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31.
Bielaszewska M Zhang W Mellmann A Karch H 《Berliner und Münchener tier?rztliche Wochenschrift》2007,120(7-8):279-287
Enterohaemorrhagic Escherichia coli (EHEC) O26:H11 have emerged as the most important non-O157:H7 EHEC, with respect to their ability to cause diarrhoea and the haemolytic uraemic syndrome (HUS). HUS is a leading cause of acute renal failure in children, and is mainly caused by EHEC expressing Shiga toxins (Stx) 1 and/or 2. Since 1996, EHEC O26, which produce Stx2 only and appear to have enhanced virulence, have been increasingly isolated from HUS patients in Germany. In contrast, EHEC O26 found in cattle predominantly produce Stx1 as the sole Stx. Additional potential virulence factors of EHEC O26 include cytolysins (EHEC hemolysin), serine proteases (EspP), lymphotoxins (Efal) and adhesins (intimin). The genes encoding the virulence factors are located within pathogenicity islands (eae, efa1), bacteriophages (stx) or plasmids (EHEC-hlyA, espP). In addition, EHEC O26 possess, in contrast to other EHEC, the "high pathogenicity island" (HPI), which is also present in pathogenic Yersiniae.This island contains genes involved in the biosynthesis, regulation and transport of the siderophore yersiniabactin. Comparative genomic analyses between EHEC O26 and non-pathogenic E. coli, as well as investigations of mechanisms involved in the transfer of virulence genes, provide a deeper insight into the evolution of EHEC O26.These studies demonstrate how horizontal transfer of virulence genes, even from distantly related organisms, can lead in brief intervals to the rise of a highly virulent clone within a particular E. coli serotype.The classical bacteriological methods are no longer sufficient to determine the risk posed by EHEC O26. However, knowledge of the complete virulence profiles of these pathogens and understanding their stepwise evolution form a foundation for developing new strategies to prevent human infections and new methods for their laboratory diagnosis. 相似文献
32.
Background and aims
Increasing demand for lithium (Li+) for portable energy storage is leading to a global risk of Li+ pollution from the manufacture, use, and disposal of Li+-containing products. Although Li+, a reactive alkali metal, has no essential function in plants, they readily take it up and accumulate it in large amounts in their tissues. The underlying mechanisms for this Li+ uptake and accumulation are, however, not well described. Our aim has been to investigate the effects of other alkali metals with similar physicochemical properties on the uptake, accumulation, and toxicity of Li+ at low and high osmolarity.Methods
To determine the way in which Li+ affects the accumulation of other cations under saline conditions, sugar beet plants were grown in hydroponic culture with equimolar amounts of Li+, potassium (K+), and sodium (Na+) at low and high concentrations in various combinations.Results
Sugar beet plants tolerated high Li+ concentrations in the leaf and petiole. Low Li+ concentrations had no impact on plant growth but induced stomata closure. The presence of other monovalent cations at equimolar concentrations did not affect Li+ accumulation, but Li+ application altered the ratio of monovalent and divalent cations in leaves. Plants treated with high Li+ in combination with Na+ or K+ showed reduced plant growth and leaf necrosis, indicating the severe stress caused by Li+ toxicity.Conclusion
The presence of cations with similar physicochemical properties to those of Li+ cannot mitigate its toxicity. 相似文献33.
Peter Juroszek Marie Laborde Benno Kleinhenz Marina Mellenthin Paolo Racca Helge Sierotzki 《Plant pathology》2022,71(4):775-784
Fungicides are one possible way to manage fungal and oomycete plant pathogens in order to safeguard yield and quality of crops and to improve shelf-life of produce in agriculture and horticulture. However, global warming and the resulting temperature increase may affect the effectiveness of some important fungicides, including efficacy and duration of plant disease control. Nevertheless, according to our literature survey, there is little specific information available on whether and how temperature influences the effectiveness of fungicides. The very few publications that show specific data are summarized herein. Specific data are mainly gained under controlled conditions, both based on in vitro and in planta experiments. Field data are more or less missing. Most researchers assume that indirect effects of temperature on fungicide efficacy are particularly important. For example, temperature effects on pathogen spore germination and hyphal growth (optimal versus sub- and supra-optimal), whereby optimal temperature conditions can improve pathogen fitness, thereby increasing the tolerance of pathogens to fungicides. Presumably, these indirect effects are often more important than the direct effects of temperature on fungicide performance. However, the data needed to prove this assumption are lacking. Therefore, it would be beneficial to conduct more in-depth laboratory, greenhouse and field experiments in order to investigate the potential direct and indirect influence of temperature on the effectiveness of important fungicides. This would enable the establishment of appropriate recommendations for fungicide use in an increasingly warmer world and would assist the development of future fungicide solutions, based on improved knowledge. 相似文献
34.
