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   5324篇
  免费   366篇
  国内免费   177篇
耳鼻咽喉   76篇
儿科学   52篇
妇产科学   39篇
基础医学   739篇
口腔科学   703篇
临床医学   292篇
内科学   406篇
皮肤病学   132篇
神经病学   232篇
特种医学   310篇
外科学   368篇
综合类   827篇
预防医学   187篇
眼科学   297篇
药学   763篇
  1篇
中国医学   249篇
肿瘤学   194篇
  2023年   53篇
  2022年   59篇
  2021年   133篇
  2020年   144篇
  2019年   138篇
  2018年   121篇
  2017年   118篇
  2016年   109篇
  2015年   133篇
  2014年   250篇
  2013年   320篇
  2012年   205篇
  2011年   266篇
  2010年   220篇
  2009年   224篇
  2008年   249篇
  2007年   258篇
  2006年   214篇
  2005年   225篇
  2004年   221篇
  2003年   207篇
  2002年   199篇
  2001年   164篇
  2000年   159篇
  1999年   129篇
  1998年   124篇
  1997年   93篇
  1996年   78篇
  1995年   110篇
  1994年   79篇
  1993年   80篇
  1992年   83篇
  1991年   76篇
  1990年   65篇
  1989年   50篇
  1988年   50篇
  1987年   42篇
  1986年   48篇
  1985年   55篇
  1984年   54篇
  1983年   41篇
  1982年   51篇
  1981年   33篇
  1980年   32篇
  1979年   26篇
  1978年   23篇
  1977年   18篇
  1976年   12篇
  1975年   11篇
  1974年   6篇
排序方式: 共有5867条查询结果,搜索用时 15 毫秒
1.
The microvascular anatomy of the non-lobulated liver of adult Xenopus laevis was studied by scanning electron microscopy of vascular corrosion casts. Hepatic portal veins and hepatic arteries entered hepatic lobes at the hiluses, hepatic veins left at these sites. Intraparenchymal, hepatic portal veins branched up to 10 times before terminal portal venules supplied liver sinusoids. Hepatic arteries closely followed portal vessels. Arteriolar side branches formed anastomoses with close by portal venules (arteriolar-portal anastomoses; APAs), liver sinusoids (arteriolar-sinusoidal anastomoses; ASAs), and peribiliary plexus vessels. Distally, hepatic arteries anastomosed with terminal portal venules having >100 μm in diameter. Liver sinusoids formed a dense three-dimensional network displaying signs of non-sprouting and sprouting angiogenesis evidenced by “holes” and blind ending tapering cast vascular structures (sprouts), respectively. Sinusoids drained via efferent hepatic veins. Right and left hepatic veins drained into the posterior caval vein. Locally, a dense honeycomb-like 3D-meshwork of resin structures was found around terminal portal venules and hepatic arteries. These networks were fed by hepatic arterioles and drained into adjacent terminal portal venules. As their morphologies differed significantly from sinusoids and they were found at sites where diffuse lymphoid tissue is described, we are convinced that they represent the vasculature of diffuse lymphoid tissue areas. Frequencies and diameter ratios of hepatic portal venules versus hepatic arterioles anastomosing with the former (APAs) implicate that the arterial supply contributes to the oxygenation of parenchymal and stromal cells rather than to a significant increase in blood flow towards hepatic sinusoids.  相似文献   
2.
目的对于急性缺血性脑卒中(AIS)大脑中动脉闭塞患者,比较单时相、多时相CT血管造影(sCTA、mCTA)评估的侧支循环评分与定量灌注参数之间的关联性及在预测临床预后中的价值。方法搜集2019年12月至2020年12月于急救中心行一站式CT检查的发病时间在24 h内的大脑中动脉闭塞患者的临床资料及影像学资料,从CT灌注成像(CTP)原始图像中重组的动脉峰值期定义为sCTA,头颈部动脉峰值期、头颅静脉峰值期和头颅静脉晚期定义为mCTA,以Menon等提出的0~5分法进行单期、多期的侧支循环评估,并评价评分人员间可靠性。将sCTA与mCTA分为侧支良好组与不良组,统计并分析了两组之间核心梗死体积、低灌注体积、最终梗死体积、NIHSS评分、发病时间、90天后改良Rankin量表(mRS)评分的差异。结果最终纳入本研究的患者共43例[男29例,平均年龄(66.63±13.17)岁],sCTA、mCTA的评分者间有良好的一致性(Kappa分别为0.712和0.723)。sCTA与mCTA相比,低估了侧支状态(P<0.05),sCTA显示23.3%患者的侧支状态为良好,而mCTA有55.8%...  相似文献   
3.
