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41.
Two isolates of the marine pennate diatom Phaeodactylum tricornutum Bohlin were grown in semi-continuous, nutrient-sufficient culture at varying irradiances on a 12-h light, 12-h dark illumination cycle. The reponse of the isolates to varying degrees of light limitation differed with respect to all of the compositional parameters measured, including growth rates, elemental composition, chlorophyll content, and the partitioning of cellular carbon into four biochemical classes: proteins, lipids, polysaccharides, and low-molecular weight intermediates. The isolates also differed with respect to the relative contributions of light-period and dark-period uptake to the total uptake of ammonium and phosphate ions, although in all cases uptake took place at a reduced rate in the dark. They did not differ with respect to the diel periodicity of cell division, chlorophyll synthesis, and biochemical synthesis. Slightly more cell division took place during the dark period than during the light period. The specific rate of chlorophyll synthesis in the light period, when expressed as a function of irradiance, saturated rapidly; the rate was nearly constant for all irradiances > 100 βE · m?2 · s?1. Chlorophyll synthesis in the dark was positively correlated with irradiance over the entire range of irradiances, except where photoinhibition was involved. Protein was synthesized in both the light and dark periods, but at a reduced rate in the dark. Polysaccharides were synthesized during the light period and consumed during the dark period. Lipids and low molecular weight intermediates were synthesized during the light period, but showed little net change during the dark period.  相似文献   
42.
H Yamada  R Kuroki  M Hirata  T Imoto 《Biochemistry》1983,22(19):4551-4556
The salt bridge between Lys-13 (epsilon-NH3+) and Leu-129 (alpha-COO-) in lysozyme was converted to an amide bond by 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) reaction in the presence of imidazole (0.3-1 M) at pH 5 and room temperature, followed by dialysis at pH 10. Absence of imidazole under a similar condition did not give this intramolecularly cross-linked lysozyme derivative (CL-lysozyme) but resulted in the formation of intermolecularly cross-linked lysozyme oligomers. From the mechanistic studies on the formation of CL-lysozyme, imidazole was suggested to play the following three roles. (1) Some carboxyl groups activated by EDC in lysozyme were converted to acylimidazole groups which protected them from the reaction with amino groups in other lysozyme molecules at pH 5. These could be hydrolyzed at pH 10 to regenerate free carboxyls. (2) High concentrations of imidazole (pH 5) increased the ionic strength of the solution which weakened the salt bridge in lysozyme and facilitated the activation of the alpha-carboxyl group by EDC. (3) The alpha-carboxyl group activated by EDC was converted to an acylimidazole group which could react with the epsilon-amino group of Lys-13 in the same molecule to form an amide bond. The last step may involve some conformational change of the backbone of lysozyme and be slower than the hydrolysis reaction of the alpha-carboxyl group activated by EDC itself. However, acylimidazole groups are stable against hydrolysis at pH 5. This may afford enough time to allow the epsilon-amino group of Lys-13 to attack the acylimidazole group of Leu-129.  相似文献   
43.
Parenchymal cells, isolated from untreated (control), phenobarbital(PB)-or 3-methylcholanthrene(3-MC)-treated rats, were separated into four subpopulations according to cell density, and glucuronidation and sulfation of p-nitrophenol (PNP) in the hepatocyte subpopulations were investigated. PB enhanced the glucuronidation almost 2-fold but not the sulfation, while 3-MC enhanced both glucuronidation (3-fold) and sulfation (2-fold) in the original cell suspensions. Some gradation trends were found in the conjugation activities among the hepatocyte subpopulations: In the control experiment, the extent of glucuronidation in four subpopulations was virtually the same but sulfation in high-density hepatocytes was slightly higher than in low-density ones. Both glucuronidation and sulfation were higher in low-density hepatocytes from PB-treated rats, though the gradation was very modest. Glucuronidation and sulfation tended to be slightly higher in middle-density hepatocytes in the 3-MC experiment. However, no definite correlation in conjugation activities vs. cell density, like those seen in cytochrome P-450s vs. cell density in the hepatocytes isolated from PB-treated rats, were found in the subpopulations from control or inducer-treated rats. Simultaneous studies on acetylation of p-aminobenzoic acid (PABA) revealed that the activities in the subpopulations were virtually the same and the inducers had little influence on the activity.  相似文献   
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47.
