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   1046篇
  免费   71篇
  国内免费   1篇
耳鼻咽喉   20篇
儿科学   51篇
妇产科学   20篇
基础医学   162篇
口腔科学   10篇
临床医学   113篇
内科学   250篇
皮肤病学   12篇
神经病学   89篇
特种医学   23篇
外科学   88篇
综合类   3篇
预防医学   97篇
眼科学   17篇
药学   82篇
中国医学   1篇
肿瘤学   80篇
  2023年   9篇
  2022年   14篇
  2021年   46篇
  2020年   20篇
  2019年   29篇
  2018年   27篇
  2017年   26篇
  2016年   38篇
  2015年   49篇
  2014年   41篇
  2013年   70篇
  2012年   102篇
  2011年   83篇
  2010年   44篇
  2009年   69篇
  2008年   76篇
  2007年   75篇
  2006年   55篇
  2005年   54篇
  2004年   49篇
  2003年   46篇
  2002年   51篇
  2001年   10篇
  2000年   6篇
  1999年   6篇
  1998年   1篇
  1997年   2篇
  1995年   1篇
  1994年   3篇
  1992年   2篇
  1991年   2篇
  1986年   1篇
  1985年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1972年   1篇
  1967年   1篇
  1957年   2篇
  1953年   1篇
  1933年   1篇
排序方式: 共有1118条查询结果,搜索用时 15 毫秒
71.
According to the international medical community, adequate antenatal care, beginning by the end of the fourth month of pregnancy, is beneficial to maternal and perinatal outcomes. However, there is little research on timing of antenatal care and factors that influence it, including external barriers and women's beliefs. This research was conducted at antenatal clinics in the Democratic Republic of Congo where rates of infant and maternal mortality are among the highest in sub-Saharan Africa and where antenatal care begins later than in other countries in the region; the goal was to assess knowledge, beliefs and barriers to timely antenatal care. In this paper we present data collected in structured interviews at the women's first antenatal visit (N = 206). Although 75% of women believed antenatal care should start before the end of the fourth month, as recommended by WHO, only 22% presented by this time. Important barriers were financial (37%) and lack of knowledge about appropriate timing (35%). Gravidity was associated with gestational age at first visit (p < 0.001). Average gestational age at first visit was 4.7 months in primigravidae and 5.9 months in women with > or = 2 previous pregnancies. Most women in Kinshasa begin antenatal care later than recommended by WHO. Educating women on the importance of timely antenatal care and improving its financial accessibility should be priorities for maternal and child health programs in the DRC.  相似文献   
72.
INTRODUCTION: Annually more than 2 million pilgrims from all over the world attend the Hajj in Saudi Arabia. Overcrowding during this pilgrimage leads to a high risk of transmission of airborne infectious diseases. Tuberculosis (TB) is common among hospitalized pilgrims, but the overall risk of acquiring Mycobacterium tuberculosis infection during this pilgrimage is not known. We conducted a prospective study to assess the risk of M. tuberculosis infection among Hajj pilgrims. METHODS: We measured the immune response to TB antigens using a whole-blood assay (QuantiFERON TB assay) prior to departure and 3 months after return from the Hajj pilgrimage. RESULTS: Of 357 paired assays, 149 pilgrims were negative prior to the Hajj and 15 (10%) of these had a significant rise in immune response to TB antigens. CONCLUSIONS: Pilgrims may be at high risk of acquiring M. tuberculosis infection during the Hajj. This has significant public health implications for TB control in countries with large Muslim populations.  相似文献   
73.
