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   208篇
  免费   9篇
林业   10篇
农学   4篇
基础科学   1篇
  68篇
综合类   16篇
农作物   10篇
水产渔业   6篇
畜牧兽医   88篇
园艺   2篇
植物保护   12篇
  2023年   1篇
  2022年   1篇
  2021年   7篇
  2020年   3篇
  2019年   5篇
  2018年   6篇
  2017年   10篇
  2016年   6篇
  2015年   5篇
  2014年   7篇
  2013年   13篇
  2012年   12篇
  2011年   20篇
  2010年   11篇
  2009年   7篇
  2008年   20篇
  2007年   20篇
  2006年   19篇
  2005年   9篇
  2004年   5篇
  2003年   11篇
  2002年   4篇
  2001年   1篇
  2000年   2篇
  1998年   4篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1989年   1篇
  1980年   1篇
排序方式: 共有217条查询结果,搜索用时 15 毫秒
31.
32.
In order to evaluate the seroconversion of horses to Babesia caballi and B. canis in Hungary, blood samples were collected from 371 animals on 23 different locations of the country. The presence of antibodies to B. caballi was screened with a competitive ELISA. All 29 positive samples came from one region (the Hortobágy). The prevalence of infection did not show correlation with sexes, and reached 100% in the age group of 2-5 years. Babesia canis-specific antibodies were demonstrated by IFAT in 6.74% of animals kept in 7 regions. The titres were low or medium level (1:40 to 1:160), indicating that the horses had previously been exposed to this piroplasm, but their infection must have been limited. The highest seropositivity rate was observed in the age group of 3-4 years, and males (stallions and geldings) were significantly more frequently infected than females. However, neither B. caballi nor B. canis could be identified in the peripheral blood samples of infected horses by PCR. Since most of the B. caballi-positive horses remained negative in the B. canis IFAT, whereas seroconversion solely to B. canis was detected in several regions of the country, serological cross-reaction between the two species can be discounted. This is the first serological evidence of horses being naturally infected with B. canis, supporting the view that piroplasms are less host specific than previously thought.  相似文献   
33.
Infectious pancreatic necrosis (IPN) is an important restraint to production of salmonids in aquaculture globally. In order to implement efficacious mitigation strategies for control of this disease, it is important to understand infection routes under current production systems. IPN virus has been shown to be transmitted vertically in Rainbow trout, from broodstock to fingerlings in hatcheries, and there is circumstantial evidence suggesting that vertical transmission can also occur in Atlantic salmon, in addition to horizontal transmission between grow‐out fish in farms. In this study, we show that the smolt carries infection with IPN from hatchery to the marine farm. We do this by comparing sequences from fish groups taken both in hatcheries and on corresponding marine grow‐out farms. We use statistical analysis to prove that sequences obtained from the same fish group in both hatchery and marine farm are more similar than sequences obtained from random fish groups on hatcheries and marine farms.  相似文献   
34.
Polybrominated diphenyl ethers are lipophilic persistent organic pollutants (POPs), which accumulate in the environment, leading to human exposure. The compounds exert a negative impact on human health. Strategies to prevent or diminish their accumulation in humans are required. We investigated in rats whether the disposal rate of 14C-labeled tetrabromodiphenyl ether (BDE-47) could be enhanced by increasing fecal fat excretion through dietary treatment with nonabsorbable fat (sucrose polyester, SPE). As compared to control rats, SPE treatment increased fecal excretion rates of fat (+188%, p < 0.05) and 14C-BDE-47 (+291%, p < 0.05). On the basis of biliary secretion and fecal excretion rates of 14C-BDE-47, SPE effectively inhibited the enterohepatic circulation of 14C-BDE-47. In conclusion, dietary supplementation of nonabsorbable fat can enhance excretion of hydrophobic POPs by interruption of their enterohepatic circulation. Our data indicate that this strategy could decrease concentrations of hydrophobic POPs in the human body and thereby their impact on human health.  相似文献   
35.