Participation of P-450 in 7 alpha-hydroxylation of cholesterol   总被引:1,自引:0,他引:1  
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48.
The metabolism of arachidonic acid (AA) was investigated in purified guinea pig alveolar eosinophils and macrophages. Alveolar eosinophils produced 12S-hydroxy-5,8,10-heptadecatraenoic acid (HHT) and small amounts only of 5-lipoxygenase products when stimulated by AA (10 microM) or ionophore A23187 (2 microM). However, when the cell suspensions were stimulated with both AA and A23187, the cells produced HHT, leukotriene (LT) B4, and 5S-hydroxy-6,8,11,14-eicosatetraenoic acid, whereas LTC4, D4, and E4 were undetectable. Similarly, alveolar macrophages stimulated with A23187 produced HHT, 5-hydroxy-6,8,11,14-eicosatetraenoic acid, and LTB4 but no peptido-leukotrienes. When LTA4 was added to suspensions of eosinophils and macrophages, only LTB4 was formed, whereas in parallel experiments, intact human platelets incubated with LTA4 produced LTC4. These data suggest that guinea pig alveolar eosinophils and macrophages contain both cyclooxygenase and 5-lipoxygenase, but do not produce peptido-leukotrienes, probably lacking LTA4 glutathione transferase activity. These studies demonstrate that guinea pig eosinophils differ from eosinophils of other animal species which have been shown to be major sources of leukotriene C4. The present data imply that eosinophils and macrophages are not the source of peptido-leukotrienes in anaphylactic guinea pig lungs.  相似文献   
49.
Biological activities of two groups of synthesized lipid A analogs, the counterpart of biosynthetic precursor, Lehmann's Ia type, 406, and E. coli lipid A type, 506, as well as their non-phosphorylated, and mono-phosphorylated analogs were investigated. The activities employed included four bone marrow cell reactions in mice, mice skin reaction, leukocytes migration in rabbits' cornea, and hemagglutination. Compound 406 and 506 elicited bone marrow reactions in mice and hemagglutination of mouse RBC, although 406 failed to elicit hemorrhage and necrosis also in mice skin. Compound 406 did not elicit corneal reaction in rabbits. The results suggest that for elicitation of this reaction and mice skin reaction, acyloxyacyl structure is required. Cytotoxicity and thromboplastin production of four bone marrow reactions had been reported by us to be endotoxic reactions, since these had not been elicited by peptidoglycan of Lactobacillus and Staphylococcus (1981) and 300 series synthesized analogs (1984) which did not have endotoxic structures. From these results, it seems that these two marrow reactions and hemagglutination require, as does the limulus test, the lipid A part structure as is present in 406.  相似文献   
50.
A series of inositol 1,4,5-trisphosphate (IP3) analogs and positional isomers was examined to explore the structure-activity relationships among IP3 5-phosphatase, IP3 3-kinase, and the release of Ca2+. All analogs with additional groups on the 2nd position of IP3 inhibited the hydrolysis of [5-32P]IP3 catalyzed by erythrocyte ghosts, with a lower Ki value than seen with IP3. IP3 dehydroxylated at the 2nd position also had a lower Ki, while 2,4,5-IP3 or cyclic(1:2), 4,5-IP3 had higher Ki values. Among these compounds 2-deoxy-IP3 was as potent as IP3 in inhibiting the phosphorylation by [3H] IP3-3-kinase in rat brain cytosol. The other compounds, except for 2,4,5-IP3 inhibited the phosphorylation, however, 2-30 times higher concentrations were required. By lowering free Ca2+, the concentrations required for half-maximal inhibition were low, while those of IP3, 2-deoxy-IP3, and positional isomers remained unchanged. These compounds acted as full agonists in releasing Ca2+ from permeabilized macrophages, although 1.6-50-fold higher concentrations than IP3 were required. These compounds also inhibited the binding of [3H]IP3 to rat cerebellum and bovine adrenal cortex microsomes, but the potencies were 2.9-33 times less than that of IP3. Thus, the 2nd position of IP3 can be modified with only a slight loss of biological activity.  相似文献   
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