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   2461篇
  免费   145篇
  国内免费   6篇
耳鼻咽喉   15篇
儿科学   73篇
妇产科学   99篇
基础医学   299篇
口腔科学   50篇
临床医学   286篇
内科学   553篇
皮肤病学   32篇
神经病学   241篇
特种医学   87篇
外科学   195篇
综合类   10篇
一般理论   1篇
预防医学   207篇
眼科学   35篇
药学   192篇
中国医学   7篇
肿瘤学   230篇
  2024年   5篇
  2023年   53篇
  2022年   73篇
  2021年   141篇
  2020年   76篇
  2019年   101篇
  2018年   105篇
  2017年   71篇
  2016年   85篇
  2015年   85篇
  2014年   125篇
  2013年   133篇
  2012年   189篇
  2011年   223篇
  2010年   129篇
  2009年   99篇
  2008年   157篇
  2007年   146篇
  2006年   146篇
  2005年   111篇
  2004年   89篇
  2003年   94篇
  2002年   73篇
  2001年   19篇
  2000年   9篇
  1999年   9篇
  1998年   10篇
  1997年   7篇
  1996年   4篇
  1995年   5篇
  1994年   1篇
  1993年   2篇
  1992年   2篇
  1991年   3篇
  1990年   6篇
  1989年   4篇
  1988年   3篇
  1987年   3篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1978年   1篇
  1970年   3篇
  1969年   1篇
  1968年   3篇
  1967年   1篇
  1964年   1篇
  1932年   1篇
排序方式: 共有2612条查询结果,搜索用时 31 毫秒
101.
Four different types of multi-walled carbon nanotubes (MWCNTs) were used and compared for the treatment of benzoic acid contaminated water. The types of nanotubes used were: (1) non-purified (CNTsUP), as made; (2) purified (CNTsP), not containing the catalyst; (3) oxidized (CNTsOX), characterized by the presence of groups such as, –COOH; (4) calcined (CNTs900), with elimination of interactions between nanotubes. In addition, activated carbon was also used to allow for later comparison. The adsorption tests were conducted on an aqueous solution of benzoic acid at concentration of 20 mg/L, as a model of carboxylated aromatic compounds. After the adsorption tests, the residual benzoic acid concentrations were measured by UV-visible spectrometry, while the carbon nanotubes were characterized by TG and DTA thermal analyses and electron microscopy (SEM). The results show that the type of nanotubes thermally treated at 900 °C has the best performances in terms of adsorption rate and amounts of collected acid, even if compared with the performance of activated carbons.  相似文献   
102.
The Covid-19 pandemic has required nonpharmaceutical interventions, primarily physical distancing, personal hygiene and face mask use, to limit community transmission, irrespective of seasons. In fact, the seasonality attributes of this pandemic remain one of its biggest unknowns. Early studies based on past experience from respiratory diseases focused on temperature or humidity, with disappointing results. Our hypothesis that ultraviolet (UV) radiation levels might be a factor and a more appropriate parameter has emerged as an alternative to assess seasonality and exploit it for public health policies. Using geographical, socioeconomic and epidemiological criteria, we selected twelve North-equatorial-South countries with similar characteristics. We then obtained UV levels, mobility and Covid-19 daily incidence rates for nearly the entire 2020. Using machine learning, we demonstrated that UV radiation strongly associated with incidence rates, more so than mobility did, indicating that UV is a key seasonality indicator for Covid-19, irrespective of the initial conditions of the epidemic. Our findings can inform the implementation of public health emergency measures, partly based on seasons in the Northern and Southern Hemispheres, as the pandemic unfolds into 2021.  相似文献   
103.
Immune profiling of patients with COVID-19 has shown that SARS-CoV-2 causes severe lymphocyte deficiencies (e.g., lymphopenia, decreased numbers, and exhaustion of T cells) and increased levels of pro-inflammatory monocytes. Peripheral blood (PB) samples from convalescent plasma (CP) donors, COVID-19 patients, and control subjects were analyzed by multiparametric flow cytometry, allowing the identification of a wide panel of immune cells, comprising lymphocytes (T, B, natural killer (NK) and NKT cells), monocytes, granulocytes, and their subsets. Compared to active COVID-19 patients, our results revealed that the immune profile of recovered donors was restored for most subpopulations. Nevertheless, even 2 months after recovery, CP donors still had reduced levels of CD4+ T and B cells, as well as granulocytes. CP donors with non-detectable levels of anti-SARS-CoV-2-specific antibodies in their serum were characterized by higher Th9 and Th17 cells, which were possibly expanded at the expense of Th2 humoral immunity. The most noticeable alterations were identified in previously hospitalized CP donors, who presented the lowest levels of CD8+ regulatory T cells, the highest levels of CD56+CD16 NKT cells, and a promotion of a Th17-type phenotype, which might be associated with a prolonged pro-inflammatory response. A longer follow-up of CP donors will eventually reveal the time needed for full recovery of their immune system competence.  相似文献   
104.
105.
106.
Sustainable development (SD) as popularized by the Brundtland Commission and politically enshrined in the Sustainable Development Goals has been the explicit focus of sustainability science. While there is broad agreement that the trend of human well-being (W) over time should serve as a sustainability criterion, the literature so far has mostly addressed this in terms of its determinants rather than focusing on W itself. There is broad agreement that an indicator for W should have multiple constituents, clearly going beyond gross domestic product. Here, we propose a tailor-made indicator to serve precisely this purpose following a set of specified desiderata, including its applicability to flexibly defined subnational populations by gender, place of residence, ethnicity, and other relevant characteristics. The indicator, years of good life (YoGL), reflects the evident fact that in order to be able to enjoy any quality of life, one has to be alive and thus is primarily based on life expectancy. However, since mere survival is not considered good enough, life years are counted conditional on meeting minimum standards in two dimensions: the objective dimension of capable longevity (consisting of being out of absolute poverty and enjoying minimal levels of physical and cognitive health) and the subjective dimension of overall life satisfaction. We illustrate the calculation of this indicator for countries and subpopulations at different stages of development and with different degrees of data availability.

