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   69篇
  免费   6篇
  2021年   3篇
  2020年   7篇
  2017年   3篇
  2016年   1篇
  2015年   2篇
  2014年   2篇
  2013年   2篇
  2012年   2篇
  2011年   3篇
  2010年   6篇
  2009年   10篇
  2008年   6篇
  2006年   1篇
  2005年   2篇
  2004年   3篇
  2001年   1篇
  1997年   2篇
  1994年   3篇
  1993年   2篇
  1991年   1篇
  1990年   2篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1983年   1篇
  1981年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1972年   1篇
  1966年   1篇
排序方式: 共有75条查询结果,搜索用时 31 毫秒
11.
Temperate species are projected to experience the greatest temperature increases across a range of modelled climate change scenarios, and climate warming has been linked to geographical range and population changes of individual species at such latitudes. However, beyond the multiple modelling approaches, we lack empirical evidence of contemporary climate change impacts on populations in broad taxonomic groups and at continental scales. Identifying reliable predictors of species resilience or susceptibility to climate warming is of critical importance in assessing potential risks to species, ecosystems and ecosystem services. Here we analysed long‐term trends of 110 common breeding birds across Europe (20 countries), to identify climate niche characteristics, adjusted to other environmental and life history traits, that predict large‐scale population changes accounting for phylogenetic relatedness among species. Beyond the now well‐documented decline of farmland specialists, we found that species with the lowest thermal maxima (as the mean spring and summer temperature of the hottest part of the breeding distribution in Europe) showed the sharpest declines between 1980 and 2005. Thermal maximum predicted the recent trends independently of other potential predictors. This study emphasizes the need to account for both land‐use and climate changes to assess the fate of species. Moreover, we highlight that thermal maximum appears as a reliable and simple predictor of the long‐term trends of such endothermic species facing climate change.  相似文献   
12.
Two Orthotrichum species of the subgenus Orthophyllum were compared with other representatives of this genus using the internally transcribed spacer regions 1 and 2, the chloroplast trnH-psbA region and ISSR and ISJ DNA markers. The applied DNA markers revealed many bands and mutations specific only to O. gymnostomum and O. obtusifolium. A phylogenetic analysis clearly supported the previous concepts postulating that species of the subgenus Orthophyllum should be recognized as separate genus Nyholmiella.  相似文献   
13.
The ultrastructure of the head end and surface structure of the cuticle of Syphacia petrusewiczi, S. nigeriana, S. frederici and S. stroma was studied. These species may be easily separated on the basis of the differences in their morphology: S. frederici possesses longitudinal septa on the body surface, a row of denticles on each of the three main teeth, and cervical alae; S. nigeriana has longitudinal septa and denticles but lack cervical alae; S. petrusewiczi has longitudinal septa and cervical alae but lacks denticles; S. stroma lacks these three characters.  相似文献   
14.
The morphogenesis of the crocodilian and avian columella auris is analysed, using Alligator and Struthio as models that are studied in detail, and Crocodylus, Gallus, and Coturnix as models for comparative purposes. This investigation was undertaken to address controversies emanating from previous studies concerning the identity of archosaurian hyal elements, and to clarify confounding nomenclature that has been used for both topographic and phylogenetic purposes. We found that confusion in the identification of the reptilian and avian hyoid arch derivatives is attributable to: (1) redundant and/or inconsistently applied topographical terminology; (2) mixing of topographical and phylogenetic terminology; (3) interpretation in a recapitulatory framework; and (4) failure to consider that developmental pathways of recent archosaurians (reptilians and birds) might be divergently modified. Our analysis identifies errors in previous interpretations, misinterpretations of prior work, and histological observations that have been idealized. The most controversial issues are addressed – the derivation of the supracolumellar process; the concept of the laterohyal component; and segmentation of the distal part of the reptilian and avian columella auris. Based on new data, we suggest that the osteichthyan infrapharyngohyal, suprapharyngohyal, epihyal, and ceratohyal are not applicable terms for reptilian and avian columellar components from a phylogenetic perspective, and should not be used as topographical terms either. We further propose that the original morphogenetic program of the hyoid arch has been overwritten in newly derived evolutionary pathways of crocodilians and birds, in which a new functional and morphological patterning of the hyoid arch, as a specific sound‐transmitting apparatus, have evolved. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 384–410.  相似文献   
15.
