首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   61篇
  免费   2篇
林业   1篇
  15篇
综合类   3篇
农作物   4篇
水产渔业   30篇
畜牧兽医   8篇
园艺   2篇
  2023年   1篇
  2022年   1篇
  2020年   4篇
  2019年   2篇
  2018年   1篇
  2016年   1篇
  2015年   2篇
  2014年   3篇
  2013年   11篇
  2010年   2篇
  2009年   3篇
  2008年   1篇
  2007年   2篇
  2006年   3篇
  2005年   1篇
  2003年   3篇
  2002年   1篇
  1997年   1篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   4篇
  1989年   1篇
  1987年   2篇
  1985年   3篇
  1984年   1篇
  1978年   1篇
排序方式: 共有63条查询结果,搜索用时 15 毫秒
11.
The threat posed by invasive alien species to global crop production and biodiversity is recognized as one of the major drivers of global change today. Here we report on a successful implementation and operational use of new technology to support risk- and crisis management in the case of fighting an invasive plant disease. The open geospatial standards Web Feature Service Transaction (WFS-T) was implemented in software for GPS-enabled mobile phones communicating with a GeoServer backend in order to track down and eradicate disease outbreaks and susceptible host plants. This new technology offering georeferenced events online from field provides new possibilities for real time action in risk and crisis management.  相似文献   
12.
Abstract

Temporal changes in the scores of selected soil fertility indices were studied over six years in three different cases of organic crop rotation located in southern, eastern and central Norway. The cropping history and the initial scores of fertility indices prior to conversion to organic cropping differed between the sites. Crop yields, regarded as an overall, integrating fertility indicator, were in all rotations highly variable with few consistent temporal trends following the first year after conversion. On the site in eastern Norway, where conversion followed several years of all-arable crop rotations, earthworm number and biomass and soil physical properties improved, whereas the system was apparently degrading with regard to P and K trade balances and contents in soil. On the other two sites, the picture was less clear. On the southern site, which had a relatively fertile soil before conversion, the contents of soil organic matter and K decreased during the six-year period, but the scores of other fertility indices showed no trends. On the site in central Norway, there were positive trends for earthworm-related indices such as worm biomass and tubular biopores, and negative trends for soil porosity. The results, especially those from the eastern site, illustrate the general difficulty in drawing conclusions about overall fertility or sustainability when partial indicators show divergent trends. Consequently, the study gave no unambiguous support to the initial working hypothesis that organic farming increases inherent overall soil fertility, but rather showed that the effect varied among indicators and depended on status of the cases at conversion. It is concluded that indicators are probably better used as tools to learn about and improve system components than as absolute measures of sustainability.  相似文献   
13.
Abstract