An inoculation method for Exobasidium splendidum and Exobasidium vaccinii was developed on the dwarf shrub Vaccinium vitis-idaea. Using inoculated ramets, we investigated whether there are differences between V. vitis-idaea populations in the susceptibility to Exobasidium infections and whether the defence reaction of V. vitis-idaea is visible at a molecular level. Sixteen V. vitis-idaea clones from four populations were propagated in tissue cultures and the ramets were inoculated with E. splendidum or E. vaccinii fungi. The expression of three flavonoid biosynthetic genes (chalcone synthase, dihydroflavonol 4-reductase and anthocyanidin synthase) and the accumulation of flavonoids and hydroxycinnamic acids were determined in response to E. splendidum infection. A pathogenesis-related (PR 4) gene was isolated and its expression was studied in host ramet leaves. To our knowledge, this was the first successful artificial infection reported with E. splendidum. Disease frequencies of the inoculated ramets were between 32% and 47% for E. splendidum and 33% for E. vaccinii, but below 10% in uninoculated control ramets. There were no differences in disease frequencies between V. vitis-idaea populations. Both symptomatic leaves and healthy leaves of diseased ramets showed activation of flavonoid biosynthesis at the gene level, whereas expression of PR 4 was observed only in symptomatic leaves. The increase of flavonoid biosynthesis in healthy leaves of diseased ramets may represent a general response to stress or a role in defence against the pathogen E. splendidium. Ability of V. vitis-idaea to defend chemically against Exobasidium fungi and the heterogeneity of genotypes, age, size, and growth rates in host plant populations might be reasons for the low infection incidence of Exobasidia in nature.  相似文献   
36.
Host immune responses conducted against antigens of Eimeria bovis are key factors for the development of protective immunity against this protozoan disease. In this study we investigated the expression of E. bovis-derived antigens on the host cell surface membrane during E. bovis first merogony in vitro. Host cells carrying E. bovis-meront I stages expressed E. bovis host cell surface antigens (EbHCSAg) on their surface membrane which were recognised by hyperimmune sera of calves and by sera from rats immunized with E. bovis merozoites I, when tested by indirect immune fluorescent antibody test (IIFAT), laser scanning confocal microscopy (LSCM) and immune electron microscopy. Expression of EbHCSAg on permissive host cells was earliest detected 7 days p. i., thus coinciding with the onset of the parasite replication. Membrane-associated EbHCSAg were removed from infected host cells by proteinase K, partially by Triton X-100, Triton X-114 and Triton X-405, but not by 1 M NaCl, CHAPS or phospholipase C treatment. Antibodies, affinity-purified on paraformaldehyde/glutardialdehyde (PAGA)-fixed E. bovis meront I-infected bovine host cells bound to the surface meront I-carrying cells and to merozoites I (IIFAT, LSCM) but, in contrast to untreated sera, not to sporozoites. When tested on methanol-fixed merozoites I and sporozoites by IIFAT, affinity-purified antibodies bound to structures in the apical complex area of merozoites I, but not to sporozoites, whilst untreated sera caused diffuse labelling of internal structures of both parasite stages. Immune electron microscopy demonstrated binding of affinity-purified antibodies to micronemes and dense granules of merozoites I. Although the function of EbHCSAg is still unknown, results of this study might suggest an involvement in the development of protective immunity against E. bovis infections.  相似文献   
37.
ABSTRACT: Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides, is an important livestock disease in Africa. The current control measures rely on a vaccine with limited efficacy and occasional severe side effects. Knowledge of the protective arms of immunity involved in this disease will be beneficial for the development of an improved vaccine. In previous studies on cattle infected with M. mycoides subsp. mycoides, a correlation was detected between the levels of mycoplasma-specific IFN-γ-secreting CD4+ T lymphocytes and reduced clinical signs. However, no cause and effect has been established, and the role of such cells and of protective responses acquired during a primary infection is not known.We investigated the role of CD4+ T lymphocytes in CBPP by comparing disease patterns and post mortem findings between CD4+ T cell depleted and non-depleted cattle. The depletion was carried out using several injections of BoCD4 specific murine monoclonal antibody on day 6 after experimental endotracheal infection with the strain Afadé. All cattle were monitored clinically daily and sacrificed 28-30 days post-infection. Statistically significant but small differences were observed in the mortality rate between the depleted and non-depleted animals. However, no differences in clinical parameters (fever, signs of respiratory distress) and pathological lesions were observed, despite elimination of CD4+ T cells for more than a week. The slightly higher mortality in the depleted group suggests a minor role of CD4+ T cells in control of CBPP.  相似文献   
38.
