全文获取类型
收费全文 | 355283篇 |
免费 | 18541篇 |
国内免费 | 1037篇 |
专业分类
林业 | 25630篇 |
农学 | 14852篇 |
基础科学 | 3180篇 |
50450篇 | |
综合类 | 53242篇 |
农作物 | 18219篇 |
水产渔业 | 19389篇 |
畜牧兽医 | 156058篇 |
园艺 | 6738篇 |
植物保护 | 27103篇 |
出版年
2019年 | 3947篇 |
2018年 | 4872篇 |
2017年 | 5375篇 |
2016年 | 5414篇 |
2015年 | 4763篇 |
2014年 | 6166篇 |
2013年 | 16825篇 |
2012年 | 9331篇 |
2011年 | 12051篇 |
2010年 | 8956篇 |
2009年 | 9224篇 |
2008年 | 11270篇 |
2007年 | 10628篇 |
2006年 | 10608篇 |
2005年 | 9847篇 |
2004年 | 9570篇 |
2003年 | 9436篇 |
2002年 | 8690篇 |
2001年 | 9651篇 |
2000年 | 9417篇 |
1999年 | 8102篇 |
1998年 | 4561篇 |
1997年 | 4597篇 |
1996年 | 4337篇 |
1995年 | 4977篇 |
1994年 | 4391篇 |
1993年 | 4085篇 |
1992年 | 6500篇 |
1991年 | 6790篇 |
1990年 | 6699篇 |
1989年 | 6701篇 |
1988年 | 6043篇 |
1987年 | 6067篇 |
1986年 | 6056篇 |
1985年 | 6066篇 |
1984年 | 5280篇 |
1983年 | 4810篇 |
1982年 | 3650篇 |
1981年 | 3445篇 |
1980年 | 3361篇 |
1979年 | 4798篇 |
1978年 | 4032篇 |
1977年 | 3616篇 |
1976年 | 3476篇 |
1975年 | 3536篇 |
1974年 | 4038篇 |
1973年 | 4076篇 |
1972年 | 3854篇 |
1971年 | 3648篇 |
1970年 | 3612篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Ⅱ型猪环状病毒 (PCV2 )现已被证明是断奶后全身消耗性综合征 (PMWS)的致病因子 ,这一综合征是一种可造成世界各地严重经济损失的猪病。最近的研究还证实此病毒与加拿大和欧洲猪群的繁殖障碍有关。但是 ,绝大多数PCV2感染都是亚临床性的。刺激仔猪免疫系统是感染此病毒后产生临床疾病的重要因子吗 ? 相似文献
982.
Amy M Grooters Joseph Taboada 《Veterinary Clinics of North America: Small Animal Practice》2003,33(4):749-58, vi
Fungal pathogens are becoming increasingly important for human and small animal medicine. This article highlights many standards-of-care and new agents for treatment of these pathogens for small animals and people. 相似文献
983.
984.
荷兰是全世界畜牧业高度发达的国家之一。养猪业也象奶牛业一样发展很好,特别是猪场管理很值得我国养猪同行学习。该国的养猪规模很大,一般都在2000头左右。其养猪业的先进性在于:年头均产胎指数2.3,年头均母猪出栏仔猪23头,胎产活仔数11.8头,受胎率85%,仔猪早期断奶及母猪年更新率为50%。 相似文献
985.
