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21.
Membrane phospholipid phase separations in plants adapted to or acclimated to different thermal regimes 总被引:8,自引:4,他引:4 下载免费PDF全文
The phase separation temperatures of total leaf phospholipids from warm and cool climate plants were determined in order to explore the relationship of lipid physical properties to a species' thermal habitat. The separation temperatures were determined by measuring the fluorescence intensity and fluorescence polarization of liposomes labeled with the polyene fatty acid probe trans-parinaric acid. To focus on a single climatic region, Mojave Desert dicots (chiefly ephemeral annuals) were examined, with plants grown under identical conditions whenever possible. Winter active species showed lower phase separation temperatures than the summer active species. A group of warm climate annual grasses showed separation temperatures distinctly higher than those of a group of cool climate grasses, all grown from seed under the same conditions. Growth at low temperature seems correlated with (and may require) a low phase separation temperature. Winter active ephemerals appear genetically programmed to synthesize a mixture of phospholipids which will not phase separate in the usual growth conditions. When the lipids of desert perennials were examined in cool and warm seasons, there was a pronounced seasonal shift in the phase separation temperature, implying environmental influences on lipid physical properties. The relationship of these results to high and low temperature tolerance is discussed. 相似文献
22.
L E Limbird A DeLean A R Hickey L J Pike R J Lefkowitz 《Biochimica et biophysica acta》1979,586(2):298-314
A detailed comparison of the interaction of beta-adrenergic receptors with adenylate cyclase stimulation and modification of this interaction by guanine nucleotides has been made in two model systems, the frog and turkey erythrocyte. Objective analysis of the data was facilitated by the development of new graphical methods which involve the use of logit-logit transformations of percent receptor occupancy versus percent enzyme stimulation plots (coupling curves). Receptor-cyclase coupling in turkey erythrocyte membranes demonstrates a proportional relationship between receptor occupancy and adenylate cyclase activation and is unaffected by exogenous guanine nucleotides. By comparison, the proportional relationship of receptor occupancy and adenylate cyclase activation observed in frog erythrocyte membranes in the absence of guanine nucleotides is modified by the addition of exogenous guanine nucleotides such that a greater fractional enzyme stimulation is elicited by low receptor occupancy. Methodological criteria crucial for valid comparison of receptor occupancy and adenylate cyclase activity are delineated. In addition, the possible molecular mechanisms of receptor-cyclase coupling which might give rise to the coupling curves observed are discussed. 相似文献
23.
For endangered species that persist as apparently isolated populations within a previously more extensive range, the degree of genetic exchange between those populations is critical to conservation and management. A lack of gene flow can exacerbate impacts of threatening processes and delay or prevent colonization of sites after local extirpation. The broad-headed snake, Hoplocephalus bungaroides, is a small venomous species restricted to a handful of disjunct reserves near Sydney, Australia. Mark-recapture studies have indicated low vagility for this ambush predator, suggesting that gene flow also may be low. However, our analyses of 11 microsatellite loci from 163 snakes collected in Morton National Park, from six sites within a 10-km diameter, suggest relatively high rates of gene flow among sites. Most populations exchange genes with each other, with one large population serving as a source area and smaller populations apparently acting as sinks. About half of the juvenile snakes, for which we could reliably infer parentage, were collected from populations other than those in which we collected their putative parents. As expected from the snakes' reliance on rocky outcrops during cooler months of the year, most gene flow appears to be along sandstone plateaux rather than across the densely forested valleys that separate plateaux. The unexpectedly high rates of gene flow on a landscape scale are encouraging for future conservation of this endangered taxon. For example, wildlife managers could conserve broad-headed snakes by restoring habitats near extant source populations in areas predicted to be least affected by future climate change. 相似文献
24.
Effects of antigens and lymphokines on early activation of single hapten-specific B lymphocytes 总被引:1,自引:0,他引:1
M R Alderson B L Pike G J Nossal 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(4):1056-1063
An assay was developed to monitor early activation of single fluorescein-specific B cells obtained from the spleens of nonimmunized adult mice by prefractionation on hapten gelatin. Early activation was assessed as a significant increase in the diameter of individual B cells after 24 hr in vitro. Significant enlargement of the single B cells was induced within 24 hr by either T-independent antigens acting alone or a crude source of B cell growth and differentiation factors (EL-BGDF-pik) acting alone. In contrast, T-dependent antigens acting alone were ineffective. When selected T-independent antigens and EL-BGDF-pik acted together, a greater number of B cells were induced to enlarge. B cell stimulatory factor 1 (BSF 1) behaved in a similar manner as EL-BGDF-pik, inducing early B cell enlargement both in the absence and more so in the presence of antigen. Both EL-BGDF-pik and BSF 1 enhanced the survival of single hapten-specific B cells during the 24-hr period. Interleukin 1 was unable to cause B cell enlargement when acting alone, although it was able to augment B cell enlargement induced by antigen. Interleukin 2 did not induce cell enlargement in either the presence or absence of antigen. Activation was demonstrated among cells of all sizes, regardless of the stimulus, although a greater response was demonstrated amongst the larger cell population. The addition of 3T3 filler cells enhanced early B cell activation and cell survival during the 24-hr period. The 24-hr B cell enlargement assay as applied to isolated single cells provides an unequivocal approach to the analysis of early B cell activation, adding a further parameter for the dissection of the precise roles of antigen and the various factors in the B cell differentiation pathway. 相似文献
25.
