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   144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   3篇
  2012年   3篇
  2011年   3篇
  2010年   6篇
  2009年   12篇
  2008年   5篇
  2006年   3篇
  2005年   2篇
  2004年   4篇
  2002年   1篇
  2001年   1篇
  1997年   2篇
  1996年   3篇
  1995年   1篇
  1994年   6篇
  1993年   2篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1987年   1篇
  1983年   3篇
  1982年   1篇
  1981年   3篇
  1978年   6篇
  1977年   2篇
  1976年   3篇
  1973年   1篇
  1972年   3篇
  1971年   1篇
  1966年   1篇
  1965年   1篇
  1959年   3篇
  1958年   6篇
  1957年   8篇
  1956年   3篇
  1955年   2篇
  1954年   4篇
  1953年   3篇
  1952年   3篇
  1951年   1篇
  1950年   3篇
  1949年   2篇
  1948年   1篇
排序方式: 共有150条查询结果,搜索用时 251 毫秒
31.
Prey selection and annual harvest of game in a rural Zambian community   总被引:1,自引:1,他引:0  
The selection and hunting patterns of Valley Bisa hunters were studied as part of a broader ecological investigation of human communities between the two sections of the Luangwa Valley Game Reserves in Zambia. This article provides information on the frequency and duration of hunts recorded for 1 year, yields of individual hunters, prey selection, frequency of kill, community meat supplies and the effect of human and carnivore predation on population levels on a study area of some 155 km2. Individuals who hunted were classified into four categories–resident, transient, occasional, and official, dependent upon their role in the community, length of time spent on the study area and their village of primary residence. The most frequent hunters were residents followed in rank order by officials, transients and occasionals. Hunts were of shorter duration during the dry season, when game was close to villages, than during the wet season. Generally hunters who owned or had access to modern weapons were more successful in their pursuits of game than were those who used muzzle-loading guns. A total of 27 451 kg of meat (carcass yield) was made available to 466 local residents during the course of the year; 40% of this was attributed to the activities of the game guards. Valley Bisa hunters killed primarily buffalo, impala, warthogs, and waterbuck; most of these were males and adults. The kills recorded for carnivores suggest that they took primarily female buffalo and zebra. There was no evidence to suggest that either type of predation was damaging to the game herds on the study area.  相似文献   
32.
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   
33.
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   
34.
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   
35.
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   
36.
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   
37.
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   
38.
39.
40.
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