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   190篇
  免费   16篇
  国内免费   2篇
林业   4篇
农学   5篇
基础科学   4篇
  28篇
综合类   57篇
农作物   8篇
水产渔业   7篇
畜牧兽医   84篇
园艺   2篇
植物保护   9篇
  2023年   2篇
  2021年   2篇
  2020年   5篇
  2019年   3篇
  2018年   4篇
  2017年   2篇
  2016年   4篇
  2015年   6篇
  2013年   5篇
  2011年   14篇
  2010年   4篇
  2009年   2篇
  2008年   9篇
  2007年   9篇
  2006年   5篇
  2005年   6篇
  2004年   11篇
  2003年   8篇
  2002年   8篇
  2001年   2篇
  2000年   10篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1992年   6篇
  1991年   6篇
  1989年   4篇
  1988年   3篇
  1986年   4篇
  1985年   4篇
  1984年   5篇
  1983年   3篇
  1980年   2篇
  1970年   1篇
  1968年   1篇
  1944年   1篇
  1943年   1篇
  1942年   2篇
  1941年   1篇
  1940年   1篇
  1937年   1篇
  1935年   2篇
  1934年   1篇
  1933年   3篇
  1932年   1篇
  1931年   1篇
  1929年   2篇
  1928年   1篇
  1881年   2篇
  1880年   1篇
排序方式: 共有208条查询结果,搜索用时 15 毫秒
51.
Association of Campylobacter jejuni with enteritis in dogs and cats   总被引:1,自引:0,他引:1  
Campylobacter jejuni was recovered from 59 of 505 (11.7 per cent) dogs with diarrhoea as compared with only two of 122 (1.6 per cent) dogs without diarrhoea. However, there was no significant difference between campylobacter isolations from 142 cats with and without diarrhoea. C jejuni infections were commonly associated with chronic diarrhoea in both species and appropriate therapy abolished clinical signs and excretion of the organism in faeces in most cases. C jejuni may be responsible for some forms of enteritis in dogs and cats and is a zoonosis in which the companion animal may be the vector.  相似文献   
52.
The factors of feed efficiency, growth rate, carcass trim at slaughter, amount of antibiotic treatment, and death rate were compared among groups of pigs fed ("finished") in an open-front feedlot in Kansas. The factor having the greatest influence on performance was the month of entry of the pigs into the feedlot. Carcass trim at slaughter was greater in groups wherein each pig was given more than 4 ml of antibiotic than in groups wherein less than 4 ml of antibiotic was given to each pig. Death rates of pigs that remained in the feedlot longer than 150 days were nearly twice those of pigs that had been sent to slaughter before 150 days.  相似文献   
53.
Volumetric imaging (VOL), a three‐dimensional magnetic resonance imaging (MRI) technique, has been described in the literature for evaluation of the human brain. It offers several advantages over conventional two‐dimensional (2D) spin echo (SE), allowing rapid, whole‐brain, isotropic imaging with submillimeter voxels. This retrospective, observational study compares the use of 2D T1‐weighted SE (T1W SE), with T1W VOL, for the evaluation of dogs with clinical signs of intracranial disease. Brain MRI images from 160 dogs who had T1W SE and T1W VOL sequences acquired pre‐ and postcontrast, were reviewed for presence and characteristics of intracranial lesions. Twenty‐nine of 160 patients were found to have intracranial lesions, all visible on both sequences. Significantly better grey‐white matter (GWM) differentiation was identified with T1W VOL (P < .001), with fair agreement between the two sequences (weighted κ = 0.35). Excluding a mild reduction in lesion intensity in three dogs precontrast on the T1W VOL images compared to T1W SE, and meningeal enhancement noted on the T1W VOL images in one dog, not identified on T1W SE, there was otherwise complete agreement between the two sequences. The T1W VOL sequence provided equivalent lesion evaluation and significantly improved GWM differentiation. Images acquired were of comparable diagnostic quality to those produced using a conventional T1W SE technique, for assessment of lesion appearance, number, location, mass effect, and postcontrast enhancement. T1W VOL, therefore, provides a suitable alternative T1W sequence for canine brain evaluation and can facilitate a reduction in total image acquisition time.  相似文献   
54.
