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   602篇
  免费   105篇
  国内免费   89篇
农学   5篇
基础科学   2篇
  8篇
综合类   145篇
农作物   2篇
水产渔业   609篇
畜牧兽医   23篇
植物保护   2篇
  2024年   1篇
  2023年   3篇
  2022年   6篇
  2021年   8篇
  2020年   15篇
  2019年   14篇
  2018年   5篇
  2017年   24篇
  2016年   28篇
  2015年   18篇
  2014年   25篇
  2013年   34篇
  2012年   20篇
  2011年   25篇
  2010年   36篇
  2009年   23篇
  2008年   29篇
  2007年   30篇
  2006年   29篇
  2005年   41篇
  2004年   31篇
  2003年   38篇
  2002年   34篇
  2001年   41篇
  2000年   28篇
  1999年   37篇
  1998年   29篇
  1997年   32篇
  1996年   28篇
  1995年   24篇
  1994年   15篇
  1993年   11篇
  1992年   18篇
  1991年   4篇
  1990年   5篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
排序方式: 共有796条查询结果,搜索用时 328 毫秒
61.
A3α肽聚糖对凡纳对虾幼体生长及抗病毒感染力的影响   总被引:6,自引:1,他引:6  
用含不同量的A3α肽聚糖(PG)(0.005%、0.01%、0.1%)的幼体饵料投喂凡纳对虾幼体,另在育苗水体中添加不同水平(0.005mg·mL-1、0.01mg·mL-1、0.05mg·mL-1)PG浸浴并以投喂不添加PG的幼体饵料的实验组作为对照,另设投喂活饵的实验组作参考,分别考察Z1-M1期、M1-PL1期、Z1-PL1期幼体的成活率,M1期、PL1期幼体体长,PL1期幼体体重,另外,PL1期仔虾经7d饲养后,检测体内酚氧化酶(PO)活性,并用白斑综合症病毒(WSSV)料投喂感染。结果显示:与投喂不添加PG幼体饵料组相比,在Z1-M1期,活饵组、0.01%PG添加量的幼体饵料组、0.005mg·mL-1PG的浸浴组幼体的成活率有极显著(P<0.01)提高,而在Z1-PL1、M1-PL1期,各实验组除0.05mg·mL-1浸浴组外均有极显著地(P<0.01)提高;各实验组除0.01mg·mL-1、0.05mg·mL-1PG浸浴组外,M1期幼体体长、PL1期幼体体重也有显著(P<0.01)增长,且各实验组PL1期幼体都有极显著(P<0.01)增长;各实验组仔虾PO活力均有极显著(P<0.01)提高;各实验组除0.1%PG添加量的幼体饵料组外,感染WSSV后仔虾的存活率有不同程度地提高。  相似文献   
62.
A feeding trial was conducted to determine the dietary folic acid requirement of juvenile grass shrimp, Penaeus monodon. Purified basal diets were formulated using vitamin-free casein as the protein source. Graded levels (0, 1, 2, 5, 10, 15, 30, and 60 mg folic acid/kg diet) of folic acid were added to the basal diet, resulting in eight dietary treatments in the experiment. Each diet was fed to three replicate groups of shrimp initially averaging 0.79±0.01 g for 8 weeks. Shrimp fed diets supplemented with 2 mg folic acid/kg diet had greater (P<0.05) weight gain and hepatopancreatic folic acid concentrations than shrimp fed the unsupplemented control diet. Feed efficiency (FE) was highest in shrimp fed the diets supplemented with 2 mg folic acid/kg diet, followed by the groups fed 1 mg/kg, then the control group. Hepatosomatic index (HSI) was highest in shrimp fed the control diet, followed by 1 mg folic acid/kg and lowest in shrimp fed diets supplemented with 2 mg folic acid/kg. Weight gain percentage, hepatopancreatic folic acid concentration and hepatosomatic index of the shrimp analyzed by broken-line regression indicated that the adequate dietary folic acid concentration in growing P. monodon is 1.9–2.1 mg/kg diet.  相似文献   
63.
本文报道了1993年和1994年在山东烟台地区养殖对虾发生严重流行病原因的调查结果,着重从养殖环境和饲养管理技术上分析产生疾病的原因,提出了在养殖过程中增强对虾体质、预防疾病的七项措施。  相似文献   
64.
用烧结法标志中国对虾,在靖海湾和五垒岛湾进行增殖放流,研究其回游与分布规律。重捕资料表明,6月中旬幼对虾对湾内河口浅水区生活随体长增长,逐步向深水扩散;8月上,中旬主群陆续游向湾外,按地形走向向西南回游,部分向东或东南;10月份回游对湾外水域的对虾有向东,东北或东南回游的现象。  相似文献   
65.
感染白斑综合病毒(WSSV)对虾相关免疫因子的研究   总被引:12,自引:6,他引:12       下载免费PDF全文
129尾中国对虾(Penaeus chinensis)分别捕自未暴发白斑综合症(WSSV病毒所致)虾池、WSSV暴发虾池以及曾暴发WSSV虾池。用斑点杂交和组织病理学方法确定各尾对虾的染毒(WSSV)程度。用96孔酶标板法测量相应个体血淋巴上清液的抗菌活力(Ua)、溶菌活力(UL)、酚氧化酶(PO)活性以及过氧化酶(POD)相对活性;用硝酸纤维膜斑点法测定其碱性磷酸酶(ALP)相对活性;用血凝法测定其凝集效价(HAT)。通过对以上免疫指标进行统计分析,结果表明,WSSV感染与对血淋巴PO活性以及ALP相对活性变化有紧密联系;不同虾池各免疫因子差异显著,发病虾池虾样各免疫指标平均值均低于其他虾池;曾发病虾池的虾样PO活性较强;WSSV与HPV感染无统计学意义上的相关性;未发病虾池与曾发病虾池实验对虾的Ua与UL相关性极显著,发病虾池实验对虾Ua与UL呈负相关;发病虾池对虾PO与ALP活性相关性显著。不同性别中国对虾血淋巴上清液的免疫因子活性没有显著差异。  相似文献   
66.
