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   16332篇
  免费   1528篇
  国内免费   576篇
耳鼻咽喉   93篇
儿科学   145篇
妇产科学   166篇
基础医学   2361篇
口腔科学   1579篇
临床医学   1460篇
内科学   2601篇
皮肤病学   272篇
神经病学   604篇
特种医学   577篇
外科学   1246篇
综合类   1871篇
现状与发展   3篇
预防医学   1013篇
眼科学   1049篇
药学   1912篇
  5篇
中国医学   960篇
肿瘤学   519篇
  2024年   36篇
  2023年   329篇
  2022年   457篇
  2021年   1200篇
  2020年   778篇
  2019年   688篇
  2018年   679篇
  2017年   642篇
  2016年   652篇
  2015年   680篇
  2014年   1096篇
  2013年   1264篇
  2012年   838篇
  2011年   943篇
  2010年   722篇
  2009年   668篇
  2008年   642篇
  2007年   666篇
  2006年   583篇
  2005年   536篇
  2004年   408篇
  2003年   395篇
  2002年   346篇
  2001年   294篇
  2000年   261篇
  1999年   218篇
  1998年   216篇
  1997年   194篇
  1996年   158篇
  1995年   133篇
  1994年   158篇
  1993年   141篇
  1992年   131篇
  1991年   104篇
  1990年   107篇
  1989年   93篇
  1988年   101篇
  1987年   97篇
  1986年   114篇
  1985年   137篇
  1984年   104篇
  1983年   68篇
  1982年   103篇
  1981年   65篇
  1980年   54篇
  1979年   40篇
  1978年   26篇
  1977年   29篇
  1976年   15篇
  1975年   8篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
91.
The surface of the ovary has been found to be composed of two types of epithelial cells called A and B cells which are found in their own respective zones, the A and B zones. A quantitative study was undertaken to determine the mean cell volumes and cell ultrastructure. Ovarian biopsies were taken from six women and A and B zones, having been identified by scanning electron microscopy, were re-embedded for transmission electron microscopy. Stereological measurements using point sampled intercepts were made on vertical sections and showed that B cells are significantly larger than A cells. The volume weighted mean cell volumes of the A and B cells were 237.3 microns 3 and 676.8 microns 3 respectively. The volume fractions of the nucleus and mitochondria were similar in the two cell types. Although the vesicle content of each type was similar, a large variation between cases made the interpretation difficult. The stereological tools used in this study proved to be easy and efficient estimators of surface cell ultrastructure and give an important direction for ultrastructural research.  相似文献   
92.
对经 HBV-DNA 转染的 MT-5细胞的培养条件进行观察。发现重金属离子Zn 和 Cd 对 MT-5细胞表达 HBsAg 有诱导作用,而咖啡因、地塞米松、氢化可的松、丙酸睾丸酮、苯丙酸诺龙对 MT-5细胞的 HBsAg 均无诱导作用。  相似文献   
93.
用实验方法比较三种常用的缩颈方法及评价锤造全冠的边缘适合性。结果表明各组边缘间隙均大于0.180mm,说明锤造全冠边缘适合性较差,临床检查难以确定其间隙大小。各组近胎面轴壁间隙较小,这与冠成形时此处受力较大,冠周径变小有关,提示临氏上应避免用力和反复锤击此处。各组胎面间隙均大于0.130mm,表明面升高,边缘浮出量较大,冠尚未完全就位。当硬铅代型与缩颈器之间未预留冠套间隙时,所得的锤造全冠适合性更差,面间隙最大(0.945mm)。  相似文献   
94.
To investigate risk factors for spinal fracture, we studied the relationship between the prevalence of asymptomatic spinal fracture and various morphological measures including spinal bone mineral density (BMD) in women. A total of 122 women ranging in age from 55 to 79 years were studied. The group consisted of 46 women aged 55–59 years (18 with fracture), 51 women aged 60–69 years (26 with fracture), and 26 women aged 70–79 years (14 with fracture). BMD of cortical and trabecular bone from L1 to L3 was measured using quantitative computed tomography (QCT). Run-length analysis was applied to evaluate the spinal trabecular textural features using CT images; the texture indices which represent the mean width of trabeculae (the T-texture) and that of intertrabecular spaces (the I-texture) were obtained. Anthropometric factors including body weight and height, psoas muscle area, and vertebral bone volume were measured using CT images. Among the various factors, trabecular BMD in women aged 55–69 years showed the highest odds ratio for the presence of fracture per standard deviation (SD) decrease in bone density. However, in women aged 70–79 years, the highest odds ratio was observed for trabecular texture index but not for trabecular BMD. The I-texture in women aged 55–59 years, the muscle area in women aged 60–69 years, and cortical BMD and muscle area in women aged 70–79 years were also considered significantly related to the risk of fracture. Received: 31 December 1995 / Accepted: 24 July 1996  相似文献   
95.
在实验室绝热反应器中进行了乙苯脱氢制苯乙烯的反应动力学研究。根据不同反应机理,提出五种反应模型,经残差分析及模拟计算规律与实验规律的比较,确定Carra双曲模型为最佳反应动力学模型。通过对实验数据的回归拟合,经参数估计求得了速率方程的频率因子和活化能。  相似文献   
96.
