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   1691篇
  免费   93篇
  国内免费   21篇
耳鼻咽喉   8篇
儿科学   23篇
妇产科学   11篇
基础医学   317篇
口腔科学   43篇
临床医学   96篇
内科学   91篇
皮肤病学   57篇
神经病学   131篇
特种医学   99篇
外国民族医学   2篇
外科学   114篇
综合类   123篇
预防医学   346篇
眼科学   24篇
药学   169篇
  1篇
中国医学   20篇
肿瘤学   130篇
  2023年   16篇
  2022年   45篇
  2021年   75篇
  2020年   50篇
  2019年   47篇
  2018年   38篇
  2017年   24篇
  2016年   30篇
  2015年   48篇
  2014年   95篇
  2013年   112篇
  2012年   96篇
  2011年   112篇
  2010年   67篇
  2009年   80篇
  2008年   105篇
  2007年   70篇
  2006年   70篇
  2005年   51篇
  2004年   30篇
  2003年   49篇
  2002年   30篇
  2001年   31篇
  2000年   35篇
  1999年   28篇
  1998年   36篇
  1997年   27篇
  1996年   26篇
  1995年   25篇
  1994年   25篇
  1993年   22篇
  1992年   22篇
  1991年   19篇
  1990年   13篇
  1989年   20篇
  1988年   14篇
  1987年   16篇
  1986年   12篇
  1985年   22篇
  1984年   13篇
  1983年   10篇
  1982年   8篇
  1981年   7篇
  1980年   8篇
  1979年   7篇
  1978年   6篇
  1977年   4篇
  1976年   4篇
  1973年   3篇
  1971年   1篇
排序方式: 共有1805条查询结果,搜索用时 15 毫秒
1.
Precise data on food chemical composition is crucial for any quantitative nutrition research and indispensable for evaluation and planning of computer-based menus. Moreover, exact food chemical composition is of the utmost importance in composing specific diets that may be low in certain essential nutrients. Therefore, this research evaluated a weekly vegan menu using three different food composition databases (FCDB): the Croatian, the official Danish Food Composition Database and the United States Department of Agriculture (USDA) – National Nutrient Database for Standard Reference. Significant differences (p < 0.05) were determined in evaluated and optimised offers for the same menu when using different FCDBs. Furthermore, in these menus quantities of some nutrients have not reached official daily recommendations needed for prevention of non-communicable diseases. In this research, new vegan menus that can provide adequate quantity of essential nutrients, regardless of FCDB utilized, were created with linear optimisation (LO). This resulted in high quality daily menu offers. However, depending on the FCDB that was used, optimal menus differed in daily meal combinations, and the effectiveness of the optimisation in the minimisation of differences caused by differences of data in FCDBs was tested. Linear optimisation has been proved to be an effective tool in planning of specific diets, such as vegan diets. Nonetheless, the quality of computer-planned menus depends heavily on the quality of FCDB used.  相似文献   
2.
目的 探讨电子直线加速器照射对细胞周期及细胞凋亡的影响。方法 采用直线加速器对NIH 3T3细胞进行照射,观察细胞周期及细胞凋亡的改变情况;同时测定损伤前后p53蛋白的表达情况。结果 照射后细胞凋亡数增加,p53蛋白表达量上升。结论 电子直线加速器照射损伤可诱导细胞凋亡。  相似文献   
3.
左心室巨大室壁瘤不同左心室成形方法的对比研究   总被引:5,自引:3,他引:2  
目的研究左心室巨大室壁瘤的左心室成形方法,对改进的左心室心内膜环缩技术和传统的线性缝合技术进行近、远期疗效对比。方法自1992年1月至2004年12月,对148例左心室巨大室壁瘤患者进行手术治疗,按照手术中左心室成形方法不同分为两组,传统术式组:89例,采用传统的线性缝合成形技术;改良术式组:59例,采用改良的心内膜环缩成形技术,旷置梗死的心肌组织,再缝合环缩后的切口。采用多次信访、电话随访和门诊复查相结合的方法对两组患者术后的近、远期疗效进行对比观察。结果手术死亡5例(3.4%),其中传统术式组4例,改良术式组1例(P=0.320)。术后主要并发症为低心排血量和心室颤动。随访134例(93.7%),随访时间51.4±27.0月。远期死亡21例,术后早期心功能Ⅲ级以上是影响远期死亡的危险因素(P=0.000)。改良术式组5年和8年生存率明显优于传统术式组(91.6%vs.76.3%,P=0.040;91.6%vs.61.4%,P=0.000)。两组心功能分级(NYHA)和左心室射血分数(LVEF)术后早期和随访期间较术前改善和升高(P<0.05),改良术式组改善更明显。两组左心室舒张期末内径(LVEDD)术后早期与术前比较明显减小(P=0.000),但随访30个月时有重新增大的趋势(P=0.046)。传统术式组随访30个月时LVEDD扩大比率明显高于改良术式组(38.8%vs.16.7%,P=0.030)。结论左心室巨大室壁瘤的手术近、远期疗效满意,保持适当的左心室形态和容积是手术的关键。心内膜环缩法进行左心室成形是一种简单有效的手段,其远期结果优于线性缝合法。  相似文献   
4.
