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41.
BRUCE MICHAEL PAVLIK 《Plant, cell & environment》1984,7(7):531-539
Abstract Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure-volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration () and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+ 0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+ 0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ) and to a lesser degree, decreased symplasmic water content (28% of Δ). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (max went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis, As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5–0.6 MPa at the lowest water potentials of mid-August. Laboratorygrown plants exhibited the species-specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species-specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content. 相似文献
42.
Calcification in aquatic plants 总被引:1,自引:0,他引:1
MICHAEL A. BOROWITZKA 《Plant, cell & environment》1984,7(6):457-466
Abstract. The CaCO3 deposits of aquatic plants may be intra-, inter- and extracellular. Calcification is mainly the result of photosynthetic CO2 or HCO− 3 assimilation. This raises the local pH and CO2− 3 concentration resulting from shifts in the dissolved inorganic carbon equilibrium, due to either net CO2 depletion as in Halimeda or localized OH− efflux (or H+ influx) as in Chara. The plant cell wall may be important in CaCO3 nucleation by acting as an epitaxial substratum or template, or by creating a microenvironment enriched in Ca2+ compared to Mg2+ . Hypotheses on the reason for the lack of calcification in many aquatic plants are presented. 相似文献
43.
Structure and properties of pectin gels in plant cell walls 总被引:20,自引:4,他引:16
MICHAEL C. JARVIS 《Plant, cell & environment》1984,7(3):153-164
Abstract This review deals with recent advances in the structural characterization of pectins and the gels which they form, in relation to auxin-induced extension growth, the ripening of fruit, and cellular recognition. Pectins are block polysaccharides. Heavily branched, largely methyl-esterified blocks alternate with unbranched blocks of varying degrees of esterification. The unbranched, non-esterified blocks can aggregate through calcium binding to form the junction zones that hold a gel together. The aggregates are of two, or possibly four, chains at low calcium levels, and larger with excess calcium. The fall in wall pH during auxin-induced growth activates glycanase enzymes. These may attack some components of the pectic fraction, as well as xyloglucans. Pectin-bound calcium ions may be displaced but this probably has little effect on gel strength. Pectins may be cross-linked by diferulate esters when growth stops. The softening of ripe fruit is due to loss of cohesion in the pectin gel. In apples this results from replacement of the pectins by more esterified forms. In many other fruits it results from depolymerization by polygalacturonases, assisted by pectinesterases, so that the remaining segments are too short for effective calcium binding. Pectins have a further role in the recognition reactions between plant cells and some of their bacterial and fungal pathogens. 相似文献
44.
The Possible Involvement of Cyclic AMP and Volatile Substance (s) in the Development of a Macrocyst-Forming Strain of Dictyostelium mucoroides 总被引:2,自引:2,他引:0
A mutant MF1 previously isolated from Dictyostelium mucoroides -7 (Dm7) formed macrocysts with or without light when plated on agar at high cell dinsities. At lower cell densities, however, the MF1 cells formed only fruiting bodies. This failure to form macrocysts was shown to be due to the subthreshfold concentration of a volatile substance(s) required for macrocyst formation. Although ammonia is a volatile substance produced by both the Dm7 and MF1 cells, no evidence of its involvement in macrocyst formation was obtained. Mixing the Dm7 and MF1 in a one-to-one ratio resulted only in fruiting body formation suggesting that the Dm7 cells produced a factor which allowed MF1 cells to form fruiting bodies. This factor may be cyclic AMP (cAMP) since addition of cAMP to the medium directed development of MF1 cells to fruiting body formation. The effect of cAMP was exhibited most conspicuously when MF1 cells were exposed at the aggregation stage. Based on these results it is suggested that developmental pathway of the D. mucoroides macrocystforming strain Dm7 and its mutant MF1 may be determined by the relative concentrations of the volatile, macrocyst-inducing substance(s) and cAMP at the aggregation stage. 相似文献
45.
DAVID R. KOBLUK MICHAEL J. RISK 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1977,10(2):135-143
Algal borings in the shells of the articulate brachiopods Plaesiomys subquadrata (Hall) and Hebertella sinuata (Hall) from the Richmond Formation of Ohio are empty, or partially to entirely filled with pyrite. The pyrite occurs as single framboids and other crystal forms, or in chains filling the bores. The borings provide some insight into the early diagenetic history of the Richmond sediments near Cincinnati. Pyritization probably occurred within a few years, only a short distance (a few centimeters) below the sediment surface through the activities of sulfur-reducing bacteria. Pyrite precipitated around a nucleus such as a bacterium or algal cell, or developed within an organic structure such as an algal cell or organic membrane. 相似文献
46.
MICHAEL W. PIENKOWSKI JEREMY J. D. GREENWOOD 《Biological journal of the Linnean Society. Linnean Society of London》1979,12(1):85-94
In some wading birds (Charadrii) each adult rears a brood alone. The female leaves her first clutch with her first mate before herself rearing a clutch fertilized by a second male, who is already tending its first mate's first clutch. We here develop a simple model to account for the exchange of mates between clutches, and relate it to reported field studies. We suggest that females are attempting to be polygamous, rather than simply bigamous. Provided a female has a chance of obtaining a second, unmated male and that the costs of leaving the first male before remating are not high, matechanging will be favoured over monogamy. The implications of this model to the evolution of the more usual forms of polyandry and of male-like females are discussed. 相似文献
47.
