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   303篇
  免费   9篇
林业   25篇
农学   7篇
基础科学   1篇
  68篇
综合类   4篇
农作物   23篇
水产渔业   24篇
畜牧兽医   142篇
园艺   4篇
植物保护   14篇
  2023年   5篇
  2022年   5篇
  2021年   18篇
  2020年   16篇
  2019年   13篇
  2018年   13篇
  2017年   10篇
  2016年   7篇
  2015年   8篇
  2014年   17篇
  2013年   14篇
  2012年   31篇
  2011年   32篇
  2010年   11篇
  2009年   17篇
  2008年   23篇
  2007年   11篇
  2006年   13篇
  2005年   17篇
  2004年   12篇
  2003年   9篇
  2002年   7篇
  2001年   1篇
  1996年   1篇
  1994年   1篇
排序方式: 共有312条查询结果,搜索用时 31 毫秒
231.
A dog was examined with a history of weight loss and lameness of the left hind limb. A painful response to examination of the left hip joint, and lymphadenopathy were noted. Amastigote forms of Leishmania sp. were observed by cytology in samples from the popliteus lymph node, and anti-Leishmania sp. antibodies at a titer of 1:640 were detected in serum by indirect immunofluorescence. Radiological changes included osteolysis and a periosteal proliferative reaction in the left femoral greater trochanter. These changes were histologically characterized as an osteolytic granulomatous osteomyelitis associated with amastigotes within macrophages. Non-decalcified fragments of the periosteum were processed for immunohistochemistry, observed with prominent immunolabelling of amastigotes of Leishmania sp. within macrophages. The diagnosis was further confirmed by positive PCR for Leishmania sp., belonging to the Leishmania donovani complex.  相似文献   
232.
The aim of this work was to characterize the distribution of myofibers in the gluteus medius muscle of inactive horses of the Brasileiro de Hipismo (BH) breed at different ages by means of histochemical analyses, according to sex and depth of the biopsy. A total of 78 inactive horses (9 castrated males, 35 stallions, and 34 females) of the BH breed, aged 1 to 4 years, were used. A percutaneous muscle biopsy was obtained with a 6.0-mm Bergström-type needle, which allowed the removal of muscle fragments at depths of 20 and 60 mm. Myofiber types were determined based on myofibrillar adenosine triphosphatase (mATPase) and nicotinamide dinucleotide tetrazolium reductase (NADH-TR) techniques. Morphometry of the fibers was determined based on cross-sectional area (CSA), mean frequency (F), and relative cross-sectional area (RCSA). The current study demonstrated that BH horses 3 and 4 years of age show a greater percentage of, and area occupied by, type IIA fibers and lower percentage of type IIX fibers in the gluteus medius muscle compared with horses 1 and 2 years of age. No difference was found between sexes in the frequency of and area occupied by the different fiber types at any of the depths and ages studied. In this study, females showed a greater CSA for all fibers in comparison with males, at 1 year of age. The results of the current study indicate that the gluteus medius muscle of inactive BH horses shows modifications in its structural and biochemical composition during the growth of the animals, leading to a better oxidative capacity.  相似文献   
233.
The objective of this study was to determine the prevalence of gastrointestinal nematode (GIN) infection in goat flocks on semi-arid rangelands of northeastern Mexico (25° N, 350–400 mm annual precipitation). The study included 668 pluriparous goats from 18 herds in five municipalities of Coahuila and Nuevo Leon, Mexico. Five genetic groups were considered (predominance of Boer, Nubian, Alpine, Saanen, and Toggenburg). Fecal samples were taken from the rectum of each animal to determine the number of eggs per gram (EPG) of GIN. The prevalence of flocks with GIN infections was 88.9%. Similar results were observed for the number of goats infected in the flocks. The Alpine breed presented the highest prevalence and highest EPG loads of GIN, whereas Boer and Nubian were the genetic groups with the lowest (P?<?0.05) EPG. There was a negative effect of GIN infection on the live weight of goats (P?<?0.05). The GIN genera found were Trichostrongylus spp. and Haemonchus spp. It was concluded that in the goat flocks of the semi-arid zones of Mexico was found a high prevalence of infections with gastrointestinal nematodes. The municipality and the breed of the animals were factors that showed influence on this prevalence and the level of infection of the goats.  相似文献   
234.
