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   116001篇
  免费   5955篇
  国内免费   138篇
耳鼻咽喉   1772篇
儿科学   5196篇
妇产科学   3928篇
基础医学   16066篇
口腔科学   2832篇
临床医学   8319篇
内科学   21986篇
皮肤病学   3357篇
神经病学   8984篇
特种医学   5043篇
外国民族医学   32篇
外科学   19014篇
综合类   1595篇
一般理论   29篇
预防医学   5805篇
眼科学   3393篇
药学   8042篇
  2篇
中国医学   324篇
肿瘤学   6375篇
  2018年   887篇
  2017年   773篇
  2016年   1091篇
  2015年   1215篇
  2014年   1598篇
  2013年   2363篇
  2012年   3090篇
  2011年   3139篇
  2010年   1969篇
  2009年   1926篇
  2008年   3246篇
  2007年   3480篇
  2006年   3624篇
  2005年   3742篇
  2004年   3685篇
  2003年   3553篇
  2002年   3504篇
  2001年   7013篇
  2000年   6957篇
  1999年   5857篇
  1998年   1622篇
  1997年   1558篇
  1996年   1334篇
  1995年   1201篇
  1994年   1091篇
  1993年   1119篇
  1992年   3765篇
  1991年   3575篇
  1990年   3561篇
  1989年   3348篇
  1988年   2985篇
  1987年   2894篇
  1986年   2803篇
  1985年   2617篇
  1984年   1943篇
  1983年   1594篇
  1982年   927篇
  1981年   915篇
  1980年   765篇
  1979年   1822篇
  1978年   1346篇
  1977年   1111篇
  1976年   936篇
  1975年   1178篇
  1974年   1212篇
  1973年   1198篇
  1972年   1040篇
  1971年   975篇
  1970年   880篇
  1969年   787篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
71.
OBJECTIVE: To study the relationship between vitamin C and the severity of periodontitis. MATERIAL AND METHODS: The study population consisted of subjects from the Malabar/Purbasari tea estate on West Java, Indonesia. In 2002, clinical measurements were performed in 128 subjects, including evaluation of plaque, bleeding on probing, pocket depth and attachment loss. In 2005, 123 out of 128 subjects could be retrieved who were present at the examination of 2002. Blood samples were taken to measure plasma vitamin C levels. Information about the subject's dietary habit was obtained by means of a personal interview guided by a questionnaire. RESULTS: Plasma levels of vitamin C ranged from 0.02 to 34.45 mg/l with a mean of 7.90 mg/l (+/-5.35). The correlation coefficient between plasma vitamin C level and periodontal attachment loss was -0.199 (p<0.05); stepwise linear regression revealed that vitamin C levels explained 3.9% of the variance in periodontal attachment loss. Subjects with vitamin C deficiency (14.7% of the study population) had more attachment loss compared with those with depletion or normal plasma vitamin C values. CONCLUSION: The negative association between plasma vitamin C levels and periodontal attachment loss suggests that vitamin C deficiency may contribute to the severity of periodontal breakdown.  相似文献   
72.
The short-term fluoride release of a giomer (Reactmer), a compomer (Dyract AP), a conventional glass ionomer cement (Fuji II Cap) and a resin-modified glass ionomer cement (Fuji II LC) was evaluated and compared. Specimen discs (6 +/-0.2 mm diameter and 1 +/- 0.2 mm thick) were prepared for each material using custom molds. Each disc was placed in 1 ml of deionized for 24 hours at 37 degrees C. After one day, the water was extracted and analyzed. The specimen discs were then re-immersed into another 1 ml of fresh deionized water. The procedure of removing and refilling the water was repeated for 28 days. Sample solutions taken during the first seven days and at days 14, 21 and 28 were introduced into a capillary electrophoresis system using field amplified sample injection (FASI) to determine fluoride release. Data was analyzed using factorial ANOVA/Scheffe's post-hoc test at significance level 0.05. An initial fluoride "burst" effect was observed with glass ionomers. Both compomer and giomer did not show an initial fluoride "burst" effect. With the exception of the compomer, fluoride release at day one was generally significantly greater than at the other time intervals. The glass ionomers released significantly more fluoride than the compomer and giomer at day one. Although fluoride release of the giomer was significantly greater than the other materials at day seven, it became significantly lower at day 28.  相似文献   
73.
