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961.
Malic enzyme is shown to be widely distributed in higher plants and contrary to earlier reports is present in the roots of flood tolerant species. Excluding members of the Gramineae, the malic enzyme from 27 out of 28 species examined was shown to exhibit allosteric properties. On the other hand the malic enzyme present in members of the Gramineae shows little or no allosteric properties. 相似文献
962.
Anuradha Chaudhuri 《Journal of biosciences》1986,10(3):323-333
Tubulin was purified from the brain of the catfishHeteropneustes fossilis by cycles of temperature-dependent assembly and disassembly. Fish tubulin assembles into microtubules in the absence of high
molecular weight microtubule associated proteins. Its subunits comigrate with goat brain α andβ tubulin subunits and is composed of 4 major α andβ tubulins each as analyzed by isoelectric focusing and two dimensional gel electrophoresis. Peptide mapping showed it to be
very similar to goat brain tubulin. Polymerization of catfish brain tubulin occurs optimally between 18–37°C and the critical
protein concentrations of assembly at 18°C and 37°C are the same, as opposed to mammalian brain tubulins. 相似文献
963.
964.
Summary A method of isolating intact needle cuticles is presented. Cuticles were separated enzymatically from needles of Abies alba Mill., Picea abies (L.) Karst., Picea pungens Engelm., Pinus mugo Turra, and Taxus baccata L. Cuticle separation depended on the enzyme concentration, the developmental stage of the needles and the duration of incubation in the hydrolytic pectinase/cellulase solution. Cuticles could not be removed from needles older than 2 years. Scanning electron micrographs of enzymatically isolated cuticles are presented. The permeance coefficients for water and oxygen transport across the isolated cuticular membranes indicate their functional intactness. But permeance coefficients also show that isolation of cuticular membranes with chromic acid is an unacceptable method, since they are lo longer structurally or functionally intact following isolation by this method. 相似文献
965.
Protective mechanisms and acclimation to solar ultraviolet-B radiation in Oenothera stricta 总被引:2,自引:1,他引:1
Abstract Mechanisms of plant protection and acclimation to potentially damaging solar ultraviolet-B (UV-B, 280–320 nm) radiation incident on the Earth's surface were examined in Oenothera stricta. Attenuation of this radiation in the upper leaf epidermis reduces the penetration of UV-B radiation to the mesophyll where damage to physiologically sensitive targets can occur. The epidermis is a highly selective radiation filter that can attenuate up to 95% of the incident UV-B radiation and yet transmit between 70% and 80% of the visible radiation. Exposure to UV-B radiation significantly reduced the degree of epidermal UV-B transmittance by as much as 33%. No significant reduction in epidermal transmittance of visible radiation was observed as a result of UV-B exposure. The plasticity in epidermal UV-B transmittance results from production of flavonoid and related phenolic compounds in the tissue. Absorbance of UV-B radiation in llavonoid extract solutions from epidermal and mesophyll tissues significantly increased by as much as 100% and 35%, respectively, after exposure to UV-B radiation. Photosynthetic rates of leaves exposed to UV-B radiation were not significantly reduced at dose rates representative of the radiation flux found in the habitat of this species, but significant photosynthetic depression was observed at dose rates that exceed the field UV-B flux. The phenotypic plasticity in epidermal UV-B transmittance resulting in decreased penetration of damaging UV-B radiation to the mesophyll may reduce the rate of damage to a level where repair mechanisms can keep pace with reduced injury. 相似文献
966.
Abstract. We recently discussed a method for measuring optical properties of light scattering and absorbing plant tissue ( Seyfried, Fukshansky & Schafer, 1983 ). This method has been used to measure the changes in optical properties of cotyledons between 360 and 1000 run during the first 7d of development. The seedlings were either etiolated or grown under continuous white light, the latter either herbicide-treated (SAN 9789 = Norflurazon) or untreated. Some of the observed changes in seedlings grown under white light are due to chlorophyll accumulation. This accumulation leads to an increase in absorption coefficients at all wavelengths except in the 750 to 850 nm region. Reflectance, transmittance, and the scattering coefficient decreased markedly. Other changes seem to be independent of light conditions since they occur in much the same way under all treatments. These are a generally decreasing reflectance and scattering coefficient and an even stronger decrease of reflectance from the upper face of the cotyledon as compared to the reflectance from the lower face, in particular in the blue region of the spectrum. The observed changes are discussed in terms of light gradients and the resulting problems for in vivo spectroscopy. 相似文献
967.
968.
Living metacestodes of Taenia pisiformis maintained in vitro discharge into the surrounding medium a protease inhibitor, which has been purified from the medium by affinity chromatography on bovine α-chymotrypsin immobilized to CNBr-activated Sepharose 4B. The purified inhibitor was shown to inactivate the hydrolysis of ethyl ester and ethyl ester, respectively, by trypsin and chymotrypsin of bovine, rabbit and dog origin, and also the hydrolysis of casein by both bovine trypsin and bovine α and β chymotrypsins, but it did not affect the enzymic activity of subtilisin, elastase, collagenase, pepsin, rennin and papain. The inhibitor withstood heating at 100°C for up to 30 min, was stable in the pH range of 1.5–8.0, was unaffected by 8 M-urea or 0.2 M-2-mercaptoethanol, and had a molecular weight of about 7000 as calculated from its gel chromatographic behaviour. The inhibitor specifically inhibits either trypsin or chymotrypsin with the formation of stable enzyme inhibitor complexes that are not dissociated by 4 M-KCl. Inhibition of trypsin and chymotrypsin is non-competitive and is linear with inhibitor concentration up to 70–80% inhibition. Inhibitory activities toward both enzymes are functions of the same binding site of the inhibitor molecule. Complex formation between the inhibitor and the enzymes is timedependent; it requires 3–4 min for completion. 相似文献
969.
J. G. Iyer 《Plant and Soil》1980,54(1):159-162
Summary The use of sorghum-sudan green manure has recently attained popularity among nurserymen because of the assumption that toxic excretions of these hybrids control root-rot fungi. Greenhouse trials of 2-year duration have revealed that green manure of sorghum-sudan inflicts severe damage of tree seedlings, largely by eradication of mycorrhiza-forming fungi. Early plowing under of green manure, periodic watering, and late fall seeding of nursery crop may alleviate phytotoxicity of the sorghum-sudan residues, but the biocidic properties of these plants defeat the primary purpose of using green manure in contemporary nurseries, namely the biodegradation of toxic compounds.Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and the Wisconsin Department of Natural Resources. 相似文献
970.
Arginase [l-arginine amidinohydrolase] in Jerusalem artichoke tubers occurs in a particulate fraction from which it was released in active form by detergent treatment. The particulate enzyme was purified 450-fold with ca 3% yield. The enzyme has a MW of ca 140 000 and pI of 5.3. The enzyme required Mn2+ for activity and was unstable when Mn2+ was removed. In tissue extracts the Km for arginine was ca 1OmM, but when purified the Km (arginine) was 145 mM. The artichoke arginase was shown to be more substrate specific than other plant and animal arginases which have been described, and to be very sensitive to competitive inhibition by indospicine, ornithine and citrulline. 相似文献