全文获取类型
收费全文 | 316篇 |
免费 | 22篇 |
出版年
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 20篇 |
2012年 | 33篇 |
2011年 | 44篇 |
2010年 | 21篇 |
2009年 | 14篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有338条查询结果,搜索用时 15 毫秒
11.
Lemmetyinen J Hassinen M Elo A Porali I Keinonen K Mäkelä H Sopanen T 《Physiologia plantarum》2004,121(1):149-162
12.
Anssi Laurila 《Freshwater Biology》2000,43(2):161-174
- 1 I examined the competitive ability of larval common frogs (Rana temporaria) and common toads (Bufo bufo) in a laboratory experiment by manipulating the number and size of Rana and the number of Bufo.
- 2 Bufo was the most active tadpole type, whereas small Rana was more active than large Rana.
- 3 Especially at high food availability, the growth rate of large Rana at metamorphosis was reduced in the presence of small Rana, whereas that of small Rana was not affected by larger conspecifics.
- 4 Both size classes of Rana were negatively affected by the presence of Bufo. Size at metamorphosis of Bufo was greater when large Rana was present. These results suggest that activity level is important in determining competitive ability.
- 5 To study competition in the field, tadpoles of Bufo were introduced to small rock‐pools that did not support Bufo naturally, but were with or without Rana.
- 6 In the experimental pools, there were no interspecific effects on the growth rate of either species. However, the growth rate of Bufo was lower in the experimental pools than in pools inhabited naturally. Futher, survival of Bufo was low in small pools. Lower food availability or physical factors associated with small pools, rather than interspecific competition, may be the reason why Bufo avoids breeding in small rock‐pools.
13.
In animals with complex life cycles, the environment experienced early during the development may have strong effects on later performance and fitness. We investigated the intraspecific variation in the effects of larval temperature environment on the morphology and locomotory performance of juvenile pool frogs Rana lessonae originating from three closely located populations of the northern fringe metapopulation in central Sweden. Tadpoles were raised individually at two temperatures (20 and 25 °C) until metamorphosis. We measured the morphology of the metamorphs and tested the jumping performance of the froglets after complete tail absorption. We found that early temperature environment affected juvenile morphology, metamorphs from high-temperature environments having relatively longer hindlimbs (tibiofibulas) and longer tails when weight at metamorphosis was accounted for. In absolute terms, froglets from low temperature jumped significantly longer; however, after correcting for size differences the relationship was reversed, individuals raised at high temperature performing better. In both temperatures, relative jumping performance was positively associated with tibiofibula and body length. Populations differed both in metamorphic traits and in jumping capacity, especially at low temperature, suggesting microgeographical variation in temperature sensitivity within the metapopulation. Our results indicate that the temperature environment experienced during the early aquatic stages can influence the morphology and performance of juvenile frogs, and that these effects can be population specific. 相似文献
14.
A High Power‐Density,Mediator‐Free,Microfluidic Biophotovoltaic Device for Cyanobacterial Cells
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Paolo Bombelli Thomas Müller Therese W. Herling Christopher J. Howe Tuomas P. J. Knowles 《Liver Transplantation》2015,5(2)
Biophotovoltaics has emerged as a promising technology for generating renewable energy because it relies on living organisms as inexpensive, self‐repairing, and readily available catalysts to produce electricity from an abundant resource: sunlight. The efficiency of biophotovoltaic cells, however, has remained significantly lower than that achievable through synthetic materials. Here, a platform is devised to harness the large power densities afforded by miniaturized geometries. To this effect, a soft‐lithography approach is developed for the fabrication of microfluidic biophotovoltaic devices that do not require membranes or mediators. Synechocystis sp. PCC 6803 cells are injected and allowed to settle on the anode, permitting the physical proximity between cells and electrode required for mediator‐free operation. Power densities of above 100 mW m‐2 are demonstrated for a chlorophyll concentration of 100 μM under white light, which is a high value for biophotovoltaic devices without extrinsic supply of additional energy. 相似文献
15.
Seppo Andersson Yurong Wang Raili P?nni Tuomas H?nninen Marko Mononen Haiqing Ren Ritva Serimaa Pekka Saranp?? 《植物学报(英文版)》2015,(4):388-395
We studied in detail the mean micro fibril angle and the width of cellulose crystals from the pith to the bark of a 15-year-old Maidenhair tree(Ginkgo biloba L.). The orientation of cellulose micro fibrils with respect to the cell axis and the width and length of cellulose crystallites were determined using Xray diffraction. Raman microscopy was used to compare the lignin distribution in the cell wall of normal/opposite and compression wood, which was found near the pith. Ginkgo biloba showed a relatively large mean micro fibril angle,varying between 19° and 39° in the S2 layer, and the average width of cellulose crystallites was 3.1–3.2 nm. Mild compression wood without any intercellular spaces or helical cavities was observed near the pith. Slit-like bordered pit openings and a heavily lignified S2 L layer con firmed the presence of compression wood. Ginkgo biloba showed typical features present in the juvenile wood of conifers. The micro fibril angle remained large over the 14 annual rings. The entire stem disc,with a diameter of 18 cm, was considered to consist of juvenile wood. The properties of juvenile and compression wood as well as the cellulose orientation and crystalline width indicate that the wood formation of G. biloba is similar to that of modern conifers. 相似文献
16.
