全文获取类型
收费全文 | 5902篇 |
免费 | 149篇 |
国内免费 | 537篇 |
专业分类
林业 | 195篇 |
农学 | 1100篇 |
基础科学 | 27篇 |
599篇 | |
综合类 | 2507篇 |
农作物 | 788篇 |
水产渔业 | 10篇 |
畜牧兽医 | 932篇 |
园艺 | 178篇 |
植物保护 | 252篇 |
出版年
2024年 | 32篇 |
2023年 | 76篇 |
2022年 | 146篇 |
2021年 | 158篇 |
2020年 | 144篇 |
2019年 | 174篇 |
2018年 | 139篇 |
2017年 | 205篇 |
2016年 | 300篇 |
2015年 | 262篇 |
2014年 | 322篇 |
2013年 | 440篇 |
2012年 | 454篇 |
2011年 | 409篇 |
2010年 | 349篇 |
2009年 | 333篇 |
2008年 | 283篇 |
2007年 | 360篇 |
2006年 | 285篇 |
2005年 | 274篇 |
2004年 | 201篇 |
2003年 | 176篇 |
2002年 | 127篇 |
2001年 | 110篇 |
2000年 | 94篇 |
1999年 | 89篇 |
1998年 | 90篇 |
1997年 | 67篇 |
1996年 | 58篇 |
1995年 | 59篇 |
1994年 | 61篇 |
1993年 | 41篇 |
1992年 | 67篇 |
1991年 | 38篇 |
1990年 | 43篇 |
1989年 | 43篇 |
1988年 | 25篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1962年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有6588条查询结果,搜索用时 15 毫秒
61.
锌、铁、钼配施对紫花苜蓿产草量及锌铁钼含量和吸收量的影响 总被引:2,自引:1,他引:2
采用随机区组试验设计,研究锌、铁、钼配施对紫花苜蓿(Medicago sativa L.)产草量及锌铁钼含量和吸收量的影响,为其合理施肥提供依据。结果表明:锌、铁、钼以不同比例配施均能提高紫花苜蓿产草量,且单施锌(12kg·hm-2)、铁(15 kg·hm-2)、钼(0.5 kg·hm-2)或两两配施效果显著(P<0.05);尤其是锌(12 kg·hm-2)和钼(0.5 kg·hm-2)配施,产草量最高(7.01 t·hm-2),较对照增产25.40%。锌、铁、钼以不同比例配施对紫花苜蓿锌铁钼含量和吸收量影响不尽相同,锌(12 kg·hm-2)、铁(15 kg·hm-2)、钼(0.5 kg·hm-2)三者互作能显著(P<0.05)提高苜蓿锌铁钼的含量和锌钼吸收量,钼锌互作能显著(P<0.05)提高苜蓿钼和锌的含量和吸收量;单施锌或锌铁互作能显著(P<0.05)提高苜蓿锌的含量和吸收量;单施钼或钼铁互作能显著(P<0.05)提高苜蓿钼的含量和吸收量;而单施铁或与锌或钼互作均未能显著提高苜蓿铁的含量和吸收量。 相似文献
62.
对3个桑品种生理生态特征的比较研究 总被引:2,自引:2,他引:2
研究了湖桑32号、农桑14号和丰田2号等3个桑树品种的光合特征及叶绿素的部分参数。3个品种的光补偿点为3.58~50.10μmol/(m2.s),表观量子效率为0.022~0.051,湖桑32号>农桑14号>丰田2号;光饱和点为1 436.78~1 571.43μmol/(m2.s),丰田2号>农桑14号>湖桑32号;CO2补偿点为62.87~103.40μmol/mol,CO2饱和点为921.88~1 055.56μmol/mol,其中,湖桑32号的CO2补偿点和饱和点、羧化效率及二磷酸核酮糖羧化酶的最大再生速率(Pmax)均较显著高于其它两个品种;叶绿素相对含量丰田2号>农桑14号>湖桑32号,表明丰田2号单位叶面叶绿体数量较多,具有相对较大的光合潜力;光化学效率和光合电子传递效率分别为0.746 2~0.801 8、1.58~3.43,其中丰田2号的叶绿素荧光参数值显著高于其它2个品种,具有一定光适应和抗逆性能力。 相似文献
63.
64.
以加燕2号为试验材料,用一氧化氮(NO)供体硝普钠(SNP)、NO清除剂牛血红蛋白(Hb)及SNP类似物亚铁氰化钠处理燕麦植株,研究NO对NaCl胁迫下燕麦幼苗生长和氧化损伤的缓解效应。结果表明,NaCl胁迫下添加外源NO提高了燕麦幼苗的株高,提高了SOD、POD、CAT和APX活性,降低自由基含量和膜脂过氧化程度,表明外源NO能缓解NaCl胁迫诱导的氧化损伤,增强植株的耐盐性。NO供体SNP的类似物亚铁氰化钠(不产生NO)对NaCl胁迫燕麦植株的株高和氧化伤害无缓解效应;施用Hb提高了自由基含量,降低了抗氧化酶活性,而添加外源NO能缓解Hb对燕麦生长的抑制,表明内源NO也可能参与燕麦幼苗耐盐性的调节。 相似文献
65.