In this study 595 lactating cows originating from 31 carinthian farms were investigated in accordance of liver fluke infection using individual and tank milk as well as individual blood and faecal samples. Two commercial ELISAs were used to test the milk and blood serum, and the results were compared with coproscopy and a commercial copro-antigen ELISA. Receiver operating characteristics (ROC) and two-graph operating characteristics (TG ROC) of tank milk results were conducted based on the individual milk to determine the minimum reliable in-herd antibody prevalence for the predominant condition in the investigation area. In 17.8% of the examined individuals located in 64.5% of the farms eggs were detected by coproscopy. The copro-antigen ELISA delivered 13.4% positive individuals from 54.8% of the farms. The milk ELISAs showed 42.7% (Euroclone) and 44.2% (Pourquier) positive cows on 90.3% of the farms. The blood samples were positive in 43% (Euroclone) and 45.2% (Pourquier) of the individuals from 90.3% to 96.8% of the herds, respectively. Based on the milk and the blood an average in-herd prevalence of 30-45% can be assumed. The serum and milk samples delivered correlating results with kappa values between 0.94 and 0.97, whereas the coproscopy and copro-antigen ELISA did not correlate well with the ELISA results. The two different ELISA tests highly correlated on individual and on herd level. Both showed a reliable minimum in-herd prevalence of ~20%, meaning that one fifth of the individuals in a herd have to be positive to obtain a positive bulk tank milk result. In the investigated area a higher in-herd prevalence is expected, therefore the tank milk is useful as a monitoring tool and can be used as a basis for intervention strategies.  相似文献   
39.
Biochar amendments to soils have been suggested as a strategy to sequester carbon and therefore mitigate global climate change. The enrichment of soils with charred materials also increases their fertility. This fertilising effect of biochar may be caused by various mechanisms; an acceleration of nutrient cycling has been suggested as one such mechanism. The rate-limiting step in nutrient cycling is thought to be the extracellular enzymatic attack on biological macromolecules. In this study, therefore, the effects of chestnut wood char (specific surface area 2.0 m2 g−1) and of activated carbon (specific surface area approximately 900 m2 g−1) on an extracellular enzymatic reaction involved in the degradation of cellulose (i.e., hydrolysis of cellobiose by β-glucosidase from Aspergillus niger) were investigated. Cellobiose was not adsorbed by chestnut wood char, whereas activated carbon absorbed more than 97% of it. Both charred materials adsorbed more than 99% of β-glucosidase. For chestnut wood char, adsorption of the enzyme caused a decrease of approximately 30% in the reaction rate, whereas for activated carbon, the nearly complete absorption of both substrate and enzyme entirely inhibited the reaction. These results show that β-glucosidase from A. niger retains most of its activity when adsorbed to chestnut wood char and that the reaction it catalyses in nature is only slightly affected by this charred material. On the other hand, a material characterised by a high specific surface area and high porosity, such as activated carbon, can make even a highly soluble substrate unavailable for soil enzymes and therefore completely inhibit the reaction. Thus, charred materials may affect nutrient cycling mainly by regulating the availability of substrates: the degradation of highly soluble substrates may be accelerated by materials with low specific surface area, which maintain an active and protected enzyme pool, whereas materials with high specific surface and high porosity may slow down the degradation by making substrates unavailable.  相似文献   
40.
Soil, olive leaves, and fruits, were sampled from an olive grove 200 ha, irrigated with treated municipal wastewater (TMWW), located at Al-Tafilah wastewater processing plant (WWPP), Jordan. Similar samples were also taken from plants not irrigated with TMWW (Control). The heavy metal and essential nutrients were determined in all samples, and the data were statistically processed. The following were found: Much smaller quantities of heavy metals than essential elements were accumulated in the leaves and fruits, the accumulation being independent of the TMWW heavy metal concentration, suggesting a selective uptake of the metals by the olive plants. Also the elemental interactions, which occurred in the olive fruits, contributed mainly essential nutrients and secondarily heavy metals. The trend of heavy metal transfer from soil to olive fruits, and leaves, was almost the same, showing a consistency of transfer.  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