全文获取类型
收费全文 | 1585篇 |
免费 | 242篇 |
出版年
2020年 | 15篇 |
2019年 | 21篇 |
2016年 | 31篇 |
2015年 | 50篇 |
2014年 | 51篇 |
2013年 | 52篇 |
2012年 | 63篇 |
2011年 | 70篇 |
2010年 | 45篇 |
2009年 | 41篇 |
2008年 | 54篇 |
2007年 | 46篇 |
2006年 | 48篇 |
2005年 | 59篇 |
2004年 | 51篇 |
2003年 | 54篇 |
2002年 | 49篇 |
2001年 | 42篇 |
2000年 | 34篇 |
1999年 | 35篇 |
1998年 | 25篇 |
1997年 | 27篇 |
1996年 | 31篇 |
1995年 | 16篇 |
1994年 | 32篇 |
1993年 | 20篇 |
1992年 | 32篇 |
1991年 | 35篇 |
1990年 | 27篇 |
1989年 | 31篇 |
1988年 | 17篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 30篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1973年 | 16篇 |
1972年 | 17篇 |
1971年 | 19篇 |
1970年 | 23篇 |
1969年 | 17篇 |
1968年 | 16篇 |
排序方式: 共有1827条查询结果,搜索用时 78 毫秒
151.
152.
Janet M. Rowe John R. Dunlap Christopher J. Gobler O. Roger Anderson Mary D. Gastrich Steven W. Wilhelm 《Journal of phycology》2008,44(1):71-76
We have been working to characterize viruses that infect the HAB‐forming pelagophyte Aureococcus anophagefferens Hargraves et Sieburth. Field samples were collected during brown‐tide events in 2002 and tested for the presence of lytic agents. Here, we describe a recently isolated, lytic virus‐like particle (VLP) that is morphologically similar to particles observed in thin sections of infected A. anophagefferens cells from natural samples. TEM and SEM have revealed VLPs consistent with the morphological characteristics of previously described Phycodnaviridae. Large icosahedral particles (~140 nm) of similar shape and morphology dominate cell lysates and are accompanied by smaller phage‐like particles and heterotrophic prokaryotes that appear to be incurable from our cultures. To determine which of these particles interacts with the Aureococcus cells, we preserved cultures during the early stage of infection so that SEM could be used to visualize those particles that attach to the surface of naïve cultures. SEM revealed that 63% of the large icosahedral‐shaped particles attached to A. anophagefferens cells after only 30 min of exposure, while no significant frequency of attachment to the alga was observed for the phage‐like particles. The results of these observations are in contrast to previous studies, where phage‐like particles were reported to infect cells. When considered in conjunction with field observations, the results suggest that this newly isolated virus represents the dominant virus‐morphotype associated with bloom collapse and termination. 相似文献
153.
Implications of land‐use change to Short Rotation Forestry in Great Britain for soil and biomass carbon 下载免费PDF全文
Aidan M. Keith Rebecca L. Rowe Kim Parmar Mike P. Perks Ewan Mackie Marta Dondini Niall P. McNamara 《Global Change Biology Bioenergy》2015,7(3):541-552
Land‐use change can have significant impacts on soil and aboveground carbon (C) stocks and there is a clear need to identify sustainable land uses which maximize C mitigation potential. Land‐use transitions from agricultural to bioenergy crops are increasingly common in Europe with one option being Short Rotation Forestry (SRF). Research on the impact on C stocks of the establishment of SRF is limited, but given the potential for this bioenergy crop in temperate climates, there is an evident knowledge gap. Here, we examine changes in soil C stock following the establishment of SRF using combined short (30 cm depth) and deep (1 m depth) soil cores at 11 sites representing 29 transitions from agriculture to SRF. We compare the effects of tree species including 9 coniferous, 16 broadleaved and 4 Eucalyptus transitions. SRF aboveground and root biomass were also estimated in 15 of the transitions using tree mensuration data allowing assessments of changes in total ecosystem C stock. Planting coniferous SRF, compared to broadleaved and Eucalyptus SRF, resulted in greater accumulation of litter and overall increased soil C stock relative to agricultural controls. Though broadleaved SRF had no overall effect on soil C stock, it showed the most variable response suggesting species‐specific effects and interactions with soil types. While Eucalyptus transitions induced a reduction in soil C stocks, this was not significant unless considered on a soil mass basis. Given the relatively young age and limited number of Eucalyptus plantations, it is not possible to say whether this reduction will persist in older stands. Combining estimates of C stocks from different ecosystem components (e.g., soil, aboveground biomass) reinforced the accumulation of C under coniferous SRF, and indicates generally positive effects of SRF on whole‐ecosystem C. These results fill an important knowledge gap and provide data for modelling of future scenarios of LUC. 相似文献
154.
