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   81篇
  免费   2篇
  国内免费   1篇
林业   2篇
农学   3篇
  9篇
综合类   5篇
农作物   14篇
水产渔业   5篇
畜牧兽医   41篇
植物保护   5篇
  2023年   2篇
  2022年   4篇
  2021年   2篇
  2020年   5篇
  2019年   10篇
  2018年   2篇
  2017年   3篇
  2016年   6篇
  2015年   1篇
  2014年   3篇
  2013年   7篇
  2012年   2篇
  2011年   6篇
  2010年   3篇
  2008年   5篇
  2007年   4篇
  2006年   1篇
  2005年   6篇
  2004年   2篇
  2000年   2篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1994年   1篇
  1992年   1篇
  1990年   1篇
  1956年   1篇
排序方式: 共有84条查询结果,搜索用时 31 毫秒
21.
For successful breeding programs, it is important to quantify the useful period of a male's reproductive life and it is often done simply by measurement of semen quality. This information is lacking for Japanese quail so we tested whether there is a decline in ejaculate quality and sperm kinematics with age, and whether the decline varies among strains. Nine males (n = 9) from each of 5 strains (A, B, C, D and E) were subjected to 4 semen collections (n = 16 per male) at 8, 16, 26 and 36 weeks of age. Ejaculate volume, sperm concentration and total sperm per ejaculate were measured, and sperm kinematics were analysed using a Sperm Class Analyser (SCA®). There was a significant effect of age for ejaculate volume, total sperm per ejaculate and per cent medium sperm. The effect of the interaction between age and strain was significant for percent progressive motile sperm, percent rapid sperm, velocity curvilinear, velocity straight line, velocity average path, linearity, straightness and beat cross frequency. Ejaculate volume peaked at Week 26 in all strains, while peak values for sperm concentration and total sperm per ejaculate were observed at Week 16 for most strains. There were declines in percent motile sperm, progressive motile sperm and rapid sperm, and in velocity curvilinear velocity, velocity straight line and velocity average path, by Week 16 for most strains. Linearity declined by Week 26 in some strains, and all strains showed a significant decline in beat cross frequency by that age. In conclusion, the ability of CASA to detect age-related changes in sperm kinematics makes it a valuable tool for identifying the best males and thus improving quail flock fertility. It is essential that breeders understand that age affects both sperm production and sperm kinematics, and that the changes vary with strain.  相似文献   
22.
23.
The recent slow down in productivity growth in the irrigated areas of the Indo-Gangetic Plains of South Asia has led to a quest for resource-conserving technologies that can reduce production costs, save water and improve production. Findings from farm surveys are used to evaluate the on-farm impacts of zero tillage (ZT) wheat in the rice–wheat systems of India's Haryana state and Pakistan's Punjab province. ZT-induced effects primarily apply to the establishment and production costs of the wheat crop. Both study sites confirmed significant ZT-induced resource-saving effects in farmers’ fields in terms of diesel, tractor time and cost savings for wheat cultivation. Water savings are, however, less pronounced than expected from on-farm trial data. It was only in Haryana, India that there were significant ZT-induced water savings in addition to significant yield enhancement. The higher yield and water savings in Haryana, India result in significantly higher water productivity indicators for ZT wheat. In both sites, there are limited implications for the overall wheat crop management, the subsequent rice crop and the rice–wheat system as a whole. The combination of a significant “yield effect” and “cost-saving effect” makes adoption worthwhile and provide a much needed boost to the returns to wheat cultivation in Haryana, India. In Punjab, Pakistan, ZT is primarily a cost-saving technology for wheat cultivation. The prime driver for ZT adoption is not water savings or natural resource conservation but monetary gain in both sites. Water savings are only a potential added benefit.  相似文献   
24.
25.
