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991.
Cushion Peatlands in the High Andes of Northwestern Argentina as Archives for Palaeoenvironmental Research Karsten Schittek. Schweizerbart Scientific (J. Cramer), Stuttgart, 2014. Dissertationes Botanicae,Band 412, 176 pp. Price € 48.00. ISBN 978‐3‐443‐64325‐6 (paperback).
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Geoffrey Hope 《Austral ecology》2017,42(8):e20-e20
992.
Ali Reza Nazmi Linley R. Schofield Renwick C.J. Dobson Geoffrey B. Jameson Emily J. Parker 《Journal of molecular biology》2014
Many proteins adopt homomeric quaternary structures to support their biological function, including the first enzyme of the shikimate pathway that is ultimately responsible for the biosynthesis of the aromatic amino acids in plants and microorganisms. This enzyme, 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase (DAH7PS), adopts a variety of different quaternary structures depending on the organism in which it is found. The DAH7PS from the hyperthermophilic archaebacterium Pyrococcus furiosus was previously shown to be tetrameric in its crystalline form, and this quaternary association is confirmed in an improved structure in a different crystal system. This tetramer is also present in solution as revealed by small-angle X-ray scattering and analytical ultracentrifugation. This homotetrameric form has two distinct interfaces, both of which bury over 10% each of the surface area of a single monomer. Substitution of Ile for Asp in the hydrophobic region of one interface gives a protein with a remarkable 4-fold higher maximum catalytic rate than the wild-type enzyme. Analytical ultracentrifugation at pH 7.5 reveals that the tetrameric form is destabilized; although the protein crystallizes as a tetramer, equilibrium exists between tetrameric and dimeric forms with a dissociation constant of 22 μM. Thus, under the conditions of kinetic assay, the enzyme is primarily dimeric, revealing that the dimeric form is a fully functional catalyst. However, in comparison to the wild-type protein, the thermal stability of the dimeric protein is significantly compromised. Thus, an unusual compromise of enzymatic activity versus stability is observed for this DAH7PS from an organism that favors a hyperthermophilic environment. 相似文献
993.
Yi Yang Amira M El-Ganiny Geoffrey E Bray David A R Sanders Susan G W Kaminskyj 《Fungal genetics and biology : FG & B》2008,45(5):749-759
Aspergillus nidulans strains containing the hypB5 temperature sensitive allele have a restrictive phenotype of wide, highly-branched hyphae. The hypB locus was cloned by phenotype complementation using a genomic plasmid library. hypB5 is predicted gene AN6709 in the A. nidulans genome database, which encodes a putative Sec7 domain protein, likely to act early in COPI-mediated vesicle formation for retrograde Golgi to ER transport. The A. nidulans hypB5 allele has a single mutation, cytosine to guanine predicted to cause a nonconservative amino acid change, alanine to proline, in a conserved helix adjacent to the Sec7p nucleotide binding site. This would likely reduce the stability of a highly conserved loop important for nucleotide binding, and is consistent with temperature sensitivity of hypB5 strains. Deletion of AN6709 showed that hypB(Sec7) was not essential. AN6709Delta hyphae resembled the hypB5 restrictive phenotype. As has been shown previously for hypA1 mutants, shifting established hypB5 mutant hyphae from a growth temperature of 28-42 degrees C caused septation in and death of tip cells and growth activation of basal cells. 相似文献
994.
995.
Zachary Rosenes Yee-Foong Mok Shuo Yang Michael D. W. Griffin Terrence D. Mulhern Danny M. Hatters Frank Hensel Geoffrey J. Howlett 《PloS one》2013,8(4)
The tumour-derived monoclonal IgM antibody PAT-SM6 specifically kills malignant cells by an apoptotic mechanism linked to the excessive uptake of plasma lipids. The mechanism is postulated to occur via the multi-point attachment of PAT-SM6 to the unfolded protein response regulator GRP78, located on the surface of tumour cells, coupled to the simultaneous binding of plasma low density lipoprotein (LDL). We prepared and characterised LDL and oxidized LDL using sedimentation velocity and small-angle X-ray scattering (SAXS) analysis. Enzyme-linked immunosorbent (ELISA) techniques indicated apparent dissociation constants of approximately 20 nM for the binding of LDL or oxidized LDL to PAT-SM6. ELISA experiments showed cross competition with LDL inhibiting PAT-SM6 binding to immobilised GRP78, while, in the reverse experiment, GRP78 inhibited PAT-SM6 binding to immobilized LDL. In contrast to the results of the ELISA experiments, sedimentation velocity experiments indicated relatively weak interactions between LDL and PAT-SM6, suggesting immunoabsorbance to the microtiter plate is driven by an avidity-based binding mechanism. The importance of avidity and the multipoint attachment of antigens to PAT-SM6 was further investigated using antigen-coated polystyrene beads. Absorption of GRP78 or LDL to polystyrene microspheres led to an increase in the inhibition of PAT-SM6 binding to microtiter plates coated with GRP78 or LDL, respectively. These results support the hypothesis that the biological action of PAT-SM6 in tumour cell apoptosis depends on the multivalent nature of PAT-SM6 and the ability to interact simultaneously with LDL and multiple GRP78 molecules clustered on the tumour cell surface. 相似文献
996.
Electrochemical Energy Storage: Ordered Network of Interconnected SnO2 Nanoparticles for Excellent Lithium‐Ion Storage (Adv. Energy Mater. 5/2015)
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997.
998.
Zachary Rosenes Terrence D. Mulhern Danny M. Hatters Leodevico L. Ilag Barbara E. Power Chris Hosking Frank Hensel Geoffrey J. Howlett Yee-Foong Mok 《PloS one》2012,7(9)
The monoclonal IgM antibody PAT-SM6 derived from human tumours induces apoptosis in tumour cells and is considered a potential anti-cancer agent. A primary target for PAT-SM6 is the unfolded protein response regulator GRP78, over-expressed externally on the cell surface of tumour cells. Small angle X-ray scattering (SAXS) studies of human GRP78 showed a two-domain dumbbell-shaped monomer, while SAXS analysis of PAT-SM6 revealed a saucer-shaped structure accommodating five-fold symmetry, consistent with previous studies of related proteins. Sedimentation velocity analysis of GRP78 and PAT-SM6 mixtures indicated weak complex formation characterized by dissociation constants in the high micromolar concentration range. In contrast, enzyme-linked immunosorbant assays (ELISAs) showed strong and specific interactions between PAT-SM6 and immobilized GRP78. The apparent binding constant estimated from a PAT-SM6 saturation curve correlated strongly with the concentration of GRP78 used to coat the microtiter tray. Experiments using polyclonal antiGRP78 IgG antibodies or a monoclonal IgG derivative of PAT-SM6 did not show a similar dependence. Competition experiments with soluble GRP78 indicated more effective inhibition of PAT-SM6 binding at low GRP78 coating concentrations. These observations suggest an avidity-based binding mechanism that depends on the multi-point attachment of PAT-SM6 to GRP78 clustered on the surface of the tray. Analysis of ELISA data at high GRP78 coating concentrations yielded an apparent dissociation constant of approximately 4 nM. We propose that the biological action of PAT-SM6 in tumour cell apoptosis may depend on the multivalent nature of PAT-SM6 and the high avidity of its interaction with multiple GRP78 molecules clustered on the tumour cell surface. 相似文献
999.
1000.