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   845篇
  免费   37篇
林业   29篇
农学   17篇
基础科学   6篇
  93篇
综合类   154篇
农作物   30篇
水产渔业   31篇
畜牧兽医   469篇
园艺   17篇
植物保护   36篇
  2021年   8篇
  2020年   7篇
  2019年   7篇
  2018年   14篇
  2017年   7篇
  2016年   13篇
  2015年   14篇
  2014年   18篇
  2013年   60篇
  2012年   23篇
  2011年   33篇
  2010年   19篇
  2009年   23篇
  2008年   25篇
  2007年   42篇
  2006年   23篇
  2005年   25篇
  2004年   23篇
  2003年   30篇
  2002年   21篇
  2001年   28篇
  2000年   16篇
  1999年   18篇
  1998年   15篇
  1996年   8篇
  1992年   19篇
  1991年   20篇
  1990年   13篇
  1989年   16篇
  1988年   10篇
  1987年   9篇
  1986年   20篇
  1985年   15篇
  1984年   13篇
  1983年   10篇
  1982年   7篇
  1981年   6篇
  1979年   18篇
  1978年   10篇
  1976年   14篇
  1975年   7篇
  1974年   15篇
  1973年   10篇
  1972年   10篇
  1970年   9篇
  1969年   9篇
  1968年   7篇
  1967年   13篇
  1966年   9篇
  1958年   5篇
排序方式: 共有882条查询结果,搜索用时 375 毫秒
181.
Rice quality, specifically head rice yield (HRY), can vary inexplicably from one lot to another, and from year to year. In an effort to correlate air temperatures during various growth stages to HRY, growth staging data expressed in degree day units was used to predict the occurrence of sequential growth stages within a set of 17‐year historical data, which included HRY and 50% heading dates for two long‐grain rice cultivars, (Oryza sativa L) Newbonnet and Lemont, and area weather data. HRY was most strongly affected by the average daily low temperature (or nighttime temperature) during the R8 developmental stage. Lower HRY were associated with high nighttime air temperatures during this stage for both Newbonnet and Lemont. When used as a single variable in a regression model, the nighttime temperature during the R8 developmental stage explained over 25% of the variation in HRY.  相似文献   
182.
Red pine (Pinus resinosia Ait) and southern pine (Pinus spp.) sapwood blocks were pressure treated with CCA-C at retention of 6.4, 2.0, 1.5 kgm-3 followed by fixation using 11 post-treatment schedules ranging from 50–70 °C and 5 different relative humidity conditions. The effect of these post-treatment schedules on fixation rate, chemical leachability and decay resistant once were evaluated to better understand the effects of fixation/drying conditions on leachability and biodeterioration. Southern pine blocks fixes slightly slower than red pine. Fixation of CCA at high temperature high humidity, essential initially fixation at high humidity for fixation/drying schedules, resulted in lower leaching of chromium and arsenic elements than high temperature low humidity or initially fixation at the high temperature low humidity conditions. Copper leaching was indicated no significant difference under 11 fixation/drying conditions for both species. Weight losses for southern pine byChaetomium globosum was lower than red pine byGloeophyllom trabeum. There were some different capacities of decay resistance for both species under those post treatment conditions.  相似文献   
183.
Sorptive interactions between Escherichia coli (ATCC 11303B) and a purified allophane clay fraction were studied quantitatively using electronic particle counting and electrophoresis. Adsorption was influenced by pH and ions present at the allophane surface. These effects could be rationalized by considering changes in the net surface charge of the components. Electronic particle counting studies at pH 5.5 and above gave adsorption isotherms that obeyed single-term Langmuir kinetics. At pH 4.5, a more complex two-step isotherm was obtained, which was attributed to aggregation of unadsorbed cells by Al solubilized from the allophane surface.  相似文献   
184.