The clinical efficacy of becaplermin (Regranex, Ortho-McNeil Pharmaceutical, Inc., Raritan, New Jersey 08869) on head and lateral line erosion syndrome (HLLES) in ocean surgeonfish (Acanthurus bahianus) was examined in a two-part study to determine suitable application frequencies of the drug and the effects of the environment on outcome of treatments. In the first part of the study, 12 ocean surgeonfish with prior HLLES were equally divided into three treatment groups, varying in application frequency of becaplermin: 1) one application, 2) three applications every 3 wk, and 3) no applications. After 9 wk, it was determined through photograph and computer analysis that fish treated with becaplermin did heal significantly more than the fish that were not treated. No significant difference was found when comparing the two treatment regimes; therefore, a one-time treatment of becaplermin was just as effective as the three-time application, reducing cost of the treatment, staff labor, and stress to the animals. In the second part of the study, the effect of the water environment on HLLES development was documented before and after a one-time treatment of becaplermin. When fish were treated and placed into a system known to cause HLLES, the becaplermin treatment had no effect on reducing the HLLES progression, whereas treated fish that were placed into a system that did not cause HLLES showed a significant decrease in erosion after the treatment. Therefore, treating fish being placed into a HLLES-causing system serves no beneficial purpose to healing HLLES.  相似文献   
55.
戊型肝炎病毒研究新进展   总被引:3,自引:0,他引:3  
戊型肝炎病毒(hepatitis Evirus,HEV)是非甲非乙型急性肝炎的病原体,主要经粪-口途径传播,也有报道可以通过血液传播。戊型肝炎在亚洲、非洲及美洲的墨西哥等发展中国家常呈爆发流行,我国1986-1988年在新疆曾经发生戊型肝炎暴发流行[1],而在包括发达国家在内的世界各地呈散在传  相似文献   
56.
Bedding material is an important factor in determining stable air quality in terms of ammonia formation. The objective of this study was to analyze different bedding materials used for horse stables under standardized conditions, to determine which material is best suited for improving the climate of a stable. The particular concern was a reduction in gaseous ammonia concentrations. Therefore, the following materials were examined: wheat straw, wood shavings, hemp shives, linen shives, wheat straw pellets, and paper cuttings. Twelve containers were constructed in an environmentally controlled room, and the same material was placed into two containers, with the amount of material used being determined by its carbon content. A defined ratio of horse manure/urine mixture was added daily to each container over a period of 14 days. The concentrations of gaseous ammonia, carbon dioxide, nitrous oxide, and water vapor were measured continuously above the bedding within the containers. Means of gaseous ammonia were found to be 178.0 mg/m3 for wheat straw, 155.2 mg/m3 for wood shavings, 144.6 mg/m3 for hemp, 133.7 mg/m3 for linen, 60.3 mg/m3 for straw pellets, and 162.6 mg/m3 for paper cuttings. In conclusion, the results of this study have shown that straw pellets are suitable for horse stables, not only to improve air quality but also, first and foremost, in relation to ammonia binding and ammonia transformation within the bedding material, respectively. However, straw pellets may also have disadvantages. The high substrate temperatures that were measured in straw pellets could favor the growth of pathologic germs that can adversely affect animals' health.  相似文献   
57.
Samples of serum and urine were obtained simultaneously from 56 healthy lactating cows to determine ranges of fractional excretion (FE) of calcium (Ca), phosphate (PO4), magnesium (Mg), sodium (Na), potassium (K), and chloride (Cl). Samples were obtained at 3 stages of lactation: period 1 = 1 to 7 days, 2 = 83 to 112 days, and 3 = 175 to 197 days. The FE of electrolytes were significantly different among periods 1, 2, and 3 for Ca (P less than 0.001), PO4 (P less than 0.025) and Mg (P less than 0.025), but were not significantly different for Na, K, and Cl. Least squares mean FE of Ca was lowest in period 1 and not significantly different for periods 2 and 3, whereas mean FE values for PO4 and Mg were highest in period 2 and not significantly different for periods 1 and 3. The mean FE values of Na, K, and Cl did not change with stage of lactation. Age and category of milk production (high, medium, and low) did not influence the FE values of the electrolytes.  相似文献   
58.