Chonemorpha fragrans is an endangered medicinal woody climber,regarded among alternative plant sources of camptothecin.Camptothecin is a monoterpene indole anti-cancer alkaloid with annual trade value of over three billion U.S.dollars in the recent,and is used in the production of its analog drugs approved for the chemotherapy of cancer of varied types.Effects of plant growth regulators,culture media strength and photoperi-odic duration on the micropropagation ef ciency of C.fragrans from nodal segment explants were studied on Murashige and Skoog(MS)medium amended with Thidiazuron(TDZ),Benzylaminopurine(BAP)or Kinetin(Kin).Thidiazuron was more ef cient over BAP and Kin when half basal MS medium was used over full or quarter strength.Results of carbon source experiment showed sucrose as the most effective over glucose,fructose,and maltose in the clonal production.Studies on the photope-riodic incubation duration showed 12 h as the best light period and sub or supra-optimal resulted in the production of abnormal and albino micro shoots.Experimental results on the evaluation of physiological,biochemical parameters showed the role of pigment molecules and antioxidant systems in the production of albino micro shoots.  相似文献   
26.
The objective of this study was to determine the effect of two different freezing rate then thaw‐aging regimens on the quality attributes of lamb loins. The loins were randomly allocated to one of five different freezing/thawing/aging regimes: fast‐(FF1A0) and slow‐(SF1A0) frozen only; fast‐(FF1A2) and slow‐(SF1A2) frozen then thaw‐aged for 14 days; aged for 14 days never frozen (A2). FF1A2 samples had a significantly higher water‐holding capacity compared to the slow frozen regardless of further aging periods. FF1A2 samples had lower (p < 0.05) shear force values than A2 and higher (p < 0.05) water‐holding capacity compared to the SF1A2. Fast freezing resulted in more intracellular cryo‐damage, whereas slow freezing resulted in extracellular cryo‐damage. FF1A0 and SF1A0 samples had lower (p < 0.05) myofibrillar proteins degradation. This study demonstrated that fast freezing then thaw‐aging can result in an improved water‐holding capacity and tenderness through the minimization of extracellular ice crystal formation, reduction in purge and drip losses, and improved proteolysis in thawed lamb.  相似文献   
27.
The objective of this study was to create various pH/temp decline rates in hot‐boned bull beef M. longissimus lumborum (LL) through a combination of electrical stimulation (ES) and pre‐rigor holding temperature. The relationship between the pre‐rigor interventions, the activities of µ‐calpain and small heat shock proteins (sHSP), and the impacts on meat product quality were determined. Paired LL loins from 13 bulls were hot‐boned within 40 min of slaughter, immediately ES and subjected to various holding temperatures (5, 15, 25, and 35°C) for 3 hr. The rate of muscle pH decline, sarcomere length, shear force, and proteolysis of muscle proteins were measured. ES‐25°C had a longer sarcomere length compared to non‐electrical stimulation samples. ES‐25°C and ES‐35°C samples had lower shear force values, higher µ‐calpain activity and higher desmin, troponin‐T, and sHSP degradation. The above findings suggest that pH/temp decline rates created in hot‐boned muscle impacted muscle protein proteolysis by increasing the activity of proteases and degradation of sHSP.  相似文献   
28.
MKM–OS anesthesia provides general anesthesia with minimum cardiovascular depression in experimental horses. The purpose of this study was to evaluate the effect of MKM–OS anesthesia in clinical cases. Sixty‐eight horses were anesthetized with MKM–OS anesthesia for selective or emergency surgery. The horse physical status was categorized based upon the American Society of Anesthesiologists (ASA) classification scheme. Forty‐four horses were classified as ASA I or II (low‐risk; 30 soft tissue, eight ophthalmic, and six orthopedic surgeries) and 24 horses were classified as ASA III to V (high‐risk; 24 emergency colic surgeries). All horses were administered medetomidine (0.005 mg kg–1 IV) as premedication and anesthetized with ketamine (2.5 mg kg–1 IV) and midazolam (0.04 mg kg–1 IV). The horses were orotracheally intubated and connected to a large animal breathing circuit that delivered oxygen‐sevoflurane and administered the midazolam (0.8 mg mL–1)‐ketamine (40 mg mL–1)‐medetomidine (0.05 mg mL–1) drug combination at a rate of 0.025 mL kg–1 hour–1. Surgical anesthesia was maintained by controlling the dial setting of the sevoflurane vaporizer and achieved by delivering 1.6–1.8% of end‐tidal sevoflurane concentration. All horses were mechanically ventilated during anesthesia. Hypercapnia and hypoxia were not sufficiently improved in high‐risk horses (PaCO2; low‐risk 45–53 mm Hg versus high‐risk 56–60 mm Hg, p < 0.01: PaO2 low‐risk 248–388 mm Hg versus high‐risk 95–180 mm Hg, p < 0.01). Heart rate was significantly higher in high‐risk horses (low‐risk 37–42 bpm versus high‐risk 44–73 bpm, p < 0.01). Dobutamine infusion was required in five low‐risk (11%) and 17 high‐risk horses (68%) to maintain mean arterial blood pressure >70 mm Hg. Eleven high‐risk horses died during the perioperative period (three euthanized during surgery, two died during recovery, six died after recovery). The quality of recovery was good in low‐risk horses and good to satisfactory in high‐risk horses. MKM–OS anesthesia provided excellent surgical anesthesia with minimal to mild cardiovascular depression in low risk‐horses and mild to moderate cardiovascular depression in high risk‐horses. The possibility of preserve cardiovascular function could be the advantage of MKM–OS anesthesia in high‐risk horses.  相似文献   
29.