The jackass penguin Spheniscus demersus (L.) is confined to the coastal waters of southern Africa, and breeds on 18 islands predominantly within the region of the cold, nutrient rich Benguella current. Since the early 1900s the species' population has declined in numbers of unknown magnitude. The decline appears to be continuing, although the absence of reliable census data precludes an accurate measurement of the rate of change. The initial fall in numbers was undoubtedly due to severe disturbance of nesting birds and excessive commercial exploitation of eggs. The average annual egg crop for the period 1900-30 exceeded 450,000 eggs from Dassen Island alone. Egg collection has been suspended temporarily, but the species now appears to be threatened by oil pollution, and by competition with a pelagic shoal fish industry. Threats to breeding colonies are posed by harbour developments. These factors are discussed and evaluated. South African marine organisms are considered officially to be an economic resource and are heavily exploited. Legislation governing the control of this resource is the concern of the Ministry for Economic Affairs. There is no provision for any government body to investigate the status and biology of economically insignificant, but yet integral, components of the marine ecosystem. The major priority of conservations is to safeguard the jackass penguin population at its present level. This includes proclamation of several offshore islands and their surroundings as national nature reserves. We consider current efforts to rescue, clean and rehabilitate oiled seabirds as contributing little to conservation in real terms, even though the activity has an important humanitarian and educational function. Research priorities include a comprehensive census of the jackass penguin and other seabird populations in southern Africa; a study of mortality and recruitment, with particular attention to factors affecting the rates of these processes; a study of the dynamics of the penguin/prey interaction, with special reference to the possible effects of competition with the pelagic fishing industry; an evaluation of the degree of disturbance that nesting penguins can tolerate; an investigation into the temporal and spatial patterns of oil pollution incidents, oil slick occurrence and movement, and the development of methods of keeping birds away from oil slicks; and, lastly, an evaluation of the efficacy of rehabilitating oiled penguins as a contribution to maintaining or increasing the current jackass penguin population. The responsibility for these projects rests with the South African government.  相似文献   
185.
186.
187.
Specific pathogen free day-old chicks were inoculated with a virulent strain of Mycoplasma gallisepticum. Birds received either danofloxacin (50 ppm), tylosin (500 ppm) or no medication in the drinking water from 24 hours after infection for three days. The effects of medication on mortality, weight gain, serology, lesions and reisolation of M gallisepticum 21 days following infection were studied. Treatment with danofloxacin and tylosin significantly decreased mortality and increased weight gain compared with infected unmedicated birds. Twenty-one days after infection, M gallisepticum was isolated from 96 per cent of unmedicated birds compared with only 6 per cent of danofloxacin-treated and 40 per cent of tylosin-treated birds, and the percentage showing positive serological tests was reduced from 100 per cent of unmedicated birds to 0 per cent of danofloxacin-treated and 29 per cent of tylosin-treated birds. In both cases, the proportion of positive birds from the danofloxacin-treated group was significantly lower than that from the tylosin-treated group. The occurrence of air sac lesions was also significantly lower in danofloxacin-treated than in tylosin-treated birds.  相似文献   
188.
Sheep were drenched with a single toxic dose of dried and milled Isotropis forrestii in water. Intoxication resulted in early onset of glycosuria, enzymuria and proteinuria. Terminal gross lesions included pale kidneys and perirenal oedema. Histologically and ultrastructurally the renal lesions were typical of primary nephrotoxicosis, with extensive proximal tubular epithelial necrosis. The tubular damage was sufficient to cause acute primary renal failure, characterised by oliguria, azotemia and failure of urinary concentrating mechanisms.  相似文献   
189.
Infectious coryza in meat chickens in the San Joaquin Valley of California   总被引:1,自引:0,他引:1  
Two cases of infectious coryza in meat chickens are reported. The first case involved 6-week-old broiler chickens in which only Haemophilus paragallinarum was isolated. The second case involved 11-week-old roaster chickens in which H. paragallinarum and Mycoplasma synoviae were isolated. Both farms were in close proximity to layer-chicken farms where infectious coryza had been previously diagnosed. In both cases, only certain houses on the farm were affected, and mortality in these houses increased slightly. At processing, the condemnation rates for affected houses were considerably higher than rates for unaffected houses. Condemnations for affected houses were mostly due to airsacculitis. A dissecting fibronopurulent cellulitis was a prominent lesion in the second case. This lesion could lead to confusion with chronic fowl cholera and swollen-head syndrome.  相似文献   
190.
Experimental viral myocarditis: parvoviral infection of neonatal pups   总被引:2,自引:0,他引:2  
Myocarditis was produced in seronegative five-day-old pups by oral and by intraperitoneal inoculation of canine parvovirus. The disease was subclinical. Histologic lesions were compatible with, but less extensive than, those seen in naturally occurring canine parvoviral myocarditis. In pups necropsied 23 days after inoculation, scattered cardiac myocytes contained intranuclear inclusion bodies, and virus-infected myocytes were demonstrated by immunofluorescence. Degeneration and loss of cardiac myocytes usually was not associated with a cellular infiltrate. At 51 days after inoculation, the myocardium contained an extensive lymphocytic infiltrate which was sometimes associated with fragmented myocytes, and was often contiguous with areas of interstitial fibrosis. At 108 days after inoculation, inflammatory lesions had regressed, and there were multifocal areas of myocardial fibrosis.  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