收费全文 | 6703篇 |
免费 | 296篇 |
国内免费 | 8篇 |
林业 | 230篇 |
农学 | 343篇 |
基础科学 | 82篇 |
824篇 | |
综合类 | 363篇 |
农作物 | 247篇 |
水产渔业 | 197篇 |
畜牧兽医 | 3750篇 |
园艺 | 105篇 |
植物保护 | 866篇 |
2023年 | 30篇 |
2022年 | 41篇 |
2021年 | 58篇 |
2020年 | 83篇 |
2019年 | 86篇 |
2018年 | 110篇 |
2017年 | 106篇 |
2016年 | 119篇 |
2015年 | 95篇 |
2014年 | 135篇 |
2013年 | 498篇 |
2012年 | 296篇 |
2011年 | 351篇 |
2010年 | 175篇 |
2009年 | 175篇 |
2008年 | 333篇 |
2007年 | 320篇 |
2006年 | 273篇 |
2005年 | 272篇 |
2004年 | 285篇 |
2003年 | 256篇 |
2002年 | 248篇 |
2001年 | 234篇 |
2000年 | 215篇 |
1999年 | 195篇 |
1998年 | 59篇 |
1997年 | 57篇 |
1996年 | 56篇 |
1995年 | 62篇 |
1994年 | 38篇 |
1993年 | 45篇 |
1992年 | 105篇 |
1991年 | 116篇 |
1990年 | 135篇 |
1989年 | 108篇 |
1988年 | 100篇 |
1987年 | 84篇 |
1986年 | 67篇 |
1985年 | 71篇 |
1984年 | 66篇 |
1983年 | 44篇 |
1982年 | 30篇 |
1981年 | 41篇 |
1980年 | 44篇 |
1979年 | 45篇 |
1975年 | 25篇 |
1974年 | 25篇 |
1973年 | 26篇 |
1972年 | 35篇 |
1971年 | 32篇 |
METHODS: Holstein dairy cows were allocated to two herds with similar parity, days in milk and milk production. They were grazed in one paddock that was divided in two, with a fixed water trough at one end. Cows were moved twice daily to grazing plots within the paddock. Control cows (n=66) could only access water from the fixed trough, whereas supplemented cows (n=67) also received water from a mobile trough within the grazing plot. Milk production of each cow, and water consumption of the two herds were measured daily over 62 days. Milk composition for each herd was determined weekly from Days 18 to 60 of the study, and grazing behaviour was observed between 08:00 and 16:00 hours on Days 11–15, 19–22 and 39–43.
RESULTS: Over the 62 days of the study, supplemented cows produced 1.39 (SE 0.11) L/cow/day more milk than Control cows (p=0.027). Estimated mean daily water intake was 50.4 (SE 2.1) L/cow/day for supplemented cows and 58.2 (SE 2.7) L/cow/day for Control cows (p=0.004). Percentage total solids in milk was higher for supplemented (12.5 (SE 0.06)%) than Control (12.4 (SE 0.04)%) cows (p=0.047). During the periods of behavioural observation, a higher percentage of cows in the water supplemented than the Control herd were observed in the grazing area (p=0.012).
CONCLUSIONS AND CLINICAL RELEVANCE: This preliminary study demonstrated that provision of water to dairy cows within the grazing plot was beneficial for milk production and composition, and may be associated with longer periods spent within the grazing area, during hot weather in the Pampa region of Argentina. 相似文献
METHODS: Ninety lambs, aged approximately 6 months, were grazed on plots of perennial ryegrass infected with either AR98 endophyte (containing lolitrem B), standard endophyte (containing lolitrem B and ergovaline) or no endophyte, for up to 42 days from 2 February 2010. Ten lambs were grazed on three replicate plots per cultivar. Herbage samples were collected for alkaloid analysis and lambs were scored for ryegrass staggers (scores from 0–5) weekly during the study. Any animal which was scored ≥4 was removed from the study.
RESULTS: Concentrations of lolitrem B did not differ between AR98 and standard endophyte-infected pastures during the study period (p=0.26), and ergovaline was present only in standard endophyte pastures. Ryegrass staggers was observed in sheep grazing both the AR98 and standard endophyte plots, with median scores increasing in the third week of the study. Prior to the end of the 42-day grazing period, 22 and 17 animals were removed from the standard endophyte and AR98 plots, respectively, because their staggers scores were ≥4. The cumulative probability of lambs having scores ≥4 did not differ between animals grazing the two pasture types (p=0.41).
CONCLUSIONS AND CLINICAL RELEVANCE: There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated. 相似文献