Molybdenum (Mo) is an essential micro-mineral nutrient for plant growth and development. As an important legume forage, alfalfa (Medicago sativa) is frequently planted in marginal lands of northern China where water scarcity and infertile soil are limiting factors for alfalfa production. Mo plays an important role in nitrogen (N) metabolism in general and N fixation in legume species in particular. To evaluate the role of Mo fertilizer in alfalfa quality and production in semi-arid areas of northern China, we conducted a three-year field experiment in Inner Mongolia from 2012 to 2014. Mo fertilizer at the doses of 0, 150 g hm?2, 300 g hm?2yr?1 was applied consecutively across the three years. Application of Mo at 300 g hm?2yr?1 significantly increased dry yield of alfalfa in 2014. Crude protein (CP) content of alfalfa without application of Mo exhibited a decline trend from 2012 to 2014. Application of Mo significantly enhanced total CP in 2012 and 2014, and delayed the reduction in total CP across the three years. In contrast to CP, Mo fertilizer had no significant effects on neutral detergent fiber and acid detergent fiber content. In addition, we found that nitrate reductase activity of alfalfa was increased by Mo fertilizer, which may account for the enhanced CP content in alfalfa. These findings highlight that application of Mo fertilizer can be an effective way to improve alfalfa production and quality in semi-arid areas in northern China. 相似文献
66.
The objectives of this study were to investigate constraints affecting sorghum production and farmers' approaches of Striga management in the semi-arid regions of Tanzania. Focus group discussions based on a semi-structured questionnaire and observations following transect walks were used for data collection. Only 35%, 15%, and 10% of the farmers from Igunga, Kishapu, and Meatu districts, respectively, reported growing newly released varieties. The major constraints affecting sorghum production in the study areas included Striga infestation, drought, storage pests, damage by birds, a lack of access to improved varieties, and a lack of access to production inputs, such as fertilizers, insecticides, fungicides and herbicides. Hand weeding, crop rotation, fallowing, intercropping, and organic manure application were the most common practices of farmers for reducing Striga infestations, but most farmers (79.7%) had little knowledge of the best recommended Striga management practices. About 65% of the farmers did not use fertilizers and herbicides for soil fertility improvement and weed management, respectively, creating favourable conditions for Striga infestation. A systematic breeding programme aiming at improving sorghum varieties for Striga resistance, including farmers' preferred traits, should be designed and implemented to increase the adoption of these new varieties by the farmers. 相似文献
67.
E. J. Cother D. H. Noble R. J. Van De Ven V. Lanoiselet G. Ash N. Vuthy P. Visarto B. Stodart 《Plant pathology》2010,59(5):944-953
A study of rice diseases in Cambodia from 2005 to 2007 showed widespread occurrence of diseases caused by Acidovorax avenae subsp. avenae, Burkholderia gladioli, B. cepacia and Pantoea ananatis. This is the first report of these pathogens in Cambodia. Additionally, a pseudomonad causing a widespread disease similar to sheath brown rot (caused by Pseudomonas fuscovaginae) was isolated. The studied strains were pathogenic to rice cvs Sen Pidau and IR 66, producing similar, though slightly less severe, symptoms to those observed in the field. Based on comparative 16S rDNA gene sequence analysis, combined with cell wall fatty acid analysis and metabolic profiles, the isolated strains were allocated to the genus Pseudomonas. The novel species were differentiated from Pseudomonas fuscovaginae and P. putida by their inability to metabolize d ‐fructose, d ‐galactose, d ‐galactonic acid lactone, d ‐galacturonic acid, d ‐glucosaminic acid, d ‐glucuronic acid, p‐hydroxy phenylacetic acid, d ‐saccharic acid and urocanic acid. The major fatty acids were C16:0, summed feature 3 (C16:1ω7c and C16:1ω6c) and summed feature 8 (C18:1ω7c), representing 80% of the total. Partial 16S rRNA gene sequences (1460 bp) were identical, except for two nucleotide changes amongst the six strains. Alignment of the causal strains within type‐culture databases revealed similarities of 99·7% with Pseudomonas parafulva AJ 2129T, 99·2% with P. fulva IAM 1592T, 98·9% with P. plecoglossicidia FPC 951T, and 98·1% with P. fuscovaginae MAFF 301177T. On the basis of data from this polyphasic study, it is proposed that the unknown strains isolated from rice represent a novel species of the genus Pseudomonas. 相似文献
68.
69.
70.
Doubled haploids (DHs) are becoming increasingly important in crop breeding programmes but methods for producing oat DHs remain inefficient. In this study haploid and DH oat plants were produced using the oat × maize hybridization method. Factors influencing the rate of caryopsis and haploid embryo production including genotype, post‐pollination plant growth regulator application and temperature were investigated. The four growth regulators tested showed significant differences in their capacity to induce caryopsis formation with dicamba producing the highest numbers of caryopses, followed by picloram, 2,4‐dichlorophenoxyacetic acid (2,4‐D) and gibberellic acid (GA3). No significant differences were observed between these growth regulators for their effect on embryo production. The concentration of dicamba was also important and was found to influence caryopsis but not embryo production, with 50 and 100 mg/l dicamba producing significantly more caryopses than 25 or 5 mg/l. Temperature had a significant impact on both caryopsis and embryo production with the magnitude and direction of response depending on genotype. Rates of haploid embryo production observed were between 0.8% and 6.7% of the pollinated florets. The proportion of haploids, which survived and were successfully doubled with colchicine following transfer to soil was between 72% and 81%. 相似文献