全文获取类型
收费全文 | 669篇 |
免费 | 31篇 |
国内免费 | 2篇 |
专业分类
702篇 |
出版年
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 15篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 15篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1972年 | 5篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1969年 | 7篇 |
1959年 | 17篇 |
1958年 | 21篇 |
1957年 | 25篇 |
1956年 | 19篇 |
1955年 | 25篇 |
1954年 | 30篇 |
1953年 | 32篇 |
1952年 | 26篇 |
1951年 | 22篇 |
1950年 | 17篇 |
1949年 | 19篇 |
1948年 | 12篇 |
排序方式: 共有702条查询结果,搜索用时 15 毫秒
71.
72.
73.
Energy dispersive X-ray microanalysis has been used to study the binding of two inhibitors of hatching in Globodera rostochiensis, ruthenium red and lanthanum, to a calcium binding site on the eggshell. Eggs were treated with either buffered ruthenium red or buffer only, and the levels of ruthenium and calcium that could be detected from the surface of eggshells were measured before and after repeated etching in a plasma oven. Counts for ruthenium increased during etching to a maximum after 8–12 min, just before the eggshell was eroded from the juvenile. The calcium levels on eggshells binding ruthenium red were suppressed relative to those from buffer. Similar experiments with lanthanum showed a significant increase in this inhibitor after 10 min etching and an accompanying suppression of calcium levels. The nature of the binding site was probed by measuring ruthenium red binding after pretreatment with selected enzymes. A non-specific protease, pronase, reduced the subsequent binding of this inhibitor but the site was resistant to trypsin in the presence of calcium. Neuraminidase also had an effect suggesting that the protein is a sialoglycoprotein. Phospholipase A2 but not Phospholipase C influenced the subsequent binding of ruthenium red. Phospholipase A2 caused a loss of hatching ability and the degradation of a phospholipid from the eggshell. Ruthenium red binding was also reduced by treatment of eggshells with detergents or sonication. Apparently a calcium-binding sialoglycoprotein forms part of the integral proteins of an eggshell membrane located on the inner surface of the eggshell. 相似文献
74.
3-(3,5-Dichlorophenoxy)butyric acid and 2-(3,5-dichlorophenoxy)ethylamine were both shown to exert pronounced dwarfing effects on tomato seedlings. Examination of extracts of the treated plants revealed the conversion of these compounds to 3,5-dichlorophenoxyacetic acid (3,5-D) and it is concluded that the physiological activity shown in each case depends on such a conversion to 3,5-D within the tissues. 相似文献
75.
The main source of inoculum of Helminthosporium solani was the seed tuber; the fungus was not detected in soils in which infected potatoes had been grown the previous year. Lesions spread rapidly on seed tubers after planting, so that within a few weeks the entire surface was covered. As lesions aged they lost the capacity to sporulate, so most inoculum was produced in the first few weeks after planting. Infection of progeny tubers was first detected at the heel (stolon attachment) end soon after their initiation. Once established, lesions spread slowly on the surface of progeny tubers when in the soil; more rapid spread took place during storage. Potatoes which seemed unaffected at lifting became diseased during storage. 相似文献
76.
77.
78.
MICHAEL ALAN TAYLOR 《Zoological Journal of the Linnean Society》1987,91(2):171-195
Mechanical theory is used to erect a paradigm predicting the manipulations used by carnivorous aquatic amphibians, reptiles, birds and mammals to catch, subdue, process and swallow their prey. These predictions are confirmed by observational evidence. Most aquatic predatory tetrapods use long, prehensile tooth-armed jaws as pincer jaws to snap shut onto the prey and catch and kill it, although some use the flexibility of long necks in spear fishing and some odontocetes may stun prey with sonar. Most do not have cutting or nipping dentitions as these cannot be used on prey which is freely floating. They use caniniform dentition to hold and kill prey, or in some cases crushing dentition to break open hard-shelled prey. They dismember prey by dynamic loading, snatching bites so quickly that the prey tears. They use shake feeding, shaking the prey apart from side to side above the water. If the prey is too large to lift above the water they use twist feeding, twisting pieces off. Small pieces are easily swallowed but larger pieces are held above the water and swallowed by tilting the head back in gravity feeding, or by jerking the head back and forth in incrtial feeding. Some animals use mobile jaws to pull prey back into the mouth in ratchet feeding. Filter feeding evades these problems by feeding on very small prey. The use of paradigms in functional analysis is discussed with special reference to this work. The paradigm method is shown to be the most suitable one. There has been repeated convergent and parallel evolution of adaptations to feed in water. 相似文献
79.
80.
SYNOPSIS. Mallard ducks, Anas platyrhynchos and a black crested night heron, Nycticorax nycticorax were fed trout infected with Myxosoma cerebralis (Hofer) in 2 separate experiments. Feces from the birds were deposited in troughs containing M. cerebralis -free mud as well as in 1 trough without mud. Spore suspensions were also added directly to mud in 1 trough and to another trough without mud. Susceptible rainbow trout, Salmo gairdneri , developed whirling disease in all troughs containing mud contaminated with M. cerebralis but remained free of infection when exposed to M. cerebralis in troughs without mud. This demonstrates the possibility of bird transmission of the organism causing whirling disease to previously non-contaminated waters. 相似文献