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排序方式: 共有151条查询结果,搜索用时 15 毫秒
101.
Abstract.
- 1 Females of the aphid hyperparasitoid Dendrocerus carpenteri (Curtis) search successfully for hosts during both day and night. Oviposition numbers per host patch did not differ significantly between day and night.
- 2 D.carpenteri females also displayed a nocturnal flight activity, showing that they are not only capable of searching on a given host plant but also of dispersing between host plants.
- 3 Nocturnal oviposition activity was mainly influenced by egg load. Females with a high egg load laid more eggs at night than females with a comparatively low egg load. Thus, D.carpenteri females may use nocturnal foraging to compensate for the lack of oviposition opportunities during day.
- 4 D.carpenteri females which foraged continuously for hosts both day and night (= for 24 h per day) benefitted from an 1.4-fold increase in lifetime reproductive success when compared to females which foraged only by day (= for 16 h per day).
- 5 The benefit of night foraging for this species is a significantly increased reproductive success.
102.
The immunocompetence handicap hypothesis (ICHH) posits that the hormone testosterone mediates a trade‐off between investment in reproduction and immunological condition. In this study, we tested the ICHH in the Red Bishop Euplectes orix, a polygynous weaverbird. Males of this strongly sexually dimorphic species show an elaborate courtship display to attract females and compete aggressively with other males for nesting sites in breeding colonies. We experimentally elevated testosterone levels in breeding male Red Bishops kept in an aviary with a subcutaneous implantation of testosterone‐releasing pellets. We then compared behaviour, development of territory size and immunological condition (as assessed through a white blood cell count) of the experimental group with a control group treated with placebos. In addition, we measured the primary and secondary response to phytohaemagglutinin (PHA) to investigate the effect of testosterone on both innate and acquired immunity. Males with elevated levels of testosterone enlarged their territories and conducted more courtship behaviour, while showing a decrease in health, expressed by an increased heterophil/lymphocyte ratio compared with the control group. Males of the control group showed an increase of the secondary response to PHA, as expected under the assumption that repeated exposure to an antigen enhanced the immune response due to acquired immunity. However, males with experimentally increased testosterone levels did not show such an enhanced immune response in the secondary PHA test (although sample size and power of the statistical tests were low), indicating that testosterone treatment might directly or indirectly suppress some component of the acquired immune response. 相似文献
103.
The expected upward shift of trees due to climate warming is supposed to be a major threat to range‐restricted high‐altitude species by shrinking the area of their suitable habitats. Our projections show that areas of endemism of five taxonomic groups (vascular plants, snails, spiders, butterflies, and beetles) in the Austrian Alps will, on average, experience a 77% habitat loss even under the weakest climate change scenario (+1.8 °C by 2100). The amount of habitat loss is positively related with the pooled endemic species richness (species from all five taxonomic groups) and with the richness of endemic vascular plants, snails, and beetles. Owing to limited postglacial migration, hotspots of high‐altitude endemics are situated in rather low peripheral mountain chains of the Alps, which have not been glaciated during the Pleistocene. There, tree line expansion disproportionally reduces habitats of high‐altitude species. Such legacies of climate history, which may aggravate extinction risks under future climate change have to be expected for many temperate mountain ranges. 相似文献
104.
WOLFGANG W. LUEKKEN HEINZ BREER MARTINA HARTKKEMEYER 《The Journal of eukaryotic microbiology》1981,28(4):414-417
ABSTRACT. Conjugating cells of Euplotes vannus (syngens Naples and Barcarès) were investigated for Con A-binding sites by means of fluorescence microscopy. Cells fixed with 0.4% paraformaldehyde and incubated with 15 μg/ml FITC-Con A showed a distinct region of strong fluorescence, the size, shape and localization of which characteristically changed during the course of conjugation, first appearing at courtship stage (cells contact without forming pairs) and vanishing soon after the migration pronuclei have been exchanged, but before cells have separated. Con A binding and conjugation were blocked by cyclohexamide and α-galactosidase. Con A-binding was also inhibited by α-mannosidase, α-glucosidase and β-galactosidase without affecting conjugation except a delay of pair formation. The results suggest an involvement of newly formed or translocated glycoconjugates in cell pairing during conjugation. 相似文献
105.
WOLFGANG STERRER 《Zoologica scripta》1991,20(2):137-146
This paper deals with nine species of Gnathostomulida from the Pacific Ocean, all in established genera. Of the nine species one is cosmopolitan ( Haplognathia rosacea (Sterrer, 1970)), four have been described previously from other localities in the Indo-Pacific ( Cosmognathia manubrium Sterrer, 1991; Gnathostomula maldivarum Gerlach, 1958; Austrognathia nannulifera Sterrer, 1991; Austrognatharia pecten Sterrer, 1991), and four are new to science ( Pterognathia ugera sp.n.; Gnathostomula algreti sp.n.; Austrognatharia macroconifera sp.n.; Austrognatharia mooreensis sp.n.). 相似文献
106.
