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   345篇
  免费   27篇
林业   24篇
农学   12篇
基础科学   1篇
  72篇
综合类   39篇
农作物   21篇
水产渔业   16篇
畜牧兽医   160篇
园艺   7篇
植物保护   20篇
  2023年   2篇
  2022年   2篇
  2021年   10篇
  2020年   5篇
  2019年   12篇
  2018年   10篇
  2017年   8篇
  2016年   9篇
  2015年   11篇
  2014年   14篇
  2013年   8篇
  2012年   28篇
  2011年   26篇
  2010年   12篇
  2009年   10篇
  2008年   29篇
  2007年   14篇
  2006年   19篇
  2005年   14篇
  2004年   17篇
  2003年   11篇
  2002年   7篇
  2001年   9篇
  2000年   2篇
  1999年   2篇
  1998年   4篇
  1995年   3篇
  1993年   2篇
  1991年   4篇
  1989年   3篇
  1987年   2篇
  1983年   3篇
  1982年   4篇
  1981年   2篇
  1980年   3篇
  1979年   2篇
  1978年   6篇
  1976年   2篇
  1975年   2篇
  1974年   3篇
  1973年   6篇
  1972年   3篇
  1971年   4篇
  1968年   3篇
  1967年   2篇
  1966年   2篇
  1962年   2篇
  1959年   2篇
  1945年   2篇
  1944年   1篇
排序方式: 共有372条查询结果,搜索用时 31 毫秒
1.
Atopy.     
Atopy should be considered an immunological disorder that may result in several clinical conditions including respiratory disease, allergic dermatitis, food allergy dermatitis, and perhaps flea allergy dermatitis. The clinical course of the disease tends to fluctuate from season to season, which makes objective evaluation of injection therapy difficult. The disease is subject to both familial and environmental influences, and dogs maintain the atopic state throughout their life. The disease cannot be cured; however, a combination of symptomatic and specific injection therapy usually provides adequate control of the clinical signs. Owners of atopic dogs should appreciate that their pet has inherently itching skin, a cure for which is unlikely to be found.  相似文献   
2.
3.
Sainfoin (Onobrychis viciifolia) is a tanniniferous, leguminous plant that has potentially beneficial effects on protein utilization in ruminants. As ensiling causes protein breakdown and elevated levels of buffer soluble N (BSN), we studied the distribution of N before and after ensiling sainfoin. Three varieties of sainfoin were either direct‐cut and frozen directly or wilted and frozen before later ensiling in mini‐silos with and without acidification with Promyr (PM; an acidifying commercial mixture of propionic and formic acid) and with or without polyethylene glycol (PEG). Extractable tannins (ET) and protein‐bound tannins (PBT) were measured with an HCl/butanol method in an attempt to correlate tannin levels to N fractions. The sainfoin silages showed good ensiling characteristics and had relatively high concentrations of undegraded protein. The effect of wilting on BSN levels (g/kg N) was dependent on sainfoin variety (P < 0·001). PEG increased and PM decreased the level of BSN in the silages (P < 0·001). PM treatment also produced less non‐protein N and ammonia‐N (P < 0·05) as compared with no additive. Addition of PEG to the silage increased the BSN‐proportion 1·8‐ and 2·6‐fold for both DM stages. A strong tannin‐protein binding effect is, therefore, confirmed in sainfoin. However, correlations between tannin levels (ET and PBT) and BSN were poor in the (non‐PEG) silages, indicating either that the HCl/butanol method is unsuitable for measuring tannin in silages or that qualitative attributes of tannins are more relevant than quantitative. The HCl/butanol method seems therefore not to be useful to predict degradation of protein in sainfoin silages.  相似文献   
4.
The objective of this study was to test for correlations between alopecia and ruminal drinking in young calves. 331 calves up to an age of 31 days were tested for evidence of generalized hair loss daily during their stay in the clinic. Incidence of diarrhoea and the results of ruminal fluid and blood analysis were compared between the groups with and without alopecia. Calves with alopecia showed a significantly higher incidence of diarrhoea and of ruminal acidosis persisting for at least 24 hours. Blood analysis revealed significant differences in degree of acidosis, in concentrations of D-lactate, urea, and creatinine in serum as well as in the activities of glutathione peroxidase, aspartate amino transferase, and creatine kinase. Alopecia in calves is correlated to longer periods of diseases, which are known to be accompanied by the production of D-lactate in the gastrointestinal tract, such as diarrhoea and ruminal drinking. The question, whether alopecia is due to formation of toxic substances or to deficiency of essential substances can not be answered.  相似文献   
5.
This paper explores the plasticity of sexually dimorphic characters in subadult female Brevimyrus niger, an African weakly electric mormyrid species. Thirty-five fish were exposed in a staggered fashion (five fish a week) to aromatizable 17α-methyltestosterone over a period of 7 weeks; 18 fish served as untreated controls. 17α-MT induced precocious vitellogenesis that mirrored the natural maturational process during seasonal ovarian recrudescence. At the same time, 17α-MT exposure resulted in complete masculinization of the females’ anal fin support structure normally observed during rainy season in adult males. We discuss possible hormonal mechanisms acting along the brain-pituitary-gonad axis that would explain the occurrence of precocious vitellogenesis and the male-typical transformation of the female’s anal fin ray bases. Our findings are relevant to commercial aquaculture as the use of 17α-MT in fish hatcheries can pose serious environmental issues.  相似文献   
6.
The removal of the cyanobacterial peptide toxin microcystin-LR at 4 and 37 degrees C by six commercial probiotic strains and Lactobacillus plantarum strains IS-10506 and IS-20506 isolated from dadih, Indonesian traditional fermented milk, was assessed in this study. The aim was to evaluate the main factors influencing the viability and metabolic activity of the probiotic strains, as well as their capacity to remove microcystin-LR. Both L. plantarum strains isolated from dadih, as well as Bifidobacterium lactis strains Bb12 and 420, were shown to be more resistant, and >85% remained viable in phosphate-buffered saline (PBS) solution for 48 h of incubation at either temperature, while the viability of the other four commercial bacteria decreased markedly over time. The effect of glucose on viability and removal of toxin was shown to be a strain-specific and strain-dependent property, but in general, the efficiency of microcystin-LR removal increased when glucose was added to the solution. A maximum removal of 95% was observed for L. plantarum strain IS-20506 (37 degrees C, 10 (11) colony-forming units mL(-1)) with 1-2% glucose supplementation and 75% in PBS alone.  相似文献   
7.
Journal of Plant Diseases and Protection - The study assessed the genetic variability among Macrophomina phaseolina (Tassi) Goid. isolates originating from six different countries (Turkey,...  相似文献   
8.
新疆杨(Populus bolleana LAUCHE)是山西省北部乃至中国西北部重要的阔叶树造林树种,但目前发现只有雄性植株,它很可能是一个或几个无性系通过无性繁殖而大规模传播开来,基因变异狭窄,会给造林带来巨大的潜在危险。于2004年到2005年在山西省境内随机采集59个样树,在德国爱博斯瓦尔德大学(FH-Eberswalde)的生态实验室进行了同工酶分析。分析结果显示,在山西省境随机采样的59个新疆杨树中,88%的被猜测为是一个或同样的无性系。初步证实山西省境内的新疆杨造林基因变异有限,这就是说在山西境内新疆杨的造林潜在着巨大的风险。同时就避免或降低这种风险的可能性进行讨论。  相似文献   
9.
10.
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