David A. Pike 《Global Change Biology》2013,19(10):3082-3092
Some species are adapting to changing environments by expanding their geographic ranges. Understanding whether range shifts will be accompanied by increased exposure to other threats is crucial to predicting when and where new populations could successfully establish. If species overlap to a greater extent with human development under climate change, this could form ecological traps which are attractive to dispersing individuals, but the use of which substantially reduces fitness. Until recently, the core nesting range for the Critically Endangered Kemp's ridley sea turtle (Lepidochelys kempii) was ca. 1000 km of sparsely populated coastline in Tamaulipas, Mexico. Over the past twenty‐five years, this species has expanded its range into populated areas of coastal Florida (>1500 km outside the historical range), where nesting now occurs annually. Suitable Kemp's ridley nesting habitat has persisted for at least 140 000 years in the western Gulf of Mexico, and climate change models predict further nesting range expansion into the eastern Gulf of Mexico and northern Atlantic Ocean. Range expansion is 6–12% more likely to occur along uninhabited stretches of coastline than are current nesting beaches, suggesting that novel nesting areas will not be associated with high levels of anthropogenic disturbance. Although the high breeding‐site fidelity of some migratory species could limit adaptation to climate change, rapid population recovery following effective conservation measures may enhance opportunities for range expansion. Anticipating the interactive effects of past or contemporary conservation measures, climate change, and future human activities will help focus long‐term conservation strategies. 相似文献
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Kurt G. Pike Karine Malagu Marc G. Hummersone Keith A. Menear Heather M.E. Duggan Sylvie Gomez Niall M.B. Martin Linette Ruston Sarah L. Pass Martin Pass 《Bioorganic & medicinal chemistry letters》2013,23(5):1212-1216
The optimization of a potent and highly selective series of dual mTORC1 and mTORC2 inhibitors is described. An initial focus on improving cellular potency whilst maintaining or improving other key parameters, such as aqueous solubility and margins over hERG IC50, led to the discovery of the clinical candidate AZD8055 (14). Further optimization, particularly aimed at reducing the rate of metabolism in human hepatocyte incubations, resulted in the discovery of the clinical candidate AZD2014 (21). 相似文献
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G. Michael Taylor Katie Tucker Rachel Butler Alistair W. G. Pike Jamie Lewis Simon Roffey Philip Marter Oona Y-C Lee Houdini H. T. Wu David E. Minnikin Gurdyal S. Besra Pushpendra Singh Stewart T. Cole Graham R. Stewart 《PloS one》2013,8(4)
Nine burials excavated from the Magdalen Hill Archaeological Research Project (MHARP) in Winchester, UK, showing skeletal signs of lepromatous leprosy (LL) have been studied using a multidisciplinary approach including osteological, geochemical and biomolecular techniques. DNA from Mycobacterium leprae was amplified from all nine skeletons but not from control skeletons devoid of indicative pathology. In several specimens we corroborated the identification of M. leprae with detection of mycolic acids specific to the cell wall of M. leprae and persistent in the skeletal samples. In five cases, the preservation of the material allowed detailed genotyping using single-nucleotide polymorphism (SNP) and multiple locus variable number tandem repeat analysis (MLVA). Three of the five cases proved to be infected with SNP type 3I-1, ancestral to contemporary M. leprae isolates found in southern states of America and likely carried by European migrants. From the remaining two burials we identified, for the first time in the British Isles, the occurrence of SNP type 2F. Stable isotope analysis conducted on tooth enamel taken from two of the type 3I-1 and one of the type 2F remains revealed that all three individuals had probably spent their formative years in the Winchester area. Previously, type 2F has been implicated as the precursor strain that migrated from the Middle East to India and South-East Asia, subsequently evolving to type 1 strains. Thus we show that type 2F had also spread westwards to Britain by the early medieval period. 相似文献
30.