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   381篇
  免费   35篇
  国内免费   36篇
林业   30篇
农学   10篇
  63篇
综合类   92篇
农作物   46篇
水产渔业   44篇
畜牧兽医   118篇
园艺   5篇
植物保护   44篇
  2021年   7篇
  2020年   6篇
  2019年   4篇
  2018年   4篇
  2017年   6篇
  2016年   16篇
  2015年   4篇
  2014年   17篇
  2013年   27篇
  2012年   28篇
  2011年   31篇
  2010年   24篇
  2009年   13篇
  2008年   15篇
  2007年   16篇
  2006年   25篇
  2005年   15篇
  2004年   15篇
  2003年   22篇
  2002年   31篇
  2001年   29篇
  2000年   10篇
  1999年   10篇
  1998年   9篇
  1997年   5篇
  1995年   4篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1987年   5篇
  1981年   2篇
  1977年   2篇
  1975年   2篇
  1972年   2篇
  1968年   1篇
  1962年   1篇
  1961年   6篇
  1960年   4篇
  1914年   1篇
  1904年   2篇
  1903年   1篇
  1902年   1篇
  1901年   3篇
  1900年   1篇
  1899年   1篇
  1898年   3篇
  1896年   1篇
  1887年   1篇
  1885年   1篇
  1881年   1篇
排序方式: 共有452条查询结果,搜索用时 15 毫秒
61.
62.
Gastroscopic examinations were performed in 62 Thoroughbred broodmares (33 pregnant, 29 non-pregnant) at one breeding farm to investigate the prevalence of gastric ulceration. Age, pregnancy status, race earnings, last race start, herd size, medical history, number of live foals, breeding years, feed type and number of feedings were recorded, plus coat condition and body condition score were determined. Twenty-one mares were re-evaluated after foaling, and the foaling date, foal weight at birth and placenta weight were recorded.The overall prevalence of gastric ulcers was 70.9%, with a median ulcer score of 3.0 (range: 2–5). Most ulcers were present on the squamous portion of the stomach, while two mares had glandular ulcers. There were no differences in the presence, location and severity of gastric ulcers between pregnant and non-pregnant mares. Furthermore, there were no significant associations between the variables measured and the presence of gastric ulceration. The prevalence of gastric ulceration in this specific population of horses was higher than expected and further investigation is warranted to determine the factors that contributed to this finding.  相似文献   
63.

Purpose  

As input to a cost-benefit analysis of large-scale remediation measures of contaminated sediments in the Grenland fjords in Norway, we conducted a contingent valuation (CV) survey of a representative sample of households from municipalities adjacent to these fjords.  相似文献   
64.
A laboratory procedure for the analysis of the oxygen-18/oxygen-16 isotope ratios of ethanol derived from sugars and fruit juices by pyrolysis-isotope ratio mass spectrometry (IRMS) has been applied to the study of isotopic fractionation induced by the isotope effects of fermentation and distillation. For both processes, an experimental model has been established to describe and explain the observed fractionation phenomena. It is shown that reproducible results can be obtained when appropriate analytical conditions are used. Moreover, the ability of ethanol to act as a reliable indicator of the (18)O/(16)O ratio of sugars in orange juice (and therefore to be used as an internal reference for detecting water addition) is demonstrated both in theory and in practice.  相似文献   
65.
沿铺面道路和未铺面道路,调查了4种路边环境(缓变区,附近区,中间区和非缓变区)的Pteleopsis suberosa苗木种群结构和其更新机制。沿道路平行线调查了2m×5m的203块样方,记录每个样方内的种苗总数和每个种苗的活枝数。通过评价基部和水平枝芽和挖掘地下根系来确定更新机制。结果表明,在4种路边环境中,单一主干和多主干苗木的总密度及各自密度都有明显的变化(p〈0.05)。所有苗木都是无性繁殖而来,根出条占98%,眠芽蘖和萌生各占1%左右。研究表明,铺面道路和未铺面道路缓变区中等水平土壤的干扰可以刺激Pteleopsis suberosa根出条更新 道路类型(铺面和未铺面)对苗木密度没有影响,但对路边立地的P.suberosa种群的萌生能力来说,道路类型是一个重要变量。P.suberosa是一个耐干扰的物种,受道路网干扰后可以通过根出条繁殖。  相似文献   
66.
