全文获取类型
收费全文 | 1028篇 |
免费 | 135篇 |
国内免费 | 40篇 |
出版年
2023年 | 25篇 |
2022年 | 16篇 |
2021年 | 28篇 |
2020年 | 58篇 |
2019年 | 45篇 |
2018年 | 46篇 |
2017年 | 40篇 |
2016年 | 36篇 |
2015年 | 52篇 |
2014年 | 43篇 |
2013年 | 57篇 |
2012年 | 40篇 |
2011年 | 43篇 |
2010年 | 44篇 |
2009年 | 45篇 |
2008年 | 44篇 |
2007年 | 37篇 |
2006年 | 46篇 |
2005年 | 52篇 |
2004年 | 34篇 |
2003年 | 33篇 |
2002年 | 43篇 |
2001年 | 33篇 |
2000年 | 15篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 14篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有1203条查询结果,搜索用时 15 毫秒
1.
2.
3.
ZhiMeng Xu ChengBin Li QingLing Liu Hua Yang Ping Li 《Journal of cellular biochemistry》2019,120(10):18388-18397
Insufficient nutrients supply will greatly affect the function of cardiac myocytes. The adaptive responses of cardiac myocytes to nutritional stress are not fully known. Ginsenoside Rg1 is one of the most pharmacologically active components in Panax Ginseng and possesses protective effects on cardiomyocyte. Here, we investigate the effects of ginsenoside Rg1 on H9c2 cells which were subjected to nutritional stress. Nutritional stress-induced by glucose deprivation strongly induced cell death and this response was inhibited by ginsenoside Rg1. Importantly, glucose deprivation decreased intracellular ATP levels and mitochondrial membrane potential. Ginsenoside Rg1 rescued ATP levels and mitochondrial membrane potential in nutrient-starved cells. For molecular mechanisms, ginsenoside Rg1 increased the expressions of PTEN-induced kinase 1 (PINK1) and p-AMPK in glucose deprivation treated H9c2 cells. Reducing the expression of aldolase in H9c2 cells inhibited ginsenoside Rg1′s actions on PINK1 and p-AMPK. Further, the nutritional stress mice were used to verify the mechanisms obtained in vitro. Ginsenoside Rg1 increased the expressions of aldolase, p-AMPK, and PINK1 in starved mice heart. Taken together, our results reveal that ginsenoside Rg1 limits nutritional stress-induced H9c2 cells injury by regulating the aldolase /AMP-activated protein kinase/PINK1 pathway. 相似文献
4.
- Although aggregation in non‐social arthropods is common, its adaptive value is not always clear. Oviposition behaviour of the viburnum leaf beetle (Pyrrhalta viburni) is aggregative, with females preferring to lay eggs on twigs already infested by conspecifics. We previously showed that aggregative oviposition aided in overcoming host plant defences. Here we explore two additional benefits of this behaviour: reduction of time investment in oviposition; and improvement of host use by larval group feeding.
- In video‐recorded trials, the presence of conspecific egg masses did not have an impact on the time associated with oviposition, but it did affect females' pre‐oviposition behaviour: the length of foraging movements was 21% shorter on infested than on non‐infested twigs, and was concentrated near the infested area.
- In two separate studies of insect performance, larvae were reared to maturity in groups of different densities (five or 10, and five or 20, respectively) on several hosts (four and 17 Viburnum spp., respectively). Independent of host species, adults were > 13% heavier (groups of 10 vs. five), and pupation success was 27% higher (groups of 20 vs. five) at higher larval density.
- Two additional effects were dependent on host species: larval survivorship (groups of 10 vs. five), and adult mass (groups of 20 vs. five). These effects were not associated with plant defensive traits (i.e. trichomes or leaf toughness), but adult mass was associated with host nutritional quality (i.e. foliar nitrogen content).
