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1.
2.
Harald Köthe 《Journal of Soils and Sediments》2006,6(2):75-83
Background Under anoxic conditions typically prevailing in disposal sites for dredged sediment, methanogenesis is the terminal step
during microbial degradation of sediment organic matter. Sediment gas production may pose several problems to site management
and post-closure utilisation. Depending on the magnitude of gas/methane formation and the intended utilisation of the site,
countermeasures will have to be effected during and after deposition of the dredged material. For this purpose it may be of
interest to pre-estimate the extent of gas formation from simple sediment variables. Therefore, the aim of the investigations
presented here was to analyse the interrelations between gas formation and sediment physical, chemical and biological qualities.
Methods Freshly sampled riverbed sediment from nine German federal waterways was analysed for standard solid physical and chemical
parameters, pore water composition, cell counts of methanogenic and sulfate-reducing bacteria, and gas formation over a period
of 500 days. Particle size and density fractionation were carried out in order to characterise organic matter quality. Correlations
between methane formation and sediment chemical, physical and microbiological characteristics were tested using linear and
multiple correlation analysis.
Results and Discussion The selected sediments, including two with marine influence, differed strongly regarding texture, chemical parameters, pore
water composition, and methanogen cell counts. The course of methane formation was found to follow distinct phases. The commencement
of methane formation was preceded by a lag phase of variable duration. The lag phase was followed by a strong increase of
the methane formation rate up to a sediment-characteristic maximum of 5–30 nmol CH4 h–1 g dw–1. Eventually, the rate of methane
formation decreased and reached a more stable, long-term level. The extent and amplitude of each phase varied strongly between
sediments and could be correlated well with only a few standard analytical parameters, despite the strong heterogeneity of
sediment with respect to chemical, physical, and biological characteristics. Lag phase duration depended strongly on the content
of inorganic electron acceptors and also on the number of methanogens present at the beginning of the experiment. Maximum
and steady state methanogenesis were mainly determined by sediment total nitrogen. As analysis of sediment density fractions
revealed that total nitrogen reflected the share of readily degradable macroorganic matter.
Conclusion and Outlook The results imply that the observed methane formation is a function of the temporally changing balance of the availability
of electron acceptors and H2, and the share of easily degradable organic matter. For fresh riverbed sediments, the latter
may be deduced from total nitrogen content. Overall, the results showed that methane formation by freshly dredged material
may well be pre-estimated from standard analytical data within the first few years of deposition. However, the differently
degradable organic matter pools will change over time with respect to size, chemical nature and association with the sediment
mineral phase. It can thus be expected that the correlations found in this study will not be readily transferable to older
materials. Further studies on the gas formation and organic matter quality by older sediments, e.g. from older dredged material
disposal sites of known age, should be conducted and results should be combined with existing organic matter degradation models
in order to improve the prediction of sediment gas formation over time. 相似文献
3.
Predicting the temperature of the Barents Sea 总被引:4,自引:0,他引:4
Knowledge of the influence of the physical environment on commercially important fish stocks in the North Atlantic has increased during the last decade. To allow this information to be used in fisheries management, some forecast of the environment is important. Predictions of temperature in the Arcto-boreal Barents Sea have been given for many years, both as subjective opinions of scientists and implicitly in stock assessment assumptions of, e.g., mortality rates. To evaluate an objective statistical forecasting system, we have analysed time series representing mechanisms previously proposed as influencing the temperature of the Barents Sea. These include components of suggested periodic nature, large-scale advective effects, regional processes, and atmospheric teleconnections. The predictability of Barents Sea temperature based on the above mechanisms was evaluated through calculations of auto- and cross-correlations, linear regression, spectral analysis and autoregressive modelling. Forecasts based on periodic fluctuations in temperature performed poorly. Advection alone did not explain a major part of the variability. The precision of predictions six months ahead varied with season; forecasts from spring to autumn had least uncertainty. A first-order autoregressive model, including modelled atmospherically driven volume flux to the western Barents Sea during the preceding year and the position of the Gulf Stream off the eastern coast of the USA two years earlier, explained 50% of the total historical temperature variability. 相似文献
4.
5.
