全文获取类型
收费全文 | 2830篇 |
免费 | 169篇 |
国内免费 | 131篇 |
专业分类
林业 | 954篇 |
农学 | 209篇 |
基础科学 | 31篇 |
224篇 | |
综合类 | 1041篇 |
农作物 | 149篇 |
水产渔业 | 58篇 |
畜牧兽医 | 203篇 |
园艺 | 175篇 |
植物保护 | 86篇 |
出版年
2024年 | 1篇 |
2023年 | 26篇 |
2022年 | 43篇 |
2021年 | 62篇 |
2020年 | 67篇 |
2019年 | 100篇 |
2018年 | 52篇 |
2017年 | 84篇 |
2016年 | 116篇 |
2015年 | 86篇 |
2014年 | 125篇 |
2013年 | 181篇 |
2012年 | 232篇 |
2011年 | 183篇 |
2010年 | 146篇 |
2009年 | 155篇 |
2008年 | 137篇 |
2007年 | 134篇 |
2006年 | 151篇 |
2005年 | 109篇 |
2004年 | 104篇 |
2003年 | 86篇 |
2002年 | 64篇 |
2001年 | 98篇 |
2000年 | 70篇 |
1999年 | 42篇 |
1998年 | 48篇 |
1997年 | 70篇 |
1996年 | 62篇 |
1995年 | 54篇 |
1994年 | 38篇 |
1993年 | 36篇 |
1992年 | 26篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 29篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有3130条查询结果,搜索用时 15 毫秒
931.
Understanding the interactions between nutrition and immune system is crucial for adjusting nutrient allowances in dietary formulations that optimize production efficiency. Among various animal proteins, fish meal (FM) is rich in protein (amino acids), readily available throughout most of the world, and competitively priced against other animal proteins (e.g. milk and blood). In addition, many researchers reported that FM is traditionally recognized as a high digestible protein with a high content of amino acids, vitamins and minerals for pigs. Supplementation of fatty acids by FM and fish oil (FO) is one strategy to modify an animal immune response. As a result of FM and FO effects, those supplementations can result in improved performance and immunity of young animals. 相似文献
932.
选取了3种铁高效园艺作物,木本小金海棠,藤本葡萄‘SO4’,草本番茄‘合作906’,对其缺铁应答反应机制进行了分析和比较。结果发现,3种植物中缺铁处理都可以诱导Fe3+还原酶活性升高及根际pH下降;但在缺铁加去顶双重处理时,除番茄Fe3+还原酶活性升高和根际pH下降外,苹果和葡萄没有变化,说明苹果和葡萄中缺铁应答反应的调控有赖于地上部系统信号的存在,而番茄中根系局部信号至少能够触发缺铁应答反应。分根处理表明,在苹果和番茄中部分根系缺铁可导致非缺铁根系产生缺铁应答反应,而葡萄中没有缺铁应答反应,说明苹果和番茄中系统信号可以诱发缺铁应答反应,而葡萄可能需要系统信号和根系局部信号的共同作用。研究还发现,缺铁可诱导苹果和番茄根毛的形成,葡萄则没有。以上结果表明,不同的物种缺铁应答反应的调控机制可能不同。 相似文献
933.
Watersprout occurrence and growth were investigated over a two-year period in an early maturing peach cultivar (Alexandra) under different intensities of dormant pruning for fruited and defruited trees. A preliminary study focused on identifying the laws that determine the probability of presence and occurrence of watersprouts in relation to watersprout-bearing shoot (WBS) length. The increase in watersprout probability of presence and occurrence resulting from greater WBS length illustrated the high capacity of peach for sprouting. Watersprout lengths were measured, as well as the lengths of young shoots, one-year-old fruit-bearing shoots (FBSs) and older branches considered as WBS in order to evaluate total shoot growth within the tree. Watersprout number and total length tended to be higher under severe dormant pruning and in fruited trees than under light dormant pruning and in defruited trees. This stimulation of watersprout length appeared to compensate for the concomitant lower total length of young shoots, resulting in a constant overall vegetative growth rate for the whole tree. In the second year of the experiment, watersprouts were either removed by summer pruning or not in order to evaluate watersprout incidence on the rest of the tree. After light and severe watersprout removal (WSR), the annual diametrical growth of FBS tended to be higher and lower, respectively, compared to trees not submitted to summer pruning. Light WSR might favour light interception in the centre of the canopy, thus improving assimilate production and allocation to FBS, whereas severe WSR could prevent carbohydrate export from watersprouts to FBS. Under our conditions, the limit at which WSR intensity became detrimental for FBS diametrical growth appeared to be after approximately 75% of the watersprouts were removed. Severe WSR appeared likely to improve fruit diameter, whereas it had no significant impact on the percentage of soluble solids. 相似文献
934.
