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   7231篇
  免费   779篇
  国内免费   937篇
  2024年   21篇
  2023年   113篇
  2022年   301篇
  2021年   447篇
  2020年   337篇
  2019年   406篇
  2018年   367篇
  2017年   296篇
  2016年   397篇
  2015年   557篇
  2014年   648篇
  2013年   617篇
  2012年   704篇
  2011年   585篇
  2010年   392篇
  2009年   333篇
  2008年   329篇
  2007年   242篇
  2006年   223篇
  2005年   203篇
  2004年   197篇
  2003年   170篇
  2002年   163篇
  2001年   90篇
  2000年   78篇
  1999年   76篇
  1998年   36篇
  1997年   40篇
  1996年   23篇
  1995年   31篇
  1994年   30篇
  1993年   27篇
  1992年   57篇
  1991年   43篇
  1990年   45篇
  1989年   43篇
  1988年   25篇
  1987年   31篇
  1986年   28篇
  1985年   24篇
  1984年   24篇
  1983年   17篇
  1982年   10篇
  1980年   14篇
  1979年   8篇
  1977年   9篇
  1972年   11篇
  1971年   9篇
  1970年   9篇
  1969年   9篇
排序方式: 共有8947条查询结果,搜索用时 31 毫秒
991.
992.

Background

Polysaccharides, one of the active ingredients in herbal medicine, are proved to enhance innate immunity against infections. The aim of this study is to explore the immunoregulatory ability of polysaccharides from Rhynchosia minima root in vitro and in vivo.

Methods

Polysaccharide fractions of R. minima root were obtained by chromatographic column. The content of NO was measured by spectrophotometry. The levels of cytokines (tumor necrosis factor-α, TNF-α; interleukin-6, IL-6; and monocyte chemoattractant protein-1, MCP-1) were determined by enzyme-linked immuno-sorbent assay (ELISA) kits. The translocation of p65 into the nucleus was imaged by confocal microscopy. The mRNA expression of TNF-α, IL-6, and MCP-1 was determined by quantitative real-time PCR. T-lymphocyte subgroups of spleen from immunosuppressive mouse were evaluated by flow cytometry.

Results

PRM3 remarkably enhanced the phagocytic ability of macrophages and promoted the release of NO and the secretion of cytokines (TNF-α, IL-6, and MCP-1) from macrophages. Simultaneously, PRM3 potently activated NF-κB signaling pathway via Toll-like receptor 4 (TLR4). In addition, PRM3 obviously increased the levels of serum cytokines, markedly up-regulated the percentages of CD3+ and CD4+ T lymphocytes and the CD4+/CD8+ ratio of splenocytes, and effectively attenuated cyclophosphamide induced immunosuppression in mice.

Conclusions

PRM3 profoundly enhanced the immune function in vitro and in vivo through TLR4-NF-κB pathway and is a promising candidate of immunopotentiator which could be applied in functional foods or drugs.

