首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   596篇
  免费   45篇
林业   53篇
农学   27篇
基础科学   5篇
  125篇
综合类   18篇
农作物   40篇
水产渔业   47篇
畜牧兽医   213篇
园艺   13篇
植物保护   100篇
  2024年   1篇
  2023年   5篇
  2022年   3篇
  2021年   17篇
  2020年   15篇
  2019年   18篇
  2018年   18篇
  2017年   23篇
  2016年   23篇
  2015年   25篇
  2014年   23篇
  2013年   35篇
  2012年   49篇
  2011年   56篇
  2010年   24篇
  2009年   24篇
  2008年   44篇
  2007年   51篇
  2006年   24篇
  2005年   31篇
  2004年   19篇
  2003年   19篇
  2002年   15篇
  2001年   15篇
  2000年   10篇
  1999年   10篇
  1998年   8篇
  1996年   7篇
  1995年   1篇
  1994年   3篇
  1993年   1篇
  1992年   2篇
  1991年   4篇
  1987年   3篇
  1986年   3篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1981年   2篇
  1980年   1篇
  1976年   1篇
  1973年   1篇
排序方式: 共有641条查询结果,搜索用时 15 毫秒
1.
In order to characterise and classify an unknown maize-infecting potyvirus isolated from fields in northeast Spain, the entire coat protein gene and the C-terminal twothirds of the large nuclear inclusion protein (NIb) gene were cloned and sequenced. Protein sequencing enabled the cleavage site between the two proteins to be deduced and also revealed that on storage the viral coat protein undergoes a specific degradation in which the N-terminal 39 amino acids are removed. Comparison of the nucleotide sequence of the 3 non-coding region of the viral RNA and the predicted amino acid sequence of the coat protein with the equivalent regions of other members of the potyvirus group revealed that the Spanish virus is closely related to maize dwarf mosaic virus strain A.  相似文献   
2.
Rabbit does from R line selected for growth rate present a low reproductive performance and this study aimed to evaluate both the recovery efficacy and viability of recovered embryos after vitrification and the reproductive performance of donor does subjected to in vivo recovery. Does were divided into three groups: 28 does without in vivo recovery (control), 25 does in which in vivo recovery was started in the nulliparous state (group 1) and 30 does with at least one litter before in vivo recovery (group 2). Does were superovulated with a single subcutaneous injection of 50 IU of equine chorionic gonadotropin (eCG) per female, and were then artificially inseminated 60 h later and immediately administered an intravenous dose of 75 IU of human chorionic gonadotropin (hCG) per female. Does from group 1 and 2 were recovered in vivo 76-80 h post-insemination by repeated laparoscopies at one to four times and permitted one or two parturitions between recoveries [in vivo (IV) recovery]. At the end of the experiment, about 16 does of all groups were recovered post-mortem (PM recovery). All normal embryos were vitrified, devitrified and then cultivated in vitro to evaluate the viability after thawing. A significant increase in the ovulation rate was found in does recovered PM than in those recovered IV in the nulliparous state. However, no significant differences were observed in the recovery rate, the donor rate, the number of normal embryos recovered with at least one normal embryo per doe and the viability after thawing between the PM and IV groups. A significant decrease in the fertility rate, total born, live born and weaned kids was found for does from group 1 in comparison with does from group 2. Results support the use of repeated laparoscopy to increase the number of recovered embryos per donor doe especially in such R line does, if they are permitted to produce at least one litter before the beginning of in vivo recovery.  相似文献   
3.
Egg yolk is a common additive to sperm cryopreservation diluents. Because of its animal origin, however, it also represents a potential risk of microbiological contamination in the diluent. This potential contamination can be avoided by using powdered egg yolk, instead of fresh egg yolk, as it is pasteurized. This study was conducted to determine ram sperm cryosurvival was affected by the type of egg yolk used (powdered egg yolk or fresh egg yolk) and by yolk concentration (10, 15 or 20%) in the diluent. Microbiological analyses were also performed to quantify the microbiological contamination in the diluents containing the two types of egg yolk. Sperm cryosurvival was determined by motility and morphology analyses after thawing. Motility parameters were assessed using a computer-assisted sperm analysis (CASA) system, and the percentage of sperm with a normal apical ridge was evaluated using a differential interference contrast microscope. No significant differences were observed between diluents in the percentage of sperm with normal apical ridge. However, higher percentages of total motile cells were observed for samples containing powdered egg yolk (69%) compared to samples containing fresh egg yolk (60%). However, sperm in diluents containing fresh egg yolk, exhibited higher values for average-path velocity, straight-line velocity and beat cross frequency and lower values for amplitude of lateral head displacement (p <0.05), compared to cells in diluents containing powdered egg yolk. Microbiological contamination was similar (<200 CFU/ml) in both diluents, and no bacterial growth was observed in either, when antibiotics were added. Therefore, powdered egg yolk can be effective used in diluents for the freezing of ram semen. However, the in vivo fertility of sperm frozen in diluents containing powdered egg yolk should be tested, as some motility parameters were different for sperm treated with powdered egg yolk compared to fresh egg yolk.  相似文献   
4.
