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   1553篇
  免费   63篇
  1616篇
  2022年   12篇
  2021年   23篇
  2020年   18篇
  2019年   19篇
  2018年   26篇
  2017年   30篇
  2016年   28篇
  2015年   43篇
  2014年   54篇
  2013年   76篇
  2012年   109篇
  2011年   81篇
  2010年   62篇
  2009年   33篇
  2008年   60篇
  2007年   67篇
  2006年   59篇
  2005年   50篇
  2004年   38篇
  2003年   42篇
  2002年   37篇
  2001年   48篇
  2000年   41篇
  1999年   40篇
  1998年   17篇
  1997年   17篇
  1996年   13篇
  1995年   18篇
  1994年   18篇
  1993年   10篇
  1992年   25篇
  1991年   38篇
  1990年   34篇
  1989年   29篇
  1988年   31篇
  1987年   26篇
  1986年   15篇
  1985年   12篇
  1984年   12篇
  1983年   12篇
  1981年   12篇
  1979年   19篇
  1978年   12篇
  1975年   9篇
  1974年   9篇
  1973年   15篇
  1972年   11篇
  1971年   15篇
  1970年   13篇
  1969年   14篇
排序方式: 共有1616条查询结果,搜索用时 15 毫秒
951.
Artemisia judaica L., an Egyptian medicinal plant used in the treatment of gastrointestinal disorders, was mass-propagated and grown using solid, paper-bridge-support liquid, liquid-flask and bioreactor cultures. The liquid-flask culture using 50 ml MS liquid medium in 250 ml flask yielded significantly greater shoot proliferation than either solid cultures or paper-bridge-support liquid cultures. Increasing flask capacity from 100 to 500 ml improved shoot proliferation and growth. Mass-propagation efficiencies of various bioreactor systems, viz. temporary immersion reactors and bubble column reactors, were also compared. The temporary immersion bioreactor was found to have significant advantages for A. judaica shoot proliferation. The shoot cultures from the temporary immersion reactor formed complete plantlets when subcultured onto a medium containing 1 micromoll(-1) indole-3-butyric acid (IBA), and mature plants were established, acclimatized and thrived in standard greenhouse conditions. Assays of antioxidant activity and total flavonoid content of in vitro and in vivo grown tissues were evaluated as gross parameters of medicinal efficacy. Significantly higher antioxidant activity and flavonoid contents were observed in the tissues of mature greenhouse-grown plants. The efficient in vitro production systems developed in this study provided sterile, consistent tissues for investigation of bioactivity and germplasm conservation of A. judaica.  相似文献   
952.

Background

Strategies to prevent pyrexia in patients with acute neurological injury may reduce secondary neuronal damage. The aim of this study was to determine the safety and efficacy of the routine administration of 6 grams/day of intravenous paracetamol in reducing body temperature following severe traumatic brain injury, compared to placebo.

Methods

A multicentre, randomised, blind, placebo-controlled clinical trial in adult patients with traumatic brain injury (TBI). Patients were randomised to receive an intravenous infusion of either 1g of paracetamol or 0.9% sodium chloride (saline) every 4 hours for 72 hours. The primary outcome was the mean difference in core temperature during the study intervention period.

Results

Forty-one patients were included in this study: 21 were allocated to paracetamol and 20 to saline. The median (interquartile range) number of doses of study drug was 18 (17–18) in the paracetamol group and 18 (16–18) in the saline group (P = 0.85). From randomisation until 4 hours after the last dose of study treatment, there were 2798 temperature measurements (median 73 [67–76] per patient). The mean ± standard deviation temperature was 37.4±0.5°C in the paracetamol group and 37.7±0.4°C in the saline group (absolute difference -0.3°C; 95% confidence interval -0.6 to 0.0; P = 0.09). There were no significant differences in the use of physical cooling, or episodes of hypotension or hepatic abnormalities, between the two groups.

Conclusion

The routine administration of 6g/day of intravenous paracetamol did not significantly reduce core body temperature in patients with TBI.

Trial Registration

Australian New Zealand Clinical Trials Registry ACTRN12609000444280  相似文献   
953.
    
