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271.
Bàrbara Baraibar Raquel LedesmaAritz Royo-Esnal Paula R. Westerman 《Crop Protection》2011,30(9):1144-1148
Harvester ants from the species Messor barbarus (L.) are important seed predators in semi-arid cereal fields of NE Spain, and can contribute substantially to weed control. However, occasionally they harvest newly sown crop seeds at sowing in autumn, or ripe cereal grains close to harvest in summer, causing yield losses.A preliminary study was conducted in 34 commercial winter cereal fields to measure yield loss, and to identify factors that influence it. The area affected by ants was measured ten days prior to the anticipated harvest date. Ant colony size, nest density, crop height, weed densities and temperatures at sowing were assessed.At sowing, harvester ants did not cause yield losses (0.2% of potential yield on average). At harvest, yield losses were generally low as well (0.6%) although occasionally higher losses were recorded (max. 9.2%). Yield losses significantly increased with increasing nest density, nest size and with number of years of no-till. The results of this study show that in 2009 yield losses caused by M. barbarus were insignificant and more than offset by the benefits provided by the destruction of weed seeds. 相似文献
272.
Dos Santos Monteiro AC de Oliveira Neto OB Del Sarto RP de Magalhães MT Lima JN Lacerda AF Oliveira RS Scharfstein J da Silva MC Valencia JW Jiménez AV Grossi-de-Sa MF 《Pest management science》2008,64(7):755-760
BACKGROUND: The activity of the major digestive cysteine proteinase detected in the intestinal tract of larvae of the bean weevil, Acanthoscelides obtectus (Say), was efficiently inhibited by the well-characterized cysteine proteinase synthetic inhibitor E-64 and also by a recombinant form of chagasin (r-chagasin), a tight-binding cysteine proteinase inhibitor protein from Trypanosoma cruzi. RESULTS: Incorporation of r-chagasin into an artificial diet system at 0.1 g kg(-1) retarded growth rate, decreased larval survival and led to complete mortality of A. obtectus at the end of the trial. The observed differences in growth rates occurred particularly in the first and second development stages. Artificial seeds containing high levels of r-chagasin (0.5-30 g kg(-1)) completely inhibited larval penetration. CONCLUSION: Together, the results reported in this paper support the hypothesis that the inhibitory activity of r-chagasin towards the major insect gut cysteine proteinase in vitro and in vivo is an accurate prediction of its insecticidal effects. The selectivity of this inhibitor against insect digestive proteinases supports the key role in parasite virulence by affecting the endogenous proteinase activity in its natural host. 相似文献
273.
Laureano RG Lazo YO Linares JC Luque A Martínez F Seco JI Merino J 《Tree physiology》2008,28(11):1721-1728
We tested whether growth and maintenance costs of plant organs vary with environmental stress. Quercus ilex L. seedlings from acorns collected from natural populations in the northern Iberian Peninsula and in a lower elevation and putatively less stressful habitat in the southern Iberian Peninsula were grown in pots under the same conditions. Growth and maintenance respiration were measured by CO(2) exchange. Young leaves from 5-month-old seedlings of both populations had similar mean specific leaf areas, nitrogen and carbon concentrations and specific growth rates, and almost identical growth costs (1.26 g glucose g(-1)). Leaf maintenance cost was higher in northern than in the southern population (27.3 versus 22.4 mg glucose g(-1) day(-1), P < 0.01). In both populations, leaf maintenance cost decreased by 90% as leaves aged, but even in mature leaves, the maintenance cost was higher in the northern population than in the southern population (3.38 versus 2.53 mg glucose g(-1) day(-1), P < 0.01). The growth costs of fine roots < 1 mm in diameter were similar in the two populations (1.20 g glucose g(-1)), whereas fine root maintenance cost was higher in the northern population than in the southern population (9.86 versus 7.45 mg glucose g(-1) day(-1); P < 0.05). The results suggest that the cost of organ maintenance is related to the severity of environmental stress in the native habitat. Because the observed differences in both leaves and roots were constitutive, the two populations may be considered ecotypes. 相似文献
274.
The effect of warm storage (15°C) for 0, 15 or 31 days, applied after cold storage until April, and date of lifting to cold
storage on the physiological condition and field performance of two-year-old oak seedlings (Quercus robur L.) was investigated. Assessments before planting included plant moisture status, root and shoot dry weight, root growth
potential (RGP), while after planting root growth, shoot growth phenology, shoot and root dry matter accumulation and stem
quality were assessed. Warm storage effects were large, but lift date effects were small. Warm storage for 31 days reduced
height and diameter growth, stem quality, total biomass, root growth, and reduced stem quality in the field, but 15 days storage
had a smaller effect. Warm storage delayed bud break and shoot growth cessation but survival was unaffected. The depletion
of food reserves during storage and low moisture availability might have caused shoot dieback leading to the development of
poor quality stems. There was evidence that dry weight fraction of both the shoot tip and the taproot provided good information
on the quality of the stock before planting. RGP was also a good indicator of quality. Electrolyte leakage readings from fine
and taproots were not reliable indicators of plant quality. 相似文献
275.
