全文获取类型
收费全文 | 13469篇 |
免费 | 1156篇 |
国内免费 | 10篇 |
出版年
2022年 | 93篇 |
2021年 | 228篇 |
2020年 | 142篇 |
2019年 | 185篇 |
2018年 | 206篇 |
2017年 | 172篇 |
2016年 | 329篇 |
2015年 | 564篇 |
2014年 | 586篇 |
2013年 | 793篇 |
2012年 | 955篇 |
2011年 | 979篇 |
2010年 | 633篇 |
2009年 | 557篇 |
2008年 | 828篇 |
2007年 | 868篇 |
2006年 | 777篇 |
2005年 | 747篇 |
2004年 | 768篇 |
2003年 | 714篇 |
2002年 | 656篇 |
2001年 | 145篇 |
2000年 | 91篇 |
1999年 | 143篇 |
1998年 | 166篇 |
1997年 | 124篇 |
1996年 | 116篇 |
1995年 | 103篇 |
1994年 | 94篇 |
1993年 | 107篇 |
1992年 | 101篇 |
1991年 | 72篇 |
1990年 | 80篇 |
1989年 | 63篇 |
1988年 | 78篇 |
1987年 | 75篇 |
1986年 | 61篇 |
1985年 | 81篇 |
1984年 | 79篇 |
1983年 | 80篇 |
1982年 | 107篇 |
1981年 | 94篇 |
1980年 | 88篇 |
1979年 | 54篇 |
1978年 | 53篇 |
1977年 | 54篇 |
1976年 | 53篇 |
1975年 | 44篇 |
1974年 | 49篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
J. Sherrod DeVerse Keith A. Bailey Greg A. Foster Vaishali Mittal Stuart M. Altman Scott I. Simon Anthony G. Passerini 《Journal of visualized experiments : JoVE》2012,(65)
Atherogenesis is potentiated by metabolic abnormalities that contribute to a heightened state of systemic inflammation resulting in endothelial dysfunction. However, early functional changes in endothelium that signify an individual''s level of risk are not directly assessed clinically to help guide therapeutic strategy. Moreover, the regulation of inflammation by local hemodynamics contributes to the non-random spatial distribution of atherosclerosis, but the mechanisms are difficult to delineate in vivo. We describe a lab-on-a-chip based approach to quantitatively assay metabolic perturbation of inflammatory events in human endothelial cells (EC) and monocytes under precise flow conditions. Standard methods of soft lithography are used to microfabricate vascular mimetic microfluidic chambers (VMMC), which are bound directly to cultured EC monolayers.1 These devices have the advantage of using small volumes of reagents while providing a platform for directly imaging the inflammatory events at the membrane of EC exposed to a well-defined shear field. We have successfully applied these devices to investigate cytokine-,2 lipid-3, 4 and RAGE-induced5 inflammation in human aortic EC (HAEC). Here we document the use of the VMMC to assay monocytic cell (THP-1) rolling and arrest on HAEC monolayers that are conditioned under differential shear characteristics and activated by the inflammatory cytokine TNF-α. Studies such as these are providing mechanistic insight into atherosusceptibility under metabolic risk factors. 相似文献
22.
23.
Stephen C. Votier Anthony Bicknell Samantha L. Cox Kylie L. Scales Samantha C. Patrick 《PloS one》2013,8(3)
Commercial capture fisheries produce huge quantities of offal, as well as undersized and unwanted catch in the form of discards. Declines in global catches and legislation to ban discarding will significantly reduce discards, but this subsidy supports a large scavenger community. Understanding the potential impact of declining discards for scavengers should feature in an eco-system based approach to fisheries management, but requires greater knowledge of scavenger/fishery interactions. Here we use bird-borne cameras, in tandem with GPS loggers, to provide a unique view of seabird/fishery interactions. 20,643 digital images (one min−1) from ten bird-borne cameras deployed on central place northern gannets Morus bassanus revealed that all birds photographed fishing vessels. These were large (>15 m) boats, with no small-scale vessels. Virtually all vessels were trawlers, and gannets were almost always accompanied by other scavenging birds. All individuals exhibited an Area-Restricted Search (ARS) during foraging, but only 42% of ARS were associated with fishing vessels, indicating much ‘natural’ foraging. The proportion of ARS behaviours associated with fishing boats were higher for males (81%) than females (30%), although the reasons for this are currently unclear. Our study illustrates that fisheries form a very important component of the prey-landscape for foraging gannets and that a discard ban, such as that proposed under reforms of the EU Common Fisheries Policy, may have a significant impact on gannet behaviour, particularly males. However, a continued reliance on ‘natural’ foraging suggests the ability to switch away from scavenging, but only if there is sufficient food to meet their needs in the absence of a discard subsidy. 相似文献
24.
