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21.
The percentage hatch of eggs of Meloidogyne javanica increased asymptotically as the oxygen concentration increased from 0·2 to 21%. Hatch was unaffected by suction pressures of less than pF 3·4 at any oxygen concentration but was decreased by higher suctions. Both the development of embryos and the migration of larvae approached a maximum at an oxygen concentration of about 15%. Hatching was not limited by the rate oxygen diffused through the gelatinous matrix of the egg sac nor was the concentration of oxygen at the surface of an egg sac significantly lower than that within an individual egg. The maximum rate of metabolism appeared to need an oxygen concentration within the egg greater than 10%. 相似文献
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The Effect of Environmental and Nutritional Factors on the Development of Flower Apices Cultured in vitro 总被引:2,自引:0,他引:2
Flower buds of Viscaria candida, excised at 12 mm inlength, have been grown to maturity in sterile culture, oftenproducing normal flower parts. The calyx and the corolla developedunder a wide range of conditions provided gibberellic acid waspresent. The development of the ovary and of the ovules tendedto be irregular and no consistent effects of treatment couldbe obtained. Pollen production was promoted by a temperatureof 15 °C as opposed to one of 25 °C, and by the additionof gibberellic acid to the medium; it was inhibited by the additionof kinetin or hydrolysed casein to the medium, and by growthin continuous darkness as compared with that in 8 or 16 h oflight daily. 相似文献
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Fungal community responses to precipitation 总被引:2,自引:0,他引:2
CHRISTINE V. HAWKES STEPHANIE N. KIVLIN JENNIFER D. ROCCA VALERIE HUGUET MEREDITH A. THOMSEN KENWYN BLAKE SUTTLE 《Global Change Biology》2011,17(4):1637-1645
Understanding how fungal communities are affected by precipitation is an essential aspect of predicting soil functional responses to future climate change and the consequences of those responses for the soil carbon cycle. We tracked fungal abundance, fungal community composition, and soil carbon across 4 years in long‐term field manipulations of rainfall in northern California. Fungi responded directly to rainfall levels, with more abundant, diverse, and consistent communities predominating under drought conditions, and less abundant, less diverse, and more variable communities emerging during wetter periods and in rain‐addition treatments. Soil carbon storage itself did not vary with rainfall amendments, but increased decomposition rates foreshadow longer‐term losses of soil carbon under conditions of extended seasonal rainfall. The repeated recovery of fungal diversity and abundance during periodic drought events suggests that species with a wide range of environmental tolerances coexist in this community, consistent with a storage effect in soil fungi. Increased diversity during dry periods further suggests that drought stress moderates competition among fungal taxa. Based on the responses observed here, we suggest that there may be a relationship between the timescale at which soil microbial communities experience natural environmental fluctuations and their ability to respond to future environmental change. 相似文献
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X-Ray Analysis of Structure of Human Lysozyme at 6 Å Resolution 总被引:3,自引:0,他引:3
The tertiary structures of human and hen egg white lysozyme are very similar and a comparison of the two has provided some interesting results. 相似文献
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1. Stable isotopes of nitrogen are useful for quantifying the trophic structure of food webs, but only if the variation in trophic enrichment (ΔN), which is the difference in δ15N between a consumer and its food, is small relative to the value of ΔN itself. 2. We examined the sources of variation in zooplankton ΔN by measuring the trophic enrichment (ΔN) of seven species of freshwater cladocerans, and by testing for an effect of age and temperature on the ΔN of Daphnia pulicaria. 3. We found that ΔN was similar among Cladocera and was not correlated with body size. Overall, the ΔN for D. pulicaria was 1.4‰ (SE = 0.69, n = 57), as was expected for the detritus diet that we used in our experiments. We found no effect of temperature (15–25 °C) on ΔN, but found that ΔN of D. pulicaria increased with increasing age (10–30 days). 4. We developed a new method to test for trophic‐level variation in a group of consumers that explicitly accounts for the uncertainty in ΔN. Using this approach, we confirmed that natural assemblages of zooplankton feed at several trophic levels in lake food webs. 相似文献