Ulrich Gisi Helge Sierotzki 《European journal of plant pathology / European Foundation for Plant Pathology》2008,122(1):157-167
Among oomycetes, Plasmopara viticola on grape and Phytophthora infestans on potato are agronomically the most important pathogens requiring control measures to avoid crop losses. Several chemical
classes of fungicides are available with different properties in systemicity, specificity, duration of activity and risk of
resistance. The major site-specific fungicides are the Quinone outside inhibitors (QoIs; e.g. azoxystrobin), phenylamides
(e.g. mefenoxam), carboxylic acid amides (CAAs; e.g. dimethomorph, mandipropamid) and cyano-acetamide oximes (cymoxanil).
In addition, multi-site fungicides such as mancozeb, folpet, chlorothalonil and copper formulations are important for disease
control especially in mixtures or in alternation with site-specific fungicides. QoIs inhibit mitochondrial respiration, phenylamides
the polymerization of r-RNA, whereas the mode of action of the other two site-specific classes is unknown but not multi-site.
The use of site-specific fungicides has in many cases selected for resistant pathogen populations. QoIs are known to follow
maternal, largely monogenic inheritance of resistance; they bear a high resistance risk for many but not all oomycetes. For
phenylamides, inheritance of resistance is based on nuclear, probably monogenic mechanisms involving one or two semi-dominant
genes; resistance risk is high for all oomycetes. The molecular mechanism of resistance to QoIs is mostly based on the G143A
mutation in the cytochrome b gene; for phenylamides it is largely unknown. Resistance risk for CAA fungicides is considered
as low to moderate depending on the pathogen species. Resistance to CAAs is controlled by two nuclear, recessive genes; the
molecular mechanism is unknown. For QoIs and CAAs, resistance in field populations of P. viticola may gradually decline when applications are stopped. 相似文献
35.
To assess the influence of gap age and microsite type within a near-natural montane Norway spruce stand at the Harz National Park in Germany, we tested the following hypotheses: (1) The relationship between Picea abies regeneration and gap age is represented by an optimum curve. (2) Within gaps, tree regeneration mainly occurs on gap-induced microsites. (3) The contribution of specific microsites to regeneration changes with gap age. 相似文献
36.
Helge Bonesmo Kristin Kaspersen Anne Kjersti Bakken 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(2):76-82
We have developed an image analysis system for mapping white clover pastures. The information from digital colour photographs is processed by software (Trifolium.exe) specially designed for the purpose. The software estimates the coverage of clover, weeds and bare ground, and the unidentified remainder of the total area is regarded as covered by grass. To evaluate the reliability of the estimates of clover content, the clover on paper printouts of non-processed images were marked manually and analysed by a photo scanner and commercially available software. The outputs from Trifolium.exe and the estimates from scanned manual markings were highly correlated (r 2=0.81). A sensitivity test was conducted to quantify the impact of changes of six user-adjustable parameters of Trifolium.exe. The software output of clover coverage was sensitive for changes in three, soil coverage for changes in one, and weed coverage for changes in all parameters. The fact that the digital image acquisition and analysis produce nearly continuous and exactly positioned data, implies further that it is a very appropriate tool for analyses of spatial dynamics in grass-clover pastures. 相似文献
37.
This study compared the effect of two principal pyrolysis methods on the chemical characteristics of biochar and the impact on C and N dynamics after soil incorporation. Biochar was produced from wheat straw that was thermally decomposed at 525 °C by slow pyrolysis (SP) in a nitrogen flushed oven and by fast pyrolysis (FP) using a Pyrolysis Centrifuge Reactor (PCR). After 65 days of soil incubation, 2.9% and 5.5% of the SP- and FP-biochar C, respectively, was lost as CO2, significantly less than the 53% C-loss observed when un-pyrolyzed feedstock straw was incubated. Whereas the SP-biochar appeared completely pyrolyzed, an un-pyrolyzed carbohydrate fraction (8.8% as determined by acid released C6 and C5 sugars) remained in the FP-biochar. This labile fraction possibly supported the higher CO2 emission and larger microbial biomass (SMB-C) in the FP-biochar soil. Application of fresh FP-biochar to soil immobilized mineral N (43%) during the 65 days of incubation, while application of SP-biochar led to net N mineralization (7%). In addition to the carbohydrate contents, the two pyrolysis methods resulted in different pH (10.1 and 6.8), particle sizes (113 and 23 μm), and BET surface areas (0.6 and 1.6 m2 g?1) of the SP- and FP-biochars, respectively. The study showed that independently of pyrolysis method, soil application of the biochar materials had the potential to sequester C, while the pyrolysis method did have a large influence on the mineralization-immobilization of soil N. 相似文献
38.
