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941.
Ordered conformation of polypeptides and proteins in acidic dodecyl sulfate solution 总被引:17,自引:0,他引:17
The conformation of some polypeptides and proteins in sodium dodecyl sulfate (NaDodSO4) solutions was studied by circular dichroism. The type and extent of induced structure depend on their helix- and beta-forming potential. Anionic side groups in segments of helix or beta form tend to destabilize the ordered structure unless they are protonated. beta-Endorphin has one Glu inside a predicted helical segment; its helicity in a NaDodSO4 solution is enhanced at pH below 4. alpha-Melanocyte-stimulating hormone having a Glu in a beta segment undergoes a pH-induced coil to beta transition in 1.25 mM NaDodSO4 (excess surfactant will disrupt the beta form). Reduced somatostatin assumes a beta form in 2 mM NaDodSO4 and a partial helix in 25 mM NaDodSO4, both of which are unchanged in acidic pH because it lacks -COOH groups. The unordered gastrin with five consecutive Glu's becomes helical in a NaDodSO4 solution at pH 4. Neurotensin with one Glu has no structure-forming potential and is unordered in both neutral and acidic NaDodSO4 solutions. This charge effect also manifests in segments of ordered structure for polypeptides and proteins such as glucagon, cytochrome c, parvalbumin, ribonuclease A, and lysozyme. The effect is especially predominant in tropomyosin that is rich in clusters of anionic side groups. Its more than 90% helicity is reduced to about one-half in a neutral NaDodSO4 solution, but most of it can be restored by lowering the pH to 2.4. 相似文献
942.
Chia-Ping H. Yang 《Biologia Plantarum》1981,23(3):214-219
The action of light on ribosome formation was examined in the cabbage seedlings, a system extensively used in the studies
of anthocyanin synthesis. Ribosomes were extracted 18 h after the beginning of the irradiation and separated by sucrose gradient
centrifugation. In the cotyledons of dark-grown cabbage seedlings, a brief red light induces an increase both in total ribosomes
and in the fraction present as polysomes; the effect of red light is reversed by far red light, indicating the involvement
of phytochrome in polysome formation in cabbage seedlings. Continuous red and continuous far red light are about equally effective
in bringing about an increase of total ribosomes and of the polysome fraction. Streptomycin, which inhibits chlorophyll synthesis
and chloroplast development, and enhances anthocyanin synthesis in cabbage seedlings, causes a decrease of total ribosomes
and of the fraction present as polysomes. In hypocotyls, the red-far red reversibility is evident only for the polysome content
and streptomycin does not decrease the polysome/monosomo ratio as it does in cotyledons. 相似文献
943.
Chung S. Yang Wasyl Sydor Mary B. Martin Katherine F. Lewis 《Chemico-biological interactions》1981,37(3):337-350
The effects of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on the aryl hydrocarbon hydroxylase (AHH) activities in the liver, lung and skin of rats and mice have been studied to examine the possible mechanisms of the anticarcinogenic actions of these compounds. Both compounds inhibit the hydroxylase activities of hepatic microsomes and nuclei, with BHA a more potent inhibitor than BHT. The AHH of lung microsomes is inhibited to a lesser extent by BHA and BHT than that of the liver. The AHH activities of both liver and lung microsomes become less susceptible to the inhibition after pretreatment of the animals with 3-methylcholanthrene (MC) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) but phenobarbital (PB) pretreatment does not produce such an effect. In skin homogenates, however, the AHH activities of control rats and mice are not inhibited by BHA and BHT. The only skin sample which is inhibited by BHA and BHT is that from TCDD-pretreated mice. It has been established that the extent of inhibition with different samples is related to the concentration of BHA in the incubation but not to the amounts or specific activities of microsomes used. Double reciprocal plots suggest that BHA exerts a mixed inhibition on the hydroxylase of liver microsomes with a Ki of 7.7 μM. Analysis of the metabolites of benzo[a]pyrene (BP) shows that BHA inhibits the formation of various metabolites uniformly without changing the regio-selectivity of the enzyme system. The mechanism of inhibition has also been studied with a reconstituted AHH system consisting of cytochrome P-450 (P-450), reductase and phospholipid. The system with P-450 isolated from PB-induced microsomes is inhibited to a much greater extent than that with MC-induced P-450. The results indicate that the inhibitory action of BHA is dependent on the species of the animal, tissue types and treatment with inducers. 相似文献
944.
Insulin antagonism of glucocorticoid induction of tyrosine aminotransferase in cultured foetal hepatocytes 总被引:7,自引:0,他引:7
Polyadenylated RNA from developing Artemia salina cysts was fractionated by centrifugation through a sucrose gradient containing methylmercuric hydroxide (CH3HgOH). Aliquots of each fraction were directly added to a rabbit reticulocyte lysate to program protein synthesis in vitro. The translation products were assayed for eukaryotic elongation factor Tu (eEF-Tu) by immunoprecipitation with an antibody raised in rabbits and purified by affinity chromatography. The immunoprecipitated radioactivity was analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. Sequences coding for eEF-Tu sediment in the 20-S region of the gradient and form a major component of the poly(A)-containing RNA. The mRNA of the 20-S region, comprising about 10% of the poly(a)-containing RNA fractionated on the gradient, has been translated in vitro and 30% of the translation products represent immunoprecipitable eEF-Tu protein chains with an Mr of 50000. 相似文献
945.