目的探讨多模态MRI对子宫内膜癌诊断及病理分型临床价值。方法选取我院80例子宫内膜癌疑似患者,均行多模态MRI检查,以分段诊断性刮宫病理结果为金标准计算多模态MRI诊断子宫内膜癌的漏误诊率、灵敏/特异度及病理分型敏感特异性,建立接受者操作特征(ROC)曲线分析多模态MRI诊断子宫内膜癌的效能,对比不同类型患者的表观弥散系数(ADC)值。结果金标准诊断显示,80例疑似患者中经分段诊断性刮宫病理检查最终确诊子宫内膜癌共53例(66.25%)。MRI扫描显示,多模态MRI诊断子宫内膜癌的符合率81.25%、误诊率14.81%、漏诊率20.75%、灵敏度79.25%、特异度85.19%、阳性预测值91.30%;多模态MRI对Ⅰ型子宫内膜癌的分型敏感性67.57%、特异性81.40%、阳性预测值75.75%,对Ⅱ型子宫内膜癌的分型敏感性81.25%、特异性81.25%、阳性预测值52.00%。子宫内膜癌患者ADC低于非癌患者(t=11.284),Ⅰ型患者ADC低于Ⅱ型患者(t=2.133),高分化患者ADC高于低分化患者,Ⅲ期患者ADC低于Ⅰ~Ⅱ期患者(t=2.478),以上差异均有统计学意义(P<0.05)。结论多模态MRI对子宫内膜癌具有较高的筛查诊断效能,可通过多模态MRI影像组学特征及ADC数值差异进行子宫内膜癌临床诊断。  相似文献   
4.
《Journal of endodontics》2022,48(9):1169-1177
IntroductionThe aim of this study was to evaluate the effect of previous root canal treatment on dentinal tubule penetration of calcium silicate–based sealers during endodontic retreatment and to compare 2 different (commonly used and modified) tubule penetration depth measurement techniques.MethodsThe crowns of mandibular premolar teeth were removed, and root canals were prepared (ProTaper Universal; Dentsply Sirona, York, PA) and obturated using AH Plus (AH; Dentsply DeTrey, Konstanz, Germany), MTA Fillapex (MTAF; Angelus, Londrina, Brazil), and WellRoot ST (WRST; Vericom, Gyeonggi-do, South Korea); 0.1% red Rhod-2 dye (Chemodex, St Gallen, Switzerland) was added to the sealers. After storage for 3 weeks (37°C, 100% humid), the following sealer combination subgroups were created (the sealer used during the primary root canal treatment/the sealer used during the retreatment, n = 8): AH/AH, AH/MTAF, and AH/WRST; MTAF/AH, MTAF/MTAF, and MTAF/WRST; and WRST/AH, WRST/MTAF, and WRST/WRST. Green Fluo-3 dye (0.1%) was added to the sealers during retreatment. Sealer penetration depths were measured at 8 points and averaged, and the ratio of the retreatment sealer to the initial sealer was recorded as the mean tubule penetration depth ratio in the first technique, whereas the percentage of the circumferential penetration area ratios of the retreatment and initial sealers was calculated in the second technique. Statistical analyses were performed using Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests.ResultsThe mean penetration depth of AH and MTFA was found to be higher at the coronal third region in the control groups (P < .05). Both methods showed a significant difference among the groups at the coronal and median regions (P < .05). The AH/WRST, MTAH/AH, MTAF/MTAF, MTAF/WRSTS, and WRST/WRST groups showed deeper tubule penetration (first technique, P = .01). Both techniques showed that the penetration depth of the sealers was the same at the apical region (P > .05), whereas a difference was found among the techniques at the coronal and median regions. The sealers used in the previous root canal treatment limited the penetration depth of the sealers used during the retreatment process (P < .05). When MTAF was used as the initial sealer, the penetration depth of the second sealer did not change, whereas if WRST was the initial sealer, the penetration depth of the sealers at the median and apical regions is negatively affected during the retreatment process (P < .05).ConclusionsPrevious root canal treatment affects the penetration depth of calcium silicate–based sealers. The use of AH Plus and MTA Fillapex during the retreatment process showed an advantage. Both measurement techniques showed similar performances at the apical region, whereas the results varied at the coronal and midcoronal regions; therefore, a more stable sealer penetration measurement technique is still necessary.  相似文献   
5.
