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   68796篇
  免费   3094篇
  国内免费   50篇
林业   2817篇
农学   1952篇
基础科学   500篇
  7034篇
综合类   15163篇
农作物   2705篇
水产渔业   2581篇
畜牧兽医   34236篇
园艺   761篇
植物保护   4191篇
  2018年   625篇
  2017年   658篇
  2016年   653篇
  2014年   670篇
  2013年   2273篇
  2012年   1520篇
  2011年   1810篇
  2010年   1088篇
  2009年   1051篇
  2008年   1774篇
  2007年   1717篇
  2006年   1653篇
  2005年   1674篇
  2004年   1599篇
  2003年   1636篇
  2002年   1580篇
  2001年   1689篇
  2000年   1650篇
  1999年   1354篇
  1997年   588篇
  1995年   649篇
  1994年   607篇
  1993年   603篇
  1992年   1388篇
  1991年   1482篇
  1990年   1550篇
  1989年   1572篇
  1988年   1475篇
  1987年   1422篇
  1986年   1451篇
  1985年   1431篇
  1984年   1202篇
  1983年   1043篇
  1982年   742篇
  1981年   725篇
  1980年   677篇
  1979年   1167篇
  1978年   938篇
  1977年   835篇
  1976年   784篇
  1975年   881篇
  1974年   1143篇
  1973年   1081篇
  1972年   1158篇
  1971年   1105篇
  1970年   1039篇
  1969年   892篇
  1968年   725篇
  1967年   858篇
  1966年   704篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
GREIG  B. J. W.; LOW  J. D. 《Forestry》1975,48(2):147-163
Stump removal was found to singnificantly reduce killing byFomes annosus in second rotation crops of pine. Poisoning andgirdling of trees prior to felling and also stump poisoningfailed to control the disease. In this experiment no significantdifferences were detected in the susceptibility of Scots andCorsican pine to attack. Increasing periods of delay beforereplanting resulted in less mortality. An equation is presented,based on factors of the first rotation crop which may be usedto predict losses likely to occur when a site is replanted.Root attack by F. annosus results in reduced growth and yieldas well as mortality. The results from the experiment are discussed in trems of themangement of pine crops attacted by F. annosus in Theford Chase.  相似文献   
92.
93.
94.
95.
96.
97.
98.
Summary Richard Hakluyt (ca. 1553–1616) collected together and published first-hand accounts of the voyages of English seamen, including several 16th century voyages to South America. These accounts provide some of the earliest published references to the potato, but unfortunately they make no mention of its introduction into Europe.  相似文献   
99.
100.
A survey, covering some 140 fields, totalling 1540 acres, in Kent was conducted in 1961 on the effect of different methods of management on yields of perennial ryegrass and white clover seed. The main results were: (a) the majority of seed growers harvested seed from short-term leys and only a limited acreage of permanent pasture was used for producing seed. Yields of both ryegrass and clover seed were considerably higher on the younger leys; (b) the highest seed yields in 1961 were obtained from fields where sheep grazing was stopped on 24 May. However, a large number of growers continued sheep grazing well after this date: (c) mechanical defoliation, especially when used to supplement sheep grazing, proved an effective method for producing high yields of clover seed; (d) honey bees are important in increasing seed yields, particularly on recently sown leys; (e) combine harvesting from the swath was the most common method of harvesting and no instance of the use of tripods was reported. Seed yields from baling methods were generally low, but direct combining produced a high average yield of clover seed. From these results it was concluded that there was much scope for raising the general level of clover seed yields, especially by giving greater attention to details of management.  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