全文获取类型
收费全文 | 2386篇 |
免费 | 164篇 |
国内免费 | 1篇 |
专业分类
2551篇 |
出版年
2023年 | 6篇 |
2022年 | 38篇 |
2021年 | 64篇 |
2020年 | 31篇 |
2019年 | 40篇 |
2018年 | 52篇 |
2017年 | 39篇 |
2016年 | 61篇 |
2015年 | 113篇 |
2014年 | 113篇 |
2013年 | 147篇 |
2012年 | 184篇 |
2011年 | 190篇 |
2010年 | 136篇 |
2009年 | 113篇 |
2008年 | 172篇 |
2007年 | 149篇 |
2006年 | 148篇 |
2005年 | 151篇 |
2004年 | 110篇 |
2003年 | 118篇 |
2002年 | 102篇 |
2001年 | 23篇 |
2000年 | 22篇 |
1999年 | 25篇 |
1998年 | 32篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 10篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1967年 | 2篇 |
1901年 | 2篇 |
1887年 | 1篇 |
1879年 | 1篇 |
排序方式: 共有2551条查询结果,搜索用时 0 毫秒
941.
Lovegrove FE Gharib SA Peña-Castillo L Patel SN Ruzinski JT Hughes TR Liles WC Kain KC 《PLoS pathogens》2008,4(5):e1000068
Although acute lung injury (ALI) is a common complication of severe malaria, little is known about the underlying molecular basis of lung dysfunction. Animal models have provided powerful insights into the pathogenesis of severe malaria syndromes such as cerebral malaria (CM); however, no model of malaria-induced lung injury has been definitively established. This study used bronchoalveolar lavage (BAL), histopathology and gene expression analysis to examine the development of ALI in mice infected with Plasmodium berghei ANKA (PbA). BAL fluid of PbA-infected C57BL/6 mice revealed a significant increase in IgM and total protein prior to the development of CM, indicating disruption of the alveolar-capillary membrane barrier-the physiological hallmark of ALI. In contrast to sepsis-induced ALI, BAL fluid cell counts remained constant with no infiltration of neutrophils. Histopathology showed septal inflammation without cellular transmigration into the alveolar spaces. Microarray analysis of lung tissue from PbA-infected mice identified a significant up-regulation of expressed genes associated with the gene ontology categories of defense and immune response. Severity of malaria-induced ALI varied in a panel of inbred mouse strains, and development of ALI correlated with peripheral parasite burden but not CM susceptibility. Cd36(-/-) mice, which have decreased parasite lung sequestration, were relatively protected from ALI. In summary, parasite burden and CD36-mediated sequestration in the lung are primary determinants of ALI in experimental murine malaria. Furthermore, differential susceptibility of mouse strains to malaria-induced ALI and CM suggests that distinct genetic determinants may regulate susceptibility to these two important causes of malaria-associated morbidity and mortality. 相似文献
942.
943.
944.
Tackaberry ES Prior FA Rowlandson K Tocchi M Mehic J Porter S Walsh M Schleiss MR Ganz PR Sardana RK Altosaar I Dudani AK 《Molecular biotechnology》2008,40(1):1-12
Production of recombinant subunit vaccines in transgenic plants may be a means of reducing vaccine costs while increasing availability and safety. A plant-derived product found safe and effective for oral administration would provide additional advantages when used as a vaccine. Outstanding issues with the technology include transgene stability through successive generations and consistent bioproduction. We previously reported expression of glycoprotein B (gB) of human cytomegalovirus in seeds of transgenic tobacco. Here the goal was to determine if gB could be similarly expressed in rice, and if so, to examine expression over several plant generations. Results show that immunoreactive gB was successfully expressed in transgenic rice seeds, with sustained expression over three generations. The gB contained several neutralizing epitopes and was stable over 27 months. 相似文献
945.
Electrical excitability in cells such as neurons and myocytes depends not only upon the expression of voltage-gated sodium channels but also on their correct targeting within the plasma membrane. Placing sodium channels within a broader cell biological context is beginning to shed new light on a variety of important questions such as the integration of neuronal signaling. Mutations that affect sodium channel trafficking have been shown to underlie several life-threatening conditions including cardiac arrhythmias, revealing an important clinical context to these studies. 相似文献
946.
947.
