全文获取类型
收费全文 | 816篇 |
免费 | 64篇 |
出版年
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 20篇 |
2015年 | 32篇 |
2014年 | 32篇 |
2013年 | 55篇 |
2012年 | 66篇 |
2011年 | 52篇 |
2010年 | 30篇 |
2009年 | 28篇 |
2008年 | 38篇 |
2007年 | 42篇 |
2006年 | 41篇 |
2005年 | 40篇 |
2004年 | 36篇 |
2003年 | 42篇 |
2002年 | 35篇 |
2001年 | 19篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 4篇 |
排序方式: 共有880条查询结果,搜索用时 15 毫秒
91.
Roselani I. Henry Simon A. Cobbold Richard J. W. Allen Asif Khan Rhys Hayward Adele M. Lehane Patrick G. Bray Susan M. Howitt Giancarlo A. Biagini Kevin J. Saliba Kiaran Kirk 《The Journal of biological chemistry》2010,285(24):18615-18626
The intraerythrocytic malaria parasite exerts tight control over its ionic composition. In this study, a combination of fluorescent ion indicators and 36Cl− flux measurements was used to investigate the transport of Cl− and the Cl−-dependent transport of “H+-equivalents” in mature (trophozoite stage) parasites, isolated from their host erythrocytes. Removal of extracellular Cl−, resulting in an outward [Cl−] gradient, gave rise to a cytosolic alkalinization (i.e. a net efflux of H+-equivalents). This was reversed on restoration of extracellular Cl−. The flux of H+-equivalents was inhibited by 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid and, when measured in ATP-depleted parasites, showed a pronounced dependence on the pH of the parasite cytosol; the flux was low at cytosolic pH values < 7.2 but increased steeply with cytosolic pH at values > 7.2. 36Cl− influx measurements revealed the presence of a Cl− uptake mechanism with characteristics similar to those of the Cl−-dependent H+-equivalent flux. The intracellular concentration of Cl− in the parasite was estimated to be ∼48 mm in situ. The data are consistent with the intraerythrocytic parasite having in its plasma membrane a 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid-sensitive transporter that, under physiological conditions, imports Cl− together with H+-equivalents, resulting in an intracellular Cl− concentration well above that which would occur if Cl− ions were distributed passively in accordance with the parasite''s large, inwardly negative membrane potential. 相似文献
92.
Silverman JM Clos J Horakova E Wang AY Wiesgigl M Kelly I Lynn MA McMaster WR Foster LJ Levings MK Reiner NE 《Journal of immunology (Baltimore, Md. : 1950)》2010,185(9):5011-5022
We investigated the properties of leishmania exosomes with respect to influencing innate and adaptive immune responses. Exosomes from Leishmania donovani modulated human monocyte cytokine responses to IFN-γ in a bimodal fashion by promoting IL-10 production and inhibiting that of TNF-α. Moreover, these vesicles were inhibitory with respect to cytokine responses (IL-12p70, TNF-α, and IL-10) by human monocyte-derived dendritic cells. Exosomes from wild-type (WT) L. donovani failed to prime monocyte-derived dendritic cells to drive the differentiation of naive CD4 T cells into IFN-γ-producing Th1 cells. In contrast, vesicles from heat shock protein (HSP)100(-/-) L. donovani showed a gain-of-function and proinflammatory phenotype and promoted the differentiation of naive CD4 lymphocytes into Th1 cells. Proteomic analysis showed that exosomes from WT and HSP100(-/-) leishmania had distinct protein cargo, suggesting that packaging of proteins into exosomes is dependent in part on HSP100. Treatment of C57BL/6 mice with WT L. donovani exosomes prior to challenge with WT organisms exacerbated infection and promoted IL-10 production in the spleen. In contrast, HSP100(-/-) exosomes promoted spleen cell production of IFN-γ and did not adversely affect hepatic parasite burdens. Furthermore, the proparasitic properties of WT exosomes were not species specific because BALB/c mice exposed to Leishmania major exosomes showed increased Th2 polarization and exacerbation of disease in response to infection with L. major. These findings demonstrate that leishmania exosomes are predominantly immunosuppressive. Moreover, to our knowledge, this is the first evidence to suggest that changes in the protein cargo of exosomes may influence the impact of these vesicles on myeloid cell function. 相似文献
93.
