全文获取类型
收费全文 | 398篇 |
免费 | 2篇 |
出版年
2013年 | 9篇 |
2012年 | 6篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 31篇 |
2008年 | 19篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 18篇 |
2004年 | 12篇 |
2003年 | 5篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 17篇 |
1971年 | 7篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1960年 | 4篇 |
1959年 | 4篇 |
1958年 | 2篇 |
1956年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有400条查询结果,搜索用时 15 毫秒
111.
COOPERATION between bone marrow-derived (B) and thymus-derived (T) lymphocytes in antibody formation in mice is well established1 and with sheep red blood cells (SRBC) as the antigen the detectable antibody-forming cells are of marrow and not thymus origin2. Gershon and Kondo have recently suggested that the T cells requiring B cell cooperation for antibody production may also require it for tolerance induction, but that other B cells do not require T cell cooperation for either process3. 相似文献
112.
Declining acceptability of a food plant for the polyphagous grasshopper Schistocerca americana: the role of food aversion learning 总被引:1,自引:0,他引:1
ABSTRACT Successive contacts with a food that was initially acceptable to the acridid Schistocerca americana (Drury) (Orthoptera: Acrididae) were monitored. It was found that acceptability, as measured by meal length, declined with experience until the food, spinach, was completely rejected. Reduced acceptability of spinach was maintained even after feeding for three meals on a fully acceptable and suitable food, a period of 2–3 h. Experiments with spinach-filled capsules placed in the gut suggested that the decline in acceptability was not due to direct feedback from the gut or haemolymph on the sensory or feeding control systems. Food aversion learning is indicated as the mechanism underlying the decline in acceptability. 相似文献
113.
114.
THE ROLES OF AMINO ACIDS IN ANIMAL EMBRYOGENESIS 总被引:1,自引:0,他引:1
115.
The well-defined ant succession following disturbance of coastal heathland in eastern Australia includes community replacement triggered by one dominant species of Iridomyrmex (species C) being replaced by another (species A). This paper investigates the consequences of experimentally reducing the abundance of species A by injecting petrol into the nest entrances of colonies. The response of species C was monitored at 2 and 10 months after removal and shows highly significant increases in the number of pitfall traps occupied and the area of territory maintained by this species. It is confirmed that interspecific competition plays an important role in maintaining the observed mosaic pattern of ant distribution and is also important in ant succession. The mechanism of competition is interference or, more exactly, territorial competition. The species appear to actively defend territorial space by patrolling territory boundaries that are breached when the defenders are eliminated. 相似文献
116.
JONATHAN A. TODD ELIZABETH M. HARPER 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2011,44(2):214-222
Todd, JA. & Harper, EM. 2011: Stereotypic boring behaviour inferred from the earliest known octopod feeding traces: Early Eocene, southern England. Lethaia, Vol. 44, pp. 214–222. A bulk sample of 267 disarticulated valves of the bivalve Venericor clarendonensis (Wood) collected from the Lower Eocene London Clay (southern UK) yielded 38 individuals that had been perforated by small drill holes (0.70–2.14 mm in outer diameter). These drill holes had more or less circular plan views, with slightly irregular openings, and taper as they pass through the valve, conforming to the ichnotaxon Oichnus simplex Bromley. They show stereotypic positioning, being concentrated in the posterior region on the prey, moreover there is remarkable preference for perforating the sites of muscle attachment (principally the posterior adductor). We consider the most likely culprits to be octopods. As such these are the oldest octopod drill holes yet recorded. They provide the only evidence of these important top predators in this shallow marine community and also demonstrate that the sophisticated predatory behaviour shown by modern octopods had been evolved by at least the Early Eocene. □Eocene, octopod behaviour, Oichnus, stereotypic boring. 相似文献
117.
ELIZABETH J. WARHAM 《The Annals of applied biology》1990,116(1):43-60
Three inoculation techniques for Karnal bunt (Tilletia indica) disease of wheat were compared: 1) boot inoculation - injection of inoculum with a hypodermic syringe into the boot; 2) spray inoculation - inoculum sprayed at growth stages between heading and anthesis, and 3) cotton wool inoculation - small pieces of cotton wool saturated in inoculum placed either inside the floret or between the spikelet and rachis. Each inoculation technique was assessed using susceptible cultivars to determine the optimum inoculum concentration, the ideal plant growth stage and the humidity requirements for successful infection.
Boot inoculation did not require high humidity and gave reliable infection with low secondary sporidia concentrations (1000–10 000/ml). The ideal plant growth stages for inoculation were early-boot and mid-boot. Spray inoculation required high secondary sporidia concentrations (50 000/ml) and 48 h of high humidity, but infection was initiated over a range of growth stages throughout heading and anthesis. Cotton wool inoculation gave low levels of infection at growth stages throughout heading and anthesis, even with high secondary sporidia concentrations (100 000/ml). 相似文献
Boot inoculation did not require high humidity and gave reliable infection with low secondary sporidia concentrations (1000–10 000/ml). The ideal plant growth stages for inoculation were early-boot and mid-boot. Spray inoculation required high secondary sporidia concentrations (50 000/ml) and 48 h of high humidity, but infection was initiated over a range of growth stages throughout heading and anthesis. Cotton wool inoculation gave low levels of infection at growth stages throughout heading and anthesis, even with high secondary sporidia concentrations (100 000/ml). 相似文献
118.
Population genetics and shell morphology have been studiedin 11
populations of the poorly colonizing land caenogastropodPomatias
elegans. The total area of suitable habitats in northwestEurope is
shrinking and many isolated populations are becomingvulnerable to
extinction. In this study we tested whether theconcept of management
units (i.e. groups of population withsignificantly different allele
frequencies due to demographicindependence) is applicable to the
conservation of P. elegans.Fst values indicated strong genetic
differentiation and thuslittle genetic exchange between
populations. Allozyme differentiationcould be explained with an
isolation by distance model, whereasmorphological differentiation
could not. A morphological differenceexists between sexes but not
sufficient to discriminate malesand females. A Mantel test showed no
significant relationshipbetween morphological distance (size
corrected or not) and geneticdistance. Since allele frequencies
differed even among populationsin areas where P. elegans is not
threathened, we conclude thatin the case of P. elegans, defining
management units with allozymesmay not be an appropriate way to
select the most suitable populationsfor conservation. (Received 3 April 2000; accepted 25 August 2000) 相似文献
119.
ELIZABETH A. POVINELLI 《American anthropologist》2004,106(2):421-422
The Empire of Things: Regimes of Value and Material Culture. Fred R. Myers, ed. Santa Fe, NM: SAR Press, 2001. 366 pp. 相似文献
120.