全文获取类型
收费全文 | 25574篇 |
免费 | 1463篇 |
国内免费 | 3077篇 |
专业分类
林业 | 1574篇 |
农学 | 2742篇 |
基础科学 | 1148篇 |
7465篇 | |
综合类 | 10219篇 |
农作物 | 2256篇 |
水产渔业 | 935篇 |
畜牧兽医 | 2068篇 |
园艺 | 635篇 |
植物保护 | 1072篇 |
出版年
2024年 | 148篇 |
2023年 | 563篇 |
2022年 | 952篇 |
2021年 | 1049篇 |
2020年 | 1107篇 |
2019年 | 1155篇 |
2018年 | 945篇 |
2017年 | 1429篇 |
2016年 | 1612篇 |
2015年 | 1186篇 |
2014年 | 1410篇 |
2013年 | 1968篇 |
2012年 | 2159篇 |
2011年 | 1938篇 |
2010年 | 1487篇 |
2009年 | 1471篇 |
2008年 | 1207篇 |
2007年 | 1350篇 |
2006年 | 1215篇 |
2005年 | 946篇 |
2004年 | 690篇 |
2003年 | 535篇 |
2002年 | 427篇 |
2001年 | 379篇 |
2000年 | 317篇 |
1999年 | 319篇 |
1998年 | 270篇 |
1997年 | 237篇 |
1996年 | 224篇 |
1995年 | 253篇 |
1994年 | 164篇 |
1993年 | 180篇 |
1992年 | 152篇 |
1991年 | 134篇 |
1990年 | 121篇 |
1989年 | 114篇 |
1988年 | 86篇 |
1987年 | 61篇 |
1986年 | 47篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1962年 | 7篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
本文综述了硝酸还原酶与氮素利用的关系及其遗传特性和在作物育种中应用的某些最新进展。氮吸收、利用等性状的生理和遗传特性极其复杂,受环境影响很大,对其进行遗传改良需考虑多种指标。对硝酸还原酶活性(NRA)与品质性状和产量的关系的争论很多,有些研究表明 NRA 可作为品质、产量性状的选择指标,有些则相反。逆境条件下 NRA 的变化非常敏感,NRA 可能与抗逆性有关。 相似文献
62.
In this study, the effects of nitrogen (N) rate (60, 120, 180 and 240 kg N ha?1 applied in three equal dressings at seeding and after the first and second cuttings) and stubble height (7, 14 and 21 cm) on the dry matter (DM) yield, crude protein (CP) content, and CP yield of a sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf., cv. Pioneer 988] in the three‐cut system was investigated. The N rate had no significant effect in the first and third cuttings, but in the second cutting DM yields increased significantly with increase in N rate. The highest yield of 9.1 t ha?1 was obtained with 80 kg N ha?1 for the average of 2 years at the second cutting, but no significant difference was found among the 40, 60 and 80 kg N ha?1 rates. CP content and yield were not significantly affected by N rate at the first and third cuttings, but CP content and yield were significantly affected by application of N at the second cutting. Stubble height had a significant effect on CP content at the third cutting. However, it had no significant effect on CP content at the first and second cuttings. Stubble height had a significant effect on the CP yield at the first cutting, but no significant effect on CP yield at the second and third cuttings. 相似文献
63.
几种优良人工牧草矿质元素含量的比较研究 总被引:1,自引:0,他引:1
就地上部而言,在3种豆科牧草中,白三叶以N、P、K、Fe、Co、Na含量较高,红三叶以Mg、Zn含量较高。在3种禾本科牧草中,鸭茅以P、K、Mg、Mn、Cu、Zn、Mo含量较高,草地早熟禾以Fe较高。3种豆科牧草N、Ca、Mg、V、Sr的平均含量显著高于禾本科牧草。地上部与地下部比较,豆科牧草的P、K、Ca、Mn、Zn、Na含量前者显著高于后者;禾本科牧草的N、P、K、B含量,前者明显高于后者。 相似文献
64.
65.
66.