Agave tequilana is the raw material for the production of the alcoholic beverage tequila. A bacterial disease has affected the A. tequilana crop in recent years. Previous reports based on colony and cell morphology, Gram stain and potato rot indicated that Erwinia sp. is the main pathogen. We isolated a several bacterial isolates capable of producing soft-rot symptoms in greenhouse pathogenicity assays. An extensive characterisation involving pathogenicity tests, fatty acid profile, metabolic and physiological properties, ribosomal DNA sequence and intergenic transcribed spacer amplification (ITS-PCR) and restriction banding pattern (ITS-RFLP) was made of each isolate. Three different species: Erwinia cacticida, Pantoea agglomerans and Pseudomonas sp. were identified. Fatty acid and metabolic profiles gave low similarity values of identification but 16S rDNA sequence, ITS-PCR and ITS-RFLP confirmed the identification of E. cacticida. In the phylogenetic tree, E. cacticida from blue agave was grouped neither with E. cacticida type strains nor with Erwinia carotovora. This is the first report that associates E. cacticida with A. tequilana soft-rot symptoms.  相似文献   
5.
This study describes the macroscopic and microscopic lesions in farmed rainbow trout (Oncorhynchus mykiss) naturally infected with genetically identified Aeromonas salmonicida, A. hydrophila, and A. veronii species. The genus Aeromonas includes bacteria that naturally inhabit both waterways and organisms. At least 27 Aeromonas species have been identified to date, some of which can cause significant economic losses in aquaculture. As up to 68.8% of Aeromonas isolates may be misidentified in routine biochemical and phenotypic tests, however, reported cases of Aeromonas infection in fish may be wrongly identified. Our findings confirmed that the 3 Aeromonas species studied are associated with septicemia and dermal lesions in rainbow trout.  相似文献   
6.
7.
8.
Xanthomonas campestris pv. campestris (Xcc) is the causal agent of black rot in Brassicaceae. It is widespread in Italy and severe outbreaks occur under conditions that favour disease development. In this study a multilocus sequence typing approach (MLST) based on the partial sequence of seven loci was applied to a selection of strains representative of the main areas of cultivation and hosts. The aim was to investigate whether the long tradition of brassica crops in Italy has influenced the evolution of different Xcc populations. All loci were polymorphic; 14 allelic profiles were identified of which 13 were unique to Italian strains. Based on the seven loci, the most common genotype within the Italian Xcc strains (AP1) was also the most representative genotype found in worldwide Xcc strains. This genotype was included in a new clonal complex in addition to three other clonal complexes already identified in Xcc populations. The phylogenetic reconstruction using a concatenated dataset of four conserved protein-coding genes, dnaK, fuyA, gyrB and rpoD, showed that the Italian strains belonged to two genetic groups. Physiological races were also investigated for the first time in Italy. The race structure of Xcc was determined by inoculating eight differential Brassica lines belonging to five species and showed that, in Italy, race 4 is the most widespread, followed by races 1 and 6. No correlation was found between allelic profiles, host of isolation, geographical origin and races, although a prevalent race was identified within the same clonal complex.  相似文献   
9.
Two parallel experiments were conducted to evaluate the effect of partial substitution of fish meal by two different animal protein sources, blood meal (B) and haemoglobin meal (H) at 0, 50 and 100 g kg−1 of level inclusion in diets for gilthead sea bream, considering a long feeding period for juveniles (Trial 1) and a short feeding period (Trial 2) for on-growing fish. In Trial 1, 33 g juveniles were fed for 242 days and the fish fed with 5% and 10% of haemoglobin dietary inclusion obtained less growth, although feed efficiency, protein efficiency ratio and muscle composition were similar in all diets. In Trial 2, 179 g initial weight fish were fed for 164 days and growth of fish fed H10 showed the lowest growth, although nutrient efficiency and muscle composition were not affected significantly. The results of these experiments demonstrated that blood meal can substitute fish meal (up to 10%) with no effect on performance, but may lead to sensory differences compared with fish fed diet 0, while the inclusion of 5% blood meal had no effect on growth or sensory characteristics. Fish fed 10% haemoglobin inclusion had the poorest growth values.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号