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   9996篇
  免费   546篇
  国内免费   635篇
林业   1285篇
农学   406篇
基础科学   390篇
  471篇
综合类   4611篇
农作物   418篇
水产渔业   151篇
畜牧兽医   3097篇
园艺   270篇
植物保护   78篇
  2024年   68篇
  2023年   187篇
  2022年   321篇
  2021年   483篇
  2020年   393篇
  2019年   499篇
  2018年   196篇
  2017年   321篇
  2016年   406篇
  2015年   420篇
  2014年   675篇
  2013年   622篇
  2012年   878篇
  2011年   822篇
  2010年   645篇
  2009年   596篇
  2008年   506篇
  2007年   605篇
  2006年   478篇
  2005年   402篇
  2004年   263篇
  2003年   291篇
  2002年   193篇
  2001年   181篇
  2000年   127篇
  1999年   116篇
  1998年   77篇
  1997年   71篇
  1996年   39篇
  1995年   41篇
  1994年   40篇
  1993年   37篇
  1992年   38篇
  1991年   21篇
  1990年   29篇
  1989年   21篇
  1988年   10篇
  1987年   13篇
  1986年   5篇
  1982年   5篇
  1981年   1篇
  1980年   2篇
  1979年   7篇
  1978年   5篇
  1977年   3篇
  1976年   2篇
  1975年   1篇
  1974年   8篇
  1973年   2篇
  1956年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.

Objectives

To describe colostrum management practices carried out in northern Victorian dairy herds and to identify weaknesses in these areas that may affect calf health and welfare by comparing the results with the current industry recommendations

Methods

A questionnaire to obtain information about colostrum management and calf‐rearing practices was sent to commercial dairy farming clients of Rochester Veterinary Practice between June and September 2013. The questionnaire consisted of a general herd overview and colostrum harvesting practices.

Results

The response rate was 39% (58/150). Many dairy producers were not meeting the current industry recommendations in the following areas: (1) time of removal calf from the dam, (2) relying on calf suckling colostrum from the dam to achieve adequate passive transfer, (3) failing to supplement calves with colostrum, (4) feeding inadequate volumes of colostrum, (5) delayed colostrum harvesting, (6) pooling of colostrum, (7) failing to objectively assess colostrum quality or relying on visual assessment and (8) storing colostrum for a prolonged periods of time at ambient temperatures.

