| 收费全文 | 75798篇 |
| 免费 | 3842篇 |
| 国内免费 | 50篇 |
| 林业 | 3559篇 |
| 农学 | 2336篇 |
| 基础科学 | 392篇 |
| 7783篇 | |
| 综合类 | 15348篇 |
| 农作物 | 3012篇 |
| 水产渔业 | 3376篇 |
| 畜牧兽医 | 38470篇 |
| 园艺 | 899篇 |
| 植物保护 | 4515篇 |
| 2018年 | 856篇 |
| 2017年 | 926篇 |
| 2016年 | 856篇 |
| 2015年 | 778篇 |
| 2014年 | 952篇 |
| 2013年 | 2600篇 |
| 2012年 | 1676篇 |
| 2011年 | 2068篇 |
| 2010年 | 1359篇 |
| 2009年 | 1285篇 |
| 2008年 | 2035篇 |
| 2007年 | 2076篇 |
| 2006年 | 1894篇 |
| 2005年 | 1831篇 |
| 2004年 | 1751篇 |
| 2003年 | 1780篇 |
| 2002年 | 1690篇 |
| 2001年 | 2215篇 |
| 2000年 | 2192篇 |
| 1999年 | 1797篇 |
| 1997年 | 668篇 |
| 1995年 | 808篇 |
| 1993年 | 690篇 |
| 1992年 | 1488篇 |
| 1991年 | 1551篇 |
| 1990年 | 1661篇 |
| 1989年 | 1644篇 |
| 1988年 | 1527篇 |
| 1987年 | 1477篇 |
| 1986年 | 1528篇 |
| 1985年 | 1516篇 |
| 1984年 | 1247篇 |
| 1983年 | 1145篇 |
| 1982年 | 771篇 |
| 1981年 | 717篇 |
| 1980年 | 664篇 |
| 1979年 | 1248篇 |
| 1978年 | 979篇 |
| 1977年 | 848篇 |
| 1976年 | 803篇 |
| 1975年 | 913篇 |
| 1974年 | 1201篇 |
| 1973年 | 1239篇 |
| 1972年 | 1255篇 |
| 1971年 | 1182篇 |
| 1970年 | 1102篇 |
| 1969年 | 1003篇 |
| 1968年 | 863篇 |
| 1967年 | 906篇 |
| 1966年 | 837篇 |
Genetic parameters were estimated for 5 economically important egg production traits using records collected over 9 years in chickens reared under tropical conditions in Thailand. The data were from two purebred lines and two hybrid lines of layer parent stocks.
The two purebred lines were Rhode Island Red (RIR) and White Plymouth Rock (WPR) and the hybrid lines were formed by crossing a commercial brown egg laying strain to Rhode Island Red (RC) and White Plymouth Rock (WC), respectively.
Five egg production traits were analysed, including age at first egg (AFE), body weight at first egg (BWT), egg weight at first egg (EWFE), number of eggs from the first 17 weeks of lay (EN) and average egg weight over the 17th week of lay (EW).
Fixed effects of year and hatch within year were significant for all 5 traits and were included in the model.
Maternal genetic and permanent environmental effects of the dam were not significant, except for EN and EW in RIR and BWT and EW in WPR.
Estimated heritability of AFE, BWT, EWFE, EN and EW were 0.45, 0.50, 0.29, 0.19 and 0.43 in RIR; 0.44, 0.38, 0.33, 0.20 and 0.38 in WPR; 0.37, 0.41, 0.38, 0.18 and 0.36 in RC; and 0.46, 0.53, 0.36, 0.38 and 0.45 in WC lines, respectively.
The EN was negatively correlated with other traits, except for BWT in RC and AFE and BWT in WC.
It was concluded that selection for increased EN will reduce other egg production traits in purebred and hybrid chicken and therefore EN needs to be combined with other egg production traits in a multi-trait selection index to improve all traits optimally according to a defined breeding objective.
The advantage of supplemental sodium bicarbonate (NaHCO3) on eggshell quality in laying hens changes with age. Besides increasing calcium (Ca) secretion in the eggshell gland, it may improve Ca absorption in the intestine or kidney.
Hy-Line Brown layers (n = 384), 25 weeks of age, were allocated to two treatment groups in two experiments, each of which included 4 replicates of 24 hens. Hens were fed a basal diet (control) or the basal diet containing 3 g NaHCO3 g/kg for 50 or 20 weeks in Experiment 1 or 2, respectively. A 24-h continuous lighting regimen was used to allow hens to consume the dietary supplements during the period of active eggshell formation.
In Experiment 1, particularly from 25 to 50 weeks of age, and in Experiment 2, NaHCO3 supplementation favoured hen-d egg production at the expense of lower egg weight. The increased eggshell thickness should have nothing to do with the additional eggshell formation, because of the unchanged egg mass and daily eggshell calcification.
