全文获取类型
收费全文 | 137696篇 |
免费 | 7857篇 |
国内免费 | 5365篇 |
专业分类
林业 | 9612篇 |
农学 | 11452篇 |
基础科学 | 5214篇 |
19330篇 | |
综合类 | 27411篇 |
农作物 | 5815篇 |
水产渔业 | 6674篇 |
畜牧兽医 | 53897篇 |
园艺 | 2651篇 |
植物保护 | 8862篇 |
出版年
2022年 | 1612篇 |
2021年 | 2575篇 |
2020年 | 2437篇 |
2019年 | 2723篇 |
2018年 | 2761篇 |
2017年 | 3467篇 |
2016年 | 3288篇 |
2015年 | 3640篇 |
2014年 | 3764篇 |
2013年 | 6233篇 |
2012年 | 5902篇 |
2011年 | 6829篇 |
2010年 | 5392篇 |
2009年 | 5189篇 |
2008年 | 6105篇 |
2007年 | 5852篇 |
2006年 | 5726篇 |
2005年 | 5250篇 |
2004年 | 3707篇 |
2003年 | 3535篇 |
2002年 | 3147篇 |
2001年 | 4187篇 |
2000年 | 4289篇 |
1999年 | 3877篇 |
1998年 | 2168篇 |
1997年 | 2055篇 |
1996年 | 1820篇 |
1995年 | 1882篇 |
1994年 | 1754篇 |
1993年 | 1665篇 |
1992年 | 2549篇 |
1991年 | 2495篇 |
1990年 | 2334篇 |
1989年 | 2245篇 |
1988年 | 1864篇 |
1987年 | 1779篇 |
1986年 | 1716篇 |
1985年 | 1599篇 |
1984年 | 1271篇 |
1983年 | 1066篇 |
1982年 | 748篇 |
1979年 | 1068篇 |
1978年 | 826篇 |
1975年 | 816篇 |
1974年 | 898篇 |
1973年 | 864篇 |
1972年 | 806篇 |
1971年 | 796篇 |
1970年 | 800篇 |
1969年 | 780篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
882.
The effect of azadirachtin and salannin, two triterpenoids isolated from seeds of neem (Azadirachta indica A. Juss), on the feeding response ofSpodoptera littoralis (Boisd.) andEarias insulana (Boisd.) larvae, was investigated. Styropor (foamed polystyrene) lamellae were painted on both sides with a mixture of 5% sucrose with different concentrations of either azadirachtin or salannin dissoled in methanol-water (3∶7). Azadirachtin strongly suppressed feeding inS. littoralis larvae even at 0.001%, whereas salannin showed some antifeedant activity at 0.005% and above. Larvae ofE. insulana were deterred from feeding on azadirachtin-treated lamellae even at 0.005%, whereas salannin was effective only at 0.01% and above. Azadirachtin applied on cotton leaves deterred larvae ofS. littoralis from feeding at all concentrations ranging between 0.001 and 0.02%. 相似文献
883.
884.
885.
886.
Two compounds with highly potent juvenile hormone activity were isolated and identified from the oil of sweet basil, Ocimum basilicum L., Labiatae. 相似文献
887.
J K Skeeles M Slavik J N Beasley A H Brown C F Meinecke S Maruca S Welch 《American journal of veterinary research》1980,41(9):1458-1461
Specific-pathogen-free White Leghorn chickens were inoculated with a field strain of infectious bursal disease virus. One group (A) was inoculated at 17 days after the chicks were hatched, and the other groups (C and E) were inoculated at posthatch day 42. Blood samples were obtained for determination of clotting times (whole blood recalcification, prothrombin, and activated partial thromboplastin times), virus-neutralizing antibody, and total hemolytic complement. There were significant increases in clotting times for groups C and E at 3 and 5 days after they were inoculated. There were no significant increases in clotting times at 3 days after inoculation in the group A chickens (inoculated at 17 days after hatching). There were no significant decreases in total complement activity in any of these chickens (groups A, C, and E). This study indicates that the mortality and clinical symptoms observed in chickens experimentally infected with infectious bursal disease virus may be associated with a clotting abnormality because it was noted only in chickens that developed severe clinical disease (inoculated at 42 days after hatching) and was not noted in chickens that remained clinically normal (inoculated at 17 days). 相似文献
888.
889.
The effects of canopy cover, seeding depth, and soil moisture on emergence of Centaurea maculosa Lam. and C. diffusa Lam. were studied. Canopy cover had no effect on ermergence rate (seedlings/day/100 seeds) of either species. Seeds of both species emerged faster when placed on the soil surface. Emergence rate decreased as seeding depth increased. Both species required more than 55% initial soil moisture to initiate emergence, with 65–70% being optimum. Percentage emergence followed exactly the same trend as emergence rate. C. maculosa had better emergence characteristics over a wider range of conditions than C. diffusa, possibly being some of the reasons for the former having a wider geographical distribution in the United States and Canada. 相似文献
890.