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   99篇
  免费   1篇
林业   14篇
农学   3篇
基础科学   1篇
  16篇
综合类   8篇
农作物   15篇
水产渔业   8篇
畜牧兽医   17篇
园艺   4篇
植物保护   14篇
  2023年   1篇
  2022年   3篇
  2021年   4篇
  2020年   3篇
  2019年   5篇
  2018年   11篇
  2017年   8篇
  2016年   5篇
  2015年   3篇
  2014年   4篇
  2013年   9篇
  2012年   4篇
  2011年   11篇
  2010年   7篇
  2009年   5篇
  2008年   7篇
  2007年   3篇
  2004年   2篇
  2002年   1篇
  1997年   1篇
  1991年   1篇
  1989年   2篇
排序方式: 共有100条查询结果,搜索用时 15 毫秒
61.
This investigation was conducted to evaluate the comparative productive performances and effect of some environmental factors on wool characteristics of Arkharmerino × Ghezel (Ar × Gh) and Arkharmerino × Moghani (Ar × Mo) crossbreed sheep. The mid-side fleece samples taken from animals during 2 years (2007–2008) were analyzed. Each sample was measured for average fiber diameter, fiber diameter variability, staple length, proportion of medullated fiber, proportion of kemp, and comfort factor. The comparative values for these fleece characteristics in F3 generation Ar × Gh were 28.78 ± 0.48 μm, 36.84 ± 1.16%, 11.94 ± 0.35 cm, 7.07 ± 0.93%, 1.02 ± 0.23%, and 68.93%, respectively; while those traits were 29.79 ± 0.43 μm, 41.86 ± 1.16%, 11.96 ± 0.37 cm, 8.13 ± 1.06%, 2.71 ± 0.45%, and 63.33 ± 3.66% for Ar × Mo, respectively. The effects of genotype, sex, birth type, and year of birth were analyzed. Genotype had a significant (P < 0.01) effect on average fiber diameter and proportion of kemp, and Ar × Gh crossbreeds had lower diameter with less proportion of kemp. The two differences in fiber characteristics that were attributable to sex were fiber diameter variability and proportion of medullated fiber, and females had higher measure than males for both traits. Statistical analysis showed that crossbreeding with Arkharmerino generally had positive effects on the fleece favored to be used in the hand woven authentic carpet production.  相似文献   
62.
This study shows how the air permeability of thermally modified wood contributes to its water-repellent efficiency. For this purpose, freshly cut boards of hornbeam(Carpinus betulus), poplar(Populus nigra), and heartwood of oak(Quercus castanifolia) were modified at a steam temperature of 180 °C for 3 h inside a Thermo Wood kiln.The porous structure, permeability, and water uptake of wood were affected differently by thermal modification,depending on the wood species. The creation of microcracks in the cell walls, due to collapsing of fiber cells,resulted in a noticeable increase in the permeability of hornbeam. Despite checking in the poplar wood structure,its permeability was negatively affected by thermal modification. In contrast to oak and poplar, a negative waterrepellent efficiency was observed for the modified hornbeam, caused by an increase in the permeability.  相似文献   
63.
Height–diameter relationships are essential elements of forest assessment and modeling efforts.In this work,two linear and eighteen nonlinear height–diameter equations were evaluated to find a local model for Oriental beech(Fagus orientalis Lipsky) in the Hyrcanian Forest in Iran.The predictive performance of these models was first assessed by different evaluation criteria: adjusted R~2(R~2_(adj)),root mean square error(RMSE),relative RMSE(%RMSE),bias,and relative bias(%bias) criteria.The best model was selected for use as the base mixed-effects model.Random parameters for test plots were estimated with different tree selection options.Results show that the Chapman–Richards model had better predictive ability in terms of adj R~2(0.81),RMSE(3.7 m),%RMSE(12.9),bias(0.8),%Bias(2.79) than the other models.Furthermore,the calibration response,based on a selection of four trees from the sample plots,resulted in a reduction percentage for bias and RMSE of about 1.6–2.7%.Our results indicate that the calibrated model produced the most accurate results.  相似文献   
64.
[目的]研究细茎石斛多糖的最佳提取条件及其抗氧化活性。[方法]通过单因素试验和响应面分析,研究细茎石斛多糖(DMP)的最佳提取条件。通过体外试验评价细茎石斛多糖的体外抗氧化活性。[结果]在料液比为1∶53,时间为3 h,温度为83℃的提取条件下,DMP最高产量可达185 mg/g。体外抗氧化活性研究结果表明,DMP对超氧阴离子自由基、ABTS自由基、羟基自由基具有明显的清除作用,其中对ABTS自由基清除能力与维生素C相当;DMP对DPPH自由基的清除能力和还原能力效果比较适中。[结论]该研究揭示细茎石斛多糖可以作为一种天然抗氧化剂,为基于多糖的药物及保健食品的开发提供新思路。  相似文献   
65.
Owing to high water requirements of turfgrass, it is essential to find suitable turfgrasses for cultivation in arid and semi-arid conditions. For this purpose, physiological responses of Agropyron desertorum and Poa pratensis cv. “Barimpala” that were subjected to outdoor with holding irrigation were evaluated. Seeds of these two genuses were cultured in polyvinyl chloride tubes and were irrigated daily until drainage occurred. After establishment, irrigation was stopped until leaf wilting occurred. P. pratensis and A. desertorum were wilted during 15 and 20 days after drought treatment, respectively. Turf quality and relative water content were decreased due to drought stress, butthe extent of decrease in A. desertorum was less than that it was in P. pratensis. Five days after stress, malondialdehyde levels increased in P. pratensis more quickly than A. desertorum, while electrolyte leakage rose immediately after with holding irrigation in these genuses. Superoxide dismutase and catalase activities in the two stressed plants increased and then decreased with stress development. In these conditions activities of AT, 3-amino-1,2,4-triazole, peroxidase and glutathione peroxidase had a similar pattern in P. pratensis, while A. desertorum showed continuous increase in these enzyme activities.  相似文献   
66.
