全文获取类型
收费全文 | 274篇 |
免费 | 7篇 |
出版年
2016年 | 4篇 |
2015年 | 4篇 |
2013年 | 9篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 9篇 |
2007年 | 13篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1966年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1956年 | 5篇 |
1955年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有281条查询结果,搜索用时 31 毫秒
141.
The leaf is a multi-scale dynamic unit that is determined by mechanisms at different organizational scales (cell, tissue, whole leaf and whole plant) and affected by both internal (genotype) and external (environmental) determinisms. The recent development of phenotyping platforms and imaging techniques provides new insights into the temporal and spatial patterns of leaf growth as affected by those determinisms. Conclusions about the overriding mechanisms often depend on the considered organizational scale and of time resolution which varies from minutes to several weeks. Analyses of leaf growth responses to environmental conditions have revealed robust emerging properties at whole plant or whole leaf scales. They have highlighted that the control of individual leaf expansion is more complex than merely the sum of cellular processes, and the control at the whole plant level is more complex than the sum of individual leaf expansions. However, in many cases, the integrated leaf-growth variable can be simplified to a limited set of underlying variables to be measured for comparative analyses of leaf growth or modelling purposes. 相似文献
142.
143.
ANDREW R. THOMPSON CHRISTINE E. THACKER EMILY Y. SHAW DAWN M. ROJE 《Molecular ecology resources》2006,6(3):918-920
We developed 16 pairs of primers for microsatellite loci of the fierce shrimpgoby, Ctenogobiops feroculus. Analysis of 35–40 gobies per locus from five islands in French Polynesia indicated that allele frequency varied from two to 30 per locus, while observed heterozygosity ranged between 0.05 and 0.98. These microsatellites should provide insight into patterns of dispersal and connectivity among populations of this common coral reef fish. 相似文献
144.
N. A. DYER A. FURTADO† J. CANO‡ F. FERREIRA§ M. ODETE AFONSO¶ N. NDONG-MABALE P. NDONG-ASUMU†† S. CENTENO-LIMA§ A. BENITO‡ D. WEETMAN M. J. DONNELLY J. PINTO† 《Molecular ecology》2009,18(15):3268-3282
Tsetse flies of the palpalis group are major vectors of Human African Trypanosomiasis in Africa. Accurate knowledge of species identity is essential for vector control. Here, we combine ribosomal internal transcribed spacer 1 ( ITS1 ), mitochondrial Cytochrome Oxidase 1 ( COI ) and microsatellites to determine the population structure and phylogenetic relations of Glossina p. palpalis in Equatorial Guinea. CO1 sequence data suggest that G. p. palpalis in Equatorial Guinea is a distinct subspecies from previously described G. p. palpalis in West Africa and Democratic Republic of Congo. Glossina p. palpalis in Equatorial Guinea and DRC share a common ancestor which diverged from West African G. p. palpalis around 1.9 Ma. Previous ITS1 length polymorphism data suggested the possible presence of hybrids in Equatorial Guinea. However, ITS1 showed incomplete lineage sorting compared with clearly defined COI groups, and data from 12 unlinked microsatellites provided no evidence of hybridization. Microsatellite data indicated moderate but significant differentiation between the populations analysed (Rio Campo, Mbini and Kogo). Moreover, unlike previous studies of G. p. palpalis , there was no evidence for heterozygote deficiency, presence of migrants or cryptic population structure. Variance effective population size at Rio Campo was estimated at 501–731 assuming eight generations per year. This study of the population genetics of G. p. palpalis in central Africa provides the first estimate of genetic differentiation between geographically separated G. p. palpalis populations. 相似文献
145.
