全文获取类型
收费全文 | 2152篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
2191篇 |
出版年
2013年 | 47篇 |
2012年 | 31篇 |
2011年 | 44篇 |
2010年 | 94篇 |
2009年 | 106篇 |
2008年 | 74篇 |
2007年 | 113篇 |
2006年 | 66篇 |
2005年 | 67篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 15篇 |
2001年 | 20篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 46篇 |
1997年 | 40篇 |
1996年 | 40篇 |
1995年 | 45篇 |
1994年 | 37篇 |
1993年 | 39篇 |
1992年 | 42篇 |
1991年 | 40篇 |
1990年 | 30篇 |
1989年 | 50篇 |
1988年 | 44篇 |
1987年 | 32篇 |
1986年 | 37篇 |
1985年 | 33篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 33篇 |
1981年 | 33篇 |
1980年 | 46篇 |
1979年 | 36篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 29篇 |
1975年 | 32篇 |
1974年 | 40篇 |
1973年 | 37篇 |
1972年 | 51篇 |
1971年 | 70篇 |
1965年 | 16篇 |
1959年 | 20篇 |
1958年 | 20篇 |
1957年 | 20篇 |
1956年 | 16篇 |
1955年 | 15篇 |
1953年 | 15篇 |
排序方式: 共有2191条查询结果,搜索用时 15 毫秒
91.
TROY G. MURPHY TIFFANY T. PHAM 《Biological journal of the Linnean Society. Linnean Society of London》2012,106(3):673-681
Coloration plays an important role in sexual and social communication, and in many avian species both males and females maintain elaborate colours. Recent research has provided strong support for the hypothesis that elaborate female traits can be maintained by sexual or social selection; however, most research on female ornamentation has focused on pigment‐based colours, and less is known about how structural colours are maintained. Both sexes of the turquoise‐browed motmot (Eumomota superciliosa) have a blue‐green racket‐tipped tail, and it remains unknown if tail coloration serves as a sexual or social signal in one or both sexes. Here, we describe sexual dichromatism in the blue‐green portion of the tail racket, and we test for a relationship between coloration and condition, as indicated by growth bars. Tail colour of both sexes has a similar spectral shape, and there is significant, although moderate, sexual dichromatism: males are brighter than females, and males have marginally greater blue‐green saturation than females. The length of feather grown per day is positively related to overall feather brightness, but this relationship is only present in males. The relationship between male coloration and condition suggests that tail colour has the potential to convey information about individual quality during mate choice or contest competition. The lack of a similar relationship in females suggests that female tail colour does not convey the same condition‐dependent information that we suggest may be reflected by male colour. Female tail colour may therefore reflect other aspects of condition, be involved in other (non‐condition‐dependent) forms of communication, or be expressed as a non‐functional byproduct of genetic correlation between the sexes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 673–681. 相似文献
92.
ROBERT M. MAY 《Ibis》1995,137(S1):S85-S86
Over the past few years, I have written several reviews about the effects of infectious diseases upon the distribution and abundance of their host populations. One general review and synthesis is in the fmd chapter of a book whose earlier chapters focus mainly on human diseases (Anderson & May 1991). A bird-specific discussion, with particular reference to conservation issues, is given by Dobson and May (1991). Broadly related questions about the invasion, persistence and spread of infectious diseases within animal communities are explored by Anderson and May (1986) and with emphasis on bird populations by Dobson and May (1986). Also relevant are a set of papers from the Society for Conservation Biology's first-ever symposium on Conservation and Disease (for an overview, see May 1988, Scott 1988).
Rather than burdening the literature with a recapitulation of these existing reviews, this paper gives a sign-posted guide for those who are not familiar with this particular literature. I first sketch reasons for believing that infectious diseases play an important part in the life history of birds. Next I point towards an analytic framework for understanding the dynamics of host-pathogen associations. Finally I list some of the implications for the conservation biology of bird populations. 相似文献
Rather than burdening the literature with a recapitulation of these existing reviews, this paper gives a sign-posted guide for those who are not familiar with this particular literature. I first sketch reasons for believing that infectious diseases play an important part in the life history of birds. Next I point towards an analytic framework for understanding the dynamics of host-pathogen associations. Finally I list some of the implications for the conservation biology of bird populations. 相似文献
93.
ROBERT J. WALL 《Animal genetics》1989,20(4):325-327
94.
95.
96.
97.
RICHARD D. WARD 《Systematic Entomology》1976,1(3):227-240
Immature stages of Lutzomyia anduzei (Rozeboom), L.antunesi (Coutinho), L. flaviscutellata (Mangabeira), Psychodopygus davisi (Root), Ps.paraensis (Costa Lima) and Ps.lainsoni Fraiha & Ward are described from specimens reared in the laboratory. The Lutzomyia species are members of the intermedia group, though L. flaviscutellata larvae more closely resemble those of Psychodopygus species. The larvae of L.anduzei and L. antunesi are separable on minor setal differences and are similar to previously described members of the intermedia group. Ps. paraensis is distinguishable from the other two Psychodopygus species described, by the absence of prothoracic seta 2. Head seta 5 of Ps.davisi is about twice the length of that in Ps. paraensis and larvae of Ps.lainsoni are pale and characterized by colourless body setae 4 and 10. A key to the fourth instar larvae is given which includes all the known larvae of the intermedia group and of the genus Psychodopygus. Morphological differences in the Psychodopygus larvae do not appear to reflect the separation of the adults into series. 相似文献
98.
99.
Stomatal Response to Humidity and Lanthanum 总被引:1,自引:0,他引:1
ANTHONY E. HALL WILLIAM W. THOMSON CHARLES W. ASBELL KATHRYN PLATT-ALOIA ROBERT T. LEONARD 《Physiologia plantarum》1977,41(2):89-94
Lanthanum fed to the base of excised leaves of Sesamum indicum L. and Helianthus annuus L. was used as a tracer to investigate by electron microscopy the path of water in the apoplast of leaves. The generally random distribution of lanthanum in cell walls provided no support for the hypothesis that cuticular transpiration may be greater for guard cells than for adjacent epidermal cells. Occasionally, accumulations of lanthanum were observed in anticlinal walls of epidermal cells and at the outer surface of the plasma membrane but lanthanum was not observed in the symplast. The influx of 86Rb to excised roots of sesame and sunflower was inhibited during incubation with 0.5 mM lanthanum or calcium for 15 or for 180 min. Stomata of sunflower partially closed when 2.5 mM lanthanum was supplied to the base of excised shoots in a potometer, whereas this treatment had little effect on stomatal conductance of sesame shoots maintained in a constant environment. Supplying 2.5 mM lanthanum to the base of sesame shoots strongly inhibited stomatal opening response to increase in ambient humidity but had little effect on stomatal opening response to light. It was concluded that stomatal opening response to increased humidity may be dependent upon some process, such as ion influx, that is inhibited by lanthanum, and that opening response to humidity may differ in mechanism from stomatal opening response to increased irradiance. 相似文献
100.