全文获取类型
收费全文 | 1399篇 |
免费 | 46篇 |
国内免费 | 1篇 |
出版年
2013年 | 25篇 |
2011年 | 17篇 |
2010年 | 38篇 |
2009年 | 38篇 |
2008年 | 34篇 |
2007年 | 50篇 |
2006年 | 21篇 |
2005年 | 26篇 |
2004年 | 16篇 |
2002年 | 16篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 17篇 |
1993年 | 23篇 |
1992年 | 16篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 22篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1982年 | 23篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1974年 | 16篇 |
1973年 | 26篇 |
1972年 | 27篇 |
1971年 | 18篇 |
1965年 | 39篇 |
1964年 | 24篇 |
1963年 | 35篇 |
1962年 | 28篇 |
1961年 | 34篇 |
1960年 | 24篇 |
1959年 | 44篇 |
1958年 | 41篇 |
1957年 | 30篇 |
1956年 | 23篇 |
1955年 | 15篇 |
1954年 | 20篇 |
1953年 | 20篇 |
1951年 | 14篇 |
1950年 | 20篇 |
1949年 | 14篇 |
排序方式: 共有1446条查询结果,搜索用时 15 毫秒
1.
2.
Robert Blake II Elizabeth A. Shute James Waskovsky Arthur P. Harrison JR. 《Geomicrobiology journal》2013,30(3-4):173-192
Abstract Microorganisms capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Phylogenetically distinct organisms were shown to express spectrally distinct redox‐active biomolecules during autotrophic growth on soluble iron. A new iron‐oxidizing eubacterium, designated as strain Funis, was investigated. Strain Funis was judged to be different from other known iron‐oxidizing bacteria on the bases of comparative lipid analyses, 16S rRNA sequence analyses, and cytochrome composition studies. When grown autotrophically on ferrous ions, Funis produced conspicuous levels of a novel acid‐stable, acid‐soluble yellow cytochrome with a distinctive absorbance peak at 579 nm in the reduced state. Stopped‐flow spectrophotometric kinetic studies were conducted on respiratory chain components isolated from cell‐free extracts of Thiobacillus ferrooxidans. Experimental results were consistent with a model where the primary oxidant of ferrous ions is a highly aggregated c‐type cytochrome that then reduces the periplasmic rusticyanin. The Fe(II)‐dependent, cytochrome c‐catalyzed reduction of the rusticyanin possessed three kinetic properties in common with corresponding intact cells that respire on iron: the same anion specificity, a similar dependence of the rate on the concentration of ferrous ions, and similar rates at saturating concentrations of ferrous ions 相似文献
3.
ROGER M. EVANS 《Ibis》1995,137(3):340-344
Gannets (Sulidae) and some other pelecaniforms incubate their eggs under the webs of their totipalmate feet. These species have a wide latitudinal distribution from tropics to subarctic, but little is known of the incubation temperatures attained. I measured egg temperatures of the Australasian Gannet Morns serrator at Cape Kidnappers, New Zealand, employing a data logger to obtain records every 15 min for day-long sample periods at undisturbed nests. Egg surface temperatures were relatively stable and little affected by ambient temperature. Mean surface temperature of natural eggs was 34.9o C for samples taken during the first 4 days of incubation, but this then increased and stabilized at 36.5o C. Internal temperature of pipped eggs was about 1o C higher, attributable to embryonic heat production. Upper surface temperature of eggs kept in a fixed position was about 2o C below deep adult body temperature (40.3o C), suggesting heat is transferred directly from the body through the feet. Clutch size does not appear to be limited by an inability to warm two eggs. These results are in general agreement with measurements from other web incubators and are well within the range for species with conventional brood patch incubation. 相似文献
4.
5.
6.
