全文获取类型
收费全文 | 105817篇 |
免费 | 5924篇 |
国内免费 | 778篇 |
专业分类
林业 | 4034篇 |
农学 | 3200篇 |
基础科学 | 823篇 |
13493篇 | |
综合类 | 19453篇 |
农作物 | 3952篇 |
水产渔业 | 4654篇 |
畜牧兽医 | 55158篇 |
园艺 | 1410篇 |
植物保护 | 6342篇 |
出版年
2021年 | 897篇 |
2020年 | 1007篇 |
2019年 | 1233篇 |
2018年 | 1796篇 |
2017年 | 2038篇 |
2016年 | 1798篇 |
2015年 | 1584篇 |
2014年 | 1894篇 |
2013年 | 4283篇 |
2012年 | 3488篇 |
2011年 | 4247篇 |
2010年 | 2901篇 |
2009年 | 2762篇 |
2008年 | 3890篇 |
2007年 | 3758篇 |
2006年 | 3332篇 |
2005年 | 3079篇 |
2004年 | 2811篇 |
2003年 | 2836篇 |
2002年 | 2626篇 |
2001年 | 3021篇 |
2000年 | 3073篇 |
1999年 | 2358篇 |
1998年 | 986篇 |
1997年 | 877篇 |
1995年 | 957篇 |
1992年 | 1840篇 |
1991年 | 2041篇 |
1990年 | 1970篇 |
1989年 | 1923篇 |
1988年 | 1750篇 |
1987年 | 1806篇 |
1986年 | 1849篇 |
1985年 | 1658篇 |
1984年 | 1454篇 |
1983年 | 1264篇 |
1979年 | 1450篇 |
1978年 | 1095篇 |
1977年 | 991篇 |
1976年 | 1094篇 |
1975年 | 1158篇 |
1974年 | 1452篇 |
1973年 | 1382篇 |
1972年 | 1316篇 |
1971年 | 1174篇 |
1970年 | 1156篇 |
1969年 | 1166篇 |
1968年 | 1027篇 |
1967年 | 1094篇 |
1966年 | 1029篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
Ligon WV 《Science (New York, N.Y.)》1979,204(4389):198-200
High electric fields have been used to extract organic cations from solutions of small organic molecules in polyphosphoric acid. The cations have been analyzed by mass spectrometry. Production of ions by this method is shown to be related to ease of protonation by acid rather than to ionization potential. 相似文献
102.
103.
The life cycle of Moniezia expansa was studied experimentally using 10 species of oribatid mites as intermediate hosts. Four of them became infected, namely Scheloribates laevigatus (76.2%), Sch. latipes (70.8%), Liacarus coracinus (20%) and Platynothrus peltifer (1.1%). The last was found for the first time to serve as intermediate host of M. expansa in Czechoslovakia. The development of the cysticercoid of M. expansa in the oribatid mites at 28 degrees C and 85% relative humidity is completed within 27 days. At 18-20 degrees C and the same relative humidity the development lasts even 97 days. 相似文献
104.
Ultrastructure of the cuticle and pseudobursa of adult males of four species of Trichinella has been studied by SEM. T. nativa differs markedly from T. spiralis, T. nelsoni and Trichinella sp. in the form of the pseudobursa. Trichinella sp. differs only slightly from T. spiralis and T. nelsoni. The ultrastructure of the cuticle revealed no characters suitable for the differentiation of the taxons under study. 相似文献
105.
106.
McNichols JL 《Science (New York, N.Y.)》1979,204(4398):1184-1185
107.
Ruttan VW 《Science (New York, N.Y.)》1982,216(4541):23-29
The considerations involved in defining appropriate roles for the public and private sectors in agricultural research are examined with respect to mechanization, plant variety, and insecticide research and development. It is concluded that the public sector should continue to give mechanization a low priority. Varietal improvement should remain a relatively high priority until the effects of plant variety protection legislation become more apparent. Simultaneous achievement of safety, environmental, and productivity objectives in insect pest control will require that the public sector play a larger role in research and development. 相似文献
108.
Melnick VL 《Science (New York, N.Y.)》1982,215(4535):913-914
109.
110.