The objective of this study was to use mouse embryos as a model system to investigate the effect of co-culture of cumulus cells in Sydney IVF sequential media (Cook) on embryo development, based on the hypothesis that feeder cells in co-culture with a sequential medium could work synergistically to further improve in vitro culture conditions for mammalian preimplantation embryos. The culture systems described here were evaluated by the ability to consistently produce high blastocyst formation rates and high cell number per blastocyst. The role of embryo-to-cell contact was assessed by using Transwell inserts with transparent microporous membranes. Pronuclear embryos of ICR mice were cultured to blastocysts in Cook sequential media, with and without mouse primary cultures of cumulus cells, and with or without inserts. Blastocyst formation rates and cell numbers of in vitro developing embryos in the different culture systems were compared to each other, and to in vivo derived blastocysts. Blastocyst formation rates for Cook medium only was 27.8% (without inserts) and 32.9% (with inserts), whereas Cook-Cumulus cells in identical culture systems was significantly higher at 45.8% (without inserts, P<0.05) and 55.6% (with inserts, P<0.05). When the embryos are suspended above the bottom of the well, for Cook medium significantly lower blastocyst formation rates were observed at 4.2% compared to Cook-Cumulus cells at 17.5% (P<0.05). Mean cell numbers of blastocysts obtained in all co-culture systems were significantly higher (P<0.05) compared to those developing in culture medium only. Although the putative mechanism is as yet unexplained, the improved blastocyst formation rates and cell numbers in co-culture when there is direct contact between the embryo and the cell monolayer suggest that the close proximity between the feeder cells and embryos is in part responsible for these effects.  相似文献   
30.
金钱鱼(Scatophagus argus)是我国东南沿海名优养殖鱼类, 具有 XY 性别决定系统, Dmrt1 是其性别决定候选基因。金钱鱼生长具有性别二态性, 雌鱼生长快于雄鱼。目前缺乏快速鉴定金钱鱼遗传性别的分子标记, 阻碍了其性别控制育种技术的建立。本研究以公布的金钱鱼基因组数据, 在 Dmrt1 附近设计多对标记引物, 并通过 PCR 扩增验证标记的性别特异性。其中, 标记引物 Dmrt1-Marker-4-F/R 在雌鱼中仅扩增出一条 593 bp X 染色体条带, 而在雄鱼中能扩增出 593 bp 和 693 bp 两条条带, 分别来自 X 和 Y 染色体, 表明该标记为共显性标记。利用该标记检测我国南海沿岸 3 个不同地理群体 213 尾金钱鱼的遗传性别与表型性别完全一致。此外, 快速 DNA 提取试剂盒提取的片段较短 DNA 样品也可用于该对标记引物准确鉴定遗传性别。本研究建立了一种快速、准确、经济可靠的金钱鱼遗传性别鉴定方法, 将旨为促进金钱鱼性别控制育种技术的建立, 并为金钱鱼性别决定与分化机制研究提供依据。  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