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31.
Microtubule arrays in the cortex and near the germinal vesicle of immature starfish oocytes 总被引:7,自引:0,他引:7
An extensive array of long, crisscrossing microtubules has been discovered in the cortex of oocytes of the starfish Pisaster ochraceus. The microtubules were visualized in cortex preparations by indirect immunofluorescence microscopy using antibodies to tubulin. The cortical array of microtubules is present in all oocytes before and for about 30 min after the application of 1-methyladenine, the hormone that induces oocyte maturation. The presence of microtubules was confirmed by electron microscopy. The microtubules in this array are depolymerized when oocytes are treated with colchicine or nocodozole and are augmented when oocytes are treated with taxol. Dihydrocytochalasin B treatment of the oocytes causes the microtubules to aggregate, presumably by altering a microfilament network also found in the cortex. The distribution of microtubules was also explored in whole oocytes stained with antitubulin. One or two aster-like structures were observed adjacent to the germinal vesicle of each oocyte. 相似文献
32.
33.
Otto Fröhlich 《The Journal of membrane biology》1982,65(1-2):111-123
Summary The interaction between chloride and the anion transport inhibitor DNDS (4,4-dinitro stilbene-2,2-disulfonate) at the external anion binding site of the human erythrocyte anion transporter was examined by two techniques: a) chloride tracer flux experiments in the presence of varying concentrations of DNDS, and b) DNDS equilibrium binding experiments in the presence of varying concentrations of intracellular and extracellular chloride, Cl
i
and Cl
o
. DNDS inhibited competitively the Cl
o
-stimulated chloride efflux from intact red cells at 0°C and pH 7.8 with an inhibitor constant of 90nm. Under the same conditions DNDS bound reversibly to one class of binding sites on intact cells with a capacity of 8.5×105 molecules/cell. Cl
o
competitively inhibited DNDS binding with an inhibitor constant of 6mm. In the absence of Cl
o
the DNDS binding constant was 84mm. The competition between chloride and DNDS was also tested in nystatintreated cells in which Cl
o
always equaled Cl
i
. Under these conditions the values of the DNDS binding constant and the chloride inhibitor constant were significantly larger. All these data were in quantitative agreement with a single-site, alternating access kinetic scheme with ping-pong-type kinetics that we have previously developed for modeling chloride exchange transport. The data also served to rule out special cases of an alternative two-sited sequential-type kinetic scheme. DNDS binding experiments were also performed at 10 and 20°C. We found that neither the DNDS binding constant nor the Cl
o
inhibitor constant were significantly changed compared to 0°C. 相似文献
34.
The incorporation of a chaotic component in a computing system is incompatible with its being effectively programmable. The
example presented shows that concepts of programming suitable for biological systems may differ from those which have grown
out of our experience with present day digital computers. 相似文献
35.
Summary The relationships between different microbiological and biochemical parameters and the development of bacterial luminescence associated with the spoilage of marine fish from the Mediterranean-Sea was studied during storage at different temperatures. The bioluminescence level of the bacterial suspensions that were taken from the fish skin increased during the storage; at 20°–25°C the growth and luminescence of the luminuous bacteria correlated well with the total bacterial count while at 5°C the bacterial proliferation was not accompanied by a parallel increase in luminescence.The shift in storage temperature from 25°C to 5°C stabilized the level of the luminescence of bacterial suspension taken from the winter fish which were comprised mainly by Photobacterium phosphoreum, and caused a drop in the luminescence of bacterial suspension taken from the fish caught in the summer which were comprised mainly by Beneckea barveyi. The increase in the bioluminescence level appeared earlier than the increase in trimethylamine level and occured approximately at the same time as the increase in the hypoxanthine concentration. The potential value of the use of bacterial bioluminescence as an early indication for marine fish spoilage is discussed. 相似文献
36.
Flow cytogenetics of uncloned and cloned Chinese hamster cells 总被引:2,自引:0,他引:2
Flow cytometry has greatly facilitated the routine use of DNA content as a cellular indicator of the stages of the cell cycle and ploidy. DNA content can also be used to distinguish individual chromosomes. Fluorescent staining of chromosome DNA was done with a combination of ethidium bromide and mithramycin in hypotonic solution. Subsequent detergent treatment of the cells with Triton X-100 facilitated chromosome isolation. DNA flow cytometry of chromosomes of four established uncloned Chinese master cell lines showed 10 to 12 major subpopulations of chromosomes with varying degrees of overlap in the range of low and intermediate DNA content. Cloning of B14F28 cells, the line with the largest heterogeneity in chromosome number and DNA content, considerably reduced the dispersion in chromosome number and improved the resolution of DNA content distributions. Thus, cloned cells with a relatively homogeneous karyotype permit better discrimination of chromosome subpopulations by DNA content than uncloned cells and provide a more sensitive system to study mutagenic effects. 相似文献
37.
