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61.
The heavy (H) and light (L) chains of antibodies consist of variable (V) and constant (C) regions. The V regions of the heavy and light chains form the antibody combining site. To determine whether a V region could be functional when joined to a polypeptide other than its own C region, we constructed a chimaeric gene encoding the V region of a mouse heavy chain and the C region of a mouse kappa light chain ( VHC kappa). The heavy-chain gene is derived from an A/J mouse hybridoma cell line 36-65 whose antibody product (gamma 1, kappa) is specific for the hapten azophenylarsonate. We report here that, when introduced into a mouse myeloma cell line, the chimaeric gene is expressed and a protein of the expected molecular weight is secreted into the medium. As light chains tend to dimerize we expected that the VHC kappa protein might associate with light chain from the cell line 36-65 to form an antibody-binding molecule. Affinity binding experiments and Ka determination indicate that this is the case. Dimers of this type offer a novel and interesting alternative to existing antibody-binding molecules. 相似文献
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63.
Swarming of Proteus--a solution to an old problem? 总被引:3,自引:0,他引:3
64.
Résumé Comparée à celle des cellules en sérum, la réponse oxydative des cellules de moelle osseuse de rat dans une solution de tyrode est réduite. L'addition de disodium éthylénédiaminététracétatedihydrate (Na2EDTA) à la solution de tyrode abaissa davantage la consommation d'O2 des cellules de moelle osseuse. Cette réduction atteignit un niveau plus bas (p<0,05) à 15 min d'incubation et fut bien marquée (p<0,01) à 20, 25 et 30 min d'incubation. 相似文献
65.
66.
D. M. Windsor D. W. Morrison M. A. Estribi B. de Leon 《Cellular and molecular life sciences : CMLS》1989,45(7):647-653
Summary Fruit and leaf initiation by 26 trees representing five stranglerFicus species in the subgenusUrostigma were monitored for 5–8 years in a seasonal lowland forest of central Panamá. Individual trees of each species initiated fruit in synchronized crops. High variation in the number of crops, intervals between crops and dates of crop initiation indicate that these species, like species in the subgenusPharmacosycea, initiate fruit crops the year around. Nevertheless, mean crop initiation dates for four of five species fell within the four-month dry season. Similarly, all species produced new leaf flushes throughout the year, however, mean leaf flush dates of all species fell within the first three months of the dry season. 相似文献
67.
Increasing p16INK4a expression decreases forebrain progenitors and neurogenesis during ageing 总被引:2,自引:0,他引:2
Molofsky AV Slutsky SG Joseph NM He S Pardal R Krishnamurthy J Sharpless NE Morrison SJ 《Nature》2006,443(7110):448-452
Mammalian ageing is associated with reduced regenerative capacity in tissues that contain stem cells. It has been proposed that this is at least partially caused by the senescence of progenitors with age; however, it has not yet been tested whether genes associated with senescence functionally contribute to physiological declines in progenitor activity. Here we show that progenitor proliferation in the subventricular zone and neurogenesis in the olfactory bulb, as well as multipotent progenitor frequency and self-renewal potential, all decline with age in the mouse forebrain. These declines in progenitor frequency and function correlate with increased expression of p16INK4a, which encodes a cyclin-dependent kinase inhibitor linked to senescence. Ageing p16INK4a-deficient mice showed a significantly smaller decline in subventricular zone proliferation, olfactory bulb neurogenesis, and the frequency and self-renewal potential of multipotent progenitors. p16INK4a deficiency did not detectably affect progenitor function in the dentate gyrus or enteric nervous system, indicating regional differences in the response of neural progenitors to increased p16INK4a expression during ageing. Declining subventricular zone progenitor function and olfactory bulb neurogenesis during ageing are thus caused partly by increasing p16INK4a expression. 相似文献
68.
Morrison EE 《Cellular and molecular life sciences : CMLS》2007,64(3):307-317
Microtubule dynamic instability is fundamentally important to the way cells respond to their environment and segregate their genetic material. A disparate class of proteins defined by their localisation to growing microtubule plus ends ('+TIPS') play a key role in controlling microtubule dynamics and organisation. They directly impact upon the behaviour of the microtubule tip and link this structure to interfaces that include kinetochores and the cortex of the cell. Surprisingly, some +TIPs also have important functions at the microtubule minus end. These properties contribute to the important roles played by +TIPs in processes such as mitosis and cell migration. This review examines how recent advances have impacted our understanding of +TIP function in mammalian cells, with emphasis on the emergence of the EB1 family as a core component of +TIP activities. An overview of the use of +TIP imaging as a tool for the cell biologist is also presented. 相似文献
69.