Organic farming may contribute substantially to future agricultural production worldwide by improving soil quality and pest control, thereby reducing environmental impacts of conventional farming. We investigated in a comprehensive way soil chemical, as well as below and aboveground biological parameters of two organic and two conventional wheat farming systems that primarily differed in fertilization and weed management strategies. Contrast analyses identified management related differences between “herbicide-free” bioorganic (BIOORG) and biodynamic (BIODYN) systems and conventional systems with (CONFYM) or without manure (CONMIN) and herbicide application within a long-term agricultural experiment (DOK trial, Switzerland). Soil carbon content was significantly higher in systems receiving farmyard manure and concomitantly microbial biomass (fungi and bacteria) was increased. Microbial activity parameters, such as microbial basal respiration and nitrogen mineralization, showed an opposite pattern, suggesting that soil carbon in the conventional system (CONFYM) was more easily accessible to microorganisms than in organic systems. Bacterivorous nematodes and earthworms were most abundant in systems that received farmyard manure, which is in line with the responses of their potential food sources (microbes and organic matter). Mineral fertilizer application detrimentally affected enchytraeids and Diptera larvae, whereas aphids benefited. Spider abundance was favoured by organic management, most likely a response to increased prey availability from the belowground subsystem or increased weed coverage. In contrast to most soil-based, bottom-up controlled interactions, the twofold higher abundance of this generalist predator group in organic systems likely contributed to the significantly lower abundance of aboveground herbivore pests (aphids) in these systems. Long-term organic farming and the application of farmyard manure promoted soil quality, microbial biomass and fostered natural enemies and ecosystem engineers, suggesting enhanced nutrient cycling and pest control. Mineral fertilizers and herbicide application, in contrast, affected the potential for top-down control of aboveground pests negatively and reduced the organic carbon levels. Our study indicates that the use of synthetic fertilizers and herbicide application changes interactions within and between below and aboveground components, ultimately promoting negative environmental impacts of agriculture by reducing internal biological cycles and pest control. On the contrary, organic farming fosters microbial and faunal decomposers and this propagates into the aboveground system via generalist predators thereby increasing conservation biological control. However, grain and straw yields were 23% higher in systems receiving mineral fertilizers and herbicides reflecting the trade-off between productivity and environmental responsibility.  相似文献   
59.
A series of selection experiments on potato cyst nematode Globodera pallida, pathotype Pa1, tested the virulence response of the nematode to a range of resistant potato Solanum genotypes. Alleles conferring virulence against all four Solanum sources used in the study (i.e. Solanum vernei, S. multidissectum, S. sanctae-rosae and S. tuberosum ssp. andigena) were detected. Selection for multiple virulence against a combination of resistant sources resulted in the originally-selected virulence genes being retained or lost. The mechanism, or basis, of potato cyst nematode resistance differs between the Solanum species. The appropriate use of resistance cultivars produced from a range of Solanum-resistant species offers a management tool for controlling potato cyst nematode levels in infested land.  相似文献   
60.
A variety of Bartonella species were detected in two species of ticks and three species of fleas collected from marsupial hosts; brush-tailed bettong or woylie (Bettongia penicillata) and western barred bandicoots (Perameles bougainville) and from a rodent host; Rattus fuscipes in Western Australia. Bartonella species were detected using nested-PCR of the gltA gene and the 16S–23S ribosomal internal transcribed spacer region (ITS), and species were characterized using DNA sequencing of the 16S rRNA, gltA, rpoB, ftsZ genes and the ITS region. Bartonella rattaustraliani and B. coopersplainsensis were detected in Ixodes spp. ticks and fleas (Stephanocircus pectinipes) respectively collected from rodents. Two novel Bartonella species were detected from marsupials; Candidatus Bartonella woyliei n. sp. was detected in both fleas (Pygiopsylla hilli) and ticks (Ixodes australiensis) collected from woylies and Candidatus Bartonella bandicootii n. sp. was detected in fleas (Pygiopsylla tunneyi) collected from western barred bandicoots. Concatenated phylogenetic analysis of all 5 loci clarified the marsupial cluster of Bartonella species in Australia and confirmed the species status of these two Bartonella species in ticks and fleas from woylies and western barred bandicoots, which are classified as threatened species and are vulnerable to extinction.  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