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71.
InEscherichia coli, NADP+-specific isocitrate dehydrogenase (EC 1.1.1.42) may undergo a phosphorylation catalyzed by a cAMP-independent protein kinase, with a concomitant decrease in catalytic activity. In this report, we describe the purification and amino acid sequence of a32P-labeled peptide obtained from in vivo32P-labeled isocitrate dehydrogenase. The32P-labeled peptide was isolated from a tryptic digest and found to contain seven amino acids, including a single serine residue. Following automated Edman degradation and reversephase high-pressure liquid chromatography of the phenylthiohydantoin-amino acids, the sequence of this peptide was established to be-Ser(P)-Leu-Asn-Val-Ala-Leu-Arg.  相似文献   
72.
Abstract Nocodazole, a temporary inhibitor of microtubule formation, has been used to partly synchronize Ehrlich ascites tumour cells growing in suspension. the gradual entry of cells into mitosis and into the next cell cycle without division during drug treatment has been studied by flow cytometric determination of mitotic cells, analysing red and green fluorescence after low pH treatment and acridine orange staining. Determination of the mitotic index (MI) by this method has been combined with DNA distribution analysis to measure cell-cycle phase durations in asynchronous populations growing in the presence of the drug. With synchronized cells, it was shown that in the concentration range 0.4–4.0 μg/l, cells could only be arrested in mitosis for about 7 hr and at 0.04 μg/ml, for about 5 hr. After these time intervals, the DNA content in nocodazole-blocked cells was found to be increased, and, in parallel, the ratio of red and green fluorescence was found to have changed, showing entry of cells into a next cell cycle without division (polyploidization). It was therefore only possible to partially synchronize an asynchronous population by nocodazole. However, a presynchronized population, e.g. selected G1 cells or metabolically blocked G1/S cells, were readily and without harmful effect resynchronized in M phase by a short treatment (0.4 μg/ml, 3–4 hr) with nocodazole; after removal of the drug, cells divided and progressed in a highly synchronized fashion through the next cell cycle.  相似文献   
73.
Summary The ultrastructure of the thread-like hairs (sensilla) on the tibia of the front leg ofAcheta domesticus (Gryllidae) Saltatoria was examined by serial sectioning. The presence of a tubular body indicates that these sensilla are mechanosensitive; electrophysiological measurements also confirmed this. The opposing forces on the articulating apparatus of single hairs and the sensitivity of the single receptor cell were measured after deflection of the hair in different directions. The articulating apparatus is characterized by three cuticular elements: a joint membrane, suspension fibers, and a socket septum. These elements form the basis for a structural bilateral symmetry along whose plane of symmetry the direction line of both the minimum receptor sensitivity and the minimum opposing forces lie. The tubular body embedded in the tip of the socket septum is attached to the base of the hair shaft. The hair provides the leverage for displacing the tubular body and the socket septum limits the extent to which it may be laterally displaced.These investigations have been supported by the Deutsche Forschungsgemeinschaft  相似文献   
74.
A photoreactive analog of aminopterin, 2′-azidoaminopterin (VI), was synthesized and evaluated as a potential inhibitor and photoaffinity label of folate-utilizing enzymes. The compound was tightly bound to dihydrofolate reductase (DHFR) from escherichia coli (MB 1428) with K1 equal to 3 × 10?11M and to the enzyme from mouse (S-180) cells with K1 approximately equal to 2 × 10?10M. Dissociation constants measured by equilibrium dialysis using radioactive 2′-azidoaminopterin gave a value of KD = 3.2 × 10?9M for the bacterial enzyme. The presence of NADPH enhanced the affinity by more than an order of magnitude. Azidoaminopterin is also an inhibitor of thymidylate synthetase from Lactobacillus casei, competitive with methylene-tetrahydrofolate (Ki 7 × 10?7M). Photolysis of the radioactive inhibitor in complex with DHFR from E. coli led to approximately 3% covalent incorporation of label into protein. The greater part of this attachment was nonspecific as shown by the lack of protection in the presence of methotrexate. Thymidylate synthetase from L. casei was not significantly inactivated upon photolysis in the presence of the inhibitor and deoxyuridylate. Model studies showed that photoreaction of the inhibitor led to covalent linkages with thiol, lysyl amino groups, and the hydroxyl groups of alcohols. Azidoaminopterin may be useful in labeling other enzymes of folate metabolism, although a minor photoproduct reacts nonspecifically with many proteins. The antifolate can be photoconjugated to polylysine as well as to proteins. The polylysine conjugates inhibit DHFR. Difference spectrum analysis of the photoproducts from the irradiation of the DHFR I complex indicates that water reacts efficiently with the enzyme-bound nitrene and must therefore have access to at least part of the bound p-aminobenzoyl group. This analysis suggests that azide analogs of protein ligands may be useful as reporter groups in probing the hydrophobicity of binding sites.  相似文献   
75.
