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排序方式: 共有90条查询结果,搜索用时 93 毫秒
71.
Spawning behaviour of Penaeus (Fenneropenaeus) merguiensis de Man and the effect of light intensity on spawning 总被引:2,自引:0,他引:2
An experiment was conducted to investigate the effect of light intensity just prior to and during spawning of Penaeus (Fenneropenaeus) merguiensis de Man in the laboratory. Neither the presence of light nor light intensity (0, 10 and 1100 lux) had a significant effect on the spawning process or hatching rate in P. merguiensis. Difference in the percentage of spawners, percentage of incomplete spawning, fecundity and hatching rate were all insignificant (P > 0.05) among the three light treatments. However, spawning was delayed (up to 21 min on average) under 1100 lux with a high percentage of incomplete spawning, compared with the Control (0 lux). For the first time, spawning behaviour of P. merguiensis was observed and fully described. The spawning process can be divided into four phases: dormant, pre‐spawning, spawning and post‐spawning by distinct behaviour of prawn broodstock. The dormant phase was characterized by a quiescent and non‐feeding period, whereas movement of prawn broodstock was active during the pre‐spawning and post‐spawning phases. Depending on the individual, spawning was completed within 3–5 min. Prawns often stayed still on the water surface during spawning with occasional manoeuvres to change the position. After a short rest at the termination of the spawning phase, prawn broodstock re‐exhibited active movement as in the pre‐spawning phase, but showing conspicuous care to the deposited eggs. The role of light in controlling ovarian development and spawning, and the behaviour of prawn broodstock in relation to maximizing fertilization rate are discussed. 相似文献
72.
W Yi PM Clark DE Mason MC Keenan C Hill WA Goddard EC Peters EM Driggers LC Hsieh-Wilson 《Science (New York, N.Y.)》2012,337(6097):975-980
Cancer cells must satisfy the metabolic demands of rapid cell growth within a continually changing microenvironment. We demonstrated that the dynamic posttranslational modification of proteins by O-linked β-N-acetylglucosamine (O-GlcNAcylation) is a key metabolic regulator of glucose metabolism. O-GlcNAcylation was induced at serine 529 of phosphofructokinase 1 (PFK1) in response to hypoxia. Glycosylation inhibited PFK1 activity and redirected glucose flux through the pentose phosphate pathway, thereby conferring a selective growth advantage on cancer cells. Blocking glycosylation of PFK1 at serine 529 reduced cancer cell proliferation in vitro and impaired tumor formation in vivo. These studies reveal a previously uncharacterized mechanism for the regulation of metabolic pathways in cancer and a possible target for therapeutic intervention. 相似文献
73.
On 15 September,2010,a Pechora Pipit Anthus gustavi Swinhoe was found in the Hami prefecture(41°13’N and 93°29’E,1,143 m a.s.l.),Xinjiang,during the period of a comprehensive scientific survey in Lop Nur region.The bird,which was photographed,is a new avian record for Xinjiang.The pipit reproduces in northern Eurasia,mainly in wide meadows and low hills,and can be found in open forests and nearby residential areas in the process of on migration.The species is an insectivore and is a rare migrant or vagrant in Xinjiang.The geographical distribution,character,habitat,ecological habit and subspecies of the Pechora Pipit were discussed in this paper. 相似文献
74.
75.
Photosynthetic responses to temperature, light and carbon dioxide partial pressure were studied in two-year-old Flindersia brayleyana F. Muell. and Castanospermum australe Cunn. & C. Fraser ex Hook. growing on coastal lowland and upland rainforest sites in tropical Queensland, Australia. Climatic conditions ranged from moist and cool (17-19 degrees C) to dry and warm (22-24 degrees C). The optimum temperature for photosynthesis was 23.7-25.6 degrees C for C. australe and 21.2-24.6 degrees C for F. brayleyana. Mean maximum rate of electron transport for each species did not differ between sites but was higher (60-62 &mgr;mol m(-2) s(-1)) in F. brayleyana than in C. australe (42-44 &mgr;mol m(-2) s(-1)). Ribulose-bisphosphate carboxylation rate did not differ significantly between sites or species. Maximum rates of photosynthesis at 1000 &mgr;Pa Pa(-1) CO(2) did not differ significantly between sites for each species, but did differ significantly between species. At 350 &mgr;Pa Pa(-1) CO(2), photosynthetic light use efficiencies of F. brayleyana and C. australe were 0.05 and 0.015, respectively, at the upland site, and the corresponding values at the lowland site were 0.025 and 0.05. In C. australe, these differences were reflected in significantly greater maximum rates of photosynthesis at 350 &mgr;Pa Pa(-1) CO(2) at the lowland site than at the upland site (5.2 versus 3.3 &mgr;mol m(-2) s(-1)). 相似文献
76.
77.
After nearly a century of recovery from overhunting, sea otter populations are in abrupt decline over large areas of western Alaska. Increased killer whale predation is the likely cause of these declines. Elevated sea urchin density and the consequent deforestation of kelp beds in the nearshore community demonstrate that the otter's keystone role has been reduced or eliminated. This chain of interactions was probably initiated by anthropogenic changes in the offshore oceanic ecosystem. 相似文献
78.
79.
Kemachandra Ranatunga Rodney J. Keenan Stan D. Wullschleger Wilfred M. Post M. Lynn Tharp 《Forest Ecology and Management》2008
Understanding long-term changes in forest ecosystem carbon stocks under forest management practices such as timber harvesting is important for assessing the contribution of forests to the global carbon cycle. Harvesting effects are complicated by the amount, type, and condition of residue left on-site, the decomposition rate of this residue, the incorporation of residue into soil organic matter and the rate of new detritus input to the forest floor from regrowing vegetation. In an attempt to address these complexities, the forest succession model LINKAGES was used to assess the production of aboveground biomass, detritus, and soil carbon stocks in native Eucalyptus forests as influenced by five harvest management practices in New South Wales, Australia. The original decomposition sub-routines of LINKAGES were modified by adding components of the Rothamsted (RothC) soil organic matter turnover model. Simulation results using the new model were compared to data from long-term forest inventory plots. Good agreement was observed between simulated and measured above-ground biomass, but mixed results were obtained for basal area. Harvesting operations examined included removing trees for quota sawlogs (QSL, DBH >80 cm), integrated sawlogs (ISL, DBH >20 cm) and whole-tree harvesting in integrated sawlogs (WTH). We also examined the impact of different cutting cycles (20, 50 or 80 years) and intensities (removing 20, 50 or 80 m3). Generally medium and high intensities of shorter cutting cycles in sawlog harvesting systems produced considerably higher soil carbon values compared to no harvesting. On average, soil carbon was 2–9% lower in whole-tree harvest simulations whereas in sawlog harvest simulations soil carbon was 5–17% higher than in no harvesting. 相似文献
80.
Colin Filer Rodney J. Keenan Bryant J. Allen John R. Mcalpine 《Annals of Forest Science》2009,66(8):813-813