Conclusion

The results from this survey highlight the need for greater awareness of industry standards for colostrum management and feeding hygiene.
  相似文献   
52.
This study was conducted to evaluate the influence of back‐fat thickness (BF), at mating of sows, on the maternal and newborn circulating lipids, expression of placental fatty acids (FA) transporters and lipid accumulation in placenta. Full‐term placentas were obtained by vaginal delivery from BFI (9–14 mm; n = 37), BFII (15–19 mm; n = 43) and BFIII (20–27 mm; n = 38) sows according to BF at mating, and frozen placental sections were analysed for fat accumulation. Blood samples were collected from the sows of day 105 pregnancy and from cord blood at delivery. mRNA and protein expression levels were evaluated with real‐time RT‐PCR and Western blotting. Our results demonstrated that BFII females had significantly increased litter weight and placental efficiency, decreased maternal triglyceride (TG) and non‐esterified fatty acids (NEFA) levels, decreased maternal IL‐6, TNFα and leptin levels compared to BFIII females (< .05). BFIII sows were associated with significantly decreased newborn TG levels, increased newborn glucose, IL‐6 and TNFα levels compared to BFI or BFII sows (< .05). BFI and BFII females had significantly decreased placental TG, NEFA and cholesterol (CHOL) contents compared to BFIII females (< .05). Moreover, decreased CD36, FATP1, FABP4, and FABP1 mRNA and protein and FATP4 protein expression, and increased LPL activity were also observed in BFIII group compared with BFII group (< .05). PPARγ mRNA and protein and lipogenic genes such as SREBP‐1c, ACSL1, ACCα, FAS and SCD mRNA expression were downregulated or upregulated, respectively, in the placentas of BFIII sows compared to BFI or BFII sows (< .05). Overall, this study demonstrated that there is no advantage, in terms of litter live size, litter weight and placental FA transport and metabolism, in performing the mating of sows with BF>19 mm.  相似文献   
53.
54.
Two 125‐day experiments of the same design were conducted to evaluate the effects of a heterotrophically grown microalgae (AURA) containing docosahexaenoic acid (DHA) on pig performance, carcass traits and the fatty acid composition of lean and adipose tissue. In each experiment, 144 Hypor pigs were blocked by sex, allocated to three treatment groups, and fed 0, 0.25% or 0.50% AURA in isonutritive, isocaloric diets. Pigs were weighed on days 0, 28, 56, 84 and 112. Feed and water intakes were measured every 28 days. Pigs were slaughtered on day 125. Data from the two studies were analysed as a single data set. Performance and carcass traits did not differ between treatments. Both microalgae treatment levels enriched (< .05) Longissimus lumborum (LL) and backfat in DHA and improved (< .05) their ratios of n‐6 to n‐3 fatty acids.  相似文献   
55.
花卉是21世纪的朝阳产业,我国花卉种植面积已居世界第一,而贵州花卉处于起步阶段,许多花卉仍需从外地进货,这对于经济条件并不富裕,而地理环境条件都有利于花卉种植的贵州极为不利。通过对贵州花卉产业发展现状、发展优势的深入分析,探索相应的发展对策,以期对贵州花卉产业的健康发展提供参考。  相似文献   
56.
采取新鲜血液压片相衬观察和末梢血液涂片染色镜检法,对河南省新乡地区3000头猪附红细胞体病发病情况进行了调查;并且对体温升高、镜检附红细胞体感染强度为 病猪的血液,分别用光学显微镜、扫描电子显微镜进行形态观察和血液生化指标检测.结果表明:猪附红细胞体病的发病率为46.33%,死亡率为13.88%,隐性感染率为55.93%(755/1350).在光学显微镜下观察,红细胞呈现菠萝样;染色血片观察附红体在红细胞表面及边缘呈各种形式排列,可见强折光性发亮的圆形小体;扫描电子显微镜观察.附红体寄生的红细胞凹陷区,有大、小球体,有的小球体与大球体相连.血清胆红素、白蛋白、尿素氮、谷丙转氨酶、谷草转氨酶增加,血糖、血清总蛋白、超氧化物歧化酶活性下降.  相似文献   
57.
采用PCR-RFLP-ApaⅠ方法检测高坡猪GH基因-119~ 486 bp片段的多态性,探讨了不同基因型对其部分生产性能的影响。结果表明:产生2个等位基因A(449 bp)和B(316 133 bp),其频率分别为0.54和0.46;3种基因型:AA、AB和BB,其频率分别为0.26、0.56和0.18;除6月龄腹围和背膘厚外,其余指标值均以BB基因型最高,AA基因型的6月龄腹围和瘦肉率与BB基因型相比差异显著(P<0.05),其他指标在各基因型间差异均不显著(P>0.05)。表明,A可能是小型猪的有利等位基因,B则可能是大型猪的有利等位基因。  相似文献   
58.
纳雍糯谷猪种质特性的研究报告   总被引:1,自引:0,他引:1  
屠宰20头180日龄纳雍县农村户养糯谷猪,经测定,结果表明:糯谷猪的屠宰率较高,达74.46%,瘦肉率适中,肉质优良,肉色、嫩度、熟肉率、失水率均优于其他品种猪。初情期和性成熟早,发情周期稳定,发情征状明显。在生产调查记录中还未发现遗传性疾病,后代外貌特征表现良好。  相似文献   
59.
遵义市辣椒产业发展的现状、问题与对策   总被引:2,自引:0,他引:2  
本文概述了遵义市辣椒产业发展的基本情况及存在的问题,进一步提出了当前遵义辣椒产业发展的思路与措施。  相似文献   
60.
奶业产业链纵向价格传导受阻,导致奶牛养殖长期处于价值链的低增值环节,甚至出现“行业萎缩”现象.本文对上游奶牛养殖成本向下游乳品加工环节价格传导机制进行理论分析,并基于2008年1-12月份奶牛饲养成本和原料奶价格的月度数据,运用有限分布滞后模型测度价格传导的滞后效应.结果 表明:饲养成本向下游传导存在显著的滞后性,饲养...  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