全文获取类型
收费全文 | 1935篇 |
免费 | 29篇 |
出版年
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 47篇 |
2012年 | 62篇 |
2011年 | 71篇 |
2010年 | 133篇 |
2009年 | 133篇 |
2008年 | 112篇 |
2007年 | 155篇 |
2006年 | 81篇 |
2005年 | 91篇 |
2004年 | 43篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 18篇 |
2000年 | 30篇 |
1999年 | 33篇 |
1998年 | 29篇 |
1997年 | 53篇 |
1996年 | 64篇 |
1995年 | 28篇 |
1994年 | 36篇 |
1993年 | 40篇 |
1992年 | 45篇 |
1991年 | 39篇 |
1990年 | 41篇 |
1989年 | 40篇 |
1988年 | 30篇 |
1987年 | 38篇 |
1986年 | 17篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 24篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1978年 | 27篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 16篇 |
1973年 | 12篇 |
1972年 | 23篇 |
1971年 | 24篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1968年 | 4篇 |
排序方式: 共有1964条查询结果,搜索用时 15 毫秒
991.
TIM C. G. RICH DAVID MARDON IAN CURTIS STAN J. HEYWARD VERA G. HEYWARD DOUGLAS R. MCKEAN TONY HALL STACEY HARRIS ANTONY O'ROURKE ROBYN S. COWAN MICHAEL F. FAY fls 《Botanical journal of the Linnean Society. Linnean Society of London》2005,147(2):203-211
Sagina boydii F. B. White (Caryophyllaceae), Boyd's pearlwort, is an enigmatic taxon of unknown geographical origin which is only known in cultivation and is of uncertain taxonomic status. Morphological, cytological and geographical evidence suggests that it is most similar to S. procumbens L. and S. saginoides (L.) H. Karst., but it differs in its compact growth form. Genetically, AFLP analysis shows that it can be included as part of the variation in S. procumbens . In cultivation, it will grow true from seed. Other compact growth forms occur in S. procumbens but do not grow true from seed. As S. boydii is part of the variation in S. procumbens , is of uncertain geographical origin, is known only in cultivation, and grows true from seed, it is best treated as a new cultivar, Sagina procumbens 'Boydii'. A neotype and standard specimen is designated. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 203–211. 相似文献
992.
EVELYN H. MERRILL JERRY J. HARTIGAN MICHAEL W. MEYER 《The Journal of wildlife management》2005,69(1):57-67
Abstract: Past studies suggest that the productivity of common loons (Gavia immer) is lower on acidic lakes in northern Wisconsin, USA, than on neutral lakes. Two hypotheses have been proposed to explain low chick survival: (1) reduced food consumption related to changes in prey communities on lower pH lakes and (2) high mercury (Hg) exposure on lower pH lakes. To address these hypotheses, we quantified prey and Hg consumption by loon chicks on 51 lakes and survival on 55 lakes ranging in pH from 4.9 to 9.5 in northern Wisconsin in 1995 and 1996. The time adults spent providing prey to chicks was unrelated to lake pH but increased with number of chicks and chick age. The number of prey caught per provisioning time declined as lake pH declined because adults made fewer dives, not because success of prey capture declined. Chicks consumed more insect larvae on acidic lakes and more crayfish (Family Astacidae) on neutral lakes. Biomass consumed ranged from an average 1.99 ± 1.05 (SE) g/hr/chick during the first week of a chick's life to a peak of 7.93 ± 1.93 g/hr/chick during the eighth week. Biomass intake per chick body weight (g/Wg/hr) declined with lake acidity but was not related to chick survival (P = 0.25). Although the Hg concentration in the 3 major prey species was positively related to lake acidity and blood Hg level of chicks at a lake, total Hg consumption (μg/Wg/hr) was highest on moderately acidic lakes rather than on the most acidic lakes. We suggest that loon chick survival in northern Wisconsin lakes is more likely related to prey availability than to Hg exposure. When we removed from our analysis 1 lake where 2 11-day-old chicks were killed by predators, chick survival was negatively related to lake acidity but not to biomass or Hg consumption. We discuss mechanisms of Hg excretion that may allow young chicks to survive on acidic lakes in northern Wisconsin despite high Hg intake. 相似文献
993.
994.
995.
THOMAS WILLIAM CHAPMAN KAREN LEAH FRANCIS-GEYER MICHAEL PHILIP SCHWARZ 《Insect Science》2006,13(5):391-400
Many species of gall-inducing Acacia thrips are attacked by kleptoparasitic thrips who enter the gall, destroy the occupants, and then use the gall for producing their own offspring. The hypothesis tested here is that pressure exerted by ldeptoparasites (genus Koptothrips) not only provoked the evolution of soldiers in the gall-inducing clade, but have also influenced the evolution of gall size and morphology. Various size dimensions of invaded galls were compared to those of uninvaded galls using data from six gall-inducing species and their kleptoparasites. For the non-social gall-inducing species (K. ellobus and K. nicholsoni) invaded galls showed no significant size differences from galls that had not been invaded. For the four social gall-inducingspecies (K. habrus, K. intermedius, K. waterhousei and K. morrisi) invaded galls were significantly narrower and/or shorter than uninvaded galls. Galls of social species that had not been invaded and contained adult soldiers were significantly larger than galls where soldiers were still at a larval stage, suggesting that gall size is related to gall age in these species. An hypothesis is proposed that links the timing of invasion by kleptoparasites to size of the host gall: induction of a smaller gall by host founders will reduce the period of vulnerability to invasion (before soldiers become adults) for social thrips by allowing foundresses in these smaller galls to begin laying soldierdestined eggs relatively sooner. 相似文献
996.
