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   281篇
  免费   21篇
林业   20篇
农学   9篇
基础科学   5篇
  57篇
综合类   25篇
农作物   20篇
水产渔业   22篇
畜牧兽医   117篇
园艺   6篇
植物保护   21篇
  2024年   1篇
  2023年   1篇
  2022年   14篇
  2021年   12篇
  2020年   13篇
  2019年   15篇
  2018年   12篇
  2017年   10篇
  2016年   14篇
  2015年   9篇
  2014年   22篇
  2013年   14篇
  2012年   28篇
  2011年   26篇
  2010年   16篇
  2009年   14篇
  2008年   12篇
  2007年   12篇
  2006年   10篇
  2005年   13篇
  2004年   6篇
  2003年   3篇
  2002年   8篇
  2001年   1篇
  2000年   4篇
  1998年   1篇
  1997年   2篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1989年   1篇
  1986年   1篇
  1984年   1篇
  1977年   2篇
排序方式: 共有302条查询结果,搜索用时 15 毫秒
221.
A 4-bp deletion in the ATP-binding cassette subfamily B member 1 (ABCB1) gene, also referred to as the multidrug resistance gene (MDR1), produces stop codons that cause premature termination of P-glycoprotein 1 (P-gp) synthesis. Dogs with the homozygous mutation do not express functional P-gp, which increases their sensitivity markedly to many common veterinary drugs. We detected the nt230 (del4) ABCB1 mutation in Border Collie dogs in western Mexico with a simple and affordable primer-introduced restriction analysis PCR (PIRA-PCR). PIRA-PCR clearly identified all genotypes in our sample of 104 dogs. Genotype frequencies were 0.952 (wild/wild), 0.029 (wild/mut) and 0.019 (mut/mut). Allele frequencies were 0.033 (mutant alleles) and 0.966 (wild-type alleles). In this small subset of the Mexican dog population, we found a higher prevalence of the nt230 (del4) MDR1/ABCB1 gene mutation than reported in other countries.  相似文献   
222.
223.
A study was conducted on 124 farms in Sweden and Norway where fungal (all farms) and mycotoxin (100 of the 124 farms) presence was examined in wrapped forage bales. Samples were also analysed for chemical composition, and data on the bale production and storage system on each farm were collected. Fungi, analysed by three common sampling methods, were found in bales from 89% of the visited farms (110 farms). The most frequently isolated fungal species from the bale surface was Penicillium roqueforti. Mycotoxins were present in 39% of the 100 samples analysed. The most common mycotoxins present were enniatin B (14 farms) followed by deoxynivalenol (12 farms). The risk of finding fungi in baled forage samples was higher with odds ratio (OR) of 5.1 when less than eight layers of stretch film were applied, low seal integrity of wrapping (OR 172 at <10 s of seal integrity), higher dry‐matter content (OR 1.17–1.56 per % unit DM) and higher concentrations of acetic acid (OR 47.5 per g DM) and ethanol (OR 3.4 per g DM). Mycotoxin presence was not found to be correlated with any of the chemical characteristics of the baled forage, or with any forage production and management factors. A positive correlation was present between total fungal counts and general mycotoxin presence, but not between specific mycotoxins and the toxin‐producing fungal species.  相似文献   
224.
Introduction of non-native species, such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), can be a means of mitigating the effects of climate change by meeting the growing demand for biomass and high quality wood. The aim of this study was to investigate early growth, survival and damage from late-spring frost and winter desiccation. A provenance trial with four coastal and three interior provenances of Douglas-fir originating from British Columbia, Canada, was established in Southwest Sweden (56°43′N, 13°08′E). Seedling height, length of the leading shoot, and occurrence of frost damage, were measured after one, three, and six growing seasons. Timing of bud break in spring was also observed. The interior Douglas-fir were more frequently damaged by late-spring frost compared to the coastal Douglas-fir. The interior Douglas-fir still had a higher survival after six growing seasons compared to the coastal variety. All provenances were damaged by winter desiccation, but the provenances originating from the coastal area were more severely damaged. Choice of variety may reduce the risk for either late-spring frost or winter desiccation.  相似文献   
225.