General significance

This study reported a polysaccharide PRM3 from R. minima root exhibited potent immunoenhancing activity and significantly alleviated cyclophosphamide-induced immunosuppression through TLR4-NF-κB pathway.  相似文献   
993.
994.
995.
Aluminum (Al) is an important environmental metal factor that can be potentially associated with pathological changes leading to neurotoxicity. The silkworm, Bombyx mori, is an important economic insect and has also been used as a model organism in various research areas. However, the toxicity of Al on silkworm physiology has not been reported. Here, we comprehensively investigate the toxic effects of Al on the silkworm, focusing on its effects on viability and development, superoxide dismutase (SOD) activity, and the expression of presenilin and cAMP response element‐binding protein (CREB) in BmE cells and silkworm larvae. BmE cell viability decreased after treatment with aluminum chloride (AlCl3) in both dose‐ and time‐dependent manners. When AlCl3 solution was injected into newly hatched fifth instar larvae, both larval weight gain and survival rate were significantly decreased in a manner correlating with AlCl3 dose and developmental stage. Furthermore, when BmE cells and silkworm larvae were exposed to AlCl3, SOD activity decreased significantly relative to the control group, whereas presenilin expression increased more than twofold. Additionally, CREB and phosphorylated CREB (p‐CREB) expression in the heads of fifth instar larvae decreased by 28.0% and 50.0%, respectively. These results indicate that Al inhibits the growth and development of silkworms in vitro and in vivo, altering SOD activity and the expressions of presenilin, CREB, and p‐CREB. Our data suggest that B. mori can serve as a model animal for studying Al‐induced neurotoxicity or neurodegeneration.  相似文献   
996.
Existing evidence on the relationship between cardiovascular health(CVH) metrics and cardiovascular disease(CVD) was primarily derived from western populations. We aimed to evaluate the benefits of ideal CVH metrics on preventing incident atherosclerotic CVD(ASCVD) in Chinese population. This study was conducted among 93,987 adults from the China-PAR project(Prediction for ASCVD Risk in China) who were followed up until 2015. Cox proportional hazard regression models were used to estimate the hazard ratios(HRs) and their corresponding 95% confidence intervals(CIs) of CVH metrics for the risk of ASCVD, including coronary heart disease(CHD), stroke and ASCVD death. We further estimated the population-attributable risk percentage(PAR%) of these metrics in relation to each outcome. We observed gradient inverse associations between the number of ideal CVH metrics and ASCVD incidence. Compared with participants having ≤2 ideal CVH metrics, the multivariable-adjusted HRs(95% CIs) of ASCVD for those with 3, 4, 5, 6 and 7 ideal CVH metrics were 0.83(0.74–0.93), 0.66(0.59–0.74), 0.55(0.48–0.61), 0.44(0.38–0.50) and 0.24(0.18–0.31), respectively(P for trend 0.0001). Approximately 62.1% of total ASCVD, 38.7% of CHD, 66.4% of stroke, and 60.5% of ASCVD death were attributable to not achieving all the seven ideal CVH metrics. After adjusting effects of ideal health factors, having four ideal health behaviors could independently bring adults health benefits in preventing 17.4% of ASCVD, 18.0% of CHD, 16.7% of stroke, and 10.1% of ASCVD death. Among all the seven CVH metrics, to keep with ideal blood pressure(BP) implied the largest public health gains against various ASCVD events(PAR% between 33.0% and 47.2%), while ideal diet was the metric most difficult to be achieved in the long term. Our study indicates that the more ideal CVH metrics adults have, the less ASCVD burden there is in China. Special efforts of health education and behavior modification should be made on keeping ideal BP and dietary habits in general Chinese population to prevent the epidemic of ASCVD.  相似文献   
997.
998.
999.
Like protein and DNA, different types of RNA molecules undergo various modifications. Accumulating evidence suggests that these RNA modifications serve as sophisticated codes to mediate RNA behaviors and many important biological functions. N6-methyladenosine (m6A) is the most abundant internal RNA modification found in a variety of eukaryotic RNAs, including but not limited to mRNAs, tRNAs, rRNAs, and long non-coding RNAs (lncRNAs). In mammalian cells, m6A can be incorporated by a methyltransferase complex and removed by demethylases, which ensures that the m6A modification is reversible and dynamic. Moreover, m6A is recognized by the YT521-B homology (YTH) domain-containing proteins, which subsequently direct different complexes to regulate RNA signaling pathways, such as RNA metabolism, RNA splicing, RNA folding, and protein translation. Herein, we summarize the recent progresses made in understanding the molecular mechanisms underlying the m6A recognition by YTH domain-containing proteins, which would shed new light on m6A-specific recognition and provide clues to the future identification of reader proteins of many other RNA modifications.  相似文献   
1000.
A facile two‐step strategy is developed to design the large‐scale synthesis of hierarchical, unique porous architecture of ternary metal hydroxide nanowires grown on porous 3D Ni foam and subsequent effective sulfurization. The hierarchical Zn–Co–S nanowires (NWs) arrays are directly employed as an electrode for supercapacitors application. The as‐synthesized Zn–Co–S NWs deliver an ultrahigh areal capacity of 0.9 mA h cm?2 (specific capacity of 366.7 mA h g?1) at a current density of 3 mA cm?2, with an exceptional rate capability (≈227.6 mA h g?1 at a very high current density of 40 mA cm?2) and outstanding cycling stability (≈93.2% of capacity retention after 10 000 cycles). Most significantly, the assembled Zn–Co–S NWs//Fe2O3@reduced graphene oxide asymmetric supercapacitors with a wide operating potential window of ≈1.6 V yield an ultrahigh volumetric capacity of ≈1.98 mA h cm?3 at a current density of 3 mA cm?2, excellent energy density of ≈81.6 W h kg?1 at a power density of ≈559.2 W kg?1, and exceptional cycling performance (≈92.1% of capacity retention after 10 000 cycles). This general strategy provides an alternative to design the other ternary metal sulfides, making it facile, free‐standing, binder‐free, and cost‐effective ternary metal sulfide‐based electrodes for large‐scale applications in modern electronics.  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