全文获取类型
收费全文 | 3843篇 |
免费 | 189篇 |
国内免费 | 447篇 |
专业分类
林业 | 550篇 |
农学 | 640篇 |
基础科学 | 305篇 |
661篇 | |
综合类 | 1031篇 |
农作物 | 183篇 |
水产渔业 | 95篇 |
畜牧兽医 | 647篇 |
园艺 | 108篇 |
植物保护 | 259篇 |
出版年
2024年 | 11篇 |
2023年 | 51篇 |
2022年 | 115篇 |
2021年 | 161篇 |
2020年 | 158篇 |
2019年 | 151篇 |
2018年 | 126篇 |
2017年 | 166篇 |
2016年 | 122篇 |
2015年 | 183篇 |
2014年 | 177篇 |
2013年 | 196篇 |
2012年 | 244篇 |
2011年 | 223篇 |
2010年 | 233篇 |
2009年 | 242篇 |
2008年 | 199篇 |
2007年 | 224篇 |
2006年 | 188篇 |
2005年 | 183篇 |
2004年 | 86篇 |
2003年 | 80篇 |
2002年 | 74篇 |
2001年 | 88篇 |
2000年 | 94篇 |
1999年 | 90篇 |
1998年 | 92篇 |
1997年 | 68篇 |
1996年 | 67篇 |
1995年 | 72篇 |
1994年 | 55篇 |
1993年 | 71篇 |
1992年 | 45篇 |
1991年 | 39篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1956年 | 1篇 |
1950年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有4479条查询结果,搜索用时 15 毫秒
31.
绿竹笋俗称马蹄竹笋,为合轴丛生型的笋用竹.我县绿竹笋种植面积达到了6万亩,年鲜笋产量2万多吨.栽培品种为细叶矮脚早,出笋期在5月中旬至9月中旬,产笋期长,产量较高,鲜笋亩产量700kg,高的达1000kg. 相似文献
32.
33.
Dietary supplementation with Acanthopanax senticosus extract enhances gut health in weanling piglets
Jun Fang F.Y. Yan X.F. Kong Z. Ruan Z.Q. Liu R.L. Huang T.J. Li M.M. Geng F. Yang Y.Z. Zhang Peng Li Joshua Gong G.Y. Wu M.Z. Fan Y.L. Liu Y.Q Hou Y.L. Yin 《Livestock Science》2009,123(2-3):268-275
The present study was conducted to investigate the effects of Acanthopanax senticosus extract (ASE) as a dietary additive on gut health in weanling piglets by examining diarrhea frequency, intestinal microbiota and morphology. A total of 96 Duroc× (Landrace × Yorkshire) piglets weaned at 21 days of age with an average initial body weight (BW) of 5.6 ± 0.4 kg were randomly assigned to 3 treatment groups with 4 duplicates of 8 piglets each. The piglets were fed basal diet to which had been added 0 or 1 g/kg of ASE, or 0.7 g/kg antibiotics, respectively. Fecal consistence was monitored twice daily and the frequency of diarrhea was calculated. On day 21 after the initiation of supplementation, 8 piglets were randomly selected from each treatment group (2 piglets per pen) and slaughtered. The jejunum, ileum, colon and cecum were then excised and fixed in 10% neutral formalin solution to determine villus height and crypt depth, after their contents were collected to determine microbiota. The results showed that dietary supplementation with ASE increased (P < 0.05) the density of bacterial populations that co-migrated with Lactobacillus amylovorus, Lactobacillus salivarius, Bacillus subtilis, and Clostridium lituseburens, but decreased (P < 0.05) those co-migrating with Staphylococcus aureus, Salmonella typhimurium, Ruminococcus forques, and E. coli O157:H7 in the PCR-DGGE profiling analysis when compared with the control group. The villus height of the duodenum, jejunum and ileum increased (P < 0.05) by 14.8, 13.7 and 10.0%, while the crypt depth decreased (P < 0.05) by 17.9, 9.1 and 12.1%, respectively, in response to dietary ASE supplementation. Additionally dietary supplementation with ASE or an antibiotic decreased (P < 0.05) the frequency of diarrhea by 55.6 and 52.2%, respectively, compared with the control group. In conclusion, these findings suggest that dietary supplementation with ASE could regulate the microbiota composition and maintain a normal morphology of gut mucosa in weanling piglets, thereby decreasing diarrhea that resulted from weaning stress. 相似文献
34.