文章以宝鸡市为例,在广泛深入分析其自然、社会、经济环境特点的基础上,根据国内外城市森林建设的理论和实践经验,阐述了宝鸡多样性生态圈建设的思路;通过对其林业建设存在问题和建设潜力的具体分析,从城市森林规划实证性与规范性兼顾原则出发,提出了"一轴、两山、三网、多点"规划布局。    相似文献   
67.
GA Optimization for Variable Cross Section frame wind turbine   总被引:2,自引:0,他引:2  
在对果蔬涂膜保鲜机理研究与分析的基础上,系统介绍了国内外不同种类涂膜剂的性能和特点,并综合分析了现阶段存在的问题和今后发展的方向,为果蔬涂膜保鲜技术的发展和应用提供了技术借鉴。  相似文献   
68.
Antibody-presenting liposomes present high interest as drug delivery systems. The association of antibodies to liposomes is usually realized by covalent coupling of IgGs or their antigen-binding fragments to lipid polar head groups by means of hetero-bifunctional crosslinkers. We present here an original platform of IgG-presenting liposomes which is based on a fusion protein between Annexin-A5 (Anx5) and the IgG-binding ZZ repeat derived from Staphylococcus aureus protein A. The Anx5ZZ fusion protein acts as a bi-functional adaptor that anchors IgGs to liposomes in a non covalent and highly versatile manner. The interactions between IgGs, Anx5ZZ and liposomes were characterized by PAGE, dynamic light scattering and fluorescence quenching assays, establishing that binding of Anx5ZZ to IgGs and of Anx5ZZ-IgG complexes to liposomes is complete with stoichiometric amounts of each species. We found that the sequence of assembly is important and that Anx5ZZ-IgG complexes need to be formed first in solution and then adsorbed to liposomes in order to avoid aggregation. The targeting capacity of Anx5ZZ-IgG-functionalized liposomes was demonstrated by electron microscopy on an ex vivo model system of atherosclerotic plaques. This study shows that the Anx5ZZ adaptor constitutes an efficient platform for functionalizing liposomes with IgGs. This platform may present potential applications in molecular imaging and drug delivery.  相似文献   
69.
For detection of the plant pathogenic Tulip virus X (TuVX), a panel of six recombinant antibodies was identified. To this end, a repertoire of variable domains from heavy-chain immunoglobulins (VHH) was cloned from an alpaca, which had been immunized with TuVX. Binding domains were selected by phage display and panning on immobilized TuVX particles. Recombinant VHH antibodies were tested for sensitivity in a sandwich ELISA, and were demonstrated to be readily able to distinguish TuVX-infected tulip leaf material from uninfected leafs. No cross-reactivity of the VHH antibodies to related flexiviridae was observed. Recombinant VHHs maintained their reactivity upon storage at −20°C for over a year. The effect of incubation at higher temperatures for prolonged time was studied. Two out of three VHH proteins retained activity after several weeks of storage at 37°C.  相似文献   
70.
为了明确杨梅疏果核仁中苦杏仁苷的提取方法,采用丁岙种杨梅的疏果为原料,以苦杏仁苷提取率为响应值,在超声波提取单因素试验和二水平试验的基础上,选择乙醇浓度、料液比、提取温度作为试验因子,利用Design Expert 80软件进行三因素三水平的响应面试验设计,并建立二次回归方程的预测模型。试验确定了杨梅疏果核仁中苦杏仁苷的最佳提取工艺条件: 乙醇浓度27%,料液比1∶45 (m/V),提取时间20 min,提取温度44℃,超声功率250 W。在该条件下苦杏仁苷理论提取率为9403%,实际提取率为9380%,与模型预测值基本相符。  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