全文获取类型
收费全文 | 355篇 |
免费 | 14篇 |
出版年
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 16篇 |
2012年 | 10篇 |
2011年 | 9篇 |
2010年 | 16篇 |
2009年 | 22篇 |
2008年 | 13篇 |
2007年 | 19篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1959年 | 8篇 |
1958年 | 13篇 |
1957年 | 16篇 |
1956年 | 16篇 |
1955年 | 9篇 |
1954年 | 10篇 |
1953年 | 13篇 |
1952年 | 6篇 |
1951年 | 9篇 |
1950年 | 4篇 |
排序方式: 共有369条查询结果,搜索用时 15 毫秒
1.
The release from dormancy of Euonvmus europaeus L embryos bya brief treatment with GA3 has been studied During 48 h incubationof dormant embryos in GA-free medium, phospholipid levels increasedat first, then declined sharply over the last 6 h When the embryoswere placed in GA3 medium during this 6 h period levels of totalphospholipids as well as of phosphatidylethanolamine increasedwhilst phosphatidylinositol and phosphatidylcholine declinedslightly Fine structural changes stimulated by a brief GA3 treatmentwere of different character depending on tissue region (1) destructivechanges occurred in the superficial procortical parenchyma onthe hypocotyl/radicle boundary, involving autolysis and decompartmentationof organelles, (2) positive changes occurred inregions close to root and shoot apical meristems, involvingdegradation of protein bodies and their conversion into vacuoles,and the proliferation of various organelles A number of differenceswere noted when the changes in GA3-treated embryos were comparedwith those induced by low temperature, which also overcomesdormancy The results suggest that germination is accompaniedby different cytological events depending on whether it is inducedby cold or GA3 The growth of embryos in which dormancy was overcomeby GA3 was due to the activation of the apical root meristemclose to the quiescent centre, whilst in embryos in which germinationwas induced by low temperature, the periphery of hypotocotyl/radicleboundary was the site of activation Euonymus europaeus L, dormant embryo, fine structure, phospholipids, GA3 and cold treatments 相似文献
2.
ABSTRACT. Bloodstream forms of Trypanosoma musculi, cultured in Schneider's drosophila medium at room temperature, multiply and differentiate through a series of developmental stages into infective metacyclic trypomastigotes in 10 days. Oral inoculation with these culture forms into CBA mice produced a parasitemia similar to that produced by intraperitoneal infection with bloodstream forms except for a three-day longer prepatent period. Attempts to induce parasitemia with bloodstream forms given orally were unsuccessful. 相似文献
3.
The effects of temperature on the yield of in vivo modulatedchlorophyll fluorescence were measured in intact leaves of atrazineresistantand -susceptible biotypes of the weed Senecio vulgaris L. At25 ?C, the photochemical quenching (qQ of steady-state chlorophyllfluorescence was reduced by around 30% in the atrazine-resistantmutant as compared to the susceptible wild type, indicatinga higher reduction state of the primary electron acceptor QAof photosystem II in the former biotype. Moderately elevatedtemperatures (above 30 ?C) further increased the steady-stateconcentration of reduced in the mutant. Analysis of the temperature dependence of both the photochemicalquenching qQ and the initial fluorescence level Fo clearly indicateda drastically enhanced heat-sensitivity of the photochemicalapparatus in the atrazine-resistant Senecio leaves. The heat-inducedchanges in F0 and qQ were closely correlated, suggesting thatthe phenomenon responsible for the rise in F0 was also involvedin the inhibition of the photosynthetic electron flux. Low temperaturesalso affected reoxidation but, in contrast to heating, no apparent differences were observed in the behaviourof the two biotypes exposed to chilling stress. Key words: Atrazine-resistance, chlorophyll fluorescence, heat stress, Senecio vulgaris 相似文献
4.
