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   49115篇
  免费   2696篇
  国内免费   33篇
林业   1707篇
农学   1661篇
基础科学   253篇
  5848篇
综合类   8224篇
农作物   1548篇
水产渔业   2719篇
畜牧兽医   26409篇
园艺   575篇
植物保护   2900篇
  2019年   417篇
  2018年   779篇
  2017年   823篇
  2016年   750篇
  2015年   609篇
  2014年   752篇
  2013年   1754篇
  2012年   1356篇
  2011年   1698篇
  2010年   1163篇
  2009年   1105篇
  2008年   1689篇
  2007年   1600篇
  2006年   1507篇
  2005年   1386篇
  2004年   1399篇
  2003年   1376篇
  2002年   1190篇
  2001年   1913篇
  2000年   1984篇
  1999年   1498篇
  1998年   569篇
  1997年   500篇
  1996年   450篇
  1995年   612篇
  1994年   524篇
  1993年   459篇
  1992年   1152篇
  1991年   1211篇
  1990年   1178篇
  1989年   1097篇
  1988年   1056篇
  1987年   1081篇
  1986年   1035篇
  1985年   966篇
  1984年   803篇
  1983年   683篇
  1982年   421篇
  1981年   385篇
  1979年   636篇
  1978年   501篇
  1977年   441篇
  1976年   409篇
  1975年   453篇
  1974年   524篇
  1973年   509篇
  1972年   533篇
  1971年   450篇
  1970年   426篇
  1969年   465篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
85.
86.
87.
88.
Understanding insect movement and distribution is critical for developing an effective insect pest management protocol. Movement and distribution of adult Cryptolestes ferrugineus (Stephens) in response to nominal temperature differences of 5, 10, 15, and 20°C in 1- and 2-m horizontal columns filled with 12.5% moisture content wheat were studied in 24, 48, and 72 h of movement times. In the wheat columns without temperature differences, adults had a diffusion distribution pattern caused by their random movement. Adults showed bias movement to the warmer grain in wheat columns with temperature differences and preferred the warmer grain regardless of the magnitude of temperature differences in less than 24 h. Their distribution did not have significant differences among different movement times in 1- or 2-m columns. About 40% of adults moved to the warmer wheat located at 0.4 to 0.5 m in the 1 m column but did not move to the warmer wheat located at 0.9 to 1 m in the 2-m column. Therefore, length of grain column influenced detection of warmer grain by insects. Adults under different temperatures had a similar response as that under linear temperature gradients.  相似文献   
89.
Pituitaries were collected from late follicular phase (n = 5), mid-luteal phase (n = 5), and anestrous ewes (n = 4) to assess changes in intrapituitary LH heterogeneity at selected reproductive states. After homogenization, an aliquot of each pituitary extract was desalted by flow dialysis against water and chromtofocused on a pH 10.5 to 4.0 gradient. Concentrations of LH in pituitary extracts and chromatofocusing fractions were determined by RIA. The LH in pituitary extracts resolved into 13 isoforms during chromatofocusing, which were coded with letters beginning with the most basic isoform. Follicular and mid-luteal phase ewes exhibited similar distributions of intrapituitary LH among its isoforms. Relative to follicular and luteal phase ewes, anestrous ewes had lower percentages of isoforms D and E as well as higher percentages of isoforms G, H, J and K. Isoform F, the predominant molecular form of LH, constituted a similar percentage in all treatment groups (P > .05). Thus, the distribution of intrapituitary LH among its isoforms did not change significantly between the mid-luteal and follicular phases of the estrous cycle, but higher percentages of the weakly basic and acidic forms of LH were present during anestrus. These observations suggest that intrapituitary LH heterogeneity changes minimally throughout the estrous cycle of ewes during the breeding season.  相似文献   
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