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   71445篇
  免费   4075篇
  国内免费   34篇
林业   3310篇
农学   2539篇
基础科学   478篇
  8769篇
综合类   11494篇
农作物   2596篇
水产渔业   3694篇
畜牧兽医   36971篇
园艺   923篇
植物保护   4780篇
  2018年   1067篇
  2017年   1138篇
  2016年   1063篇
  2015年   921篇
  2014年   1154篇
  2013年   2655篇
  2012年   2091篇
  2011年   2502篇
  2010年   1700篇
  2009年   1763篇
  2008年   2625篇
  2007年   2385篇
  2006年   2358篇
  2005年   2151篇
  2004年   2217篇
  2003年   2200篇
  2002年   2063篇
  2001年   2383篇
  2000年   2389篇
  1999年   1938篇
  1998年   924篇
  1997年   829篇
  1996年   788篇
  1995年   868篇
  1994年   846篇
  1993年   772篇
  1992年   1531篇
  1991年   1555篇
  1990年   1670篇
  1989年   1514篇
  1988年   1464篇
  1987年   1349篇
  1986年   1388篇
  1985年   1347篇
  1984年   1136篇
  1983年   1030篇
  1982年   635篇
  1979年   1006篇
  1978年   798篇
  1977年   721篇
  1976年   677篇
  1975年   723篇
  1974年   770篇
  1973年   835篇
  1972年   808篇
  1971年   753篇
  1970年   733篇
  1969年   747篇
  1967年   661篇
  1966年   637篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
997.
998.
A study was conducted to assess the combined effect of heat stress and nutritional restriction on growth and reproductive performances in Malpura rams. Twenty‐eight adult Malpura rams (average body weight (BW) 66.0 kg) were used in this study. The rams were divided into four groups: CON (n = 7; control), HES (n = 7; heat stress), NUS (n = 7; nutritional stress) and COS (n = 7; combined stress). The study was conducted for a period of 2 months. CON and HES rams had ad libitum access to their feed while NUS and COS rams were under restricted feed (30% intake of CON rams) to induce nutritional stress. The HES and COS rams were kept in climatic chamber at 42 °C and 55% relative humidity for 6 h a day between 10 : 00 h and 16 : 00 h to induce heat stress. Body weight increased significantly (p < 0.05) in CON as compared to NUS and COS. When compared within groups, scrotal width morning, scrotal width afternoon, scrotal circumference morning and scrotal circumference afternoon were significantly (p < 0.05) larger in CON while smaller in COS rams. The higher testicular length was recorded both during morning (p < 0.05) and afternoon (p < 0.01) in COS rams while the lowest in NUS rams. The highest plasma testosterone concentration was recorded in CON and lowest in COS rams. Semen volume and mass motility also differed significantly (p < 0.05) between the groups. The highest semen volume and mass motility was recorded in CON and NUS while lowest in both HES and COS rams. It can be concluded from this study that when two stressors occur simultaneously, they may have severe impact on reproductive performance of rams.  相似文献   
999.
This study was conducted to investigate the effect of spray‐dried porcine plasma (SDPP) in broiler chickens under Salmonella sofia disease challenge. The experiment comprised five starter diets: positive control (no supplement), diet supplemented with in‐feed antibiotics (IFA; salinomycin 0.05% + zinc bacitracin 0.033%) and diets supplemented with SDPP at 10 or 20 g/kg diet. All four of these groups were challenged with Ssofia, while a fifth group was unchallenged and used as the negative control. The experimental diets were fed to 14 days; then, the birds were switched to commercial‐type grower and finisher diets. Oral inoculation of the challenged groups with Ssofia occurred on day 8, 10 and 12. Body weight was significantly higher in the birds fed diets containing IFA and SDPP than in the challenged control group, but it was only significant in starter and grower phases. In general, there was an improvement in the weights of the immune‐related organs, but it was only significant for the weight of the bursa of SDPP‐fed birds at 13 days. At day 13, blood potassium content was lower and the concentrations of IgG and IgM tended to be lower in the birds fed on low‐SDPP starter diets than those of the other groups. There were significant differences in the concentration of lactic acid in the ileum and acetic acid, formic acid, butyric acid and propionic acid in the caeca. Inclusion of SDPP to the starter diets of broiler chicks had positive effects on broiler performance, immunity and gut health during exposure to highly pathogenic conditions.  相似文献   
1000.
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