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Plant species coexistence in cliff habitats 总被引:1,自引:0,他引:1
Alan Cooper 《Journal of Biogeography》1997,24(4):483-494
An ecological analysis of the ledge and crevice vegetation of cliffs in north-east Ireland was carried out using a sampling programme based on multivariate land classification. The composition of the vegetation was shown to be determined primarily by distance from the sea, elevation and rock type. The chemical composition and physical structure of the cliffs, together with environmental gradients associated with aspect, elevation and nearness to the sea provide a wide range of habitats in which plants coexist. Certain types of cliff vegetation contained associations of species with a contrasting ecology, such as arctic–montane, maritime, woodland, calcicole and calcifuge plants. The positions of these species in ordination space were found to be unique but overlapping. A model is described to account for these observations. It proposes that species dominance in cliff habitats is prevented by factors such as physical disturbance and that plants are able to coexist in cliff habitats which meet their common environmental tolerances and preferences. The model predicts that cliff habitats with the greatest diversity of species are likely to be subject to less extremes of environmental variability. These habitats include inland sites with nutrient enrichment by sea spray, north-facing sites, seepage sites, base-rich sites, low elevation sites and sites with a heterogeneous physical structure. 相似文献
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強皮肤促癌物十四烷酰佛波醋酸酯(TPA)局部应用时可触发一系列的生物化学改变,其中最明显的事件之一就是对ODC活性的短暂而急到的诱导,而这种诱导作用与其促癌作用密切相关。利用Northern印迹分析和条带(Slot)印迹分析证明,10nmol/L TPA一次局部处理小鼠背部皮肤可刺激ODC mRNA(2.0kb大小)表达,在4h左右最为明显,随后逐渐降低。10nmol/L TPA多次处理小鼠皮肤(每2天一次,共4次)也有类似的促进作用,但却在6h左右最为明显。在二甲基苯蒽和巴豆油诱发的二阶段小鼠皮肤乳头瘤和癌组织中也观察到了相同大小的ODC mRNA的高水平表达,尤以癌组织最高。新维甲类化合物R8605虽能明显抑制巴豆油诱导的ODC活性,但却未见对TPA诱导的ODC mRNA增加有明显抑制作用。 相似文献
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转化生长因子β是一种细胞多功能调节肽,目前研究认为其和促癌过程有密切关系。本文利用Northern印迹分析技术研究了TGF-β mRNA在促癌物佛波酯刺激的小鼠表皮和化学性诱发的小鼠二阶段皮肤肿瘤中的表达情况。结果证明,巴豆油2—20 μL和TPA 5—40nmol一次局部涂用于小鼠皮肤,均可明显增加小鼠表皮TGF-β mRNA,呈较好的浓度依赖性。TGF-β mRNA表达在二甲基苯蒽(DMBA)和巴豆油诱发的二阶段小鼠皮肤乳头瘤和癌中均高于正常和瘤旁表皮。所检测到的TGF-βmRNA为2.5kb和1.9kb二种条带,但以2.5kb为主。 相似文献
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Abstract. We studied distribution patterns of vascular plant species and environmental variables for three years along a permanent transect traversing a closed-drainage watershed in the northern Chihuahuan Desert of south-central New Mexico, USA. The transect extended for 2.7 km from a basin floor playa (1310 m elevation, fine-textured soil), across a piedmont slope, and onto the base of a granitic mountain (1410 m elevation, coarse-textured soil). The gradients in elevation and soils across our transect, along with variable seasonal rainfall, downslope redistribution of water and organic matter, and soil texture-related variation in infiltration, water holding capacity, and moisture release characteristics, interact to generate a complex spatial and temporal gradient of available soil water and nitrogen. We grouped plant species into guilds according to growth form and photo synthetic pathway type. These guilds are spatially and temporally differentiated along the transect such that particular groups utilize particular seasonal phases or spatial regions of the gradient. We identified six distinct plant communities along the transect. C4 perennial grasses dominated the mesic/high nitrogen portion of the gradient, which occurred at the highest (upper piedmont grassland, dominated by Bouteloua eriopoda) and lowest (playa, dominated by Panicum obtusum) elevations along the transect. C3 shrubs were dominant in the xeric/low nitrogen portion of the gradient located near the middle of the transect (bajada shrubland, dominated by Larrea tridentata). C3 shrubs also dominated a narrow zone of vegetation located adjacent to the playa (playa fringe, dominated by Prosopisglandulosa). C4 perennial grasses, C3 subshrubs, and C3 and C4 perennial forbs and annuals were co-dominant in the intermediate locations along the gradient, which occurred below (mixed basin slopes) and above (lower piedmont grassland) the bajada shrubland. Life-form distribution patterns at the small scale of our study reflect some of the patterning that occurs at larger scales in response to climate gradients. The distributions of some species and guilds along the transect are apparently modified by competitive interactions. 相似文献
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模拟失重大鼠心肌与血管组织的热应激诱导HSP70表达 总被引:1,自引:0,他引:1
为研究模拟失重是否可以引起大鼠心肌与血管组织HSP70的诱导表达发生改变,用尾部悬吊大鼠模型模拟失重,以研究失重对生理的影响,用Northern杂交与Western印迹分析检测4周模拟失重大鼠热应激后并在室温下恢复1h(SUS-H1)或2h(SUS-H2_心肌,血管组织HSP70表达的变化,结果表明,热应激后,各组大鼠心肌组织的HSP72 mRNA表达的均显著增加,但SUS-H2大鼠心肌组织的表达显著低于CON-H2组;各组大鼠心肌组织HSP72表达也均显著增加,但SUS-H1与SUS-H2大鼠的表达与相应对照组相比,则仅呈降低趋势,其底动脉血管组织的HSP72 mRNA与HSP72诱导表达均显著增高,而在股动脉则两者仅呈降低趋势,上述结果提示,模拟失重可导致大鼠心肌发生类似衰老的心肌改变;身体前,后部血管组织HSP70的诱导表达变化可能与血管的分化性适应方向一致。 相似文献