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141.
The aim with this study was to, under controlled conditions, determine the food preference of mountain haresLepus timidus Linnaeus, 1758 and bank volesClethrionomys glareolus (Schreber, 1780) for a substantial part of the woody plants potentially available for these herbivores during winter.
In addition, we compared hare and vole preference patterns. Thirteen woody plant species were simultaneously presented to
9 captive voles and 9 captive hares in preference tests during winter. Consumption by hares from 50 g bundles (one per species)
was measured after 3 h, whereas shoot consumption by voles was measured after 12 h. Both hares and voles preferred deciduous
species to conifers,Populus tremula, andVaccinium myrtillus being the most preferred species. However, there was considerable variation in palatability among deciduous plant species
and only a marginally significant correlation was found between hare and vole preference. One striking differences between
hares and voles was that Sorbusaucuparia was the most utilised by voles but the least preferred by hares. In conclusion, deciduous plant species were generally considerably
more palatable to hares and voles than conifers, which is consistent with current theories. Nevertheless, the high variation
in palatability among deciduous trees and the difference in preference between hares and voles indicate more complex and species-specific
patterns with regard to plant— animal interactions. The latter also suggests that hares and voles differ in their dietary
adaptations and have different dietary constrains. 相似文献
142.
Chromosomal sex determination and male heterogamety have been thought to seriously impede direct sex ratio control. However, in Pityohyphantes phrygianus, a solitary sheetweb spider with a skewed sex ratio, earlier experimental studies suggested that there are options for female control of offspring sex ratio, if females change their position during the normal mating sequence. Here we show that under natural conditions there is considerable between-female variation in positions, especially after termination of mating. Computer simulations of the orientation of female inner genitalia suggest that sperm are placed in different storage sites depending on the positions adopted. This means that a specific position after mating might potentially influence offspring sex ratio. The variance in offspring sex ratio among females in earlier experiments was binomially distributed, which leads us to conclude that females control the mean sex ratio but do not exercise direct control of the sex of individual offspring. 相似文献
143.
Interactions of Insecticidal Toxin Gene Products from Xenorhabdus nematophilus PMFI296 总被引:3,自引:0,他引:3
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Martin Sergeant Paul Jarrett Margaret Ousley J. Alun W. Morgan 《Applied microbiology》2003,69(6):3344-3349
Four genes on a genomic fragment from Xenorhabdus nematophilus PMFI296 were shown to be involved in insecticidal activity towards three commercially important insect species. Each gene was expressed individually and in combinations in Escherichia coli, and the insecticidal activity of the lysates was determined. The combined four genes (xptA1, xptA2, xptB1, and xptC1), in E. coli, showed activity towards Pieris brassicae, Pieris rapae, and Heliothis virescens. The genes xptA1, xptB1, and xptC1 were involved in expressing activity towards P. rapae and P. brassicae, while the genes xptA2, xptB1, and xptC1 were needed for activity towards H. virescens. When each of these three genes was expressed individually in E. coli and the cell lysates were used in insect assays or mixed and then used, insecticidal activity was detected at a very low level. If the genes xptB1 and xptC1 were expressed in the same E. coli cell and this cell lysate was mixed with cells expressing xptA1, activity was restored to P. rapae and P. brassicae. Similarly mixing XptB1/C1 lysate with XptA2 lysate restored activity towards H. virescens. Individual gene disruptions in X. nematophilus PMFI296 reduced activity to insects; this activity was restored by complementation with cells expressing either xptA1 or xptA2 for their respective disruptions or E. coli expressing both xptB1 and xptC1 for individual disruptions of either of these genes. The genes xptA2, xptC1, and xptB1 were expressed as an operon in PMFI296 and inactivation of xptA2 or xptC1 resulted in silencing of downstream gene(s), while xptA1 was expressed as a single gene. Therefore, the two three gene product combinations interact with each other to produce good insecticidal activity. 相似文献
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147.
Kjell Undheim 《International journal of peptide research and therapeutics》1998,5(2-3):227-233
Summary Stereoselective syntheses are described of bridged bis(glycines) as conformationally constrained substitutes for cystine,
and of cyclic α-amino acids where the α-carbon of the amino acid is part of a five-, six- or seven-membered ring which may
hold a hydroxy group as a threonine analogue. 相似文献
148.
Kjell Hansson Mild 《Bulletin of mathematical biology》1971,33(1):19-26
The diffusion equation according to Fick’s law is solved for a spherical cell, surrounded by an infinite medium with different
diffusion properties. The method of Laplace transform is used to obtain the formal solution, however, no inversion can be
found for all times and an expansion suitable for small times is performed. The final expression found is expanded further
to be more suited for the determination of the diffusion coefficient from an experimental curve. Application to a biological
problem is dissussed. 相似文献
149.
Stine Lastein Erik Höglund Øyvind Øverli Kjell B. Døving 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2008,194(12):1007-1012
The corticotrophin-releasing factor (CRF) receptors show striking homogeneity throughout the vertebrate subphylum. In mammals, the CRF(1) receptor (CRFR(1)) plays an important role in mediating behavioral and endocrine responses to fear and stress. The specific roles of this receptor subtype in fear and stress reactions in non-mammalian vertebrates are largely unknown. Crucian carp displays the olfactory-mediated fright reaction, a stereotypic behavioral response to waterborne cues from damaged skin of conspecifics. This reaction shows several similarities to basic components of avoidance behavior in mammals. In the present study, we applied the non-peptide CRFR(1) antagonist, antalarmin, to crucian carp 1 h before exposure to conspecific skin extract. This treatment resulted in a suppression of the fright reaction. After skin extract exposure, antalarmin treatment also lead to lower plasma cortisol values, as compared to vehicle treatment. This suppression of the behavioral fright reaction and the stress induced rise in plasma cortisol in crucian carp suggests that the functions of the CRFR(1) are conserved by evolution. 相似文献
150.