to overweight, obesity and abdominal obesity at 31 y. CONCLUSIONS: These results suggest that obesity in adolescence and in adulthood, and also weight gain after adolescence, particularly in the presence of abdominal obesity, are associated with self-reported PCOS symptoms in adulthood. Thus, based on the results from intervention studies treating PCOS and the results of this study, the prevention of obesity and abdominal obesity is important among young women.  相似文献   
559.
A new indole alkaloid, named donasine, has been isolated from the rhizomes of Arundo donax L. Its structure was determined by X-ray crystallographic analysis and spectral methods. The primary pharmacological test showed that the compound has an action of reducing fever.  相似文献   
560.
AIM: To assess ex vivo the accuracy of various electronic apex locators in locating the apical terminus of root-end resected teeth. METHODOLOGY: Ninety extracted human posterior teeth (182 root canals) were prepared to a minimum size of 40 and filled with gutta-percha and sealer. After resection of the apical 3 mm of the root, the root canal filling was removed using HERO rotary instruments. The size of the root canal at the apical terminus after removal of the filling ranged from size 50 to 90. The root canal length to the apical terminus was determined using 3 apex locators (Root ZX, Raypex4 and Apex Pointer). A new mounting model that utilized a micrometer was used to perform the measurements and to visually determine the actual position of the apical terminus. The frequency of locating the apical terminus and the corresponding 95% confidence interval (CI) were calculated. Additionally, the coefficient of repeatability of each apex locator and the limits of inter-operator agreement were determined. RESULTS: All apex locators showed an acceptable repeatability (0.02-0.03 mm coefficient of repeatability) and narrow limits of inter-operator agreement (+0.07 and -0.07 mm). The accuracy of determining the apical terminus within 1 mm in the root canal was as follows: Root ZX 90% (164/182 root-canals) [95%CI: 86-94%], Raypex4 74% (135/182 root-canals) [95%CI: 68-80%], and Apex Pointer 71% (129/182 root canals) [95%CI: 65-77%]. No over-instrumentation resulted when the Root ZX device was used. In contrast, using the Raypex4 or the Apex Pointer device resulted in over-instrumentation in 8 of 182 root canals (4%). CONCLUSIONS: Under the conditions of this study all three apex locators were able to detect the apical terminus of root-end resected teeth with an acceptable range. The Root ZX device was the most accurate without over-instrumentation of the root canals.  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