The soldier caste represents the most conspicuous realization of termite eusociality, characterized by an extreme anatomical, behavioural, and physiological specialization. Numerous strategies have evolved in soldiers, including extreme adaptations such as self‐sacrifice by autothysis. In the present study, we investigated the structure and function of defensive glands in Glossotermes oculatus soldiers aiming to understand their use in combat. Three glands are involved in defence: labral, frontal, and labial glands. Mandibles are used to bite the enemy, whereas the secretions of labral and labial glands are discharged into the wound. A striking characteristic of G. oculatus is the lack of the frontal pore; the secretion of the frontal gland is discharged by a rupture of the body wall. We hypothesized that this self‐sacrifice is an efficient way of blocking a gallery under attack. A similar development of the frontal gland occurs in Serritermes serrifer, which supports the close relationship between the two genera inferred from morphological and genetic analyses. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 839–848.  相似文献   
16.
Abstract: We present the first record of the cardiid genus Monodacna from the Pliocene of Anatolia, Turkey. Monodacna imrei sp. nov. was found in the Pliocene Killik Formation from the western margin of the Baklan Basin, in very marginal brackish to freshwater lacustrine deposits. The new record extends the stratigraphic range of the modern Ponto‐Caspian genus back into the Pliocene and adds to earlier evidence that modern Ponto‐Caspian taxa originated in the Pliocene of south‐western Turkey.  相似文献   
17.
Recent studies have revealed high local diversity and endemism in groundwaters, and showed that species with large ranges are extremely rare. One of such species is the cave shrimp Troglocaris anophthalmus from the Dinaric Karst on the western Balkan Peninsula, apparently uniform across a range of more than 500 kilometres. As such it contradicts the paradigm that subterranean organisms form localized, long-term stable populations that cannot disperse over long distances. We tested it for possible cryptic diversity and/or unexpected evolutionary processes, analysing mitochondrial (COI, 16S rRNA) and nuclear (ITS2) genes of 232 specimens from the entire range. The results of an array of phylogeographical procedures congruently suggested that the picture of a widespread, continuously distributed and homogenous T. anophthalmus was wrong. The taxon is composed of four or possibly five monophyletic, geographically defined phylogroups that meet several species delimitation criteria, two of them showing evidence of biological reproductive isolation in sympatry. COI genetic distances between phylogroups turned out to be a poor predictor, as they were much lower than the sometimes suggested crustacean threshold value of 0.16 substitutions per site. Most results confirmed the nondispersal hypothesis of subterranean fauna, but the southern Adriatic phylogroup displayed a paradoxical pattern of recent dispersal across 300 kilometres of hydrographically fragmented karst terrain. We suggest a model of migration under extreme water-level conditions, when flooded poljes could act as stepping-stones. In the north of the range (Slovenia), the results confirmed the existence of a zone of unique biogeographical conflict, where surface fauna is concordant with the current watershed, and subterranean fauna is not.  相似文献   
18.
Roĉek, Z. & Rage, J.-C. 1994 10 15: The presumed amphibian footprint Notopus petri from the Devonian: a probable starfish trace fossil.
A presumed amphibian footprint from the late Middle or early Late Devonian of Brazil, described as the ichnotaxon Notopus petri Leonardi, 1983, has been reinvestigated. Various morphological and paleoecological data, taken as a whole, cast doubts on the original interpretation. It is not excluded that the specimen represents an imperfect impression produced by an asteroid or ophiurid echinoderm similar to those that are allocated to the ichnogenus Asteriacites Schlotheim, 1820, nor can some other reported trackways be taken as unequivocal evidence of Devonian amphibians. Notopus petri, ichnofossil, Devonian, Echinodermata, starfish, Amphibia, Brazil .  相似文献   
19.
20.
The relationship between agricultural intensification and a decline in farmland bird populations is well documented in Europe, but the results are mostly based on data from the western part of the continent. In the former socialist eastern and central European countries, political changes around 1990 resulted in a steep decline in the intensity of agriculture. Therefore, one would expect populations of farmland birds to have recovered under these conditions of lower agricultural intensity. We explored population trends of 19 farmland bird species in the Czech Republic between 1982 and 2003 using data from a large‐scale monitoring scheme, and, additionally, we looked for relationships between such population changes and a number of variables describing the temporal development of Czech agriculture. Most farmland species declined during the focal period, and this decline was steepest in farmland specialists (Northern Lapwing Vanellus vanellus, Skylark Alauda arvensis, Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella). Although the intensity of agriculture was lower after than before 1990, the overall decline continued in most farmland bird species, albeit at a slower rate. The correlations between agricultural intensity and farmland bird decline showed opposite patterns to that found in other European studies, because bird populations were highest in years with the most intensive agriculture. We speculate that this pattern could have resulted from the impact of different driving forces causing farmland bird decline in different periods. The high intensity of agriculture could have caused the decline of the originally abundant populations before 1990. After 1990, the decreasing area of arable land could be the most important factor resulting in the continued decline of farmland bird populations. Our results demonstrate that the drivers of farmland bird population changes could differ across Europe, and thus investigations into the effect of farmland management in different parts of the continent are urgently required.  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