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   182008篇
  免费   10026篇
  国内免费   94篇
林业   7896篇
农学   6241篇
基础科学   1197篇
  23277篇
综合类   27279篇
农作物   6862篇
水产渔业   9397篇
畜牧兽医   95410篇
园艺   2438篇
植物保护   12131篇
  2019年   1741篇
  2018年   2769篇
  2017年   3077篇
  2016年   2855篇
  2015年   2456篇
  2014年   3079篇
  2013年   7435篇
  2012年   5480篇
  2011年   6578篇
  2010年   4517篇
  2009年   4592篇
  2008年   6657篇
  2007年   6310篇
  2006年   5996篇
  2005年   5476篇
  2004年   5466篇
  2003年   5478篇
  2002年   5087篇
  2001年   6105篇
  2000年   6012篇
  1999年   4927篇
  1998年   2061篇
  1997年   2020篇
  1996年   1835篇
  1995年   2177篇
  1994年   1891篇
  1993年   1863篇
  1992年   3786篇
  1991年   3950篇
  1990年   3979篇
  1989年   3893篇
  1988年   3575篇
  1987年   3527篇
  1986年   3471篇
  1985年   3326篇
  1984年   2737篇
  1983年   2465篇
  1982年   1619篇
  1979年   2391篇
  1978年   1897篇
  1977年   1671篇
  1976年   1577篇
  1975年   1722篇
  1974年   1955篇
  1973年   2064篇
  1972年   1980篇
  1971年   1777篇
  1970年   1777篇
  1969年   1737篇
  1967年   1502篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
331.
332.
333.
334.
335.
Two cats with chronic eosinophilic skin disease were investigated. The clinical investigation of the skin disease in one cat was limited and inflammatory bowel disease was diagnosed post mortem. A history of weight loss and a palpably thickened bowel in the second cat suggested concurrent gastrointestinal disease. Diagnosis of inflammatory bowel disease was confirmed on biopsy. Treatment with azathioprine and methylprednisolone acetate resolved the signs of gastrointestinal disease, the pruritus and 95% of the skin lesions. The concurrence of eosinophilic papulocrustous dermatitis and eosinophilic bowel disease raises the possibility of their being linked bv a common aetiology or pathophysiology.  相似文献   
336.
1. ISA Brown hens were housed as groups of 4 from 18 to 72 weeks in 24 cages 450 mm deep, each with a softwood perch of rectangular cross‐section fitted across the rear. There were 4 treatments, each with 6 cages: cage widths and perch lengths were 480, 520, 560 or 600 mm.

2. Daytime perching did not differ significantly between the treatments. At night, over the whole year, 81% of birds in the 480 mm cages and 86% in the 520 mm cages roosted on the perch. This figure reached about 95% in the 560 and 600 mm cages, significantly more at most ages than in the 480 mm cages.

3. Feather damage was slightly less, but claw problems slightly more, in the 2 wider treatments than in the 2 narrower treatments. Birds in the wider cages were calmer when approached or handled by humans than those in the narrower cages. This may have been associated with variation in space allowance between the treatments.

4. There was a trend for lower production in the 480 mm cages than in the other treatments which may have been associated with the reduced feeding space in this treatment. There were few other treatment differences in production traits.

5. The balance of the evidence from this study is that when perches are provided in laying cages for medium weight hybrids, 140 mm of perch space per hen is adequate. For the amelioration of a number of the welfare problems of conventional cages, provision of perches should be combined with other modifications.  相似文献   

337.
338.
339.
340.
A model is proposed for the East Coast Magnetic Anomaly that, for the first time, incorporates an observed basement feature-a normal fault that consistently lies below the landward flank of the anomaly. The East Coast Magnetic Anomaly is similar to slope anomalies found over passive continental margins in many parts of the world. Thus the proposed model can be used to interpret slope anomalies in general.  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