全文获取类型
收费全文 | 706篇 |
免费 | 29篇 |
出版年
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 11篇 |
2013年 | 27篇 |
2012年 | 32篇 |
2011年 | 20篇 |
2010年 | 30篇 |
2009年 | 30篇 |
2008年 | 24篇 |
2007年 | 36篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 12篇 |
2002年 | 23篇 |
2001年 | 34篇 |
2000年 | 32篇 |
1999年 | 27篇 |
1998年 | 29篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 7篇 |
1971年 | 4篇 |
1954年 | 4篇 |
1953年 | 3篇 |
1952年 | 4篇 |
1951年 | 6篇 |
1948年 | 4篇 |
排序方式: 共有735条查询结果,搜索用时 15 毫秒
1.
2.
S. L. GLOCKLING FLS G. W. BEAKES 《Botanical journal of the Linnean Society. Linnean Society of London》2001,136(3):329-338
Two new species of Haptoglossa , one zoosporic, H. northumbrica , and one aplanosporic, H. polymorphs, , were isolated from samples of manure and horse dung in north-east England. The zoosporic H. northumbrica is morphologically similar to H. dickii but differs in having slightly smaller infection gun cells with a unique internal arrangement of cones in the apical missile chamber. The thallus of the aplanosporic H. polymorpha is similar to H. heteromorpha but produces three different types of aplanospore. The smaller cysts either develop into broad, arcuate gun cells or form curved adhesive cells that have a rounded base. These curved adhesive cells have very different internal ultrastructural organization. The large cysts develop into infection cells that are morphologically similar to the curved adhesive cells, but their internal structure has not yet been observed. 相似文献
3.
EMMA DESPLAND MARIA GUNDERSEN SIMON P. DAOUST BRIAN J. MADER NATHALIE DELVAS PAUL J. ALBERT ERIC BAUCE 《Physiological Entomology》2011,36(1):39-46
The pattern of feeding of Eastern spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera, Tortricidae) is compared on foliage from white spruce Picea glauca (Moench) Voss. (Pinaceae) trees previously determined to be susceptible and resistant to defoliation by budworm. No differences are observed in electrophysiological responses from taste sensilla to aqueous extracts of the two foliage types, nor is there a preference for either extract type in a choice test. Acetone extracts from the two foliage types are both preferred to a control sucrose solution, although neither elicits a preference relative to the other. These results suggest that there is no difference in phagostimulatory power of internal leaf contents of the two foliage types. Longer‐term observation of feeding behaviour in a no‐choice situation shows no difference in meal duration, confirming the lack of difference in phagostimulatory power. However, on average, intermeal intervals are twice as long on the resistant foliage, leading to an overall lower food consumption during the assay. This result suggests an anti‐digestive or toxic effect of the resistant foliage that slows behaviour and limits food intake. Previous research has shown that waxes of the resistant foliage deter initiation of feeding by the spruce budworm and that this foliage contains higher levels of tannins and monoterpenes. The data suggest that the resistant foliage contains a post‐ingestive second line of defence against the spruce budworm. 相似文献
4.
Proteaceae are most diverse in southern Africa and Australia, especially in the south-western portions of these regions. Most genera have some species in flower at all times of the year, although generally there is a preponderance of species that flower between late winter and early summer. The one genus that is an exception to this generalization is Banksia, which either has approximately the same percentage of species in flower at various times of the year (southwestern Australia) or peaks in autumn (southeastern Australia). Within particular communities, opportunities for hybridization among congeneric species are minimized by staggered flowering times, different pollen vectors and/or various incompatibility mechanisms. Birds, mammals and arthropods have been identified as visitors to the inflorescences of many Proteaceae. The most common avian visitors to the majority of genera in Australia are honeyeaters, although lorikeets, silvereyes and approximately 40 other species sometimes may be important. Sugarbirds and sunbirds are seen most frequently at inflorescences of Protea, Leucospermum and Mimetes in southern Africa, although they rarely visit other genera. In most cases, avian visitors forage in a manner that permits the acquisition and transfer of pollen. Limited evidence supports the hypothesis that birds are selective in their choice of inflorescences, responding to morphological and/or colour changes and usually visiting those inflorescences that offer the greatest nectar rewards. Arthropods may be equally selective, although it is possible that only the larger moths, bees and beetles are important pollinators, even for those plant species that rely entirely on arthropods for pollen transfer. Mammals are pollen vectors for some Proteaceae, especially those that have geoflorous and/or cryptic inflorescences. In Australia, small marsupials may be the most important mammalian pollinators, although rodents fill this niche in at least some southern African habitats. All but two genera of Proteaceae are hermaphroditic and protandrous, the exceptions being the dioecious southern African genera Aulax and Leucadendron. For hermaphroditic species, the timing of visits by animals to inflorescences is such that they not only acquire pollen from freshly opened flowers but also brush against pollen presenters and stigmas of others that have lost self-pollen and become receptive. Birds and insects (and probably mammals) generally forage in such a way as to facilitate both outcrossing and selfing. Some species are self-compatible, although many require outcrossing if viable seed is to be formed. Regardless of which animals are the major pollen vectors, fruit set is low relative to the number of flowers available, especially in Australian habitats. Functional andromonoecy of the majority of flowers is advanced as the major cause of poor fruit set. The pollination biology and breeding systems of Australian and southern African Proteaceae resemble one another in many ways, partly because of their common ancestry, but also due to convergence. Divergence is less obvious, apart from the dichotomy between dioecious and hermaphroditic genera, and differences in the levels of seed set for Australian and African species. Future studies should concentrate on identifying the most important pollinators for various Proteaceae, the manner in which their visits are integrated with floral development and factors responsible for limiting fruit set. 相似文献
5.
6.
7.
8.
9.
Isolated intact plant mitochondria, including those from turnipand mung bean, show low endogenous Mg2+-ATPase activity and,unlike mammalian mitochondria, lack significant uncoupler-stimulatedATPase activity. In contrast, the rates of respiration-drivenATP synthesis are comparable to those in mammalian mitochondria,suggesting the presence of an ATPase inhibitor. Disruption ofintact turnip mitochondria only results in limited increasesin ATPase activity, indicating that a permeability barrier toATP transport is not primarily responsible for the low endogenousactivity. The ATPase activity of turnip mitochondria and membraneparticles can be increased up to 50-fold when assayed underoptimum conditions. Time-dependent increases in activity inducedby ageing, exposure to salts and trypsin treatment, are allconsistent with an inhibitor protein being responsible for thelow endogenous activity and lack of uncoupler-stimulation. TheATPase activity of particles under optimum conditions and afterageing is sufficient to account for the rates of ATP synthesis.After activation, turnip mitochondrial ATPase activity is similarto the mammalian enzyme in inhibitor sensitivity, pH optimum,bivalent cation requirement, and sensitivity to activatinganions. In mung bean mitochondria, a permeability barrierto ATP is only partly responsible for the low endogenous ATPaseactivity, together with the inhibitory factor. On the basisof variation in the relative Ca2+ and Mg2+ -ATPase activitiesafter various treatments, a Ca2+-regulatory site which affectsATPase activity is proposed to exist in the F1ATPase complex. Key words: Plant mitochondrial ATPase, calcium/magnesium -ATPase, inhibitor+ nucleotide specificity, cation/anion effects 相似文献
10.