收费全文 | 135689篇 |
免费 | 7948篇 |
国内免费 | 70篇 |
林业 | 5588篇 |
农学 | 4645篇 |
基础科学 | 863篇 |
17511篇 | |
综合类 | 18966篇 |
农作物 | 5095篇 |
水产渔业 | 7112篇 |
畜牧兽医 | 73085篇 |
园艺 | 1808篇 |
植物保护 | 9034篇 |
2020年 | 1180篇 |
2019年 | 1427篇 |
2018年 | 2234篇 |
2017年 | 2495篇 |
2016年 | 2301篇 |
2015年 | 2001篇 |
2014年 | 2454篇 |
2013年 | 5742篇 |
2012年 | 4357篇 |
2011年 | 5187篇 |
2010年 | 3513篇 |
2009年 | 3556篇 |
2008年 | 5171篇 |
2007年 | 4982篇 |
2006年 | 4650篇 |
2005年 | 4268篇 |
2004年 | 4119篇 |
2003年 | 4184篇 |
2002年 | 3820篇 |
2001年 | 4773篇 |
2000年 | 4643篇 |
1999年 | 3748篇 |
1998年 | 1474篇 |
1997年 | 1453篇 |
1996年 | 1345篇 |
1995年 | 1601篇 |
1994年 | 1328篇 |
1993年 | 1359篇 |
1992年 | 2763篇 |
1991年 | 2901篇 |
1990年 | 2866篇 |
1989年 | 2897篇 |
1988年 | 2610篇 |
1987年 | 2592篇 |
1986年 | 2539篇 |
1985年 | 2401篇 |
1984年 | 1956篇 |
1983年 | 1715篇 |
1982年 | 1154篇 |
1979年 | 1649篇 |
1978年 | 1286篇 |
1977年 | 1135篇 |
1976年 | 1100篇 |
1975年 | 1164篇 |
1974年 | 1357篇 |
1973年 | 1448篇 |
1972年 | 1378篇 |
1971年 | 1195篇 |
1970年 | 1247篇 |
1969年 | 1146篇 |
2. Birds in all treatments gained similar amounts of weight from 12–14 weeks of age. Thereafter, birds in C maintained gains, the body weight gains of birds in EC and EH declined moderately and birds in H lost weight.
3. Birds in C produced more metabolic heat. Those in H showed increased heat production as they became older.
4. Protein retention was greater in turkeys in C, EC and EH. It was lower in H, becoming negative between 18–20 weeks of age. Birds in H suffered body fat losses which increased with age.
5. Birds in EH and EC gained similar amounts of body weight. Birds in EH exhibited lower heat production and greater energy retention than those in EC.
6. Body temperatures were higher in H than in the other environments. 相似文献
2. Culture media deficient in either sodium or chloride ions reduced the volume of SEF secreted by up to a quarter. Ionic composition of the fluid was little altered, and sodium was transported against a concentration gradient.
3. Amiloride, an inhibitor of Na+/H+ exchange, reduced SEF production by half, whereas ionic composition and osmolality of the fluid was unchanged.
4. Likewise, acetazolamide, an inhibitor of carbonic anhydrase, reduced SEF production by the blastoderm, and left the ionic composition and osmolality of the fluid unaltered.
5. Neither furosemide or 4,4´‐diisothiocyanatostilbene‐2,2´‐disulfonic acid at the concentrations used changed the volume of SEF formed or its ionic composition.
6. It is concluded that the secretion of SEF is dependent upon the active transport of sodium across the blastoderm; an amiloride‐sensitive Na+/H+ exchanger and carbon dioxide hydration catalysed by carbonic anhydrase are also involved.
7. Furthermore, it is proposed that fluid transport across the blastoderm is the result of local osmotic gradients, not from a sub‐embryonic fluid hyperosmotic to albumen, as has been suggested previously. 相似文献