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   614篇
  免费   25篇
  国内免费   14篇
林业   29篇
农学   13篇
基础科学   4篇
  57篇
综合类   188篇
农作物   50篇
水产渔业   20篇
畜牧兽医   253篇
园艺   14篇
植物保护   25篇
  2023年   9篇
  2022年   6篇
  2021年   9篇
  2020年   5篇
  2019年   10篇
  2018年   7篇
  2017年   13篇
  2016年   16篇
  2015年   17篇
  2014年   19篇
  2013年   30篇
  2012年   26篇
  2011年   27篇
  2010年   24篇
  2009年   19篇
  2008年   21篇
  2007年   21篇
  2006年   23篇
  2005年   22篇
  2004年   21篇
  2003年   17篇
  2002年   16篇
  2001年   10篇
  2000年   10篇
  1999年   14篇
  1998年   10篇
  1997年   5篇
  1996年   14篇
  1995年   4篇
  1994年   12篇
  1993年   4篇
  1992年   13篇
  1991年   12篇
  1990年   9篇
  1989年   14篇
  1988年   6篇
  1986年   9篇
  1985年   10篇
  1981年   4篇
  1971年   4篇
  1966年   6篇
  1960年   3篇
  1959年   3篇
  1958年   6篇
  1954年   3篇
  1944年   4篇
  1941年   3篇
  1936年   3篇
  1904年   4篇
  1903年   3篇
排序方式: 共有653条查询结果,搜索用时 31 毫秒
71.
Pheochromocytoma in the dog   总被引:1,自引:0,他引:1  
  相似文献   
72.
73.
74.
Two infectious bursal disease viruses (IBDVs)--a cell-culture-adapted chicken strain designated Edgar strain and a recent isolate from turkeys in Missouri--were used to assay sera from 10 Iowa turkey flocks collected between 1 and 16 weeks of age. The two viruses were serologically distinct in cross-neutralization tests. For all flocks, a similar serologic pattern was found consisting of (1) low maternal antibody titers to turkey IBDV and occasionally to Edgar strain IBDV between 1 and 3 weeks of age, (2) a period of very low or no detectable titers between 3 and 7 weeks of age, and (3) sharply rising high titers to turkey IBDV with low titers to Edgar IBDV beginning at 5 to 8 weeks of age. These findings indicate that infection with IBDV of the serotype represented in this study by the turkey isolate is common in Iowa turkey flocks, whereas infection with IBDV represented by Edgar strain is uncommon. Infection occurred between 3 and 7 weeks of age during the late brooding period or after birds had been moved to an intermediate growing facility. All flocks developed complicated respiratory disease with excessive mortality caused by Escherichia coli septicemia, typically between 3 and 6 weeks of age. Although there was a temporal relationship between IBDV infection and respiratory disease, the possible role of IBDV in the process is unknown.  相似文献   
75.
76.
Reply     
  相似文献   
77.
78.
海西东部及环青海湖地区40多年的气候变化研究   总被引:11,自引:3,他引:8  
利用1961~2004年地面观测资料,分析了海西东部及环青海湖地区年、季气候变化的特征和规律。结果表明,海西东部及环青海湖40多年来年季平均气温平均增温幅度为0.3~0.6℃,平均最低和最高气温多数季节增温具有非对称性。并且20世纪90年代四季增暖最为明显。夏季和冬季降水略有增加,而过渡季节降水变化基本呈减少趋势。年均和秋、冬、春、夏四季的气温变化倾向率均为正值.分别为0.48、0.57、0.692、0.337、0.373℃/10a。冬、夏季降水变化的倾向率为0.442、4.672mm/10a;而秋、春季了水变化的倾向率为-2.304、-0.022mm/10a。冬季降水量和累计积雪量的缓慢增加容易导致该地区地表积雪的积累,极易形成雪灾或低温冻害。春季气温升高、降水减少。干旱发生的频次将增加;秋、冬季气温上升幅度比较大.将有利于病虫害的越冬、繁殖,加重病虫害对农牧业生产的危害程度。  相似文献   
79.
The three objectives of this study were to 1) test for the existence of beef tenderness markers in the CAPN1 gene segregating in Brahman cattle; 2) test existing CAPN1 tenderness markers in indicus-influenced crossbred cattle; and 3) produce a revised marker system for use in cattle of all subspecies backgrounds. Previously, two SNP in the CAPN1 gene have been described that could be used to guide selection in Bos taurus cattle (designated Markers 316 and 530), but neither marker segregates at high frequency in Brahman cattle. In this study, we examined three additional SNP in CAPN1 to determine whether variation in this gene could be associated with tenderness in a large, multisire American Brahman population. One marker (termed 4751) was associated with shear force on postmortem d 7 (P < 0.01), 14 (P = 0.015), and 21 (P < 0.001) in this population, demonstrating that genetic variation important for tenderness segregates in Bos indicus cattle at or near CAPN1. Marker 4751 also was associated with shear force (P < 0.01) in the same large, multisire population of cattle of strictly Bos taurus descent that was used to develop the previously reported SNP (referred to as the Germplasm Evaluation [GPE] Cycle 7 population), indicating the possibility that one marker could have wide applicability in cattle of all subspecies backgrounds. To test this hypothesis, Marker 4751 was tested in a third large, multisire cattle population of crossbred subspecies descent (including sire breeds of Brangus, Beefmaster, Bonsmara, Romosinuano, Hereford, and Angus referred to as the GPE Cycle 8 population). The highly significant association of Marker 4751 with shear force in this population (P < 0.001) confirms the usefulness of Marker 4751 in cattle of all subspecies backgrounds, including Bos taurus, Bos indicus, and crossbred descent. This wide applicability adds substantial value over previously released Markers 316 and 530. However, Marker 316, which had previously been shown to be associated with tenderness in the GPE Cycle 7 population, also was highly associated with shear force in the GPE Cycle 8 animals (P < 0.001). Thus, Marker 316 may continue to be useful in a variety of populations with a high percentage of Bos taurus backgrounds. An optimal marker strategy for CAPN1 in many cases will be to use both Markers 316 and 4751.  相似文献   
80.
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