ANA SOFIA SOARES-CORDEIRO SIMON P. DRISCOLL TILL K. PELLNY ENRIQUE OLMOS MARIA CELESTE ARRABAÇA & CHRISTINE H. FOYER 《Plant, cell & environment》2009,32(12):1833-1844
Photosynthesis and associated signalling are influenced by the dorso-ventral properties of leaves. The degree of adaxial/abaxial symmetry in stomatal numbers, photosynthetic regulation with respect to light orientation and the total section areas of the bundle sheath (BS) cells and the surrounding mesophyll (M) cells on the adaxial and abaxial sides of the vascular bundles were compared in two C4 [ Zea mays (maize) and Paspalum dilatatum ] and one C3 [ Triticum turgidum (Durum wheat)] monocotyledonous species. The C3 leaves had a higher degree of dorso-ventral symmetry than the C4 leaves. Photosynthetic regulation was the same on each side of the wheat leaves, as were stomatal numbers and the section area of the BS relative to that of the M cells (BS/M section area ratio). In contrast, photosynthetic regulation in maize and P. dilatatum leaves showed a marked surface-specific response to light orientation. Compared to the adaxial sides of the C4 monocotyledonous leaves, the abaxial surfaces had more stomata and the BS/M section area ratio was significantly higher. Differences in dorso-ventral structure, particularly in Kranz anatomy, serve not only to maximize photosynthetic capacity with respect light orientation in C4 monocotyledonous leaves but also allow adaxial and abaxial-specific signalling from the respective M cells. 相似文献
146.
CHRISTINE S. FELLOWS STUART E. BUNN FRAN SHELDON NERIDA J. BEARD 《Freshwater Biology》2009,54(2):236-253
1. Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River. 2. Both rivers have similar variable hydrology and high levels of turbidity (photic depths < 0.4 m), but fish abundance in Cooper Creek is 10 times than that of the Warrego River. Therefore, an additional aim of the study was to determine if fish abundances reflected underlying differences in benthic primary production. 3. Benthic gross primary production (GPP), benthic respiration, nutrient concentrations and light penetration were measured immediately after flow had ceased (‘post‐flow’) and after at least 2 months of zero flow (‘no‐flow’) in 15 waterholes from each river. A subset of four waterholes from each river was sampled on two additional occasions to determine if patterns were consistent over time. 4. Cooper Creek generally had higher rates of GPP and a more autotrophic benthic zone than the Warrego River. As a result, the expected positive relationship between fish abundance and GPP was generally observed at a broad catchment scale. 4. Light was the major control in benthic GPP in both rivers, as nutrient concentrations were high on all sampling occasions. However, for similar values of photic depth, GPP was greater in Cooper Creek than in the Warrego River. This suggests that more frequent disturbance of the littoral zone may inhibit biofilm development in waterholes of the Warrego River. 5. Although flow variability in dryland rivers is extreme compared with other rivers worldwide, cycles of expansion and contraction of aquatic habitat in these two rivers were associated with a shift in the dominance of regional scale (subcatchments contributing to river flow) versus local scale (waterhole morphology) influences on ecosystem functioning, similar to floodplain rivers in tropical and temperate regions. 相似文献
147.
JEFFERY R. BROWN CHRISTINE A. BISHOP RONALD J. BROOKS 《The Journal of wildlife management》2009,73(3):419-425
ABSTRACT Short-distance translocation (SDT) is commonly used to mitigate snake-human interactions, yet little is known about its effectiveness or its effects on behavior and welfare of snakes. Between April 2004 and October 2005, we evaluated SDT as a conservation and management tool by investigating how 500-m SDT affected spatial ecology, body condition, and behavior of western rattlesnakes (Crotalus oreganus) surgically implanted with radiotransmitters in a field study near Osoyoos, British Columbia, Canada. Of 14 rattlesnakes subjected to SDT, 12 (85.7%) returned on ≥1 occasion (range 1–7 times) to the general area they were removed from. Rattlesnakes that underwent SDT showed an increase in total distance moved over an active season compared to non-translocated snakes, but there was no evidence to suggest SDT had an effect on activity range size. There was no evidence to suggest SDT affected body condition, behavior, or mortality rates. Short-distance translocation to high-quality undisturbed habitats was unsuccessful as a long-term solution to snake-human conflict because most translocated snakes returned to conflict areas within a short time (x̄x = 19.9 ± 8.7 days). However, SDT may be an effective short-term tool to manage snake-human conflict in areas where human presence is seasonal or short-lived if careful attention is paid to species-specific biological needs, habitat quality at the release site, and the location of the release site in relation to conflict areas. 相似文献
148.
