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- 1. Lake Habitat Survey (LHS) provides a standard method for characterizing the physical habitat of lakes and reservoirs, but has not been tested for its relevance to the composition and abundance of macroinvertebrates. This study investigated the relationship between the metrics used in LHS and components of macroinvertebrate communities found in the littoral zone of a shallow calcareous lake in the west of Ireland.
- 2. A scoring system, the Habitat Quality Assessment (HabQA), developed from the Lake Habitat Quality Assessment (LHQA) of the LHS, was used to assess the relationship between habitat quality based on physical structure within 10 LHS ‘habplots’ and metrics of the macroinvertebrate community.
- 3. Macroinvertebrate taxon richness, both of adults found in the riparian zone and larvae found in the littoral zone, correlated positively with the HabQA score. Macrophytes within the littoral zone, and complexity of riparian vegetation within the riparian zone, were particularly important in driving the HabQA score. While overall abundance of macroinvertebrates did not vary with HabQA score, that of particular genera did.
- 4. The HabQA score was a useful surrogate of taxon richness for adult and larval aquatic macroinvertebrates, suggesting that, in general, LHS provides a useful conservation assessment tool relevant for macroinvertebrates. However, in some circumstances, such as wave‐washed stony substrates devoid of macrophytes, the HabQA score may not capture the quality of a site for macroinvertebrates, and the importance of natural but low diversity sites should not be neglected in conservation assessment of lakes. Similarly, while the LHS method notes the presence of alien species, further work on how these could be incorporated into the method would be useful.
- 5. Reliance on a single, or overall combined, metric score across quality elements, whether based on biotic or structural assessment, has some potential limitations. It is clear that for conservation management a holistic assessment of naturalness, representativeness and species rarity needs to be made in conjunction with scoring systems.
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Nathalie Jarosz Yves Brunet Eric Lamaud Mark Irvine Jean-Marc Bonnefond Denis Loustau 《Agricultural and Forest Meteorology》2008,148(10):1508-1523
Carbon dioxide, water vapour and energy fluxes were measured above and within a maritime pine forest during an atypical year with long-lasting reduced soil water availability. Energy balance closure was adequately good at both levels. As compared with what is usually observed at this site the ecosystem dissipated less energy via latent heat flux and more via sensible heat flux. The understorey canopy was responsible for a variable, significant component of the whole canopy fluxes of water vapour and carbon dioxide. The annual contribution of the understorey was 38% (154 mm) of the overall evaporation (399 mm) and 32% (89 mm) of the overall sensible heat flux (274 mm). The participation of the understorey reached 45% of the overall evaporation and 30% of the daytime overall assimilation during significant soil water deficit periods in summertime. Even during winter, understorey photosynthesis was consistent as it compensated soil and understorey respiration. The ecosystem behaved as a sink of carbon, with a negative annual carbon budget (−57 g C m−2). However, due to high soil water deficit, the annual ecosystem GPP was 40% less than usually observed at this site. This budget resulted from a sink of −131 g C m−2 for the overstorey and a source of +74 g C m−2 for the understorey. Moreover, on an annual basis the overstorey layer contributed to almost two-thirds of the ecosystem respiration. Finally, the effect of long-lasting soil water deficit on the maritime pine forest was found more important than the effect of the heat wave and drought of summer 2003. 相似文献
84.
As part of a project to identify PCB sources in combined sewer overflows discharging to the Buffalo River, NY, nine street and two unpaved aggregate parking lot dust and dirt samples were collected and analyzed for selected PCB congeners and total PCBs. Without exception, the dust and dirt samples had greater concentrations associated with the higher-chlorinated homologue groups. PCB-congeners 153, 138, 101, 118, and 180 contributed >50% of the total PCBs mass in each sample, suggesting contamination with Aroclors 1254 and 1260. Total PCB concentrations for the dust and dirt samples ranged between 90 and 1700 ng g-1. Samples with the highest concentrations were located across the street and downwind from an industrial lot that had been remediated for PCB contamination in 1988. The industrial lot had been contaminated with Aroclors 1254 and 1260, indicating that contaminated soil had been locally redistributed through natural and vehicle-generated wind. Calculations based on the particle size of the street dust confirm the possibility of wind-induced redistribution. Street and aggregate lot dust and dirt potentially contribute to Buffalo River PCBs loadings through combined sewer overflows and stormwater runoff. Best management practices such as more frequent street sweeping may be useful in reducing these loadings. 相似文献
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Nitrogen fertilizer and urease inhibitor effects on canola seed quality in a one-pass seeding and fertilizing system 总被引:1,自引:0,他引:1
Cynthia A. Grant Doug A. Derksen Debra L. McLaren R. Byron Irvine 《Field Crops Research》2011,121(2):201-208
Field studies were conducted over three years on a clay loam (CL) and fine sandy loam (FSL) soil on the eastern Canadian prairies to evaluate the impact of urea and urea ammonium nitrate (UAN), with or without the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), placed near the seed-row in a one-pass seeding and fertilizing operation on seed protein, oil, chlorophyll and glucosinolate content of canola (Brassica napus L.). Application of N fertilizer as a side-band application at the time of seeding increased protein concentration and decreased oil concentration. Protein and oil yield increased with low to moderate N rates, but stabilized or fell with high N rates due to reductions in yield from seedling toxicity. Both chlorophyll and glucosinolate concentrations increased with increasing N rates. Use of UAN led to higher protein, chlorophyll and glucosinolate and lower oil concentration than urea on the CL soil. Use of the urease inhibitor NBPT generally increased oil concentration on both soils and reduced the chlorophyll and glucosinolate concentration on the CL soil. Observed difference may have been due to delayed maturity and reduced stand density caused by seedling damage and high N rates. High N rates applied as a side-band of urea or UAN near the canola seed row can negatively influence both seed yield and quality in canola and the negative effects may be reduced by the use of the urease inhibitor NBPT. 相似文献
87.
We investigated the effect of drought on canopy stomatal conductance (g(c)), and examined the hypothesis that g(c) is controlled by the chemical messenger abscisic acid (ABA) produced in roots. Beginning in November 1994, we subjected a mature stand of Scots pine (Pinus sylvestris L.) to an imposed 11-month drought. Control plots were maintained at average-season soil water content. Xylem sap was extracted from shoots at regular intervals from April to November 1995. Soil water, sap flow and leaf water potentials (predawn to dusk) were recorded at the same time. Canopy stomatal conductance was calculated from sap flow data and xylem sap ABA concentrations ([ABA(xyl)]) were measured by radioimmunoassay. Mean [ABA(xyl)] in control trees was 250 micromol m(-3). No diurnal variation in [ABA(xyl)] was detected. With soil drying, [ABA(xyl)] increased to a maximum in summer (600 micromol m(-3)), but decreased again toward autumn; however, no significant increase in ABA flux to the leaves occurred. A decline in g(c) was detected when volumetric soil water content declined below 0.12. The decline in g(c) could not have been mediated by increasing [ABA(xyl)] because stomatal closure appeared to precede any increase in [ABA(xyl)]. Peak sap flow velocity data were used to estimate delivery times for root-to-shoot signals in 15-m tall trees. Under normal field conditions, a signal would take 12 days to travel from the site of production (roots) to the presumed site of action (shoots). However, under drought conditions it may take a chemical signal in excess of 6 weeks. We conclude that a feedforward model of short-term stomatal response to soil drying, based solely on the action of a chemical messenger from the roots, is not applicable in mature conifer trees because signal transmission is too slow. 相似文献
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