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   787篇
  免费   42篇
  国内免费   1篇
  2022年   4篇
  2021年   8篇
  2020年   6篇
  2019年   12篇
  2018年   11篇
  2017年   16篇
  2016年   21篇
  2015年   47篇
  2014年   43篇
  2013年   38篇
  2012年   52篇
  2011年   64篇
  2010年   40篇
  2009年   30篇
  2008年   48篇
  2007年   33篇
  2006年   36篇
  2005年   22篇
  2004年   27篇
  2003年   26篇
  2002年   32篇
  2001年   6篇
  2000年   5篇
  1999年   5篇
  1998年   6篇
  1997年   7篇
  1995年   5篇
  1994年   4篇
  1993年   10篇
  1991年   6篇
  1990年   7篇
  1989年   6篇
  1988年   4篇
  1986年   4篇
  1985年   5篇
  1984年   8篇
  1970年   6篇
  1968年   3篇
  1967年   5篇
  1966年   9篇
  1965年   3篇
  1962年   4篇
  1959年   4篇
  1957年   6篇
  1956年   4篇
  1955年   4篇
  1954年   5篇
  1951年   4篇
  1940年   3篇
  1937年   3篇
排序方式: 共有830条查询结果,搜索用时 600 毫秒
181.
ObjectivesThis study examined the effect of a 10 and 20% meal price increase when choosing French fries and a 10 and 20% meal price reduction when choosing fruit for dessert on university students’ purchasing behaviour in an on-campus restaurant. The moderating effect of gender was also investigated. Secondly, this study aimed at gaining further insight into reasons why these price manipulations did or did not change students’ purchasing behaviour.SignificancePricing may be a promising strategy to improve university students’ eating behaviour. The likelihood of intervention success may increase when combining pricing strategies with offering healthy, tasty and meal matching starchy alternatives to French fries and offering a variety of fresh and appealing fruits.  相似文献   
182.
Experimental evidence of environmental features important for physical activity is challenging to procure in real world settings. The current study aimed to investigate the causal effects of environmental modifications on a photographed street''s appeal for older adults'' walking for transport. Secondly, we examined whether these effects differed according to gender, functional limitations, and current level of walking for transport. Thirdly, we examined whether different environmental modifications interacted with each other. Qualitative responses were also reported to gain deeper insight into the observed quantitative relationships. Two sets of 16 panoramic photographs of a streetscape were created, in which six environmental factors were manipulated (sidewalk evenness, traffic level, general upkeep, vegetation, separation from traffic, and benches). Sixty older adults sorted these photographs on appeal for walking for transport on a 7-point scale and reported qualitative information on the reasons for their rankings. Sidewalk evenness appeared to have the strongest influence on a street''s appeal for transport-related walking. The effect of sidewalk evenness was even stronger when the street''s overall upkeep was good and when traffic was absent. Absence of traffic, presence of vegetation, and separation from traffic also increased a street''s appeal for walking for transport. There were no moderating effects by gender or functional limitations. The presence of benches increased the streetscape''s appeal among participants who already walked for transport at least an hour/week. The protocols and methods used in the current study carry the potential to further our understanding of environment-PA relationships. Our findings indicated sidewalk evenness as the most important environmental factor influencing a street''s appeal for walking for transport among older adults. However, future research in larger samples and in real-life settings is needed to confirm current findings.  相似文献   
183.
Ilse Foissner 《Protoplasma》1990,154(2-3):80-90
Summary The formation of wall appositions (plugs) by ionophore A 23187, CaCl2, LaCl3, and nifedipine was studied in mature internodal cells of characeaen algae. CaCl2 at concentrations above 10–2M induces thick fibrillar plugs without callose inNitella flexilis. InChara corallina andNitella flexilis ionophore A 23187 (1.25×10–5 to 5×10–5M) and LaCl3 (7.5×10–5 to 2.5×10–4M) cause flat appositions which contain callose and have a more granular structure. Plug formation by ionophore A 23187, CaCl2, and LaCl3 is pH-dependent and occurs beneath the alkaline regions of the cell. Nifedipine (10–4 to 10–5M) induces plugs inNitella flexilis after previous injury. These callose-containing wall appositions consist of a heterogeneous granular core which is covered by a fibrillar layer. The results of this work are compared with previous studies on wound wall formation and chlortetracycline (CTC)-induced plug formation which reveal that abundant coated vesicles occur only when a thick fibrillar wall layer is formed. Neither LaCl3 nor nifedipine inhibit the formation of CaCl2- or CTC-plugs. The unusual effects of these substances, which normally act as Ca2+ antagonists and therefore should prevent and not induce plug formation, are discussed. It is suggested that La3+ mimicks the effects of calcium and that nifedipine binding to the Ca2+ channels is altered in the alkaline regions of characean internodes and allows an influx of Ca2+.Abbreviations AFW artificial fresh water - CTC chlortetracycline - DCMU dichlorphenyldimethylurea - DMSO dimethylsulfoxide - EGTA ethyleneglycoltetraacetic acid - MES 2-(N-morpholino) ethanesulfonic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - TAPS N-tris[hydroxymethyl]methyl-3-aminopropanesulfonic acid  相似文献   
184.
