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   3528篇
  免费   143篇
  国内免费   176篇
林业   481篇
农学   267篇
基础科学   255篇
  246篇
综合类   1700篇
农作物   149篇
水产渔业   64篇
畜牧兽医   311篇
园艺   263篇
植物保护   111篇
  2024年   7篇
  2023年   36篇
  2022年   56篇
  2021年   74篇
  2020年   64篇
  2019年   95篇
  2018年   50篇
  2017年   89篇
  2016年   137篇
  2015年   136篇
  2014年   177篇
  2013年   176篇
  2012年   279篇
  2011年   294篇
  2010年   226篇
  2009年   196篇
  2008年   205篇
  2007年   281篇
  2006年   242篇
  2005年   195篇
  2004年   110篇
  2003年   121篇
  2002年   85篇
  2001年   82篇
  2000年   73篇
  1999年   54篇
  1998年   44篇
  1997年   26篇
  1996年   36篇
  1995年   39篇
  1994年   36篇
  1993年   23篇
  1992年   19篇
  1991年   26篇
  1990年   13篇
  1989年   11篇
  1988年   6篇
  1987年   9篇
  1986年   6篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1979年   1篇
  1975年   1篇
排序方式: 共有3847条查询结果,搜索用时 15 毫秒
71.
思政教育是高职院校教学的重点内容,对学生的思想、行为会产生直接影响,同时与工匠精神存在紧密关系,需要对其予以融合。为了提升高职机械类专业教学的质量,引入思政教育极为重要,其在推动学生全面发展方面也发挥出了重要作用。基于此,主要以机械基础类专业教学为例,分析了高职机械类专业课程与思政教育的联系为切入点。同时,通过调整教学思路与路径,结合机械发展史展开思政教育,引入大国重器实际研发案例,落实全面评价这些思政教育的融入策略。  相似文献   
72.
基于像元尺度耕地质量局部空间自相关的基本农田划定   总被引:2,自引:0,他引:2  
划定永久基本农田保护区是我国农业可持续发展的战略要求,耕地质量是保护区位置选择的重要依据。以湖北省嘉鱼县为例,引入植被指数信息,完善耕地质量综合评价指标体系,通过网络层次分析法确定指标权重,结合局部空间自相关分析结果,分别对基于耕地质量与莫兰指数的基本农田逐像元补划结果进行了分析。研究结果表明,嘉鱼县耕地综合质量在空间上表现出较强的相关性,全域和耕地范围的局部自相关系数分别为0. 864 5和0. 991 6;基于耕地质量和莫兰指数的划定结果在空间上保持高度的一致性,两种方法均优先将空间上呈HH型聚集的99. 97%的像元划入了基本农田保护区;两种方法互为补充,可以为最终决策提供参考。  相似文献   
73.
The inactivation of pollen by soft X-ray irradiation and subsequent artificial pollination are time-intensive practices used in the production of seedless watermelons (Citrullus lanatus L.). Watermelon generally has a lot of staminate flowers; however, they only have a small amount of pollen. Watermelon pollen cannot be used in pollination under the present situation. Therefore, the objective of this study was to determine which is the most effective pollen extender medium for cultivation of watermelon with soft X-ray irradiated pollen. In this experiment, ‘Agar,’ ‘Marriage powder,’ and ‘Sekishoshi’ (Lycopodium dyed red with safflower pigment) were used as extender media with soft X-ray irradiated pollen at equal or twice the weight of the pollen. When ‘Sekishoshi’ was used as an extender medium, fruit set was very low. A lot of deformed fruit was produced when agar was used with the pollen. On the other hand, when ‘Marriage powder’ was used in equal proportions with the pollen, fruit set was about 70% and, moreover, Brix was high. Thus, the mixture of ‘Marriage powder’ with an equal amount of pollen was the best for use in actual cultivation. We conclude, then, that soft X-ray irradiated pollen in an extender medium can be effectively adapted for producing seedless watermelons.  相似文献   
74.
