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   1126篇
  免费   83篇
  国内免费   1篇
  2023年   5篇
  2021年   15篇
  2020年   15篇
  2019年   18篇
  2018年   22篇
  2017年   18篇
  2016年   38篇
  2015年   59篇
  2014年   56篇
  2013年   75篇
  2012年   93篇
  2011年   63篇
  2010年   36篇
  2009年   45篇
  2008年   57篇
  2007年   56篇
  2006年   60篇
  2005年   48篇
  2004年   49篇
  2003年   41篇
  2002年   41篇
  2001年   4篇
  2000年   8篇
  1999年   12篇
  1998年   20篇
  1997年   15篇
  1996年   15篇
  1995年   21篇
  1994年   19篇
  1993年   12篇
  1992年   17篇
  1991年   9篇
  1990年   11篇
  1989年   7篇
  1988年   4篇
  1987年   4篇
  1986年   4篇
  1984年   5篇
  1983年   5篇
  1982年   9篇
  1981年   13篇
  1980年   6篇
  1979年   4篇
  1978年   5篇
  1976年   10篇
  1975年   10篇
  1974年   6篇
  1973年   5篇
  1967年   6篇
  1957年   4篇
排序方式: 共有1210条查询结果,搜索用时 31 毫秒
1.
2.
The adaptation of littorinid molluscs to prolonged aerial exposure was investigated by the determination of heat production.Littorina saxatilis, inhabiting the upper eulittoral, reached a maximum metabolic activity during submersion (heat production: 3.26×10−3J s−1 (gadw)−1. On the first three days of desiccation, the heat production was continuously reduced to 40% of the submersed value. A prolonged aerial exposure was lethal for this species. In the supralittoralL. neritoides, three stages of energy metabolism could be observed: An intermediate heat production during submersion (1.97×10−3Js−1 (gadw)−1), an increased metabolism during the first hour of aerial exposure (heat production 204% of submersed value), and a minimal metabolism (39% of the submersed value and 19% of maximum value) during the following days and weeks of desiccation. Recovery depended on water salinity;L. saxatilis proved to be less euryhaline thanL. neritoides. Thus, the metabolic adaptations correlate with the level of littoral habitat; inactivity combined with a drastically reduced energy consumption is a metabolically economic way to survive in periodically dry environments.  相似文献   
3.
The glycerolipid production by rat renal papillary slices varied inversely with the urea concentration (0a–1660 mM) whether the production was measured as labelling of the glycerol backbone from glucose or as incorporation of labelled arachidonic acid and palmitic acid. The rate of phospholipid formation was most dependent on medium urea concentrations in the range between 0 and 1100 mM. The production of prostaglandins PGE2 and PGF, measured radioimmunologically or by an isotope derivative method was in the same range inversely related to the production of glycerolipids and chain elongations. The effect of urea on prostaglandin formation is probably indirectly caused by the inhibition of the phospholipid formation and chain elongation, since the effect was abolished by 1% defatted albumin in the medium. The data suggest that the level of free arachidonic acid within the cells is controlled to an important extent by glycerolipid formation and chain elongation.  相似文献   
4.
Summary Growth of yeast cells on glucose resulted in complete inactivation of maltose transport and repression of the high affinity glucose transport system. When the cells were grown on maltose or subjected to substrate starvation, an increase in glucose and maltose transport was observed in both brewing and non-brewing yeast strains. The concentration of glucose employed in the growth medium was also observed to affect sugar transport activity. The higher the glucose concentration, the more pronounced the repressive effect. In addition, the time of growth of yeast on glucose or maltose also intermining the rate of sugar transport. These results are consistent with the repressive effect of glucose on the high affinity glucose and maltose transport systems.  相似文献   
5.
6.
