收费全文 | 85137篇 |
免费 | 4432篇 |
国内免费 | 46篇 |
林业 | 4019篇 |
农学 | 2965篇 |
基础科学 | 498篇 |
11527篇 | |
综合类 | 10223篇 |
农作物 | 3119篇 |
水产渔业 | 4157篇 |
畜牧兽医 | 47181篇 |
园艺 | 1027篇 |
植物保护 | 4899篇 |
2019年 | 808篇 |
2018年 | 1472篇 |
2017年 | 1614篇 |
2016年 | 1508篇 |
2015年 | 1155篇 |
2014年 | 1485篇 |
2013年 | 3810篇 |
2012年 | 2552篇 |
2011年 | 3129篇 |
2010年 | 2126篇 |
2009年 | 2033篇 |
2008年 | 2954篇 |
2007年 | 2923篇 |
2006年 | 2678篇 |
2005年 | 2380篇 |
2004年 | 2270篇 |
2003年 | 2249篇 |
2002年 | 2039篇 |
2001年 | 2925篇 |
2000年 | 2770篇 |
1999年 | 2188篇 |
1998年 | 884篇 |
1997年 | 818篇 |
1996年 | 772篇 |
1995年 | 905篇 |
1994年 | 765篇 |
1992年 | 1607篇 |
1991年 | 1738篇 |
1990年 | 1817篇 |
1989年 | 1690篇 |
1988年 | 1546篇 |
1987年 | 1542篇 |
1986年 | 1494篇 |
1985年 | 1406篇 |
1984年 | 1212篇 |
1983年 | 981篇 |
1979年 | 1220篇 |
1978年 | 916篇 |
1977年 | 811篇 |
1976年 | 932篇 |
1975年 | 942篇 |
1974年 | 1100篇 |
1973年 | 1036篇 |
1972年 | 1031篇 |
1971年 | 922篇 |
1970年 | 934篇 |
1969年 | 936篇 |
1968年 | 876篇 |
1967年 | 900篇 |
1966年 | 832篇 |
An experiment was conducted to determine the effect of reciprocal crossing of turkeys on early and 24 h post-mortem changes in quality traits of their breast muscles.
The turkeys of slow-growing (SG) and fast-growing (FG) lines as well as SF (SG × FG) and FS crosses (FG × SG) were reared with access to free range.
After slaughter turkey breast muscles were examined in the following terms: 5 min, 45 min, 2 h and 24 h post-mortem, for: temperature, pH, glycogen content (G), lactate content (L) and electrical conductivity (EC). Quality attributes of the breast meat were evaluated based on chemical composition, water holding capacity (WHC), cooking loss (%), shear force (N) and colour (L*, a*, b*).
Despite differences in the rate of post-mortem changes, the genotype of turkeys had no significant effect upon many quality traits assessed 24 h post-mortem. Meat of lighter birds (SG and SF) was characterised by a lower fat content but a similar protein content compared to meat of FS and FG turkeys. In addition, meat of males from these groups was darker. Meat from the breast muscles of heavier birds (FS and FG) was harder.
Significant negative maternal effects were determined for temperature of meat of both male and female turkeys, for pH2 and EC24 of males as well as for L2, L24 and cooking loss of female meat. Positive heterosis was confirmed only for pH2 of female meat and for G2 of male meat.
In summary, the direction of fast- and slow-growing turkey crossing may affect the quality of their meat. However, meat of both types of hybrids reared under semi-confined conditions (with the possibility of using free range) was characterised by appropriate quality parameters.
The aim of this work was to improve natural anti-predator behaviour of farm-reared gamebirds.
We evaluated the anti-predator behaviour of reared red-legged partridge Alectoris rufa chicks kept in brooder houses in large groups (>350 chicks), trained and not trained by parent red-legged partridges acting as experienced tutors.
The experiment consisted of two conditioned tests (a raptor model and a human) and two control tests, which were conducted during three consecutive phases of life (1–4, 15–17 and 30–32 d after hatching). The motor anti-predator behaviour, its duration, the intensity of response in chicks and alarm calls elicited by adults were recorded.
Tutors elicited aerial alarm calls (76% of tests) and showed prolonged crouching (59% of tests) in response to the raptor model whereas uttering the ground alarm call (73% of tests) and showing vigilance behaviour (78% of tests) was the main pattern during the human test.
Trained and not trained chicks showed similar motor behaviour in response to the raptor model (crouching) and the human test (escaping), but frequency of strong responses (all chicks responding) from chicks trained with tutors was double that of chicks trained without them, and chicks trained with tutors showed a higher frequency of long responses (41–60 s).
This study indicates that anti-predator training programmes before release may improve behaviour of farm-reared partridges which may confer benefits to survival of birds.
Two experiments, which differed in breeder age, strain and season, were conducted to study the influence of low-intensity, short-duration thermal stimuli during the late phase of incubation on hatchability and performance. The first experiment conducted in April–June used eggs from Cobb × Ross broiler breeders at 35–41 weeks of age and the second experiment performed in February–April used eggs from Hubbard × Cobb broiler breeders at 49–53 weeks of age.
Eggs in the test group had the same physical environment as eggs in the control group except that incubation temperature was increased by 1?C for 2 h/d above the control group from 18 to 20 d of incubation (DI).
The results demonstrated that thermal stimulation of 1?C for 2 h/d above control incubation temperature during 18–21DI did not have any adverse effects on hatch and post-hatch performance of broilers.
In both experiments, treatment did not significantly alter the secondary sex ratio in hatched chickens, but hatch residue showed that the proportion of unhatched male embryos was significantly lower in the test groups than in the control groups.
In the first experiment, thermal stimulation improved feed conversion by 1.82% compared with the control.
Three experiments with a 2 × 2 × 2 factorial arrangement were conducted to evaluate maize-based diets for broilers containing different lipid sources [soybean oil (S) or beef tallow (T)] supplemented with or without lysophospholipids and organic acids on nutrient balance (Experiment I, evaluation period of 10–14 d), on liver concentration of fat-soluble vitamins, on jejunal microbiota (Experiment II, sampling at d 14) and on performance (Experiment III, accumulated periods of 1–14, 1–21 and 1–42 d).
A total of 1344 male chicks were used. In each experiment, the birds were allotted in a completely randomised design with 8 replications. The lysophospholipids were mainly composed of lysolecithins and the organic acids blend was constituted by lactic (40%), acetic (7%) and butyric acids (1%).
An interaction between lipid sources and lysophospholipids was observed on faecal apparent digestibility of lipid (ADL), which improved with lysophospholipids addition in T diets. Broilers fed on S had higher ADL and faecal apparent digestibility of nitrogen-corrected gross energy (ADGEN).
It was not possible to demonstrate a significant treatment effect on the liver concentration of vitamins A and E, even with the differences in fatty acid profile between S and T.
Enterobacteria values were below the detection threshold. Lysophospholipid supplementation reduced gram-positive cocci in T-fed birds. S diets promoted lower total anaerobe counts compared with T diets, independent of additives.
S diets increased BW gain and feed:gain ratio in all evaluation periods. Lysophospholipids and organic acids improved feed:gain ratio at 1–21 d in T diets. Furthermore, main effects were observed for lysophospholipids and organic acids at 1–42 d, which increased BW gain and improved feed:gain ratio, respectively.
No positive interactions between additives were found.