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   4824篇
  免费   280篇
  国内免费   13篇
耳鼻咽喉   44篇
儿科学   91篇
妇产科学   111篇
基础医学   956篇
口腔科学   93篇
临床医学   408篇
内科学   783篇
皮肤病学   147篇
神经病学   407篇
特种医学   161篇
外科学   589篇
综合类   14篇
一般理论   2篇
预防医学   396篇
眼科学   102篇
药学   614篇
中国医学   29篇
肿瘤学   170篇
  2023年   46篇
  2022年   42篇
  2021年   85篇
  2020年   89篇
  2019年   123篇
  2018年   247篇
  2017年   151篇
  2016年   194篇
  2015年   167篇
  2014年   268篇
  2013年   388篇
  2012年   499篇
  2011年   571篇
  2010年   305篇
  2009年   123篇
  2008年   131篇
  2007年   96篇
  2006年   91篇
  2005年   48篇
  2004年   42篇
  2003年   45篇
  2002年   32篇
  2001年   50篇
  2000年   47篇
  1999年   49篇
  1998年   45篇
  1997年   40篇
  1996年   35篇
  1995年   40篇
  1994年   31篇
  1992年   50篇
  1991年   41篇
  1990年   54篇
  1989年   44篇
  1988年   38篇
  1987年   25篇
  1986年   37篇
  1985年   33篇
  1984年   38篇
  1982年   36篇
  1981年   25篇
  1979年   33篇
  1978年   24篇
  1977年   29篇
  1975年   29篇
  1974年   31篇
  1973年   30篇
  1971年   22篇
  1970年   23篇
  1967年   24篇
排序方式: 共有5117条查询结果,搜索用时 15 毫秒
1.
2.
Clinical Oral Investigations - The aim of this study was the analysis of WNT10A variants in seven families of probands with various forms of tooth agenesis and self-reported family history of...  相似文献   
3.
4.
5.
6.
Motion is a major confound in diffusion‐weighted imaging (DWI) in the body, and it is a common cause of image artefacts. The effects are particularly severe in cardiac applications, due to the nonrigid cyclical deformation of the myocardium. Spin echo‐based DWI commonly employs gradient moment‐nulling techniques to desensitise the acquisition to velocity and acceleration, ie, nulling gradient moments up to the 2nd order (M2‐nulled). However, current M2‐nulled DWI scans are limited to encode diffusion along a single direction at a time. We propose a method for designing b‐tensors of arbitrary shapes, including planar, spherical, prolate and oblate tensors, while nulling gradient moments up to the 2nd order and beyond. The design strategy comprises initialising the diffusion encoding gradients in two encoding blocks about the refocusing pulse, followed by appropriate scaling and rotation, which further enables nulling undesired effects of concomitant gradients. Proof‐of‐concept assessment of in vivo mean diffusivity (MD) was performed using linear and spherical tensor encoding (LTE and STE, respectively) in the hearts of five healthy volunteers. The results of the M2‐nulled STE showed that (a) the sequence was robust to cardiac motion, and (b) MD was higher than that acquired using standard M2‐nulled LTE, where diffusion‐weighting was applied in three orthogonal directions, which may be attributed to the presence of restricted diffusion and microscopic diffusion anisotropy. Provided adequate signal‐to‐noise ratio, STE could significantly shorten estimation of MD compared with the conventional LTE approach. Importantly, our theoretical analysis and the proposed gradient waveform design may be useful in microstructure imaging beyond diffusion tensor imaging where the effects of motion must be suppressed.  相似文献   
7.
BACKGROUND Degree of portal hypertension(PH) is the most important prognostic factor for the decompensation of liver cirrhosis and death, therefore adequate care for patients with liver cirrhosis requires timely detection and evaluation of the presence of clinically significant PH(CSPH) and severe PH(SPH). As the most accurate method for the assessment of PH is an invasive direct measurement of hepatic venous pressure gradient(HVPG), the search for non-invasive methods to diagnose these conditions is actively ongoing.AIM To evaluate the feasibility of parameters of endogenously induced displacements and strain of liver to assess degree of PH.METHODS Of 36 patients with liver cirrhosis and measured HVPG were included in the casecontrol study. Endogenous motion of the liver was characterized by derived parameters of region average tissue displacement signal(dantero, dretro, d RMS) and results of endogenous tissue strain imaging using specific radiofrequency signal processing algorithm. Average endogenous strain μ and standard deviation σ of strain were assessed in the regions of interest(ROI)(1 cm × 1 cm and 2 cm × 2 cm in size) and different frequency subbands of endogenous motion(0-10 Hz and 10-20 Hz).RESULTS Four parameters showed statistically significant(P 0.05) correlation with HVPG measurement. The strongest correlation was obtained for the standard deviation of strain(estimated at 0-10 Hz and 2 cm × 2 cm ROI size). Three parameters showed statistically significant differences between patient groups with CSPH, but only dretro showed significant results in SPH analysis. According to ROC analysis area under the curve(AUC) of the σROI[0…10 Hz, 2 cm × 2 cm] parameter reached 0.71(P = 0.036) for the diagnosis of CSPH; with a cut-off value of 1.28 μm/cm providing 73% sensitivity and 70% specificity. AUC for the diagnosis of CSPH for μROI[0…10 Hz, 1 cm × 1 cm] was 0.78(P = 0.0024); with a cut-off value of 3.92 μm/cm providing 73% sensitivity and 80% specificity. Dretro parameter had an AUC of 0.86(P = 0.0001) for the diagnosis of CSPH and 0.84(P = 0.0001) for the diagnosis of SPH. A cut-off value of-132.34 μm yielded 100% sensitivity for both conditions, whereas specificity was 80% and 72% for CSPH and SPH respectively.CONCLUSION The parameters of endogenously induced displacements and strain of the liver correlated with HVPG and might be used for non-invasive diagnosis of PH.  相似文献   
8.
9.

Background  

Reports on childhood cancer survivors estimated cumulative probability of developing secondary neoplasms vary from 3,3% to 25% at 25 years from diagnosis, and the risk of developing another cancer to several times greater than in the general population.  相似文献   
10.
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