全文获取类型
收费全文 | 13322篇 |
免费 | 836篇 |
国内免费 | 825篇 |
专业分类
林业 | 1728篇 |
农学 | 1958篇 |
基础科学 | 589篇 |
1223篇 | |
综合类 | 5058篇 |
农作物 | 1091篇 |
水产渔业 | 356篇 |
畜牧兽医 | 1665篇 |
园艺 | 479篇 |
植物保护 | 836篇 |
出版年
2024年 | 88篇 |
2023年 | 262篇 |
2022年 | 466篇 |
2021年 | 524篇 |
2020年 | 510篇 |
2019年 | 565篇 |
2018年 | 365篇 |
2017年 | 604篇 |
2016年 | 692篇 |
2015年 | 499篇 |
2014年 | 681篇 |
2013年 | 786篇 |
2012年 | 984篇 |
2011年 | 955篇 |
2010年 | 748篇 |
2009年 | 765篇 |
2008年 | 625篇 |
2007年 | 659篇 |
2006年 | 532篇 |
2005年 | 473篇 |
2004年 | 360篇 |
2003年 | 335篇 |
2002年 | 238篇 |
2001年 | 257篇 |
2000年 | 233篇 |
1999年 | 217篇 |
1998年 | 221篇 |
1997年 | 185篇 |
1996年 | 154篇 |
1995年 | 161篇 |
1994年 | 136篇 |
1993年 | 146篇 |
1992年 | 109篇 |
1991年 | 100篇 |
1990年 | 99篇 |
1989年 | 62篇 |
1988年 | 39篇 |
1987年 | 33篇 |
1986年 | 25篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1962年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
Brasisca Juncea , cv. Pusa Bold, and B. campestris , cv. Pusa Kalyani, were raised under field conditions with varying levels of N supply from 0–120 kg ha-1 . The production profile of branches and pods thereon was measured, per unit area basis, throughout the crop ontogeny. At maturity, data on the yield contributing characters, viz. pod dry weight, pod number, seed number per pod, 1000 seed weight, seed wall ratio and seed yield in different order branches, was recorded.
The branching pattern and the number of pods produced on different order branches, in the two species, was favourably modified by the increasing levels of N supply. Primary and secondary branches contributed to the seed yield to an extent of 80 % of the total yield. Nitrogen treatment had no significant effect on 1000 seed weight. B. juncea exhibited significantly higher yield over B. campestris. N supply up to 120 kg ha-1 linearly increased seed yield in both the species. However, it exerted a negative effect too partitioning of assimilates from pod wall to seed. The study indicated that rapeseed-mustard, grown under short winter-season environment with adequate soil moisture, has the potential for higher N-fertilizer optima exceeding 120 kg ha -1 . 相似文献
The branching pattern and the number of pods produced on different order branches, in the two species, was favourably modified by the increasing levels of N supply. Primary and secondary branches contributed to the seed yield to an extent of 80 % of the total yield. Nitrogen treatment had no significant effect on 1000 seed weight. B. juncea exhibited significantly higher yield over B. campestris. N supply up to 120 kg ha
992.
对紫光大圆茄(暂用名)种子外部形态及内部结构的研究表明,紫光大圆茄种子较小且种脐、种孔较大,种皮细胞中淀粉粒含量较少,种皮结构较疏松,外覆胶质层较薄,胚和胚乳发育良好,导致其种子萌发速度高于其它茄子品种. 相似文献
993.
M. A. Cheema M. A. Malik A. Hussain S. H. Shah & S. M. A. Basra 《Journal of Agronomy and Crop Science》2001,186(2):103-110
A field study was conducted to investigate the influence of variable rates of application of N and P fertilizers in splits at various times on the growth and the seed and oil yields of canola (Brassica napus L.) during 1995–97. Rates of fertilizer application were 0 and 0 (F0), 60 and 0 (F1), 0 and 30 (F2), 60 and 30 (F3), 90 and 60 (F4) and 120 and 90 (F5) kg N ha?1 and kg P2O5 ha?1. All the P was applied at sowing while N was applied in splits, i.e. all at sowing, half at sowing and half with first irrigation, or half at sowing and half at flowering. The responses of growth, seed yield and components of yield were consistent in both years. Increasing the rate of fertilizer application from F4 (90/60 kg N/P2O5 ha?1) to F5 (120/90 kg N/P2O5 ha?1) increased the leaf area index (LAI) relative to the control and to lower rates of fertilizer application. For both crops, application of 90/60 kg N/P2O5 ha?1 significantly enhanced total dry matter (TDM) and seed yield. Seed yield increased mainly due to a greater number of pods per plant and seeds per seed‐pod. The time of fertilizer application did not significantly affect seed yield or components of yield in either season. Oil yield generally followed seed yield, increasing with increasing rate of fertilizer application up to 90/60 kg N/P2O5 ha?1. The maximum oil contents were obtained from the control. The results show that seed and oil yields of canola were maximized at the F4 (90/60 kg N/P2O5 ha?1) rate of application under the agro‐ecological conditions of Faisalabad, Pakistan. 相似文献
994.
