收费全文 | 280530篇 |
免费 | 15644篇 |
国内免费 | 682篇 |
林业 | 23603篇 |
农学 | 14040篇 |
基础科学 | 2957篇 |
43457篇 | |
综合类 | 36415篇 |
农作物 | 17265篇 |
水产渔业 | 17167篇 |
畜牧兽医 | 111561篇 |
园艺 | 6352篇 |
植物保护 | 24039篇 |
2020年 | 2865篇 |
2019年 | 3647篇 |
2018年 | 3963篇 |
2017年 | 4287篇 |
2016年 | 4753篇 |
2015年 | 4325篇 |
2014年 | 5699篇 |
2013年 | 16285篇 |
2012年 | 6363篇 |
2011年 | 8297篇 |
2010年 | 7370篇 |
2009年 | 7904篇 |
2008年 | 7703篇 |
2007年 | 6886篇 |
2006年 | 7511篇 |
2005年 | 6765篇 |
2004年 | 6654篇 |
2003年 | 6442篇 |
2002年 | 5849篇 |
2001年 | 6424篇 |
2000年 | 6154篇 |
1999年 | 5726篇 |
1998年 | 4197篇 |
1997年 | 4262篇 |
1996年 | 3951篇 |
1995年 | 4550篇 |
1994年 | 3963篇 |
1993年 | 3695篇 |
1992年 | 4849篇 |
1991年 | 5050篇 |
1990年 | 4855篇 |
1989年 | 4900篇 |
1988年 | 4437篇 |
1987年 | 4444篇 |
1986年 | 4322篇 |
1985年 | 4648篇 |
1984年 | 4179篇 |
1983年 | 3924篇 |
1982年 | 3152篇 |
1981年 | 3037篇 |
1980年 | 2980篇 |
1979年 | 3815篇 |
1978年 | 3309篇 |
1977年 | 3048篇 |
1976年 | 2883篇 |
1974年 | 3300篇 |
1973年 | 3256篇 |
1972年 | 3132篇 |
1971年 | 3068篇 |
1970年 | 2884篇 |
2. The rate of lay observed with a Step‐Up treatment which gave increases in photoperiod from 8L:16D at 18 weeks to 15L:9D at 27 weeks of age was not significantly different from that of treatments which held the birds on 11L:13D during peak egg production but gave increments up to 15L:9D later in the laying year.
3. A control group maintained on 11L:13D from 20 to 72 weeks laid 295 eggs per bird housed and a further group held on 8L:16D from 0 to 72 weeks laid 284 eggs per bird. These yields were lower than the Step‐Up treatment (299 eggs) but show the potential of modern hybrid stocks to lay prolifically even without light stimulation.
4. It is concluded that the stocks tested in this experiment showed no advantage when given lighting programmes in the first laying year which were designed to minimise the adverse effects of photorefractoriness. 相似文献
2. Hepatocytes that stained with trypan blue were considered to be dead or dying before fixation and represented damaged cells.
3. The proportion of trypan blue‐stained hepatocytes in the livers of ascitic birds was slightly less than half that observed in the hypoxia‐induced birds but significandy more than the proportion of stained cells observed in control birds.
4. Liver damage in the ascitic birds was also assessed biochemically by an altered enzyme profile.
5. The study demonstrated that increased trypan blue uptake in the livers of ascitic birds reared at sea‐level may be the consequence of hypoxia stress caused by reduced oxygen utilisation. 相似文献
2. Daytime perching did not differ significantly between the treatments. At night, over the whole year, 81% of birds in the 480 mm cages and 86% in the 520 mm cages roosted on the perch. This figure reached about 95% in the 560 and 600 mm cages, significantly more at most ages than in the 480 mm cages.
3. Feather damage was slightly less, but claw problems slightly more, in the 2 wider treatments than in the 2 narrower treatments. Birds in the wider cages were calmer when approached or handled by humans than those in the narrower cages. This may have been associated with variation in space allowance between the treatments.
4. There was a trend for lower production in the 480 mm cages than in the other treatments which may have been associated with the reduced feeding space in this treatment. There were few other treatment differences in production traits.
5. The balance of the evidence from this study is that when perches are provided in laying cages for medium weight hybrids, 140 mm of perch space per hen is adequate. For the amelioration of a number of the welfare problems of conventional cages, provision of perches should be combined with other modifications. 相似文献
2. A panel of 180 MAbs was generated, from which 14 were chosen for their specificity.
3. These MAbs were characterised immunohistologically on frozen sections of embryonic, newly‐hatched and adult, male and female, left gonads.
4. Three of these MAbs are described: AGC5, AGC7, and AGC13 which recognise respectively germinal epithelial cells, supporting cells and germ cells.
5. These MAbs may be useful in following the developmental pathways in the chicken gonad and analysing the interactive role(s) taking place between gonadal stromal cells and primordial germ cells. 相似文献