Selamawit Tekle Helge Skinnes ?smund Bj?rnstad 《European journal of plant pathology / European Foundation for Plant Pathology》2013,135(1):147-158
Mycotoxin contamination and reduced germination capacity (GC) of oats affected by Fusarium head blight (FHB) have become serious concerns in Norway. Spawn- and spray-inoculated field trials were conducted from 2007 to 2010 to screen for resistant genotypes and to study the relationship between GC and deoxynivalenol (DON) contamination. Correlation coefficients between GC and DON level varied from ?0.412 to ?0.711 (P?<?0.001). The strongest and the weakest correlations were recorded for the spray- and spawn-inoculated experiments of 2009, respectively. High DON levels were associated with low GCs but low DON levels did not guarantee higher GCs. DON did not inhibit initiation of germination, but did retard seedling growth in a germination assay conducted on DON-amended water agar. Most of the seedlings grown on the modified WA containing even as little as 2?ppm DON had abnormal morphology and would not be considered as ??germinated?? in official tests. A greenhouse experiment studying the effect of time of inoculation on GC, DON level, and seed infection (SI) showed a rapid reduction in DON levels resulting from later inoculations. Increments in GC were observed although they were not as strong as the decrements in DON level. Seed infection remained consistently high (> 60?%) for all inoculations. Seed dressing and dehulling individually were not effective in improving GC, but when combined increased GC to the percentage of kernels having viable germ. We hypothesize that in addition to the level of DON, SI influences the GC of Fusarium-damaged oats, especially in wet years that may facilitate late-initiated infections. 相似文献
39.
QoI fungicides, inhibitors of mitochondrial respiration at the Qo site of cytochrome b in the mitochondrial bc(1) enzyme complex, are commonly applied in vineyards against Plasmopara viticola (Berk. & MA Curtis) Berl. & De Toni. Numerous treatments per year with QoI fungicides can lead to the selection of resistant strains in the pathogen population owing to the very specific and efficient mode of action. In order to evaluate the resistance risk and its development, two different methods, biological and molecular, were applied to measure the sensitivity of oospores differentiated in vineyards, both treated and untreated with azoxystrobin, from 2000 to 2004. Assays using oospores have the advantage of analysing the sensitivity of bulked samples randomly collected in vineyards, describing accurately the status of resistance at the end of the grapevine growing season. Both methods correlated well in describing the resistance situation in vineyards. QoI resistance was not observed in one vineyard never treated with QoI fungicides. In the vineyard where azoxystrobin had been used in mixture with folpet, the selection of QoI-resistant strains was lower, compared with using solely QoI. In vineyards where QoI treatments have been stopped, a decrease in resistance was generally observed. 相似文献
40.
Hüttner C Beuerle T Scharnhop H Ernst L Beerhues L 《Journal of agricultural and food chemistry》2010,58(22):11977-11984
The Rosaceous subtribe Pyrinae (formerly subfamily Maloideae) is well-known for its economically important fruit trees, such as apple and pear, and also includes Sorbus aucuparia. Elicitor-treated S. aucuparia cell cultures are used to study the biosynthesis of the Pyrinae-specific phytoalexins, biphenyls and dibenzofurans. Three biphenyls (aucuparin, noraucuparin, 2'-hydroxyaucuparin) and a dibenzofuran (eriobofuran) were isolated and structure elucidated using GC-MS and NMR. A second dibenzofuran of low abundance was tentatively assigned as noreriobofuran. Treatment of S. aucuparia cell cultures with yeast extract induced the formation of aucuparin as the major phytoalexin. In contrast, addition of preparations from the fire blight bacterium, Erwinia amylovora, and the scab-causing fungus, Venturia inaequalis, resulted in accumulation of eriobofuran as the major inducible constituent. Methyl jasmonate was a poor elicitor. The observations are suggestive of a biogenic relationship between biphenyls and dibenzofurans. Elicitor-treated S. aucuparia cell cultures provide an interesting in vitro system for studying biphenyl and dibenzofuran metabolism in the economically valuable Pyrinae. 相似文献