In a poplar clonal plantation with different species and hybrids, established at 13,333 cuttings ha?1, biomass production was assessed at the end of the first rotation (3 years) and the potential of the different clones for sugar production was evaluated. The highest biomass production was observed for clones ‘AF2’ and ‘Viriato’ (46.5 and 42 t dm ha?1, respectively). After a mild acid pretreatment and an enzymatic saccharification, the highest sugar digestibility was found for ‘Viriato’ and ‘Unal’. A clear relation between sugar digestibility and xylan removal during pretreatment was observed, while no relation with lignin content was found. Taking into account the results, the highest production of sugars per hectare was estimated for the poplar clone ‘Viriato’, being 18–48% higher than that achieved with the other clones. Therefore, this clone is a promising candidate to be used as feedstock for sugar production in a forest biorefinery.  相似文献   
235.
Cocoa is a rich source of flavanols and procyanidin oligomers with antioxidative properties, providing protection against oxidation and nitration. The present study investigated the potential protective effect of a polyphenolic extract from cocoa on cell viability and antioxidant defenses of cultured human HepG2 cells submitted to oxidative stress induced by tert-butylhydroperoxide (t-BOOH). Pretreatment of cells with 0.05-50 microg/mL of cocoa polyphenolic extract (CPE) for 2 or 20 h completely prevented cell damage and enhanced activity of antioxidant enzymes induced by a treatment with t-BOOH. Moreover, lower levels of GSH caused by t-BOOH in HepG2 cells were partly recovered by a pretreatment with CPE. Increased reactive oxygen species (ROS) induced by t-BOOH was dose-dependently prevented when cells were pretreated for 2 or 20 h with CPE. These results show that treatment of HepG2 in culture with CPE (within the physiological range of concentrations) confers a significant protection against oxidation to the cells.  相似文献   
236.
BackgroundSuid gammaherpesvirus 3, 4, and 5 (porcine lymphotropic herpesvirus – PLHV-1, -2, and -3) are viruses that infect domestic and feral pigs.ObjectivesThis study examined the presence of PLHV DNA in biological samples from free-living wild boars circulating in a Brazilian geographical region with a high density of commercial domestic pigs.MethodsLung samples of 50 free-living wild boars were collected by exotic wildlife controller agents between 2017 and 2019 in the state of Paraná, southern Brazil. Lung and spleen fragments were obtained from six fetuses collected by hysterectomy post mortem from a pregnant sow. A polymerase chain reaction (PCR) assay using consensus primers (pan-herpesviruses) was performed to detect PLHV DNA. The samples showing positive results for PLHV DNA were submitted to single-round PCR assays with the specific primers for identifying PLHV-1 (213-S/215-As), PLHV-2 (208-S/212-As), and PLHV-3 (886s/886As). The specificity of the species-specific PCR products was assessed by nucleotide sequencing of the amplicons.ResultsForty-eight (96%) of the 50 lung samples analyzed were positive for PLHV by PCR using pan-herpesvirus primers. In 33 (68.75%) of the positive samples, at least two PLHV species were identified simultaneously. The DNA of PLHV-1, -2, and -3 was found in free-living wild boars of all ages, but not in the fetuses, even though they were from a sow that tested positive for all three viruses.ConclusionThese viruses are endemic to the population of feral pigs in the Brazilian region evaluated, as well as in domesticated pigs.  相似文献   
237.
Synovial fluid (SF) is capable of reflecting infectious, immunological, or inflammatory joint conditions in horses by altering its composition and appearance. Although plasma and SF compositions are quantitatively different, this latter compartment reflects changes in plasma macromolecules. Therefore, changes in serum immunoglobulin protein concentrations tend also to alter intracapsular levels. Therefore, it is necessary to know the physiological concentrations of proteins present in SF. The aim of this study was to determine the levels of total protein, albumin, transferrin, haptoglobin, α1-acid glycoprotein, ceruloplasmin, and immunoglobulins A and G in SF of six healthy horses. The synovial proteinogram was obtained by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The SF proteins reached a maximum of 25% of serum concentrations, varying inversely with molecular weight of the protein, except for the ceruloplasmin.  相似文献   
238.