We evaluate the ecological sustainability of extracting the oleoresin of Copaifera multijuga Hayne and some factors influential in its production. We monitored oleoresin production after initial extraction in 43 mother trees in the Adolpho Ducke Forest Reserve, near Manaus, Brazil (2°57′43″ S, 59°55′38″ W). We evaluated production relative to tree diameter (DBH), collection interval, soil clay content, competition intensity, and termite infestation. 57% of productive trees had DBH ≥ 41 cm and were responsible for 95% of total production. Although these trees had the highest initial production, after one year only 28% of initial oleoresin production was recuperated, much slower than in trees with DBH < 41 cm. Production was positively correlated with DBH and dominance within mother tree. Oleoresin production varied slightly with season. Trees that never produced oleoresin did not have termite infestations. 相似文献
276.
Eva Pose‐Juan Marcos Paradelo‐Pérez Raquel Rial‐Otero Jesus Simal‐Gándara José E López‐Periago 《Pest management science》2009,65(6):615-623
BACKGROUND: Flow shear stress induced by rainfall promotes the loss of the pesticides sprayed on crops. Some of the factors influencing the losses of colloidal‐size particulate fungicides are quantified by using a rotating shear system model. With this device it was possible to analyse the flow shear influencing washoff of a commercial fungicide formulation based on a copper oxychloride–metalaxyl mixture that was sprayed on a polypropylene surface. A factor plan with four variables, i.e. water speed and volume (both variables determining flow boundary stress in the shear device), formulation dosage and drying temperature, was set up to monitor colloid detachment. RESULTS: This experimental design, together with sorption experiments of metalaxyl on copper oxychloride, and the study of the dynamics of metalaxyl and copper oxychloride washoff, made it possible to prove that metalaxyl washoff from a polypropylene surface is controlled by transport in solution, whereas that of copper oxychloride occurs by particle detachment and transport of particles. Average losses for metalaxyl and copper oxychloride were, respectively, 29 and 50% of the quantity applied at the usual recommended dosage for crops. CONCLUSION: The key factors affecting losses were flow shear and the applied dosage. Empirical models using these factors provided good estimates of the percentage of fungicide loss. From the factor analysis, the main mechanism for metalaxyl loss induced by a shallow water flow is solubilisation, whereas copper loss is controlled by erosion of copper oxychloride particles. Copyright © 2009 Society of Chemical Industry 相似文献
277.
Lucélia Tessaro Cesar Pereira Rebechi de Toledo Giovano Neumann Ricardo Andrei Krause Fábio Meurer Maria Raquel Marçal Natali Robie Allan Bombardelli 《Aquaculture Research》2014,45(9):1425-1433
This study was conducted to evaluate the effects of different diet energy levels on animal performance. Specifically, this investigation examined the reproductive and histological aspects of the liver and gonads of female silver catfish (Rhamdia quelen). These fish were fed for 210 days with diets containing 30% digestible protein (DP) and digestible energy (DE) that corresponded to 11.93, 12.98, 14.03, 15.07 and 16.12 MJ of DE kg?1. The initial and final lengths, weights, and weight gains, the visceral, gonadal, and hepatosomatic indices, and the histological parameters hepatocytes area and gonadal stages were evaluated. In the reproductive season, the fish were submitted to an artificial reproduction protocol and the percentage of spawning females and their relative and absolute fecundity were evaluated. DE did not affect reproductive or animal performance aspects (P > 0.05). Cytoplasmic vacuoles in hepatocytes were observed in higher DE levels. Thus, female Rhamdia quelen can be fed a diet of 30% DP with 11.93 MJ of DE kg?1 without reproductive or performance losses. 相似文献
278.
279.
Atmir Romero-Pérez Elizabeth García-García Araceli Zavaleta-Mancera J. Efren Ramírez-Bribiesca Alma Revilla-Vázquez Luz M. Hernández-Calva Raquel López-Arellano Rosy G. Cruz-Monterrosa 《Veterinary research communications》2010,34(1):71-79
Sodium selenite is used to prevent selenium deficiency known as nutritional muscular dystrophy or white muscle disease. In
ruminants, selenium supplements are transformed partiality in insoluble form by ruminal microorganisms and its process decrease
the selenium absorption in digestive gastrointestinal. However, the objective in this research was focused in encapsulated
sodium selenite to be release into of a pH less than four, similarity to an intestinal environment. It was encapsulated by
nanoprecipitation and emulsion–evaporation methods, within polymeric nanoparticles. The effect of these methods, polymer proportion
(Eudragit RL and RS) and solvent (ethanol and acetone) on the physicochemical (drug entrapment, polidispersity index (PDI)
and z potential) and morphological characteristics (particle morphology and particle size) were evaluated. Particle size from
each nanoparticles, formulation ranged from 36.64 to 213.86 nm. Particle size, z potential and PDI increased (P ≤ 0.01) when
nanoprecipitation and ethanol were used. No significant differences (P > 0.05) were observed when different polymeric proportions
were used. Selenium entrapment was 26% when emulsion–evaporation method was used and 78% with nanoprecipitation. Nanoparticles
produced by nanoprecipitation were spherical and had a great variation in particle size; on the other hand, nanoparticles
produced by emulsion–evaporation were spherical as well as amorphous and presented a homogeneous nanopartcicle size distribution.
The release of selenium from nanoparticles was higher in acid pH (less than 4), this condition may represent a better availability
of the mineral in the small intestine. 相似文献
280.