J.A. Díez P. Hernaiz M.J. Muñoz A. de la Torre A. Vallejo 《Soil Use and Management》2004,20(4):444-450
Abstract. The repeated application of pig slurry to agricultural soils may result in an accumulation of salts and a risk of aquifer pollution due to nitrate leaching and salinization. Under Mediterranean conditions, a field experiment on a sandy loam soil (Typic Xerofluvent) was performed with maize (Zea mays) in 1998, 1999 and 2001 to study the effects of applying optimal (P1) and excessive rates (P3) of pig slurry on soil salinization, nitrate leaching and groundwater pollution. The rate of pig slurry was established considering the optimal N rate for maize in this soil (170, 162 and 176 kg N ha?1 for 1998, 1999 and 2001, respectively). Pig slurry treatments were compared to an optimal N rate supplied as urea (U) and a control treatment without N fertilizer (P0). The composition of the slurries showed great variability between years. Mean NO3? leaching losses from 1998 to 2001 were 329, 215, 173 and 78 kg N ha?1 for P3, P1, U and P0 treatments, respectively. The amount of total dissolved salts (TDS) added to the soil in slurry application between 1998 and 2001 was 2019 kg TDS ha?1 for the P1 treatment and 6058 kg TDS ha?1 for the P3 treatment. As a consequence, the electrical conductivity (EC) of the slurry‐treated soils was greater than that of the control soil. The EC correlated significantly with the sodium concentration of the soil solution. Over the entire experimental period, 2653, 2202 and 2110 kg Na ha?1 entered the aquifer from the P3, P1 and P0 treatments, respectively. The P3 treatment did not significantly increase grain production in 1999 and 2001 compared with that achieved with the optimal N rate treatment (P1). This behaviour shows the importance of establishing application guidelines for pig slurry that will reduce the risk of soil and groundwater pollution. 相似文献
986.
987.
988.
989.
Effects of monensin on Mg, Ca, P and Zn metabolism and tissue concentrations in lambs 总被引:1,自引:0,他引:1
A study consisting of two trials was conducted to determine the effects of monensin on the apparent absorption and retention of magnesium (Mg), phosphorus (P), calcium (Ca) and zinc (Zn) and to determine mineral changes in tissue and ruminal fluid. Eight lambs (39 kg) were used in trial 1, and 10 lambs (37 kg) were used in trial 2. Animals were blocked by weight and fed a high concentrate diet with or without 20 mg/kg monensin. Trials began with a dietary adjustment period lasting 18 d in trial 1 and 21 d in trial 2. Animals were then placed in metabolism stalls for a 10-d stall adjustment period followed by a 12-d collection period. Collections to determine mineral balance were made during the first 10 d of the collection period. Blood and ruminal fluid samples were taken on d 11 of the collection period. Lambs were slaughtered on d 12 of the collection period and tissue samples were collected. Monensin supplementation increased (P less than .05) Mg retention 42.0%. Urinary Ca excretion decreased (P less than .05) 60.0% when monensin was fed. Monensin supplementation decreased (P less than .05) liver Ca and bone Ca, 45.5 and 2.9%, respectively. Apparent P digestibility increased (P less than .05) 40.0% and P retention increased (P less than .10) 26.8% due to monensin supplementation. Both apparent absorption and retention of Zn increased (P less than .01) 50.0 and 45.0%, respectively, with monensin supplementation. Ruminal fluid Zn concentrations decreased (P less than .05) 33.0% with the addition of monensin.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
990.
The utilization of dietary lysine for protein synthesis is affected by the digestibility of protein-bound lysine, by its intestinal resorption and by its oxidative catabolism. The approach chosen in this paper enables a comparison of the cumulative effect of these processes on the utilization of free and protein-bound lysine, respectively. The principle of the approach is based on a quantification of the expiration of 14C-labelled carbon dioxide after an oral administration of a diet, which contains L-(U-14C)-lysine either as a free amino acid or bound to yeast proteins. During an adaptation phase cockerels of the Japanese quail received a diet based mainly on ground wheat and wheat gluten. This diet was supplemented either with yeast proteins or with a mixture of L-amino acids which simulates the composition of the yeast proteins. In the main experiment the expiration of labelled carbon dioxide was measured during 240 minutes after the administration of the corresponding labelled diets. Just before treatment the animals were either in the postprandial phase or in a state of slight hunger. The maximum of expiration of labelled carbon dioxide occurred around the 60th minute after administration of the corresponding labelled diets. The cumulative expiration of labelled carbon dioxide, expressed in per cent of the radioactive dose used, amounts to 15.5% and 14.3% for free and protein-bound lysine, respectively. The utilization of both forms of lysine in the Japanese quail is lower than in broilers. 相似文献