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91.
1. Many insects host secondary bacterial symbionts that are known to have wide‐ranging effects on their hosts, from host‐plant use to resistance against natural enemies. This has been most widely studied in aphids, which have become a model system to study insect–bacteria interactions. 2. While there is an increasing understanding of the role of symbionts in aphids from controlled laboratory studies, we are only beginning to explore the impact of hosting these symbionts on eco‐evolutionary dynamics in natural systems. To date, many research groups have identified bacterial symbionts from various aphid species, providing us with a bank of literature on aphid–symbiont associations in natural populations. 3. The role of secondary symbionts in aphids is discussed, and the taxonomic and geographical distribution of symbionts among aphids are summarised, and the potential reasons for the patterns observed. The need to test for multiple symbiont species (and co‐infections) across many individuals and the whole distribution range of an aphid is highlighted, including sampling on all known host‐plant species. 4. It is further important also to consider variation within the symbiont, the aphid‐host and the surrounding community, e.g. host‐plants or the natural enemies, to understand how these have the potential to mediate aphid–symbiont interactions. 5. Finally, the knowledge gained from experimental work should now be used to understand the role of aphid secondary symbionts in field systems, to fully understand the potentially far‐reaching consequences of aphid endosymbionts on community and ecosystem processes. 相似文献
92.
AMOS FRISCH WOLFGANG BESSLER HANS JOACHIM LIPPS DIETER AMMERMANN 《The Journal of eukaryotic microbiology》1976,23(3):427-430
SYNOPSIS. Interaction of several plant lectins with the ciliates Stylonychia mytilus, Euplotes aediculatus, and Tetrahymena pyriformis GL, was investigated. The motility of Stylonychia is specifically inhibited by treatment with concanavalin A, with which the 2 other ciliates react only weakly. Stylonychia can regain its motility by shedding the lectin-loaded surface components and rebuilding a new pellicle. Other lectins used in this study did not interact with these ciliates. 相似文献
93.
The Capacity of Testicular Cells of the Postnatal Rat to Reorganize into Histotypic Structures 总被引:2,自引:0,他引:2
MARIA TERESA ZENZES WOLFGANG ENGEL 《Differentiation; research in biological diversity》1981,20(1-3):157-161
Cell reorganization experiments in vitro were performed with dissociated rat testes at different ages of postnatal development namely, newborn, 8–10, 18–25, 35–40, and 90 days. Only newborn and juvenile rat testicular cells reassociated into testicular-like organization in rotation culture. Puberal and adult rat testicular cells show morphogenetic organization when they were deprived of germ cells by busulphan pretreatment. A factor present in testicular tissue of puberal and adult rats inhibits reorganization. The inhibitor is confined to the spermatic cell fraction in the testis. 相似文献
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95.
WOLFGANG ENGELMANN ERS JOHNSSON H. G. KARLSSON R. KOBLER M.-L. SCHIMMEL 《Physiologia plantarum》1978,43(1):68-76
The circadian petal movement rhythm of Kalanchoë flowers has been studied. The amplitude of the rhythm can be drastically reduced by an appropriate stimulus of a light pulse. It has also been shown that it is possible to stop the rhythm permanently by administering a single light pulse to the flowers. This is interpreted to indicate that the light pulse has sent the circadian rhythm into a stable state of singularity. The conditions which attenuate the rhythm have been investigated both theoretically (on the basis of a previously published model for circadian rhythms) and experimentally. 120 min red light of 230 μW · cm?2, starting briefly before the second petal closure about 30 h after transfer to constant safe light conditions is optimal in inducing rhythm-damping. Damping requires the same duration when the light is given at the corresponding phase during the third or fourth cycle of the rhythm. However, in the first cycle 240 min red light of 230 μW · cm?2 is required to get optimal damping of the rhythm. Conditions to achieve damping for other irradiances are investigated. Individual recordings are presented which show the behaviour of the rhythm when perturbed by light stimuli close to its singularity. 相似文献
96.
KLAUS VOGEL WOLFGANG FRIEDRICH GUTMANN 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1980,13(3):269-275
A new model for the origin of pelecypods based on physiological and biomechanical viewpoints is presented. It seems that some early molluscs developed a bivalved shell in response to their migration from firm bottom onto soft sediments as epibenthic crawlers. Here a univalved shell cannot sufficiently protect the mantle cavity from getting clogged by sediment particles. The evolution of the pelecypod shell, of the necessary adductors and ligament, of the byssus and the change from grazing to filter-feeding life habit is explained as a step-by-step change, each stage providing an adaptational improvement. 相似文献
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99.
The expected upward shift of trees due to climate warming is supposed to be a major threat to range‐restricted high‐altitude species by shrinking the area of their suitable habitats. Our projections show that areas of endemism of five taxonomic groups (vascular plants, snails, spiders, butterflies, and beetles) in the Austrian Alps will, on average, experience a 77% habitat loss even under the weakest climate change scenario (+1.8 °C by 2100). The amount of habitat loss is positively related with the pooled endemic species richness (species from all five taxonomic groups) and with the richness of endemic vascular plants, snails, and beetles. Owing to limited postglacial migration, hotspots of high‐altitude endemics are situated in rather low peripheral mountain chains of the Alps, which have not been glaciated during the Pleistocene. There, tree line expansion disproportionally reduces habitats of high‐altitude species. Such legacies of climate history, which may aggravate extinction risks under future climate change have to be expected for many temperate mountain ranges. 相似文献
100.
Photoautotrophic Growth and Photosynthesis in Cell Suspension Cultures of Chenopodium rubrum 总被引:4,自引:0,他引:4
A method is described for growing cell suspension cultures of Chenopodium rubrum photoautotrophically for prolonged periods of time. By using a two-tier culture vessel the growth medium with the cells was separated from the CO2 reservoir. Definite CO2 concentrations were established by a K2CO3/KHCO3 buffer. Photoautotrophic growth in C. rubrum cell suspension cultures was correlated with the CO2 level. At 0.5% CO2 the cell cultures contained 68 μg chlorophyll/g fresh weight and showed an increase in fresh weight of about 80% in 18 days. At 1% CO2 an increase in fresh weight of 165% in 18 days was observed. The chlorophyll content rose up to 84 μg/g fresh weight. The photoautotrophic growth was also greatly influenced by the 2,4-D content of the medium. Cell growth was enhanced by lowering the auxin concentration. Best growth was attained (210% increase in fresh weight) at 10?8M 2,4-D. The photosynthetic activity of the cells was measured by the light dependent 14CO2 incorporation. At 0.5% CO2 the cell suspensions assimilated about 100 μmol CO2/mg chlorophyll × h. In the presence of 1% CO2 the light driven assimilation was raised up to 185 μmol CO2/mg chlorophyll × h. In both cases, the dark incorporation of CO2 was merely 1.8% of the values obtained in light. 相似文献