NATHALIE NIQUIL GRETTA BARTOLI JOTARO URABE GEORGE A. JACKSON LOUIS LEGENDRE CHRISTINE DUPUY M. KUMAGAI 《Freshwater Biology》2006,51(8):1570-1585
1. A steady‐state model of carbon flows was developed to describe the summer planktonic food web in the surface mixed‐layer of the North Basin in Lake Biwa, Japan. This model synthesised results from numerous studies on the plankton of Lake Biwa. 2. An inverse analysis procedure was used to estimate missing flow values in a manner consistent with known information. Network analysis was applied to characterise emergent properties of the resulting food web. 3. The system strongly relied on flows related to detrital particles. Whereas primary production was mainly by phytoplankton >20 μm, microzooplankton were active and mainly ingested detritus and bacteria. 4. The main emergent property of the system was strong recycling, through either direct ingestion of non‐living material by zooplankton, or ingestion of bacteria after degradation of detritus to release dissolved organic carbon. 相似文献
149.
CHRISTINE L. HUFFARD NORAH SAARMAN HEALY HAMILTON W. BRIAN SIMISON 《Biological journal of the Linnean Society. Linnean Society of London》2010,101(1):68-77
The ‘Mimic Octopus’Thaumoctopus mimicus Norman & Hochberg, 2005 exhibits a conspicuous primary defence mechanism (high‐contrast colour pattern during ‘flatfish swimming’) that may involve facultative imperfect mimicry of conspicuous and/or inconspicuous models, both toxic and non‐toxic (Soleidae and Bothidae). Here, we examine relationships between behavioural and morphological elements of conspicuous flatfish swimming in extant octopodids (Cephalopoda: Octopodidae), and reconstructed ancestral states, to examine potential influences on the evolution of this rare defence mechanism. We address the order of trait distribution to explore whether conspicuous flatfish swimming may be an exaptation that usurps a previously evolved form of locomotion for a new purpose. Contrary to our predictions, based on the relationships we examined, flatfish swimming appears to have evolved concurrently with extremely long arms, in a clade of sand‐dwelling species. The conspicuous body colour pattern displayed by swimming T. mimicus may represent a secondary adaptation potentially allowing for mimicry of a toxic sole, improved disruptive coloration, and/or aposematic coloration. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 68–77. 相似文献
150.
by MICHAEL J. VENDRASCO SUSANNAH M. PORTER† ARTEM KOUCHINSKY‡ GUOXIANG LI§ CHRISTINE Z. FERNANDEZ¶ 《Palaeontology》2010,53(1):97-135
Abstract: Numerous new cases of preserved shell microstructure were discovered in molluscs from the Middle Cambrian Gowers Formation (Ptychagnostus atavus/Peronopsis opimus Zone, Floran Stage) in the Georgina Basin, Australia. The new data provide further evidence that, by the Middle Cambrian, molluscan shell microstructures were diverse, and many molluscs had a complex shell with multiple types of shell microstructure. In addition, many new occurrences of laminar microstructures are described herein. For many, the nature of these laminar microstructures is not known, but in three species the microstructure is foliated calcite, and in at least two the microstructure is more likely to have been calcitic semi‐nacre, a type of microstructure known in brachiopods and bryozoans but unknown in modern molluscs. This commonality among these three closely related lophotrochozoans underscores a similar mechanism of biomineralization. Moreover, these observations suggest a prevalence of calcite‐shelled lineages among molluscs from the Middle Cambrian, a time of calcite seas. In addition, the broad occurrence of laminar, nacre‐like microstructures in many of these fossils reveals how widespread these strong (fracture‐resistant) microstructures were in Middle Cambrian molluscs. Additionally, a few specimens of Yochelcionella preserve imprints of a bilaterally symmetrical pair of muscle scars. New taxa described here include Corystos thorntoniensis gen. et sp. nov., Yochelcionella snorkorum sp. nov., Yochelcionella saginata sp. nov., and Anhuiconus? agrenon sp. nov. 相似文献