全文获取类型
收费全文 | 859篇 |
免费 | 76篇 |
国内免费 | 4篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 17篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 18篇 |
2015年 | 35篇 |
2014年 | 51篇 |
2013年 | 46篇 |
2012年 | 62篇 |
2011年 | 59篇 |
2010年 | 31篇 |
2009年 | 45篇 |
2008年 | 42篇 |
2007年 | 42篇 |
2006年 | 51篇 |
2005年 | 51篇 |
2004年 | 47篇 |
2003年 | 64篇 |
2002年 | 47篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有939条查询结果,搜索用时 15 毫秒
931.
Rethinking the thermal melanism hypothesis: rearing temperature and coloration in pygmy grasshoppers
Anders Forsman 《Evolutionary ecology》2011,25(6):1247-1257
Selection for efficient conversion of solar radiation to body heat has favored the evolution of dark coloration in many ectotherms.
The thermal melanism hypothesis posits that dark coloration is beneficial under conditions of low ambient temperatures because
it results in faster heating rates and higher body temperatures. Fast heating rates, however, may come at a cost of overheating
unless compensated for by thermal physiology or behaviour. Pygmy grasshopper (Orthoptera, Tetrigidae) populations that inhabit
fire-ravaged areas characterized by blackened backgrounds and hot surface temperatures due to high absorbance of solar radiation
show an increased frequency of black phenotypes. I raised the progeny of wild-captured Tetrix undulata in cold and hot temperatures and used data on color patterns and survival in a greenhouse to examine whether a cold thermal
environment triggered the development of melanic coloration or differently affected survival of melanic versus non-melanic
individuals. My results indicate that melanism was not influenced by rearing temperature but by genes or epigenetic maternal
effects. Temperature also did not affect survival. However, melanic individuals produced by melanic mothers survived longer
than melanic individuals produced by non- melanic mothers, whereas non-melanic individuals produced by non-black mothers survived
longer than melanic individuals produced by non-black mothers. This suggests a mismatch between color and physiology in offspring
belonging to a different color morph than their mother. Future investigations into the evolution of melanism should consider
conflicting selection pressures on thermal capacity and camouflage as well as the influence of correlated responses to selection
on traits associated with coloration. 相似文献
932.
933.
L. Kalevi Korhonen Elsa Korhonen Markku Hyyppä Reijo Punnonen 《Histochemistry and cell biology》1966,6(2):164-167
Summary Positive histochemioal reaction for carbonic anhydrase (CAH) activity was observed in the glandular and lining epithelium of human and rat uteri. The CAH activity in the rat endometrium showed cyclic changes during the estrous cycle. Only one main component of CAH activity was revealed by electrophoresis, under conditions when the erythrocytes showed several isozymes. 相似文献
934.
935.
Breeding habitat choice and investment decisions are key contributors to fitness in animals. Density of individuals is a well-known cue of habitat quality 相似文献
936.
Juha Karjalainen Minna Rahkola Markku Viljanen Inna N. Andronikova Valentin A. Avinskii 《Hydrobiologia》1996,322(1-3):249-253
The results of a joint Russian-Finnish investigation on zooplankton in Lake Ladoga are presented, and a comparison is made between two sampling techniques, tube sampler and plankton net, and between two counting methods. The precision of subsampling and sampling is further discussed on the basis of zooplankton data gathered in Lake Saimaa, Finland. The comparison clearly indicates that a tube sampler is required for reliable sampling of small-sized animals, while a plankton net saves time and is a more economical sampler for large, rare or active animals. The comparison between the results obtained by Finnish and Russian workers, using different counting procedures, shows that the main groups of crustacean zooplankton are similarly counted and identified in the two laboratories. 相似文献
937.
938.
Color polymorphisms in animals may result from plasticity of the developmental system in response to genetic cues in the form
of allelic variation at polymorphic loci, environmental cues, or a combination of genetic and environmental cues. An increased
understanding of the evolution of color polymorphisms requires better knowledge of when we should expect genetic and environmental
cues respectively to influence phenotype determination. Theory posits that the developmental systems of organisms should evolve
sensitivity to such cues that most accurately predict coming selective conditions. Pygmy grasshoppers (Orthoptera, Tetrigidae)
vary in color pattern within and among populations and show fire melanism, i.e., an increased frequency of black and dark
colored phenotypes in high density populations inhabiting fire-ravaged areas. We examined if the population density experienced
by individuals during development influenced the phenotypic expression of color pattern in Tetrix subulata. Individuals were experimentally reared either in solitude, at intermediate density or under crowded conditions. We found
that color patterns of experimental individuals were independent of rearing density but strongly influenced by maternal color
pattern. High population density and crowding may not constitute reliable predictors of the selective regime that characterizes
post-fire environments. 相似文献
939.
Kati Pasanen Jari Parkkari Matti Pasanen Hannele Hiilloskorpi Tanja M?kinen Markku J?rvinen Pekka Kannus 《BMJ (Clinical research ed.)》2008,337(7661):96-99
Objective To investigate whether a neuromuscular training programme is effective in preventing non-contact leg injuries in female floorball players.Design Cluster randomised controlled study.Setting 28 top level female floorball teams in Finland.Participants 457 players (mean age 24 years)—256 (14 teams) in the intervention group and 201 (14 teams) in the control group—followedup for one league season (six months).Intervention A neuromuscular training programme to enhance players’ motor skills and body control, as well as to activate and prepare their neuromuscular system for sports specific manoeuvres.Main outcome measure Acute non-contact injuries of the legs.Results During the season, 72 acute non-contact leg injuries occurred, 20 in the intervention group and 52 in the control group. The injury incidence per 1000 hours playing and practise in the intervention group was 0.65 (95% confidence interval 0.37 to 1.13) and in the control group was 2.08 (1.58 to 2.72). The risk of non-contact leg injury was 66% lower (adjusted incidence rate ratio 0.34, 95% confidence interval 0.20 to 0.57) in the intervention group.Conclusion A neuromuscular training programme was effective in preventing acute non-contact injuries of the legs in female floorball players. Neuromuscular training can be recommended in the weekly training of these athletes.Trial registration Current Controlled Trials ISRCTN26550281. 相似文献