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51.
The peptidoglycan crosslinking enzyme system in Streptomyces strains R61, K15 and rimosus 总被引:3,自引:0,他引:3
M Leyh-Bouille J Dusart M Nguyen-Distèche J M Ghuysen P E Reynolds H R Perkins 《European journal of biochemistry》1977,81(1):19-28
The DD-carboxypeptidase-transpeptidase enzyme system in Streptomyces strain K15 consists of: (1) a membrane-bound transpeptidase capable of performing low DD-carboxypeptidase activity; and (2) a set of DD-carboxypeptidases: (a) membrane-bound, (b) lysozyme-releasable and (c) exocellular, having low transpeptidase activities in aqueous media and at low acceptor concentrations. The DD-carboxypeptidases are related to each other and may belong to the same pathway leading to enzyme excretion. A similar enzyme system occurs in Streptomyces strain R61 except that the membrane-bound DD-carboxypeptidase activity is low when compared with the membrane-bound transpeptidase activity. In Streptomyces rimosus the enzyme system consists almost exclusively of the membrane-bound transpeptidase and the levels of membrane-bound, lysozyme-releasable and exocellular DD-carboxypeptidases are very low. 相似文献
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Prostaglandins (PG) of the E series and catecholamines stimulate adenosine 3':5'-monophosphate (cAMP) formation in human astrocytoma cells (1321N1). These two classes of effectors activated adenylate cyclase upon interaction with different receptor systems. No evidence for a mediatory role for PG in the action of catecholamines was found. PG interacted with 1321N1 cells with an order of potency of PGE1 = PGE2 greater than PGA1 greater than PGF2 alpha. The effect of combinations of the various PG indicated that all efficacious PG interacted with a common receptor. 7-Oxa-13-prostynoic acid and indomethacin were shown to be competitive inhibitors of the effect of PGE1 with Ki values of 4 and 150 micron, respectively. These two compounds did not inhibit the effect of isoproterenol. Polyphloretin phosphate caused a complex pattern of inhibition of the effects of PGE1 and at higher concentrations also inhibited the effects of isoproterenol. The mefenamate class of nonsteroidal anti-inflammatory agents was found to inhibit the effects of PGE1 with a potency order of meclofenamic acid greater than flufenamic acid = mefenamic acid. The inhibitory action of meclofenamic acid was complex involving specific, but partial, insurmountable antagonism of PGE1 as well as competitive inhibition of PGE1 effects. At higher concentrations of meclofenamic acid a nonspecific inhibition of the effects of both PGE1 and isoproterenol was observed. These studies suggest that the inhibition by nonsteroidal anti-inflammatory agents of the physiological effects of PGE1 in animals may occur, at least in part, at the level of adenylate cyclase. The possibility that multiple classes of adenylate cyclase-linked PGE receptors might exist in nature is discussed. 相似文献
54.
Age-related changes in T cell function. 总被引:4,自引:0,他引:4
A comparison was made of the abilities of carrier (BGG)-primed T cell populations from young (4-month old), middle-aged (14- and 19-month old) and old (31- and 34-month old) mice to collaborate with hapten (DNP)-primed B cells from young mice in a cell-transfer system. The plaque-forming cell responses to 2,4-dinitrophenol (DNP) were measured by a modification of the Jerne plaque assay. The DNP-specific antibody-forming cell responses of old T cell/young B cell combinations were significantly lower than those of young T cell/young B cell combinations, both in the number of T cells needed for peak response and in the size of that response. These data indicate that the primed T cell populations of old mice are deficient by a factor of 6 in their ability to initiate B cell proliferation and differentiation into antibody-forming cells. 相似文献
55.
Comparative effects of Aroclor 1254 (polychlorinated biphenyls) and phenanthrene on glucose uptake by freshwater microbial populations. 总被引:10,自引:9,他引:1 下载免费PDF全文
The effects of polychlorinated biphenyl (PCB) and phenanthrene stress on glucose uptake by natural microbial populations were examined by the heterotrophic potential technique. Temporal and spatial distributions in glucose uptake velocities were examined for natural samples as well as PCB- and phenanthrene-stressed samples. Statistical analysis indicated significant variability among the various samples. It was demonstrated that the environmental variables contributed significantly to the variability in uptake kinetics. Although general trends indicated a PCB-induced stimulation in uptake velocities, these trends were in part masked by sample variability. Data analysis indicated no statistically significant PCB or phenanthrene effect on either total glucose uptake velocities or the proportion of 14CO2 evolved, as compared to natural unstressed samples. 相似文献
56.