LYNNE M. MULLEN RACHEL J. HIRSCHMANN KELLY L. PRINCE TRAVIS C. GLENN MICHAEL J. DEWEY HOPI E. HOEKSTRA 《Molecular ecology resources》2006,6(1):36-40
We isolated and characterized 60 novel microsatellite markers from the closely related oldfield mouse (Peromyscus polionotus) and deer mouse (Peromyscus maniculatus) for studies of conservation, ecological, quantitative and population genetics. We assessed all 60 markers in a wild population of Peromyscus polionotus rhoadsi (N = 20) from central Florida and found an average of nine alleles per marker and an observed heterozygosity (HO) of 0.66 (range = 0.00–1.00). These polymorphic markers contribute to the growing number of genomic resources for Peromyscus, an emerging model system for ecological and evolutionary research. 相似文献
997.
CAROLYN K. TEPOLT MARK J. BAGLEY JONATHAN B. GELLER MICHAEL J. BLUM 《Molecular ecology resources》2006,6(2):343-345
Carcinus maenas (Decapoda: Portunidae) has proven a highly successful invasive marine species whose potential economic and ecological impacts are of great concern worldwide. Here, we characterize 14 polymorphic microsatellite loci in C. maenas and its sister species Carcinus aestuarii. These markers will prove useful for fine‐scale genetic analyses of native and introduced populations, for assessment of the sources and routes of invasion and for evaluation of post‐invasion population dynamics. 相似文献
998.
999.
1000.
Host-plant use in the range expansion of the pine processionary moth, Thaumetopoea pityocampa 总被引:1,自引:0,他引:1
MICHAEL STASTNY REA BATTISTI EDOARDO PETRUCCO-TOFFOLO FREDRIK SCHLYTER STIG LARSSON 《Ecological Entomology》2006,31(5):481-490
Abstract. 1. During range expansions of phytophagous insects, secondary or novel hosts may allow colonisation of areas without primary hosts. Because plant species often differ in their relative attractiveness and suitability for insects, insect preference for, and performance on, these hosts can determine recruitment potential in the current and future expansion areas.
2. This study explores the relative roles of female preference and larval performance in an important pine defoliator, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera, Notodontidae), which colonises three Pinus species at its current range margin in the Italian Alps: P. nigra (primary host), P. sylvestris (secondary host), and P. mugo (novel host).
3. Host use patterns in multiple insect populations were studied through choice and no-choice oviposition experiments in cages, field surveys of mixed stands, and laboratory and field monitoring of larval growth and mortality. It was predicted that a specific life-history trait – time limitation of short-lived females to lay a single batch of eggs – would act as a component of female performance, and lead to similar rates of host acceptance in no-choice settings.
4. In the choice experiment, P. nigra was accepted the most frequently while P. sylvestris was accepted the least frequently, confirming nest density patterns in the field. Contrary to prediction, females remained discriminating in no-choice settings in spite of time limitation. In contrast, relative growth rate (RGR) and mortality of larvae did not differ significantly among the three hosts, highlighting a discrepancy between female preference and larval performance.
5. Recruitment potential of T. pityocampa in future expansion into stands of P. sylvestris and P. mugo is evaluated by combining host quality, conservatism in oviposition behaviour, habitat suitability, and the opportunity for local adaptation. 相似文献
2. This study explores the relative roles of female preference and larval performance in an important pine defoliator, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera, Notodontidae), which colonises three Pinus species at its current range margin in the Italian Alps: P. nigra (primary host), P. sylvestris (secondary host), and P. mugo (novel host).
3. Host use patterns in multiple insect populations were studied through choice and no-choice oviposition experiments in cages, field surveys of mixed stands, and laboratory and field monitoring of larval growth and mortality. It was predicted that a specific life-history trait – time limitation of short-lived females to lay a single batch of eggs – would act as a component of female performance, and lead to similar rates of host acceptance in no-choice settings.
4. In the choice experiment, P. nigra was accepted the most frequently while P. sylvestris was accepted the least frequently, confirming nest density patterns in the field. Contrary to prediction, females remained discriminating in no-choice settings in spite of time limitation. In contrast, relative growth rate (RGR) and mortality of larvae did not differ significantly among the three hosts, highlighting a discrepancy between female preference and larval performance.
5. Recruitment potential of T. pityocampa in future expansion into stands of P. sylvestris and P. mugo is evaluated by combining host quality, conservatism in oviposition behaviour, habitat suitability, and the opportunity for local adaptation. 相似文献