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   2916篇
  免费   172篇
  国内免费   10篇
林业   264篇
农学   186篇
基础科学   43篇
  643篇
综合类   179篇
农作物   425篇
水产渔业   319篇
畜牧兽医   631篇
园艺   96篇
植物保护   312篇
  2024年   4篇
  2023年   21篇
  2022年   79篇
  2021年   118篇
  2020年   126篇
  2019年   172篇
  2018年   201篇
  2017年   195篇
  2016年   200篇
  2015年   108篇
  2014年   140篇
  2013年   295篇
  2012年   178篇
  2011年   210篇
  2010年   153篇
  2009年   99篇
  2008年   196篇
  2007年   88篇
  2006年   65篇
  2005年   61篇
  2004年   39篇
  2003年   44篇
  2002年   34篇
  2001年   24篇
  2000年   33篇
  1999年   18篇
  1998年   21篇
  1997年   14篇
  1996年   16篇
  1995年   15篇
  1994年   9篇
  1993年   7篇
  1992年   8篇
  1991年   6篇
  1990年   8篇
  1989年   9篇
  1988年   6篇
  1987年   7篇
  1986年   5篇
  1985年   5篇
  1984年   11篇
  1983年   8篇
  1981年   5篇
  1979年   5篇
  1978年   5篇
  1975年   3篇
  1973年   3篇
  1972年   3篇
  1971年   3篇
  1967年   4篇
排序方式: 共有3098条查询结果,搜索用时 15 毫秒
21.
This study was conducted to investigate the effects of probiotic (Primalac), prebiotic (TechnoMos) and synbiotic (Primalac + TechnoMos) supplementation on performance, immune responses, intestinal morphology and bacterial populations of ileum in broilers. A total of 240 one‐day‐old broiler chicks were randomly divided into four treatment groups which included 60 birds. Control group did not receive any treatment. The chicks in the second, third and fourth groups were fed probiotic (0.9 g/kg), prebiotic (0.9 g/kg) and probiotic (0.9 g/kg) plus probiotic (0.9 g/kg; synbiotic), respectively, at entire period. Daily feed intake, daily weight gain and feed conversion ratio were evaluated. The birds were immunized by sheep red blood cell (SRBC) on days 12 and 29 of age and serum antibody titres were measured on days 28, 35 and 42. Newcastle vaccines administered on days 9, 18 and 27 to chicks and blood samples were collected on day 42. Intestinal morphometric assessment and enumeration of intestinal bacterial populations were performed on day 42. The results indicated that consumption of probiotic, prebiotic and synbiotic had no significant effect on daily feed intake, daily body weight gain, feed conversion ratio, carcass traits, intestinal morphology and bacterial populations of ileum (p > 0.05). Consumption of prebiotic increased total and IgM anti‐SRBC titres on days 28 and 42 and antibody titre against Newcastle virus disease on day 42 (p < 0.05). Synbiotic increased only total anti‐SRBC on day 28 (p < 0.05). It is concluded that consumption of prebiotic increased humoral immunity in broilers. Therefore, supplementation of diet with prebiotic for improvement of humoral immune responses is superior to synbiotic supplementation.  相似文献   
22.
以电生功能水为研究对象,采用喷雾施药方法,研究了不同有效氯浓度的电功能水对南瓜果腐病防治效果。试验结果表明,电生功能水对南瓜果腐病的防治效果随有效氯含量的增加而提高,当电生功能水有效氯浓度为95 mg/L时效果最佳,防效达82.94%,与对照药剂50%多菌灵可湿性粉剂的防效89.41%不存在显著性差异。  相似文献   
23.
OBJECTIVE: To evaluate effects of small intestinal submucosa (SIS) on elution properties of plaster of Paris (POP). SAMPLE POPULATION: 27 POP cylinders, 27 POP spheres, and 9 polymethylmethacrylate (PMMA) spheres. PROCEDURES: Pellets were loaded with gentamicin (50 mg/g) and divided into 7 groups of 9 beads each: PMMA spheres; POP cylinders coated with 0, 4, or 8 layers of SIS; and POP spheres coated with 0, 4, or 8 layers of SIS. Gentamicin concentration was measured 6, 12, 18, 24, 32, 40, and 48 hours and 3, 4, 5, 7, 14, 21, 28, 35, and 42 days after wrapping. Porosity was evaluated via scanning electron microscopy. Curvature factor of elution curves, total amount of drug released (TDR), time required to reach 50% of total release (TDR(t50)), and number of days with concentrations > or = 1 microg/mL were compared among groups. RESULTS: SIS decreased the curvature factor and increased the TDR(t50) and TDR of POP spheres and cylinders. Curvature factor of the PMMA-release curve remained lower than that for any POP group, but all POP groups wrapped in SIS released more gentamicin than PMMA spheres. Gentamicin concentrations remained > or = 1 microg/mL in SIS-wrapped POP and PMMA groups throughout the study. Wrapping POP in SIS minimized the increase in porosity of pellets. CONCLUSIONS AND CLINICAL RELEVANCE: Wrapping POP with SIS slows the release and increases the amount of gentamicin leaching from spheres and cylinders. All groups wrapped in SIS maintained antimicrobial concentrations greater than the minimum inhibitory concentration of most pathogens.  相似文献   
24.
