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11.
Effects of insect herbivory on early plant succession: comparison of an English site and an American site 总被引:1,自引:0,他引:1
STEPHEN D. HENDRIX VALERIE K. BROWN ALAN C. GANGE 《Biological journal of the Linnean Society. Linnean Society of London》1988,35(3):205-216
We examined the survival, size, and agonistic behaviour of faster and slower developing rainbow trout ( Salmo gairdneri ) in an artificial stream channel with a simulated redd. The analysis was performed at two levels: between three full-sib families genetically marked at a hexosaminidase locus, and within families segregating for a regulatory allele Pgml-t(b) that is associated with faster developmental rate. The families differed significantly in their hatching times but showed little variation in emergence times. Fishes with the Pgml-t(b) allele hatched and emerged significantly earlier than their full-sibs without the allele. Despite the mortality of at least 50% of emerged fishes in the selection experiment, there was no significant difference in survival between either the three families or fishes with different genotypes at the Pgml-t locus. However, fishes from the faster developing family and those with the Pgml-t(b) allele had significantly higher levels of agonistic behaviour and had a tendency to be larger than slower developing individuals. 相似文献
12.
EFFECTS OF HERBICIDES ON THE GROWTH OF SOIL FUNGI 总被引:4,自引:4,他引:0
13.
Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply 总被引:1,自引:0,他引:1
VALERIE M. FRANCK BRUCE A. HUNGATE F. STUART CHAPIN III CHRISTOPHER B. FIELD 《Biogeochemistry》1997,36(3):223-237
We investigated the effect of CO2 concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO2 altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO2 had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO2 decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO2 on N loss fromlitter also differed among species, with Vulpia litter from high-CO2 plants releasing N more slowly than ambient-CO2litter, whereas growth under elevated CO2 caused increased Nloss from Avena litter. CO2 effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO2 on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO2 effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO2. 相似文献
14.
15.
Synthesis of Cell Coat in Normal and Transformed Cells 总被引:6,自引:0,他引:6
THE surface of transformed cells has been a focus of considerable attention recently because some of the properties which distinguish these cells from their precursors, such as decreased cell adhesiveness, altered cell orientation and loss of contact and density dependent inhibition1–3, may relate to changes on their surface. A common feature of vertebrate cells is the cell coat, a glycoprotein structure surrounding the plasma membrane4. Electron microscopy has revealed that transformed cells have a thicker coat than normal cells5 and we have now found that coat synthesis in cells transformed by an oncogenic DNA virus and in cells transformed by a chemical carcinogen occurs faster than in normal controls whereas only in the virus-transformed cells is the coat significantly thicker. 相似文献
16.
Plants and insects in early old-field succession: comparison of an English site and an American site 总被引:1,自引:0,他引:1
VALERIE K. BROWN STEPHEN D. HENDRIX HUGH DINGLE 《Biological journal of the Linnean Society. Linnean Society of London》1987,31(1):59-74
The plant and insect communities of early, secondary succession beginning with bare ground in an Old World site (southern Britain) and a New World site (Iowa, U.S.A.) shared a number of characteristics. Both sites showed similar temporal patterns of plant species cover and species richness, although overall richness was greater at the Old World site. Annuals dominated at both sites during the first year of succession and were largely replaced by perennials in the second year. Monocotyledons were more abundant at the Old World site, especially in the second year. The two sites differed markedly in the contribution of native and introduced plant species, with the Old World site dominated by natives and the New World site by alien plant species. Insect herbivore load was greater at the Old World site, when expressed in terms of structural complexity of the vegetation, suggesting that there may be major differences in the influence of herbivores on the direction and rate of succession at the two sites. 相似文献
17.
Expanding forests and changing growth forms of Siberian larch at the Polar Urals treeline during the 20th century 总被引:3,自引:0,他引:3
NADEZHDA DEVI FRANK HAGEDORN† PAVEL MOISEEV HARALD BUGMANN‡ STEPAN SHIYATOV VALERIE MAZEPA ANDREAS RIGLING† 《Global Change Biology》2008,14(7):1581-1591
The ongoing climatic changes potentially affect plant growth and the functioning of temperature‐limited high‐altitude and high‐latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest–tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright‐growing trees are <80 years old. Because thousands of more than 500‐year‐old subfossil trees occur in the same area but tree remnants of the 15–19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree‐free tundra during the last century by about 20–60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi‐stem tree clusters, 90% of the trees emerging after 1950 were single‐stemmed. Tree‐ring analysis of horizontal and vertical stems of multi‐stemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5–20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above‐ and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40–75 t ha?1 and a carbon accumulation of approximately 20–40 g C m?2 yr?1 during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 °C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals. 相似文献
18.