Cheng-Fang Hong Marin T. Brewer Phillip M. Brannen Harald Scherm 《Plant pathology》2020,69(9):1721-1730
The North Georgia Mountains are the southernmost region along the United States East Coast where European wine grapes (Vitis vinifera) are grown commercially. Epidemics of downy mildew, caused by Plasmopara viticola, are frequent and severe, but little is known about the epidemiology and population biology of the pathogen in this region. Disease monitoring in an experimental vineyard from 2015 to 2017 indicated that times of disease onset and progress rates were highly variable across years and cultivars. Oospores were observed microscopically, and simulation with a process-based model indicated presence of conditions favourable for oospore germination in the spring and early summer each year. A total of 409 P. viticola isolates collected over three years were genotyped with seven microsatellite markers, revealing very high genotypic diversity, which when combined with the observation of oospores is indicative of a sexually reproducing population. Among the 409 isolates, 225 multilocus genotypes (MLGs) were identified, of which 164 were detected only once and 61 were repeated (clonal). Eight MLGs (represented by 28 isolates) were detected across years, suggesting the possibility of asexual overwintering of P. viticola in this region. Across sampling dates, the percentage of isolates belonging to nonrepeated (unique) MLGs ranged from 27.3% to 63.2%. Even towards the end of the annual epidemic, the percentage of isolates in nonrepeated MLGs was still relatively high, around 30%. These MLGs may have originated from oospores germinating late during the growing season, although incomplete sampling at earlier dates and contribution by immigration cannot be fully excluded. 相似文献
6.
The effect of spraying winter rape and winter wheat with deltamethrin on the numbers of epigeal Carabidae, Staphylinidae and Linyphiidae caught in pitfall traps was studied in Northern Germany in 1980 and 1981. Two experiments were performed with each crop, deltamethrin being sprayed at 7.5 g a.i. ha?1 in 300 litres of water in springtime on rape, and in midsummer on wheat. Sprayed plots were rectangles of 2 and 3 ha; unsprayed plots were squares of 0.5 ha each (two replicates). Ten pitfall traps were placed per replicate at least 3 weeks before spraying and were left for at least 3 weeks after spraying, the traps being emptied weekly. Beneficial Carabid species which have been shown already to have an economic significance, were rare during this study, but four other species (three of them were autumn breeders) were not affected by deltamethrin. At the spraying dates the autumn breeders were hidden in the soil as pupae. Three Staphylinid species, studied in only one experiment each, appeared to be strongly reduced in numbers by deltamethrin. The Linyphiid spiders were affected most heavily by deltamethrin sprayed in spring or in midsummer; the initial mortality of more than 92% lasted longer than 4 weeks, and an adverse effect was still significant in winter wheat 6 weeks after spraying. Overall, deltamethrin appears to have a broad spectrum effect concerning the epigeal predatory arthropods. 相似文献
7.
Angular deformities of 25 or 37 degrees valgus were created by transverse wedge osteotomies in the diaphysis of the radius in 3-month-old Cocker Spaniels. Spontaneous correction was judged from radiographs until skeletal maturity. The magnitude of correction was estimated, using the opposite normal leg as a control. Asymmetrical physeal growth corrected the induced angulation between the proximal and distal radial joint plane surfaces (joint plane angle). The average correction of the joint plane angle was 80% in the 25 degree group, and 72% in the 37 degree group. Bone remodeling of the radial shaft corrected the induced diaphyseal angulation by 50% in both groups during the study. 相似文献
8.
Studies on carbohydrate digestion in rainbow trout 总被引:5,自引:0,他引:5
Trout are poor starch digesters. The reason for the different digestibilities of carbohydrates were investigated and discussed. The inclusion of soluble starch products in the diet increases the volume of intestinal juices. Crude starch in the diet reduces amylase activity, amylase is adsorbed to crude starch so that starch hydrolysis is inhibited. Crude starch accelerates the passage through the intestine, thus reducing the time available for absorption. 相似文献
9.
Rabbit-fish, Siganus oramin, reared in a closed seawater system on an artificial diet, were brought to maturity and spawned artifically after human chorionic gonadotropin (HCG) injections. Eggs were incubated under different salinity regimes. Hatching success between 20.9 and 32.2‰ S was ≥95%. 相似文献
10.