This 12‐month preliminary study investigated the development of sexual characters, primary sexual maturity, ovarian maturity and spawning performance of pond‐reared Penaeus merguiensis in relation to culture conditions in south‐east Queensland, Australia. Post‐larvae of P. merguiensis were produced and cultured in two 60‐m3 tanks during the first 14 weeks. Before winter, they were harvested and stocked in three different overwintering facilities: a 200‐m2 covered pond, two 60‐m3 outdoor tanks and a 15‐m3 indoor, recirculated tank at a stocking density of 10 individuals m?2. The development of sexual characters was found to be similar to that reported previously in wild P. merguiensis. Males matured at younger ages and smaller sizes than females. Overall, the average size at primary sexual maturity of pond‐reared P. merguiensis was 23.1 mm carapace length for males (possessed spermatophores) and 29.3 mm for females (being impregnated). Water temperature and the availability of natural food strongly influenced prawn growth, maturity rate and their subsequent spawning performance. Growth, maturity rate and spawning performance of prawns in the covered pond were significantly higher than in the other overwintering facilities. Prawns started mating at 6–7 months, reached full ovarian maturation and spawned as early as about 8 (peaked at 9–11) months from hatching, producing high fecundity and viable larvae. There was a strong relationship (P < 0.001) between prawn size and fecundity. The results of this study suggest a potential for using pond‐reared broodstock P. merguiensis for hatchery production and for domestication or selective breeding programmes.  相似文献   
67.
Cholesterol is considered a required nutrient for penaeid shrimps, but an optimal level has not been defined. A 68-day grow-out trial was conducted in 1300-L outdoor tanks in Hawaii, USA, to determine the cholesterol level required in a soyabean meal-based diet for juvenile Pacific white shrimp, Penaeus vannamei (Boone). Test feeds were prepared by adding six cholesterol levels (1.0-10.2 g kg?1, as-fed basis) to a standard diet high in plant-protein meals, starch and flour. These feeds were provided to the shrimp three times daily. Harvest weights and weekly growth increments varied significantly among diets. The 2.3 g kg?1 and 4.2 g kg?1 cholesterol diets yielded better growth than the 1.0 g kg?1 and 10.2 g kg?1 diets. Survival and feed conversion ratios did not vary significantly among diets. Significant dietary cholesterol effects on growth of P. vannamei in conditions resembling commercial grow-out indicate that its inclusion in practical diets at more accurately defined levels is necessary. Optimal cholesterol levels for juvenile shrimp may be lower than those now utilized, and may vary relative to the contribution of free sterols from natural foods in shrimp ponds.  相似文献   
68.
69.
对不同条件下的墨吉明对虾氮磷代谢进行了相关实验。实验结果表明:温度、体质量、盐度、p H、摄食状态和光照条件都对墨吉明对虾磷、硝酸氮、亚硝酸氮和氨氮代谢影响显著。在20~30℃范围内,随温度升高,墨吉明对虾磷、亚硝酸氮、氨氮代谢率均显著升高;硝酸氮代谢率在25℃条件下最大;磷、亚硝酸氮、硝酸氮代谢率随体质量增加而减慢,氨氮代谢加快;盐度在10~30范围内,随盐度升高,磷、亚硝酸氮代谢率提高,硝酸氮、氨氮代谢率下降;p H在7.5~9.0范围内,随p H值升高,磷代谢水平明显下降,氨氮代谢率显著升高,亚硝酸氮代谢率在p H 8.5时出现最大值(0.451±0.039)μg/(g·h);硝酸氮代谢率在p H 8.0时有最小值(1.364±0.028)μg/(g·h);饱食状态下墨吉明对虾磷、硝酸氮、亚硝酸氮、氨氮代谢率相对于饥饿组分别提高了33.85%、68.07%、233.81%、72.22%;正常光照条件下墨吉明对虾磷、硝酸氮、亚硝酸氮、氨氮代谢率相对于遮光组分别提高了130.79%、37.58%、120.23%、103.93%。  相似文献   
70.
基于物联网的南美白对虾疾病远程智能诊断系统   总被引:1,自引:0,他引:1  
为降低南美白对虾养殖风险,提高其疾病诊断与防治水平,将多种传感器在线采集的对虾养殖生态环境数据、3G手机获取的疾病图片和疾病诊治经验等多种数据进行融合,采用基于案例推理和规则推理相集成的混合推理、粗糙集融合多分类支持向量机、图像处理等多种方法,研制了基于物联网的南美白对虾疾病远程智能诊断系统。在浙江、广东等省对虾养殖区域进行现场验证,试验结果表明:该系统不仅实现了远程监测对虾养殖生态环境数据、对虾疾病图像、诊治经验数据和诊治推理规则等知识管理功能,还能够在多种数据融合的基础上,实现对虾疾病远程智能诊断与防治、疾病预警等功能。  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