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   144522篇
  免费   8309篇
  国内免费   117篇
林业   6493篇
农学   5021篇
基础科学   945篇
  19877篇
综合类   19276篇
农作物   5630篇
水产渔业   8096篇
畜牧兽医   75824篇
园艺   1997篇
植物保护   9789篇
  2021年   1241篇
  2020年   1414篇
  2019年   1656篇
  2018年   2632篇
  2017年   2909篇
  2016年   2699篇
  2015年   2289篇
  2014年   2822篇
  2013年   6315篇
  2012年   5027篇
  2011年   5834篇
  2010年   3895篇
  2009年   3894篇
  2008年   5684篇
  2007年   5459篇
  2006年   5037篇
  2005年   4612篇
  2004年   4451篇
  2003年   4475篇
  2002年   4069篇
  2001年   4894篇
  2000年   4777篇
  1999年   3855篇
  1998年   1504篇
  1997年   1495篇
  1996年   1370篇
  1995年   1639篇
  1994年   1352篇
  1993年   1376篇
  1992年   2804篇
  1991年   2940篇
  1990年   2894篇
  1989年   2933篇
  1988年   2642篇
  1987年   2630篇
  1986年   2572篇
  1985年   2445篇
  1984年   1985篇
  1983年   1740篇
  1982年   1170篇
  1979年   1678篇
  1978年   1311篇
  1977年   1160篇
  1975年   1171篇
  1974年   1382篇
  1973年   1491篇
  1972年   1404篇
  1971年   1221篇
  1970年   1255篇
  1969年   1159篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
882.
883.
One of the major challenges of melon (Cucumis melo L.) yield is the decrease of fruit yield and quality caused by soil diseases. Soil disinfection with methyl bromide (MB) has been used to prevent soil-borne diseases damage; however, use of MB is being restricted because this substance damages the ozone layer. Searching for new MB alternatives, field experiments were carried out in open fields in soils infested with Fusarium oxysporum f. sp. melonis, Olpidium bornovanus, and Melon Necrotic Spot Virus (MNSV) in Colima, Mexico, where melons had only been grown previously using soil fumigation with MB. Yield and quality of melon cultivar Cruiser F1 (Harris Moran seed company) grafted on two rootstocks of Cucurbita maxima Duchesne × Cucurbita moschata Duchesne (“RS841”; Séminis seed company and “Shintosa Camelforce”; Nunhens seed company) were evaluated during two consecutive years. Each experiment had five treatments, two of which with non-grafted plants at a density of 18,519 plants/ha, with and without MB fumigation. The other three treatments consisted of grafted plants in non-fumigated soil with plant densities of 14,815, 11,111, and 9260 plants/ha. The use of melon grafted on “RS841” and “Shintosa Camelforce” rootstocks significantly increased the average fruit weight and the total yield of melons in soil without the need for MB. Grafting may be considered an alternative to MB fumigation. With the use of grafted melon plants, planting density may be reduced by 60%, obtaining higher yields than those obtained from non-grafted plants grown on fumigated land. Fruits harvested from grafted plants had equal firmness than those harvested from non-grafted plants, without affecting the content of soluble solids.  相似文献   
884.
885.
886.
887.
888.
A brachycephalic dog was presented with an acute onset of retching and abdominal discomfort. The dog had a chronic history of stertor and exercise intolerance suggestive of brachycephalic airway obstructive syndrome. Radiographs were consistent with a Type II hiatal hernia. The dog was referred and within hours of admission became acutely painful and developed tympanic abdominal distension. A right lateral abdominal radiograph confirmed gastric dilatation and volvulus with herniation of the pylorus through the hiatus. An emergency exploratory coeliotomy was performed, during which the stomach was derotated, and an incisional gastropexy, herniorrhaphy and splenectomy were performed. A staphylectomy was performed immediately following the exploratory coeliotomy. The dog recovered uneventfully. Gastric dilatation and volvulus is a potentially life‐threatening complication that can occur in dogs with Type II hiatal hernia and should be considered a surgical emergency .  相似文献   
889.
A nitrogen (N) balance digestion trial was conducted to determine the protein requirement of collared peccaries (Pecari tajacu). In a 4 × 4 Latin square design, four captive adult male peccaries were fed four isoenergy diets containing four different levels of N (11.7, 16.3, 22.8, and 26.7 g N/kg of dry matter—DM). After 15 days of adaptation, a total collection of feces and urine was carried out for five consecutive days. Regression analyses between N intake and N in feces and urine allowed to calculate the metabolic fecal nitrogen (MFN = 2.3 g N/kg of dry matter intake—DMI) and daily endogenous urinary N (EUN = 185 mg N/kg0.75). Likewise, by regression analyses between consumption of nitrogen and the nitrogen balance (NB = N ingested ? N excreted, mg N/kg0.75), a daily requirement of 514 mg N/kg0.75 was calculated. Therefore, if food intake is unrestricted, collared peccaries require a minimum in their diet of about 5.4% crude protein on DM basis. These values are almost as low as those found for browsing and frugivorous wild ruminants, which reinforce the proposition that peccaries’ digestive physiology is nearer to that of domestic and wild ruminants than domestic pigs. This relatively low protein requirement of collared peccary and its great ability to digest protein reveal the relevance of the forestomach for the species on nitrogen/protein metabolism and allow the use of diets with lower crude protein levels than the commercial ones used for the domestic pig, which reduces feed costs.  相似文献   
890.
Two separate groups of nine-week-old specific pathogen free cockerels maintained in isolation were infected with a field strain of infectious laryngotracheitis (ILT) virus, either by intratracheal or combined intranasal and supraconjunctival inoculation. Birds were monitored for virus shedding from five sites on alternate days during the acute phase and three times weekly until week 17. They were then treated with cyclophosphamide on three consecutive days and thereafter swabbed daily. During the acute phase clinical signs were observed and virus was recovered from ocular and nasal sites for up to six to eight days. Initially after the acute phase no virus could be detected. However, from the seventh week after infection intermittent, apparently spontaneous shedding was detected in four of five birds in each group. There was no clear effect of cyclophosphamide treatment on re-excretion patterns, possibly because of the high levels of virus shedding already occurring. Thus, a carrier state for ILT virus has been demonstrated experimentally in live clinically recovered birds.  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