At 35 weeks of age in both experiments, NaHCO3 supplementation increased duodenal expression of calbindin-d28k (CaBP-D28k) protein, contributing to higher Ca retention and balance.
From 50 to 75 weeks of age in Experiment 1, the hens had little response to NaHCO3 supplementation and showed a negative trend on eggshell thickness and strength.
It is concluded that dietary supplementation with 3 g NaHCO3 g/kg improves Ca absorption and eggshell quality of laying hens during the peak but not late production period, with the introduction of continuous lighting.
The objective was to investigate inbreeding depression for some economic traits of Mazandaran native fowls using data collected from 1992 to 2012 (21 generations) using a REML animal model of significant fixed and random effects with inbreeding of birds and dams as covariates.
The mean inbreeding coefficient (F) for the whole population and dams was 4.67% and 4.12%, respectively, and most of the inbred birds (75.79%) and inbred dams (72.58%) had F < 12.5%.
Individual and dam inbreeding trends were 0.55% and 0.53% per year.
Inbreeding depression for body weight at hatch, at 8 weeks and 12 weeks of age, age at sexual maturity, weight at sexual maturity, egg weight at 1st d of laying and average egg weight at 28, 30 and 32 weeks of laying due to a 1% increase in individual inbreeding were ?0.11 g, ?3.1 g, ?1.3 g, 0.15 d, 0.59 g, ?0.05 g and ?0.03 g, respectively.
A 1% increase in maternal inbreeding resulted in a reduction of 0.06, 0.6 and 3.6 g in body weight at hatch, 8 weeks and 12 weeks of age.
The onset and progression of Salmonella infections was investigated in commercial turkey flocks from placement at 1 d old until slaughter in “brood and move” systems using a longitudinal observational approach based on faeces and environmental sampling with subsequent culture of Salmonella.
Persistent Salmonella Newport contamination was found within rearing houses and on their external concrete aprons after cleaning and disinfection between crops of heavily shedding young birds.
Salmonella shedding was often detected by 5 d of age and the frequency of positive samples peaked at 14–35 d. Thereafter Salmonella isolations declined, especially in the later (fattening) stages. Samples were still Salmonella-positive at low prevalence in half of the intensively sampled houses at slaughter age.
A number of management interventions to combat Salmonella infection of flocks, including sourcing policy, competitive exclusion cultures and cleaning and disinfection, were inadequate to prevent flock infection, although improved disinfection on one unit was associated with a delay in the onset of flock infection.
2. Polymorphisms in BMP15 exon1 and GDF9 exon2 were detected by DNA sequencing and PCR-RFLP. Three SNPs were detected in each of BMP15 (A111G, C231T and C34T) and GDF9 (G593A, T824C and C896T). C34T leads to the substitution of Leu by Phe, which was predicted to affect protein function.
3. Results of the association analysis indicated that C34T had an effect on total egg production at 300 d of age (EN) and age at first laying (AFE). G593A affected EN and both C231T and C896T influenced AFE. The TGC1TGC1 diplotype in BMP15 had the highest EN.
4. In conclusion, EN may be significantly improved by marker-assisted selection of the BMP15 genotypes in maternal lines of Shaobo hens. 相似文献
There is much interest in quantifying the nutritional value of UK wheat distillers dried grains with solubles (W-DDGS) for livestock species. A study was designed to evaluate caecal parameters (pH, short chain fatty acids (SCFAs) and bacterial diversity) in layer hens fed on balanced diets containing graded concentrations of W-DDGS.
A total of 32 layer hens (Bovans Brown strain at 27 weeks of age) were randomly allocated to one of 4 dietary treatments containing W-DDGS at 0, 60, 120 or 180 g/kg. Each treatment was fed to 8 replicate individually housed layer hens over a 5-d acclimatisation period, followed by a 4-week trial. Individual feed intakes were monitored and all eggs were collected daily for weeks 2, 3 and 4 of the trial, weighed and an assessment of eggshell “dirtiness” made. All hens were culled on d 29 and caecal pH and SCFAs measured. Polymerase chain reaction denaturing gradient gel electrophoresis of the bacterial 16 S rDNA gene was used to assess total bacterial diversity of luminal caecal content from hens fed the 0 and 180 g W-DDGS/kg diets. Unweighted pair group method with arithmetic mean (UPGMA) dendrograms were generated from DGGE banding patterns.
Increasing W-DDGS dietary concentrations resulted in a more acidic caecal environment. Caecal SCFAs were unaffected by diet aside from a quadratic effect for molar proportions of isobutyric acid. Diversity profiles of the bacterial 16S rRNA gene from luminal caecal contents were unaffected by W-DDGS inclusion.
The results of the current study suggest that W-DDGS can be successfully formulated into nutritionally balanced layer diets (supplemented with xylanase and phytase) at up to 180 g/kg with no detrimental effects to the caecal environment.
下载免费PDF全文