25.
Responses of bovine adrenal capillary endothelial cells (BACE) on treatment with transforming growth factor beta 1 (TGF-beta 1) have been characterized and tested for sensitivity to inactivation of pertussis toxin-sensitive G-proteins. TGF-beta 1 elicited growth inhibition, monolayer remodeling, elevation of steady state mRNA levels for collagen type 1 (alpha 1(1) and alpha 2(1)) and TGF-beta 1, and inhibition of p34cdc2 histone H1 kinase activity in BACE cells. Pertussis toxin treatment enhanced both inhibition of BACE cell [3H]methylthymidine uptake and remodeling of BACE monolayers by TGF-beta 1. These findings contrast with studies of mink lung epithelial cells, in which TGF-beta 1 growth inhibition has been shown to be pertussis-sensitive. Further investigation revealed that pertussis toxin treatment of BACE cells had no effect on TGF-beta 1-stimulated elevation of steady state mRNA levels for collagen type 1 (alpha 1(1) or alpha 2(1)) or for TGF-beta 1. Analysis of p34cdc2 activity in BACE cells revealed potent inhibition of p34cdc2 histone H1 kinase activity by TGF-beta 1. Pertussis toxin treatment also abolished the increase in p34cdc2 activity, however, precluding the determination of the pertussis toxin sensitivity of this response to TGF-beta 1. Consistent with suppression of p34cdc2 activation, pertussis toxin also caused substantial inhibition of mitogen-stimulated BACE cell [3H]methylthymidine uptake. It is concluded that TGF-beta 1 signal transduction in this cell type does not involve G-proteins of the pertussis toxin-sensitive class and that, in view of its potent effects on DNA synthesis and p34cdc2 activation, the use of pertussis toxin to determine G-protein involvement in cytokine signalling pathways should be approached with caution. 相似文献
26.
Wayne W. Poon Anthony J. Carlos Brittany L. Aguilar Nicole C. Berchtold Crystal K. Kawano Vahe Zograbyan Tim Yaopruke Michael Shelanski Carl W. Cotman 《The Journal of biological chemistry》2013,288(23):16937-16948
We previously found that BDNF-dependent retrograde trafficking is impaired in AD transgenic mouse neurons. Utilizing a novel microfluidic culture chamber, we demonstrate that Aβ oligomers compromise BDNF-mediated retrograde transport by impairing endosomal vesicle velocities, resulting in impaired downstream signaling driven by BDNF/TrkB, including ERK5 activation, and CREB-dependent gene regulation. Our data suggest that a key mechanism mediating the deficit involves ubiquitin C-terminal hydrolase L1 (UCH-L1), a deubiquitinating enzyme that functions to regulate cellular ubiquitin. Aβ-induced deficits in BDNF trafficking and signaling are mimicked by LDN (an inhibitor of UCH-L1) and can be reversed by increasing cellular UCH-L1 levels, demonstrated here using a transducible TAT-UCH-L1 strategy. Finally, our data reveal that UCH-L1 mRNA levels are decreased in the hippocampi of AD brains. Taken together, our data implicate that UCH-L1 is important for regulating neurotrophin receptor sorting to signaling endosomes and supporting retrograde transport. Further, our results support the idea that in AD, Aβ may down-regulate UCH-L1 in the AD brain, which in turn impairs BDNF/TrkB-mediated retrograde signaling, compromising synaptic plasticity and neuronal survival. 相似文献
27.
Using a modified postmodern perspective, Canada's policy of multiculturalism and the emphasis upon ‘unity within diversity’ are related to the theme of globalization and the development of ‘a new world order’. It is argued that Canada is not unique in its efforts to come to terms with the contradictions and conflicts generated by postindustrialism and the realignment of superpowers. Questions of identity, collective self‐determination and the problematic relation between universalism and particularism, in relation to sovereignty, legitimacy, human rights and participation are explored. 相似文献
28.
29.
Anthony C. Postle 《法国昆虫学会纪事》2018,54(3):247-256
Carayonovus insignis n. gen., n. sp., a remarkable new genus and species of Heteroptera, is described from Reunion Island. It is tentatively placed in the family Anthocoridae (Cimicoidea), but because of its remarkable sexual dimorphism and possession of characters not normally associated with this family or even with Cimicoidea, the genus is discussed in terms of the validity or otherwise of including it in these taxa. Its habitat preference is also examined. 相似文献
30.