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   1801810篇
  免费   132077篇
  国内免费   3002篇
耳鼻咽喉   26078篇
儿科学   55517篇
妇产科学   49841篇
基础医学   257465篇
口腔科学   51975篇
临床医学   159283篇
内科学   340838篇
皮肤病学   38740篇
神经病学   140927篇
特种医学   71880篇
外国民族医学   370篇
外科学   277558篇
综合类   43364篇
现状与发展   3篇
一般理论   510篇
预防医学   133533篇
眼科学   42442篇
药学   140648篇
  7篇
中国医学   4074篇
肿瘤学   101836篇
  2018年   17339篇
  2016年   15458篇
  2015年   17604篇
  2014年   24584篇
  2013年   36549篇
  2012年   49675篇
  2011年   52395篇
  2010年   30680篇
  2009年   28826篇
  2008年   48905篇
  2007年   52711篇
  2006年   53149篇
  2005年   51308篇
  2004年   49720篇
  2003年   47725篇
  2002年   46126篇
  2001年   86896篇
  2000年   89004篇
  1999年   74780篇
  1998年   20081篇
  1997年   18059篇
  1996年   17988篇
  1995年   16922篇
  1994年   15757篇
  1993年   14921篇
  1992年   59318篇
  1991年   57522篇
  1990年   56547篇
  1989年   54589篇
  1988年   50151篇
  1987年   49089篇
  1986年   46442篇
  1985年   44246篇
  1984年   32981篇
  1983年   28163篇
  1982年   16563篇
  1981年   14804篇
  1979年   31524篇
  1978年   21973篇
  1977年   19154篇
  1976年   17058篇
  1975年   19019篇
  1974年   22887篇
  1973年   22001篇
  1972年   21012篇
  1971年   19635篇
  1970年   18418篇
  1969年   17890篇
  1968年   16008篇
  1967年   14546篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
We report on a child with several café au lait spots in association with a lumbar lipomeningomyelocele as an apparently new association. Cutaneous markers, the identification of which plays a crucial role in the early diagnosis and management of spinal malformations, can accompany occult spinal dysraphism. Herein we report a case of lumbar lipomeningomyelocele associated with an overlying café au lait spot that served as a marker of occult spinal dysraphism. The patient also had segmental café au lait spots on the face, making the association unique.  相似文献   
33.
34.
35.
36.
37.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
38.
39.
40.
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   
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