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   1426篇
  免费   118篇
  1544篇
  2023年   7篇
  2022年   18篇
  2021年   29篇
  2020年   16篇
  2019年   14篇
  2018年   29篇
  2017年   17篇
  2016年   46篇
  2015年   74篇
  2014年   90篇
  2013年   89篇
  2012年   129篇
  2011年   128篇
  2010年   80篇
  2009年   60篇
  2008年   96篇
  2007年   93篇
  2006年   98篇
  2005年   93篇
  2004年   53篇
  2003年   80篇
  2002年   49篇
  2001年   19篇
  2000年   12篇
  1999年   9篇
  1998年   12篇
  1997年   6篇
  1996年   8篇
  1995年   7篇
  1994年   5篇
  1993年   2篇
  1992年   5篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   5篇
  1987年   6篇
  1986年   2篇
  1985年   3篇
  1982年   2篇
  1981年   2篇
  1979年   5篇
  1977年   3篇
  1976年   2篇
  1974年   3篇
  1971年   2篇
  1970年   2篇
  1967年   2篇
  1963年   2篇
  1961年   4篇
排序方式: 共有1544条查询结果,搜索用时 15 毫秒
991.
992.

Background

Missed hospital appointments are a major cause of inefficiency worldwide. Healthcare providers are increasingly using Short Message Service reminders to reduce ‘Did Not Attend’ (DNA) rates. Systematic reviews show that sending such reminders is effective, but there is no evidence on whether their impact is affected by their content. Accordingly, we undertook two randomised controlled trials that tested the impact of rephrasing appointment reminders on DNA rates in the United Kingdom.

Trial Methods

Participants were outpatients with a valid mobile telephone number and an outpatient appointment between November 2013 and January 2014 (Trial One, 10,111 participants) or March and May 2014 (Trial Two, 9,848 participants). Appointments were randomly allocated to one of four reminder messages, which were issued five days in advance. Message assignment was then compared against appointment outcomes (appointment attendance, DNA, cancellation by patient).

Results

In Trial One, a message including the cost of a missed appointment to the health system produced a DNA rate of 8.4%, compared to 11.1% for the existing message (OR 0.74, 95% CI 0.61–0.89, P<0.01). Trial Two replicated this effect (DNA rate 8.2%), but also found that expressing the same concept in general terms was significantly less effective (DNA rate 9.9%, OR 1.22, 95% CI 1.00–1.48, P<0.05). Moving from the existing reminder to the more effective costs message would result in 5,800 fewer missed appointments per year in the National Health Service Trust in question, at no additional cost. The study’s main limitations are that it took place in a single location in England, and that it required accurate phone records, which were only obtained for 20% of eligible patients. We conclude that missed appointments can be reduced, for no additional cost, by introducing persuasive messages to appointment reminders. Future studies could examine the impact of varying reminder messages in other health systems.

