全文获取类型
收费全文 | 17519篇 |
免费 | 887篇 |
国内免费 | 1414篇 |
专业分类
林业 | 2290篇 |
农学 | 2263篇 |
基础科学 | 974篇 |
1803篇 | |
综合类 | 6870篇 |
农作物 | 1444篇 |
水产渔业 | 285篇 |
畜牧兽医 | 2130篇 |
园艺 | 663篇 |
植物保护 | 1098篇 |
出版年
2024年 | 92篇 |
2023年 | 297篇 |
2022年 | 524篇 |
2021年 | 516篇 |
2020年 | 562篇 |
2019年 | 687篇 |
2018年 | 413篇 |
2017年 | 720篇 |
2016年 | 892篇 |
2015年 | 702篇 |
2014年 | 868篇 |
2013年 | 967篇 |
2012年 | 1322篇 |
2011年 | 1249篇 |
2010年 | 983篇 |
2009年 | 1039篇 |
2008年 | 852篇 |
2007年 | 946篇 |
2006年 | 758篇 |
2005年 | 686篇 |
2004年 | 558篇 |
2003年 | 506篇 |
2002年 | 369篇 |
2001年 | 390篇 |
2000年 | 353篇 |
1999年 | 311篇 |
1998年 | 294篇 |
1997年 | 261篇 |
1996年 | 240篇 |
1995年 | 223篇 |
1994年 | 205篇 |
1993年 | 204篇 |
1992年 | 163篇 |
1991年 | 148篇 |
1990年 | 152篇 |
1989年 | 109篇 |
1988年 | 68篇 |
1987年 | 47篇 |
1986年 | 37篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1962年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
991.
Soil nitrogen (N) is considered an important driver of crop‐weed interactions, yet the mechanisms involved have been only partially explored, especially with respect to early‐season growth, when competitive hierarchies are formed. This study characterises the effects of different N levels on biomass accumulation and plant morphology for maize (Zea mays), and four important weed species (Amaranthus retroflexus, Abutilon theophrasti, Setaria faberi, and Chenopodium album). Under glasshouse conditions, plants were grown in separate pots and irrigated with nutrient solution at four N concentrations (0.2, 0.5, 2, 5 μm L−1) until 57 days after emergence. Except for S. faberi, which was unresponsive to N, the relative biomass growth rates (RGR) of maize and the broad‐leaved weeds were positively and similarly affected by increasing nitrogen. At all N levels, maize had a height advantage by virtue of its larger seed size, which conferred early growth benefits independent of RGR. At low N, biomass growth was instrumental to S. faberi’s improved competitive position, whereas height development per unit biomass improved the competitive position of A. theophrasti, C. album and A. retroflexus. The approach presented could be applied to other crop‐weed systems to evaluate environmental impacts on competitive outcomes. 相似文献
992.
993.
Jennifer Anne Davidson Rohan B. E. Kimber 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(1):99-110
Ascochyta blight causes significant yield loss in pulse crops worldwide. Integrated disease management is essential to take
advantage of cultivars with partial resistance to this disease. The most effective practices, established by decades of research,
use a combination of disease-free seed, destruction or avoidance of inoculum sources, manipulation of sowing dates, seed and
foliar fungicides, and cultivars with improved resistance. An understanding of the pathosystems and the inter-relationship
between host, pathogen and the environment is essential to be able to make correct decisions for disease control without compromising
the agronomic or economic ideal. For individual pathosystems, some components of the integrated management principles may
need to be given greater consideration than others. For instance, destruction of infested residue may be incompatible with
no or minimum tillage practices, or rotation intervals may need to be extended in environments that slow the speed of residue
decomposition. For ascochyta-susceptible chickpeas the use of disease-free seed, or seed treatments, is crucial as seed-borne
infection is highly effective as primary inoculum and epidemics develop rapidly from foci in favourable conditions. Implemented
fungicide strategies differ according to cultivar resistance and the control efficacy of fungicides, and the effectiveness
of genetic resistance varies according to seasonal conditions. Studies are being undertaken to develop advanced decision support
tools to assist growers in making more informed decisions regarding fungicide and agronomic practices for disease control. 相似文献
994.
S. Stankovic J. Levic T. Petrovic A. Logrieco A. Moretti 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(2):165-172
Fusarium proliferatum can occur on a wide range of economically important vegetable plants but its role in disease is not always well established.