67.
This study was conducted to evaluate the effect of feeding different sources of fat during flushing period on the reproductive performance, lambing percent, and twin numbers of Afshari ewes. A total of 84 ewes (mean weight 48 ± 3 kg; age: 3–4 years) were divided into seven groups of 12 animals and received flushing-specific rations for 5 weeks. The control group just received a basic ration (non-flushing). Lipid sources were calcium salt of palm oil (CaP), pure palm oil (PO), calcium salt of flaxseed (CaFL), calcium salt of sunflower oil (CaSF), flaxseed oil (FLO), and sunflower oil (SFO). Estrous cycles were synchronized in all ewes using 14-day CIDRs followed by 400-IU PMSG injection at the time of CIDR removal. Fertility and lambing percent were higher in ewes fed with diets containing calcium salts of flaxseed and SFO, as compared to other treatments. Total number of lambs in flushing treatments was significantly higher than that in the control group (p < 0.01). Serum cholesterol and progesterone levels were significantly greater in omega-3 (CaFL) and omega-6 (CaSF) treatments relative to other treatments (p < 0.01). It was concluded that supplementing the flushing diet with calcium salts of fatty acids (CSFA) increased blood metabolites and hormones related to reproductive performance; and improved fertility, lambing rate and ewes of CaFL treatment have the highest number of lambs (16 lambs) between different groups. Using saturated and unsaturated fatty acids, especially in their CSFA forms during flushing period, could improve the reproduction problems induced by progesterone deficiency, lack of durability of the fetus due to hormonal instability, and abortion control factors.  相似文献   
68.
A wide range has been reported for the ultrasonographic measurements of the normal adrenal gland in rabbits. Therefore, having sufficient information about the normal measurements of the adrenal gland and their relationship with indicators such as weight, sex and the diameter of the internal abdominal aorta will be of great help in diagnosing diseases of the adrenal gland. In the present study, 21 healthy adult intact rabbits were selected. The abdominal cavity of the animals was examined using ultrasound; adrenal gland parameters such as length, width, height, circumference and area on the right and left sides were measured in both sagittal and transverse planes. Additionally, the diameter of the abdominal aorta in the sagittal plane was imaged. After statistical analysis, the parameters of the adrenal glands on the right and left showed a positive significant correlation with the weight and the diameter of the abdominal aorta, although no significant correlation was found between these parameters and sex. The ratio of adrenal gland parameters to abdominal aortic diameter was calculated and the statistical analysis of the values showed that, except for the ratio of left adrenal area to aortic diameter, the other ratio of adrenal gland parameters to abdominal aortic diameter was not significantly related to weight. Therefore, these ratios can be used as suitable indicators for assessing the change in size of the adrenal gland of rabbits of different sizes. Knowing the relationship between normal adrenal measurements and the indices such as weight, sex and diameter of the abdominal aorta can help clinicians and researchers evaluate the changes in the size of the adrenal gland.  相似文献   
69.
The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and the onion thrips, Thrips tabaci Lind. (Thysanoptera: Thripidae), are significant field pests of potato in the Ardabil region of Iran. Orius niger (Wolf.) and O. minutus (L.) (Hemiptera: Anthocoridae) are locally the predominant natural enemies of these pests. This study compared the functional responses of O. niger and O. minutus to female mites and second instar thrips larvae across a range of prey densities (5, 10, 20, and 40 prey/arena) under controlled conditions of 24 ± 1°C, 50 ± 5% RH and 16:8 h (L:D). The resulting data were appropriately fit to Type II functional response models in four predator–prey interactions, including: (1) O. niger to second instar thrips larvae (a = 0.009 h−1; and T h = 1.62 h); (2) O. niger to females mites (a = 0.006 h−1 and T h = 1.28 h); (3) O. minutus to second instar thrips larvae (a = 0.008 h−1 and T h = 1.93 h) and (4) O. minutus to females mites (a = 0.01 h−1 and T h = 1.1 h). The number of second instar thrips larvae attacked by O. niger was greater than that by O. minutus (P ≤ 0.01); conversely, the number of females mites attacked by O. minutus was greater than that by O. niger (P ≤ 0.01). These results confirm the potential for both O. niger and O. minutus to make valuable contributions to a biological control program against onion thrips and the two-spotted spider mites infesting potato fields in this region.  相似文献   
70.
研究伞伐更新法对赫卡尼亚森林系统中森林再生和林分结构的影响。在伊朗北部优势种为山毛榉(Fagus orientalisLipsky)的硬木林,采取伞伐更新法和非伞伐更新法方法设计实验区。结果表明,在山毛榉(F orientalis Lipsky)林中采用伞伐更新法处理,明显影响林下草本植物种的频度和密度。伞伐更新法处理后,林堇菜(Viola silvestris Lam.)、车叶草(Asperula odorata L.)、苔草(Carex spp.)和悬钩子(Rubushyrcanus Juz)的种频度明显增加。在对照区,树种的胸高直径(57.50&#177;2.15cm)大于被处理区(50.67&#177;1.88cm)的树种的胸高直径(50.67&#177;1.88 cm),但对照区和处理区的树种的高度值相似。在1995-2005年间,波斯铁木(Parrotia persica)苗木数量增加到13.2%,而山毛榉(F orientalis)和欧洲鹅耳枥(Carpinus betulus)的苗木数量却明显减少。总之,应该利用其它育林方法,如,带状择伐作业,而不是伞伐更新法培育赫卡尼亚森林中山毛榉林。  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