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   303篇
  免费   13篇
  国内免费   13篇
林业   9篇
农学   29篇
基础科学   14篇
  31篇
综合类   135篇
农作物   11篇
水产渔业   12篇
畜牧兽医   69篇
园艺   8篇
植物保护   11篇
  2024年   1篇
  2023年   1篇
  2022年   5篇
  2021年   6篇
  2020年   7篇
  2019年   5篇
  2018年   5篇
  2017年   7篇
  2016年   8篇
  2015年   12篇
  2014年   11篇
  2013年   13篇
  2012年   23篇
  2011年   23篇
  2010年   14篇
  2009年   14篇
  2008年   13篇
  2007年   14篇
  2006年   9篇
  2005年   9篇
  2004年   10篇
  2003年   7篇
  2002年   10篇
  2001年   9篇
  2000年   16篇
  1999年   8篇
  1998年   6篇
  1997年   9篇
  1996年   7篇
  1995年   8篇
  1994年   7篇
  1993年   11篇
  1992年   2篇
  1991年   3篇
  1990年   4篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1981年   2篇
  1979年   1篇
  1975年   1篇
  1973年   1篇
排序方式: 共有329条查询结果,搜索用时 15 毫秒
81.
王蕾  庞宏伟 《安徽农业科学》2011,(17):10570-10571,10574
以具有典型意义的河北省曲阳县羊平村为例,分析了曲阳县乡村民间文化旅游概况,阐述了其旅游资源丰富、区位条件优越、旅游业已经获得一定发展的优势,也总结了其道路绿化不足、环境污染严重、高层次人才缺乏、小型商品开发不足的劣势,在此基础上提出了应该以商旅互动、立足文化、动态参与、系统规划、统筹兼顾等原则指导乡村民间文化旅游的开发设计,并总结了相关发展战略。针对羊平村,从环境建设、石岗雕刻公园休闲区设计、黄石广场功能区设计、乡村旅游商品设计方面展开了重点建设项目探讨,以期能对我国民间文化旅游资源开发提供参考。  相似文献   
82.
Summary Cell cultures were developed from dihaploid clones ofSolanum tuberosum L. Selection in cell suspensions as well as plating of cells on selective medium supplemented with 5 mmol Al produced tolerant cell lines. The constancy of Al-tolerance of cell lines was confirmed by culturing the calli for 3 months in Al-free medium and then transferring them back to selective medium. 4 tolerant regenerant clones were obtained which maintained Al-tolerance also after subculture in control medium. Two of the 4 clones that constantly maintained Al-tolerance, originated from cell lines subcultured for 5 months under stress conditions. However, the regeneration rate of these cell lines was low compared with that of lines obtained after a shorter selection period.  相似文献   
83.
A total of 147 dogs and 85 cats was surveyed for faecal carriage of thermophilic Campylobacters. Isolates were obtained from 33 (22.4 %) of the dogs and from 10 (11.8 %) of the cats investigated. The isolation rates recorded for diarrhoeic and non-diarrhoeic dogs and cats were not significantly different. Likewise, Campylobacters were isolated with about equal frequencies from puppies and mature dogs as well as from bitches and male dogs. Nineteen canine and 7 feline strains were biotyped and serotyped. A large majority (88.5 %) of these 26 strains belonged to serotypes previously recovered from human G. coli and C. laridis constituted 7.7 % and 3.8 %, respectively. Three strains belonged to serotypes previously recovered from human patients in Norway.  相似文献   
84.
文章旨在研究犊牛开食料中添加不同含量的苜蓿干草对犊牛生长发育、营养物质消化率和瘤胃发酵参数的影响。试验选择45头刚出生的中国荷斯坦母犊牛,按照体重划分区组,采用完全随机区组试验设计,将新生犊牛分配到3个处理组中,每组15头犊牛。对照组犊牛开食料中不添加苜蓿干草;在试验组Ⅰ犊牛开食料中添加10%的苜蓿干草(干物质基础);试验组Ⅱ犊牛开食料中添加20%的苜蓿干草(干物质基础)。犊牛在60日龄断奶,断奶结束后试验继续进行20 d。试验期间,1~50 d为哺乳期,犊牛饲喂常乳(正常饲喂量)+开食料;51~60 d为断奶过渡期,犊牛饲喂常乳(减量)+开食料;61~80 d为断奶后期,犊牛饲喂开食料。犊牛7日龄时开始饲喂开食料,犊牛14日龄时,在开食料中开始添加苜蓿干草。每天记录开食料采食量,分别于试验第1天、第50天、第80天在早晨饲喂前称重犊牛体重,分别于第50天和第80天在犊牛采食开食料3 h后采集瘤胃液,测定挥发性脂肪酸浓度和NH3-N浓度。于试验最后3 d,采集粪便进行消化试验,测定营养物质消化率。试验结果表明,犊牛开食料中添加苜蓿干草显著提高了犊牛体重、平均日增重和干物质采食量,而且与添加剂量呈线性相关,以20%的添加量组犊牛具有最佳的生长性能,而对犊牛的饲喂效率没有显著影响。犊牛开食料中添加苜蓿干草显著改善了瘤胃发酵功能,增加了瘤胃液pH,提高了瘤胃液乙酸与丙酸的比值。苜蓿干草对犊牛的营养物质表观消化率没有显著影响。因此,本试验结果表明,犊牛开食料中添加20%的苜蓿干草显著提高了犊牛生长性能,改善了犊牛瘤胃发育和发酵功能。  相似文献   
85.
