全文获取类型
收费全文 | 363篇 |
免费 | 14篇 |
国内免费 | 5篇 |
专业分类
林业 | 10篇 |
农学 | 6篇 |
47篇 | |
综合类 | 52篇 |
农作物 | 29篇 |
水产渔业 | 26篇 |
畜牧兽医 | 172篇 |
园艺 | 4篇 |
植物保护 | 36篇 |
出版年
2019年 | 4篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 19篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2002年 | 3篇 |
2001年 | 3篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1965年 | 3篇 |
1963年 | 6篇 |
1961年 | 3篇 |
1960年 | 3篇 |
1958年 | 10篇 |
1957年 | 6篇 |
1956年 | 9篇 |
1955年 | 4篇 |
1954年 | 6篇 |
1953年 | 6篇 |
排序方式: 共有382条查询结果,搜索用时 390 毫秒
241.
Leaf age structure and canopy photosynthesis in rotationally and continuously grazed swards 总被引:2,自引:0,他引:2
The leafage structure of ryegrass canopies and its role in canopy photosynthesis were compared under continuous and rotational grazing by sheep. Under continuous grazing, an increase in the intensity of grazing increased the proportion (by leaf area) of young leaves in the sward. A mechanistic mathematical model was used to demonstrate how this may have arisen, even though it would largely have been the young leaves that were eaten.
However, the observations do not confirm the hypothesis that continuously grazed swards have a characteristically greater proportion of young leaves, and so a greater photosynthetic potential, than rotationally grazed ones. The proportion of young leaves increased during regrowth following severe rotational grazing (residual LAI < 05) and the photosynthetic potential of the canopy became greater than under continuous grazing.
A model of canopy photosynthesis was used to demonstrate that the observed difference in the proportion of young leaves alone was unlikely to account for all the differences in canopy photosynthesis between managements, and further differences in canopy structure were evaluated. Despite the delay in the restoration of leaf area following severe grazing in a rotation, the total photosynthetic uptake of a system involving some 12–13 days regrowth and 3 days grazing exceeded that of a well-utilized continuously grazed sward. Re growths of longer duration led to progressively greater total photosynthetic uptake, though this was not considered synonymous with greater yield. 相似文献
However, the observations do not confirm the hypothesis that continuously grazed swards have a characteristically greater proportion of young leaves, and so a greater photosynthetic potential, than rotationally grazed ones. The proportion of young leaves increased during regrowth following severe rotational grazing (residual LAI < 05) and the photosynthetic potential of the canopy became greater than under continuous grazing.
A model of canopy photosynthesis was used to demonstrate that the observed difference in the proportion of young leaves alone was unlikely to account for all the differences in canopy photosynthesis between managements, and further differences in canopy structure were evaluated. Despite the delay in the restoration of leaf area following severe grazing in a rotation, the total photosynthetic uptake of a system involving some 12–13 days regrowth and 3 days grazing exceeded that of a well-utilized continuously grazed sward. Re growths of longer duration led to progressively greater total photosynthetic uptake, though this was not considered synonymous with greater yield. 相似文献
242.
Objective: To determine the efficacy of a novel copper based footbath preparation (CHF-1020) for treatment of ovine footrot during the spread period.
Design: A series of field trials with treated and control groups run together.
Animals: Mobs of at least 125 sheep on each of six properties in southern New South Wales with equal numbers of controls.
Procedure: Sheep of group A were treated after minimal paring by making them stand in CHF-1020 for 15 minutes. Treatment was undertaken at intervals throughout the period of the trials (14 September to 17 December 1993). Group A sheep were run on the same pasture as those from group B (untreated sheep).
Results: The percentage of sheep exhibiting clinical signs of ovine footrot at the start of the trial ranged from 35 to 88% at score 3 or higher, using a 0 to 5 footscoring system. During the trial, the percentage of infected sheep (greater or equal to score 2) in group B increased and ranged from 40 to 90%. The level of infected sheep in group A on each property was reduced progressively to 1 to 16%. Cure rates of 45 to 94% were achieved, with the lowest rate being on a property with a metal footbath. The next lowest cure rate was 73%. Results indicated that treatment should be undertaken at 2-weekly intervals while spread continues. Treated sheep can be returned to contaminated pastures.
Conclusion: CHF-1020 is effective during the spread period and can be used for the progressive eradication of ovine footrot. 相似文献
Design: A series of field trials with treated and control groups run together.
Animals: Mobs of at least 125 sheep on each of six properties in southern New South Wales with equal numbers of controls.
Procedure: Sheep of group A were treated after minimal paring by making them stand in CHF-1020 for 15 minutes. Treatment was undertaken at intervals throughout the period of the trials (14 September to 17 December 1993). Group A sheep were run on the same pasture as those from group B (untreated sheep).
Results: The percentage of sheep exhibiting clinical signs of ovine footrot at the start of the trial ranged from 35 to 88% at score 3 or higher, using a 0 to 5 footscoring system. During the trial, the percentage of infected sheep (greater or equal to score 2) in group B increased and ranged from 40 to 90%. The level of infected sheep in group A on each property was reduced progressively to 1 to 16%. Cure rates of 45 to 94% were achieved, with the lowest rate being on a property with a metal footbath. The next lowest cure rate was 73%. Results indicated that treatment should be undertaken at 2-weekly intervals while spread continues. Treated sheep can be returned to contaminated pastures.
Conclusion: CHF-1020 is effective during the spread period and can be used for the progressive eradication of ovine footrot. 相似文献
243.
