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991.
E del Río J M González-Ma?as J I Gurtubay F M Go?i 《Archives of biochemistry and biophysics》1991,291(2):300-306
Purple membrane bacteriorhodopsin can be easily solubilized by Triton X-100 and other detergents, but not by deoxycholate. In order to understand this behavior, we have examined the effects of a variety of surfactants. We show that detergents containing the cholane ring (cholate, taurocholate, 3[(3-cholamidopropyl)diethyl-ammonio]propanesulfonic acid...) are virtually unable to solubilize native bacteriorhodopsin. However, when the protein is reconstituted in dimyristoyl phosphatidylcholine and solubilization is assayed at a temperature such that bacteriorhodopsin is in the form of monomers, solubilization by cholane detergents does occur. We propose that steric factors prevent access of the rigid planar surfactant molecules to the hydrophobic protein regions. These are perhaps located in the monomer-monomer interface, whose solvation by surfactants is essential for solubilization to occur. We note that the capacity of some detergents to solubilize bacteriorhodopsin is always associated within the same range of surfactant concentrations with bleaching (partial or total) of the protein chromophore. The detergent-induced bleaching is at least partially reversible, suggesting that free retinal remains associated to some membrane components. While some surfactant molecules remain tightly bound to the membrane protein, cholane detergents can be completely removed from bacteriorhodopsin. Our results indicate that a structure-function relationship exists for detergents applied to the solubilization of bacteriorhodopsin. 相似文献
992.
Regulation of Cl-dependent K transport by oxy-deoxyhemoglobin transitions in trout red cells. 总被引:7,自引:0,他引:7
The oxygenation of trout red cells opens a Cl-dependent K pathway inhibited by furosemide, and by inhibitors of the erythrocyte anion exchanger such as DIDS and niflumic acid. The trigger is the deoxy-oxy conformational change of hemoglobin. The binding of carbon monoxide to heme, which induces a similar conformational change, mimics the effect of oxygen. The possible mechanisms enabling molecular oxygen to control the transport protein are discussed. This oxygenation-activated K transport appears to play a regulatory role in the control of the extracellular K concentration. 相似文献
993.
We have isolated, after exhaustive detergent treatments, a 33 kDa tau-related protein isolated from paired helical filaments from Alzheimer's disease patient brains. The N-terminal sequence of the 33 kDa protein begins at residue 71 of the sequence described for human fetal tau protein. This truncated form of tau is not the consequence of the translation of a tau RNA lacking a region at its 5' end, as measured by primer extension analyses, suggesting that the 33 kDa protein must be generated by proteolysis of previously synthesized tau. This tau-related protein has only one blocked cysteine residue and also has a decreased tubulin binding capacity as compared with that of tau protein. 相似文献
994.
An energy-dependent efflux system for potassium ions in yeast 总被引:3,自引:0,他引:3
An efflux of potassium ions was demonstrated in mutants of yeast cells lacking a functional high affinity carrier system for monovalent cations. This efflux showed the following characteristics: (a) It was stimulated by the presence of a substrate, either glucose or ethanol. (b) It was stimulated by several cationic organic molecules, such as ethidium bromide, dihydrostreptomycin, diethylaminoethyldextran, and also by trivalent cations, such as Al3+ and lanthanides; this stimulation also depended on the presence of a substrate. (c) K+ efflux was decreased in yeast mutants with decreased ATPase activity, which generated a lower membrane potential. (d) Although the efflux appeared to be of an electrogenic nature, producing hyperpolarization of cells, it was accompanied by the efflux of phosphate, probably as an anion partially compensating for the large amount of cations leaving the cell. (e) K+ efflux was also accompanied by an uptake of protons. (f) The efflux appeared more clearly in cells grown in YPD medium, and not in more complex media nor in the same YPD medium if supplemented with Ca2+ or Mg2+. Efflux of monovalent cations produced by Tb3+ and organic cationic agents was also demonstrated in wild type strains. This efflux system appears to be, at least partially, electrogenic, but seems to be also an exchange system for protons and to function as a symport with phosphate; it may be involved in the regulation of the internal pH of the cell, and appears to be regulated by its link to the energetic status of the cell, probably through the membrane potential. 相似文献
995.
An improved method for the isolation of leaf mesophyll protoplasts ofSolanum tuberosum L. cvs. Xenia and Bintje, their culture and regeneration to plants is described. The improvements involve the culture of nodal stem explants on Schenk and Hildebrandt (SH) medium supplemented with AgNO3 (7.5 mg 11) and Alar 85 (5 mg 1?1), and the pre-treatment of donor plants for 2–3 weeks at a short photoperiod (6 h), a low irradiance (17 (μmol m?2s?1) and a low temperature (20 °C). Regeneration of cell wals was observed within 2–3 d and cell divisions within 7–12 d after resuspending freshly isolated protoplasts in Sidorov et al. (SW) medium. The resulting microcalli were cultured on solid media containing zeatin (1–2,5 mg 1?1) and/or NAA (0.1 and/or 0.01 mg 1?1) and subsequently on medium with BAR (0.25 mg1?1) and GA?3 (0.1 mg 11) for shoot regeneration. 相似文献
996.