The Ebola virus (EBOV) is a lipid-enveloped virus with a negative sense RNA genome that can cause severe and often fatal viral hemorrhagic fever. The assembly and budding of EBOV is regulated by the matrix protein, VP40, which is a peripheral protein that associates with anionic lipids at the inner leaflet of the plasma membrane. VP40 is sufficient to form virus-like particles (VLPs) from cells, which are nearly indistinguishable from authentic virions. Due to the restrictions of studying EBOV in BSL-4 facilities, VP40 has served as a surrogate in cellular studies to examine the EBOV assembly and budding process from the host cell plasma membrane. VP40 is a dimer where inhibition of dimer formation halts budding and formation of new VLPs as well as VP40 localization to the plasma membrane inner leaflet. To better understand VP40 dimer stability and critical amino acids to VP40 dimer formation, we integrated computational approaches with experimental validation. Site saturation/alanine scanning calculation, combined with molecular mechanics-based generalized Born with Poisson-Boltzmann surface area (MM-GB/PBSA) method and molecular dynamics simulations were used to predict the energetic contribution of amino acids to VP40 dimer stability and the hydrogen bonding network across the dimer interface. These studies revealed several previously unknown interactions and critical residues predicted to impact VP40 dimer formation. In vitro and cellular studies were then pursued for a subset of VP40 mutations demonstrating reduction in dimer formation (in vitro) or plasma membrane localization (in cells). Together, the computational and experimental approaches revealed critical residues for VP40 dimer stability in an alpha-helical interface (between residues 106–117) as well as in a loop region (between residues 52–61) below this alpha-helical region. This study sheds light on the structural origins of VP40 dimer formation and may inform the design of a small molecule that can disrupt VP40 dimer stability.  相似文献   
954.
    
Journal of Plant Research - To fine tune defense response output, plants recruit both positive and negative regulators. Here we report Arabidopsis DORMANCY/AUXIN ASSOCIATED FAMILY PROTEIN 2(DAP2)...  相似文献   
955.
    
Plant tissue culture techniques have been used to propagate horticultural crops at a commercial scale for more than three decades. However, due to the high cost it is generally only used for high value crops. To increase production efficiency and make micropropagation viable for a wider range of species, new approaches to address key steps of the process with high labor inputs need to be evaluated. For this study, a two‐piece scaffold system was designed, prototyped using 3D printing, and tested to physically hold plants upright thereby facilitating liquid based rooting. This system was evaluated with Malus domestica, Betula lenta, and Musa sp. using static liquid culture as well as rocker based temporary immersion system and compared to rooting in semi‐solid based medium as is commonly practiced. Significantly, earlier rooting was observed in all three species in liquid when compared to semi‐solid culture system, and plants cultured in liquid on the rocker generally performed better than those in static liquid. In addition to quicker, more uniform rooting, reducing labor requirements, and preventing root damage. This newly designed system is simple, easy to use, will help to improve efficiency, and reduce the cost of micropropagation.  相似文献   
956.
    
Alterations in the circadian system are characteristic of aging on Earth. With the decline in physiological processes due to aging, several health concerns including vision loss, cardiovascular disorders, cognitive impairments, and muscle mass loss arise in elderly populations. Similar health risks are reported as “red flag” risks among astronauts during and after a long-term Space exploration journey. However, little is known about the common molecular alterations underlying terrestrial aging and space-related aging in astronauts, and controversial conclusions have been recently reported. In light of the regulatory role of the circadian clock in the maintenance of human health, we review here the overlapping role of the circadian clock both on aging on Earth and spaceflight with a focus on the four most affected systems: visual, cardiovascular, central nervous, and musculoskeletal systems. In this review, we briefly introduce the regulatory role of the circadian clock in specific cellular processes followed by alterations in those processes due to aging. We next summarize the known molecular alterations associated with spaceflight, highlighting involved clock-regulated genes in space flown Drosophila, nematodes, small mammals, and astronauts. Finally, we discuss common genes that are altered in terms of their expression due to aging on Earth and spaceflight. Altogether, the data elaborated in this review strengthen our hypothesis regarding the timely need to include circadian dysregulation as an emerging hallmark of aging on Earth and beyond.  相似文献   
957.
    

Optimal bladder compliance is essential to urinary bladder storage and voiding functions. Calculated as the change in filling volume per change in pressure, bladder compliance is used clinically to characterize changes in bladder wall biomechanical properties that associate with lower urinary tract dysfunction. But because this method calculates compliance without regard to wall structure or wall volume, it gives little insight into the mechanical properties of the bladder wall during filling. Thus, we developed Pentaplanar Reflected Image Macroscopy (PRIM): a novel ex vivo imaging method to accurately calculate bladder wall stress and stretch in real time during bladder filling. The PRIM system simultaneously records intravesical pressure, infused volume, and an image of the bladder in five distinct visual planes. Wall thickness and volume were then measured and used to calculate stress and stretch during filling. As predicted, wall stress was nonlinear; only when intravesical pressure exceeded ~ 15 mmHg did bladder wall stress rapidly increase with respect to stretch. This method of calculating compliance as stress vs stretch also showed that the mechanical properties of the bladder wall remain similar in bladders of varying capacity. This study demonstrates how wall tension, stress and stretch can be measured, quantified, and used to accurately define bladder wall biomechanics in terms of actual material properties and not pressure/volume changes. This method is especially useful for determining how changes in bladder biomechanics are altered in pathologies where profound bladder wall remodeling occurs, such as diabetes and spinal cord injury.

  相似文献   
958.
959.
960.
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