<正>普通菜豆(Common bean),俗称芸豆(Kidney bean),为豆科(Fabaceae)菜豆属一年生草本植物,营养丰富,蛋白质含量高,既是蔬菜又是粮食,是重要的农副产品。内蒙古自治区是我国种植普通菜豆的主要地区之一。随着普通菜豆栽培面积以及连作年限不断增加,病虫害问题日益突出,尤其是枯萎病,严重影响了普通菜豆的产量和品质,已成为限制普通菜豆产业可持续发展的主要因素之一。2021年7月,  相似文献   
25.
26.
This paper designed and developed a multi-objective programming (MOP) model to illustrate the dynamic relationship among technologies, productive activities, constraints and farmers’ objectives in the peri-urban vegetable production system and use the model as an economic tool in analysing probable consequences of a given action or innovation on the farm. The best compromise solution was generated using four analytical steps, as follows: single-objective optimization (to determine the ideal and anti-ideal values of the objective functions); constrained optimization (to generate the set of Pareto non-dominated solutions); cluster analysis (to trim down efficient set into smaller homogeneous groups); and compromise programming (to determine where the best compromise solution lies).  相似文献   
27.
Superintensive shrimp culture in zero‐exchange, biofloc‐dominated production systems is more biosecure and sustainable than traditional shrimp farming practices. However, successful application of this technology depends upon optimizing dietary formulations, controlling Vibrio outbreaks, and managing accumulative changes in water quality and composition. A 49‐d study investigated the effect of two commercial feeds of differing protein content and an indoor limited‐exchange, biofloc‐dominated culture environment on Litopenaeus vannamei performance and tissue composition, water quality and ionic composition, and Vibrio dynamics. Juveniles (5.3 g) were stocked at 457/m3 into four 40 m3 shallow raceways containing biofloc‐dominated water and fed one of two commercial feeds with differing protein content, 35 or 40%. Shrimp performance, Vibrio populations, and changes in shrimp and culture water composition were monitored. There were no significant differences (P > 0.05) in shrimp performance (survival, weight, growth, specific growth rate, total biomass, yield, feed conversion ratio, and protein efficiency ratio) or proximate composition between feed types. The 40% protein feed resulted in higher culture water nitrate and phosphate concentrations, alkalinity consumption and bicarbonate use, and higher phytoplankton density. The presence of Vibrio, specifically Vibrio parahaemolyticus, reduced shrimp survival. This survival decrease corresponded with increased culture water Vibrio concentrations. Culture water K+ and Mg2+ increased significantly (P < 0.05), and Sr2+, Br?, and Cl? decreased significantly (P < 0.05) over time. While Cu2+ and Zn2+ did increase in shrimp tissue, no heavy metals accumulated to problematic levels in culture water or shrimp tissue. These results demonstrate the importance of monitoring Vibrio populations and ionic composition in limited‐exchange shrimp culture systems.  相似文献   
28.
29.
A study was conducted to investigate the effects of skid trail slope and traffic levels on soil disturbances at two soil depths (0–10 and 10–20 cm). The treatments were set at four traffic levels (2, 7, 12 and 20), two slope classes (<20% and >20%) and two soil depths (0–10 and 10–20 cm). Results show that skidder traffic, longitudinal slope and soil depth have significant effect on soil bulk density in skid trail. Comparison of average soil bulk density in different traffic levels shows that there are significant differences in average bulk density between different traffic levels and control (p<0.05). The average bulk densities in different slopes and soil depths are significantly increased with increase in traffic levels, maximized at 12 passes (p<0.05), but there are no significant differences between 12 and 20 passes. The interaction effects between traffic and soil depth are significant (F 0.05,3=0.109, p<0.001). For all traffic treatments, there are significant differences in soil moisture content between the two slope classes and the two depths (p<0.001). However, the interaction effects between traffic levels and slope classes are not significant (p >0.05), although skidder traffic and slope affected soil moisture content.  相似文献   
30.
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