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   245篇
  免费   25篇
林业   11篇
农学   5篇
  22篇
综合类   35篇
农作物   6篇
水产渔业   13篇
畜牧兽医   110篇
园艺   4篇
植物保护   64篇
  2020年   7篇
  2019年   5篇
  2018年   6篇
  2017年   5篇
  2016年   4篇
  2015年   2篇
  2014年   7篇
  2013年   3篇
  2012年   11篇
  2011年   11篇
  2010年   7篇
  2009年   2篇
  2008年   20篇
  2007年   20篇
  2006年   7篇
  2005年   7篇
  2004年   11篇
  2003年   12篇
  2002年   7篇
  2001年   6篇
  2000年   8篇
  1999年   7篇
  1998年   5篇
  1997年   3篇
  1996年   4篇
  1995年   2篇
  1993年   3篇
  1992年   3篇
  1991年   5篇
  1990年   8篇
  1989年   8篇
  1988年   6篇
  1987年   5篇
  1986年   3篇
  1985年   3篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1979年   4篇
  1974年   2篇
  1973年   1篇
  1972年   3篇
  1971年   2篇
  1969年   1篇
  1968年   1篇
  1965年   2篇
  1962年   2篇
  1961年   3篇
  1887年   1篇
  1885年   1篇
排序方式: 共有270条查询结果,搜索用时 15 毫秒
1.
Cerebellar disease in an adult cow   总被引:1,自引:0,他引:1       下载免费PDF全文
This is the report of clinical signs and lesions of a cerebellar disorder in an adult four year old Limousin cow grazing perennial ryegrass (Lolium perenne). The most striking histopathological lesion was a marked paucity of Purkinje cells throughout the cerebellum.  相似文献   
2.
The progress of development of stem-base pathogens in crops of second winter wheat was plotted in nine experiments in three years. The amount of each pathogen present was determined by quantitative PCR. Where Tapesia yallundae was present in quantifiable amounts, it usually developed earlier than the other eyespot pathogen, T. acuformis. Both species were usually present in greater amounts on cultivars which are more susceptible to eyespot. The sharp eyespot pathogen, Rhizoctonia cerealis, developed more erratically than either of the Tapesia spp. and there were no consistent effects on different cultivars. Fusarium spp., the cause of brown foot rot, were rarely present in quantifiable amounts, but Microdochium nivale was usually present as one or both of the varieties nivale and majus. Late-season (after anthesis) decreases in M. nivale suggest that any brown foot rot symptoms attributable to this fungus would have fully developed earlier. Cultivar differences in amounts of M. nivale were most clear in stems during internode extension and when relatively large amounts of DNA were present. Such differences approximately reflected eyespot susceptibility, cv. Soissons containing most and cv. Lynx containing least DNA. The results emphasise the difficulty in relating diagnoses, by quantitative PCR or other means, at early growth stages when decisions to apply fungicides against stem-base disease are made, to later disease severity.  相似文献   
3.
4.
5.
Analysis of the chemical components from the culture broth of the marine bacterium Saccharomonospora sp. CNQ-490 has yielded three novel compounds: saccharobisindole (1), neoasterric methyl ester (2), and 7-chloro-4(1H)-quinolone (3), in addition to acremonidine E (4), pinselin (5), penicitrinon A (6), and penicitrinon E (7). The chemical structures of the three novel compounds were elucidated by the interpretation of 1D, 2D nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS) data. Compound 2 generated weak inhibition activity against Bacillus subtilis KCTC2441 and Staphylococcus aureus KCTC1927 at concentrations of 32 μg/mL and 64 μg/mL, respectively, whereas compounds 1 and 3 did not have any observable effects. In addition, compound 2 displayed weak anti-quorum sensing (QS) effects against S. aureus KCTC1927 and Micrococcus luteus SCO560.  相似文献   
6.
