首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   201篇
  免费   2篇
  2017年   1篇
  2015年   1篇
  2014年   4篇
  2013年   5篇
  2012年   11篇
  2011年   17篇
  2010年   19篇
  2009年   17篇
  2008年   13篇
  2007年   19篇
  2006年   13篇
  2005年   18篇
  2004年   4篇
  2003年   2篇
  2002年   2篇
  2001年   3篇
  2000年   6篇
  1999年   3篇
  1998年   1篇
  1997年   5篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1993年   1篇
  1992年   4篇
  1990年   1篇
  1988年   1篇
  1987年   1篇
  1982年   2篇
  1980年   1篇
  1979年   1篇
  1972年   3篇
  1971年   1篇
  1959年   3篇
  1958年   3篇
  1957年   2篇
  1955年   4篇
  1954年   2篇
  1951年   1篇
排序方式: 共有203条查询结果,搜索用时 625 毫秒
21.
Abstract.  A revision of the Charis cleonus group of Neotropical riodinid butterflies is presented, including discussions on the taxonomy, biogeography and biology of its species, and illustrations of the adults and male and female genitalia (where known) of all taxa. We recognize twenty-two species, including nineteen new species: C. ariquemes sp.n., C. brasilia sp.n., C. breves sp.n., C. cacaulandia sp.n., C. cuiaba sp.n., C. humaita sp.n., C. ipiranga sp.n., C. iquitos sp.n., C. ma sp.n., C. manicore sp.n., C. manu sp.n., C. matic sp.n., C. maues sp.n., C. negro sp.n., C. palcazu sp.n., C. rocana sp.n., C. santarem sp.n., C. tapajos sp.n and C. tefe sp.n. A cladistic analysis using thirty-six characters of male and female genitalia and external facies generated a single most parsimonious cladogram highlighting the existence of two clades, the major and cleonus subgroups. As each species largely occupies a parapatric range, this cladogram provides the opportunity to reassess historical relationships among areas of endemism in the Amazon basin.  相似文献   
22.
Plazas are often important spatial representations of society and social hierarchy. Those built in Mesoamerica and the Caribbean under the direction of the Spanish have been interpreted as architectural representations of colonial control and oppression. Underlying these interpretations is the tacit assumption that plaza-centered urban design was of solely European derivation, in spite of considerable evidence of pre-Columbian contributions. In fact, the correspondence between the indigenous forms and Spanish reconstruction is so well documented that the denial of its significance is startling.  相似文献   
23.
Abstract Fragmented habitats are a common occurrence in many marine systems, but remain poorly studied in comparison to their terrestrial counterparts. Here, I show that crustaceans inhabiting fragmented Zostera seagrass meadows show a dramatic response (change in abundance) to patch edges, with 11 out of 12 tests showing greatest abundance at the boundary between sand and seagrass. These patterns occurred on a scale of 0.25–1 m around the patch edge. Changes in seagrass biomass are unlikely to explain this pattern, as seagrass biomass increased smoothly at the patch edge, and did not decline towards patch interiors. In contrast to crustaceans, only a few polychaete taxa responded to the patch edge (9 of 25 tests), and bivalves generally did not show a response (1 of 5 tests). These latter groups are predominantly infaunal, and their lack of response may be partly due to the presence of substantial quantities of seagrass root and rhizome material in the sand habitat, which was defined visually based on the lack of above‐ground seagrass components only.  相似文献   
24.
