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   913篇
  免费   71篇
林业   17篇
农学   14篇
基础科学   3篇
  123篇
综合类   174篇
农作物   23篇
水产渔业   66篇
畜牧兽医   481篇
园艺   16篇
植物保护   67篇
  2023年   13篇
  2022年   5篇
  2021年   13篇
  2020年   15篇
  2019年   11篇
  2018年   13篇
  2017年   15篇
  2016年   25篇
  2015年   20篇
  2014年   15篇
  2013年   35篇
  2012年   40篇
  2011年   48篇
  2010年   37篇
  2009年   15篇
  2008年   36篇
  2007年   55篇
  2006年   44篇
  2005年   34篇
  2004年   52篇
  2003年   37篇
  2002年   29篇
  2001年   24篇
  2000年   27篇
  1999年   21篇
  1997年   5篇
  1996年   5篇
  1995年   10篇
  1994年   8篇
  1992年   19篇
  1991年   11篇
  1990年   20篇
  1989年   8篇
  1988年   15篇
  1987年   9篇
  1986年   19篇
  1985年   15篇
  1984年   8篇
  1983年   5篇
  1982年   5篇
  1979年   8篇
  1978年   6篇
  1975年   5篇
  1974年   5篇
  1973年   9篇
  1972年   13篇
  1971年   14篇
  1970年   10篇
  1969年   7篇
  1966年   6篇
排序方式: 共有984条查询结果,搜索用时 15 毫秒
971.
Between 1997 and 2000, a total of 150 healthy cattle and 238 animals with respiratory disease were examined for six Mycoplasma species. Attempts were made to detect Mycoplasma canis, Mycoplasma dispar and Ureaplasma diversum in calves with recurrent disease, and all three of these species were identified in calves with recurrent disease and in healthy lungs. In healthy calves, 84 per cent of bronchoalveolar lavage fluids were mycoplasma free; when cultures were positive, Mycoplasma bovirhinis was the only species isolated. Mycoplasmas were isolated from 78 per cent of animals suffering recurrent respiratory disease and from 65 per cent of acute respiratory cases. Mycoplasma bovis was isolated from bronchoalveolar lavages from 35 per cent of calves suffering recurrent respiratory disease, and from 50 per cent of acute cases, and from 20 per cent of pneumonic cases examined postmortem. M bovis was associated with other Mycoplasma species in 44 per cent of cases. M dispar was also isolated from 45.5 per cent of calves suffering recurrent respiratory disease, often in association with M bovis. M canis was identified for the first time in diseased Belgian cattle. Other mycoplasmas, including Mycoplasma arginini, Mycoplasma alkalescens and U diversum, were isolated less frequently. Associations between mycoplasmas and other pathogens were often observed. Among lungs infected with Pasteurella and/or Mannheimia species, more than 50 per cent were mixed infections with M bovis.  相似文献   
972.
973.
A gamma-ray spectrometry system with low background was used to determine the radioactivity of crystalline rocks, breccias, and fine material. Nuclides identified were (40)K, (232)Th, (238)U, (7)Be, (22)Na (26)A1, (44)Ti, (46)Sc, (48)V, (52)Mn, (54)Mn, and (56)Co. Concentrations of K, Th, and U ranged between 480 and 2550, 1.01 and 3.30, and 0.26 and 0.83 parts per million, respectively. Concentrations of thorium and uranium were those of terrestrial basalts, while the potassium concentrations were near values for chondrites. Products of low-energy nuclear reactions showed pronounced concentration gradients at rock surfaces. Concentrations of K and of (22)Na determined here were combined with concentrations of rare gases to estimate gas-retention ages and cosmic-ray exposure ages with ranges of 2200 to 3200 and 34 to 340 million years, respectively, for three rocks.  相似文献   
974.
The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials.  相似文献   
975.
Horses are commonly infected by herpesviruses, but isolation of equine herpesvirus-5 (EHV-5) has only infrequently been reported. We describe the isolation and characterization of a strain of EHV-5 from the blood mononuclear cells of a healthy adult horse in California. The virus was initially identified by EHV-5 specific polymerase chain reaction (PCR), and it caused lytic infection of cultured rabbit kidney cells only after repeated serial passage. Virions with characteristic herpesvirus morphology were readily demonstrated in cell culture lysate by transmission electron microscopy. A portion of the glycoprotein B gene of this strain of EHV-5 had 99% identity to the published EHV-5 sequence, and it was clearly distinguishable from other EHV (1-4) by virus-specific PCR assays. Prevalence of EHV-5 infection in a group of young racehorses was estimated at 64% using the EHV-5 specific PCR on nasopharyngeal secretions.  相似文献   
976.
Sarcina species are fastidious Gram-positive anaerobic bacteria that occur in cubical packets of eight or more cells. In 2006 to 2007, they were associated with cases of acute abomasal bloat in young lambs and calves. Two incidents were in lambs aged three to six weeks that were found dead, with one or two cases in each of a group of 15 and 100 lambs. Three incidents were recorded in small groups of calves up to 10 days of age, two cases in each incident, with the calves found dead or dying after a short illness characterised by bloat. Their gross lesions included emphysema and oedema of the abomasal wall, mucosal hyperaemia and haemorrhage, and rupture of the abomasum. Histological lesions included abomasitis with congestion, haemorrhage, emphysema and oedema. Bacteria characteristic of Sarcina species were observed in sections associated with the superficial mucosa of these cases, but the bacteria were not detected in cultures.  相似文献   
977.
The objective of this survey was to describe the current state of dehorning practices by dairy producers and veterinarians in Ontario and to identify opportunities to improve on existing practices. Two hundred and seven producers and 65 veterinarians completed a survey on dehorning practices during the summer of 2004. Seventy-eight percent of dairy producers dehorn their own calves; 22% use local anesthetics. Veterinarians dehorn calves for 31% of dairy clients; 92% use local anesthetics. Pain management was the most common reason for use of local anesthetics for both groups, while time (veterinarians) and time and cost (producers) were the most common reasons for lack of use. Producers who used local anesthetics were 6.5 times more likely to have veterinary involvement in their dehorning decisions. Thirteen percent of producers were unaware of the options for pain management. These results suggest that veterinarians should take the initiative to educate their clients about the options for pain management.  相似文献   
978.
979.
980.
Micro-scale irrigation on wetlands or dambos has been practised in Zimbabwe for over 100 years with, at present, an estimated 20,000 ha under cultivation in the communal areas. The results of recent research indicate that there is great potential for increasing the area and the intensity of such cultivation. The advantages of micro-scale irrigation are discussed and it is argued that this scale of irrigation should be considered when formulating policy and allocating resources for irrigation.Abbreviations Communal areas Areas in Zimbabwe historically reserved for blacks and distinguished from the commercial farming areas with better resources  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