MICHAEL H. SILVER JEAN-MICHEL FOIDART ROBERT M. PRATT 《Differentiation; research in biological diversity》1981,18(1-3):141-149
Indirect immunofluorescence has been used to study the distribution of fibronectin and collagen types I, II, and III in the developing primary and secondary palatal processes and forelimb buds of the Swiss Webster (NIH) mouse. In the palatal processes fibronectin and types I and III collagen are distributed throughout the mesenchyme. Fibronectin is present in the basement membrane, while types I and III collagen are localized in a linear, discontinuous fashion beneath the basement membrane. Fibronectin is not observed in the epithelium, including the presumptive fusion areas. In the forelimb bud these components show a similar distribution prior to chondrogenesis (early day 11). When chondrogenesis commences (late day 11 or early day 12) fibronectin and, to a lesser degree, types I and III collagen are apparently concentrated in the core mesenchyme, suggesting that fibronectin has a role in initiating chondrogenesis, perhaps by increasing cellular aggregation. Type II collagen is observed only in chondrogenic regions. The codistribution of fibronectin and types I and III collagen supports in vitro studies which indicate that cells use fibronectin to bind to collagen in the matrix. The developing chondrogenic regions appear to lose fibronectin gradually, concomitant with the appearance of type II collagen, suggesting that fibronectin is not involved in the maintenance of functional chondrocytes in their matrices. 相似文献
48.
THOMAS SUSAN M.; HALL NIGEL P.; MERRETT MICHAEL J. 《Journal of experimental botany》1978,29(5):1161-1168
Photosynthesis, photorespiration, and ribulose bisphosphatecarboxylase/oxygenase activities were measured in intact flagleaves of wheat during ageing. Photorespiration declined verylittle as the leaves aged, and much less than photosynthesis.These changes could not be explained by changes in the ribulosebisphosphate carboxylase to oxygenase ratio of fraction 1 protein.As the leaves grew older the enzyme activities in extracts ofleaves declined in parallel so the ratio remained constant. 相似文献
49.
MICHAEL H. ROBINSON BARBARA C. ROBINSON 《Zoological Journal of the Linnean Society》1978,64(2):87-102
Ideally, diurnal orb-web spiders should be able to ignore problems of insolation when siting their webs and should be able to operate such webs without the necessity of retiring into shade. Postures that minimize the surface area of the spider exposed to insolation may help to free the spider from the danger of overheating. Such postures are here described for the first time for Argiope argentata and three species of Gasteracantha . Experiments with dead Nephila clavipes show that postures described as thermoregulatory do, in fact, reduce absolute temperatures (and the rate of temperature increase) compared to normal predatory postures.
Metalic or other reflectant coloration occurs in many species of diurnal orb-web spiders. These are partly listed herein. Experiments with one such species, Argiope argentata , show that overpainting the silver parts increases both the rate of temperature increase and the absolute temperatures reached when naturally coloured and black-painted spiders are exposed to the same radiant heat sources.
It is suggested that these results on the probable thermoregulatory function of metallic coloration can provide insights into the probable habitat distributions of species whose coloration is known but whose ecology is presently unknown. The general question of adaptive coloration in spiders is discussed in the light of these results. 相似文献
Metalic or other reflectant coloration occurs in many species of diurnal orb-web spiders. These are partly listed herein. Experiments with one such species, Argiope argentata , show that overpainting the silver parts increases both the rate of temperature increase and the absolute temperatures reached when naturally coloured and black-painted spiders are exposed to the same radiant heat sources.
It is suggested that these results on the probable thermoregulatory function of metallic coloration can provide insights into the probable habitat distributions of species whose coloration is known but whose ecology is presently unknown. The general question of adaptive coloration in spiders is discussed in the light of these results. 相似文献
50.
Translocation, distribution, metabolism and photolysis of hexachlorophene (HCP) were investigated in peanut plants (Arachis hypogea L., Spanish type) grown under standardized conditions and treated with l4C-ring-labeled HCP. Treatment time ranged from 0–114 days. Autoradiographic analyses were performed on all plants. Selected plant tissues were extracted and chromatographed, using both thin layer and gas liquid chromatography. No translocation of HCP was detected in the plant tissue. No HCP metabolites were found. Some HCP was lost from the leaves and inert controls at a specific rate per unit time. The rates were slightly different, being slower on the leaves than on the controls. At the end of the 114-day treatment and based on regression analysis of thin layer chromatographic plates, an average of 68% of the applied HCP remained unaltered on the treated plants and an average of 77% remained on the controls. This indicated that, respectively, 32 and 23% of the original HCP had been altered. This 9% difference was statistically significant. Upon further analyses of the above data, using gas chromatographic methods, as many as 14 peaks were found in the treated samples and the controls, including some parent material. Ultraviolet photolysis seems to be the mechanism responsible for alteration of the HCP on the treated plants and controls. Two photolysis products have been identified by gas liquid chromatography-mass spectral analysis. Twelve other electrophylic compounds have been found in various treated plant or control extracts. Further analyses will be necessary to verify the identification and quantification of the other degradation products. 相似文献