Eric J. Hochberg Amy M. Apprill Marlin J. Atkinson Robert R. Bidigare 《Coral reefs (Online)》2006,25(1):99-109
The spectral reflectance of coral is inherently related to the amounts of photosynthetic pigments present in the zooxanthellae. There are no studies, however, showing that the suite of major photosynthetic pigments can be predicted from optical reflectance spectra. In this study, we measured cm-scale in vivo and in situ spectral reflectance for several colonies of the massive corals Porites lobata and Porites lutea, two colonies of the branching coral Porites compressa, and one colony of the encrusting coral Montipora flabellata in Kaneohe Bay, Oahu, Hawaii. For each reflectance spectrum, we collected a tissue sample and utilized high-performance liquid chromatography to quantify six major photosynthetic pigments, located in the zooxanthellae. We used multivariate multiple regression analysis with cross-validation to build and test an empirical linear model for predicting pigment concentrations from optical reflectance spectra. The model accurately predicted concentrations of chlorophyll a, chlorophyll c
2, peridinin, diadinoxanthin, diatoxanthin and β-carotene, with correlation coefficients of 0.997, 0.941, 0.995, 0.996, 0.980 and 0.984, respectively. The relationship between predicted and actual concentrations was 1:1 for each pigment, except chlorophyll c
2. This simple empirical model demonstrates the potential for routine, rapid, non-invasive monitoring of coral-zooxanthellae status, and ultimately for remote sensing of reef biogeochemical processes. 相似文献
94.
Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types 总被引:1,自引:0,他引:1
The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species. 相似文献
95.
Intracrine modulation of gene expression by intracellular generation of active glucocorticoids 总被引:1,自引:0,他引:1
Fruchter O Zoumakis E Alesci S De Martino M Chrousos G Hochberg Z 《Steroids》2006,71(11-12):1001-1006
96.
The serotonergic nervous systems of two non-colonial species of Conochilus were examined to obtain the first immunohistochemical insights into the neuroanatomy of species of Flosculariacea (Rotifera, Monogononta). Species of Conochilus, subgenus Conochiloides, were examined using serotonin (5-HT) immunohistochemistry, epifluorescence and confocal laser scanning microscopy, and 3D computer imaging software. In specimens of C. coenobasis and C. dossuarius, the serotonergic nervous system is defined by a dorsal cerebral ganglion, apically directed cerebral neurites, and paired nerve cords. The cerebral ganglion contains approximately four pairs of small 5-HT-immunoreactive perikarya; one pair innervates the posterior nerve cords and three pairs innervate the apical field. The most dorsal pair innervates a coronal nerve ring that encircles the apical field. Within the apical field is a second nerve ring that outlines the inner border of the coronal cilia. Together, both the inner and outer nerve rings may function to modulate ciliary activity of the corona. The other two pairs of perikarya innervate a region around the mouth. Specific differences in the distribution of serotonergic neurons between species of Conochilus and previously examined ploimate rotifers include the following: (a) a lack of immunoreactivity in the mastax; (b) a greater number of apically directed serotonergic neurites; and (c) a complete innervation of the corona in both species of Conochilus. These differences in nervous system immunohistochemistry are discussed in reference to the phylogeny of the Monogononta. 相似文献
97.
In terrestrial snakes, rugose scales are uncommon and (if they occur) generally are found on both sexes. In contrast, rugose scales are seen in most sea snakes, especially in males. Why has marine life favored this sex-specific elaboration of scale rugosity? We pose and test alternative hypotheses about the function of rugose scales in males of the turtle-headed sea snake (Emydocephalus annulatus) and conclude that multiple selective forces have been involved. First, rugosities may aid male positioning during courtship, because histology shows that tubercles are more highly innervated than adjacent flat areas of each scale and hence are presumably more sensitive to tactile cues, and because biomechanical tests show that rugosities enhance friction between the bodies of males and females. Second, the occurrence of rugosities over the entire body of males and (albeit less well developed) in females as well suggests that rugosities also play a hydrodynamic role by modifying water flow across the snake's surface. Flow tank tests show that rugosities reduce the thickness of the boundary layer by almost 50% and create turbulent flow that should massively enhance rates of cutaneous oxygen uptake and hence prolong maximal courtship duration by males. 相似文献
98.
Davidson RK Waters JG Kevorkian L Darrah C Cooper A Donell ST Clark IM 《Arthritis research & therapy》2006,8(4):R124-10
Cartilage destruction in osteoarthritis (OA) is thought to be mediated by two main enzyme families; the matrix metalloproteinases
(MMPs) are responsible for cartilage collagen breakdown, whereas enzymes from the 'a disintegrin and metalloproteinase domain
with thrombospondin motifs' (ADAMTS) family mediate cartilage aggrecan loss. Tissue inhibitors of metalloproteinases (TIMPs)
regulate the activity of these enzymes. Although cartilage destruction in OA might be driven by the chondrocyte, low-grade
synovitis is reported in patients with all grades of this disease. 相似文献
99.
100.