设施农业介质消毒技术与设备的现状和发展   总被引:3,自引:0,他引:3  
针对设施农业高密度栽培及同一地块上连年种植作物,使得土传病害、病原菌得以不断的积累、生长和繁殖而造成严重减产或降低产品质量的问题,论述了栽培介质消毒技术与设备的国内外应用现状,介绍了当前常用栽培介质消毒方法及设备的原理与研究成果,指出了不同消毒方法及设备所存在的问题及适用状况;分析和讨论了设施农业栽培介质消毒设备的技术发展.作为设施农业代表性的核心装备之一,高度机械化、无污染、高新技术的运用是其主要的发展趋势.  相似文献   
75.
AIM: To study the influence of basic fibroblast growth factor(bFGF) on treating ed palatal perforation in rats. METHODS: bFGF was given to the early palatal perforation in rat. The granulation tissues in perforations were grossly and pathologically obserVed. RESULTS: The the of wound healing was significantly in- crease in the bFGF group (P<0.01 ). bFGF could obviously promote the proliferation of the granulation tissues and fibroblasts. The number of AgNORs granules in fibrablasts were 3.73 ±0.52 in the buy group and 2.11 ±0.31 in control group (P < 0.05). CONCLUSION: bFGF could promote the growth of granulation tissues and had a strong promotion on the wound healing in palatal perforation. It was helpful in repairing palatal perforation.  相似文献   
76.
Prunus avium is primarily cultivated for its fruit, sweet cherries. However, it is also used to produce high‐quality timber. In a P. avium seed orchard, gametophytic self‐incompatibility is a restriction for free pollen flow and should be considered when establishing basic forest materials. In this study, S‐locus diversity and cross‐incompatibility of wild cherry individuals in clonal banks established for breeding for timber production were investigated. Wild cherry trees (140) with outstanding forest growth habit, collected in northern Spain, grafted and planted in two clonal banks, were genotyped at the S‐locus. The self‐incompatibility S‐locus genes, S‐RNase and SFB, were analysed by PCR. Twenty‐two S‐haplotypes, resulting in 72 different S‐genotypes, were identified. The genotypes were grouped into 33 incompatibility groups and 39 unique genotypes. This initial S‐locus analysis revealed large genetic diversity of wild cherry trees from the Spanish northern deciduous forest, and provides useful information for seed orchard design. Wild P. avium displays significantly more genetic diversity than what is detected in local cultivars, revealing a narrowing of genetic diversity during local domestication.  相似文献   
77.
淮北地区氮肥群体最高生产力水稻钾素吸收利用特征   总被引:2,自引:1,他引:1  
以淮北地区有代表性的34个中熟中粳品种为试材,设置7个氮肥水平(0、150.0、187.5、225.0、262.5、300.0、337.5 kg hm~(–2)),得出各品种的最高产量,将该最高产量定义为氮肥群体最高生产力。在此基础上,明确处于顶层水平(≥10.50 t hm~(–2))、高层水平(9.75~10.50 t hm~(–2))、中层水平(9.00~9.75 t hm~(–2))和底层水平(≤9.00 t hm~(–2))水稻品种的钾素积累、分配及转运特征。结果表明,4个生产力等级水稻品种地上部植株、茎鞘和叶片的含钾率在拔节期最高;抽穗期顶层水平品种的这3个参数高于其他3个等级的品种;穗部含钾率差异不显著。随着氮肥群体生产力等级的提高,钾素总积累量增多;拔节前底层水平钾素积累量最多,两年平均为120.56 kg hm~(–2),比例占50.56%,顶层水平为最少,两年平均为108.02 kg hm~(–2),比例占35.99%;拔节至抽穗期和抽穗至成熟期顶层水平钾素阶段积累量及比例显著高于其他3个等级。移栽至拔节期,钾素积累速率为中层底层高层顶层水平,拔节后则为顶层高层中层底层水平。叶片的钾素转运量及转运率明显高于茎鞘;顶层水平叶片的钾素转运量高于其他3个等级,高层水平叶片的转运率最高;穗部增加量随生产力等级的递增而变大;抽穗到成熟期,茎鞘、叶片对穗的钾素转运贡献率表现为底层最高,中层次之,顶层最低。4个等级水稻品种籽粒生产率和百千克籽粒吸钾量差异不显著;钾素偏生产力和钾收获指数均表现为顶层高层中层底层水平。总之,氮肥群体最高生产力越高,水稻中后期植株钾素积累量及器官对钾素的吸收利用效率越显著。抽穗后保持较高的钾素吸收利用及转运效率是高产水稻品种的重要特征。  相似文献   
78.