- These results show that several traits of P. viburni larval performance are positively density‐dependent, and suggest that benefits of group feeding could have played a role in the evolution of oviposition behaviour in P. viburni. Our results also demonstrate that plant quality can mediate benefits of aggregation, underscoring the importance of ecological context in understanding the feeding strategies of insects.
5.
J. De Kok C. Van Der Schoot M. Veldhuizen H. Th. Wolterbeek 《Biological trace element research》1993,38(1):13-26
The in vitro uptake of zinc by erythrocytes was measured under near-physiological conditions, using65Zn as a radioactive tracer. Because of the presence of serum albumin—a strong zinc ligand—a low concentration of medium free
zinc was maintained. Under these conditions a high-affinity carrier for zinc transport over the cell membrane was identified.
With human erythrocytes, a Michaelis constant (K
m
) of 0.2 nM with respect to free medium zinc was measured and aV
max
of 4.5 nmoles Zn transported per h/g dry wt. TheK
m
for medium Zn increases when the size of the internal erythrocytic Zn pool is augmented, whereasV
max
remains virtually unchanged. A model to explain this phenomenon is proposed. It is suggested that this phenomenon could underlie
observations, confirmed here, that the in vitro uptake of Zn by animal erythrocytes depends on the Zn status of the animal. 相似文献
6.
7.
8.
9.
Basic optical properties of bioinspired peptide nanostructures are deeply modified by thermally mediated refolding of peptide secondary structure from α‐helical to β‐sheet. This conformational transition is followed by the appearance in the β‐sheet structures of a wideband optical absorption and fluorescence in the visible region. We demonstrate that a new biophotonic effect of optical waveguiding recently observed in peptide/protein nanoensembles is a structure‐sensitive bimodal phenomenon. In the primary α‐helical structure input, light propagates via optical transmission window demonstrating conventional passive waveguiding, based on classical optics. In the β‐sheet structure, fluorescent (active) light waveguiding is revealed. The latter can be attributed to completely different physical mechanism of exciton‐polariton propagation, characterized by high effective refractive index, and can be observed in nanoscale fibers below diffraction limit. It has been shown that peptide material requirements for passive and active waveguiding are dissimilar. Original biocompatibility and biodegradability indicate high potential future applications of these bioinspired waveguiding materials in precise photobiomedicine towards advanced highly selective bioimaging, photon diagnostics, and optogenetics. 相似文献
10.
Positive species interactions are ubiquitous in natural communities, but the mechanisms through which they operate are poorly understood. One proposed mechanism is resource conversion – the conversion by a benefactor species of a resource from a resource state that is inaccessible to a potential beneficiary species into a resource state that is accessible. Such conversion often occurs as a byproduct of resource consumption, and sometimes in exchange for non-resource benefits to the benefactor species. At least five known classes of interactions, including both facilitative and mutualistic ones, may be classified as resource conversion interactions. We formulated a generalizable mathematical model for resource conversion interactions and examined two model variants that represent processing chain and nurse plant interactions. We examined the conditions under which these conformed to the stress-gradient hypothesis (SGH), which predicts increased interaction benefits in more stressful environments. These yielded four key insights: 1) resource conversion interactions can be positive (towards the resource recipient) only when facilitator-mediated resource conversion is more efficient than the baseline, spontaneous, facilitator-independent resource conversion; 2) the sign of resource conversion interaction outcomes never switches (e.g. from net positive to net negative) with changing levels of resource availability, when all other parameters are kept constant; 3) processing chain interactions at equilibrium can never be positive in a manner that conforms to the SGH; 4) nurse plant interactions can be positive and conform to the SGH, although the manner in which they do depends largely on how resource stress is defined, and the environmental supply rate of surface soil moisture. The first two insights are likely to be generalizable across all resource conversion interactions. The general agreement of the model with empirical studies suggest that resource conversion is the mechanism underlying the aforementioned interactions, and an ecologically meaningful way of classifying these previously unassociated positive species interactions. 相似文献