Microspectrophotometry was performed on intact, pigmented vesicle-like inclusions within living sorghum cells that were accumulating phytoalexins as a response to attempted fungal infection. The results indicate that the deoxyanthocyanidin phytoalexins are present in inclusions. Moreover, the phytoalexin concentration within a single inclusion, based on luteolinidin, was calculated to be 0·15 m. The amounts of luteolinidin and apigeninidin in cells involved in the phytoalexin response at individual infection sites were also determined. The data showed that luteolinidin accumulated to levels of 0·48–1·20 ng/cell whereas apigeninidin accumulated to levels of 0·24–0·91 ng/cell. The results of both analyses confirmed that at the infection site the deoxyanthocyanidins accumulate to levels in substantial excess of those required for inhibition of the fungus Colletotrichum graminicola.  相似文献   
7.
The study in Wistar rats attempted to improve the occlusion technique of the middle cerebral artery (MCA) as a precise method for initiating stroke. In a first part it was necessary to study the exact anatomy of blood vessels of the brain in seven rats of 170-410 g body weight by corrosion cast. The lengths and diameters of defined locations of the blood vessels were measured. The temporary as well as the permanent methods were refined or replaced. The first one was completed in main training the physiological blood flow after temporary occlusion, while the permanent occlusion was performed by positioning a silicone cap in the MCA. A filament guide was introduced from the common carotid artery (CCA) via internal carotid artery (ICA) to guide the silicon cap at the branch of the MCA. Histological sections of the brain of rats showed 24 h after the permanent occlusion a reproducible infarct in the brain. This area corresponded very well with the supply of the MCA. The new occlusion method with a silicon cap was compared with the occlusion methods of CCA route and external carotid artery (ECA) route. The total infarct volume was significantly larger in the CCA route and ECA route groups than in the silicon cap group (means: CCA route 261 mm3; ECA route 191 mm3 vs. 128 mm3 silicon cap group; P  < 0,05). It could be demonstrated that the new silicon cap occlusion technique imitates the pathological situation of a cerebral infarct in man. Moreover it is less invasive for the animals and more precise and reproducible regarding the infarcted area in comparison to the other occlusion methods. Based on anatomical measurements of the blood vessels the described silicon cap method can be recommended for rats of a body weight between 340–370 g.  相似文献   
8.
9.
ABSTRACT This study investigated antifungal activity in soluble extracts from seed of a range of wheat cultivars differing in susceptibility to Fusarium head blight. Antifungal activity was assessed in terms of beta-D-glucuronidase (GUS) activity of a Fusarium culmorum GUS transformant using a sensitive laboratory assay. Significant antifungal activity was detected in seed extracts from WEK0609, CM 820036, and Arina. Initial characterization of the Arina seed extract indicated that it contained antifungal proteinaceous compounds. The Arina extract yielded two (60 and 80%) ammonium sulfate fractions containing inhibitory compounds. Gel filtration chromatography and subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis of antifungal fractions showed that the antifungal activities detected in the Arina 60 and 80% ammonium sulfate fractions were associated with putative proteinaceous compounds with apparent molecular masses of approximately 60 and 28 kDa, respectively.  相似文献   
10.
Rhodococcus equi can cause severe or fatal pneumonia in foals as well as in immunocompromised animals and humans. Its ability to persist in macrophages is fundamental to how it causes disease, but the basis of this is poorly understood. To examine further the general application of a recently developed system of targeted gene mutation and to assess the importance of different genes in resistance to innate immune defenses, we disrupted the genes encoding high-temperature requirement A (htrA), nitrate reductase (narG), peptidase D (pepD), phosphoribosylaminoimidazole-succinocarboxamide synthase (purC), and superoxide dismutase (sodC) in strain 103 of R. equi using a double-crossover homologous recombination approach. Virulence testing by clearance after intravenous injection in mice showed that the htrA and narG mutants were fully attenuated, the purC and sodC mutants were unchanged, and the pepD mutant was slightly attenuated. Complementation with the pREM shuttle plasmid restored the virulence of the htrA and pepD mutants but not that of the narG mutant. A single-crossover mutation approach was simpler and faster than the double-crossover homologous recombination technique and was used to obtain mutations in 6 other genes potentially involved in virulence (clpB, fadD8, fbpB, glnA1, regX3, and sigF). These mutants were not attenuated in the mouse clearance assay. We were not able to obtain mutants for genesfurA, galE, and sigE using the single-crossover mutation approach. In summary, the targeted-mutation system had general applicability but was not always completely successful, perhaps because some genes are essential under the growth conditions used or because the success of mutation depends on the target genes.  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