OBJECTIVES: The purpose of this study was to analyze the expression of adhesion molecules on endothelial cells in the alveolar ridge mucosa, the gingiva and the periimplant mucosa in humans. MATERIAL AND METHODS: Twelve partially edentulous subjects were included in the study. In each subject, one soft tissue biopsy was harvested from the edentulous alveolar ridge mucosa, one from a tooth site and one from an implant site. After 3 weeks of undisturbed plaque accumulation, an additional biopsy was obtained from one tooth and one implant site in each subject. The tissue samples were snap frozen and prepared for immunohistochemical analysis. RESULTS: In the alveolar ridge mucosa, smaller proportions of endothelial cells expressing ICAM-1, ELAM-1 and VCAM-1 were observed than in the gingiva. ELAM-1-positive cells occurred in lower numbers than in periimplant mucosa. After 21 days of plaque accumulation, ELAM-1 was increased in tooth sites, but decreased in periimplant mucosa. CONCLUSION: The results of the present study indicated that the proportions of activated endothelial cells and the extravasation of leukocytes is larger in gingiva and periimplant mucosa than in alveolar ridge mucosa. This might be due to the less permeable keratinized epithelial layer in the edentulous ridge mucosa, which offers proper protection against microbial pathogens. The greater expression of endothelial cell adhesion molecules during experimental gingivitis, compared to periimplant mucositis, may reflect its longer history of repeated antigenic assaults.  相似文献   
74.
A 9-year-old boy was diagnosed as having an unilateral cross-bite with mandibular deviation. This was later found to be due to unilateral hyperplasia of the right condyle. The increased growth activity subsequently led to an extreme facial asymmetry and a serious psychological condition began to develop. Consequently, surgery was performed at the age of 11 years 8 months when removal of the enlarged condyle and an oblique ramus osteotomy on the opposite side was performed. In this way the facial asymmetry was eliminated. No effort during the surgery was made, however, to restore normal occlusion. The post-operative orthodontic treatment was successful in allowing growth to bring about a normalization of the occlusal relationships. Two years after surgery, complete aesthetic and function rehabilitation has been achieved. This has also led to an improvement in the patient's psychological condition. The result was still stable 11 years post-operatively. The case illustrates the value of early treatment and co-operation between orthodontists and oral surgeons.  相似文献   
75.
Fluorescence spectra of dentine and enamel illuminated with laser light of wavelengths of 337, 488, 515 and 633 nm respectively were recorded. The fluorescence obtained by illumination with UV laser light at 337 nm had a peak at about 400 nm in dentine as well as enamel. Compared to intact enamel the fluorescence from enamel with initial carious lesions was of lower intensity and had a slight red shift. No fluorescence within the visible range was obtained by illumination with a low power He-Ne laser at 633 nm. Illumination at 488 nm produced fluorescence with a peak at about 540 nm in dentine as well as enamel. The difference in the intensity of fluorescence between sound and carious enamel was generally greater at this wavelength than at any of the others tried, and the red shift from the carious enamel was also more pronounced. Illumination at 515 nm produced fluorescence of similar wavelengths but with much less difference between intact and carious enamel. It was concluded that illumination at 488 nm was the most suitable wavelength of those investigated for the detection of initial carious lesions by the fluorescence technique.  相似文献   
76.
Haemophilia A, the most common of bleeding disorders is characterzed by bruishing and spontaneous bleeding into the joints but may remain undiagnosed if present in the mild form. A case is discussed where episodes of bruising and joint sweelling as a child were misdiagnosed as rheumatic fever and the bleeding disorder was diagnosed following recurrent episodes of bleeding after extraction of an upper molar tooth.  相似文献   
77.
78.
Dental predictors of high caries increment in children.   总被引:1,自引:0,他引:1  
A comprehensive set of dental variables was investigated to find the "best" combination of predictors for high caries increment in 7/8-year-old and 10/11-year-old children. Four populations with widely different caries prevalence were studied. Logistic regression analysis supplied multiple-input models by stepwise selection of predictors. A "low number of sound primary molars" was the best and most consistent predictor of high caries increment. The second best predictors were "high numbers of pre-cavity lesions on permanent first molars" (discolored pits and fissures in the younger age group and white spots on the smooth parts of buccolingual surfaces in the older age group). Inclusion of radiological variables did not substantially increase the quality of prediction. For practical application, models with various multiple inputs selected by stepwise procedures were compared with "fixed" three-input models. These three-input models resulted in predictive quality nearly equal to those of the multiple models. Traditional one-input models, containing DMFT or dmft, were inferior to the three-input models, particularly in the older age class. The lower the caries prevalence of the source data, the better was the prediction. As a summary measure characterizing the predictive performance of a model, we used the index "area under the receiver operating characteristic curve" A. For the 1984 data and the three-input models, the area was approximately 80%, and for the 1972 data, the area was 65-70%.  相似文献   
79.
Marginal fidelity of four methods of swaged metal matrix crown fabrication.   总被引:3,自引:0,他引:3  
The swaged metal matrix provides a method for rapidly making a metal substructure for ceramic crowns. This study determined the vertical and horizontal marginal fidelity of swaged metal substrate crowns made with four methods. No significant difference in vertical or horizontal marginal fidelity was found for metal margin crowns formed with either a plastic spacer or a paint-on die spacer. The vertical marginal fidelity was significantly better in crowns made with a metal margin (37 microns) than in crowns made with a porcelain facial margin (62 microns), and the latter were significantly better than crowns made with a 360-degrees porcelain margin (86 microns). Crowns made with all four methods were overcontoured by 46 to 82 microns. The 360-degrees porcelain margin was technically more difficult and time-consuming to make.  相似文献   
80.
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