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   2371876篇
  免费   184598篇
  国内免费   4639篇
耳鼻咽喉   33154篇
儿科学   80040篇
妇产科学   66844篇
基础医学   337166篇
口腔科学   64511篇
临床医学   212189篇
内科学   469607篇
皮肤病学   53522篇
神经病学   191485篇
特种医学   92112篇
外国民族医学   1051篇
外科学   359039篇
综合类   53940篇
现状与发展   4篇
一般理论   782篇
预防医学   184971篇
眼科学   53771篇
药学   171744篇
  3篇
中国医学   5053篇
肿瘤学   130125篇
  2019年   18246篇
  2018年   26074篇
  2017年   19738篇
  2016年   22057篇
  2015年   24797篇
  2014年   34970篇
  2013年   52636篇
  2012年   71939篇
  2011年   76292篇
  2010年   45203篇
  2009年   43025篇
  2008年   71448篇
  2007年   76055篇
  2006年   76662篇
  2005年   74529篇
  2004年   71935篇
  2003年   68938篇
  2002年   67254篇
  2001年   116508篇
  2000年   119992篇
  1999年   100914篇
  1998年   28158篇
  1997年   25419篇
  1996年   25794篇
  1995年   24508篇
  1994年   22617篇
  1993年   21153篇
  1992年   77982篇
  1991年   75299篇
  1990年   72747篇
  1989年   69361篇
  1988年   63785篇
  1987年   62564篇
  1986年   58427篇
  1985年   55892篇
  1984年   42374篇
  1983年   35740篇
  1982年   21340篇
  1981年   19156篇
  1979年   37731篇
  1978年   26440篇
  1977年   22128篇
  1976年   20845篇
  1975年   22064篇
  1974年   26181篇
  1973年   25272篇
  1972年   23456篇
  1971年   21286篇
  1970年   20221篇
  1969年   18483篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
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   
44.
The human visual system is amenable to a number of adaptive processes; one such process, or collection of processes, is the adaptation to blur. Blur adaptation can be observed as an improvement in vision under degraded conditions, and these changes occur relatively rapidly following exposure to blur. The potential important future directions of this research area and the clinical implications of blur adaptation are discussed.  相似文献   
45.
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   
46.
47.
48.
49.
50.
Pharmaceutical Chemistry Journal - Three extracts were produced from the above-ground part of the meadowsweet Filipendula ulmaria (L.) Maxim. using water, 40% ethanol, and 70% ethanol. Comparative...  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