To evaluate the effect of reduced calcium (Ca) and available P (aP) levels in starter diets on growth performance and tibia, sternum and serum characteristics, and to assay the association between Ca and P (aP) intakes and these variables, 600 one-day-old broiler chicks (Ross 308) were used in a 21-days trial. Broilers were randomly allotted to five treatments with five replicate pens. Chicks were fed on one of the five starter diets that were formulated with a 10% reduction in the Ca and aP contents, starting from the control diet and hence, named as C (0.96% Ca, 0.45% aP), L1 (0.85% Ca and 0.42% aP), L2 (0.77% Ca and 0.38% aP), L3 (0.68% Ca and 0.34% aP) and L4 (0.61% Ca and 0.31% aP). Declining dietary Ca and aP levels did not affect body weight and levels of Ca, P and alkaline phosphatase in serum, but reduced linearly feed intake, the feed conversion ratio and the bone weight and ash content. The Ca and aP intakes and Ca:aP ratio displayed a positive correlation with both tibia and sternum weights, and the mass of the bones were equally sensitive to dietary Ca and aP levels. In conclusion, the body weight of young broilers was irresponsive to changes in the skeleton when exposed to early dietary Ca and aP restrictions (up to 0.61% Ca and 0.31% aP) and the mechanostat had limits due to the association between Ca and aP intakes, and bone properties.  相似文献   
86.
Adhesion process ensures the formation of the appropriate connection between mother and foetus during placentation and further placental development, which determines physiological pregnancy course. Extracellular matrix of foetal membranes are a rich source of biologically active proteins, the synthesis of which is regulated by hormones. Depending on the stage of pregnancy, the protein profile of the placenta changes, thanks to which its remodelling is possible. The aim of the study was to evaluate the effect of decorin, as well as selected glycosylation inhibitors on the adhesion of caruncular epithelial cells derived from cows during pregnancy. Placental cells were isolated from healthy, pregnant (2nd and 4th month) cows after slaughter, which allowed for the establishment of 4 primary cell cultures without visible cells of fibroblast morphology. The presence of decorin in cell monolayer and cell lysates was determined by the use of immunocytochemistry and Western blotting, respectively. The viability of cells was evaluated by MTT assay. The adhesion of cells to fibronectin was measured spectrophotometrically. Protein N-glycosylation and O-glycosylation have a modulating effect on the adhesion and viability of placental cells during early–mid pregnancy. Decorin and tunicamycin were shown to have anti-adhesive properties with respect to caruncular cells of the pregnant bovine uterus.  相似文献   
87.
发酵温度对冻干乳酸菌发酵剂活菌数的影响   总被引:3,自引:0,他引:3       下载免费PDF全文
以脱脂乳为基础培养基,选用保加利亚乳杆菌和嗜热链球菌混合菌种在30℃、34℃、37℃、42℃发酵,用灭菌30%Na2CO3控制发酵液pH值6.0~6.3,制成冻干发酵剂,研究发酵温度对冻干酸奶发酵剂活菌数的影响。结果表明:不同发酵温度下制得的冻干发酵剂活菌数有显著差异,尤其是在30℃发酵制得的冻干发酵剂其活菌数显著高于其它发酵温度,其冻干发酵剂活菌数高达4.2×1011cfu/g。  相似文献   
88.
起动机是发动机正常工作的必要保证,其作用是通过蓄电池供电,带动发动机进入工作状态。起动机性能的好坏直接影响和制约着汽车的正常起动。本文就起动机容易出现的故障、检查以及预防措施作以简析。  相似文献   
89.
选用起动机转速信号为负反馈信号来控制起动机电压占空比,从而控制起动机通电电流的大小。设计出了起动机在起动时进入啮合前能够使起动机缓慢旋转的控制电路,保证起动机能够正常起动发动机。  相似文献   
90.
Abstract. Broadcast granular fertilizers are inefficient at supplying nitrogen (N) to wide-spaced row crops. Substantial nitrate residues can remain in the soil post-harvest, even when recommended fertilizer practices are followed. This paper explores the benefits of an alternative strategy based on targeting small amounts of liquid nitrogen starter fertilizer close to the seed at drilling to increase N use efficiency and reduce potential pollution. Bulb onion ( Allium cepa ) and crisp lettuce ( Lactuca sativa ) were grown with various rates and combinations of ammonium phosphate (AP) and urea ammonium nitrate (UAN) as 'starters', in comparison with seedbed incorporated ammonium nitrate. AP consistently improved early growth and final yield of both crops compared to broadcast ammonium nitrate, but UAN showed no additional benefits. AP in combination with broadcast N, or injected UAN, generally increased N recovery, and produced yields of marketable quality produce matched only by much higher rates of broadcast N. A reduced N input system based on starter fertilizers is likely to be acceptable to the industry, but would rely on a method to predict how much N is required to supplement that provided by the starter.  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