Bo Chen Allison L. Miller Marlon Rebelatto Yambasu Brewah Daniel C. Rowe Lori Clarke Meggan Czapiga Kim Rosenthal Tomozumi Imamichi Yan Chen Chew-Shun Chang Partha S. Chowdhury Brian Naiman Yue Wang De Yang Alison A. Humbles Ronald Herbst Gary P. Sims 《PloS one》2015,10(2)
Release of endogenous damage associated molecular patterns (DAMPs), including members of the S100 family, are associated with infection, cellular stress, tissue damage and cancer. The extracellular functions of this family of calcium binding proteins, particularly S100A8, S100A9 and S100A12, are being delineated. They appear to mediate their functions via receptor for advanced glycation endproducts (RAGE) or TLR4, but there remains considerable uncertainty over the relative physiological roles of these DAMPs and their pattern recognition receptors. In this study, we surveyed the capacity of S100 proteins to induce proinflammatory cytokines and cell migration, and the contribution RAGE and TLR4 to mediate these responses in vitro. Using adenoviral delivery of murine S100A9, we also examined the potential for S100A9 homodimers to trigger lung inflammation in vivo. S100A8, S100A9 and S100A12, but not the S100A8/A9 heterodimer, induced modest levels of TLR4-mediated cytokine production from human PBMC. In contrast, for most S100s including S100A9, RAGE blockade inhibited S100-mediated cell migration of THP1 cells and major leukocyte populations, whereas TLR4-blockade had no effect. Intranasal administration of murine S100A9 adenovirus induced a specific, time-dependent predominately macrophage infiltration that coincided with elevated S100A9 levels and proinflammatory cytokines in the BAL fluid. Inflammatory cytokines were markedly ablated in the TLR4-defective mice, but unexpectedly the loss of TLR4 signaling or RAGE-deficiency did not appreciably impact the S100A9-mediated lung pathology or the inflammatory cell infiltrate in the alveolar space. These data demonstrate that physiological levels of S100A9 homodimers can trigger an inflammatory response in vivo, and despite the capacity of RAGE and TLR4 blockade to inhibit responses in vitro, the response is predominately independent of both these receptors. 相似文献
155.
Christine Thai Yen Ying Lim Victor L. Villemagne Simon M. Laws David Ames Kathryn A. Ellis Stephanie R. Rainey-Smith Ralph N. Martins Colin L. Masters Christopher C. Rowe Paul Maruff Australian Imaging Biomarkers Lifestyle Research Group 《PloS one》2015,10(10)
High levels of β-amyloid (Aβ) in the brain and carriage of the APOE ε4 allele have each been linked to cognitive impairment in cognitively normal (CN) older adults. However, the relationship between these two biomarkers and cognitive decline is unclear. The aim of this study was to investigate the relationship between cerebral Aβ level, APOE ε4 carrier status, and cognitive decline over 18 months, in 317 cognitively healthy (CN) older adults (47.6% males, 52.4% females) aged between 60 and 89 years (Mean = 69.9, SD = 6.8). Cognition was assessed using the Cogstate Brief Battery (CBB) and the California Verbal Learning Test, Second Edition (CVLT-II). Planned comparisons indicated that CN older adults with high Aβ who were also APOE ε4 carriers demonstrated the most pronounced decline in learning and working memory. In CN older adults who were APOE ε4 non-carriers, high Aβ was unrelated to cognitive decline in learning and working memory. Carriage of APOE ε4 in CN older adults with low Aβ was associated with a significantly increased rate of decline in learning and unexpectedly, improved cognitive performance on measures of verbal episodic memory over 18 months. These results suggest that Aβ and APOE ε4 interact to increase the rate of cognitive decline in CN older adults and provide further support for the use of Aβ and APOE ε4 as biomarkers of early Alzheimer’s disease. 相似文献
156.
157.
