全文获取类型
收费全文 | 51897篇 |
免费 | 2863篇 |
国内免费 | 435篇 |
专业分类
林业 | 2108篇 |
农学 | 2038篇 |
基础科学 | 429篇 |
6326篇 | |
综合类 | 9144篇 |
农作物 | 1768篇 |
水产渔业 | 2924篇 |
畜牧兽医 | 26767篇 |
园艺 | 678篇 |
植物保护 | 3013篇 |
出版年
2020年 | 411篇 |
2019年 | 508篇 |
2018年 | 839篇 |
2017年 | 928篇 |
2016年 | 838篇 |
2015年 | 711篇 |
2014年 | 853篇 |
2013年 | 1879篇 |
2012年 | 1519篇 |
2011年 | 1888篇 |
2010年 | 1348篇 |
2009年 | 1274篇 |
2008年 | 1854篇 |
2007年 | 1747篇 |
2006年 | 1632篇 |
2005年 | 1503篇 |
2004年 | 1507篇 |
2003年 | 1490篇 |
2002年 | 1353篇 |
2001年 | 2088篇 |
2000年 | 2116篇 |
1999年 | 1588篇 |
1998年 | 628篇 |
1997年 | 545篇 |
1996年 | 491篇 |
1995年 | 656篇 |
1994年 | 553篇 |
1993年 | 506篇 |
1992年 | 1186篇 |
1991年 | 1232篇 |
1990年 | 1194篇 |
1989年 | 1112篇 |
1988年 | 1078篇 |
1987年 | 1089篇 |
1986年 | 1037篇 |
1985年 | 966篇 |
1984年 | 805篇 |
1983年 | 685篇 |
1982年 | 421篇 |
1979年 | 635篇 |
1978年 | 500篇 |
1977年 | 441篇 |
1976年 | 408篇 |
1975年 | 451篇 |
1974年 | 523篇 |
1973年 | 507篇 |
1972年 | 531篇 |
1971年 | 449篇 |
1970年 | 424篇 |
1969年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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
72.
73.
Maugh TH 《Science (New York, N.Y.)》1982,217(4561):720-721
74.
75.
Maugh TH 《Science (New York, N.Y.)》1982,218(4570):366
76.
77.
Appenzeller T 《Science (New York, N.Y.)》1992,255(5047):920-921
78.
J. A. T. Woodford 《European journal of plant pathology / European Foundation for Plant Pathology》1992,98(Z2):47-54
This paper reviews the contribution of vector activity and plant age to virus spread in potato crops. Determining which aphid species are vectors is particularly important for timing haulm destruction to minimize tuber infection by potato virus Y (PVY). Alate aphids of more than 30 species transmit PVY, and aphids such asRhopalosiphum padi, that migrate in large numbers before flights of the more efficient vector,Myzus persicae, appear to be important vectors. Differences in methodology, aphid biotypes and virus strains prevent direct comparisons between estimates of vector efficiencies obtained for aphids in different countries in north western Europe.
M. persicae is also the most efficient vector of potato leafroll virus (PLRV), but some clones ofMacrosiphum euphorbiae transmit PLRV efficiently toNicotiana clevelandii and potato test plants. The removal of infected plants early in the season prevents the spread of PLRV in cool regions with limited vector activity. The proportion of aphids acquiring PLRV from infected potato plants decreases with plant age, and healthy potato plants are more resistant to infection later in the season. Severe symptoms of secondary leafroll developed on progeny plants of cv. Maris Piper derived from mother plants inoculated with PLRV in June or July of the previous year. Progeny plants derived from mother plants inoculated in August showed only mild symptoms, but the concentration of PLRV in these plants was as high as that in the plants with severe symptoms. 相似文献
79.
80.