目的 :研究SRS2 0 0X 刀治疗系统治疗靶点定位的精确度。方法 :应用人体头颅模型内特定标记物测定CT定位的精度 ,用胶片法测定二次等中心系统精度和总的治疗精度。结果 :BRW头环CT定位精度为 0 .65mm ,最大误差为 1 .0 9mm ;SRS2 0 0二次等中心系统误差为 0 .1 9mm ;总治疗误差理论计算值为0 .68mm ,胶片法检测值为 1 .43mm。结论 :X 刀治疗系统精确度已达到放射外科质量控制要求。  相似文献   
5.
Background: The fabrication of dental prosthesis requires the transfer of interocclusal records from patient's mouth to semiadjustable articulators using different kinds of recording media. Any inaccuracy in these interocclusal records leads to occlusal errors in the final prosthesis. This study was conducted to evaluate the dimensional changes occurring in the interocclusal recording material over a given period of time and the material's resistance to compression during the cast mounting on the articulator.  相似文献   
6.
任江平 《医疗设备信息》2007,22(8):119-119,121
介绍和讨论瓦里安 2300C/D直线加速器 COLL联锁故障的发生原因和检修.  相似文献   
7.
艺术嗓音歌声客观评价初探   总被引:1,自引:0,他引:1  
目的探讨客观评价艺术嗓音歌声的方法。方法对48名声乐专业青年大学生录制专业训练歌声信号,提取歌声平均能量、频率误差、音域误差作为评价参数,使用神经网络方法和多元线性回归方法客观评价歌声质量,并与资深专业教师的主观评价进行比较。结果客观评价歌声质量的方法中,神经网络方法误差在4%之内,而线性回归方法误差在6%之内,前者较优。结论神经网络方法利用评价参数能正确客观评价歌声质量,有助于科学地指导选拔和训练艺术嗓音人才。  相似文献   
8.
Up to 30% of patients with temporal lobe epilepsy (TLE) remain without remarkable changes in MRI. In this study we investigated the role of (1)H-MR spectroscopy ((1)H-MRS) in lateralizing the affected hemisphere in the mentioned patient group. Twenty-two consecutive patients diagnosed with TLE were investigated by high resolution MRI and (1)H-MRS. We examined the incidence and diagnostic accuracy of temporal metabolite alterations determined by Linear Combination of Model Spectra (L C Model) via water reference. Metabolite values of each hemisphere of TLE patients were compared with healthy controls. Results of metabolite alterations were related to intensive video EEG focus localization. Reduction of N-acetylaspartate + N-acetylaspartyl-glutamate (tNAA) in the affected hemisphere revealed identification in six of nine patients (66%) with unilateral TLE. Group comparison revealed a significant reduction of tNAA (6.1+/-0.8*) in the involved temporal lobe compared with controls (6.67+/-0.4*, P=0.026). Choline levels were significantly increased in the affected hemisphere (1.42+/-0.17*) compared with healthy controls (1.22+/-0.17*, P=0.035). The results of our study show that (1)H-MRS is able to identify the affected hemisphere of MRI negative TLE patients and can be used as an additive tool in multimodal focus localization.  相似文献   
9.
直线加速器十年故障分析总结   总被引:1,自引:0,他引:1  
目的分析和总直线加速器十多年来的故障。方法根据十多年来的故障维修记录,统计和分析直线加速器各阶故障率及故障特点。结果直线加速器使用早期由于机器不稳定故障率比较高,使用中期及其比较稳定,故障率比较低,使用后期由于零部件老化,故障率比较高。  相似文献   
10.
A feedforward network is used to recognize short, digitized, isolated utterances. A high, multispeaker recognition rate is achieved with a small vocabulary with a single training utterance. This approach makes use of the pattern recognition property of the network architecture to classify different temporal patterns in the multidimensional feature space. The network recognizes the utterances without the need of segmentation, phoneme identification, or time alignment. We train the network with four words spoken by one single speaker. The network is then able to recognize 20 tokens spoken by 5 other speakers. We repeat the above training and testing procedure using a different speaker's utterances for training each time. The overall accuracy is 97.5%. We compare this approach to the traditional dynamic programming (DP) approach, and find that DP with slope constraints of 0 and 1 achieve 98.5% and 85% accuracies respectively. Finally we validate out statistics by training and testing the network of a four-word subset of the Texas Instruments (Tl) isolated word database. The accuracy with this vocabulary exceeds 96%. By doubling the size of the training set, the accuracy is raised to 98%. Using a suitable threshold, we are able to raise the accuracy of one network from 87% to 98.5%. Thresholding applied to all networks would then raise the overall accuracy to well over 99%.

This technique is especially promising because of the low overhead and computational requirements, which make it suitable for a low cost, portable, command recognition type of application.  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