There is an increasing interest for the role of liver enzymes as predictors of non-liver-related morbidity and mortality. The American Heart Association (AHA) described the ideal cardiovascular health concept as a score of seven cardiovascular health behaviors and factors that can be used to monitor and predict ideal cardiovascular health over time. This study aimed to examine the association of the ideal cardiovascular health (ICH), as defined by the AHA, with liver enzyme levels in European adolescents. A total of 637 adolescents (54.6% females), aged 14.6 ± 1.2 years from nine European countries participated in this cross-sectional study. Blood levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyltransferase were measured and the AST/ALT ratio calculated. Ideal cardiovascular health was defined as meeting ideal levels of the following components: four behaviors (smoking, body mass index, physical activity, and diet) and three factors (total cholesterol, blood pressure, and glucose). A higher number of ideal cardiovascular health behaviors, factors, and ideal cardiovascular health index were associated with lower ALT (P < 0.05, P < 0.001, and P < 0.001, respectively) and gamma-glutamyltransferase (P < 0.001, P < 0.01, and P < 0.001, respectively) levels. Similarly, a higher number of ideal cardiovascular health behaviors (P < 0.01), factors (P < 0.01), and ideal cardiovascular health index (P < 0.001) were associated with a higher aspartate aminotransferase to alanine aminotransferase ratio. These findings reinforce the usefulness of the ICH index as an instrument to identify target individuals and promote cardiovascular health in adolescents, and it also extends these observations to the liver manifestation of the metabolic syndrome.  相似文献   
7.
8.
The aim of this study was to estimate the quantity of antibiotics and classes of antibiotics used in the small ruminant industry in the Netherlands in 2011 and 2012. Twelve large veterinary practices, located throughout the Netherlands were selected for this study. All small ruminant farms associated with these practices that had complete records on the quantity of antibiotics prescribed were included. The veterinary practices provided data on all antibiotics prescribed, and the estimated animal used daily dose of antibiotics per year (AUDD/Y) was calculated for each farm. The median AUDD/Y in small ruminant farms was zero in both years (mean 0.60 in 2011, and 0.62 in 2012). The largest quantity of antibiotic use was observed in the professional goat industry (herds of ≥32 goats) with a median AUDD/Y of 1.22 in 2011 and 0.73 in 2012. In the professional sheep industry (flocks of ≥32 sheep), the median AUDD/Y was 0 in 2011 and 0.10 in 2012. In the small scale industry (flocks or herds of <32 sheep or goats), the median AUDD/Y never exceeded 0. The most frequently prescribed antibiotics in the small scale industry and professional sheep farms belonged to the penicillin class. In professional goat farms, antibiotics of the aminoglycoside class were most frequently prescribed. This study provides the first assessment on the quantity of antibiotic use in the small ruminant industry. Given a comparable attitude towards antibiotic use, these results might be valid for small ruminant populations in other north-western European countries as well. The antibiotic use in the small ruminant industry appeared to be low, and is expected to play a minor role in the development of antibiotic resistance. Nevertheless, several major zoonotic bacterial pathogens are associated with the small ruminant industry, and it remains important that antibiotics are used in a prudent way.  相似文献   
9.
BackgroundThe maturation cocktail composed of interleukin (IL)-6, IL-1β, tumor necrosis factor-α and prostaglandin E2 is considered the “gold standard” for inducing the maturation of dendritic cells (DCs) for use in cancer immunotherapy. Nevertheless, although this maturation cocktail induces increased expression of several activation markers, such as CD83, the co-stimulation molecules CD80, CD86 and CD40 and the chemokine receptor involved in DC homing in lymph nodes CCR7, the DC immune stimulatory function in vivo contrasts with this mature phenotype, and good clinical outcomes in patients with cancer treated with DC-based vaccines remain rare.MethodsPhenotypic characterization of the immunosuppressive status of DCs differentiated from peripheral blood mononuclear cells of healthy volunteers and matured with the “gold standard” cocktail was performed. Glucocorticoid-induced leucine zipper (GILZ) targeting small interfering RNA (siRNA) was electroporated into DCs after maturation to increase their immunogenicity.ResultsThe mature phenotype of DCs treated for 48 h with this cocktail was associated with the expression of several immunosuppressive regulators, including programmed cell death 1 ligand 1 (PD-L1), IL-10 and GILZ. Electroporation is a very efficient and safe way to deliver siRNA into DCs (80% of DCs receive at least one molecule of siRNA). Silencing GILZ in clinical-grade DCs by siRNA leads to a decrease of the PD-L1 expression associated with an increase in their IL-12 secretion and T-cell induction capability.ConclusionsGILZ silencing is a promising approach to achieving complete clinical-grade DC maturation and avoiding the immunosuppressive effects of the maturation cocktail on DCs intended for clinical use.  相似文献   
10.
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