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   2334941篇
  免费   188011篇
  国内免费   7495篇
耳鼻咽喉   32051篇
儿科学   78543篇
妇产科学   64296篇
基础医学   326241篇
口腔科学   63961篇
临床医学   209006篇
内科学   471694篇
皮肤病学   53404篇
神经病学   188620篇
特种医学   94760篇
外国民族医学   883篇
外科学   362484篇
综合类   53163篇
现状与发展   3篇
一般理论   747篇
预防医学   183425篇
眼科学   51019篇
药学   168870篇
  7篇
中国医学   4189篇
肿瘤学   123081篇
  2018年   23689篇
  2017年   18267篇
  2016年   21222篇
  2015年   23833篇
  2014年   33233篇
  2013年   50388篇
  2012年   64988篇
  2011年   69539篇
  2010年   42615篇
  2009年   41131篇
  2008年   65675篇
  2007年   70327篇
  2006年   71411篇
  2005年   69220篇
  2004年   66787篇
  2003年   65024篇
  2002年   62765篇
  2001年   112478篇
  2000年   116382篇
  1999年   97985篇
  1998年   28470篇
  1997年   25610篇
  1996年   26531篇
  1995年   26131篇
  1994年   24532篇
  1993年   22902篇
  1992年   79878篇
  1991年   78084篇
  1990年   75497篇
  1989年   72139篇
  1988年   66595篇
  1987年   65369篇
  1986年   61381篇
  1985年   59062篇
  1984年   44891篇
  1983年   37808篇
  1982年   22925篇
  1981年   20714篇
  1980年   19110篇
  1979年   40418篇
  1978年   28835篇
  1977年   24489篇
  1976年   22555篇
  1975年   23942篇
  1974年   28146篇
  1973年   27018篇
  1972年   24899篇
  1971年   22904篇
  1970年   21233篇
  1969年   19579篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
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   
72.
73.
74.
75.
76.
77.
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   
78.
The current situation in which the humanities are disparaged affects all university disciplines, including nursing, in whose historical evolution the humanities have always been present in one form or another. Looking beyond this disrepute, this study proposes that nursing renew its attention to classical philosophy. Specifically, it invites a close reading of Xenophon's Anabasis and Plato's Meno, to get three related goals: to show how the use of ancient texts are very valuable tools for the philosophical initiation of nursing students and can help them reflect on their choice of nursing as a practical activity; to reflect on the problem of virtue and the nature of the good life; and to show how the interaction with ancient texts allows students to reflect on questions and issues of life, theirs and others, that are not open to investigation through a purely scientific method. Consequently, both Anabasis and Meno readings strengthen the intellectual relationship between philosophy and nursing, enabling the latter to delve deeper into the key questions of its own thought as a discipline.  相似文献   
79.
Obesity Surgery - Laparoscopic sleeve gastrectomy (LSG) is increasingly playing a key role in obesity management. Such operations, however, carry complications sometimes including leaks. The...  相似文献   
80.
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