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   6037篇
  免费   433篇
  国内免费   3篇
林业   166篇
农学   126篇
基础科学   50篇
  645篇
综合类   1468篇
农作物   193篇
水产渔业   227篇
畜牧兽医   3346篇
园艺   62篇
植物保护   190篇
  2020年   55篇
  2018年   79篇
  2017年   72篇
  2016年   81篇
  2015年   60篇
  2014年   103篇
  2013年   236篇
  2012年   175篇
  2011年   200篇
  2010年   114篇
  2009年   132篇
  2008年   210篇
  2007年   205篇
  2006年   208篇
  2005年   183篇
  2004年   184篇
  2003年   193篇
  2002年   173篇
  2001年   155篇
  2000年   175篇
  1999年   150篇
  1998年   68篇
  1997年   64篇
  1996年   53篇
  1995年   55篇
  1992年   131篇
  1991年   127篇
  1990年   135篇
  1989年   126篇
  1988年   101篇
  1987年   98篇
  1986年   139篇
  1985年   153篇
  1984年   126篇
  1983年   115篇
  1982年   72篇
  1981年   83篇
  1980年   65篇
  1979年   110篇
  1978年   98篇
  1977年   59篇
  1976年   50篇
  1975年   54篇
  1974年   57篇
  1973年   77篇
  1972年   77篇
  1971年   67篇
  1970年   56篇
  1969年   62篇
  1968年   62篇
排序方式: 共有6473条查询结果,搜索用时 15 毫秒
81.
82.
The dominant large-scale pattern in the clouds of Venus has been described as a "gamma" or "Psi" and tentatively identified by earlier workers as a Kelvin wave. A detailed calculation of linear wave modes in the Venus atmosphere verifies this identification. Cloud feedback by infrared heating fluctuations is a plausible excitation mechanism. Modulation of the large-scale pattern by the wave is a possible explanation for the Y. Momentum transfer by the wave could contribute to sustaining the general circulation.  相似文献   
83.
84.
1. An experiment was conducted with laying hens to determine to what extent sweet white lupins (Lupinus albus, cv Buttercup) could be used as a protein source in their diets.

2. Twenty five individually caged 20 week‐old Hisex laying hens were used per treatment. The hens were housed in a convection house for the duration of the study which lasted 52 weeks. Two diets were formulated, one containing 300 g sweet lupins/kg and the other containing sunflower oil cake and fish meal as protein sources. These diets were blended to obtain seven diets with lupin inclusion rates of 0, 50, 100, 150, 200, 250 and 300 g/k.

3. Results indicated that up to 300 g lupins/kg diet can be fed to Hisex laying hens without a significant effect on egg production, egg mass, efficiency of food utilisation, egg shell thickness, Haugh units or yolk colour. Food intake was however, significantly (P<0.05) positively correlated with lupin inclusion rates.  相似文献   

85.
An improved serum ferritin assay for canine serum has been developed. It uses two monoclonal antibodies in a sandwich arrangement. Serum ferritin can be determined on undiluted canine sera with this assay. The recovery of ferritin added to canine serum ranged from 98 to 106%, the within-assay coefficient of variability was 3.3 to 4.5%, and the assay-to-assay variability was 9.8 to 10.2%. Serum ferritin from 61 apparently healthy dogs had a geometric mean of 252 ng/ml, with a range of 80 ng/ml to 800 ng/ml.  相似文献   
86.
It is important for practitioners and owners to be aware of the risk associated with an open herd. This article has discussed some of the infectious diseases that might be inadvertently introduced. Many others--including most exotic diseases and some that are regulated by governmental agencies, such as tuberculosis and brucellosis--have been omitted. It should be obvious that a simple health certificate is an inadequate guarantee of freedom from infections. Instead, producers should be prepared to invest both time and money in evaluating the health status of the herd of origin. Some of the diseases discussed, such as foot rot, cause tremendous financial losses. Others, such as pinkeye, can be easily "lived with." The point to be made is that producers should consider all these and other diseases and then make informed decisions based on the probable cost of these diseases if they became established in the herd.  相似文献   
87.
88.
89.
90.
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