施肥处理对老芒麦种子质量和产量的影响 总被引:16,自引:2,他引:14
在河北省坝上地区鱼儿出牧场中国农业大学科技攻关实验站内,以种植2种和3年的老芒麦为试验材料,通过施肥处理(尿素130kg/hm^2+磷酸二铵70kg/hm^2),研究测定种子产量和质量的变化。试验结果表明:施肥可以提高不同种植年限老芒麦种子产量,但对老芒麦种子质量的影响不一致,可明显提高种植第3年的种子质量,在种子活力测定中,加速老化测定、脱氢酶活性和酸性磷酸酯酶活性测定能较好地反映施肥对种子质量的影响,而活力指数、电导率值和浸种液含糖量测定结果变化不大,无法表现种子质量的变化。 相似文献
995.
西藏砂生槐种子萌发特性研究 总被引:13,自引:2,他引:11
自然条件下藏砂生槐种子萌发比较困难,不同收获年份砂生槐种子发芽率不同,砂生槐种子的休眠由种皮障碍所致,物理处理比化学处理发芽率高,最佳处理为刀刺破种皮及砂布磨擦种皮发毛(用具消毒),发芽率可达90%和83%。 相似文献
996.
997.
We studied the bark beetle guild (Coleoptera: Scolytidae) in the ponderosa pine forests of northern Arizona to explore if the species assemblages and relative abundance differ between managed and unmanaged stands. Four stand conditions were assessed: (1) unmanaged stands with high tree density, (2) thinned stands, (3) thinned and burned (with prescribed fire) stands and (4) stands that had been burned by stand replacing wildfires. The study was conducted in the ponderosa pine forests of the Coconino Plateau, northern Arizona. For several decades this area has been relatively free of bark beetle outbreaks despite the current overstocked condition of many stands. We found that a similar species assemblage composed of Dendroctonus frontalis, D. brevicomis, D. valens, D. approximatus, D. ponderosae, and Ips pini occurred across all four stand conditions over 3 years of study. The population levels of all these species were endemic across all stand conditions. The non-aggressive D. approximatus and D. valens were indicator species for thinned and unmanaged stands, respectively, but this was not consistent among years. The ambrosia beetle Gnathotrichus sp. and the bark beetle predator Enoclerus sp. consistently indicated stands burned by wildfire. In addition to our field experiment, we analyzed the historical pattern of attacks of bark beetles in our area of study. Our findings suggest that the pattern of attack of D. brevicomis (the only Dendroctonus species for which attacks have been reported) and Ips spp. has been through scattered small infestations in groups of 1–10 trees. Whereas small infestations by Ips spp. are increasing, those for D. brevicomis are decreasing. Although we agree that the high density stands in northern Arizona are in an “unhealthy” condition, our results do not show that they were supporting large bark beetle outbreaks. Our results challenge the theoretical assumptions about the relationship between stand structure, tree resistance and bark beetle performance. 相似文献
998.
本研究是在呼和浩特市的自然条件下,对紫羊茅种子产量在不同播种量和不同行距情况下进行了试验。结果表明,紫羊茅的最适播量7.50kg/hm2,行距为30cm,在此播种体系中种子产量平均可达662.5kg/hm2。 相似文献
999.
通过种子培养方法提高油菜贮藏种质发芽率及成苗率 总被引:1,自引:0,他引:1
以在昆明自然贮藏条件下贮藏了1a-17a的甘蓝型油菜种子为材料,探讨通过种子培养方法来获得比常规方法高的发芽率和成苗率。试验结果表明:通过种子培养方法能有效提高贮藏种质的发芽率和成苗率,发芽率比对照提高0%-25%,成苗率提高0%-25.6%。 相似文献
1000.
黄土高原地形对苜蓿种子产量和质量的影响 总被引:17,自引:6,他引:11
对产自甘肃环县黄土高原沟壑区阴坡,阳坡、沟谷阶地和塬地4种地形的苜蓿种子产量和质量进行了研究分析,结果表明,地形对种子产量和质量均有显著影响,其中,阴坡种子产量最低,分别为1.86g/株和311.74kg/hm^2,阳坡单株种子产量最高,为6.41g/株,塬地单位种子产量最高,为650.65kg/hm^2,质量最低种子也产自阴坡,其发芽率只有23%,硬实率却高达66%,地形对种子产量构成因素无显著影响,4种地形的种子产量与其构成因素的相关性完全一致,即除千粒重外,种子产量与其他各因素均存在显著正相关,相关性强弱依次为:单株生殖枝数>每生殖枝荚果数>每荚粒数>千粒重,单株生殖枝数对种子产量贡献最大。 相似文献