全文获取类型
收费全文 | 260篇 |
免费 | 1篇 |
出版年
2019年 | 2篇 |
2014年 | 5篇 |
2013年 | 15篇 |
2012年 | 4篇 |
2011年 | 11篇 |
2010年 | 16篇 |
2009年 | 10篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 18篇 |
2004年 | 9篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1957年 | 8篇 |
1956年 | 5篇 |
1955年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 62 毫秒
1.
In many high latitude-breeding avian species, reproductive andwintering seasons are separated by migratory periods that involvedramatic physiological and behavioral adjustments such as hyperphagiaand fat deposition. The endocrine mechanisms responsible forthese adjustments have been extensively studied, yet remainonly partly understood. The currently available informationindicates that food consumption and/or fattening can be experimentallymodulated by multiple hormones including testosterone, prolactin,glucocorticoids, and opioids. These hormones may control migratoryfunctions through mutual interactions rather than independently.Little is known, however, concerning the nature of these interactionsand their relative importance in the control of annual cyclesin natural conditions. This paper focuses on the role of gonadalandrogens in the control of migratory functions, and it summarizesthe information which is available on the physiological andbehavioral interactions between these androgens and other hormones. 相似文献
2.
3.
4.
Diagnosing the environmental causes of the decline in Grey Partridge Perdix perdix survival in France 总被引:1,自引:1,他引:0
We studied Grey Partridge Perdix perdix mortality during breeding to identify the environmental causes of a long‐term decline in adult survival. We radiotagged and monitored daily from mid‐March to mid‐September 1009 females on ten contrasting study sites in 1995‐97. Simultaneously, we recorded habitat features and estimated the abundance of Hen and Marsh Harriers Circus cyaneus and C. aeruginosus Red Fox Vulpes vulpes and mustelids. We experimentally tested whether scavenging could have biased predation rates. We also examined, through the necropsy of 80 carcasses of Grey Partridge, whether disease, parasites or poisoning could have been ultimate causes of high predation rates. The survival rate of radiotagged females during spring and summer ranged from 0.25 to 0.65 across study areas. Mortality peaked in May, June and July when females were laying and incubating. The direct negative impact of farming practices was low (6%). Predation was the main proximate cause of female mortality during breeding (73%) and determined the survival rate, suggesting no compensation by other causes of mortality. Ground carnivores were responsible for 64% of predation cases, and raptors for 29%, but this proportion varied across study sites. Disease and poisoning did not appear to favour predation, and scavenging was not likely to have substantially overestimated predation rates. The predation rate on breeding females was positively correlated with the abundance of Hen and Marsh Harriers, suggesting an additional mortality in areas where harriers were abundant. The proportion of raptor predation was linearly related to harrier abundance. The predation rate was not correlated with the abundance of the Red Fox and mustelids. A potential density‐dependent effect on the predation rate was confounded by the abundance of harriers. We found no convincing relationship between the predation rate and habitat features, but we observed a positive relationship between the abundance of Hen and Marsh Harriers and the mean field size. This suggested that habitat characteristics may contribute to high predation rates through predator abundance or habitat‐dependent predation. 相似文献
5.
6.
7.
8.
JEAN VIDAL PIERRE GADAL GERARD CAVALIE LUCIENNE CAILLIAU-COMMANAY 《Physiologia plantarum》1977,39(2):190-195
French bean (Phaseolus vulgaris L. cv. Contender) leaf extracts catalyse the reduction of oxaloacetate to malate in the presence of NADH and NADPH. Under the experimental conditions used, the optimum pH values are 8 and 6 respectively. After chromatography on diethylaminoethyl cellulose, two principal forms of NADH-MDH (L-malate: NAD+ oxidoreductase, E.C. 1.1.1.37) upon which NADPH activities are superposed, can be characterized. This result is confirmed by electrophoresis on polyacrylamide gel. On the other hand, after filtration on Ultrogel 34, NADH-MDH is eluted as a single peak; once again, NADPH activity is associated with it. When PtCl2?4, a powerful inhibitor of MDH, is added to the reaction medium, the degree of inhibition is the same irrespective of the cofactor employed. When root extracts are submitted to chromatography on diethylaminoethyl cellulose, activity profiles are identical to those obtained with leaves. These results suggest that the NAD dependent enzymes can also utilize NADP to reduce oxaloacetate. After addition of dithiothreitol, another NADPH-MDH activity manifests itself in the leaf extracts; it differs from the foregoing ones in its optimum pH, its chromatographic properties and its response to PtCl2?4 action. Root extracts do not exhibit this activity thus showing a specific localization of this enzyme in the green part of the plant. 相似文献
9.
10.