全文获取类型
收费全文 | 1429篇 |
免费 | 55篇 |
国内免费 | 1篇 |
专业分类
林业 | 55篇 |
农学 | 23篇 |
基础科学 | 5篇 |
157篇 | |
综合类 | 231篇 |
农作物 | 53篇 |
水产渔业 | 70篇 |
畜牧兽医 | 789篇 |
园艺 | 42篇 |
植物保护 | 60篇 |
出版年
2023年 | 8篇 |
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 28篇 |
2017年 | 17篇 |
2016年 | 31篇 |
2015年 | 15篇 |
2014年 | 29篇 |
2013年 | 59篇 |
2012年 | 69篇 |
2011年 | 74篇 |
2010年 | 38篇 |
2009年 | 33篇 |
2008年 | 80篇 |
2007年 | 94篇 |
2006年 | 64篇 |
2005年 | 88篇 |
2004年 | 65篇 |
2003年 | 63篇 |
2002年 | 65篇 |
2001年 | 28篇 |
2000年 | 21篇 |
1999年 | 32篇 |
1998年 | 29篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 13篇 |
1994年 | 21篇 |
1993年 | 8篇 |
1992年 | 33篇 |
1991年 | 36篇 |
1990年 | 35篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1970年 | 3篇 |
1927年 | 3篇 |
1922年 | 3篇 |
排序方式: 共有1485条查询结果,搜索用时 15 毫秒
191.
192.
193.
194.
Shackling can induce wing flapping in chickens. In this survey of 30 chicken processing plants the proportion of birds flapping their wings had usually subsided to less than 0.5 per cent after the birds had been conveyed 2 m away from the shackling area. Thereafter, there were many causes of wing flapping, of which the following were thought to be important; tight fitting shackles on the birds' shanks, electric shocks at the water bath stunner before stunning, sudden bright sunlight, bends in the line, temporary loss of visual contact between neighbouring birds, and unevenness in the line which jolted the birds. If it is decided that legislation is required to prescribe a minimum 'hang-on' period before stunning it is suggested that birds should not be put through the stunner less than 12 seconds after shackling because after this time 99.7 per cent of the birds had stopped flapping. 相似文献
195.
Analyses of ovulation rates in consecutive estrous cycles with multiple-trait and repeated-records animal models resulted in different estimates of heritability. The estimate from the repeated-records model was seen to be approximately the product of the average genetic correlation and the average heritability from the multiple-trait procedure. A simple model is used to show algebraically that such a result is expected, particularly if the environmental correlations are small among records of the same animal. Comparison of results of the two types of analyses of 10 replications of 10 combinations of underlying heritabilities and genetic correlations confirms this explanation. 相似文献
196.
C R Gregory I M Gourley J R Snyder J Ilkiw 《American journal of veterinary research》1992,53(1):153-156
Dissection, injection, and surgical studies in feline cadavers and in anesthetized cats were conducted to determine the feasibility of using the gracilis muscle as the basis for a free musculocutaneous flap. The vascular pedicle of the flap consisted of the femoral artery and vein. Mean length (1.6 +/- 0.2 cm) of the vascular pedicle and mean artery (1.33 +/- 0.19 mm) and vein (2.55 +/- 0.38 mm) diameters were satisfactory for microvascular transfer. Fluorometry revealed overlying cutaneous perfusion in the flaps on the basis of their muscle vascular pedicles. To ensure survival of the flap, the muscular branches of the femoral artery and vein supplying the gracilis muscle had to be carefully preserved during surgical elevation of the flap. 相似文献
197.