In order to improve the basis for utilizing white clover (Trifolium repens L) in northern agriculture, we studied the effects of defoliation intensity on spring growth in a sub-arctic climate in relation to carbohydrate and nodule status. White clover plants (cv Snowy) were studied in a pot experiment in the field on the coast of northern Norway from spring 2001 until spring 2002. The experiment was repeated with some modifications from spring 2002 until spring 2003. During the growing season from summer to autumn, the plants were totally stripped of leaves down to the stolon, cut at four or seven cm height or left undisturbed. The plants were sampled destructively in autumn, early spring and late spring and sorted into leaves, stolons and roots. The plant material was weighed and analysed for carbohydrate reserves and nodule number. Defoliation during the growing season resulted in reduced concentration of reserve carbohydrates in autumn and reduced winter survival of the stolons. The most severe defoliation treatment reduced the herbage growth in spring. In contrast, the two milder defoliation treatments had no effect on herbage growth during spring or on total plant dry matter and nodule status in late spring. In conclusion, moderate defoliation during the growing season had no effect on herbage growth the following spring nor on carbohydrate, nodule or dry matter status of the plant in late spring. Moderate defoliation increased spring growth and thereby also the nitrogen demand of the plants. This probably enhanced nodule formation and development of inactive to active nodules.  相似文献   
14.
The effect of variations in pH and salt concentration on the absorption by rainbow trout of sulphonamides from water was investigated. Two trials were carried out: 1) Absorption from fresh water of sulphanilamide (pKa 10.4) and sulphadimidine (pKa 7.4) at pH 4, 6, 8 and 10 over a period of 96 hrs., and 2) Absorption from fresh water and sea water (salinity approx. 31 ‰) of the same two sulphonamides at pH 6 and 8 over a period of 24 hrs. The degree of acetylation of the two sulphonamides in rainbow trout was investigated.  相似文献   
15.
In two container experiments, we evaluated mixtures of crushed rock, forest soil, and sewage sludge for use as growth media in green areas. We applied two types of crushed rock (0–2 mm fraction), two forest soils (sandy loam), and limed sewage sludge (pH 10), and studied the growth of ryegrass (Lolium multiflorum var. westervoldicum) during one growing season.Including ≥0.2 m3 m−3 sewage sludge in the soil mixtures initially inhibited growth, presumably due to toxic levels of ammonium-N. Up to 0.25 m3 m−3 sludge increased the total yield of ryegrass, but at a level as low as 0.1 m3 m−3, more nutrients were available than could be taken up by the crop. At present, up to 0.3 m3 m−3 sewage sludge is allowed in soil mixtures used in green areas in Norway, although that level should probably be lowered due to the risk of abnormal (enhanced or inhibited) plant growth, and leaching of nutrients. We recommend a maximum of 0.1 m3 m−3 when applying the kind of sludge used in our experiments.All mixtures containing acid forest soil gave better results than those comprising slightly alkaline forest soil. The best mixture for ryegrass was crushed rock and acid forest soil at a ratio of 1:2. Compared to pure acid forest soil ryegrass grew equally well or better on mixtures containing ≥0.50 m3 m−3 acid forest soil. The differences in growth between the various soil mixtures were due to texture and physical properties, and to dissimilarities in the effects of sewage sludge on mineralisation of nitrogen in the mixtures comprising acid and slightly alkaline forest soil.  相似文献   
16.
Visual and chemical determinations revealed that the individual optical isomers of astaxanthin were more efficacious than canthaxanthin in pigmenting the flesh of rainbow trout (Salmo gairdneri, Richardson). The visual assessment of the astaxanthin pigmentation by means of a colour scale correlated well with the chemical determination. The same utilization was found for all three astaxanthin isomers, (3S, 3′S)-, (3R, 3′S)-, (3R, 3′R)-astaxanthin and a 1 : 2 : 1 mixture of the three isomers.No epimerization took place at the chiral centres of C-3 and C-3′ in astaxanthin. Astaxanthin and canthaxanthin were not interconverted. No metabolites were detected in the flesh.  相似文献   
17.
Data from the Norwegian progeny testing program were used to examine the impact of milking characteristics and morphology of udder and teats on clinical mastitis in first- and second-lactation Norwegian cattle. The study was designed as a 1-1 matched case-control study with herd, parity, days in lactation and calving season as matching variables. Conditional maximum likelihood logistic regression was used to evaluate the effects of three primary (2 min milk, milk leakage and teat-end-to-floor distance) and six other study variables. Treatment records from the Norwegian health card system on acute and chronic clinical mastitis were used to define cases. The chosen model included 565 matched pairs. Significant risk factors of clinical mastitis were decreasing teat-end-to-floor distance (P = 0.02) and periparturient udder edema (P < 0.01).

Borderline effects were demonstrated by larger than herd-average teat diameter (P = 0.04), udder asymmetry (P = 0.05) and increasing 2 min milk (P = 0.08). Results were compared to a previous study on the same data with loge somatic cell count as the dependent variable. Inclusion of teat-end-to-floor distance in the genetic improvement scheme may increase the efficiency of genetic selection for mastitis resistance.  相似文献   

18.
19.
A mannose-terminated glycoprotein,125I-invertase, was taken up and degraded by isolated rainbow trout liver cells at 12°C. The uptake was inhibited by EGTA and no degradation occurred in the presence of ammonium ions. The liver cell suspension was fractionated by differential centrifugation in parenchymal and nonparenchymal cells, respectively. The parenchymal liver cells seemed to be the most active cells in uptake of labelled invertase bothin vitro andin vivo. Only negligible amounts of ligand were recovered in the nonparenchymal cells. Internalization of125I-invertase at different temperatures was demonstrated indirectly by releasing surface-bound ligand with EGTA. Ligand was internalized even at 0°C in trout liver cells.In vitro uptake of125I-invertase was inhibited by excess unlabelled invertase, by mannan and by N-acetylglucosamine.These data suggest that invertase is endocytosed by a mannose-specific pathway by the parenchymal liver cells of rainbow trout.  相似文献   
20.
The spectral composition and intensity of light penetrating different parts of fresh preparations of the upper part of the skull of Atlantic salmon (Salmo salar) (fork length 25–30 cm) was investigated. All measurements were made in an aqueous medium, by moving the tip of an optical fibre in a three dimensional lattice below preparations that were illuminated by a parallel light source from above. The intensity of the transmitted light showed a well-defined maximum just below the pineal groove. Light that penetrated the skull from a source vertically above was refracted to produce a focusing point in the approximate position of the pineal body. Light projected from angles of 45° relative to the vertical position was only slightly (25%) attenuated, thus indicating a wide acceptance angle. There was an almost uniform transmission of light (of 3%) between 500 and 700 nm. The transmittance of UV light (350 nm) was about 10% of that of green light. These differences are small when compared with the intensity range reported for the pineal light receptors. The transmission properties are discussed in relation to the known diurnal changes in the spectral composition of natural light.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号