The higher‐level phylogeny of the order Hemiptera remains a contentious topic in insect systematics. The controversy is chiefly centred on the unresolved question of whether or not the hemipteran suborder Auchenorrhyncha (including the extant superfamilies Fulgoroidea, Membracoidea, Cicadoidea and Cercopoidea) is a monophyletic lineage. Presented here are the results of a multilocus molecular phylogenetic investigation of relationships among the major hemipteran lineages, designed specifically to address the question of Auchenorrhyncha monophyly in the context of broad taxonomic sampling across Hemiptera. Phylogenetic analyses (maximum parsimony, maximum likelihood and Bayesian inference) were based on DNA nucleotide sequence data from seven gene regions (18S rDNA, 28S rDNA, histone H3, histone 2A, wingless, cytochrome c oxidase I and NADH dehydrogenase subunit 4) generated from 86 in‐group exemplars representing all major lineages of Hemiptera (plus seven out‐group taxa). All combined analyses of these data recover the monophyly of Auchenorrhyncha, and also support the monophyly of each of the following lineages: Hemiptera, Sternorrhyncha, Heteropterodea, Heteroptera, Fulgoroidea, Cicadomorpha, Membracoidea, Cercopoidea and Cicadoidea. Also presented is a review of the major lines of morphological and molecular evidence for and against the monophyly of Auchenorrhyncha.  相似文献   
25.
1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism. 2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt‐feeding herbivores by providing their natural enemies with stronger host/prey location cues. 3. Eucalyptus tereticornis Smith seedlings were grown under low‐ and high‐nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8‐cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined. 4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high‐ than low‐nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models. 5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high‐nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.  相似文献   
26.
Abstract: X‐ray microtomography (XMT) was applied to three species of the extinct arachnid order Trigonotarbida, hosted in siderite nodules from the late Carboniferous British Middle Coal Measures. All three, Cryptomartus hindi ( Pocock, 1911 ), Cleptomartus plautus ( Petrunkevitch, 1949 ) and Maiocercus celticus ( Pocock, 1902 ), belong to the family Anthracomartidae. As well as providing interactive three‐dimensional visualisations of their likely appearance in life, XMT study has resolved new morphological detail, yielding key data about the likely stance and habitus of these early arachnids. Similarities in the form of the carapace, eyes and coxosternal region between anthracomartids and the Devonian genus Palaeocharinus Hirst, 1923 are highlighted. Analogies in limb disposition are drawn between anthracomartids and modern crab spiders (Araneae: Thomisidae), which exhibit sit‐and‐wait style predatory behaviour. Anthracomartids are relatively common fossils at many Coal Measures localities. Although they appear to exhibit limited morphological variation, numerous genera and species have been proposed in the literature, often distinguished from each other on rather trivial characters. From our reconstruction of well‐preserved examples, we have resolved a number of common features likely to be present in a typical anthracomartid. Comparisons to this model suggest that the characters on which many anthracomartid genera are distinguished may be artefacts of preservation. We hence treat Promygale Fri?, 1901 , Brachylycosa Fri?, 1904 , Perneria Fri?, 1904 , Coryphomartus Petrunkevitch, 1945 , Cryptomartus Petrunkevitch, 1945 , Pleomartus Petrunkevitch, 1945 , Cleptomartus Petrunkevitch, 1949 and Oomartus Petrunkevitch, 1953 as junior synonyms of the type genus of the family, Anthracomartus Karsch, 1882 . Only the genera Brachypyge Woodward, 1878 and Maiocercus Pocock, 1911 are additionally retained. Within Anthracomartus, Cleptomartus planus Petrunkevitch, 1949 , Cryptomartus meyeri Guthörl, 1964 , Cleptomartus hangardi Guthörl, 1965 and Cryptomartus rebskei Brauckmann, 1984 are treated as junior synonyms of A. hindi Pocock, 1911 (all syn. nov.). Cleptomartus plautus Petrunkevitch, 1949 and Anthracomartus denuiti Pruvost, 1922 are treated as junior synonyms of A. priesti Pocock, 1911 (both syn. nov.).  相似文献   
27.
28.