VALERIE CARON ALIDA F. JANMAAT JERRY D. ERICSSON JUDITH H. MYERS 《Ecological Entomology》2008,33(4):517-522
Abstract. 1. Ecological interactions between parasitoids and their hosts are extremely strong as parasitoid offspring rely entirely on an individual host to complete development. The ability of a parasitoid to use a host is influenced directly by the degree to which the parasitoid can overcome host defences and grow within the host.
2. Hymenopteran parasitoids have evolved different host-specific strategies to defeat the host immune system, such as the use of venom, endosymbiont virus, or mimicking the host tissue. Dipteran parasitoids from the Tachinidae family do not use these subterfuges and rely mainly on avoiding the host immune system by hiding in specific tissues.
3. Little is known of the effect of this strategy on the host immune system, the absorption of nutrients by the parasitoid larvae, or the implications for parasitoid host range.
4. In this study, the impact of a polyphagous tachinid parasitoid Compsilura concinnata Meigen on a pest lepidopteran Trichoplusia ni Hübner are assessed. Phenoloxidase levels and haemolymph proteins were measured in parasitised T. ni as a function of host immune response.
5. Haemolymph phenoloxidase in the host did not vary with parasitisation but was triggered when a piece of monofilament was implanted in the haemocoel. Haemolymph proteins were depleted in heavily parasitised T. ni .
6. These results indicate that C. concinnata has a strategy that avoids the host immune system, and accesses the necessary nutrients for larval growth. This strategy could explain the success of this tachinid and its wide host range. 相似文献
2. Hymenopteran parasitoids have evolved different host-specific strategies to defeat the host immune system, such as the use of venom, endosymbiont virus, or mimicking the host tissue. Dipteran parasitoids from the Tachinidae family do not use these subterfuges and rely mainly on avoiding the host immune system by hiding in specific tissues.
3. Little is known of the effect of this strategy on the host immune system, the absorption of nutrients by the parasitoid larvae, or the implications for parasitoid host range.
4. In this study, the impact of a polyphagous tachinid parasitoid Compsilura concinnata Meigen on a pest lepidopteran Trichoplusia ni Hübner are assessed. Phenoloxidase levels and haemolymph proteins were measured in parasitised T. ni as a function of host immune response.
5. Haemolymph phenoloxidase in the host did not vary with parasitisation but was triggered when a piece of monofilament was implanted in the haemocoel. Haemolymph proteins were depleted in heavily parasitised T. ni .
6. These results indicate that C. concinnata has a strategy that avoids the host immune system, and accesses the necessary nutrients for larval growth. This strategy could explain the success of this tachinid and its wide host range. 相似文献
19.
VALERIE L. BOYARSKI GORDON H. RODDA JULIE A. SAVIDGE 《The Journal of wildlife management》2007,71(5):1704-1707
Abstract: We conducted a physical simulation experiment to test the efficacy of harmonic direction finding for remotely detecting locomotor activity in animals. The ability to remotely detect movement helps to avoid disturbing natural movement behavior. Remote detection implies that the observer can sense only a change in signal bearing. In our simulated movements, small changes in bearing (<5.7°) were routinely undetectable. Detectability improved progressively with the size of the simulated animal movement. The average (±SD) of reflector tag movements correctly detected for 5 observers was 93.9 ± 12.8% when the tag was moved ≥11.5°; most observers correctly detected tag movements ≥20.1°. Given our data, one can assess whether the technique will be effective for detecting movements at an observation distance appropriate for the study organism. We recommend that both habitat and behavior of the organism be taken into consideration when contemplating use of this technique for detecting locomotion. 相似文献
20.
VALERIE E. SANDS 《Biological journal of the Linnean Society. Linnean Society of London》1990,39(3):269-277
Catantops humilis lives on the leguminous covercrop in young rubber and oil palm plantations on the coastal plains of Peninsular Malaysia. The grasshopper has high dispersal capability, and migrates when the trees mature, so distribution of populations changes regularly. Southern populations have normal 2 n =23, XO/24, XX complements. In Selangor State two morphologically indistinguishable chromosomal forms comprising XO and neo-XY males with basic homozygote and fusion heterozygote females, exist sympatrically in the same microhabitat in eight localities. In one population where occasional sharp reduction in numbers and migration occur, the centric rearrangement has attained a 40–50% frequency. A further mixed population was found 300 km north. Consideration is given to the possibilities that these mixed populations are part of a broad region of hybridization between two chromosomal races, or that they represent a widespread polymorphism. 相似文献