244.
高微 《湖南农业大学学报(自然科学版)》2009,(2)
从音乐本身出发,从琵琶音乐语言和琵琶音乐表达的技术手段两方面对琵琶音乐语言的表现力作出作者自身的理解.琵琶音乐语言的表现力是多元性的,可以从琵琶音乐语言特性的界定以及琵琶音乐表达的技术手段来了解. 相似文献
245.
Effective conservation and management of natural resources requires accurate predictions of ecosystem responses to future climate change, but environmental science has largely failed to produce these reliable forecasts. The future response of Pacific salmon (Oncorhynchus spp.) to a changing environment and continued anthropogenic disturbance is of particular interest to the public because of their high economic, social, and cultural value. While numerous retrospective analyses show a strong correlation between past changes in the ocean environment and salmon production within the north Pacific, these correlations rarely make good predictions. Using a Bayesian time-series model to make successive 1-yr-ahead forecasts, we predicted changes in the ocean survival of Snake River spring/summer chinook salmon (O. tshawytscha) from indices of coastal ocean upwelling with a high degree of certainty (R2 = 0.71). Furthermore, another form of the dynamic times-series model that used all of the available data indicated an even stronger coupling between smolt-to-adult survival and ocean upwelling in the spring and fall (R2 = 0.96). This suggests that management policies directed at conserving this threatened stock of salmon need to explicitly address the important role of the ocean in driving future salmon survival. 相似文献
246.
DJ HARRIS CD HIBBURT† GA ANDERSON‡ PJ YOUNIS† DH FITSPATRICK§ AC DUNN¶ IW PARSONS NR McBEATH 《Australian veterinary journal》1988,65(6):171-176
A survey of 73 dairy farms in south-western Victoria was conducted to assess the cost and mean herd incidence of foot lameness for the period from calving to the end of November, 1985, and to identify the herd, management and environmental factors associated with foot lameness. The mean herd size was 125 cows (range 82 to 220). Lameness occurred in 64 (88%) herds, and the mean herd incidence was 7.0% (range 0.0 to 30.9%). The main clinical signs associated with lameness were the presence of overworn and/or bruised soles, or stones lodged in the interdigital cleft. Factors associated with lameness were: property and herd size, age of cow, bail feeding, voluntary entry into the bails, and features of the farm track including its length, the presence of steep slopes, the type of surface material, presence and treatment of broken sections and maintenance including rolling history. The association of these factors with specific clinical signs was examined. The mean cost was estimated to be $42.90 per lame cow due to loss of production, treatment, the culling or death of lame cows, and extra man hours spent managing lame cows. It was concluded that the site, construction, maintenance and use of the farm track were of major importance to the incidence of lameness in herds in this area and recommendations for reducing lameness are made. 相似文献
247.
248.
A Retrospective Comparison of Three Techniques for Femoral Head and Neck Excision in Dogs 总被引:1,自引:0,他引:1
R. D. MONTGOMERY DVM MS J. L. MILTON DVM MS R. D. HORNE DVM MS R. H. COBLE JR. DVM J. C. WILLIAMS PhD 《Veterinary surgery : VS》1987,16(6):423-426
Femoral head and neck excision was performed in 169 dogs over a 7 year period. A written questionnaire completed by 56 owners, evaluating a total of 72 joints, was the basis for retrospective evaluation of the efficacy of the procedures used. There were four surgical groups: femoral head and neck excision (FHNE) in dogs with body weights over 14 kg, the same procedure in dogs with body weights less than 14 kg (SMALL), femoral head and neck excision with muscle interposition (MI), and the wedge resection technique (WRT). Although differences in results were noted, there were no statistically significant differences between any of the groups for the percentage of leg use during normal activity (p greater than 0.05), mean postoperative time until leg use, use of the leg or hopping while running, or lameness with exercise (p greater than 0.10). The results of this study suggest that there is little advantage in performing the more time-consuming and traumatic muscle interposition and wedge resection procedures. 相似文献
249.
J. WESLEY WILLIAMS DVM MS JOHN R. PASCOE BVSC PhD DENNIS M. MEAGHER DVM PhD DiplomateACVs WILLIAM J. HORNOF DVM MS DiplomateACVR 《Veterinary surgery : VS》1990,19(2):136-141
Upper airway pressure was measured with a nasotracheal catheter system and a portable pressure transducer in 10 normal horses during maximal exercise before and after left recurrent laryngeal neurectomy. Measurements were repeated 16 weeks after prosthetic laryngoplasty (5 horses) or subtotal arytenoidectomy (5 horses). During maximal exertion, prosthetic laryngoplasty was more effective than subtotal arytenoidectomy in reversing the increases in upper airway pressure that followed left recurrent laryngeal neurectomy. 相似文献
250.
E. D. WILLIAMS 《Grass and Forage Science》1985,40(4):479-483
Results are presented after 14 and 19 years of the botanical composition and seed bank of moderately fertilized or unfertilized grazed paddocks. Agrostis capillaris, Festuca rubra and broad-leaved weeds contributed a larger proportion of the cover on unfertilized than on fertilized swards. In contrast Poa spp., Holcus lanatus, Alopecurus pratensis and Lolium perenne were relatively more abundant on the fertilized than on the unfertilized swards. A. capillaris was the most plentiful grass in the seed bank of the unfertilized swards but Poa spp. (especially P. annua) in that of the fertilized swards. Some of the relationships between the seed bank and vegetative cover are discussed and the possibility of further increasing the contribution of L. perenne highlighted. 相似文献