全文获取类型
收费全文 | 873篇 |
免费 | 46篇 |
国内免费 | 2篇 |
专业分类
林业 | 31篇 |
农学 | 39篇 |
基础科学 | 5篇 |
141篇 | |
综合类 | 113篇 |
农作物 | 47篇 |
水产渔业 | 35篇 |
畜牧兽医 | 438篇 |
园艺 | 15篇 |
植物保护 | 57篇 |
出版年
2023年 | 5篇 |
2021年 | 16篇 |
2020年 | 20篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 37篇 |
2012年 | 41篇 |
2011年 | 41篇 |
2010年 | 36篇 |
2009年 | 17篇 |
2008年 | 37篇 |
2007年 | 42篇 |
2006年 | 40篇 |
2005年 | 43篇 |
2004年 | 33篇 |
2003年 | 41篇 |
2002年 | 53篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1992年 | 12篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1969年 | 4篇 |
1967年 | 4篇 |
1943年 | 5篇 |
排序方式: 共有921条查询结果,搜索用时 15 毫秒
841.
Knowledge of the movement of herbicides and soil particles to sub-surface tile drainage may help to predict chemical leaching to surface waters and deeper groundwater systems. The movement of pendimethalin (2 years), ioxynil (1 year) and soil particles (3 years) to two tile drains was investigated on a sandy loam soil under natural weather conditions. Herbicide and particle concentrations in the drain water showed a very dynamic pattern. The largest herbicide concentrations were detected during the first tile drain flow events after application. Very little herbicide was lost with drain water later than 2 months after application. The turbidity, reflecting concentrations of soil particles, correlated positively and strongly with the pendimethalin concentration and negatively with the rate of drain water discharge, whereas it was uncorrelated with the ioxynil concentration. Peak turbidity values occurred during or shortly after rainfall events, either in break of frost situations, or on unfrozen soil coinciding with the occurrence of peak moisture contents in the topsoil well (3-7%) above field capacity. On average, 0.0013% of the applied pendimethalin and 0.0015% of the applied ioxynil were lost with drain water. The results suggest that preferential flow promotes the movement of all three substances to the tile drains but indicate somewhat different transport mechanisms for the two herbicides. 相似文献
842.
843.
Tracheal collapse was diagnosed radiographically in an eight-day-old Yorkshire-cross piglet presented with acute onset of inspiratory dyspnea. The diagnosis was confirmed by gross and microscopic pathology. This is the first reported example of tracheal collapse in a pig. 相似文献
844.
Comparison of histamine release induced by morphine and oxymorphone administration in dogs 总被引:1,自引:0,他引:1
E P Robinson A M Faggella D P Henry W L Russell 《American journal of veterinary research》1988,49(10):1699-1701
Cardiovascular effects (vasodilatation, hypotension) of morphine administration have been attributed to central actions and peripheral histamine release. In the study reported here, we compared plasma histamine (Hm) concentrations after morphine sulfate and oxymorphone HCl administration in conscious dogs. Five healthy adult dogs (mean body weight, 10.1 kg) were randomly administered morphine (2 mg/kg of body weight, IV) or oxymorphone (0.2 mg/kg, IV) by a 5-second bolus injection at weekly intervals. Venous blood samples (5 ml) were collected from jugular veins before and at 1, 2, 5, 15, 30, and 60 minutes after drug administration. Behavioral changes were recorded. Plasma was analyzed by a radioenzymatic technique, using purified histamine N-methyltransferase as an enzyme catalyst (sensitivity of assay, 40 pg Hm/ml). Mean base-line Hm value for all dogs was 0.55 ng/ml. The mean Hm value was significantly higher (P less than 0.05) than the base-line value at 1, 2, 5, 15, and 60 minutes after morphine administration (531.4, 251.0, 113.0, 31.5, and 1.0 ng of Hm/ml, respectively), but there were no significant increases in histamine values from base-line values at any time after oxymorphone administration. All dogs given morphine and 1 dog given oxymorphone showed excitatory behavior; 2 dogs given morphine and 3 dogs given oxymorphone salivated profusely. 相似文献
845.
846.
N L Henry 《Science (New York, N.Y.)》1974,186(4168):993-1004
What the United States does about the data explosion is likely to be copied on a global basis. America is the archetype of the coming technological society; we have all the advantages of being first, but others may avoid our mistakes. Let us hope that our errors are few 相似文献
847.