The peptidoglycan of Bifidobacterium globosum contains ornithine and lysine alternately in the same position of the peptide subunit. The uridine diphospho-N-acetylmuramyl-alanyl-D-glutamic acid: diamino acid ligase of this organism was purified 700-fold. Since the activities for the incorporation of ornithine and lysine into uridine diphospho-N-acetylmuramyl-tripeptide did not separate during purification and since the incorporation of ornithine is competitively inhibited by lysine and vice versa, both ornithine and lysine are assumed to be incorporated by one single enzyme. Studies on the specificity of the ligase toward analogs of ornithine have shown that the enzyme requires a diamino, monocarboxylic acid with 4–6 carbon atoms. Methylation of the -amino group or hydroxylation of the -carbon atom of lysine decreases the competitive properties of the analog, whereas the substitution of the -methylen group by sulfur (S-2-aminoethyl cysteine) results in a highly competitive compound.Abbreviations BSA
bovine serum albumine
- MurNAc
N-acetyl-muramyl
- DA
diamino acid
- Ala-DGlu--L-DA-DAla-D-Ala
pentapeptide
- Ala-DGlu--LDA
tripeptide
- Ala-DGlu
dipeptide
- DSM
Deutsche Sammlung von Mikroorganismen
- CEM
clostridial enrichment medium 相似文献
38.
Marden A. De Alvarenga Oscar Castro C. Astréa M. Giesbrecht Otto R. Gottlieb 《Phytochemistry》1977,16(11):1801-1804
Six bicyclo[3,2,1]octanoid neolignans, isolated from the benzene extract of Aniba simulans Allen (Lauraceae) trunk wood, are shown to derive from two basic structures: 1-allyl-8-hydroxy-6-(3′-methoxy-4′,5′-methylenedioxyphenyl)-7-methyl-3-oxobicyclo[3,2,1]octane, substituted by 4-hydroxy, 4-hydroxy-5-methoxy, 4-methoxy or 4,5-dimethoxy groups; and 1-allyl-8-hydroxy-6-(3′-methoxy-4′,5′-methylenedioxyphenyl)-7-methyl-4-oxobicyclo[3,2,1]oct-2-ene, substituted by 3-hydroxy or 3-hydroxy-5-methoxy groups. The structural proposals are based on spectral data, interconversions synthesis of a derivative from the known (2R,3S,3aS)-3a-allyl-5-methoxy-2-(3′-methoxy,4′,5′-methylenedioxyphenyl)-3-methyl-2,3,3a,6-tetrahydro-6-oxobenzofuran. 相似文献
39.
40.
W.David Ollis Brian T. Redman Richard J. Roberts Ian O. Sutherland Otto R. Gottlieb Mauro T. Magalhaães 《Phytochemistry》1978,17(8):1383-1388
The trunkwood of Machaerium kuhlmannii contains methyl palmitate, 3-O-acetyloleanolic acid and sitosterol; the benzene derivatives 2,3-dimethoxyphenol, 2,6-dimethoxyphenol, 2-hydroxy-3-methoxyphenol, 2,3-dimethoxybenzaldehyde and methyl 3-(2-hydroxy-4-methoxyphenyl)-propionate; the isoflavonoids formononetin and (6aS,11aS)-medicarpin; the neoflavonoids (R)-3,4-dimethoxydalbergione, (R)-3,4-dimethoxydalbergiquinol, kuhlmanniquinol [(R)-3-(4-hydroxyphenyl)-3-(5-hydroxy-2,3,4-trimethoxyphenyl)-propene], dalbergin, kuhlmannin (6-hydroxy-7,8-dimethoxy-4-phenylcoumarin) and kuhlmannene (6-hydroxy-7,8-dimethoxy-4-phenylchrom-3-ene), as well as the cinnamylphenol kuhlmannistyrene [Z-1-(5-hydroxy-2,3,4-trimethoxybenzyl)-2-(2-hydroxyphenyl)-ethylene]. Five of these compounds, in addition to (R)-4′-hydroxy-3,4-dimethoxydalbergione, were also isolated from a trunkwood extract of M. nictitans. Structural assignments were confirmed by chemical interconversion and by the synthesis of (±)-kuhlmanniquinol. 相似文献