Analysis of centromere size in human chromosomes 1, 9, 15, and 16 by electron microscopy. 总被引:2,自引:0,他引:2
Human chromosomes were treated with 5-azacytidine and analyzed by whole-mount electron microscopy. This base analogue produces undercondensation of heterochromatin and separation of the centromere from the bulk of pericentromeric heterochromatin in chromosomes 1, 9, 15, and 16, which allows clear delimitation of the centromere regions. A quantitative analysis of centromeres showed that chromosomes 1, 9, and 16 have centromeres of different size. The centromere of chromosome 15 is similar in size to that of chromosome 9 and different from those of chromosomes 1 and 16. No interindividual variation for centromere size was found. A positive correlation between centromere and chromosome size was found for the chromosomes analyzed. 相似文献
997.
J Drímal 《Physiological research / Academia Scientiarum Bohemoslovaca》1991,40(5):481-491
The cross-regulatory communication from beta-adrenergic receptors to 1,4-dihydropyridine (DHP) Ca2+ channel agonist and antagonist binding sites and cooperativity between DHP binding sites were studied in microsomal membranes of canine coronary artery (purified to a factor 2.9 for DHPs). The maximal number of binding sites (Bmax) identified in coronary artery microsomal membranes (CAM) with Ca2+ channel agonist (-)-S-(3H)BAY K 8644 was two times higher than Bmax of sites labelled with Ca2+ channel antagonist (+)-(3H)PN 200-110. The exposure of CAM to isoprenaline was accompanied with down-regulation of beta-adrenergic receptors and with increase in binding capacity for DHPs. The increase in Bmax was proportional in both groups of experiments and was related to increased affinity of DHPs. The 1,4-DHP binding sites identified in vascular smooth muscle showed characteristics typical for classification of specific 1,4-DHP receptor on Ca2+ channels. The binding was of high affinity, saturable and reversible, it showed stereoselectivity and it was positively modulated by beta-adrenergic stimulation and its showed cAMP and GTP sensitivity. The results support the hypothesis that beta-receptors also regulate the mode of Ca2+ channels in coronary artery smooth muscle. 相似文献
998.
M Pospísil J Sandula I Pipalová M Hofer S Viklická 《Physiological research / Academia Scientiarum Bohemoslovaca》1991,40(4):377-380
Carboxymethylglucan, a novel soluble derivative of beta-1,3-glucan, was found to enhance hemopoietic recovery in sublethally gamma-irradiated mice and to increase survival in lethally irradiated animals when given 24 hours prior to irradiation. Postirradiation treatment with carboxymethylglucan also induced favourable effects in terms of survival when used in combination with preirradiation cystamine administration. 相似文献
999.
H Nádvorníková O Schück V Teplan D Tomková V Reitschl?gerová 《Physiological research / Academia Scientiarum Bohemoslovaca》1991,40(1):87-94
The urinary excretion and serum concentration of amino acids were studied in 62 healthy individuals aged 15 to 70 years. In elderly subjects (61-70 years), it was found that renal amino acid clearance per 100 ml GFR (fractional excretion, FE) rose significantly in the following amino acids: CYS, VAL, MET, ILE and LEU. Since the serum concentrations of these amino acids showed no significant changes, but the GFR was reduced, it can be concluded that the raised FE of these amino acids was due to a decrease in their effective tubular reabsorption. A significant correlation was found between FENa and FE of most amino acids including those mentioned above. The findings support the assumption that changes in tubular Na+ transport probably participate in the changes of tubular amino acid transport in elderly individuals. 相似文献
1000.
The effect of experimental hyperthyroidism on renal and adrenal weight increase in mice. 总被引:1,自引:0,他引:1
P D Broulík J Marek V Schreiber 《Physiological research / Academia Scientiarum Bohemoslovaca》1991,40(5):527-532
The mouse kidneys are enlarged after the administration of thyroxine and this influence is not mediated through androgens. The administration of thyroxine increased the weight of the adrenals and the level of plasma corticosterone. Besides the direct effect of the thyroid hormones on the kidney, our findings indicate that the excess of triiodothyronine and thyroxine stimulates the activity of adrenals indirectly and evokes hyperadrenocorticism which could be related to the action of adrenal steroids on kidney function and kidney growth. In accordance with the above mentioned hypothesis it has been shown that aminoglutethimide, a potent blocker of adrenal steroidogenesis, decreases the level of plasma corticosterone and inhibits the enlargement of the kidney in hyperthyroid mice in spite of the high serum thyroxine values. 相似文献