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   134890篇
  免费   7146篇
  国内免费   81篇
林业   6424篇
农学   4476篇
基础科学   806篇
  15386篇
综合类   24500篇
农作物   5250篇
水产渔业   6474篇
畜牧兽医   68535篇
园艺   1703篇
植物保护   8563篇
  2018年   1752篇
  2017年   1871篇
  2016年   1732篇
  2015年   1536篇
  2014年   1890篇
  2013年   4830篇
  2012年   3392篇
  2011年   4117篇
  2010年   2813篇
  2009年   2781篇
  2008年   4229篇
  2007年   4033篇
  2006年   3839篇
  2005年   3606篇
  2004年   3598篇
  2003年   3610篇
  2002年   3385篇
  2001年   4126篇
  2000年   4148篇
  1999年   3389篇
  1998年   1470篇
  1997年   1402篇
  1995年   1513篇
  1994年   1351篇
  1993年   1342篇
  1992年   2743篇
  1991年   2826篇
  1990年   3008篇
  1989年   2835篇
  1988年   2675篇
  1987年   2578篇
  1986年   2663篇
  1985年   2609篇
  1984年   2166篇
  1983年   1958篇
  1982年   1281篇
  1979年   2081篇
  1978年   1629篇
  1977年   1436篇
  1976年   1363篇
  1975年   1506篇
  1974年   1815篇
  1973年   1885篇
  1972年   1872篇
  1971年   1781篇
  1970年   1689篇
  1969年   1621篇
  1968年   1347篇
  1967年   1435篇
  1966年   1348篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
161.
Above ground production of a typical Cortaderia pilosa dominant sward in the Falkland Islands was estimated over one growing season by summing significant positive increments in DM production of various sward components and by sequential cutting to ground level. The standing crop was characterized by a high proportion of standing dead matter at all times of the year. Net herbage production was estimated as 2200 kg ha-1 and 1440 kg ha-1 by the 'difference' and "sequential culling" techniques, respectively. The pattern of leaf growth was determined on another site by regular linear measurements of a population of physiologically similar C. pilosa leaves. There was very little early season growth and most of the DM was produced in a short period in the middle part of the growing season. The poor early season growth was attributed to adverse climatic conditions. A significant increase in green matter digestibility in October and November was masked by the low digestibility and high contribution to the overall DM by the standing dead component of the herbage.
The implications of these findings are briefly discussed in relation to the increased utilization of C. pilosa by improved pasture management, including burning and possibly reseeding areas with improved species. Tissue turnover studies combined with more knowledge of sheep nutrition cycles would enable grazing systems to be developed on a sounder basis than previously.  相似文献   
162.
163.
The medical records from 95 cases of coxofemoral luxation in dogs and cats were reviewed. Unilateral craniodorsal luxation was most common, (78.1% of dogs, 72.7% of cats). Trauma from being struck by an automobile was the most frequent cause (59.0%). Treatment was closed (manual) or open (surgical) reduction. The failure rate following single closed reduction was 64.8%. The surgical reduction procedure included capsular repair (capsulorrhaphy) via a craniolateral approach to the hip or via trochanteric osteotomy or gluteal tenotomy. The success rate following reduction via the craniolateral approach was 82%; no failure was recorded with trochanteric transposition, but reluxa-tion followed the single gluteal tenotomy. The Ehmer sling was the most common external fixation and was kept in place an average of 12.5 days. Thirty-three animals were available for follow-up, and no difference was recorded in limb function between the two groups of animals treated by closed vs surgical reduction. Patients with degenerative joint disease at the time of luxation were less likely to be successfully reduced; 64.3% of these animals were eventually treated by femoral head and neck excision. Thirty-eight patients had associated major injuries. Long-term follow-up results were better in those patients with concomitant orthopedic injuries than in those without other injuries.  相似文献   
164.
Abstract –  Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974–1991 and in summer (late June to early July) in 1992–2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series.  相似文献   
165.
166.
167.
168.
169.
170.
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