Summary Protein synthesis-stimulating activity was assayed in the cytosolic fraction of white muscle from teleost fish (rainbow trout, carp) and of rat liver. In vitro protein synthesis-stimulating activity in the cytosolic fraction is reduced by food deprivation. The addition of elongation factors EF1, EF2, or EF1+EF2 compensates for the starvation-induced loss of protein synthesis-stimulating activity in trout muscle cytosol. The action of EF2 is stronger than that of EF1 in this respect. However, EF1 enhances in vitro protein synthesis-stimulating activity in rat liver cytosol more than EF2. The EF2 concentration in the cytosolic fraction of white muscle from starved trout is significantly lower than in fed specimens.Abbreviations EF elongation factor(s) - SGR specific growth rate - TCA trichloroacetic acid  相似文献   
185.
186.
Strains T5K1 and AV446 isolated from apple cider vinegars during a submerged vinegar production in two separate vinegar facilities showed 94% 16S rRNA gene similarity to its closest neighbors Komagataeibacter maltaceti LMG 1529T and Gluconacetobacter entanii LTH 4560T. Further phylogenetic and phenotypic characterizations indicated that the isolates belonged to a novel species of the Komagataeibacter genus. Comparison based on 16S–23S rRNA gene ITS sequences and concatenated partial sequences of the housekeeping genes dnaK, groEL and rpoB, grouped both strains to a single phylogenetic cluster well separated from the other species of the Komagataeibacter genus. Average nucleotide identity of T5K1 and AV446 draft genome sequences compared to other Komagataeibacter type strains was below 94% and at the same time, in-silico DNA–DNA hybridization was below 70%. Both strains on the other hand showed approximately 98% (average nucleotide identity) and 87% (in silico DNA–DNA hybridization) similarity to each other. Strains T5K1 and AV446 can be differentiated from other Komagataeibacter type strains based on their ability to produce 2-keto-d-gluconic acid and at the same time inability to produce 5-keto-d-gluconic acid. Furthermore, strains of the new species do not grow on Asai medium supplemented with d-glucose or d-mannitol. The growth is also absent (T5K1) or weak (AV446) on Hoyer–Frateur medium supplemented with afore mentioned sugars. Both strains produce cellulose. In addition, draft genome analysis revealed that strains T5K1 and AV446 possess genes involved in the synthesis of acetan-like extracellular heteropolysaccharide. We propose the name Komagataeibacter pomaceti sp. nov. for the new species with LMG 30150T [= CCM 8723T = ZIM B1029T] as the type strain. Data collected in this study and in a previous study also revealed that Komagataeibacter kombuchae is a later heterotypic synonym of Komagataeibacter hansenii.  相似文献   
187.
188.
Abstract: Desiccation tolerance is a fundamental principle for resting stages of plant development which include the dormancy of seeds and the quiescent stages of resurrection plants. To prevent the deleterious effects of cellular desiccation, a complex interplay of several adaption mechanisms is required. The ability to cope with free radicals, the formation of which is well documented in desiccated tissues, is one of these basic requirements. Detoxification of free radicals by several antioxidants and scavenging enzymes include reactions of reduced glutathione (GSH) resulting in the formation of glutathione disulfide (GSSG). In free radical processing pathways GSSG is considered to be immediately reduced back to GSH by the action of glutathione reductase (EC 1.6.4.2.). However, in desiccated tissues GSSG accumulates. Protein-glutathione mixed disulfides (PSSG) are also reported to increase in plants under drought leading to the hypothesis that glutathione protects protein thiol groups from auto-oxidation. The irreversible formation of intramolecular disulfides resulting in denaturation of proteins would be one of the primary sites of desiccation injury. We suggest that PSSG is formed by the reaction of GSSG with high molecular weight thiols and introduce a thiol-disulfide cycle that involves reduction/oxidation processes of glutathione and protein thiol groups during the dehydration/rehydration processes in desiccation tolerant tissues.  相似文献   
189.
The primate visual system consists of a ventral stream, specialized for object recognition, and a dorsal visual stream, which is crucial for spatial vision and actions. However, little is known about the interactions and information flow between these two streams. We investigated these interactions within the network processing three-dimensional (3D) object information, comprising both the dorsal and ventral stream. Reversible inactivation of the macaque caudal intraparietal area (CIP) during functional magnetic resonance imaging (fMRI) reduced fMRI activations in posterior parietal cortex in the dorsal stream and, surprisingly, also in the inferotemporal cortex (ITC) in the ventral visual stream. Moreover, CIP inactivation caused a perceptual deficit in a depth-structure categorization task. CIP-microstimulation during fMRI further suggests that CIP projects via posterior parietal areas to the ITC in the ventral stream. To our knowledge, these results provide the first causal evidence for the flow of visual 3D information from the dorsal stream to the ventral stream, and identify CIP as a key area for depth-structure processing. Thus, combining reversible inactivation and electrical microstimulation during fMRI provides a detailed view of the functional interactions between the two visual processing streams.  相似文献   
190.