OBJECTIVE: To investigate whether MRI-based volumes of whole brain, medial temporal lobe and white matter hyperintensities (WMH) predict progression of cognitive decline in a sample of nondemented elderly. METHODS: Thirty-seven nondemented elderly attending a memory clinic and 28 elderly controls participated in this follow-up study. The average follow-up period was 1.8 years. Cognitive function was measured at baseline and follow-up with the Cambridge Cognitive Examination (CAMCOG). Baseline Magnetic Resonance Imaging (MRI) provided quantitative measures of whole brain, medial temporal lobe and WMH. Linear mixed models controlled for age and sex were used to assess the independent associations between MRI measures, baseline cognition, and annual decline in cognition. RESULTS: Medial temporal lobe volume was independently associated with baseline CAMCOG score (p < 0.01), whereas whole brain volume (p < 0.01) and WMH (p < 0.05) were associated with annual decline in CAMCOG score. CONCLUSIONS: These data suggest that regional damage to the medial temporal lobes underlies initial mild cognitive impairment, whereas more global brain changes, such as whole brain atrophy and WMH, contribute to further progression of cognitive decline.  相似文献   
74.
Saethre-Chotzen syndrome is a craniosynostosis syndrome characterized by facial and limb abnormalities. It is caused by mutations in the TWIST gene on chromosome 7p21. To date, more than 80 different mutations in TWIST have been reported in the literature.Recently, large deletions of chromosome 7p, encompassing the TWIST locus, have been detected in patients with clinical features of Saethre-Chotzen syndrome. Strikingly, all these patients were severely mentally retarded, which is otherwise a rare finding in Saethre-Chotzen syndrome. The authors report a patient with a large TWIST/7p deletion but with normal development. Furthermore, craniosynostosis was not present at birth or at the age of 4 months. However, skull radiographs taken at the age of 14 months showed stenosis of both coronal sutures, as well as of part of the sagittal suture. Reports on postnatal onset of craniosynostosis have been made in Crouzon syndrome but, to the authors' knowledge, never in Saethre-Chotzen syndrome.  相似文献   
75.
We carried out a multicenter performance evaluation of three new DNA-based human leukocyte antigen (HLA) typing assays: INNO-LiPA HLA-A Update, INNO-LiPA HLA-B Update, and INNO-LiPA HLA-DQB1 Update. After optimization, the accuracy rates were all 100%, and the final observed resolutions were 99.4, 92.4, and 85.6%, respectively. These rapid and easy-to-perform assays yielded results fully concordant with other DNA-based tissue typing tests.  相似文献   
76.
PURPOSE: To evaluate visual impairment in Usher syndrome 1b (USH1b) and Usher syndrome 2a (USH2a). METHODS: We carried out a retrospective study of 19 USH1b patients and 40 USH2a patients. Cross-sectional regression analyses of the functional acuity score (FAS), functional field score (FFS) and functional vision score (FVS) related to age were performed. Statistical tests relating to regression lines and Student's t-test were used to compare between (sub)groups of patients. Parts of the available individual longitudinal data were used to obtain individual estimates of progressive deterioration and compare these to those obtained with cross-sectional analysis. Results were compared between subgroups of USH2a patients pertaining to combinations of different types of mutations. RESULTS: Cross-sectional analyses revealed significant deterioration of the FAS (0.7% per year), FFS (1.0% per year) and FVS (1.5% per year) with advancing age in both patient groups, without a significant difference between the USH1b and USH2a patients. Individual estimates of the deterioration rates were substantially and significantly higher than the cross-sectional estimates in some USH2a cases, including values of about 5% per year (or even higher) for the FAS (age 35-50 years), 3-4% per year for the FFS and 4-5% per year for the FVS (age > 20 years). There was no difference in functional vision score behaviour detected between subgroups of patients pertaining to different biallelic combinations of specific types of mutations. CONCLUSIONS: The FAS, FFS and FVS deteriorated significantly by 0.7-1.5% per year according to cross-sectional linear regression analysis in both USH1b and USH2a patients. Higher deterioration rates (3-5% per year) in any of these scores were attained, according to longitudinal data collected from individual USH2a patients. Score behaviour was similar across the patient groups and across different biallelic combinations of various types of mutations. However, more elaborate studies, preferably covering longitudinal data, are needed to obtain conclusive evidence.  相似文献   
77.
78.
