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   232篇
  免费   15篇
  2023年   2篇
  2022年   2篇
  2021年   9篇
  2020年   6篇
  2019年   3篇
  2018年   5篇
  2017年   8篇
  2016年   10篇
  2015年   7篇
  2014年   12篇
  2013年   8篇
  2012年   23篇
  2011年   16篇
  2010年   13篇
  2009年   19篇
  2008年   12篇
  2007年   9篇
  2006年   14篇
  2005年   7篇
  2004年   12篇
  2003年   11篇
  2002年   15篇
  2001年   1篇
  2000年   2篇
  1999年   5篇
  1998年   2篇
  1997年   3篇
  1994年   2篇
  1992年   2篇
  1989年   1篇
  1987年   3篇
  1986年   1篇
  1982年   1篇
  1980年   1篇
排序方式: 共有247条查询结果,搜索用时 31 毫秒
91.
Recent studies suggest that individuals with better problem‐solving and/or learning performance have greater reproductive success, and that individuals may thus benefit from choosing mates based on these performances. However, directly assessing these performances in candidate mates could be difficult. Instead, the use of indirect cues related to problem‐solving and/or learning performance, such as condition‐dependent phenotypic traits, might be favored. We investigated whether problem‐solving and learning performance on a novel non‐foraging task correlated with sexually selected plumage colouration in a natural population of great tits Parus major. We found that males successful in solving the task had darker blue‐black crowns than non‐solvers, and that males solving the task more rapidly over multiple attempts (i.e. learners) exhibited blue‐black crowns with higher UV chroma and shorter‐wavelength hues than non‐learners. In contrast, we found no link between behavioural performance on the task and the yellow breast colouration in either sex. Our findings suggest that blue‐black crown colouration could serve as a signal of problem‐solving and learning performance in wild great tit males. Further research remains necessary to determine whether different sexually selected traits are used to signal cognitive performance for mate choice, either directly (i.e. cognitive performance influencing individual's health and ornamentation through diet for example) or indirectly (i.e. due to a correlation with a third factor such as individual quality or condition).  相似文献   
92.
Small distance movements are of great importance for the dynamics of local populations of insects and can indirectly be assessed using molecular markers. We isolated six polymorphic microsatellite loci in the aphid species Metopeurum fuscoviride Stroyan, monophagous on the common Tansy (Tanacetum vulgare L.). Twenty‐five to 30 aphids from seven populations were analysed. Between three and 17 alleles were found per locus and expected heterozygosities ranged from 0.14 to 0.79. In total, 114 multilocus genotypes were found in 192 parthenogenetic aphids analysed, indicating that the resolution will be high enough to study differentiation on a small spatial scale.  相似文献   
93.
94.
95.
Desminopathies, a subgroup of myofibrillar myopathies (MFMs), the progressive muscular diseases characterized by the accumulation of granulofilamentous desmin-positive aggregates, result from mutations in the desmin gene (DES), encoding a muscle-specific intermediate filament. Desminopathies often lead to severe disability and premature death from cardiac and/or respiratory failure; no specific treatment is currently available. To identify drug-targetable pathophysiological pathways, we performed pharmacological studies in C2C12 myoblastic cells expressing mutant DES. We found that inhibition of the Rac1 pathway (a G protein signaling pathway involved in diverse cellular processes), antioxidant treatment, and stimulation of macroautophagy reduced protein aggregation by up to 75% in this model. Further, a combination of two or three of these treatments was more effective than any of them alone. These results pave the way towards the development of the first treatments for desminopathies and are potentially applicable to other muscle or brain diseases associated with abnormal protein aggregation.  相似文献   
96.
The earliest direct evidence for tool-use by our ancestors are 2.6 million year old stone tools from Africa. These earliest artifacts show that, already, early hominins had developed the required advanced movement skills and cognitive capacities to manufacture stone tools. Currently, it is not well understood, however, which specific movement skills are required for successful stone knapping and accordingly it is unknown how these skills emerged during early hominin evolution. In particular, it is not clear which striking movements are indicative of skilled performance, how striking movement patterns vary with task and environmental constraints, and how movement patterns are passed on within social groups. The present study addresses these questions by investigating striking movement patterns and striking variability in 18 modern stone knappers (nine experienced and nine novices). The results suggest that no single movement pattern characterizes successful stone knapping. Participants showed large inter-individual movement variability of the elementary knapping action irrespective of knapping experience and knapping performance. Changes in task- and environmental constraints led knappers to adapt their elementary striking actions using a combination of individual and common strategies. Investigation of striking pattern similarities within social groups showed only partial overlap of striking patterns across related individuals. The results therefore suggest that striking movement patterns in modern stone knappers are largely specific to the individual and movement variability is not indicative of knapping performance. The implications of these results for the development of percussive traditions are discussed.  相似文献   
97.
