全文获取类型
| 收费全文 | 139959篇 |
| 免费 | 8260篇 |
| 国内免费 | 654篇 |
专业分类
| 林业 | 5880篇 |
| 农学 | 4494篇 |
| 基础科学 | 1055篇 |
| 16667篇 | |
| 综合类 | 26201篇 |
| 农作物 | 5320篇 |
| 水产渔业 | 6519篇 |
| 畜牧兽医 | 71940篇 |
| 园艺 | 1833篇 |
| 植物保护 | 8964篇 |
出版年
| 2019年 | 1376篇 |
| 2018年 | 2025篇 |
| 2017年 | 2327篇 |
| 2016年 | 2083篇 |
| 2015年 | 1928篇 |
| 2014年 | 2253篇 |
| 2013年 | 5095篇 |
| 2012年 | 4254篇 |
| 2011年 | 5134篇 |
| 2010年 | 3447篇 |
| 2009年 | 3340篇 |
| 2008年 | 4839篇 |
| 2007年 | 4642篇 |
| 2006年 | 4212篇 |
| 2005年 | 4021篇 |
| 2004年 | 3687篇 |
| 2003年 | 3864篇 |
| 2002年 | 3603篇 |
| 2001年 | 4106篇 |
| 2000年 | 4137篇 |
| 1999年 | 3239篇 |
| 1998年 | 1383篇 |
| 1997年 | 1356篇 |
| 1995年 | 1449篇 |
| 1994年 | 1285篇 |
| 1993年 | 1269篇 |
| 1992年 | 2661篇 |
| 1991年 | 2973篇 |
| 1990年 | 2887篇 |
| 1989年 | 2841篇 |
| 1988年 | 2670篇 |
| 1987年 | 2674篇 |
| 1986年 | 2774篇 |
| 1985年 | 2538篇 |
| 1984年 | 2220篇 |
| 1983年 | 1885篇 |
| 1982年 | 1330篇 |
| 1979年 | 2007篇 |
| 1978年 | 1569篇 |
| 1977年 | 1405篇 |
| 1976年 | 1385篇 |
| 1975年 | 1444篇 |
| 1974年 | 1859篇 |
| 1973年 | 1859篇 |
| 1972年 | 1793篇 |
| 1971年 | 1670篇 |
| 1970年 | 1637篇 |
| 1969年 | 1554篇 |
| 1968年 | 1276篇 |
| 1967年 | 1414篇 |
排序方式： 共有10000条查询结果，搜索用时 140 毫秒
991.
Wilen L 《Science (New York, N.Y.)》1993,259(5100):1469
992.
Scuderi LA 《Science (New York, N.Y.)》1993,259(5100):1433-1436
Tree ring data have been used to reconstruct the mean late-season (June through January) temperature at a timberline site in the Sierra Nevada, California, for each of the past 2000 years. Long-term trends in the temperature reconstruction are indicative of a 125-year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records. The results indicate that both the warm intervals during the Medieval Warm Epoch ( approximately A.D. 800 to 1200) and the cold intervals during the Little Ice Age ( approximately A.D. 1200 to 1900) are closely associated with the 125-year period. Significant changes in the phase of the 125-year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior. 相似文献
993.
994.
995.
Vermeij GJ 《Science (New York, N.Y.)》1993,260(5114):1603-1604
996.
997.
Elderly migration and development in small communities 总被引：1，自引：0，他引：1
"This paper develops a conceptual model of the process of community change [in the United States] in response to elderly inmigration. Analysis of intra-regional variation in elderly migration patterns in Appalachia, and synthesis of an emergent literature on the benefits and costs of attracting elderly migrants, serve as a backdrop for case studies, based on field observations and interviews, of three contrasting Appalachian communities at different stages of development as retirement destinations." 相似文献
998.
999.
1. Ileal endogenous amino acid losses were determined in broiler chickens and in cannulated cross‐bred layer strain cockerels using either a nitrogen‐free diet, regression analysis or a 48 h fast.
2. Endogenous amino acid flows to the ileum in fasted cockerels were significantly lower than those obtained both by feeding the nitrogen‐free diet, and from regression analysis in either broilers or cockerels. Regression analysis gave the highest flows.
3. The apparent digestibility coefficients of amino acids in a diet containing 200 g/kg crude protein were lower in broilers (0.84) than in cockerels (0.88). When corrected, by regression analysis, for the contribution of endogenous amino acids, the true digestibility coefficients became 0.90 and 0.92 respectively. 相似文献
1000.