OBJECTIVES/HYPOTHESIS: The differentiated character of changes in the mucous relief of the trachea as induced by air containing pollutants from the wastes of nickel-, mercury-, and cement-producing plants and by Candida albicans occurring in the waste disposal site of a large town are identified. The trachea was chosen because it is the entrance gate for the penetration of polluted air into the lungs. Changes on the trachea influence the character and extent of changes in lungs. STUDY DESIGN: Histological study with Viennese grey strain laboratory rabbits and rats caught directly on an investigated site. METHODS: We present new results of the functional morphology of the respiratory system as the results of scanning and transmission electron microscopy studies that can reveal character and range of damage of mucosal relief of trachea relevant to the functional dynamics of mucociliary clearance. Under physiological conditions this mechanism allows that only respirable dust particles enter the deep respiratory tract. RESULTS: In case of a damaged tracheal relief because of exposure to various aerosols, the functional morphology is changed, which aids in understanding the mechanisms damaging to mucociliary clearance induced by living in heavily polluted areas. CONCLUSION: Understanding of these morphological changes on base of detailed electron microscopic findings sheds new light on elaborating novel diagnostic methods for clinical practice.  相似文献   
79.
BACKGROUND: Legionella pneumophila, a Gram negative intracellular pathogen, causes Legionnaires' disease (LD). Interferon (IFN)-gamma is important for host defence against L pneumophila so reduced IFN-gamma production capacity and/or responsiveness might render humans more susceptible to infection with L pneumophila. METHODS: Seventy seven patients who suffered from LD after a point source outbreak one year earlier participated in the study. Whole blood was incubated with non-specific stimuli (lipopolysaccharide (LPS) or interleukin (IL)-12) or specific stimuli (viable or heat killed L pneumophila) to evaluate IFN-gamma production, and with IFN-gamma to evaluate IFN-gamma responsiveness. Expression of complement receptor 3 on monocytes was determined by flow cytometry. Thirty seven companions who were also exposed but had not developed LD served as controls. RESULTS: Patients released less IFN-gamma than controls in response to stimulation with LPS (mean (SE) 393 (58) pg/ml v 914 (178) pg/ml; p=0.001) and IL-12 (96 (14) pg/ml v 177 (41) pg/ml; p=0.058). IFN-gamma responsiveness, measured by release of IFN-gamma inducible protein (IP)-10, tumour necrosis factor alpha, IL-12 production capacity, and monocyte expression of complement receptor 3, did not differ between patients and controls. IFN-gamma release after stimulation with LPS and IP-10 release after stimulation with IFN-gamma were weakly associated with severity of LD in the former patient group (rho=-0.3, p=0.011 and rho=-0.3, p=0.037, respectively). CONCLUSION: These results suggest that impaired IFN-gamma production may contribute to susceptibility to L pneumophila infection.  相似文献   
80.
The present study was performed to evaluate the PDT efficacy, the singlet oxygen yield, and the plasma binding profile of the natural photosensitizer hypericin and two hypericin derivatives, hexamethylhypericin and tetrabromohypericin. All compounds exhibited an excellent 1O2 quantum yield, as documented by TEMP spin trapping experiments. The efficacy of PDT with the different compounds using a P388 lymphoma tumour model was clearly dependent on the interval between drug administration and light irradiation of the tumours. The most effective PDT treatment time was obtained with hypericin (5 mg/kg) using a 30-min drug-light interval, whereas a 24-h interval was optimal for a similar dose of tetrabromohypericin. No significant difference in survival between control animals and animals treated with PDT using tetrabromohypericin (5 mg/kg) was noted when a 30-min, 2- or 6-h interval was used. PDT with hexamethylhypericin (5 mg/kg) using different drug-light intervals was unable to prolong the life span of the tumour-bearing mice. In contrast, a dose of 20 mg/kg hexamethylhypericin, especially when administered 30 min prior to light exposure, produced a profound local reduction of tumour mass and a concomitant significant increase in survival time. The binding of the hypericins to human plasma was evaluated using density-gradient ultracentrifugation. It was found that tetrabromohypericin exhibits an affinity for plasma constituents almost similar to hypericin, in contrast to the more hydrophilic hexamethylhypericin that mainly binds to heavy proteins (e.g. albumin). Since the latter compound showed an efficacy profile similar to hypericin, no correlation could be found between the optimal drug-light interval and the plasma protein binding of the compounds.  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