Trial Registration

Controlled-Trials.com 49432571  相似文献   
993.
Centrioles form centrosomes and cilia. In most proliferating cells, centrioles assemble through canonical duplication, which is spatially, temporally, and numerically regulated by the cell cycle and the presence of mature centrioles. However, in certain cell types, centrioles assemble de novo, yet by poorly understood mechanisms. Herein, we established a controlled system to investigate de novo centriole biogenesis, using Drosophila melanogaster egg explants overexpressing Polo-like kinase 4 (Plk4), a trigger for centriole biogenesis. We show that at a high Plk4 concentration, centrioles form de novo, mature, and duplicate, independently of cell cycle progression and of the presence of other centrioles. Plk4 concentration determines the temporal onset of centriole assembly. Moreover, our results suggest that distinct biochemical kinetics regulate de novo and canonical biogenesis. Finally, we investigated which other factors modulate de novo centriole assembly and found that proteins of the pericentriolar material (PCM), and in particular γ-tubulin, promote biogenesis, likely by locally concentrating critical components.  相似文献   
994.
The Arabidopsis SUC5 protein represents a classical sucrose/H+ symporter. Functional analyses previously revealed that SUC5 also transports biotin, an essential co‐factor for fatty acid synthesis. However, evidence for a dual role in transport of the structurally unrelated compounds sucrose and biotin in plants was lacking. Here we show that SUC5 localizes to the plasma membrane, and that the SUC5 gene is expressed in developing embryos, confirming the role of the SUC5 protein as substrate carrier across apoplastic barriers in seeds. We show that transport of biotin but not of sucrose across these barriers is impaired in suc5 mutant embryos. In addition, we show that SUC5 is essential for the delivery of biotin into the embryo of biotin biosynthesis‐defective mutants (bio1 and bio2). We compared embryo and seedling development as well as triacylglycerol accumulation and fatty acid composition in seeds of single mutants (suc5, bio1 or bio2), double mutants (suc5 bio1 and suc5 bio2) and wild‐type plants. Although suc5 mutants were like the wild‐type, bio1 and bio2 mutants showed developmental defects and reduced triacylglycerol contents. In suc5 bio1 and suc5 bio2 double mutants, developmental defects were severely increased and the triacylglycerol content was reduced to a greater extent in comparison to the single mutants. Supplementation with externally applied biotin helped to reduce symptoms in both single and double mutants, but the efficacy of supplementation was significantly lower in double than in single mutants, showing that transport of biotin into the embryo is lower in the absence of SUC5.  相似文献   
995.
996.
Biological Dinitrogen Fixation in Gramineae and Palm Trees   总被引:1,自引:0,他引:1  
Biological nitrogen fixation (BNF) in the Gramineae family has been well documented, but a complete understanding of this issue is needed to turn the research into a practical approach. The literature has a long and diverse list of diazotrophic bacteria found colonizing several plant tissues, such as roots, stems, leaves, and trash as well as the rhizosphere. However, only a limited amount of research has focussed on existing associations of N2-fixing microorganisms with grasses or cereal, especially for BNF inputs and ecological studies under field conditions. The recent discovery of the endophytic diazotroph bacteria such as Acetobacter diazotrophicus, Herbaspirillum spp. and Azoarcus spp. colonizing the interior of sugarcane, rice, Kallar grass (Leptochloa fusca (L.) Kunth), respectively, and other species of grasses as well as cereals has led to a considerable interest in exploring these novel associations. There is a general consensus that plant genotype is a key factor to higher contributions of BNF together with the selection of more efficient bacterial strains. This review summarizes the present data on this field and introduces the discovery of a new group of diazotrophic bacteria colonizing palm trees and therefore opening a future perspective for using these plants, especially African oil palm, to replace diesel as a fuel.  相似文献   
997.
Photosynthesis Research - Some mosses stay green and survive long even under desiccation. Dissipation mechanisms of excess excitation energy were studied in two drought-tolerant moss species...  相似文献   
998.
Obesity is a public health problem worldwide, and especially in women in reproductive age where more than one in three have obesity. Maternal obesity is associated with an increased maternal, placental, and newborn oxidative stress, which has been proposed as a central factor in vascular dysfunction in large-for-gestational-age (LGA) newborn. However, cellular and molecular mechanisms behind this effect have not been elucidated. Untreated human umbilical artery endothelial cells (HUAEC) from LGA (LGA-HUAEC) presented higher O2 levels, superoxide dismutase activity and heme oxygenase 1 messenger RNA (mRNA) levels, paralleled by reduced GSH:GSSG ratio and NRF2 mRNA levels. In response to an oxidative challenge (hydrogen peroxide), only HUAEC from LGA exhibited an enhanced Glutathione Peroxidase 1 (GPX1) expression, as well as a more efficient antioxidant machinery measured by the biosensor probe, HyPer. An open state of chromatin in the TSS region of GPX1 in LGA-HUAEC was evidenced by the DNase-HS assay. Altogether, our data indicate that LGA-HUAEC have an altered cellular and molecular antioxidant system. We propose that a chronic pro-oxidant intrauterine milieu, as evidenced in pregestational obesity, could induce a more efficient antioxidant system in fetal vascular cells, which could be maintained by epigenetic mechanism during postnatal life.  相似文献   
999.
1000.
BackgroundThe impact of large scale Mass Drug Adminstration (MDA) of ivermectin on active onchocerciasis transmission by Simulium damnosum, which transmits the parasite O. volvulus is of great importance for onchocerciasis control programmes. We investigated in the Mbam river system area, the impact of MDA of ivermectin on entomological indices and also verify if there are river system factors that could have favoured the transmission of onchocerciasis in this area and contribute to the persistence of disease. We compared three independent techniques to detect Onchocerca larvae in blackflies and also analyzed the river system within 9 months post-MDA of ivermectin.MethodSimulium flies were captured before and after 1, 3, 6 and 9months of ivermectin-MDA. The biting rate was determined and 41% of the flies dissected while the rest were grouped into pools of 100 flies for DNA extraction. The extracted DNA was then subjected to O-150 LAMP and real-time PCR for the detection of infection by Onchocerca species using pool screening. The river system was analysed and the water discharge compared between rainy and dry seasons.Principal findingsWe used human landing collection method (previously called human bait) to collect 22,274 adult female Simulium flies from Mbam River System. Of this number, 9,134 were dissected while 129 pools constituted for molecular screening. Overall biting and parous rates of 1113 flies/man/day and 24.7%, respectively, were observed. All diagnostic techniques detected similar rates of O. volvulus infection (P = 0.9252) and infectivity (P = 0.4825) at all monitoring time points. Onchocerca ochengi larvae were only detected in 2 of the 129 pools. Analysis of the river drainage revealed two hydroelectric dams constructed on the tributaries of the Mbam river were the key contributing factor to the high-water discharge during both rainy and dry seasons.ConclusionResults from fly dissection (Microscopy), real-time PCR and LAMP revealed the same trends pre- and post-MDA. The infection rate with animal Onchocerca sp was exceptionally low. The dense river system generate important breeding sites that govern the abundance of Simulium during both dry and rainy seasons.  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