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371.
Grard Lacroix Philippe Boët Josette Garnier Franoise Lescher-Moutou Roger Pourriot Paul Testard 《International Review of Hydrobiology》1989,74(4):353-370
A two-year study on the seasonal pattern of plankton was performed in a shallow, polymictic, eutrophic lake. Autogenic successions typical of stratified lakes did not occur. Only small edible algae developed throughout the two years and Cyanophyceae rarely appeared, and did not bloom. Algal sequences depended on wind-induced periodic mixing of water. The seasonal pattern of Rotifers varied greatly from year to year and some species depended on sporadic increases of algae. In contrast, the seasonal pattern of microcrustacea was more regular. Resting stages played an important role in zooplankton development in this variable environment. Successful fish reproduction depended a great deal on climatic conditions. The changes from year to year in predation pressure from young fish appeared to be an important factor controlling zoo-plankton structure. 相似文献
372.
Although polyamine (PA) metabolism in plants responds to abiotic stresses, few studies have investigated this response in plants under natural conditions. Using high-performance liquid chromatography, we studied the amine composition of the subantarctic crucifer Pringlea antiscorbutica R. Br. both in the field (Crozet and Kerguelen Islands) and under controlled temperatures in the laboratory. Plants collected from different sites showed a large variability of amine composition and contents. The aliphatic and acetylated amine composition of leaves allowed to statistically identify two groups. The first group, composed of Kerguelen coastal plants, was characterized by high levels of acetylspermidine and acetylspermine, showing the presence in P. antiscorbutica of this uncommon regulation pathway. PA acetylation may be induced in P. antiscorbutica under conditions of low water availability. The second group, composed of plants from Kerguelen altitude sites and plants from Crozet sites, showed high levels of free spermidine (Spd). In these plants, the ratio Spd/putrescine did not positively correlate with plant size as was found in developmental studies, suggesting that free Spd may be devoted to other aims, such as cold tolerance. Some differences between Crozet and Kerguelen plant responses suggested the possibility that different regulations of amine metabolism could take place in plants from these two islands. Agmatine accumulation pattern was diverse and suggested this amine to be sensitive to combinations of environmental factors. Studies on amine variation patterns in P. antiscorbutica provide insights into the roles of rarely reported amines, such as acetylated amines, in plant metabolic adaptation to abiotic stresses. 相似文献
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Sylvie Smialowski-Fléter André Moulin Josette Perrier Antoine Puigserver 《European journal of biochemistry》2002,269(4):1109-1117
Immunoblotting analyses revealed the presence of carboxylesterase in the porcine small intestine, liver, submaxillary and parotid glands, kidney cortex, lungs and cerebral cortex. In the intestinal mucosa, the pI 5.1 enzyme was detected in several subcellular fractions including the microvillar fraction. Both fatty monoacylated and diacylated monomeric (F1), trimeric (F3) and tetrameric (F4) forms of the intestinal protein were purified here for the first time by performing hydrophobic chromatography and gel filtration. The molecular mass of these three enzymatic forms was estimated to be 60, 180 and 240 kDa, respectively, based on size-exclusion chromatography and SDS/PAGE analysis. The existence of a covalent attachment linking palmitate and myristate to porcine intestinal carboxylesterase (PICE), which was suggested by the results of gas-liquid chromatography (GLC) experiments in which the fatty acids resulting from alkali treatment of the protein forms were isolated, was confirmed here by the fact that [3H]palmitic and [3H]myristic acids were incorporated into porcine enterocytes and hepatocytes in cell primary cultures. Besides these two main fatty acids, the presence of oleic, stearic, and arachidonic acids was also detected by GLC and further confirmed by performing radioactivity counts on the 3H-labelled PICE forms after an immunoprecipitation procedure using specific polyclonal antibodies, followed by a SDS/PAGE separation step. Unlike the F1 and F4 forms, which were both myristoylated and palmitoylated, the F3 form was only palmitoylated. The monomeric, trimeric and tetrameric forms of PICE were all able to hydrolyse short chain fatty acids containing glycerides, as well as phorbol esters. The broad specificity of fatty acylated carboxylesterase is discussed in terms of its possible involvement in the metabolism of ester-containing xenobiotics and signal transduction. 相似文献
375.
The aim of this work was to determine the effect of DMSO on the uptake and translocation of potassium and phosphorus applied on corn and bean leaves. Radioactive isotopes 42K and 32P were used in most of the experiments. The results obtained reveal that DMSO (0.5% and above) increases the penetration of potassium applied as nitrate or chloride, but seems to have no effect on the penetration of 32P when applied as different phosphates. 相似文献
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Modelling phytoplankton development in whole drainage networks: the RIVERSTRAHLER Model applied to the Seine river system 总被引:7,自引:3,他引:4
Phytoplankton development in river systems is under the control of various meteorological, hydrological, chemical and biological factors. Because of the continuity of the aquatic systems which progress from headwaters to the largest rivers, the interplay of these control factors can only be understood at the scale of the entire drainage network. The RIVERSTRAHLER Model, based on the concept of stream-order, has been established for that purpose. It has been applied here on two rivers from the Seine basin: rivers Marne and Oise. It is shown that hydrological factors determine the time of onset, and the position within the drainage network, of the spring algal bloom. Phosphorus availability, when limiting, controls the intensity of the bloom. During summer, top-down control, linked to grazing and other causes of mortality, has a marked impact on algal dynamics. 相似文献