Cytoplasmic genic male sterility system based hybrids were synthesized by line × tester design and evaluated with check GTH 1 in RBD at Sardarkrushinagar, Jagudan and Khedbrahma during kharif 2007. Analysis of variance in individual and across environments revealed significant differences among genotypes and existence of overall heterosis for seed yield per plant and other thirteen traits. The top ranking on the basis of standard heterosis were CMSGT087A × GTR0525 (116.40 %) followed by CMSGT087A × AGTR0534 (108.93 %), CMSGT0307A × AGTR0538 (99.21 %) and CMSGT 0301A × AGTR 0534 (95.51 %) for seed yield per plant and for one or two of its contributing traits. Combining ability analysis revealed presence of both additive and non-additive gene effects. The specific combining ability variance was found more compaired to general combining ability variance for all the characters under studied. This favored a hybrid breeding programme. In stability analysis, linear portion was considerably high for all the traits except for days to flower and pod length. The best stable hybrids for seed yield per plant over environments were CMSGT 308A × AGTR 0534, CMSGT 307A × AGTR 0543, CMSGT 0308A × AGTR 0536 and CMSGT 0311A × GTR 0525 and also recorded stability in any one or more of its contributing traits viz. pods per plant, branches per plant, seed per pod, pod length and test weight. Top ranking hybrids had high mean performance, high heterosis and desirable sca effects and stability for seed yield per plant. Therefore, these hybrids could be valuable for commercial exploitation.  相似文献   
226.
The Nile tilapia is among the most cultivated tropical fish in the world, yet little is known about the variations in reproductive characteristics among different strains. There is an interest in evaluating the reproductive performance of females of three tilapia strains. All strains were represented in equal proportion (n = 225), being named as Supreme (SUP), Premium Aquabel (PA), and Chitralada (CHI). These fish were cultivated for 7 weeks in the Aquabel Pisciculture Station (Brazil), from January to March 2011. The PA was the largest strain, with the highest values in all the morphometric parameters we analyzed (weight, total length, standard length and body depth). Among the evaluated reproductive parameters, the PA strain differed significantly from the other two in number and weight of eggs/female, volume of eggs/spawn and number of eggs/kg of fish. The percentage of non-spawning females in the SUP and CHI strains differed significantly from one another, while results for PA showed intermediate values and no significance compared to the other strains (P > 0.05). Among the reproductive parameters analyzed, the percentage of spawned females/week, more than one spawns during 7 weeks, and hatching rate showed no significant differences between strains (P > 0.05). There was a significant correlation (r = 0.69) between water temperature and percentage of spawned females/week. When evaluating the interval between two consecutive spawns, we observed that periods of 21 days were the most frequent in all strains. In conclusion, the strain that showed the best results in all morphometric and in most reproductive parameters we evaluated was the PA.  相似文献   
227.
228.
This study investigated the effects of natural and artificial diets on growth performance and shell pigmentation of cultured abalone. A 7‐month feeding trial was conducted on 12 000 Pacific abalones (Haliotis discus hannai) with four diets including two extruder‐processed test diets (with & without addition of oleopaprika carotenoids), Pacific dulse (Palmaria mollis) and a combination of Pacific dulse and a test diet. The results showed that the two test diets resulted in higher survival of abalone, but with a lower growth rates when compared with Pacific dulse alone (P < 0.05). The combination diet achieved the highest survival and growth rates. The Pacific dulse resulted in abalone with dark‐brown shells, which are preferred by Asian markets. The test diets led to 52% and 55% of the animals with pink coloured shells and the supplementation of oleopaprika did not affect shell pigmentation. The aqueous acidic extracts from both dark‐brown and pink shells showed blue colour; HPLC‐MS chromatography revealed that the pigments in the extracts were consistent with a biliverdin and a cysteine‐biliverdin. These results are valuable for the development of abalone feed and the control of abalone shell colouration.  相似文献   
229.
The objective of this study was to determine if device that simulate methane capture equipment (DSMC) located in the frontal part of the head of dairy cows affect animal welfare using productive, behavioral, biochemical and physiological indicators. Twenty Holstein dairy cows were assigned to one of the two following treatments: cows with DSMC (CDSMC, n=10) and cows without methane capture devices (CC, n=10). Treatment did not affect neither milk production nor biochemical blood. The group CDSMC tended to ruminate less (P=0.06) and tended to eat more (P=0.08) frequently than the group CC. In conclusion, considering the data set, the welfare of the cows was not significantly affected by the use of DSMC located in their heads.  相似文献   
230.
We describe the genome sequence of the protist Trichomonas vaginalis, a sexually transmitted human pathogen. Repeats and transposable elements comprise about two-thirds of the approximately 160-megabase genome, reflecting a recent massive expansion of genetic material. This expansion, in conjunction with the shaping of metabolic pathways that likely transpired through lateral gene transfer from bacteria, and amplification of specific gene families implicated in pathogenesis and phagocytosis of host proteins may exemplify adaptations of the parasite during its transition to a urogenital environment. The genome sequence predicts previously unknown functions for the hydrogenosome, which support a common evolutionary origin of this unusual organelle with mitochondria.  相似文献   
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