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   3313篇
  免费   218篇
  国内免费   18篇
耳鼻咽喉   11篇
儿科学   83篇
妇产科学   54篇
基础医学   382篇
口腔科学   175篇
临床医学   318篇
内科学   631篇
皮肤病学   126篇
神经病学   252篇
特种医学   90篇
外科学   442篇
综合类   60篇
预防医学   253篇
眼科学   202篇
药学   300篇
中国医学   31篇
肿瘤学   139篇
  2024年   7篇
  2023年   52篇
  2022年   117篇
  2021年   229篇
  2020年   128篇
  2019年   184篇
  2018年   199篇
  2017年   144篇
  2016年   159篇
  2015年   140篇
  2014年   188篇
  2013年   224篇
  2012年   347篇
  2011年   323篇
  2010年   175篇
  2009年   141篇
  2008年   171篇
  2007年   189篇
  2006年   129篇
  2005年   114篇
  2004年   68篇
  2003年   51篇
  2002年   41篇
  2001年   4篇
  2000年   5篇
  1999年   4篇
  1998年   4篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1990年   1篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
排序方式: 共有3549条查询结果,搜索用时 0 毫秒
31.
32.
33.
Due to various factors which impress wheat growth variability, we need short–term monitoring of biophysical parameters using ultra–high resolution images. These provide an ability to monitor crops at the individual plant level. Two flight missions were carried out at altitude of 40 m with a commercial quad copter and a commercial camera. The images were taken before and after tillage over an 8.8 ha field. The 2 cm orthoimages and surface models were generated using photogrammetric software. Then, the image variables including ratio of the blue and green band, ratio of the red and blue band,ratio of the red and green band, plant height were extracted from orthoimages and surface models. Field measurement included the leaf area index, plant height and biomass for 15 plots each of area 1 m × 1 m. Due to a linear relationship between the biophysical parameters and image variables, it was used a multivariate regression model for modelling. The model using the image variables resulted in coefficient of determination (R2) of 0.95 and the lowest error measures (RMSE = 0.24). The results show that ultra–high resolution images can be used for monitoring of biophysical parameters in wheat crops but it is limited for large area.  相似文献   
34.
35.
Clinical Rheumatology - Considering the pathologic significance of inflammation and oxidative stress in rheumatoid arthritis (RA) as well as the antioxidant, anti-inflammatory and hypolipidemic...  相似文献   
36.
Metabolic Brain Disease - Alzheimer’s disease is the most common neurodegenerative disease associated with deposition of amyloid-beta and the increased oxidative stress. High free radical...  相似文献   
37.
Clinical Rheumatology - Adult-onset Still’s disease (AOSD) characterized by a high spiking fever, skin rash, arthritis, and leukocytosis. The aim of the present study was considering the...  相似文献   
38.
39.
Applications in imaging and spectroscopy rely on pulse processing methods for appropriate data generation. Often, the particular method utilized does not highly impact data quality, whereas in some scenarios, such as in the presence of high count rates or high frequency pulses, this issue merits extra consideration. In the present study, a new approach for pulse processing in nuclear medicine imaging and spectroscopy is introduced and evaluated. The new non-linear recursive filter (NLRF) performs nonlinear processing of the input signal and extracts the main pulse characteristics, having the powerful ability to recover pulses that would ordinarily result in pulse pile-up. The filter design defines sampling frequencies lower than the Nyquist frequency.In the literature, for systems involving NaI(Tl) detectors and photomultiplier tubes (PMTs), with a signal bandwidth considered as 15 MHz, the sampling frequency should be at least 30 MHz (the Nyquist rate), whereas in the present work, a sampling rate of 3.3 MHz was shown to yield very promising results. This was obtained by exploiting the known shape feature instead of utilizing a general sampling algorithm. The simulation and experimental results show that the proposed filter enhances count rates in spectroscopy. With this filter, the system behaves almost identically as a general pulse detection system with a dead time considerably reduced to the new sampling time (300 ns). Furthermore, because of its unique feature for determining exact event times, the method could prove very useful in time-of-flight PET imaging.  相似文献   
40.
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