Y. B. Ho 《Hydrobiologia》1981,77(1):43-47
The amounts of tissue nitrogen, phosphorus, potassium, sodium, calcium and iron were estimated in the green alga Ulva lactuca L. collected from 9 rural and 14 urban littoral sites in the waters around Hong Kong Island during 1978 and 1979. The mean levels of tissue nitrogen and phosphorus were respectively 65% and 87% more in urban sites than in rural ones. Very significant correlation (r = 0.920) was found between the logarithmic concentration of seawater inorganic nitrogen and that of tissue nitrogen. The same applied to soluble reactive phosphorus in seawater and tissue phosphorus (r = 0.886). The levels of potassium, sodium and calcium in the alga were relatively uniform. However considerable variation in the level of iron was detected. The potential use of Ulva as an indicator species for eutrophication is discussed. 相似文献
946.
Studies were performed to determine whether decreases in transport of calcium and glucose might be among the earliest changes triggered by the antigen-antibody reactions occurring on the cell surface of murine leukemia L5178Y cells after treatment with rabbit antisera. After treatment with antisera, in the absence of complement, these cells exhibited a decreased uptake of 45Ca, 2-deoxy[3H]glucose, and 3-0-methyl[3H]glucose. These changes occurred rapidly, within 2 minutes after the addition of antiserum, in contrast to the previously reported inhibitory effects of antiserum on DNA, RNA, and protein synthesis, which became demonstrable only after 4 to 8 hours. The kinetics of uptake of the radioactive substrates was biphasic, with a very rapid initial uptake followed by less rapid linear uptake. The precise mechanism of cell growth inhibition remains to be elucidated, but one of the initial effects of antiserum treatment may be a perturbation at the cell membrane such that transport of specific nutrients is decreased, resulting in the observed effects on macromolecular synthesis. 相似文献
947.
Intimate coupling of creatine phosphokinase and myofibrillar adenosinetriphosphatase 总被引:2,自引:0,他引:2
S P Bessman W C Yang P J Geiger S Erickson-Viitanen 《Biochemical and biophysical research communications》1980,96(3):1414-1420
ATPase and creatine phosphokinase (CPK) activities of isolated cardiac myofibrils were determined with 32P γ-labeled ATP alone and with the addition of phosphorylcreatine (PC). With ATP and PC as substrates the label in the inorganic phosphate formed is greatly diluted indicating that the ATP formed by PC through CPK can reach the ATPase active site more readily than labeled ATP from the medium. The tight coupling of the ATPase and CPK activities further strengthens our view that PC serves an important role as high energy carrier between the energy producing sites (mitochondria) and the energy utilizing sites (myofibrils). 相似文献
948.
Kei-Lai L. Fong Dah Hsi W. Ho Carol J.K. Carter Nita S. Brown Robert S. Benjamin Emil J. Freireich Gerald P. Bodey 《Analytical biochemistry》1980,105(1):281-286
A radioimmunoassay for a new anticancer drug, bruceantin, has been developed using [3H]acetylbruceantin and antibody induced by immunizing rabbits with succinylbruceantin-bovine serum albumin conjugates. [3H]Acetylbruceantin was synthesized by reacting bruceantin with [3H]acetyl anhydride. The assay is simple and reproducible. The standard curve was linear on a logit-log plot, and the lower limit of sensitivity of the assay was 1 ng/ml. Using this assay, drug levels were easily determined in tissues of experimental animals following bruceantin administration. The assay procedure does not require sample extraction for plasma, urine, and bile. Bruceantin in other tissues can be extracted quantitatively with ethanol before being measured by the radioimmunoassay. 相似文献
949.
Measurements of proton translocation in CF1-depleted, N, N′-dicyclohexylcarbodiimide-resealed broken chloroplasts were made under different light intensities. Kinetic analysis of the data shows that the outward leakage of accumulated protons through CF0 is still dependent on light intensity with a first-order rate constant equal to mR0, where R0 is the initial rate of proton uptake which normally increases with light intensity and m is a characteristic constant which is independent of proton gradient and light intensity. Measurements of proton translocation in these modified chloroplasts cross-linked with glutaraldehyde under illumination and in the dark respectively suggest that the light-dependent proton leakage through CF0 is regulated by conformation change in the membrane. It is proposed that the ovserved regulation of proton leakage through the CF1.CF0 complex in native chloroplasts is for optimizing the steady state synthesis of ATP under different light intensities. 相似文献
950.
Methods are described for the isolation of ferredoxins I and II, cytochrome c-553, cytochrome f, cytochrome c-550 and plastocyanin from large quantities of various cyanobacteria. The amino acid composition of cytochrome c-550 is reported. There is a variation in the relative amounts of these proteins in different batches of cells which may relate to the nutritional status of the organisms. 相似文献