用酸蚀法提高纯钛与光固化冠桥树脂粘结强度的研究   总被引:5,自引:1,他引:4  
目的:研究用酸蚀法提高钛与光固化复合树脂剪切粘结强度的可行性,并观察表面粗糙度与剪切粘结强度之间的关系。方法:采用不同浓度的酸蚀剂对钛铸件表面进行酸蚀,并与artglass光固化复合树脂进行粘结,以单纯喷砂组为对照,比较剪切粘结强度的差异。对酸蚀后及剪切试验后的金属表面进行扫描电镜观察,并测定其表面粗糙度。结果:用酸蚀法可以显著提高钛与复合树脂的粘结强度,HF浓度为4%时粘结强度最高。表面粗糙度随酸蚀剂的浓度增高而下降。结论:纯钛铸件用酸蚀法处理后可以获得较高的粘结强度,HF酸浓度以4%为宜。表面粗糙度对粘结强度不起决定性作用。  相似文献   
97.
突触小泡膜表面突起与微管联系的超微结构研究   总被引:1,自引:0,他引:1  
本研究用透射电镜技术观察了大脑皮质(视区)和海马(CA1区和CA3区)的神经终末内的突触小泡和微管间的联系。结果揭示:在适当的超薄切片样品上,常显示出突触小泡膜表面上有短的突起,说明突触小泡是借其膜表面的短突与其它小泡和微管进行联系的。除小泡外,在微管的表面也见一些短突并与小泡发生接触。本文首次报道了用透射电镜方法观察脑内小泡-微管借表面短突连接的联系,提示突触小泡膜表面和微管表面的短突在轴浆运输机制中负有重要的作用。  相似文献   
98.
髌骨关节面的应用解剖学研究   总被引:2,自引:0,他引:2  
本文利用150例髌骨(干燥髌骨100例,福尔马林固定膝关节内的髌骨50例)观测了髌骨关节面和关节软骨的形态及其与股骨内外侧髁关节面在屈膝0~135度范围的对应关系。结果发现中间纵嵴向后突起并由下向上逐渐变凸占100%;内侧纵嵴明显突起者占62%,此时其髌骨内侧部关节面与股骨关节面之间的间隙较大;在膝关节屈曲过程申两关节面接触的顺序为髌骨关节面自下而上、股骨内外侧关节面从前向后相对滑动,伸膝时则相反;髌骨关节面的表面积为1019±20(650~1540)mm~2。并讨论了髌骨关节面的解剖学特点及其临床意义。  相似文献   
99.
Abstract The purpose of this study was to determine the clinical response to local delivery of tetracycline in relation to clinical and microbiological conditions of the other teeth. 4 deep pockets were monitored in 19 subjects with multiple deep periodontal lesions and high counts of P. gingivalis. In 9 patients (XT) only 2 of the selected lesions were treated by placement of tetracycline fibers (Actisite®). while the rest of the dentition was left untreated. In the other 10 patients, all teeth were supragingivally scaled and then treated by application of polymeric tetracycline HCl containing fibers, the whole dentition was subject to full mouth scaling and root planing, and the patients rinsed with 0.2% chlorhexidine (FT). A significant reduction in mean PPD was observed in all treated sites after two months. This reduction was maintained over the following 4 months. The magnitude of the effect was significantly greater in the FT group (1.74 mm) than in the LT group (0.88 mm). The mean attachment level changes were similar after 2 months in locally and fully treated subjects. A tendency of relapse was noted for treated sites in LT patients from month 2 to 6. A level of statistical significance was not reached for this effect. Data from measurements recorded at 6 sites around all teeth in the full mouth treated patients were analyzed using multiple linear regression. This analysis showed local changes in PPD and AL were significantly and strongly correlated with the baseline value of the respective parameter at the same site. In addition, more pocket depth reduction was noted if a site was not bleeding on probing at 6 months, if the location of a site was not approximal and if the tooth was not a second molar. Sites located on second molars showed also less AL gain than sites located on other teeth. Smokers showed significantly less reduction in PPD and significantly less AL gain. Furthermore, if subjects had a high % of pockets deeper than 4 mm at baseline they showed significantly less attachment gain.  相似文献   
100.
羊膜建库及其临床应用研究   总被引:3,自引:0,他引:3  
目的 :制备与保存羊膜 (Amnioticmembrane,AM ) ,为临床移植治疗眼表泪液 (Ocularsur face&Teardisease ,OSTD)提供新鲜羊膜 (Freshamnioticmembrane ,FSAM )、冻干羊膜 (Frozenam nioticmembrane ,FZAM )并观察其眼表重建的特点与临床疗效。方法 :采用目前国际公认的羊膜制备与保存方法 ,制备FSAM、FZAM并进行保存研究 ,经组织染色和电子显微镜检查 ,观察保存羊膜的形态及其活性 ;并将FSAM、FZAM应用于 12例OSTD患者 ,行患眼FSAM或FZAM移植术。通过术后印迹细胞学追踪观察移植后AM上皮细胞存活与移行、替代时间 ,评估AM移植重建眼表的临床疗效。结果 :FSAM、FZAM在光镜和电镜下均与正常球结膜组织结构相近 ,主要结构为胶原纤维和网状纤维。 12例OSTD患者行羊膜移植术 (Amnioticmembranetransplantation ,AMT)后均未见明显急性排斥反应 ,术后 1~ 2周可见少量新生血管长入植片 ,AMT后印迹细胞学追踪检查 ,术后 3个月为阴性 ,4个月出现阳性反应。所有患者术后随访 5~ 18个月 ,平均 11个月 ,AM在术后 4~ 9个月逐渐溶解、消失 ,移植区眼表的色泽与结构基本恢复正常。结论 :FSAM、FZAM是目前理想的结膜替代材料并可有效地用于重建角、结膜表面 ,减轻炎症反应 ,减少新生血管的生成 ,抑制纤维组织增生 ,防止  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