In 2000 and 2001, from forty-one field samples of wilting onion and garlic plants in Serbia, F. proliferatum as the predominant fungal species was isolated from root and bulbs. Seventy isolates were firstly characterized for their
sexual fertility and were shown to be mostly members of Gibberella intermedia (sixty-seven of seventy isolates, the remaining three isolates were unfertile), the sexual stage of F. proliferatum (syn. mating population D of G. fujikuroi complex). A selected set of eleven F. proliferatum isolates from both hosts were also tested for their pathogenicity and toxigenicity. Although onion and garlic plants were
susceptible to all isolates, onion plants showed a significantly higher disease severity index. Six of the eleven isolates
of F. proliferatum produced fumonisin B1 from 25 to 3000 μg g−1, and beauvericin from 400 to 550 μg g−1; ten isolates produced fusaric acid from 80 to 950 μg g−1 and moniliformin from 50 to 520 μg g−1. Finally, all isolates produced fusaproliferin up to 400 μg g−1. These results confirm F. proliferatum as an important pathogen of garlic and onion in Europe and that there is a potential mycotoxin accumulation risk in contaminated
plants of both garlic and onion. 相似文献
995.
996.
水稻白叶枯病防治技术研究 总被引:6,自引:0,他引:6
应用中国农科院最新研制的农用抗生素中生菌素研究了其对水稻白叶枯病的防治效果和应用技术。室内浸种试验表明,用中生菌素100mg/kg、在水温58℃下浸稻种48h,可全部杀死种子表面及内部的白叶枯病菌,切断了种子带菌传病的途径。田间试验表明,用中生菌素50mg/kg、水温55~60℃的药液浸种48h,再于秧苗3~4叶期和移栽前5~7d用中生菌素15mg/kg施药保护,田间白叶枯病可迟发生20d以上,其发病程度亦显著降低,对于轻病田或轻发生年份大田可免于防治;重病田或重发生年份于发病初期再用中生菌素15mg/kg防治1次,即可控制病情的发展。作者认为用中生菌素浸种及秧田期施药保护不仅改变了以往田间发病初期用药防治的策略,而且大大降低了防治费用,经济效益、社会效益及生态效益显著。 相似文献
997.
用灰色系统理论的斜率关联度分析法,求得影响黑杨派南方型无性系高生长的主要气候因子依次为:降水量、极低温、极高温、蒸发量、日照时数、积温、年均温(或相至湿度)、相以湿度(或年均温)、无霜期。 相似文献
998.
以江苏省宿迁市农村为研究对象,分析了现阶段宿迁市农村医疗保障体系运行中存在的主要问题,研究设计一个符合我国经济欠发达地区农村居民需求的多层次新型医疗保障体系,对农村新型医疗保障体系的结构模式和各种制度政策进一步完善优化,并提出切实可行的政策措施,以期完善经济后发达地区农村医疗保障体系,满足农村居民医疗保障需求。 相似文献
999.
[目的]比较不同香型烤烟CO2膨胀前后品质变化。[方法]开展了3种主要香型烟叶CO2膨胀试验,对各样品烟丝膨胀前后的物理性能、化学成分、烟气指标和内在质量进行检测分析。[结果]清香型烟叶经过CO2膨胀,还原糖、挥发酸、焦油和烟碱含量平均降幅最大,香气质、香气量和柔细度改善或保持最佳;浓香型烟叶的平均膨胀效果最明显,总糖、总氮含量平均变化最大,杂气、刺激性、透发性和浓度改善或保持最佳;中间香型烟叶CO2膨胀后总植物碱、氯和蛋白质含量平均变化明显,重量、口数、总粒相物以及CO 4项指标降幅最大,甜度、余味指标有更好提升。[结论]不同香型烤烟各项理化、感官指标受膨胀影响程度有所差别,烤烟香型与CO2膨胀具有一定的关联性。 相似文献
1000.
《Scandinavian Journal of Forest Research》2012,27(1):10-20
Abstract Height and diameter distributions between improved and unimproved (checklot) seedlots for white spruce [Picea glauca (Moench) Voss] and black spruce [Picea mariana (Mill.) BSP] were compared using the two-parameter Weibull function. Individual tree height at age 5–15 years and diameter at breast height at age 15 years that were collected from two series of large-plot realized gain tests were used for this purpose. For both species, improved seedlots did not significantly (α=0.05) change the shape parameter of the distributions relative to their checklots, suggesting that an overall shape value will be adequate to predict tree size distributions of various improved seedlots. The most important finding was that seedlot influenced the scale parameter (related to the range of the distribution) significantly, but from a practical viewpoint, only those scale values of the higher rated seedlots (i.e. seedlots collected from a rogued seed orchard or superior families) were significantly higher (α=0.05) than those of the respective unimproved seedlot. The changes in scale value of the alternative improved seedlots relative to the checklot (ΔScale) were comparable in magnitude to the respective realized genetic gains, suggesting that tree improvement effects on the scale value can be adjusted by realized genetic gains. The results also suggest that site and age significantly affected the scale value; in general, ΔScale became larger at earlier ages or on better sites. The findings reported here will be used in the development of yield functions for genetically improved white and black spruce in New Brunswick. 相似文献