Abderrahman Khila Ehab Abouheif Locke Rowe 《Evolution; international journal of organic evolution》2014,68(8):2159-2170
Invasion of new ecological habitats is often associated with lineage diversification, yet the genetic changes underlying invasions and radiations are poorly understood. Over 200 million years ago, the semi‐aquatic insects invaded water surface from a common terrestrial ancestor and diversified to exploit a wide array of niches. Here, we uncover the changes in regulation and function of the gene Ultrabithorax associated with both the invasion of water surface and the subsequent diversification of the group. In the common ancestor of the semi‐aquatic insects, a novel deployment of Ubx protein in the mid‐legs increased their length, thereby enhancing their role in water surface walking. In derived lineages that specialize in rowing on the open water, additional changes in the timing of Ubx expression further elongated the mid‐legs thereby facilitating their function as oars. In addition, Ubx protein function was selectively reversed to shorten specific rear‐leg segments, thereby enabling their function as rudders. These changes in Ubx have generated distinct niche‐specialized morphologies that account for the remarkable diversification of the semi‐aquatic insects. Therefore, changes in the regulation and function of a key developmental gene may facilitate both the morphological change necessary to transition to novel habitats and fuel subsequent morphological diversification. 相似文献
158.
Isaline Rowe Marco Chiaravalli Klaus B. Piontek Gregory G. Germino Alessandra Boletta 《Biochemical and biophysical research communications》2014
The PKD1 gene is essential for a number of biological functions, and its loss-of-function causes autosomal dominant polycystic kidney disease (ADPKD). The gene is developmentally regulated and believed to play an essential role in renal development. Previous studies have shown that manipulating murine renal organ cultures with dominant-negative forms of the Pkd1 gene impaired ureteric bud (UB) branching. In the current study, we analyzed different stages of renal development in two distinct mouse models carrying either a null mutation or inactivation of the last two exons of Pkd1. Surprisingly, metanephric explants from Pkd1-deleted kidneys harvested at day E11.5 did not show defects of UB branching and elongation, estimated by cytokeratin staining on fixed tissues or by Hoxb7-GFP time-lapse imaging. However, renal explants from Pkd1-mutants isolated at day E14.5 showed impaired nephrogenesis. Notably, we observed cell migratory defects in the developing endothelial compartment. Previous studies had implicated the Pkd1 gene in controlling cell migration and collagen deposition through PI3 kinases. In line with these studies, our results show that wild-type explants treated with PI3-kinase inhibitors recapitulate the endothelial defects observed in Pkd1 mutants, whereas treatment with VEGF only partially rescued the defects. Our data are consistent with a role for the Pkd1 gene in the endothelium that may be required for proper nephrogenesis. 相似文献
159.
Chris D. Evans David M. Cooper Donald T. Monteith Rachel C. Helliwell Filip Moldan Jane Hall Edwin C. Rowe Bernard J. Cosby 《Biogeochemistry》2010,101(1-3):211-227
Data from long-term monitoring sites are vital for biogeochemical process understanding, and for model development. Implicitly or explicitly, information provided by both monitoring and modelling must be extrapolated in order to have wider scientific and policy utility. In many cases, large-scale modelling utilises little of the data available from long-term monitoring, instead relying on simplified models and limited, often highly uncertain, data for parameterisation. Here, we propose a new approach whereby outputs from model applications to long-term monitoring sites are upscaled to the wider landscape using a simple statistical method. For the 22 lakes and streams of the UK Acid Waters Monitoring Network (AWMN), standardised concentrations (Z scores) for Acid Neutralising Capacity (ANC), dissolved organic carbon, nitrate and sulphate show high temporal coherence among sites. This coherence permits annual mean solute concentrations at a new site to be predicted by back-transforming Z scores derived from observations or model applications at other sites. The approach requires limited observational data for the new site, such as annual mean estimates from two synoptic surveys. Several illustrative applications of the method suggest that it is effective at predicting long-term ANC change in upland surface waters, and may have wider application. Because it is possible to parameterise and constrain more sophisticated models with data from intensively monitored sites, the extrapolation of model outputs to policy relevant scales using this approach could provide a more robust, and less computationally demanding, alternative to the application of simple generalised models using extrapolated input data. 相似文献
160.
Ian G. Stiell Catherine M. Clement Jeremy M. Grimshaw Robert J. Brison Brian H. Rowe Jacques S. Lee Amit Shah Jamie Brehaut Brian R. Holroyd Michael J. Schull R. Douglas McKnight Mary A. Eisenhauer Jonathan Dreyer Eric Letovsky Tim Rutledge Iain MacPhail Scott Ross Jeffrey J. Perry Urbain Ip Howard Lesiuk Carol Bennett George A. Wells 《CMAJ》2010,182(14):1527-1532