全文获取类型
收费全文 | 289篇 |
免费 | 28篇 |
专业分类
林业 | 3篇 |
农学 | 3篇 |
26篇 | |
综合类 | 69篇 |
农作物 | 4篇 |
水产渔业 | 8篇 |
畜牧兽医 | 193篇 |
园艺 | 2篇 |
植物保护 | 9篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 3篇 |
2011年 | 7篇 |
2010年 | 3篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 16篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 16篇 |
1988年 | 8篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1976年 | 4篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1970年 | 8篇 |
1966年 | 5篇 |
1965年 | 3篇 |
1945年 | 2篇 |
1940年 | 2篇 |
1915年 | 2篇 |
1910年 | 2篇 |
1909年 | 4篇 |
1905年 | 2篇 |
排序方式: 共有317条查询结果,搜索用时 8 毫秒
41.
DT Rodbell GO Seltzer DM Anderson MB Abbott DB Enfield JH Newman 《Science (New York, N.Y.)》1999,283(5401):516-520
Debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the Pacific Ocean, in Ecuador. These storm-induced events were dated by radiocarbon, and the age of laminae that are less than 200 years old matches the historic record of El Nino events. From about 15,000 to about 7000 calendar years before the present, the periodicity of clastic deposition is greater than or equal to 15 years; thereafter, there is a progressive increase in frequency to periodicities of 2 to 8.5 years. This is the modern El Nino periodicity, which was established about 5000 calendar years before the present. This may reflect the onset of a steeper zonal sea surface temperature gradient, which was driven by enhanced trade winds. 相似文献
42.
A long-term, large-scale empirical test of the recruitment limitation hypothesis was done by sampling fish populations from the southern Great Barrier Reef after having monitored their recruitment histories for 9 years. After adjustment for demographic differences, recruitment patterns explained over 90 percent of the spatial variation in abundance of a common damselfish among seven coral reefs. The age structures from individual reefs also preserved major temporal variations in the recruitment signal over at least 10 years. Abundance and demography of this small fish at these spatial and temporal scales can be explained almost entirely as variable recruitment interacting with density-independent mortality. 相似文献
43.
44.
45.
46.
47.
Conformational problems tend to be common in llamas and alpacas. Without setting a standard, basic conformation can still be evaluated by comparing with equine conformation, especially in terms of straightness of limbs. Good conformation should evoke a sense of balance in the observer. Conformation faults predispose to unsoundness. 相似文献
48.
49.
50.