Background: Interest in the use of natural feed additives as an alternative to antimicrobials in the poultry industry has increased in recent years because of the risk of bacterial resistance. One of the most studied groups are polyphenolic compounds, given their advantages over other types of additives and their easy potentiation of effects when complexes are formed with metal ions. Therefore, the objective of the present study was to evaluate the impact of dietary supplementation of copper acetate(CA), curcumin(CR), and their combination(CA-CR)against Salmonella Typhimurium colonization, intestinal permeability, and cecal microbiota composition in broiler chickens through a laboratory Salmonella infection model. S. Typhimurium recovery was determined on day 10 post-challenge by isolating Salmonella in homogenates of the right cecal tonsil(12 chickens per group) on Xylose Lysine Tergitol-4(XLT-4) with novobiocin and nalidixic acid. Intestinal integrity was indirectly determined by the fluorometric measurement of fluorescein isothiocyanate dextran(FITC-d) in serum samples from blood obtained on d 10 post-S. Typhimurium challenge. Finally, microbiota analysis was performed using the content of the left caecal tonsil of 5 chickens per group by sequencing V4 region of 16 S rRNA gene.Results: The results showed that in two independent studies, all experimental treatments were able to significantly reduce the S. Typhimurium colonization in cecal tonsils(CT, P 0.0001) compared to the positive control(PC)group. However, only CA-CR was the most effective treatment in reducing S. Typhimurium counts in both independent studies. Furthermore, the serum fluorescein isothiocyanate dextran(FITC-d) concentration in chickens treated with CR was significantly lower when compared to PC(P = 0.0084), which is related to a decrease in intestinal permeability and therefore intestinal integrity. The effect of dietary treatments in reducing Salmonella was further supported by the analysis of 16 S rRNA gene sequences using Linear discriminant analysis effect size(LEfSe)since Salmonella was significantly enriched in PC group(LDA score 2.0 and P 0.05) compared to other groups. In addition, Coprobacillus, Eubacterium, and Clostridium were significantly higher in the PC group compared to other treatment groups. On the contrary, Fecalibacterium and Enterococcus in CR, unknown genus of Erysipelotrichaceae at CA-CR, and unknown genus of Lachnospiraceae at CA were significantly more abundant respectively.Conclusions: CR treatment was the most effective treatment to reduce S. Typhimurium intestinal colonization and maintain better intestinal homeostasis which might be achieved through modulation of cecal microbiota.  相似文献   
239.
  • ? Genetic variation in freezing resistance was evaluated among and within six populations of Spanish wild chestnut (Castanea sativa Miller). The extent to which frost susceptibility was related to phenology and the relationship between population differentiation and climatic conditions was studied.
  • ? Twigs were collected in March and November from saplings (5-year-old trees) of 41 open-pollinated families from the six populations in a provenance-progeny test, and were subjected to artificial freezing. Damage to each twig was assessed as visible browning of bud and of stem tissues.
  • ? Population differences as regards frost damage traits were highly significant (p < 0.01) in both spring and autumn. Family differences within populations were low, often non-significant, and in all cases smaller than differences among populations. Population means were closely correlated with the parental drought and frost conditions. Populations originating from dry areas or from regions where frost seldom occurs were the least resistant.
  • ? Drought is suggested to be the one of the most important selective agents that shapes population differentiation in Spanish wild chestnut, while frost may be more important in northern Spain. Phenological differences are not always good predictors of the degree of frost damage. Thus, freezing tests should be used to detect frost susceptibility in chestnuts.
  •   相似文献   
    240.
    The experiment was conducted with the aim of determining the attractability and palatability of liquid protein hydrolysates for Nile tilapia. Five experimental diets were formulated containing 5% inclusion of fishmeal (FPE; positive control), 5% inclusion of liquid protein hydrolysate of porcine mucosa (PHM), 5% inclusion of liquid protein hydrolysate of poultry (PHF), 5% inclusion of liquid fish oil (OPE) and a diet without fishmeal (negative control). Five juveniles (2.51 ± 0.13 g) were distributed in 10 L tanks, and the animals were fed five times a day, with a previous draw being made of the offered diets. The same amount of pellets was offered and the following feeding behaviours were evaluated with the aid of three‐minute footages per feeding: time to capture first pellet, number of rejections, number of approaches without capturing the pellet and number of consumed pellets. None of the observed parameters displayed significant differences (p > .05), and all diets presented negative palatability indexes in comparison to FPE. The SPE diet provided a attractability and palatability index of 6.17%, while OPE index was 2.87%, PHM 2.82% and PHF 2.74%. Both PHF and PHM reduced the final consumption of pellets in comparison to FPE in approximately 28% and 20%, respectively, although it did not present significant values.  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