KHALIFAH R. A.; LEWIS L. N.; COGGINS C. W. JR.; RADLICK P. C. 《Journal of experimental botany》1965,16(3):511-517
Evidence for the non-indolic nature of the new citrus auxinis presented on the basis of fluorometric properties, thin-layerchromatography, Ehrlich's colour reaction, paper electrophoresis,and the infra-red spectra determinations. Citrus auxin had alower Rf in TLC than IAA, did not give the typical indole reactionwith Ehrlich's reagent, and behaved differently in electrophoresis.The infra-red spectra also provided preliminary informationconcerning chemical structure. The hypothesis that indolic compoundsconstitute the only natural auxins in higher plants should berevised in view of this evidence that a non-indole auxin existsin higher plants. 相似文献
7.
8.
Major histocompatibility (B) complex and sex effects on the phytohaemagglutinin wattle response 总被引:2,自引:0,他引:2
The influence of the major histocompatibility (B) complex and sex on the phytohaemagglutinin (PHA) wattle response was studied in 136 segregants (B2/B2, B2/B5 and B5/B5) of a fourth generation cross between inbred lines 6(1) and 15(1). At 6 weeks of age, chickens were injected with 100 micrograms purified PHA-P. Wattle thickness measurements were taken 4, 24, 48, 72 and 96 h after injection. Analysis of variance showed that 4 h after injection, males had a significantly higher response than females but the sex-genotype interaction was also significant. Females had higher responses than males 24 and 48 h after injection as a consequence of more rapid development and earlier resolution of the reaction in males. B2/B2 chickens had significantly lower responses than B5/B5 chickens 72 and 96 h after injection, signifying a faster late resolution phase in the B2/B2 genotype. The developmental and early resolution phases of the PHA wattle response were influenced by sex while the late resolution phase was influenced by B genotype. 相似文献
9.
Allometric Root/Shoot Relationships and Predicted Water Uptake for Desert Succulents 总被引:3,自引:0,他引:3
Root morphology, shoot morphology, and water uptake for Agavedeserti and Ferocactus acanthodes of various sizes were studiedusing allometric relationships (y = axb) and a previously developedwater uptake model. Shoot surface area increased with shootvolume with an exponent b of 0.75 for both species. Root lengthand the ground area explored by the roots increased with shootsurface area with b's of 0.72 for A. deserti and 0.92 for F.acanthodes. Various sized individuals had about the same ratioof root length to explored ground area, with higher values occurringfor A. deserti. Predicted water uptake averaged over the exploredground area was approximately constant over a 104-fold rangein shoot surface area, suggesting that shoot size confers nointraspecific competitive advantage for water uptake. For theroot lengths per explored ground area observed in the field,water uptake was predicted to be 85 per cent of maximal; wateruptake could be increased by the production of more rain roots.When differences in shoot volume were accounted for by allometry,small plants had relatively less shoot surface area and relativelymore root length per shoot volume than did large plants, whichmay be important for the water relations of seedling establishment. Agave deserti, Ferocactus acanthodes, allometry, desert succulents, root distribution, root length, seedling growth, seedling establishment, shoot surface area, shoot volume, water uptake 相似文献
10.
Plant coated vesicles 总被引:2,自引:1,他引:1
Abstract. Coated vesicles are organelles frequently encountered in many plant cell types often in association with the plasma membrane, Golgi apparatus, partially coated reticulum and multivesicular bodies. They are readily identified by a characteristic cage or basket composed of interlocking triskelions of the protein clathrin which are bound to the surface of the vesicle membrane. Although their transport function has been well studied and characterized in mammalian systems, the possible importance of coated vesicles as transport organelles in plant cells is only just beginning to be explored. In this review, the authors describe the structure of higher plant coated vesicles and discuss their possible involvement in the endocytosis of marcromolecules, in exocytosis and in the intracellular transport of material between cytoplasmic compartments. Their possible role in maintaining the macromolecular composition of the plasma membrane whilst allowing recycling of excess lipid bilayer and their potential application as vehicles for the introduction of foreign macromolecules into plant cells are discussed. 相似文献