《Drug discovery today》2022,27(8):2076-2079
  1. Download : Download high-res image (73KB)
  2. Download : Download full-size image
  相似文献   
6.
《Radiography》2022,28(3):739-745
IntroductionRecent advances in technology have seen the introduction of remote scanning capabilities become a reality for departments, allowing staff to remotely access, observe and even scan without being by the scanner side. The COVID-19 pandemic has accelerated use of remote working which also aligns with the direction of travel for healthcare more widely. However for technology to succeed it needs to be acceptable for use by radiographers in clinical practice.MethodsFollowing trial of a remote scanning technology, a group of radiographers were surveyed for their views on its use in practice. The survey was based on the Technology Acceptance Model as well as providing opportunity for open feedback on views regarding the technology.ResultsPerceived ease of use was high but appears to have little influence over overall intention to use. Perceived usefulness was lower and demonstrated correlations with attitude towards and intended use of the remote technology, suggesting that this is a key area to address which would positively impact on acceptance. Other considerations that would help support effective implementation were highlighted with the majority stating the technology as friend rather than foe.ConclusionAs an early evaluation of practitioner views on remote scanning within MRI, the results highlight the areas that would benefit from further development before further roll out in practice. A clear vision of its use and robust governance is needed to effectively support its implementation and acceptance by radiographers.Implications for practiceIntroducing remote scanning technology has potential to support training and share skills of experienced radiographers across multiple locations. It has the potential to transform the way MRI departments work and increase safer supervision to enable wider utilization of the support workforce.  相似文献   
7.
目的 探讨320排CT靶重建联合MRI扫描在孤立性肺结节良、恶性鉴别诊断及肺癌早期诊断中的价值。方法 回顾性分析延安市人民医院320排640层CT低剂量扫描、CT标准靶重建、联合1.5TMRI检查,对临床检出的42例肺内孤立结节(SPN)进行相关诊断研究,分析本项技术是否能够明显提高诊断的准确率。结果 42例可疑孤立性肺小结节中检出42例检出率为100%,常规CT扫描病变检出正确例数28例正确率为66.67%,靶重建后检出正确例数为34例准确率为80.95%,联合CT靶重建及MRI检出正确例数40例,准确率可高达95.42%。结论 CT靶重建技术联合MRI扫描简单易行,患者容易接受,且能提高诊断的准确性。  相似文献   
8.
9.
Carbamazepine (CBZ) exists in anhydrous and dihydrate forms. These forms differ in their solubility, dissolution rate, and subsequently in their oral bioavailability. The objective of this study is to develop multivariate chemometric models for estimation of the low level of carbamazepine dihydrate (CBZ-DH) in the CBZ formulations containing excipients of the commercial formulation. The selected excipients were mixed in proportions to make sample matrices ranging from 0% to 50% CBZ-DH. Fourier transform infrared (FTIR), near infrared (NIR), and hyperspectral imaging data were mathematically pretreated before the development of partial least square and principal component analysis regression models. The developed partial least squares regression and principal component analysis models demonstrated predictability of CBZ and CBZ-DH by multiple scattering correction and standard normal variate processing methods. Among the spectroscopic techniques used the model performance parameters such as root-mean-square error, standard error, and bias were found to be low for NIR compared to FTIR. The treated data have shown better model fitting than without treatment, which was demonstrated by correlation coefficient of 0.9778, 0.9824, and 0.9852 for FTIR, NIR, and hyperspectral imaging, respectively. Furthermore, the predicted values were found to be very close to the selected low level of independent samples having 5% CBZ-DH in tablet formulation.  相似文献   
10.
目的 比较高频超声与CT诊断鼻骨骨折的临床价值。方法 回顾性分析经手术确诊的186例鼻骨骨折患者的术前高频超声和CT检查资料,比较两种检查方法对鼻骨骨折的总体检出率及不同类型骨折检出阳性率。结果 高频超声和CT对鼻骨骨折的总体检出率分别为(91.4%、94.6%),差异无统计学意义。高频超声对单纯线性骨折的检出阳性率(55.4%)高于CT(48.9%),差异有统计学意义(P<0.05);对粉碎性骨折的检出阳性率高频超声(29.6%)与CT相近(27.9%),差异无统计学意义;对复合性骨折检出阳性率高频超声(6.5%)低于CT(17.7%),差异有统计学意义(P<0.05)。结论 高频超声安全、价廉、便捷,可作为鼻骨骨折影像学检查的一项重要补充,值得临床推广应用。  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