PHILIPPE GAUCHER PATRICK PAILLAT CLAUDE CHAPPUIS MICHEL SAINT JALME FATEMEH LOTFIKHAH MICHAEL WINK 《Ibis》1996,138(2):273-282
The Houbara Bustard Chlamydotis undulata is a polytypic species with three subspecies classified according size, colour and distribution: C. u. undulata, C. u. fuertaventurae and C. u. macqueenii. A comparative study of the male display behaviour of these three subspecies has shown similarities between C. u. undulata and C. u. fuertaventurae , whereas appreciable differences exist in the visual and auditory aspects of the display between C. u. undulata and C. u. macqueenii. These observations make the current taxonomy of Houbara Bustard questionable, particularly in view of the major importance of the sexual display in bird speciation processes. Furthermore, DNA analysis of the cytochrome b gene indicates the existence of a significant differentiation between the C. u. undulata and C. u. macqueenii populations. These findings indicate the need for a revision of the taxonomy of genus Chlamydotis which should separate the macqueenii and undulata populations at species rank. Until further investigations are completed, C. u. fuertaventurae should be kept as a subspecies of undulata since the courtship display is alike in both populations. 相似文献
5.
MANUEL SÁNCHEZ-MORENO CARMEN FERNANDEZ-BECERRA EMILIO ENTRALA FRED R. OPPERDOES MICHEL DOLLET ANTONIO OSUNA 《The Journal of eukaryotic microbiology》1995,42(3):314-320
ABSTRACT. We describe the in vitro culture of Phytomonas species isolated from Euphorbia characias . The best choice between tested media was SDM-79, in which promastigotes, after 6 days of culture, reached cell densities as high as 4 × 107 cells/ml. Cells growing in LIT or MTL medium showed longer division times and lower cell densities. We succeeded in obtaining Phytomonas sp. amastigote and spheromastigote forms in modified GRACE's medium, yielding transformation rates of up to 70%. Electron microscopy studies were performed in order to characterize the ultrastructural features of these forms obtained in vitro. On the other hand, metabolic studies based on qualitative (nuclear magnetic resonance spectroscopy) and quantitative metabolic methods (enzymatic assays) showed that promastigote forms secreted mainly ethanol, acetate, glycine, glycerol, piruvate and succinate in SDM-79 medium, whereas the major metabolites found after transformation in modified Grace's medium were ethanol, acetate, glycine, piruvate and smaller amounts of glycerol. 相似文献
6.
Abstract.
- 1 The structure of local populations of a monophagous butterfly, the bog fritillary Proclossiana eunomia, was studied in a complex of suitable habitat patches separated by spruce plantations or fertilized pasture.
- 2 An unexpected high level of adult movements between habitat patches was detected by a mark—release—recapture technique. Local populations were connected by adult movements across unsuitable habitats, leading to a meta-population structure.
- 3 This evidence of the metapopulation structure of a specialist butterfly challenges the supposed relationship between habitat specialization and closed, isolated populations.
- 4 Males and females of P.eunomia exhibited different spatial behaviours; females were more likely to emigrate and dispersed further than males. These differences in spatial behaviour are related to the mating system.
7.
LAURE LECOIN PASCALE MERCIER NICOLE M. LE DOUARIN 《Pigment cell & melanoma research》1994,7(4):210-216
In the Silky Fowl (SF) breed of chicken, most of the internal organs are infiltrated with melanocytes. Previous studies have shown that this generalized mesodermal pigmentation is not due to a cell autonomous abnormality of the melanocytes but to environmental factors able to promote both the homing of pigment cell precursors in abnormal embryonic sites and their proliferation and differentiation. To analyse the mode of these environmental cues, we tested the effect of SF embryo extract (SFEE) on cultured quail neural crest cells as compared with that of EE from normal chickens of the JA57 strain (JA57EE). We found that SFEE enhances crest cell proliferation as judged by 3H-TdR incorporation and cell counting. In contrast, no effect of SFEE was observed either on the proportion of cultured cells that are engaged into the melanocytic differentiation pathway or on the amount of melanin produced by each differentiated pigment cell. The simple observation, however, reveals that SFEE has a significant effect on pigmentation of the cultured quail neural crest cells. This effect has therefore to be accounted for by the general increase in cell number induced by SFEE. The question is raised as to whether the in vivo SF phenotype is generated exclusively by this mechanism. 相似文献
8.
9.
10.