Green-light supplementation for enhanced lettuce growth under red- and blue-light-emitting diodes 总被引:9,自引:0,他引:9
Kim HH Goins GD Wheeler RM Sager JC 《HortScience : a publication of the American Society for Horticultural Science》2004,39(7):1617-1622
Plants will be an important component of future long-term space missions. Lighting systems for growing plants will need to be lightweight, reliable, and durable, and light-emitting diodes (LEDs) have these characteristics. Previous studies demonstrated that the combination of red and blue light was an effective light source for several crops. Yet the appearance of plants under red and blue lighting is purplish gray making visual assessment of any problems difficult. The addition of green light would make the plant leave appear green and normal similar to a natural setting under white light and may also offer a psychological benefit to the crew. Green supplemental lighting could also offer benefits, since green light can better penetrate the plant canopy and potentially increase plant growth by increasing photosynthesis from the leaves in the lower canopy. In this study, four light sources were tested: 1) red and blue LEDs (RB), 2) red and blue LEDs with green fluorescent lamps (RGB), 3) green fluorescent lamps (GF), and 4) cool-white fluorescent lamps (CWF), that provided 0%, 24%, 86%, and 51% of the total PPF in the green region of the spectrum, respectively. The addition of 24% green light (500 to 600 nm) to red and blue LEDs (RGB treatment) enhanced plant growth. The RGB treatment plants produced more biomass than the plants grown under the cool-white fluorescent lamps (CWF treatment), a commonly tested light source used as a broad-spectrum control. 相似文献
198.
Duarte PC Conrad PA Wilson WD Ferraro GL Packham AE Bowers-Lepore J Carpenter TE Gardner IA 《American journal of veterinary research》2004,65(8):1047-1052
OBJECTIVE: To estimate risk of exposure and age at first exposure to Sarcocystis neurona and Neospora hughesi and time to maternal antibody decay in foals. ANIMALS: 484 Thoroughbred and Warmblood foals from 4 farms in California. PROCEDURE: Serum was collected before and after colostrum ingestion and at 3-month intervals thereafter. Samples were tested by use of the indirect fluorescent antibody test; cutoff titers were > or = 40 and > or = 160 for S neurona and N hughesi, respectively. RESULTS: Risk of exposure to S neurona and N hughesi during the study were 8.2% and 3.1%, respectively. Annual rate of exposure was 3.1% for S neurona and 1.7% for N hughesi. There was a significant difference in the risk of exposure to S neurona among farms but not in the risk of exposure to N hughesi. Median age at first exposure was 1.2 years for S neurona and 0.8 years for N hughesi. Highest prevalence of antibodies against S neurona and N hughesi was 6% and 2.1 %, respectively, at a mean age of 1.7 and 1.4 years, respectively. Median time to maternal antibody decay was 96 days for S neurona and 91 days for N hughesi. There were no clinical cases of equine protozoal myeloenchaphlitis (EPM). CONCLUSIONS AND CLINICAL RELEVANCE: Exposure to S neurona and N hughesi was low in foals between birth and 2.5 years of age. Maternally acquired antibodies may cause false-positive results for 3 or 4 months after birth, and EPM was a rare clinical disease in horses < or = 2.5 years of age. 相似文献
199.
Wichtel JJ Keefe GP Van Leeuwen JA Spangler E McNiven MA Ogilvie TH 《The Canadian veterinary journal. La revue veterinaire canadienne》2004,45(2):124-132
Bulk tank milk selenium (Se) concentration was compared with mean serum Se concentration in 15 herds and was found to be an accurate reflection of the herd Se status. The Se status of 109 Prince Edward Island (PEI) dairy herds was monitored for 1 year using bulk tank milk Se concentration. Fifty-nine percent of the herds surveyed were, at some point, found to be marginal or deficient in Se, putting them at risk of disease and suboptimal production. The periods of greatest risk of deficiency were fall and winter, at which time 5% and 4%, respectively, of herds sampled fell in the range considered truly deficient in Se. Herds in which Se supplementation was provided in the form of a commercial dairy concentrate were over 4 times more likely to be Se-adequate than herds not using this method, and adjusted average daily milk yield was 7.6% greater in herds determined to be Se-adequate when compared with Se-marginal herds. We conclude that many dairy producers in PEI are providing insufficient supplementary Se in the ration to meet the recommended Se intake for lactating cows. 相似文献
200.