A field experiment was conducted during the winter seasons of 1992–93 and 1993–94 at Anand to study the effect of FYM, nitrogen and source of fertilizer on growth and yield of mustard [ Brassica juncea (L.) Czernj & Cosson]. The results showed significant variation in leaf area index (LAI), crop growth rate (CGR), dry matter production and seed yield. The direct effect of farmyard manure (FYM) was conspicuous in improving the growth of mustard. FYM application at 10 tonnes ha−1 significantly increased the LAI, CGR and dry matter accumulation per plant at almost all the stages during first year study (1992–93) and in pooled analysis. Similarly, nitrogen application registered maximum LAI, CGR at 75 kg level and RGR and NAR at 50 kg level at almost all the during both years. Sulphur carrying source (Ammonium sulphate plus single super phosphate) increased all stages growth characters. Maximum dry matter accumulation per plant and seed yield were recorded with highest levels of FYM (20 tonnes ha−1 ), N (75 kg ha−1 ) and source having S. Seed yield was strongly associated with LAI and dry matter accumulation per plant at all the stages. 相似文献
67.
Field experiments were conducted at Tamil Nadu Rice Research Institute, Aduthurai, India, during the wet seasons of 1992 and 1993 to study the effect of full and partial substitution of fertiliser N with green manure N (Sesbania rostrata) on nitrogen uptake, yield attributes and yield of rice. The experiment consisted of eight treatments with two levels of N (100 and 200 kg ha−1 ) and three sources of N application viz., fertilizer, integrated (1:1 fertilizer and green manure N) and green manure N compared to the recommended practice (150 kg fertilizer plus 6.25 t ha−1 (72 kg N) green manure) and a no N control. Nitrogen application markedly increased the N uptake. Combined use of the two N sources at 200 and 222 kg N ha−1 and of single fertilizer N at 200 kg N ha−1 recorded the maximum N uptake, increased the yield attributes such as number of panicles per unit area, weight per panicle, number of total and filled grains per panicle and test weight. At 200 kg N ha−1 full substitution of N by green manure reduced the grain yield but only partial substitution of N by green manure resulted in almost similar yield as single fertilizer N. Thus 200 kg N ha−1 applied in equal proportions of fertilizer and green manure N can be recommended for medium duration rice cultivars. 相似文献
68.
在三种库房里对五种不同含水率、两种包装的华北落叶松种子进行了60个月的贮藏试验。结果认为,含水率5.19/5~8.0%的落叶松种子可以在三种库房密封贮藏39个月。种子贮藏的最佳含水率为6.6%~8.0%,最佳的库房是冷库(0C~5C)。磨口瓶与布袋在冷库贮藏效果差异不明显;地下库不能用布袋贮藏;在普通常温库中磨口瓶比布袋能多贮藏12个~18个月。 相似文献
69.
陆家宝 《青海畜牧兽医杂志》1995,25(3):21-22
1990~1993年在柴达盆地尕海地区弃耕地进行土壤可溶性盐分测定,测定结果,该地区土壤盐分组成为氯化物-硫酸盐和硫酸盐-氯化物,大部分地区耕层盐分含量小于10g.kg^-1,少部分盐荒地表层含盐量高达70g.kg^-1,牧草生长季节中,土壤盐分含量最低期在6月份。 相似文献
70.
Alba Marina Cotes Philippe Lepoivre Jean Semal 《European journal of plant pathology / European Foundation for Plant Pathology》1996,102(5):497-506
An experimental protocol consisting in the colonisation of pregerminated bean seeds dressed withTrichoderma sp. was used in order to study the mechanisms correlated with the protective effect againstPythium splendens. Seed dressed with TH-11 (T. koningii) for 24 h presented a higher protective effect and a higher level of seed colonisation as compared to those dressed with TH-13 (T. longibranchiatum). The levels of seed coat colonisation by TH-11 and TH-13 was shown to be correlated with the carboxymethylcellulase activity, as measured in the seed coats retreived from germinating dressed bean seeds. The seed coat colonisation was also associated with an increased activities of endo-1,3--glucanase and endochitinase measured in seed extracts, and an inhibitory effect of seed extracts onPythium sporangia germination. Pretreatment of TH-13-dressed seeds with a commercial cellulase improved all parameters mentioned above, thus suggesting a role of cellulase activity in the colonisation process and the linked protective effect. The possible role of hydrolytic enzymes in the protective effects is discussed. 相似文献