全文获取类型
收费全文 | 4885篇 |
免费 | 286篇 |
国内免费 | 675篇 |
专业分类
林业 | 43篇 |
农学 | 502篇 |
基础科学 | 656篇 |
737篇 | |
综合类 | 2379篇 |
农作物 | 380篇 |
水产渔业 | 38篇 |
畜牧兽医 | 573篇 |
园艺 | 95篇 |
植物保护 | 443篇 |
出版年
2024年 | 49篇 |
2023年 | 113篇 |
2022年 | 178篇 |
2021年 | 227篇 |
2020年 | 186篇 |
2019年 | 243篇 |
2018年 | 156篇 |
2017年 | 241篇 |
2016年 | 350篇 |
2015年 | 223篇 |
2014年 | 290篇 |
2013年 | 277篇 |
2012年 | 436篇 |
2011年 | 386篇 |
2010年 | 270篇 |
2009年 | 276篇 |
2008年 | 229篇 |
2007年 | 258篇 |
2006年 | 216篇 |
2005年 | 202篇 |
2004年 | 137篇 |
2003年 | 129篇 |
2002年 | 112篇 |
2001年 | 105篇 |
2000年 | 81篇 |
1999年 | 82篇 |
1998年 | 63篇 |
1997年 | 55篇 |
1996年 | 29篇 |
1995年 | 48篇 |
1994年 | 31篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有5846条查询结果,搜索用时 15 毫秒
991.
Cadmium levels were determined in rice grains of Japonica, Indica, Javanica, and Indica-Japonica hybrid-bred varieties that were produced in the same plot of a non-polluted field in 1983 and 1985, using nameless atomic absorption spectrophotometry. Cadmium levels in the brown rice grains harvested in 1983 and 1985 ranged from 2.1 to 27 0 ppb Cd for 28 Japonica varieties, 4.1 to 55.5 for 23 Indica varieties, 4.4 to 16.5 for 5 Javanica varieties, and 24.5 to 73.6 for 4 hybrid varieties. The significant correlation of the cadmium levels between the 1983 and 1985 products may indicate the possible occurrence of varietal differences in the natural abundance of cadmium in rice grains. There was no correlation between the cadmium levels and the duration of ripening in each variety, suggesting that these differences could be partly attributed to some physiological characteristics of the rice varieties. 相似文献
992.
K. W. Freeman Kefyalew Girma R. K. Teal D. B. Arnall B. Tubana S. Holtz 《Journal of plant nutrition》2013,36(12):2021-2036
ABSTRACT Crop management strategies that improve Nitrogen Use Efficiency (NUE) increase profits while reducing the detrimental effects on the environment associated with fertilizer nitrogen (N) loss. Effective N management should include several critical factors that are very interrelated. A study was conducted at the Panhandle Research and Extension Center, Goodwell, OK to evaluate the effects of multiple nitrogen management practices including N rate, source, time of application, methods of fertilizer and residue incorporation over a long period of time on grain yield, N uptake and NUE in irrigated corn. Fourteen treatments were evaluated in a randomized complete block design with three replicates. Results of data analyzed on the individual year and averages of all years showed that grain yield and N uptake were improved with N rates and N management practices compared to checks. Both N recovery and efficiency of use were high for the 118 kg N ha? 1 rate. 相似文献
993.
Interactions between sulfur (S) and selenium (Se) uptake and accumulation in corn (Zea mays) plants were investigated in solution culture. Two concentrations (5 and 10 μ M) of Se (as selenate) and three concentrations of S (as sulfate) (0.5, 1.5, and 2.5 mM) were used. Results showed that shoot and root biomass were affected significantly by different S concentrations in solution, but not affected by Se application when S concentrations in solution were lower than 1.5 mM. Selenium concentrations as well as Se accumulation in shoots and roots on a dry weight basis increased dramatically with increasing Se concentrations in solution. At a constant Se level, increasing S in solution reduced Se concentrations. Selenium accumulation in plants was not affected by S application, except in nutrient solution with Se at a concentration of 10 μ M. Sulfur concentrations and S accumulation in shoots increased significantly with increasing Se concentrations in solution, while those in roots were unaffected by Se addition. Solution-to-shoot transfer factors and shoot-root distribution coefficients of Se and S were also discussed. These data suggest that it is necessary to manage carefully both S and Se levels in solution or in soils for supplementation of Se in plants. Results from this study indicate that human Se nutrition can be improved by supplementation of Se in crops. 相似文献
994.
Andrew A. Benson Arthur M. Nonomura Valrie A. Gerard 《Journal of plant nutrition》2013,36(7):1185-1200
Substituted glycopyranosides were applied to various plant species as foliar and root treatments, with and without nutrient supplements, and growth was compared to untreated or nutrient controls. When formulated with specific fertilizers, particularly available nitrogen, methyl and ethyl glycopyranosides significantly enhanced the overall growth of vascular plants compared to controls provided with the same nutrients. In contrast, vascular plants treated with alkylglycopyranosides without nutrients showed growth equivalent to that of untreated controls. Nitrogen-supplemented alkylglycopyranosides provided as foliar applications of 100 mM, or as root treatments between 35 and 50 mM, consistently enhanced root and shoot productivity. In addition to the vascular plant species tested, the brown alga Laminaria saccharina exhibited significant growth enhancement over nutrient controls when treated with alkylglycopyranosides supplemented with nutrients, especially under low irradiance. Overall, these results indicate that growth of photosynthetic organisms is enhanced by exogenous alkylglycopyranosides supplemented with nitrogen and micronutrients, but not by alkylglycopyranosides alone. 相似文献
995.
996.
寄主植物对亚洲玉米螟取食、生长发育和生殖的影响 总被引:8,自引:3,他引:8
本文对亚洲玉米螟在甜玉米、饲料玉米、无毒棉和有毒棉上的取食、生长发育和生殖作了比较研究。结果表明:初孵幼虫嗜食无毒棉棉叶,3龄幼虫则喜食玉米心叶。5龄幼虫在甜玉米上的取食次数最多,取食总时间最长,在有毒棉上的取食时间最短。5日龄以前,取食无毒棉的幼虫生长最快,而后取食玉米的幼虫生长加快;取食有毒棉的幼虫生长最慢,其老熟幼虫的体重仅为取食甜玉米的1/3。取食棉花的幼虫历期明显延长,虫龄增加至6龄。幼虫期存活率、蛹重和每雌产卵量以甜玉米为最高,依次为饲料玉米、无毒棉和有毒棉。试验证明,在扩种甜玉米和无毒棉以后亚洲玉米螟种群将上升。 相似文献
997.
以影响黑糯玉米产量的氮肥、磷肥、密度等限制因子为自变量,进行通用回归旋转设计,以籽粒产量建立数学模型并分析,提出了黄土高原生产特种玉米的高产、高效栽培模式.分析得出黄土高原特种玉米产量和毛收益最佳组合为:施氮466.5 kg/hm2、施磷426.0 kg/hm2,密度为10.95万株/hm2时,最高单产可以达到11.175 t/hm2;施N 424.5 kg/hm2,P2O5 211.5 kg/hm2,保苗7.05株/hm2时,最高毛收益可达到1.236万元/hm2,经济效益显著. 相似文献
998.
999.
1000.
我国玉米螟防治技术研究概况 总被引:11,自引:0,他引:11
综述了我国玉米螟防治技术的研究历史、现状及进展,着重介绍了抗螟育种、化学防治、生物防治、物理防治和农业措施防治玉米螟的研究进展,并讨论了我国玉米螟防治技术中存在的问题及发展方向。 相似文献