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   105600篇
  免费   5474篇
  国内免费   52篇
林业   4313篇
农学   3045篇
基础科学   729篇
  11685篇
综合类   20742篇
农作物   4295篇
水产渔业   4622篇
畜牧兽医   54383篇
园艺   1195篇
植物保护   6117篇
  2018年   1204篇
  2017年   1332篇
  2016年   1285篇
  2015年   1091篇
  2014年   1262篇
  2013年   3933篇
  2012年   2568篇
  2011年   3188篇
  2010年   2080篇
  2009年   2054篇
  2008年   3206篇
  2007年   2940篇
  2006年   2803篇
  2005年   2638篇
  2004年   2746篇
  2003年   2680篇
  2002年   2624篇
  2001年   3276篇
  2000年   3288篇
  1999年   2441篇
  1998年   1070篇
  1997年   1081篇
  1995年   1252篇
  1994年   1164篇
  1993年   1121篇
  1992年   2367篇
  1991年   2532篇
  1990年   2440篇
  1989年   2495篇
  1988年   2272篇
  1987年   2355篇
  1986年   2486篇
  1985年   2394篇
  1984年   1920篇
  1983年   1778篇
  1982年   1166篇
  1981年   1124篇
  1980年   1026篇
  1979年   1762篇
  1978年   1429篇
  1977年   1150篇
  1976年   1131篇
  1975年   1166篇
  1974年   1526篇
  1973年   1612篇
  1972年   1585篇
  1971年   1515篇
  1970年   1409篇
  1969年   1266篇
  1967年   1095篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
271.
SDI Goals     
  相似文献   
272.
Stairs RA 《Science (New York, N.Y.)》1987,238(4834):1634-1635
  相似文献   
273.
An outbreak of arsenic poisoning occurred in which most of a 200 cow dairy herd were affected and six died. The source of the arsenic was naturally occurring arsenic pyrites from the Waiotapu Stream, near Rotorua. Arsenic levels in the nearby soil were as high as 6618 ppm. There was little evidence to suggest that treatment affected the course of the disease. Haematology was of little use in diagnosis, post-mortem signs were not always consistent and persistence of the element in the liver appeared short. Control of further outbreaks have been based on practical measures to minimise the intake of contaminated soil and free laying water by the stock.  相似文献   
274.
275.
276.
277.
It is proposed that just as the stethoscope and thermometer are fundamental tools for individual medicine, production and health recording systems are fundamental tools for effective population medicine. Treatment and control of clinical diseases as the primary objective is no longer considered appropriate for livestock population. Disease in populations now describes a deviation between what is happening and what is expected to happen. This redefinition of disease implies that it is of multifactorial origin and thus a different problem solving approach must be implemented. Therefore, a swine enterprise must be considered as a system, a set of interdependent components continuously interacting to produce pork. As a system, it is characterized by certain properties: change, environment, counterintuitive behavior, drift to low performance, interdependency, and organization. A redefinition of diseases implies also that they are not only “treated” but managed. Management consists of planning, monitoring, evaluation, and analysis. For this process to be implemented successfully, a goal-directed recording system providing a farm-based infrastructure for problem solving is essential. Clinical problem solving (diagnosis) is thus based on epidemiological and demographic methods.  相似文献   
278.
Outbreaks of infection due to a parapoxvirus were reported on eight New Zealand deer farms. Scabby lesions were seen variably on the muzzle, lips, face, ears and neck of red deer (Cervus elaphus) with morbidity rates reaching 100%. On three farms multifocal lesions were also present on the velvet. Deaths were reported on two properties where the lesions were extensive and secondary bacterial infections had occurred. On one of these farms multifactorial disease was suspected. Poxvirus particles were seen by negative contrast electron microscopy in scab material from all eight properties. Morphologically the deer virus resembled a parapoxvirus, but restriction endonuclease analysis showed its DNA fragment patterns were distinct from those of orf (contagious ecthyma) virus.  相似文献   
279.
Blood samples from 433 periparturient recumbent cows submitted by veterinary practitioners to Ruakura Animal Health Laboratory during 1983 and 1984 were analysed and results related to whether cows recovered, died or were euthanased. Generally cows were sampled only once and the time varied from 15 minutes to 20 days after becoming recumbent. During 1983 serum calcium, magnesium, phosphorus, creatine phosphokinase (CK), aspartate amino transferase (AST), glutamate dehydrogenase (GDH), gamma glutamyl transferase (GGT) were analysed. In 1984 serum urea, creatinine, fibrinogen and haematological examination (haemoglobin, haematocrit, total and differential white cell counts) were added to the panel. Overall 39% of cows recovered, 30% died and 32% were destroyed. Precalving cows had 111% more deaths and 7% less survivors than postcalving recumbent cows (P<0.1). There was little difference (3%) in euthanasia prevalence. Tests that were most useful in predicting a lack of recovery were serum urea and muscle enzymes. Using these tests and duration of recumbency when sampled a model was produced to predict the probability of recovery from 254 cases.  相似文献   
280.
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