The teuthids of the collection R. Stahlecker, 1929, from the Isle of Maio (Cape Verde Islands) are described.Neololigosepia stahleckeri n. gen. n. sp. andMaioteuthis morroensis n. gen. n. sp. are one of the first teuthids from the Lower Cretaceous (Barremian).  相似文献   
76.
An investigation of Ursinia saxatilis afforded in addition to known compounds a new eudesmanolide derived from ursialpinolide, a germacranolide rel  相似文献   
77.
A new technique, the quantitative determination of total enzyme concentrations by specific immunoprecipitation with purified, radioiodinated antibodies, was used to investigate the presence and possible roles of inactive enzyme in the regulation of chalcone synthase. Dark-grown cell suspension cultures from parsley (Petroselinum hortense) contained neither catalytically active nor detectable amounts of immunoprecipitable chalcone synthase. Irradiation induced large increases and subsequent decreases of both. Significant differences in the peak positions and in the half-lives of active and total chalcone synthase indicated that induced cells contained inactive as well as active enzyme forms. The presence of inactive enzyme could be explained by two different modes of regulation, (i) simultaneous de novo synthesis of active and inactive enzyme (“Simultaneous Model”), or (ii) de novo synthesis of active enzyme only, with sequential steps of inactivation and degradation (“Sequential Model”). Both models were compatible with experimental results, as analyzed mathematically by investigating the relations between curves for rate of enzyme synthesis, enzyme activity, total enzyme, and half-lives of active and total enzyme. However, the “Simultaneous Model” postulated that de novo synthesis of inactive enzyme represented always the vast majority of total enzyme synthesis, while the Sequential Model integrated inactive enzyme with facility in a sequence of irreversible inactivation and degradation of active enzyme. Experiments with repeated induction indicated that cells containing large amounts of inactive enzyme increased enzyme activity by de novo synthesis rather than by activation of preexisting inactive enzyme.  相似文献   
78.
Twelve indole alkaloids belonging to the Ajmaline-, Sarpagine-, Yohimbine-, and Heteroyohimbine-type have been isolated and identified from cell suspension cultures of Rauwolfia serpentina. Ten of the alkaloids were found for the first time in cultured R. serpentina cells. The yield of the main alkaloid vomilenine was 51 times more than that of differentiated plants. Crude enzymes isolated from this cell suspension culture completely metabolize the biogenetic precursor strictosidine under formation of several alkaloidal compounds.  相似文献   
79.
Summary Addition of heterochromatin suppresses while subtraction enhances position effect variegation. The heterochromatin-sensitive period has been determined in white/white-apricot variegated eyes of Y S w a /w a ; Dp (1;3) w 265-58 flies. When such larvae, carrying a Y-short (Y S ) arm at the distal end of one X chromosome, are X-rayed, mitotic recombination leads to one daughter cell with two Y S arms and an adjacent daughter cell with no Y S arm. When induced after clonal initiation, the frequency of dark clones developing from daughter cells with two Y S arms is significantly higher than the frequency of dark clones in the rest of the eye; and this frequency is. even higher when induced before clonal initiation. The modifying action of the Y-heterochromatin is exerted, therefore, during and after clonal initiation. Surprisingly, the frequency of dark clones developing from cells with no Y S arm is not lower than the frequency of dark clones in the rest of the eye.  相似文献   
80.
Summary Iodination of proteins and lipoproteins is a widely used in vitro labelling procedure in metabolic, autoradiographic and various other studies. However, all available iodination techniques have involved the possible damage to the proteins by self-irradiation, oxidizing agents, the alkaline milieu or by the introduction of iodine into the molecular structure itself. To evaluate the integrity of iodinated lipoproteins, we observed the electron microscopic appearance of normal and iodinated rabbit very low density lipoproteins (VLDL) by negative staining with phosphotungstic acid. Iodination up to a molar iodine/protein ratio of 2.89 did not result in any change of shape, size or aggregating tendency of the particles. No stacks or disk-like particles like those of various hyperlipoproteinemic states were found. We conclude that electron microscopy is a valuable tool in assessing the morphological appearance of lipoprotein iodination, but it should be complemented by other techniques.  相似文献   
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