Sustainability science refers to the most comprehensive scholarly effort to understand the interactions between natural and social systems in order to assess whether certain developmental pathways can be considered sustainable. This should also include the possible negative effects of environmental changes, such as climate change and biodiversity loss, on future human well-being. In this paper, we propose a tailor-made indicator to assess long-term human well-being as the ultimate end of sustainable development. This indicator, called “years of good life” (YoGL), is designed in such a way that it can be both empirically measured—which is the focus of this paper—and modeled in its long-term future trends—which will be the focus of future work.When assessing changes over time in the well-being of certain human populations (or subpopulations, as defined, e.g., by gender, ethnicity, urban/rural place of residence, or other social groupings), one can focus on the determinants or the constituents of well-being. In sustainability science, thus far, empirical and theoretical research has placed more emphasis on studying the determinants, including environmental services (1), whereas specifying its constituents has received less systematic attention, often leaving us with nothing but the unspecific notion of “utility.” The focus on determinants has led to the concept of “inclusive wealth” (IW) which can be used to assess whether a society is on a sustainable development trajectory in terms of the productive base necessary to maintain a high standard of living in the future (2). However, empirically measuring the values and relative effects of the different capitals determining human well-being remains extremely challenging and “no current attempt to date can be said to be fully inclusive” (3).The idea behind YoGL, on the other hand, is to study sustainability by focusing explicitly on the constituents of well-being and its change over time. In doing so, YoGL avoids several of the pitfalls by which the IW approach is plagued (3, 4). For example, rather than making contestable quantitative assessments of the relative contributions of the different determinants of well-being, the demographic approach underlying YoGL provides numerical values of human well-being directly, expressed as the average number of years of good life a person can expect to live as part of a given subpopulation under the conditions of a specified point in time. Based on the assumed universal nature of its unit of measurement—YoGL lived today in one specific population has the same meaning as YoGL lived in the future or in another population—the indicator has a time-independent meaning. This also avoids the pitfalls of specifying a rate at which to discount future well-being, which have become apparent at least since the debates around the Stern report (5). YoGL allows us to directly compare human well-being across different subpopulations and generations. Moreover, while all estimates of the different determinants of future human well-being are highly sensitive to population growth, as a measure referring to per-person well-being the derivation of YoGL is not directly affected by assumptions about the future trajectory of population size. Finally, as stressed by Dasgupta (6), the nature of determinants can change over time and across places depending on different commodities and technological regimes, whereas the constituents of well-being—as used in YoGL—are arguably shared across space and time.In the following, we will first present the proposed design of the indicator. We will then provide a step-by-step user’s guide for empirically deriving YoGL based on the most appropriate available data source, before offering examples of how it can be calculated based on auxiliary information on populations for which the necessary data are not yet fully available. We will close with a discussion and brief outlook as to what is still needed to use this indicator for the assessment of sustainability.  相似文献   
107.
108.

Background  

Tissue inhibitors of metalloproteinases (TIMPs) play a key role in tissue degradation and remodeling. Since chronic inflammation is associated with tissue remodeling in inflammatory bowel disease (IBD), we evaluated serum TIMP-1 and TIMP-4 levels in IBD patients, in comparison with healthy controls (HC).  相似文献   
109.
110.
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