寡肽的转运机制及其影响因素 总被引:2,自引:0,他引:2
1传统的蛋白质消化吸收理论及其局限性传统的蛋白质消化、吸收理论认为:蛋白质在肠腔内,由肽蛋白酶和糜蛋白酶作用生成游离氨基酸和寡肽(含2 ̄6个氨基酸残基),寡肽在肽酶的作用下完全被水解成游离氨基酸,并以游离氨基酸形式进入血液循环。根据这一理论,蛋白质仅为动物机体提供氨基酸,即蛋白质的营养就是氨基酸的营养。因此,只要我们给动物提供充足的必需氨基酸,动物就能获得满意的生产性能。但是,许多研究表明:原体蛋白质能被单体氨基酸所替代的量是有限的,给畜禽饲喂低水平蛋白质并补充合成氨基酸日粮并不能获得最佳的生产性能和饲料效率,… 相似文献
35.
偏重亚硫酸钠钝化生豆粕胰蛋白酶抑制因子的研究 总被引:8,自引:0,他引:8
试验用不同浓度的Na2S2O5处理生豆粕,进行适宜水平研究。结果表明,当生豆粕TIA和UA分别为29.72酶活单位和1.95△pH时,分别用0.3%、0.4%、0.5%和0.6%NaS2O5处理RSBM,TIA依次降低了51.8%、55.96%、59.83%和52.05%,均极显著地低于RSBM(P<0.01)。0.3%Na2S2O5对UA无影响,其它处理UA提高约0.06△pH。 相似文献
36.
针对农业机器人应用中的自主导航问题,提出了一种基于无线测距的导航定位方法。首先,分析了机器人的机械模型和位姿描述;然后,阐述了超宽带测距的原理,并分析了基于超宽带测距的定位模型;最后,设计了基于卡尔曼滤波器的多信标传感器信息融合算法。该方法稳定性高,操作简便,解决了农业机器人在恶劣和未知作业环境中的导航定位问题。 相似文献
37.
38.
The fate of fertilizer N applied with different irrigation amounts in tobacco fields was quantitatively studied by applying 15N double-labelled NH4NO3 in lysimeters. The 15N (fertilizer N originating from the fertilizer applied in 2011) in tobacco plants, 15N in soils and 15N loss were observed continuously from 2011 to 2014. The results showed that 21.6% of 15N was utilized by tobacco plants, 72.1% remained in the 0–60 cm soil layer and 6.3% was lost from the soil–plant system after the first season’s harvest (2011) of flue-cured tobacco. During the four seasons from 2011 to 2014, cumulative utilization of 15N by tobacco plants was 34.3%, while 54.2% remained in the 0–60 cm soil layer, and 11.5% was lost via mechanisms such as leaching and volatilization. The fate of 15N in terms of accumulation in plants and soils or losses from the soil–plant system from 2012 to 2014 was greatly affected by the fertilizer and irrigation management strategies in 2011. The results of this investigation suggest that the major amount of fertilizer N applied during the first season remains available in the soil for utilization by tobacco plants after 4 years. 相似文献
39.
The People's Victory Irrigation System which diverts water from the Yellow River of China covers a total irrigable area of 59 000 ha. The system encountered some serious problems in the first decade of its operation — salinity and waterlogging of irrigated land, siltation of irrigation and drainage channels, as well as a low efficiency of water use. This paper describes a series of structural and functional measures which have been adopted in the past 24 years for the rehabilitation of the system, including: improvement of the existing drainage system and construction of new drainage system on agricultural land, conjunctive use of surface and groundwater supplies, a comprehensive programme to reduce the levels of siltation as well as the implementation of improved water management practices. A model for the optimal operation of the system by using system analysis theory as an aid in reducing the operation and maintenance (O & M) costs has been developed in recent years. The results are that the soil salinity has been controlled and the agricultural production has increased whilst the efficiency of water use has improved and the siltation levels reduced. Experience gained on this system has been successfully used in developing and managing other irrigation projects along the lower reaches of the Yellow River. The proposed procedure of solving the said optimal model has also embodied some benefits from reducing O & M costs in operation. 相似文献
40.
Zhang Ying-zi Chen Hai-tao Hou Shou-yin Ji Wen-yi Ouyang Bin-lin Dun Guo-qiang Zhang Ji-cheng 《东北农业大学学报(英文版)》2015,(2):73-79
In order to increase the applying rate of liquid fertilizer and reduce environmental pollution, a slave computer control system for applying variable-rate liquid fertilizer was designed. The system used SMC as core processor and electrically controlled pressure regulator as execution component. The characteristic equation of the system was obtained by using classical control theory. Results indicated that the characteristic equation met the requirements of routh-criterion, which indicated the working process of the system was stable. Performance of the slave computer was verified via bench tests. Results demonstrated that there was no significant influence on the response from interclass error. The fertilization error was less than 0.9, and the fertilization accuracy was larger than 97%. The liquid fertilizer emitted by the fertilizing devices had no significant difference in uniformity, which met the demands of the slave computer control system for applying variable-rate liquid fertilizer. 相似文献