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71.
HOWARD E. BUHSE JR. SANDRA NABAZAS CATHERINE BUHRFEIND PHIUIP E. RYALS† 《The Journal of eukaryotic microbiology》1991,38(2):124-129
ABSTRACT. Macrostomal cell formation is blocked by the antibiotic cerulenin at levels of 15 μg/ml or higher. Inhibition can be reversed up to 4 h following cerulenin addition by washing and resuspending cells in new, noncerulenin-treated transforming principle. In these latter cases, additional time equal to the time spent in the inhibitor, is needed for cells to reach control values of transformation. Neither the addition of saturated or unsaturated fatty acids, cholesterol added alone or in combination with stearic acid, nor a mixture of lipids extracted from Tetrahymena vorax reversed the cerulenin effect. Radioisotope incorporation data showed while protein synthesis was reduced by the end of 1 h and tetrahymanol synthesis by the end of 2 h, little or no effect of this inhibitor occurred on RNA or fatty acid synthesis during these times. One interpretation of these results is that cerulenin, by preventing first protein synthesis and later tetrahymanol synthesis, interferes with synthesis and formation of membranes required for the microstome to macrostome transition. 相似文献
72.
Seasonal progressions of tissue and cell water relations parameters in evergreen and deciduous perennials 总被引:4,自引:4,他引:0
Abstract. Tissue and cell water relations parameters were followed for Heteromeles arbutifolia, Cercis occidentalis and Aesculus californica , in an environment exhibiting seasonally increasing drought. The extensive seasonal osmotic adjustment of evergreen H. arbutifolia and the moderate adjustment in C. occidentalis closely matched their respective seasonal decreases in minimum daily water potential. Summer deciduous A. californica exhibited only small drops in osmotic potential and water potential. Experiments with irrigated plants indicated that drought was not required for the osmotic adjustment of H. arbutifolia and C. occidentalis. However, in H. arbutifolia drought treatment enhanced osmotic adjustment. In irrigated H. arbutifolia , osmotic adjustment was mainly the result of an accumulation of osmotica. In drought-stressed plants, the same change in osmotic potential resulted from a combination of accumulation of osmotica and a decrease in symplast volume. 相似文献
73.
74.
Variation among populations of Galapagos land iguanas (Conolophus): contrasts of phylogeny and ecology 总被引:1,自引:0,他引:1
HOWARD L. SNELL HEIDI M. SNELL C. RICHARD TRACY 《Biological journal of the Linnean Society. Linnean Society of London》1984,21(1-2):185-207
A phylogenetic scheme derived via multivariate analyses of adaptively neutral scale characteristics is compared to patterns of ecological adaptation in body size and shape, hatchling size, clutch size, and reproductive seasonality, in extant populations of Galapagos land iguanas (genus Conolophus). Three groups of land iguana populations are identified, the oldest being the population of Isla Santa Fe, followed by the populations of the central islands (Santa Cruz, Plaza Sur and Baltra), the youngest populations are those of the western islands (Fernandina and Isabela). Patterns of ecological similarity among these populations are not concordant with phylogenetic lineage. Populations most similar in ecological characteristics are often phylogenetically divergent. Adaptation to local conditions by iguana populations is apparently more important than phylogenetic constraint in explaining variation in ecological characteristics. The assumption that phylogenetically closely-related organisms are also ecologically more similar than less closely-related organisms is not supported by this evidence. Some previous studies may have been misled by using ecological characteristics to derive phylogenetic lineages, resulting in circular support of the assumption. 相似文献
75.
76.
Cotton (Gossypium hirsutum L. cv. Deltapine 15) seedlings were grown in solution culture in which the Mn2+ level was varied. Following an initial period, a series of shifts in manganese nutrition were employed, each lasting 14 days. Appearance was observed and fresh weight, IAA oxidase (IAAO), peroxidase and IAAO inhibitor levels were determined. After the initial 3 weeks of treatment, growth was negatively correlated with IAAO (or peroxidase) activity. All shifts in manganese nutrition resulted in predicted changes in IAAO activity, growth and plant appearance during a second 2-week period of the experiment. Continuously deficient plants exhibited highest leaf abscission and IAA oxidase activity, and lowest growth of all treatments. Plants shifted from deficient to control levels of Mn2+ exhibited a marked decline in IAAO activity, increase in growth and absence of leaf abscission. Plants shifted from borderline deficiency to deficient Mn2+ exhibited a major increase in IAAO activity, reduction in growth and extensive leaf abscission. Control and borderline toxicity plants maintained normal IAAO activity, growth, and appearance. During a final 2-week period, symptom expression was intensified. In particular, the initial borderline deficiency plants shifted to deficient levels of Mn2+ abscised most of those leaves that expanded after the shift in treatment. In addition, shifts of some plants to toxic Mn2+ levels during the third phase of the experiment produced a complete cycle of manipulation. Plants initially deficient in Mn2+ with high IAAO and low growth recovered growth and declined in IAAO when shifted to control Mn2+ and then suffered severe inhibition of growth and toxicity symptoms when shifted to high Mn2+. In all cases changes in enzyme activity, growth, leaf abscission and similar symptoms were most strongly expressed in the youngest tissue or that with the greatest potential for growth during the interval of a particular treatment. Since total growth, IAAO, leaf abscission, internode length and similar symptoms were consistently manipulated in both directions (increase or decrease in intensity or degree) by raising or lowering Mn2+ levels in the plant culture medium, we conclude that there is a causal relationship between IAAO and these responses that involves destruction of auxin. 相似文献
77.
The ephippia of Ceriodaphnia megalops and Ceriodaphnia pulchella are described. Their ephippia may be identified by their size and shape, supplemented by measurement of the length of the resting egg. The ephippia are shed free in the water and float by means of a special area of gas-filled tissue. Each ephippium contained one ellipsoid resting egg. The length, width and shape of the resting eggs of both species were investigated, and comparisons made with published data of their parthenogenetic eggs. For both species the volume of a resting egg was virtually the same as the volume of a parthenogenetic egg, but the resting egg was more elongated. The shape of resting eggs was linearly related to egg volume on logarithmic axes in a manner similar to that reported for the parthenogenetic eggs of these two species. The linear relationship between total parthenogenetic egg volume and body length reported for these two species did not apply to their resting eggs. 相似文献
78.
CARTER T. ATKINSON MASAMICHI AIKAWA EDWIN P. ROCK KEVIN MARSH PATRICIA M. ANDRYSIAK GARY H. CAMPBELL WILLIAM E. COLLINS RUSSELL J. HOWARD 《The Journal of eukaryotic microbiology》1987,34(3):267-274
This report describes the fine structure of the erythrocytic stages of Plasmodium malariae. Erythrocytic parasites from a naturally acquired human infection and an experimentally infected chimpanzee were morphologically indistinguishable and structurally similar to other primate malarias. New findings included observations of highly structured arrays of merozoite surface coat proteins in the cytoplasm of early schizonts and on the surface of budding merozoites and the presence of knobs in the membranes of Maurer's clefts. Morphological evidence is presented suggesting that proteins are transported between the erythrocyte surface and intracellular parasites via two routes: one associated with Maurer's clefts for transport of membrane-associated knob material and a second associated with caveolae in the host cell membrane for the import or export of host- or parasite-derived substances through the erythrocyte cytoplasm. 相似文献
79.
CAUSES OF DEATH IN IRRADIATED ADULT INSECTS 总被引:1,自引:0,他引:1
HOWARD S. DUCOFF 《Biological reviews of the Cambridge Philosophical Society》1972,47(2):211-238
80.
ALAN HOWARD 《American anthropologist》1972,74(4):811-823