收费全文 | 48996篇 |
免费 | 2694篇 |
国内免费 | 33篇 |
林业 | 1706篇 |
农学 | 1661篇 |
基础科学 | 251篇 |
5841篇 | |
综合类 | 8196篇 |
农作物 | 1545篇 |
水产渔业 | 2724篇 |
畜牧兽医 | 26340篇 |
园艺 | 574篇 |
植物保护 | 2885篇 |
2019年 | 418篇 |
2018年 | 779篇 |
2017年 | 826篇 |
2016年 | 744篇 |
2015年 | 607篇 |
2014年 | 750篇 |
2013年 | 1737篇 |
2012年 | 1349篇 |
2011年 | 1691篇 |
2010年 | 1155篇 |
2009年 | 1096篇 |
2008年 | 1684篇 |
2007年 | 1594篇 |
2006年 | 1498篇 |
2005年 | 1381篇 |
2004年 | 1394篇 |
2003年 | 1374篇 |
2002年 | 1186篇 |
2001年 | 1914篇 |
2000年 | 1984篇 |
1999年 | 1498篇 |
1998年 | 569篇 |
1997年 | 499篇 |
1996年 | 449篇 |
1995年 | 612篇 |
1994年 | 524篇 |
1993年 | 459篇 |
1992年 | 1151篇 |
1991年 | 1211篇 |
1990年 | 1178篇 |
1989年 | 1097篇 |
1988年 | 1056篇 |
1987年 | 1081篇 |
1986年 | 1034篇 |
1985年 | 966篇 |
1984年 | 806篇 |
1983年 | 683篇 |
1982年 | 421篇 |
1981年 | 382篇 |
1979年 | 635篇 |
1978年 | 500篇 |
1977年 | 441篇 |
1976年 | 408篇 |
1975年 | 451篇 |
1974年 | 523篇 |
1973年 | 507篇 |
1972年 | 531篇 |
1971年 | 449篇 |
1970年 | 424篇 |
1969年 | 464篇 |
2. In the first experiment, colostomy had no significant effect on mineral balance. However, broilers exposed to high cycling ambient temperature reduced their retention of phosphorus, potassium, sodium, magnesium, sulphur, manganese, copper and zinc compared with birds housed at 24°C.
3. Despite the minimal effect of high ambient temperature on urine production, minerals excreted disproportionately excreted in urine included potassium, magnesium, phosphorus and sulphur while copper and magnesium were lost primarily via the faeces.
4. In the second experiment, exposure to 35°C increased urine output from 50.7 ml/12 h per kg of body weight at 24°C to 101.3 ml/12 h per kg of body weight and was associated with an increased urine:water ratio and reduced urine osmolal‐ity.
5. Reduced urinary chloride and higher potassium, phosphorus, sulphur, sodium, magnesium, calcium and manganese excretion was observed for broilers housed in under high ambient temperatures compared to 24°C.
6. These studies suggest that high ambient temperatures adversely influence mineral metabolism and, furthermore, that the route of excretion varies with the specific mineral and the environmental temperature exposure. 相似文献
2. Agricultural research is defined as work intended to benefit agriculture and directed towards those problems which seem capable of solution. Science research is something else. Too much of the money allocated for agricultural and biotechnology research is being spent on science research. The system of rewarding agricultural scientists needs to be adjusted away from counting papers published.
3. Some examples are given of problems in poultry science which seem likely to be soluble by gene manipulation. These include “essential” amino acid synthesis within the chicken, improvement of shell strength, the prevention of many diseases, but probably not the improvement of quantitative traits or of behavioural adaptation to intensive husbandry.
4. Examples are also given of problems likely to require empirical solutions, such as the benefits of acclimatisation or the long‐term response to a lighting programme. Here the need is to develop better theories to guide modelling activities.
5. The author concludes that there is much research that can and should be done in poultry science in the next 20 years but calls for a recognition that some problems cannot be solved by a “fundamental” approach but will need experiments with whole animals coupled with model‐building activities. 相似文献
2. Hens were hypophysectomised at 6 intervals from 4.5 to 11.0 h before the expected time of ovulation. Ovulation occurred in the hens operated on from 4.5 to 7.3 h, but did not take place in birds operated on from 9.2 to 9.8 h before the expected time of ovulation.
3. When a single dose of P4 (2 mg/hen) was injected iv immediately after the removal of the anterior pituitary from 7.5 to 9.8 h before the expected time of ovulation, ovulation was induced. However, the percentage of hens responding decreased in proportion to the lapse of time between the hypophysectomy and the expected time of ovulation. No ovulation was induced in hens which were hypophysectomized and given P4 10.2 to 11.0 h before the expected time of ovulation.
4. It is suggested that ovulation is induced by P4 alone possibly in the absence of preovulatory gonadotrophins and that P4 acts directly on the ovary to induce follicle rupture. 相似文献
2. LL birds exhibited a lower growth rate than the FL when the diet was deficient in either lysine or arginine. Plotting weight gain against lysine or arginine intake suggested that most of this effect was caused by variations in food intake.
3. When protein gains (body or total proteins) were plotted against lysine or arginine intake, LL chickens appeared more efficient than FL chickens.
4. Similar growth rates, although slightly lower in FL, were obtained with low‐ and high‐protein diets. However, NEAA supplementation of the low‐protein diet reduced adiposity of LL and did not modify that of FL. Increasing crude protein content (all amino acids) was more effective than NEAA supplementation in decreasing the adiposity of both lines. 相似文献
2. Chicks fed on the tannin‐containing diets exhibited a high mortality and significant decreases in body‐weight as well as lower food intakes and higher food intake:weight gain ratios (P<0.01). In rats there was no mortality but the growth and food intake were adversely affected (P< 0.05).
3. Histological changes occurred in the ileal mucosa of chicks. Atrophy and shortening of villi with distortion of their architecture were observed. Similar histological disorders but less pronounced were also found in rats.
4. Histopathology of the liver of both chicks and rats showed an hydropic degeneration of hepatocytes, clearly more severe in the former than in the latter. 相似文献