17.
Species with a wide distribution over latitudinal gradients often exhibit increasing growth and development rates towards
higher latitudes. Ecological theory predicts that these fast-growing genotypes are, in the absence of trade-offs with fast
growth, better competitors than low-latitude conspecifics. While knowledge on key ecological traits along latitudinal clines
is important for understanding how these clines are maintained, the relative competitive ability of high latitude individuals
against low latitude conspecifics has not been tested. Growth and development rates of the common frog Rana temporaria increase along the latitudinal gradient across Scandinavia. Here we investigated larval competition over food resources within
and between two R. temporaria populations originating from southern and northern Sweden in an outdoor common garden experiment. We used a factorial design,
where southern and northern tadpoles were reared either as single populations or as mixes of the two populations at two densities
and predator treatments (absence and non-lethal presence of Aeshna dragonfly larvae). Tadpoles from the high latitude population grew and developed faster and in the beginning of the experiment
they hid less and were more active than tadpoles from the low latitude population. When raised together with high latitude
tadpoles the southern tadpoles had a longer larval period, however, the response of high latitude tadpoles to the competition
by low latitude tadpoles did not differ from their response to intra-population competition. This result was not significantly
affected by density or predator treatments. Our results support the hypothesis that high latitude populations are better competitors
than their low latitude conspecifics, and suggest that in R. temporaria fast growth and development trade off with other fitness components along the latitudinal gradient across Scandinavia. 相似文献
18.
A basic premise of conservation geneticists is that low levels of genetic variation are associated with fitness costs in terms
of reduced survival and fecundity. These fitness costs may frequently vary with environmental factors and should increase
under more stressful conditions. However, there is no consensus on how fitness costs associated with low genetic variation
change under natural conditions in relation to the stressfulness of the environment. On the Swedish west coast, natterjack
toad Bufo calamita populations show a strong population genetic structure and large variation in the amount of within-population genetic variation.
We experimentally examined the survival of natterjack larvae from six populations with different genetic variation in three
thermal environments corresponding to (a) the mean temperature of natural ponds (stable, laboratory), (b) a high temperature
environment occurring in desiccating ponds (stable, laboratory) and (c) an outdoor treatment mimicking the natural, variable
thermal conditions (fluctuating, semi-natural). We found that larvae in the outdoor treatment had poorer survival than larvae
in the stable environments suggesting that the outdoor treatment was more stressful. Overall, populations with higher genetic
variation had higher larval survival. However, a significant interaction between treatments and genetic variation indicated
that fitness costs associated with low genetic variation were less severe in the outdoor treatment. Thus, we found no support
for the hypothesis that fitness costs associated with low genetic variation increase under more stressful conditions. Our
results suggest that natural thermal stress may mask fitness losses associated with low genetic variation in these populations. 相似文献
19.
BpMADS4 has a central role in inflorescence initiation in silver birch (Betula pendula) 总被引:1,自引:0,他引:1
Elo A Lemmetyinen J Novak A Keinonen K Porali I Hassinen M Sopanen T 《Physiologia plantarum》2007,131(1):149-158
Acceleration of flowering would be beneficial for breeding trees with a long juvenile phase; conversely, inhibition of flowering would prevent the spread of transgenes from the genetically modified trees. We have previously isolated and characterized several MADS genes from silver birch ( Betula pendula Roth). In this study, we investigated the more detailed function of one of them, BpMADS4 , a member of the APETALA1/FRUITFULL group of MADS genes. The expression of BpMADS4 starts at very early stage of the male and female inflorescence development and the activity is high in the apex of the developing inflorescence. Later, some expression is detected in the bracts and in the flower initials. Ectopic expression of BpMADS4 accelerates flowering dramatically in normally flowering clones and also in the early-flowering birch clone, in which the earliest line flowered about 11 days after rooting, when the saplings were only 3 cm high. The birches transformed with the BpMADS4 antisense construct showed remarkable delay in flowering and the number of flowering individuals was reduced. Two of the transformed lines did not show any signs of flower development during our 2-year study, whereas all the control plants formed inflorescences within 107 days. Our results show that BpMADS4 has a critical role in the initiation of birch inflorescence development and that BpMADS4 seems to be involved in the transition from vegetative to reproductive development. Therefore, BpMADS4 provides a promising tool for the genetic enhancement of forest trees. 相似文献