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   197057篇
  免费   11230篇
  国内免费   780篇
林业   7720篇
农学   6055篇
基础科学   1569篇
  23432篇
综合类   36801篇
农作物   7430篇
水产渔业   9547篇
畜牧兽医   100373篇
园艺   2633篇
植物保护   13507篇
  2019年   1832篇
  2018年   2632篇
  2017年   2964篇
  2016年   2729篇
  2015年   2518篇
  2014年   2934篇
  2013年   7294篇
  2012年   5633篇
  2011年   6972篇
  2010年   4524篇
  2009年   4424篇
  2008年   6601篇
  2007年   6321篇
  2006年   5970篇
  2005年   5603篇
  2004年   5356篇
  2003年   5334篇
  2002年   5176篇
  2001年   5969篇
  2000年   5866篇
  1999年   4734篇
  1998年   1944篇
  1997年   1908篇
  1995年   2192篇
  1994年   1976篇
  1993年   1899篇
  1992年   3935篇
  1991年   4228篇
  1990年   4262篇
  1989年   4195篇
  1988年   3844篇
  1987年   3991篇
  1986年   4114篇
  1985年   3862篇
  1984年   3302篇
  1983年   2918篇
  1982年   1991篇
  1981年   1874篇
  1979年   2944篇
  1978年   2419篇
  1977年   2045篇
  1976年   1913篇
  1975年   2020篇
  1974年   2683篇
  1973年   2694篇
  1972年   2632篇
  1971年   2410篇
  1970年   2254篇
  1969年   2101篇
  1967年   1798篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
36.
In planning forest management we have the considerable advantagesin Great Britain of an almost clean sheet, fast growth, amplespecies, resourceful engineers, and inexhaustable markets. Wemust organize so that it pays to grow trees. The kind of timberwanted is discussed; how it should be presented for sale; annualquantities needed by an efficient sawmill; and the level ofprices to be paid.  相似文献   
37.
38.
Two experiments were conducted to study the effect on nutrient loss and feeding value of making hay by different means, using a barn-drier, a forage-harvester, a crimper and conventional tedding. Both forage-harvesting and crimping of the herbage significantly increased the rate of drying, compared with tedding alone. In Exp. 2 this effect enabled the crimped and forage-harvested hays to be baled for storage 3 days earlier than the tedded hay. The use of the forage-harvester significantly reduced the yield of herbage compared with conventional mowing. Nutrient losses from cutting until storage were highest for the forage-harvested hays, the loss of dry matter between cutting and storage in the forage-harvested hays being 39·9 and 19·3%, respectively, in Expt 1 and 2 with corresponding losses in the conventionally made hays of 7·1% and 9·3%. Crimping the hay resulted in higher nutrient losses than tedding. In Expt 2 there was a loss of dry matter of 17·5% in the conventionally made hay during an 18-week storage period, compared with 3·6% in barn-dried hay, 10·8% in forage-harvested hay and 8·8% in crimped hay.
In Expt 2, in which digestibility determinations were made, conservation decreased the total digestible nutrients and starch equivalent in all treatments. The use of the barn-drier gave the most efficient conservation of total digestible nutrients, followed by the crimped, forage-harvested and conventional treatments in that order. The starch equivalent values of hays made from the same sward were 43·0 when barn-dried, 39·8 when crimped, 38·6 after forage-harvesting and 31·6 after tedding.  相似文献   
39.
40.
J. Ruinard 《Euphytica》1964,13(1):19-23
In a previous publication about the selection of cacao in West New Guinea, directions have been given on the production determination of individual trees. It was tacitly assumed that the pod weight of a given tree, although variable, would not change systematically with time. However, new data brought to light that this assumption was wrong. It was established that during the main harvest the average pod weight was considerably lower than during the remaining months. But as these changes of weight appeared to have no influence on the quotient pulp weight/pod weight, the method of production determination mentioned needs no revision.Present address: University of Science and Technology, Kumasi, Ghana.  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