Fruit tree growth habit and vigour are important traits for orchard management and production, yet are difficult to select for in breeding programs because the parameters for their evaluation are complex, and their expression often requires sufficient plant size and development, entailing valuable time. Thus, in olive (Olea europaea L.) breeding, as for other fruit crops, it is critical to define growth habit and vigour parameters with selection potential, and to determine the earliest age at which they can be measured. Furthermore seedling growth habit traits are important in themselves, particularly in their relation to juvenile period length and management. To explore these issues we evaluated a series of new and standard growth habit parameters during the first year of growth in a population of unpruned olive seedlings originating from six different crosses. The influence of plant age on growth habit traits was determined by comparing measurements at two or three different times. Both parent genotype and plant age significantly affected the vigour and growth habit of the olive seedlings, and 9 months was the most appropriate age for evaluating seedling growth parameters. ‘Picual’, ‘Arbosana’ and ‘Sikitita’ were shown to be promising cultivars for use as genitors, because of their tendency to produce offspring with desirable growth habit traits such as high vigour, weeping habit and low lateral shoot number. From among the 17 parameters studied, based on parent influence and the absence of correlation among parameters, five were identified which best described olive seedling growth habit: Primary Shoot Top Diameter, Primary Shoot Conicity, Secondary Shoot Number, Secondary Shoot Insertion Angle and Longest Secondary Shoot Internode Length. 相似文献
935.
936.
A laboratory study was taken up in the Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore in the year 1986 to fix optimum concentration and to evaluate the efficiency of CCC (2-chloroethyl trimethyl ammonium chloride), succinic acid and sodium chloride as seed hardening chemicals for pearl millet. The study revealed that CCC 100 ppm, succinic acid 0.15 per cent and sodium chloride 1 per cent concentrations were better in improving the germination per cent, root : shoot ratio and vigour index of pearl millet. 相似文献
937.
不同环境下藏獒幼犬生长发育规律的初步研究 总被引:1,自引:1,他引:0
选择1月龄幼犬60条(公、母各半),分别在高海拔地区(1 500 m)和平原地区进行试养,饲养管理水平相同,通过测定1-10月龄幼犬的体质量、体尺等指标对2个地区幼犬的生长发育指标进行了比较.结果表明:3、4月龄高海拔地区的幼犬体质量比平原地区分别高5.33、.7 g,相对生长率比平原地区高3.6%和3.5%,差异达极显著水平(P<0.01).体尺发育规律分析发现:1-6月龄幼犬的体长生长速度高于胸围,8-10月龄胸围、体高的生长速度远大于体长.据此认为,环境对藏獒幼犬体质量、体高、体长的影响显著. 相似文献
938.
939.
U. R. Sangakkara U. A. Hartwig J. Nösberger 《Journal of Agronomy and Crop Science》1996,177(3):145-151
The development of an extensive root system enables plants to overcome water stress. However, there is little information on the response of food legumes to soil moisture, especially during early growth, which determines crop establishment. Thus, an experiment was conducted under controlled conditions to identify the effect of soil moisture and fertilizer potassium on root and shoot growth of french beans ( Phaseolus vulgaris L.) seedlings. The seedlings were grown in a sand medium under a high and low soil moisture regime and with 0.1, 0.8 or 3.0 mM potassium.
Root lengths, dry weights and numbers of root hairs were greater under low soil moisture conditions. Potassium increased root growth irrespective of soil moisture regimes. The impact of potassium on root length was more pronounced under a high soil moisture regime. In contrast, potassium increased root dry weights and root hairs to a greater extent when plants were grown under dry conditions. The lack of adequate soil moisture increased specific leaf weights, and this phenomenon was reduced by the application of potassium. Shoot:root ratios also showed a similar phenomenon. The development of an extensive root system by french bean seedlings under dry conditions to extract a greater quantity of available soil moisture fur establishment and plant growth and the ability of potassium to promote this phenomenon is presented in this study. 相似文献
Root lengths, dry weights and numbers of root hairs were greater under low soil moisture conditions. Potassium increased root growth irrespective of soil moisture regimes. The impact of potassium on root length was more pronounced under a high soil moisture regime. In contrast, potassium increased root dry weights and root hairs to a greater extent when plants were grown under dry conditions. The lack of adequate soil moisture increased specific leaf weights, and this phenomenon was reduced by the application of potassium. Shoot:root ratios also showed a similar phenomenon. The development of an extensive root system by french bean seedlings under dry conditions to extract a greater quantity of available soil moisture fur establishment and plant growth and the ability of potassium to promote this phenomenon is presented in this study. 相似文献
940.
应用不同浓度的多效唑对油茶树在新梢萌发前进行土壤施药和涂干处理,在新梢萌发后进行叶面喷施试验。多效唑1000、1500、2000ppm浓度叶面喷施及1.5g/m~2加水土壤施药对油茶新梢生长有强烈的抑制作用。缩短新枝长度及节间长,增加短枝的比例,并且提高了叶片的叶绿素含量、光合速率和蛋白质含量,从而有效地控制了树势,减少了养分消耗,增进了新陈代谢活动。涂干处理没有效果。 相似文献