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51.
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
52.
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
53.
54.
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
55.
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
56.
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
57.
58.
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
59.
Bark and wood of the creeper Dalbergia variabilis contain the previously described friedelin, O-acetyl-oleanolic acid, formononetin, 8-O-methylretusin, (+)-vestitol, (±)-mucronulatol, (+)- and (±)-medicarpin, besides (+)-variabilin [(6aR,11aR)-6a-hydroxy-3,9-dimethoxypterocarpan]. This structure was confirmed by the conversion of (+)-variabilin into di-O-methylcoumestrol. 相似文献
60.
Kazu Kurosawa W.David Ollis Brian T. Redman Ian O. Sutherland Herbert M. Alves Otto R. Gottlieb 《Phytochemistry》1978,17(8):1423-1426
The absolute configurations of isoflavans and isoflavanquinones isolated from Cyclolobium, Dalbergia and Machaerium species were established by comparison of their ORD curves with that of (3S)-5,7,3′,4′-tetra-methoxyisoflavan and (3S)-7,4′-dimethoxyisoflavan-2′,5′-quinone, respectively. The assignments were checked by the ozonolysis of the isoflavan (?)-duartin to (R)-paraconic acid and the oxidation of isoflavans to isoflavanquinones. The PMR spectra of the dihydropyran ring of the isoflavans are discussed in terms of the preferred conformation of this ring. 相似文献