全文获取类型
收费全文 | 420665篇 |
免费 | 19241篇 |
国内免费 | 1127篇 |
专业分类
耳鼻咽喉 | 3922篇 |
儿科学 | 13007篇 |
妇产科学 | 7468篇 |
基础医学 | 48894篇 |
口腔科学 | 6097篇 |
临床医学 | 37109篇 |
内科学 | 83048篇 |
皮肤病学 | 4093篇 |
神经病学 | 40049篇 |
特种医学 | 17116篇 |
外国民族医学 | 11篇 |
外科学 | 66260篇 |
综合类 | 5760篇 |
一般理论 | 319篇 |
预防医学 | 38625篇 |
眼科学 | 9273篇 |
药学 | 26141篇 |
6篇 | |
中国医学 | 987篇 |
肿瘤学 | 32848篇 |
出版年
2023年 | 1343篇 |
2022年 | 2420篇 |
2021年 | 5467篇 |
2020年 | 3274篇 |
2019年 | 5327篇 |
2018年 | 27042篇 |
2017年 | 21185篇 |
2016年 | 23668篇 |
2015年 | 6714篇 |
2014年 | 9361篇 |
2013年 | 12549篇 |
2012年 | 24682篇 |
2011年 | 39120篇 |
2010年 | 28506篇 |
2009年 | 20539篇 |
2008年 | 35274篇 |
2007年 | 38293篇 |
2006年 | 17781篇 |
2005年 | 19330篇 |
2004年 | 19430篇 |
2003年 | 19229篇 |
2002年 | 16464篇 |
2001年 | 2411篇 |
2000年 | 2052篇 |
1999年 | 2525篇 |
1998年 | 3272篇 |
1997年 | 2756篇 |
1996年 | 2272篇 |
1995年 | 2194篇 |
1994年 | 1843篇 |
1993年 | 1634篇 |
1992年 | 1320篇 |
1991年 | 1257篇 |
1990年 | 1142篇 |
1989年 | 1087篇 |
1988年 | 1046篇 |
1987年 | 1004篇 |
1986年 | 996篇 |
1985年 | 1013篇 |
1984年 | 1269篇 |
1983年 | 1163篇 |
1982年 | 1409篇 |
1981年 | 1330篇 |
1980年 | 1203篇 |
1979年 | 728篇 |
1978年 | 776篇 |
1977年 | 649篇 |
1976年 | 600篇 |
1975年 | 489篇 |
1974年 | 501篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Seyed Mehdi BagheriMofidi Majid Pouladian Seyed Behnamedin Jameie Ali Abbaspour Tehrani-Fard 《Australasian physical & engineering sciences in medicine / supported by the Australasian College of Physical Scientists in Medicine and the Australasian Association of Physical Sciences in Medicine》2016,39(3):717-726
Magnetic field generated by neuronal activity could alter magnetic resonance imaging (MRI) signals but detection of such signal is under debate. Previous researches proposed that magnitude signal change is below current detectable level, but phase signal change (PSC) may be measurable with current MRI systems. Optimal imaging parameters like echo time, voxel size and external field direction, could increase the probability of detection of this small signal change. We simulate a voxel of cortical column to determine effect of such parameters on PSC signal. We extended a laminar network model for somatosensory cortex to find neuronal current in each segment of pyramidal neurons (PN). 60,000 PNs of simulated network were positioned randomly in a voxel. Biot–savart law applied to calculate neuronal magnetic field and additional phase. The procedure repeated for eleven neuronal arrangements in the voxel. PSC signal variation with the echo time and voxel size was assessed. The simulated results show that PSC signal increases with echo time, especially 100/80 ms after stimulus for gradient echo/spin echo sequence. It can be up to 0.1 mrad for echo time = 175 ms and voxel size = 1.48 × 1.48 × 2.18 mm3. With echo time less than 25 ms after stimulus, it was just acquired effects of physiological noise on PSC signal. The absolute value of the signal increased with decrease of voxel size, but its components had complex variation. External field orthogonal to local surface of cortex maximizes the signal. Expected PSC signal for tactile detection in the somatosensory cortex increase with echo time and have no oscillation. 相似文献
12.
13.
14.
15.
16.
Danielle E Whittier Elizabeth J Samelson Marian T Hannan Lauren A Burt David A Hanley Emmanuel Biver Pawel Szulc Elisabeth Sornay-Rendu Blandine Merle Roland Chapurlat Eric Lespessailles Andy Kin On Wong David Goltzman Sundeep Khosla Serge Ferrari Mary L Bouxsein Douglas P Kiel Steven K Boyd 《Journal of bone and mineral research》2022,37(3):428-439
Prevalence of osteoporosis is more than 50% in older adults, yet current clinical methods for diagnosis that rely on areal bone mineral density (aBMD) fail to detect most individuals who have a fragility fracture. Bone fragility can manifest in different forms, and a “one-size-fits-all” approach to diagnosis and management of osteoporosis may not be suitable. High-resolution peripheral quantitative computed tomography (HR-pQCT) provides additive information by capturing information about volumetric density and microarchitecture, but interpretation is challenging because of the complex interactions between the numerous properties measured. In this study, we propose that there are common combinations of bone properties, referred to as phenotypes, that are predisposed to different levels of fracture risk. Using HR-pQCT data from a multinational cohort (n = 5873, 71% female) between 40 and 96 years of age, we employed fuzzy c-means clustering, an unsupervised machine-learning method, to identify phenotypes of bone microarchitecture. Three clusters were identified, and using partial correlation analysis of HR-pQCT parameters, we characterized the clusters as low density, low volume, and healthy bone phenotypes. Most males were associated with the healthy bone phenotype, whereas females were more often associated with the low volume or low density bone phenotypes. Each phenotype had a significantly different cumulative hazard of major osteoporotic fracture (MOF) and of any incident osteoporotic fracture (p < 0.05). After adjustment for covariates (cohort, sex, and age), the low density followed by the low volume phenotype had the highest association with MOF (hazard ratio = 2.96 and 2.35, respectively), and significant associations were maintained when additionally adjusted for femoral neck aBMD (hazard ratio = 1.69 and 1.90, respectively). Further, within each phenotype, different imaging biomarkers of fracture were identified. These findings suggest that osteoporotic fracture risk is associated with bone phenotypes that capture key features of bone deterioration that are not distinguishable by aBMD. © 2021 American Society for Bone and Mineral Research (ASBMR). 相似文献
17.
18.
19.
20.