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   50篇
  免费   8篇
  国内免费   2篇
林业   9篇
农学   3篇
基础科学   2篇
  2篇
综合类   14篇
水产渔业   1篇
畜牧兽医   22篇
园艺   1篇
植物保护   6篇
  2022年   3篇
  2020年   3篇
  2018年   2篇
  2017年   1篇
  2016年   2篇
  2015年   3篇
  2014年   2篇
  2013年   4篇
  2012年   5篇
  2011年   6篇
  2010年   3篇
  2009年   2篇
  2006年   2篇
  2005年   1篇
  2003年   2篇
  2002年   2篇
  2001年   8篇
  2000年   1篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
排序方式: 共有60条查询结果,搜索用时 21 毫秒
21.
林业三剩物和次小薪材的综合利用,可以减少森林资源的采伐总量,提高其综合利用率,增加林木生产者和综合利用者的收入,还可带动山区经济的发展。应在计划管理、产业结构调整、林业规费减免、税收优惠政策落实等方面采取相应的鼓励措施,以加快综合利用的步伐,从而更好地发挥林业的生态、社会和经济效益。  相似文献   
22.
Thirteen of 100 fallow deer, aged between 6 months and 10 years, died over a 5 week period. The deaths occurred in 2 outbreaks 3 weeks apart. Both outbreaks were preceded by at least 3 days of cold wet and windy weather, and were associated with water-logged pastures. Affected animals were usually found dead, with a frothy blood-stained nasal discharge. In the 8 deer necropsied, gross lesions included widespread subserosal petechial haemorrhages, severe pulmonary congestion and oedema with froth-filled airways, and fibrinous pneumonia and pleurisy in 4 deer. Two deer, also, had extensive subcutaneous petechial and ecchymotic haemorrhages and oedema of skeletal musculature. Histologically, the most significant lesions were present in the lungs. Moderate to severe pulmonary congestion and oedema, with fibrinous exudation into alveoli and septal oedema, were present in all deer. In some deer these changes were accompanied by a diffuse infiltration with polymorphonuclear leucocytes. Pasteurella multocida was isolated from a range of tissues from 7 of 8 deer examined. The remaining animal had been treated with antibiotics 8 hours before death. The isolates had identical polyacrylamide gel electrophoresis patterns and were of the same antigenic type-Carter group A, Heddleston type 3,4.  相似文献   
23.
24.
160 ovine isolates of Pasteurella haemolytica, representing each of the 16 serotypes and also untypable strains, were examined for plasmid content. Plasmid DNA was identified in, and prepared from, strains of serotypes A2, T3, A14 and A16 and also from an untypable strain. The relationship between the plasmids present in the different strains was examined both by restriction fragment profile analysis and by DNA/DNA hybridisation. Both methods gave broadly similar results and showed that each serotype tended to contain either a single plasmid species, or a limited range of species, and that structural similarities could traverse serotype boundaries. None of the plasmid-bearing strains showed any significant level of resistance to a range of antibiotics.  相似文献   
25.
我国西北平原地区林业生态服务功能评价   总被引:2,自引:0,他引:2  
[目的]评价我国西北平原地区林业的生态服务功能。[方法]通过对西北平原地区林业的调查与监测,以县为最小单位,采取普查与典型调查相结合的调查方法,在评价上利用物质量评价法对西北地区平原林业的生态服务功能进行了评估。[结果]2005年西北地区平原林业在涵养水源、保持土壤、植被固碳、土壤固碳、植被制氧、吸收二氧化硫和滞尘方面均发挥了巨大作用,其各自生态服务功能值分别为32075.8万m3/a、2.8×106、1254、2752.8、3354.3、53.0和8510万t/a。[结论]为我国西北地区平原林业的生态服务功能研究奠定了基础。  相似文献   
26.
毛竹枯梢病的发生与气候和竹林的经营管理水平密切相关。通过实施清除病原,隔断侵染源、钩梢、垦复、施肥、烟剂防治等综合防治技术,使病害发生面积下降了90%,消灭了重度和中度危害区。发病率和感病指数分别下降了94%和85%。  相似文献   
27.
The role of opioid peptides in the secretion of oxytocin (OT) and prolactin (PRL) induced by sucking was studied in goats. Seven goats were isolated with their kids (four singletons and three twins) in individual corrals 3–4 weeks after parturition. On day 1 of the experiment, the kids were separated from the does for 7 h and were weighed before and 15 min after being reunited with their mothers to assess the amount of milk obtained by sucking. The does were blood‐sampled 10 min before and at the end of the sucking period. On day 2, a similar protocol was followed, but naloxone was given immediately after the first blood sample. On day 3, the protocol was repeated but saline vehicle was injected instead of naloxone. On day 5, the naloxone experiment was repeated as on day 2. Milk ejection was evaluated as the difference in the weight of the kids before and after sucking for 15 min, and the maternal serum levels of OT and PRL were measured by radioimmunoassay. A significant decrease in the weight gain of the kids was obtained when the mothers were treated with naloxone on day 2. Consistently, serum levels of OT and PRL induced by sucking were significantly reduced; indicating that sucking‐induced OT secretion for milk ejection in lactating goats is facilitated by opioid peptides. In a second experiment performed in the same animals 10 days later, the administration of OT, immediately after naloxone administration, prevented the decrease in the weight gain induced by naloxone, suggesting that the effect of the opioid antagonist on milk ejection in goats is a result of a reduced OT secretion. The results of this study confirm the importance of sucking‐induced OT secretion for milk ejection in lactating goats, and indicate that OT and PRL secretion are regulated by opioid peptides in this species.  相似文献   
28.
Impact of lower atmospheric carbon dioxide on tropical mountain ecosystems   总被引:1,自引:0,他引:1  
Carbon-isotope values of bulk organic matter from high-altitude lakes on Mount Kenya and Mount Elgon, East Africa, were 10 to 14 per mil higher during glacial times than they are today. Compound-specific isotope analyses of leaf waxes and algal biomarkers show that organisms possessing CO2-concentrating mechanisms, including C4 grasses and freshwater algae, were primarily responsible for this large increase. Carbon limitation due to lower ambient CO2 partial pressures had a significant impact on the distribution of forest on the tropical mountains, in addition to climate. Hence, tree line elevation should not be used to infer palaeotemperatures.  相似文献   
29.
30.
 利用26对黄牛微卫星引物,对分别来自云南省泸水县凤凰山大额牛保种区和贡山县独龙野牛种源保护基地的2个大额牛群体进行遗传变异分析,研究其群体内的遗传变异和群体间的遗传分化。结果共检测到105个等位基因,每个座位的等位基因数从2~6不等,所有座位平均等位基因数、平均有效等位基因数、平均期望杂合度、平均多态信息含量分别为4.0385±0.9999,3.1393±0.9507,0.6490±0.1246和0.5904±0.1334,表明大额牛群遗传多样性比较丰富。F统计量、基因流、Nei氏遗传距离和遗传相似系数等值反映出两个群体遗传差异较小,遗传分化不明显,遗传一致性较大。  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