全文获取类型
收费全文 | 145120篇 |
免费 | 7558篇 |
国内免费 | 103篇 |
专业分类
林业 | 6113篇 |
农学 | 4221篇 |
基础科学 | 884篇 |
15846篇 | |
综合类 | 27926篇 |
农作物 | 5573篇 |
水产渔业 | 6618篇 |
畜牧兽医 | 75144篇 |
园艺 | 1651篇 |
植物保护 | 8805篇 |
出版年
2018年 | 1721篇 |
2017年 | 1886篇 |
2016年 | 1761篇 |
2015年 | 1576篇 |
2014年 | 1910篇 |
2013年 | 5161篇 |
2012年 | 3390篇 |
2011年 | 4309篇 |
2010年 | 2755篇 |
2009年 | 2770篇 |
2008年 | 4181篇 |
2007年 | 4053篇 |
2006年 | 3905篇 |
2005年 | 3570篇 |
2004年 | 3448篇 |
2003年 | 3495篇 |
2002年 | 3313篇 |
2001年 | 4394篇 |
2000年 | 4509篇 |
1999年 | 3570篇 |
1998年 | 1365篇 |
1997年 | 1395篇 |
1995年 | 1651篇 |
1994年 | 1410篇 |
1993年 | 1382篇 |
1992年 | 3062篇 |
1991年 | 3235篇 |
1990年 | 3197篇 |
1989年 | 3212篇 |
1988年 | 3002篇 |
1987年 | 3042篇 |
1986年 | 3105篇 |
1985年 | 3021篇 |
1984年 | 2452篇 |
1983年 | 2181篇 |
1982年 | 1485篇 |
1979年 | 2359篇 |
1978年 | 1884篇 |
1977年 | 1655篇 |
1976年 | 1585篇 |
1975年 | 1727篇 |
1974年 | 2228篇 |
1973年 | 2293篇 |
1972年 | 2244篇 |
1971年 | 2091篇 |
1970年 | 1996篇 |
1969年 | 1786篇 |
1968年 | 1546篇 |
1967年 | 1609篇 |
1966年 | 1442篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
J.F.D. Frazer 《Biological conservation》1973,5(4):271-276
While various experimental methods may show the number of butterflies in a given area, this, of itself, is no pointer either to general scarcity or to the reverse. Even less can it be taken as being the result of a particular set of outside influences. However, low levels in certain (otherwise plentiful) species may be taken as indicating unsuitable management trends. 相似文献
993.
994.
995.
996.
997.
Groups of 8 steers weighing 300–400 kg (660–880 Ib) were rotationally grazed on a ryegrass-dominant pasture for 115 days. The systems compared were zero grazing (Z), field grazing conducted at the same stocking rate (FC), and field grazing conducted at a stocking rate varied with the intention of giving the same liveweight gain per uiimal as zero grazing (FV). Mean daily liveweight gains were: Z, 0.98; FC, 0.78; FV, 0.90 kg/animal (2.2, 1.7 and 20 Ib/animal), and liveweight gains/unit area were in the ratio 100:78:85. Organic-matter intake, measured on four occasions, was, on average, Z, 6.54; FC, 6.18; FV, 687 kg/head daily (14.4, 13.6 and 15.1Ib). From these results it appears that a comparison of zero grazing and field grazing made at the same stocking rate is likely to underestimate the potential of field grazing for beef production from grass. 相似文献
998.
999.
D. Wilman 《Grass and Forage Science》1970,25(4):303-308
Residual response to an initial application of nitrogen was measured in 3 years and was found to be quite large, e.g. a response of 8 Ib DM per extra Ib N at the first harvest, when applying 125 Ib N/ac (140 kg/ha) rather than‘75 Ib (84 kg/ha) and allowing 6 weeks' growth, was increased to 21 Ib DM when yield from residual cuts was taken into account. Response was large in relation to the amount of N estimated to have been left behind after the first harvest. Marginal recovery of N, already quite high at the first harvest, was increased to a little over 90% when yield from residual cuts was taken into account Recovery, however, was lower than this when 10 weeks' growth was allowed before the first harvest, and it seems that, in this case, some N may have been lost from the system. A supplementary experiment suggested that the residual effect of N on DM yield could be obscured to some extent by fresh applications of N. 相似文献
1000.