Substrate components produced in the sub-tropics or tropics were combined in various proportions as substrates for the greenhouse production of ‘Big Beef’ tomato. Coir was mixed with parboiled rice hulls (PBH) or burnt rice hulls (BRH) at 0, 25, 50, 75, or 100% volume. Fruit fresh weights at equal proportions of BRH or PBH in coir were similar, with the greatest fruit yields achieved with 50 to 100% coir (0 to 50% PBH or BRH). Compared to 100% coir, PBH in coir decreased substrate container capacity and increased air porosity, while BRH in coir increased container capacity and decreased the air porosity. Pre-plant fertilisation of the PBH + coir substrates (superphosphate, gypsum, trace elements, calcium nitrate, and surfactant) increased fruit yield significantly. Substrates containing 50 to 100% coir with BRH or PBH yielded greater fruit fresh weights than was achieved in in 70% BRH + 30% gravel (a typical substrate used in the Dominican Republic), and reusing the 70% BRH + 30% gravel led to a 36% increase in fruit fresh weight. Fruit fresh weights in 100% coir or 75% coir plus 25% PBH or BRH were similar to those achieved in a commercial peat-lite. Herein we report on substrates made from tropical components that perform similarly to a peat-based substrate in the production of greenhouse-grown tomatoes.  相似文献   
79.
通过对绵羊腔前卵泡培养方法的研究,能够探索出适宜绵羊腔前卵泡生长发育的培养条件,以及为进一步揭示绵羊卵泡生长发育的规律奠定一些基础。试验一通过使用微滴法和琼脂培养基法培养腔前卵泡,观察其对绵羊腔前卵泡生长的影响;试验二通过绵羊腔前卵泡单独培养与群体培养,探讨不同培养密度对绵羊腔前卵泡生长的影响。试验结果显示,使用微滴法与琼脂培养基法培养的绵羊腔前卵泡,在培养3天时,卵泡直径增加值和存活率差异均不显著(P0.05);但培养6天时,琼脂培养基法培养的腔前卵泡的直径增加值和存活率均极显著高于微滴法培养的腔前卵泡(P0.01);在使用琼脂培养基培养的条件下,对绵羊腔前卵泡进行单独培养和群体培养,在培养的6天时间内二者卵泡直径增加值和存活率差异均不显著(P0.05)。试验结果表明,琼脂培养基法是较为适宜的绵羊腔前卵泡体外培养方法;培养密度对绵羊腔前卵泡体外培养并无显著影响。  相似文献   
80.
育苗轻型基质块配方研究   总被引:1,自引:0,他引:1  
为充分利用南方果树废弃物资源,以香蕉菠萝废弃茎叶堆肥和椰糠作为基质材料,添加粘合剂、固化剂、改良剂,制作出基质块。采用正交法设定基质块配方,通过测试分析基质块的理化性状,确定最佳的基质块配方。结果表明,香蕉菠萝废弃茎叶堆肥和椰糠的配比是影响基质块理化性状的主要因素,各因素影响的主次顺序为:基质配比改良剂粘合剂固化剂;综合分析,A3B2C3D3组合配方具有最佳的理化性状,即基质配比(堆肥:椰糠)为4:6,粘合剂(聚乙烯醇)为4%,固化剂(硼砂)为2.5%,改良剂为140%。  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