Background

Active transport is a convenient way to incorporate physical activity in adolescents’ daily life. The present study aimed to investigate which psychosocial and environmental factors are associated with walking, cycling, public transport (train, tram, bus, metro) and passive transport (car, motorcycle, moped) over short distances (maximum eight kilometres) among older adolescents (17–18 years), to school and to other destinations.

Methods

562 older adolescents completed an online questionnaire assessing socio-demographic variables, psychosocial variables, environmental variables and transport to school/other destinations. Zero-inflated negative binomial regression models were performed.

Results

More social modelling and a higher residential density were positively associated with walking to school and walking to other destinations, respectively. Regarding cycling, higher self-efficacy and a higher social norm were positively associated with cycling to school and to other destinations. Regarding public transport, a higher social norm, more social modelling of siblings and/or friends, more social support and a higher land use mix access were positively related to public transport to school and to other destinations, whereas a greater distance to school only related positively to public transport to school. Regarding passive transport, more social support and more perceived benefits were positively associated with passive transport to school and to other destinations. Perceiving less walking and cycling facilities at school was positively related to passive transport to school only, and more social modelling was positively related to passive transport to other destinations.

Conclusions

Overall, psychosocial variables seemed to be more important than environmental variables across the four transport modes. Social norm, social modelling and social support were the most consistent psychosocial factors which indicates that it is important to target both older adolescents and their social environment in interventions promoting active transport. Walking or cycling together with siblings or friends has the potential to increase social norm, social modelling and social support towards active transport.  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