Most studies on litter decomposition have assumed that all falling plant litter reaches the ground where it then decomposes. In many forests a proportion of this litter may in fact be intercepted by understorey vegetation, but the ecological significance of this remains poorly understood. We performed two experiments in a temperate rainforest in southern New Zealand, in which there was a dense understorey of the crown fern Blechnum discolor. The fronds of this fern originate from a crown, and have a funnel‐like arrangement that can trap falling litter and prevent it from reaching the ground. The first experiment measured the effects of ferns on the spatial distribution of litter accumulation over one year. The ferns intercepted a substantial proportion of the total litterfall, and the fern crowns (from which the fronds originate) retained 10% of the total incoming litterfall (despite occupying only 2% of the ground area). The retained litter had a substantially higher ratio of twig to foliar litter than did the incoming litterfall. Further, much of the litter not retained on the crowns of the ferns accumulated at the base of the fern trunks. The second experiment considered litter decomposition in fern crowns versus the ground under the ferns. The litter that had accumulated in the crowns was characterized by higher microbial basal respiration and active microbial biomass than was the litter that had accumulated on the ground. The use of litterbags revealed that litter decomposition rates were significantly higher on the fern crowns than on the ground at 30 cm and 60 cm from the fern trunks. These results show that litter interception ameliorates the decomposer environment and increases the rate of litter decomposition. In total, this study provides evidence for understorey ferns greatly influencing both the spatial distribution of litterfall and the decomposition of plant litter. Although the ecological role of understorey vegetation in forested ecosystems has received little attention to date, our results point to understorey species as an important driver of forest ecosystem processes. 相似文献
948.
Blake S Deem SL Strindberg S Maisels F Momont L Isia IB Douglas-Hamilton I Karesh WB Kock MD 《PloS one》2008,3(10):e3546
A dramatic expansion of road building is underway in the Congo Basin fuelled by private enterprise, international aid, and government aspirations. Among the great wilderness areas on earth, the Congo Basin is outstanding for its high biodiversity, particularly mobile megafauna including forest elephants (Loxodonta africana cyclotis). The abundance of many mammal species in the Basin increases with distance from roads due to hunting pressure, but the impacts of road proliferation on the movements of individuals are unknown. We investigated the ranging behaviour of forest elephants in relation to roads and roadless wilderness by fitting GPS telemetry collars onto a sample of 28 forest elephants living in six priority conservation areas. We show that the size of roadless wilderness is a strong determinant of home range size in this species. Though our study sites included the largest wilderness areas in central African forests, none of 4 home range metrics we calculated, including core area, tended toward an asymptote with increasing wilderness size, suggesting that uninhibited ranging in forest elephants no longer exists. Furthermore we show that roads outside protected areas which are not protected from hunting are a formidable barrier to movement while roads inside protected areas are not. Only 1 elephant from our sample crossed an unprotected road. During crossings her mean speed increased 14-fold compared to normal movements. Forest elephants are increasingly confined and constrained by roads across the Congo Basin which is reducing effective habitat availability and isolating populations, significantly threatening long term conservation efforts. If the current road development trajectory continues, forest wildernesses and the forest elephants they contain will collapse. 相似文献
949.
Dendritic cells (DC) are a heterogeneous cell population that bridge the innate and adaptive immune systems. CD8alpha DC play a prominent, and sometimes exclusive, role in driving amplification of CD8(+) T cells during a viral infection. Whether this reliance on a single subset of DC also applies for CD4(+) T cell activation is unknown. We used a direct ex vivo antigen presentation assay to probe the capacity of flow cytometrically purified DC populations to drive amplification of CD4(+) and CD8(+) T cells following infection with influenza virus by different routes. This study examined the contributions of non-CD8alpha DC populations in the amplification of CD8(+) and CD4(+) T cells in cutaneous and systemic influenza viral infections. We confirmed that in vivo, effective immune responses for CD8(+) T cells are dominated by presentation of antigen by CD8alpha DC but can involve non-CD8alpha DC. In contrast, CD4(+) T cell responses relied more heavily on the contributions of dermal DC migrating from peripheral lymphoid tissues following cutaneous infection, and CD4 DC in the spleen after systemic infection. CD4(+) T cell priming by DC subsets that is dependent upon the route of administration raises the possibility that vaccination approaches could be tailored to prime helper T cell immunity. 相似文献
950.
Fiona M. Brandie Veronica Aran Avani Verma James A. McNew Nia J. Bryant Gwyn W. Gould 《PloS one》2008,3(12)