The effects of dietary level of lysine and of level and source of CP on voluntary feed intake, growth performance, plasma free amino acids, and carcass characteristics were investigated in a study involving 60 female and 60 castrated male Large White finishing pigs (from 42 to 101 kg live weight) with ad libitum access to feed. Six treatments were compared according to a 2 x 3 factorial plan, with two levels of lysine (.55 and .65% selected below the recommended levels for both sexes) and three types of CP (N x 6.25) supply: a 13% CP diet based on wheat, peanut meal and soybean meal; a 15.6% CP diet providing the same amino acid pattern as that of the basal diet; and a 15.2% CP diet containing the same levels of essential amino acids as the 13% CP diet, with the addition of glutamic acid as a source of nonessential amino acids. By maintaining a constant amino acid pattern separate changes in dietary lysine and CP levels resulted in a relative independency of their effects on feed intake, growth performance, and body composition. Muscle gain increased with supplementary lysine, with a lower response at the lower CP level (13%). At the same level of lysine (.55 or .65%), increasing protein content from 13 to 15.6% did not affect feed intake, but growth rate was lower and feed/gain was increased, partly because of an additional energy cost resulting from catabolism of excess protein.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
848.
Effect of protein and lysine levels in the diet on body gain composition and energy utilization in growing pigs 总被引:9,自引:0,他引:9
Eight replicates of four Large White littermate female pigs were used to evaluate the effect of protein and lysine levels in the diet on the efficiency of protein and energy utilization. In each replicate, one pig was slaughtered at about 20 kg live weight and the others received three diets that contained (per Mcal digestible energy) 37.5 and 2.00 g (diet pl), 37.5 and 2.35 g (diet pL) or 45.0 and 2.35 g (diet PL) of digestible protein and lysine, respectively. Pigs were slaughtered after a 7-wk period. Tissue and chemical composition of the gain and energy and nitrogen gain were determined by using the comparative slaughter technique. Metabolizable energy (ME) intakes were similar in the treatments. Pigs fed the pl diet had a smaller body weight and muscle gain and retained less nitrogen and more lipids than pigs fed pL and PL diets. The decrease in the level of nonessential nitrogen in the diet (pL vs PL) did not affect body weight and muscle gain and the amount of nitrogen retained in muscle tissues. However, pigs given the PL diet had a higher total nitrogen retention and a lower fat deposition and exhibited a higher heat production. For each gram of additional protein catabolized for energy purposes (PL vs pL), heat production was increased by 1.8 kcal. The amount of lysine per unit of muscle gain (38 g/kg) or protein deposited (120 g/kg) was independent of protein and lysine levels in the diet. Estimates of energy (indirect calorimetry) and nitrogen (balance technique) retention were also obtained on the same animals; results were comparable with data obtained by direct measurements. 相似文献
849.
Koger CH Shaner DL Krutz LJ Walker TW Buehring N Henry WB Thomas WE Wilcut JW 《Pest management science》2005,61(12):1161-1167
Greenhouse and field studies were conducted to investigate response of two rice varieties, Priscilla and Cocodrie, to sub-lethal rates of glyphosate in terms of injury, shikimate accumulation and yield. In the greenhouse, more shikimate accumulated in Cocodrie than Priscilla at comparable glyphosate rates applied to plants at the three-leaf stage. In field studies, glyphosate was applied to both varieties when they were 74-cm tall and in the internode separation growth stage. Visual injury, plant height, and leaf-tissue samples for shikimate analysis were collected at 3, 7, 14, 21 and 28 days after treatment (DAT). Rice yield was also determined. Noticeable visual injury and height reduction to both varieties was observed as early as 7 and 3 DAT in Cocodrie and Priscilla, respectively. Shikimate levels in leaves began to increase in both varieties by 3 DAT in a dose-dependent manner and reached a peak between 7 and 14 DAT. Elevated shikimate levels were still detectable by 28 DAT. Similar levels of shikimate accumulated in both varieties at comparable glyphosate rates. However, glyphosate treatment at comparable rates reduced rice yields more in Cocodrie than in Priscilla. The highest rate of glyphosate reduced yield in Cocodrie by 92% whereas there was only a 60% yield reduction in Priscilla. Shikimate levels in glyphosate-treated rice were strongly correlated to yield reductions across both varieties and appeared to be a better predictor of yield reduction than was visual injury. Visual injury coupled with measured shikimate levels can be used collaboratively to identify glyphosate exposure and estimate subsequent rice yield reductions. 相似文献
850.
Stämpfli H 《The Veterinary record》2005,156(25):816; author reply 816