Abstract 1. How populations respond to environmental change depends, in part, on the connection between environmental variance during early life stages and its effect on subsequent life‐history traits. For example, environmental variation during the larval stage can influence the life histories of organisms with complex life cycles by altering the amount of time spent in each stage of the life cycle as well as by altering allocation to life‐history traits during metamorphosis. 2. The effects of larval energetic resources on developmental timing, adult mass, fecundity, mating success, and allocation to adult body structures (thorax, abdomen, wings) were examined in an aquatic caddisfly (Agrypnia deflata Milne, Trichoptera: Phryganeidae). Larval energetic reserves were manipulated by removing larval cases just prior to pupation. In the first experiment, cases of all individuals were removed just prior to pupation; experimental individuals were required to build a new case whereas control individuals were allowed to re‐enter their case without building. In the second experiment, energy differences were maximised between the two treatments by supplementing the larval diet of the control group and removing cases and not supplementing the diet of the experimental group. 3. Male and female development time, adult mass, and female fecundity were not influenced by case removal or diet supplementation. In contrast, allocation to adult body parts indicated a trade‐off between abdominal and thoracic mass among case‐removal females, suggesting that, under larval resource stress, females adjust resource allocation during metamorphosis to alleviate potential negative impacts on clutch size. In addition, latency to copulation increased when cases were removed, indicating larval resource stress could influence male mating success. 4. This study suggests that, under larval energetic stress, the negative impacts on female reproduction might be mitigated by re‐allocating resources during metamorphosis, whereas male allocation strategies might not be as flexible as female strategies.  相似文献   
29.
1. The effects of spawning coho (Oncorhynchus kisutch) and chum salmon (Oncorhynchus keta) on the limnephilid caddisfly Ecclisomyia conspersa were evaluated by experimentally excluding salmon from the upper 14‐m stretch of a spawning channel by a wire‐meshed fence. Density, and development and growth rates, of larvae upstream of the fence (without salmon) were compared with those downstream (with salmon). 2. Larval density in the stretch with salmon declined during spawning, but increased again after spawning subsided and the carcasses of dead fish became available. In the stretch with salmon, larval density on salmon carcasses was seven to 37 times greater than on the adjacent channel substratum. The rate of larval development in the stretch with salmon was greater than that in the stretch without salmon. Two months after carcasses became available, 98% of larvae sampled from the stretch with salmon were in the fifth instar, compared to only 23% from the stretch without salmon. Body weight of E. conspersa in the stretches with and without salmon increased by an average of 3.04 and 2.38 mg, respectively, over a 6‐month period. 3. 15N values of larvae from the stretch with salmon increased following the arrival of the fish, suggesting that the larvae were feeding on salmon‐derived material, such as eggs and carcasses, which contain a high proportion of the heavier stable isotope. In contrast, 15N values of larvae from the stretch without salmon remained relatively constant throughout the experiment. The availability of salmon carcasses as a high‐quality food source late in larval development may increase survival and fecundity of E. conspersa. 4. These substantial differences were consistent with the view that they were due to the experimental exclusion of salmon and salmon carcasses from the upstream stretch, though the study was un‐replicated and thus precludes ascribing causation more definitely.  相似文献   
30.
This systematic study recognizes and describes 14 species of the genus Mallos O. Pickard-Cambridge, 1902 and three species of the genus Mexitlia Lehtinen, 1967. Three species of Mallos – Mallos gertschi, Mallos chamberlini and Mallos macrolirus –and one species of Mexitlia – Mexitlia altima –are newly described. Mallos ghiggi (Caporiacco, 1938) is considered a synonym of Mexitlia grandis (O. Pickard-Cambridge, 1896). Mexitlia grandis is considered the senior synonym of Mexitlia avara (Banks, 1898). Two species, Mallos jlavovittatus (Keyserling, 1880) and Mallos nigrescens (Caporiacco, 1955) are removed from Mallos. The males of Mallos kraussi Gertsch, 1946 and Mallos blandus Chamberlin and Gertsch 1958, are described for the first time. A cladistic analysis based on 26 morphological characters produced a cladogram that supports the monophyly of Mallos and the validity of Mexitlia. This cladogram presents a phylogenetic framework for considering the evolution of social behaviour in Mallos.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号