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   94篇
  免费   15篇
林业   2篇
农学   1篇
基础科学   1篇
  8篇
综合类   16篇
农作物   4篇
水产渔业   8篇
畜牧兽医   63篇
园艺   1篇
植物保护   5篇
  2024年   1篇
  2023年   2篇
  2022年   1篇
  2021年   2篇
  2020年   1篇
  2019年   2篇
  2018年   4篇
  2017年   4篇
  2016年   5篇
  2015年   1篇
  2014年   3篇
  2013年   6篇
  2012年   8篇
  2011年   10篇
  2010年   3篇
  2009年   4篇
  2008年   4篇
  2007年   3篇
  2006年   1篇
  2005年   3篇
  2004年   1篇
  2003年   4篇
  2001年   2篇
  2000年   2篇
  1999年   3篇
  1998年   5篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1993年   2篇
  1991年   3篇
  1990年   2篇
  1987年   1篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1979年   2篇
  1976年   2篇
  1973年   1篇
  1971年   1篇
  1927年   1篇
  1920年   1篇
排序方式: 共有109条查询结果,搜索用时 15 毫秒
1.
In seawater enriched with carbon-14-labeled sodium hydrogen carbonate the sacoglossan Placobranchus ocellatus when exposed to light incorporates carbon-14 at a rate 50-fold of that for animals kept in the dark. 9,10-Deoxytridachione, a secondary metabolite of the mollusk, undergoes a photorearrangement to photodeoxytridachione in vivo.  相似文献   
2.
3.
4.
5.
The factors influencing the decision of smallholder farmers to adopt new farming technologies were studied with reference to rubber–tea intercropping in Sri Lanka. Rubber–tea intercropping has been recommended previously to rubber farmers as a means to improve productivity and income during the early pre-tapping phase of rubber growth. Although crop trials have shown that the two crops are agronomically compatible and potentially produce a combined economic yield superior to the yield of a sole crop grown on the same area of land, there is little evidence of widespread adoption of this practice among smallholder farmers in Sri Lanka. The aim of the study was to determine the major factors that influence the decision to undertake rubber–tea intercropping and to construct a predictive model that describes the likelihood of adoption of intercropping by traditional smallholder rubber growers. A rapid rural appraisal (RRA) was undertaken based on semi-structured interviews of 90 smallholder farmers in the main rubber growing low wet zone of Sri Lanka. Among a number of factors shown to significantly influence the decision to intercrop tea with rubber, three were shown to operate independently, namely level of income, source of income (i.e. solely from own farm or from farm plus additional off-farm enterprises), and availability of land considered suitable for tea cultivation. A statistical model developed through correlation and logistic analysis, which predicts the likelihood of a smallholder adopting intercropping based on these factors, is presented and discussed. The most likely combination of circumstances (82% probability) under which rubber–tea intercropping is practiced is shown to be where the farmer’s income is greater than Rs. 10,000 per month, where the farmer’s income is based solely on own farm enterprises, and where more than 80% of the farmer’s land area was judged to be suitable for tea cultivation. Conversely, 30% of smallholder farmers that chose not to intercrop did possess land suitable for tea cultivation. Qualitative responses to the RRA indicated that limitation of technical knowledge was the main problem subsequently faced by rubber farmers who had adopted rubber–tea intercropping. Results indicate that there is need for both income support through farm subsidies and further agricultural extension services, if rubber–tea intercropping is to be adopted more widely in Sri Lanka. The wider usefulness of the developed logistic model in determining the likelihood of adoption of intercropping by smallholder farmers is discussed.  相似文献   
6.
Esophagostomy feeding tubes were placed in 46 cats. Percutaneous endoscopic gastrostomy (PEG) feeding tubes were placed in 21 cats. Owner management and complications and facility of use were evaluated retrospectively by review of medical records and owner survey. Both tube types were equally effective for maintenance of body weight, ease of owner management, and complication rates. All of 12 owners surveyed were comfortable with PEG tube management. Ninety-six percent of 24 owners surveyed were comfortable with esophagostomy tube management. The esophagostomy tube can be placed less invasively, without specialized equipment, making it an excellent alternative to the PEG tube.  相似文献   
7.
Higher concentrations and total amounts of Pb were found in faeces than urine and mucus or coelomic fluid. The highest concentration of Zn was present in coelomic fluid but the highest total amount of Zn was in earthworm faeces. Metal analysis of the contents of various sections of the alimentary tract showed the highest concentration and total amount of Pb in the contents of the posterior alimentary tract. Zn and Ca showed the opposite distribution and the highest concentrations were found in anterior gut contents while the highest total amounts of Zn and Ca were found in posterior gut contents. The results are discussed in relation to dry weight of material, excretory sites and the presence of water soluble salts.The terminal segments of D. rubida were analysed for Pb and Zn and it was concluded that self-amputation or autotomy of these segments is probably not involved in the elimination of these metals.  相似文献   
8.
Field-trapping experiments with synthetic 2,7-nonadiyl dibutyrate, the female-produced sex pheromone of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin), demonstrated that pheromone traps were highly attractive to males and caught very few non-target organisms. Different formulations of pheromone were tested to identify the optimum release rate and dispenser type for use in pheromone traps in the UK. Key findings were that racemic pheromone was as effective as enantiomerically pure (2S,7R)-2,7-nonadiyl dibutyrate, that release rates higher than 0.5 microg day(-1) were not necessary and that the optimal formulation was a 1 mg pheromone loading in a rubber septum. Pheromone traps gave a reliable indication of peak midge emergence, onset of flight and abundance of midges throughout the season. A strong correlation between maximum trap catch and crop infestation levels was obtained.  相似文献   
9.
10.
Mediators and mechanisms responsible for the inhibitory modulation of trout intestinal smooth muscle were examined using a series of putative mediators and substances known to modulate neurotransmission in mammalian systems. Frequency response relationships to transmural stimulation and concentration response relationships to 5-hydroxytryptamine, carbachol, and substance P were established on paired segments of rainbow trout intestinein vitro in the presence and absence of putative modulatory agents. Modulation of neurally-mediated contractions of trout intestine was achieved with dibutyryl cyclic AMP and forskolin, agents that increase intracellular levels of cyclic AMP. The effect appears to be at the level of the smooth muscle, since the adenylate cyclase activator, forskolin, inhibited muscarinic and serotoninergic contractions as well as transmurally stimulated contractions. Substance P-induced contractions were unaffected by forskolin. The endogenous agonists/neurotransmitters which would increase cyclic AMP levels in rainbow trout intestinal smooth muscle are as yet unknown. The effects do not appear to be modulated by vasoactive intestinal peptide (VIP), calcitonin, calcitonin gene-related peptide (CGRP), or agents that activate -adrenoceptors. Prostaglandin E2 (PGE2) and 2-adrenergenic agonists are possible agents which will decrease contractility of the smooth muscle. They were only active in the proximal intestine and on transmurally stimulated contractions. The effects of both PGE2 and 2-agonists appear to be prejunctional, decreasing release of contractile neurotransmitters in the enteric nervous system.  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