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21.
RICHARD E. NORRIS 《Botanical journal of the Linnean Society. Linnean Society of London》1991,106(1):1-40
Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera. 相似文献
22.
Cold shock and heat shock: a comparison of the protection generated by brief pretreatment at less severe temperatures 总被引:1,自引:0,他引:1
Abstract Brief exposure to low (0o C) or high (40o C) temperature elicits a protective response that prevents injury when the flesh fly, Sarcophaga crassipalpis Macquart, is subjected to more severe cold (-10o C) or heat (45o C). Both the low and high temperature responses were found in all developmental stages of the fly, but were most pronounced in the pupal and pharate adult stages. The protective responses generated by brief exposure to 0 or 40o C appear similar in that both result in a rapid acquisition of cold or heat tolerance and a loss of protection after the flies are returned to 25o C. The protection generated by chilling is obvious within 10 min of exposure to 0o C while a 30 min exposure to 40o C is required to induce the high temperature protection. High temperature protects against cold shock injury within a narrow range (around 36o C) but we have no evidence that low temperature can protect against heat injury. We previously demonstrated that the rapid increase in cold tolerance correlates with concomitant increases in glycerol concentration, but in this study we found no significant elevation in glycerol in heat-shocked flies. Thus the physiological and biochemical bases for the rapid responses to cold and heat appear to be different. 相似文献
23.
RICHARD E. TRIEMER 《The Journal of eukaryotic microbiology》1986,33(3):412-415
ABSTRACT. A new genus of rigid, colorless, phagotrophic euglenoid is described from a standing pond on a salt marsh. The cell body measures 21–25 μm long, is about 18 μm wide, has a slight dorso-ventral flattening, and is marked by distinct pellicular ridges. The organism, described as Serpenomonas costata, has two unequal, antapically inserted, heterodynamic flagella. The shorter flagellum is anteriorly directed during swimming and the longer one trails posteriorly. Cells move along the substrate with a creeping motion. The ingestion apparatus is composed of separate ribs extending the length of the cell and is incorporated into the ventral pellicular ridge. The apparatus is independent of the canal and reservoir and is not protrusible. The taxonomic affinities of Serpenomonas with other euglenoids are discussed. 相似文献
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26.
RICHARD K. JOHNSON 《Freshwater Biology》1985,15(5):605-612
SUMMARY.
- 1 Absorption efficiencies of nitrogen and carbon in two Chironomus species found dominating in the profundal zone of mesotrophic Lake Erken were determined gravimetrically.
- 2 Absorption efficiencies for C. plumosus showed greater seasonal variation than those of C. anthracinus, with low efficiencies coinciding with the summer dominance of flagellate phytoplankton and with high C:N ratios.
- 3 Overall mean absorption efficiencies (±SE) for carbon and nitrogen, respectively, were 26.8% (±1.9) and 29.3% (±1.9) for C. plumosus, 24.6% (±1.7) and 28.1% (±1.8) for C. anthracinus.
- 4 Significant differences were found to exist between the C: N ratios of the superficial 2 cm sediment layers and those of Chironomus anterior midgut contents.
- 5 C. anthracinus appears to be a deposit feeder ingesting particulate matter scraped from the recently deposited surface sediments. The greater seasonal variation found in the absorption efficiencies of C. plumosus, together with the lower C:N ratios, support the contention that this species is a filter feeder with the nutritional quality of ingested matter depending primarily on pelagic inputs.
27.
Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance 总被引:2,自引:0,他引:2
NICOLAS MARC E.; SIMPSON RICHARD J.; LAMBERS HANS; DALLING MICHAEL J. 《Annals of botany》1985,55(5):743-754
A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 4060per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation 相似文献
28.
ABSTRACT.
- 1 Spider mites (Tetranychus urticae Koch) given a choice between a cotton plant previously damaged by mites and an undamaged control preferentially moved to the control plant.
- 2 This host-choice behaviour was seen in adult female mites but not in immatures.
- 3 Adult females were not found to be significantly more fecund on control plants than on previously damaged plants, but the duration of this choice experiment precluded full assessment of effects on fecundity.
- 4 Mites responded very quickly, choosing previously undamaged plants without contacting or feeding on the test plants. This suggests that an olfactory response to a chemical substance(s) is involved.
29.
SUMMARY. Diatoms from surface sediment samples from lakes on both sides of a glacial drift border in eastern Minnesota show that Araphidinate diatom genera like Fragilaria, Asterionella and Synedra are more common in lakes in drift with lower CaCO3 whereas Stephanodiscus and Melosira species are more abundant in those with high CaCo3 . In a lake sediment core from low carbonate drift Fragilaria crotonensis and Asterionella formosa increased when pioneer farmers arrived. These results confirm speculation that high A/C ratios are associated with low-alkalinity eutrophic lakes. 相似文献
30.
LYNN B. GRAVES RICHARD N. TRELEASE ALBIN GRILL WAYNE M. BECKER 《The Journal of eukaryotic microbiology》1972,19(3):527-532
SYNOPSIS. We demonstrated previously microbodies in Euglena gracilis grown in the dark on 2-carbon substrates. We have now established in Euglena the particulate nature of enzymes known in other organisms to be localized in microbodies (glyoxysomes and leaf peroxisomes). On a linear sucrose gradient the glyoxylate cycle enzymes band together at a nigner equilibrium density (1.20 g/cm3) than mitochondrial marker enzymes (1.17 g/cm3), establishing the existence in Euglena of glyoxysomes similar to those of higher plants. Glyoxylate (hydroxypyruvate) reductase and, under certain conditions, also glycolate dehydrogenase co-band with the glyoxylate cycle enzymes, suggesting that Euglena glyoxysomes, like those of higher plants, may contain peroxisomal-type enzymes. Catalase, an enzyme characteristic of microbodies from a variety of sources, was not detected in Euglena. 相似文献