全文获取类型
收费全文 | 462篇 |
免费 | 23篇 |
国内免费 | 18篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 10篇 |
2011年 | 26篇 |
2010年 | 19篇 |
2009年 | 32篇 |
2008年 | 36篇 |
2007年 | 26篇 |
2006年 | 39篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 11篇 |
2002年 | 17篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有503条查询结果,搜索用时 15 毫秒
41.
调查资料表明,黄鹀(Emberiza citronella erythrogenys)在中国境内新疆北部越冬,并非是偶见冬候鸟或迷鸟。 相似文献
42.
43.
44.
Summary An electron microscopic investigation of the extrapulmonary respiratory tract of embryos and chick of the domestic fowl (Gallus domesticus) has demonstrated for the first time in birds the presence here of a small number of epithelial cells characterised by an aminecontaining type of granule. These granular cells were scattered singly throughout the trachea, syrinx and primary bronchi and seemed more numerous in the caudal part of the airway. In favourable planes of section a small part of the cell was in contact with the luminal surface of the epithelium. The characteristic granular vesicles (approximate diameter 140 nm) appeared to be randomly distributed in the cytoplasm and there was no concentration of vesicles close to the plasma membrane. One of the cells was closely associated with an intraepithelial axon. By fluorescence microscopy, a small number of cells with a similar shape and distribution to the granular cells was observed after administration of 3,4-dihydroxyphenylalanine which may indicate the presence of an amine handlign mechanism in these cells. It is suggested that the granular cells belong to the APUD system of endocrine cells and that they may be modulated by the concentration of gas in the airways. 相似文献
45.
Attraction of Culex pipiens to uropygial gland secretions does not explain feeding preference for American robins 下载免费PDF全文
Mary C. Garvin Amy L. Austin Norberth H. Stracker Samuel P. Slowinski Jordan E. Rutter Maxwell Butler Megan Michel Rebecca J. Whelan 《Journal of vector ecology》2018,43(1):110-116
Culex pipiens, the endemic mosquito vector of West Nile virus in eastern North America, is responsible for maintenance of the virus in avian reservoir hosts, the most important of which appears to be the American robin. One reason for the greater involvement of robins is believed to be the feeding preference of Cx. pipiens, however, the basis of this preference is not understood. We tested the hypothesis that the species‐specific chemical profile of avian uropygial gland secretions are used by Cx. pipiens as cues to locate birds and, therefore, may contribute to the observed feeding preferences. We used gas chromatography‐mass spectrometry to identify the semi‐volatile components of the uropygial gland secretions of American robins and two other common reservoir host species, the house sparrow and European starling. We found that the chemical composition of the robin secretions was different from those of the sparrows and starlings. Through behavioral choice trials conducted in a dual‐port olfactometer, we also found that Cx. pipiens did not prefer the secretions of robins over the other two species. Surprisingly, however, we found that Cx pipiens were more often attracted to live starlings over robins and to the secretions of starlings over those of robins. 相似文献
46.
Striking uniformity exists in humans' preference to conceal sexual activity from conspecifics' view. Yet, little is known about the selective pressures acting upon its evolution. To investigate this question, we studied the cooperatively breeding Arabian babbler (Turdoides squamiceps), which has been suggested being the only other species where dominant individuals conceal sex regularly. We examined whether birds indeed conceal sex and tested different hypotheses postulating that sex concealment functions to avoid predators, signal dominance status, or to avoid social interference. The results showed that the birds concealed sex in all observed cases of copulation, did not prefer to copulate under shelters and concealed mating solicitations from adult conspecifics. In addition, subordinates did not attack dominants who courted the respective female. Hence, none of the tested hypotheses explains these results satisfactorily. We postulate that dominant Arabian babblers conceal sex to maintain cooperation with those helpers they prevent from mating. Empirical desiderata for testing this ‘Cooperation-Maintenance’ hypothesis are discussed. 相似文献
47.
北京雾灵山自然保护区冬春季地面活动鸟兽红外相机初步调查 总被引:4,自引:0,他引:4
为了解北京雾灵山自然保护区野生动物资源现状,于2014年11月至2015年4月,在保护区内放置30台红外相机开展调查。结果共记录鸟类5目14科27种,兽类4目8科10种,其中勺鸡(Pucrasia macrolopha)、红角鸮(Otus sunia)、纵纹腹小鸮(Athene noctua)和中华斑羚(Naemorhedus griseus)为国家Ⅱ级重点保护野生动物。鸟类物种数月变化剧烈。相对丰富度最高的6种动物为狍(Capreolus pygargus)(60.19)、红嘴蓝鹊(Urocissa erythrorhyncha)(34.14)、星鸦(Nucifraga caryocatactes)(27.78)、岩松鼠(Sciurotamias davidianus)(23.34)、松鸦(Garrulus glandarius)(23.34)、中华斑羚(21.99)。对狍、岩松鼠、中华斑羚进行日活动节律分析,狍属晨昏活动型;中华斑羚有两个活动高峰;岩松鼠的日活动高峰集中在晨间,为单峰型。本研究提供了北京雾灵山部分鸟兽资源的最新动态现状及活动节律信息,同时表明红外相机在拍摄地栖性鸟类、大中型兽类、夜行性动物方面具有优势,而对于非地栖鸟类和小型兽类,红外相机有一定局限性。本研究为应用红外相机技术开展森林野生动物多样性监测提供了经验。 相似文献
48.
Annotated genomes can provide new perspectives on the biology of species. We present the first de novo whole genome sequencing for the pink-footed goose. In order to obtain a high-quality de novo assembly the strategy used was to combine one short insert paired-end library with two mate-pair libraries. The pink-footed goose genome was assembled de novo using three different assemblers and an assembly evaluation was subsequently performed in order to choose the best assembler. For our data, ALLPATHS-LG performed the best, since the assembly produced covers most of the genome, while introducing the fewest errors. A total of 26,134 genes were annotated, with bird species accounting for virtually all BLAST hits. We also estimated the substitution rate in the pink-footed goose, which can be of use in future demographic studies, by using a comparative approach with the genome of the chicken, the mallard and the swan goose. A substitution rate of 1.38 × 10? 7 per nucleotide per generation was obtained when comparing the genomes of the two closely-related goose species (the pink-footed and the swan goose). Altogether, we provide a valuable tool for future genomic studies aiming at particular genes and regions of the pink-footed goose genome as well as other bird species. 相似文献
49.
This article explores factors that shape population structure in novel environments that have received scant theoretical attention: cities. Urban bird populations exhibit higher densities and lower diversity. Some work suggests this may result from lower predation pressure and more predictable and abundant resources. These factors may lead to populations with few winners and many losers regarding access to food, body condition, and reproductive success. We explore these hypotheses with an individual-energy-based competition model with two phenotypes of differing foraging ability. We show that low frequency resource fluctuations favor strong competitors and vice versa. We show that low predation skews equilibrium populations in favor of weak competitors and vice versa. Increasing the time between resource pulses can thus shift population structure from weak to strong competitor dominance. Given recent evidence for more constant resource input and lower predation in urban areas, the model helps understand observed urban bird population structure. 相似文献
50.
Peter D.M. Weesie 《Geobios》1984,17(6):845-849
This paper deals with some Pleistocene fossil birds from the south Aegean island of Karpathos. The species which could be identified are surveyed, and the paleogeography of the area is discussed. 相似文献