Treatment by EDTA of purified plasma membranes from MF2S cells (a variant of the murine plasmacytoma MOPC 173) solubilized proteins and increased by a 1000-fold the sensitivity of (Na+ + K+)-ATPase to ouabain. When added back with Ca2+ to treated plasma membranes, these EDTA-solubilized proteins restored the initial sensitivity of the enzyme to its inhibitor. We report the purification of a protein of Mr 32 000, isolated from the EDTA-treated membrane supernatant. This protein was purified by a one-step procedure involving a preparative polyacrylamide gel electrophoresis without detergent. In the presence of Ca2+ it was able to restore the original sensitivity to ouabain of (Na+ + K+)-ATPase from EDTA-treated membrane. This protein was shown to be similar to the β-actinin described by Maruyama by the following criteria: (1) molecular weight and amino acid composition; (2) cross-reactivity with their respective antisera; (3) in the presence of Ca2+ the same quantitative biological activity on ouabain sensitivity of the (Na+ + K+)-ATPase. A possible interaction between β-actinin, calmodulin and membrane-bound (Na+ + K+)-ATPase is discussed.  相似文献   
98.
Food restriction is the most effective modulator of oxidative stress and it is believed that a reduction in caloric intake per se is responsible for the reduced generation of reactive oxygen species (ROS) by mitochondria. Hydrogen peroxide (H(2)O(2)) generation and oxygen consumption (O(2)) by skeletal muscle mitochondria were determined in a peculiar strain of rats (Lou/C) characterized by a self-low-caloric intake and a dietary preference for fat. These rats were fed either with a standard high-carbohydrate (HC) or a high-fat (HF) diet and the results were compared to those measured in Wistar rats fed a HC diet. H(2)O(2) production was significantly reduced in Lou/C rats fed a HC diet; this effect was not due to a lower O(2) consumption but rather to a decrease in rotenone-sensitive NADH-ubiquinone oxidoreductase activity and increased expression of uncoupling proteins 2 and 3. The reduced H(2)O(2) generation displayed by Lou/C rats was accompanied by a significant inhibition of permeability transition pore (PTP) opening. H(2)O(2) production was restored and PTP inhibition was relieved when Lou/C rats were allowed to eat a HF diet, suggesting that the reduced oxidative stress provided by low caloric intake is lost when fat proportion in the diet is increased.  相似文献   
99.
Tributyl phosphate degradation by Serratia odorifera   总被引:1,自引:0,他引:1  
Several strains from tributyl phosphate (TBP)-polluted soils were isolated and screened for their ability to degraded this widely used organophosphorus compound. The most active strain, identified as Serratia odorifera, degrades up to 600 microM TBP (initially present in the medium at 2 mM) during its growth phase, within 8 h from inoculation. However, this bacterium could not utilize TBP as the sole carbon and/or phosphorus source but nevertheless is a good candidate for bioremediation of TBP-polluted industrial sites.  相似文献   
100.
Oligopeptides have been recognized as signaling molecules playing an important role in plant cell growth and development. Phytosulfokine-alpha (PSK), a plant-specific disulfated pentapeptide, is involved at nanomolar concentrations in initial steps of cellular dedifferentiation, proliferation, and re-differentiation, with a biological function similar to that of plant hormones. On the other hand, legume crops are generally known for their recalcitrance to in vitro regeneration approaches, which has restrained the exploitation of biotechnological tools for their genetic improvement. Against this background, we added PSK at concentrations of 10?10 to 10?6 M, to semisolid MS-based culture media previously shown to permit some regeneration responses with pea (Pisum sativum) and highly recalcitrant faba bean (Vicia faba). Callus, cell suspensions and embryo-derived explants of pea cultivars Frisson and Cameor and a low vicin, zero tannin faba bean genotype (Fevita©) were assessed for their embryogenic and organogenic regeneration competence. For all genotypes, PSK reliably and significantly enhanced the regeneration competence producing somatic embryos and organs that yielded regenerated plants of both pea cultivars, and had a major organogenic effect leading to plant regeneration with faba bean where somatic embryos, although produced, failed to convert into viable plants. This is the first report on the use of PSK with legume species.  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