GERHARD ROTH WOLFGANG WIGGERS 《Ethology : formerly Zeitschrift fur Tierpsychologie》1983,61(3):225-234
In the present work toads (Bufo bufo) are shown to respond with prey catching to stationary dummies without previous or accompanying visual or olfactory stimulation. The subjects very rarely showed jerky head movements which, therefore, cannot be necessary for perception of stationary objects. Size preference with respect to stationary stimuli is about the same as in experiments with moving stimuli. However, differences exist between the effects of stationary and moving stimuli with respect to shape and orientation. If a square measuring 10 times 10 mm and a rectangle measuring 5 times 20 mm, oriented either horizontally or vertically, are presented within the frontal-vertical plane, the square is preferred to the rectangles, and among these the horizontal rectangle is to the vertical one. This latter preference is due to the negative effect of the vertical extension: If the vertical rectangle is reduced in length, it becomes more effective as compared to the horizontal rectangle. In the horizontal (X-Z) plane the square and the rectangle oriented parallel to the Z-axis are equally superior to the bar oriented parallel to the X-axis. At presentation of a pair of stimuli in both planes, the one in the frontal-vertical plane is always preferred to that in the horizontal plane. Correspondences and differences of these results to those from experiments with moving prey dummies are discussed. 相似文献
107.
The influence of different light qualities on chlorophyll contentand growth of tissue cultures from Crepis capillaris (L.) WALLR. Tissue cultures from Crepis capillaris growing on media (M1; M2 ; M2-E) formed chlorophyll and intact chloroplasts onlyin the short wave length region of the visible spectrum (350550nm). In red light (600700 nm) as well as in darknessthey lost their chlorophyll after 810 weeks. The growth of Crepis-cultures was strongly influenced by lightand the nitrogen of the medium. The highest increase in freshweight (425485% increase in 3 weeks) was attained inred light or in darkness on M2 by cultures which had lost theirchlorophyll completely. M2 contains nitrates, ammonium saltsand amino acids. In contrast, the increase in fresh weight ofgreen cultures growing on M2 in blue or white light was considerablylower (155180% increase in 3 weeks). Omission of amino acids, (M2-E), resulted in the reduction ofthe growth (increase of fresh weight in 3 weeks: 120%) of thechlorophyll-free cells growing in the dark. Green cultures behaveddifferently on M2-E. In white light they attained an increasein fresh weight of 245%. This suggests that the growth promotingeffect of the amino acids can be replaced by light. Results with cultures growing on M1, which contains neitherammonium salts nor amino acids, point in the same direction.Green cultures in white or blue light grew better (90100%increase in fresh weight in 3 weeks) on this "deficient" mediumthan chlorophyll-free tissues in red light or in darkness (2030%increase in fresh weight in 3 weeks). Some aspects of thesefindings which concern the effect of light on growth are discussed. (Received November 28, 1969; ) 相似文献
108.
The Capacity of Ovarian Cells of the Postnatal Rat to Reorganize into Histiotypic Structures 总被引:1,自引:0,他引:1
MARIA T. ZENZES WOLFGANG ENGEL 《Differentiation; research in biological diversity》1981,19(1-3):199-202
Cell-reorganization experiments in vitro were performed with dissociated rat ovaries at different ages of postnatal development, namely newborn, 8–10, 15–22, and 90-day-old. Ovarian cells consistently aggregated into follicularlike structures. Follicular organization in vitro is comparable to the ovarian histology of the respective age. The histogenic properties conserved by ovarian cells are considered to be related with the morphogenetic processes steadily occurring in the ovary. 相似文献
109.
110.
IRMGARD ZIEGLER MANFRED B
HME WOLFGANG PFLEIDERER ERICH F. ELSTNER 《The Journal of eukaryotic microbiology》1981,28(3):354-357
The compound 6-(L-erythro-1,2′,3′-trihydroxypropyl)pterin, at a concentration of 50 pg/ml (“L-erythro-neopteria”), supports half-maximal growth of Crithidia fasciculata; biopterin at a concentration of 30 pg/ml is shown to yield similar growth. N2-dimethyl-6-(L-erythro-1′,2′,3′-trihydroxypropyl)pterin (A) was inactive even at 100 ng/ml. Synergism was observed with the N2-dimethylamino derivative (A) in the presence of suboptimal biopterin, its activity then being of the order of L-erythro-neopterin. In contrast, the stereoisomeric N2-dimethyl-6-(D-erythro-1′,2′,3′-trihydroxypropyl)pterin (“dimethyl-D-erythro-neopterin”) and its 3′-mono-phosphate only slightly enhanced growth under similar conditions but both threo-isomers had no supplementary activity. Biopterin-induced growth was slowed by 6-(D-erythro1′,2′,3′-trihydroxypropyl)pterin (D-neopterin); the threo-isomers had no such effect. An adaptive demethylation capacity by growing cultures and competition of biopterin uptake by D-neopterin seems likely. The report of the occurrence in Euglena of N2-dimethyl-6-(L-threo-1′,2′,3′-trihydroxypropyl)pterin and its 3′-mono-phosphate adds further interest to our observations. 相似文献