Shannon L. Farrell Michael L. Morrison R. Neal Wilkins R. Douglas Slack Andrew J. Campomizzi 《西北部美国博物学家》2011,70(4)
Loss of reproductive productivity in hosts of the Brown-headed Cowbird ( Molothrus ater ), a nest parasite, may limit the success of conservation and recovery efforts that focus on restoring avian habitat. We investigated the relationships between parasitism frequency of 2 vireos—the endangered Black-capped Vireo ( Vireo atricapillus ) and the White-eyed Vireo ( Vireo griseus )—and characteristics of the neighboring avian assemblage. Our objective was to identify assemblage characteristics that are useful for predicting parasitism frequency. We hypothesized that parasitism frequency of the vireos would decrease with increasing alternate host abundance and increase with increasing abundance of cowbirds. All Black-capped Vireo nests ( n = 20) and 81% of White-eyed Vireo nests ( n = 27) were parasitized. Parasitism frequency of White-eyed Vireos was positively correlated with the number of cowbirds detected ( r = 0.84, df = 4, P = 0.018). Parasitism frequency of White-eyed Vireos was negatively correlated with abundance of the Black-and white Warbler ( Mniotilta varia; r = 0.891, df = 4, P = 0.009) but was not correlated with abundance of other cowbird hosts. The relationship between Black-and-white Warbler abundance and parasitism frequency may be due to chance, given the small sample size and narrow range of parasitism frequencies, but the relationship may also reflect an interaction (requiring further investigation) between parasitism and the vegetation characteristics associated with Black-and white Warblers. Our results imply that reducing cowbird abundance will reduce parasitism frequency of Black-capped Vireos. When the number of cowbirds in an area predicts parasitism, land managers would benefit from identifying a target cowbird abundance based on the levels of parasitism the host population can tolerate while still meeting productivity and population objectives for the species. La disminución de productividad debido al parasitismo por el tordo negro ( Molothrus ater ) podría limitar el éxito de los esfuerzos de conservación y recuperación de las aves que se centran en la restauración del hábitat. Investigamos la relación entre la frecuencia de parasitismo en el vireo gorrinegro ( Vireo atricapilla ), que está en peligro de extinción, y en otra especie de vireo, el vireo ojiblanco ( Vireo griseus ), así como su relación con las características de la población circunvecina de aves para identificar las características que sirven para predecir la frecuencia del parasitismo. Planteamos la hipótesis de que la frecuencia de parasitismo en los vireos disminuiría con el aumento de la abundancia de huéspedes alternativos y aumentaría al incrementarse la abundancia de tordos. Todos los nidos del vireo gorrinegro ( n = 20) y el 81% de los nidos del vireo ojiblanco ( n = 27) fueron parasitados. La frecuencia de parasitismo en los vireos ojiblancos estaba correlacionada positivamente con el número de tordos detectados ( r = 0.84, gdl = 4, P = 0.018). Estaba correlacionada negativamente con la abundancia ( r = 0.891, gdl = 4, P = 0.009) del chipe trepador ( Mniotilta varia ), pero no estaba correlacionada con la abundancia de otros huéspedes de los tordos. La relación entre la abundancia de chipe trepador y la frecuencia da parasitismo podría ser aleatoria, dado lo pequeño de la muestra y la poca variación en las frecuencias de parasitismo, pero también podría reflejar una interacción entre el parasitismo y las características de la vegetación asociada con el chipe trepador que requiere más investigación. Nuestros resultados indican que la disminución de la abundancia de tordos reduce la frecuencia de parasitismo en el vireo gorrinegro. Cuando el número de tordos en una área predice el parasitismo, los administradores de recursos naturales podrían beneficiarse de la identificación de una abundancia meta del tordo, basada en los niveles de parasitismo que la población huésped pueda sostener y todavía alcanzar los objetivos de productividad y población de la especie. 相似文献
70.
Nest parasitism by Brown-headed Cowbirds ( Molothrus ater ) can negatively affect host populations. Landscape-scale factors, such as proximity to residential areas, equestrian riding stables, and grazing allotments, can affect the risk of nest parasitism as well as the abundance of Brown-headed Cowbirds. Recent increases in residential and recreational development along with a reduction in grazing allotments in the northern Sierra Nevada provide an opportunity to reevaluate factors that influence frequency of nest parasitism by Brown-headed Cowbirds. Frequency of nest parasitism increased as the distance to the nearest residential center and distance to the nearest equestrian riding stable decreased. Similarly, Brown-headed Cowbird abundance was negatively correlated with distance to the nearest residential center and distance to the nearest equestrian stable. To reduce the risk of nest parasitism, efforts should be devoted to (1) reducing further residential development at the wildland–urban interface and (2) educating landowners about bird feeders, which frequently attract Brown-headed Cowbirds. 相似文献