Seventeen male crab-eating macaques, drawn from two captive troops, were tested on a series of complex problem solving tasks
in a Wisconsin General Test Apparatus (wgta). The animals were trained on a series of 6-trial object quality learning set problems followed by a series of 10-trial object
quality learning set problems. They were then given problems in which the correct stimulus object was reversed part way through
the problem. After the animals reached criterion on this task, the reversal learning set was then extinguished. High ranking
animals made more intraproblem errors than low ranking animals on the 6-trial problems, but there was no relationship between
social status and the rapidity with which the object quality learning set was established. Animals that received overtraining
on the 6-trial problems transferred their learning virtually intact to the 10-trial problems; however, high ranking animals
without overtraining made more errors than low ranking animals. On reversal learning and reversal extinction, high ranking
animals made more errors on critical trials, indicating that they formed and extinguished the reversal set more slowly than
low ranking animals. Object quality sets, as measured by trial-2 performance, were not affected by the reversal conditions.
Supported by USAMRDC Contract No. DADA 17-73-C-3007. 相似文献
57.
The combining site of the dinitrophenyl-binding immunoglobulin A myeloma protein MOPC 315 总被引:7,自引:6,他引:1 下载免费PDF全文
Steven K. Dower Simon Wain-Hobson Peter Gettins David Givol W. Roland C. Jackson Stephen J. Perkins Christopher A. Sunderland Brian J. Sutton Carolyn E. Wright Raymond A. Dwek 《The Biochemical journal》1977,165(2):207-223
Magnetic-resonance techniques are used to refine the model of the combining site of the Fv fragment of the dinitrophenyl-binding mouse myeloma protein MOPC 315 constructed by Padlan, Davies, Pecht, Givol & Wright (1976) (Cold Spring Harbor Symp. Quant. Biol. 41, in the press). Light-absorption studies indicate a dinitrophenyl–tryptophan interaction in the Fv fragment of the type occurring in free solution. The Dnp-aspartate–tryptophan complex is therefore used as a starting point for the n.m.r. (nuclear-magnetic-resonance) analysis of the dinitrophenyl–Fv fragment interaction. Ring-current calculations are used to determine the geometry of the complex. The specificity of complex-formation between dinitrophenyl and tryptophan is confirmed by the lack of ring-current shifts of the dinitrophenyl resonances when tryptophan is replaced by any other aromatic amino acid. Proton n.m.r. difference spectra (at 270MHz), resulting from the addition of a variety of haptens to the Fv fragment, show that the combining site is highly aromatic in nature. Calculations on the basis of ring-current shifts define the geometry of the combining site, which involves a dinitrophenyl ring in van der Waals contact with four aromatic amino acid residues on the protein. The observation of a nuclear Overhauser effect on the H(3) resonance of the dinitrophenyl ring provides additional constraints on the relative geometry of the H(3) proton and an aromatic amino acid residue on the Fv fragment. The specificity of the Fv fragment for dinitrophenyl ligands arises from a stacking interaction of the dinitrophenyl ring with tryptophan-93L, in an `aromatic box' of essentially tryptophan-93L, phenylalanine-34H and tyrosine-34L; asparagine-36L and tyrosine-34L also contribute by forming hydrogen bonds with the nitro groups on the dinitrophenyl ring. The n.m.r. results also confirm that the antibody–hapten reaction may be visualized as a single encounter step. An Appendix shows the method of calculation of ring currents for the four aromatic amino acids and their use in calculating structures. 相似文献
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59.
60.
alpha 1-Antitrypsin (alpha 1-AT) is the best-characterized member of the serpin superfamily of plasma proteins. Protease inhibitor members of this family undergo a characteristic reactive-center cleavage during expression of their inhibitory activity. The physical basis of this transition in alpha 1-AT from the stressed native conformation to the more stable reactive center cleaved (split) form was studied by Fourier transform infrared (FT-IR) spectroscopy and neutron scattering. The FT-IR spectra show that, while split alpha 1-AT has three intense well-resolved components associated with the presence of antiparallel beta-sheet and alpha-helix conformations, the amide I band of native alpha 1-AT has only one intense component, associated with the presence of beta-sheet structure. 1H-2H exchange within the polypeptide backbone, studied by FT-IR and NMR spectroscopy, shows that the native form undergoes greater exchange than the split form. Under the same conditions, neutron scattering shows no differences in the radius of gyration RG of the native and the split forms. In contrast, in high concentrations of phosphate approaching those used for crystallization, the native form (unlike the split form) undergoes dimerization. These data indicate that the conformational transition largely involves localized secondary and tertiary structure rearrangements. We propose that the energetically stressed native alpha 1-AT structure is the consequence of a significantly reduced number of hydrogen bonds in secondary structure components and that reactive-site cleavage between Met358 and Ser359 is the key for the development of the fully hydrogen bonded more stable serpin structure. 相似文献