收费全文 | 2337篇 |
免费 | 123篇 |
林业 | 80篇 |
农学 | 36篇 |
基础科学 | 17篇 |
328篇 | |
综合类 | 278篇 |
农作物 | 117篇 |
水产渔业 | 115篇 |
畜牧兽医 | 1369篇 |
园艺 | 35篇 |
植物保护 | 85篇 |
2023年 | 16篇 |
2021年 | 26篇 |
2020年 | 40篇 |
2019年 | 55篇 |
2018年 | 38篇 |
2017年 | 44篇 |
2016年 | 49篇 |
2015年 | 37篇 |
2014年 | 36篇 |
2013年 | 127篇 |
2012年 | 122篇 |
2011年 | 151篇 |
2010年 | 64篇 |
2009年 | 57篇 |
2008年 | 125篇 |
2007年 | 127篇 |
2006年 | 102篇 |
2005年 | 124篇 |
2004年 | 128篇 |
2003年 | 101篇 |
2002年 | 92篇 |
2001年 | 47篇 |
2000年 | 46篇 |
1999年 | 27篇 |
1998年 | 20篇 |
1997年 | 30篇 |
1996年 | 24篇 |
1995年 | 28篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 37篇 |
1991年 | 32篇 |
1990年 | 34篇 |
1989年 | 18篇 |
1988年 | 36篇 |
1987年 | 35篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1975年 | 14篇 |
1973年 | 13篇 |
1972年 | 18篇 |
1971年 | 17篇 |
1970年 | 12篇 |
1969年 | 14篇 |
1967年 | 16篇 |
1966年 | 12篇 |
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. Significant increases in plasma LH occurred following light stimulations at 6, 9 and 12 weeks of age.
3. Changes in LH concentration 7 d after a light increase from 8 h to 8, 10, 13, 16 h were highly correlated with photoperiod length at 9 and 12 weeks of age.
4. Changes in LH were generally poorly correlated with age at sexual maturity, although the reduced influence on age at first egg of a light increase given close to sexual maturity was reflected in minimal LH responses at 18 and 20.3 weeks. 相似文献
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. The dietary treatments had no significant effect upon food intake, egg output, shell thickness, shell deformation or specific gravity of the eggs.
3. The 28‐h cycle reduced mean rate of lay by 4.5%, increased egg weight by 5.8% and increased shell thickness by 9.4%. The proportion of eggs with shell faults revealed on candling was reduced from 4.1 % to 2.8%.
4. It is concluded from this and other sources that decreasing dietary phosphorus or modifying vitamin D supplements may sometimes lead to increases in shell thickness of the order of 1 to 2%, but that these changes are unlikely to result in a measurable reduction in the proportion of cracked eggs late in the laying year.
5. A 28‐h light‐dark cycle results in a longer and more uniform interval between consecutive ovipositions and thus gives reliable increases in shell thickness which are large enough to reduce the proportion of cracked eggs in many practical situations. Whether it is profitable to use an ahemeral cycle will depend upon the relative prices paid for eggs of different sizes. 相似文献
2. Each experiment involved a total of 3 888 laying pullets. Nine diets, with crude protein contents ranging from 87 to 212 g/kg, were used in the first experiment and ten diets, with protein contents ranging from 81 to 215 g/kg, in the second experiment. Diets were denned in terms of their calculated contents of essential amino acids and the same, well‐balanced amino acid profile was used at all protein contents within one experiment. Supplementary experiments were conducted to identify the limiting amino acid (s) in the experimental diets.
3. Treatments were applied for ten weeks, starting at 30 or 32 weeks of age. Average egg output on the highest protein diets was 57.0 g/bird d in the first experiment, which used White Leghorn pullets, and 53.7 g/bird d in the second experiment, which used a crossbred brown‐egg stock.
4. The response curves obtained showed diminishing returns and, in the second experiment, a clear plateau was reached. The Reading model was fitted and compared with a two‐straight‐line model and with curves derived from quadratic and inverse polynomial equations. Only the Reading model proved satisfactory for the interpretation of the data, as judged by goodness of fit and estimation of the optimum amino acid input. Although alternative models may provide a good fit when dealing with a single set of data, none of the alternatives is consistently satisfactory when considering the results of more than one experiment. 相似文献
2. Diets prepared by serial dilution of a concentrated protein mixture, well‐balanced with respect to all essential amino acids, were fed in three experiments, while in a fourth experiment, a lysine‐deficient protein mixture was used.
3. Response curves relating body‐weight gain to increasing concentrations of protein and of lysine intake are presented.
4. A table is presented from which optimum protein intakes can be calculated according to changes in input and output costs and changes in growth potential of the chickens. 相似文献
First European Symposium on Poultry Welfare. Edited by L. Yding S0RENSEN. Published by the Danish Branch of World's Poultry Science Association. 1981. 238pp. D.Kr.90. ISBN 87–88162–00–1. 相似文献