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131.
Maria Maddalena Sperotto 《European biophysics journal : EBJ》1997,26(5):405-416
A theoretical model is proposed for the association of trans-bilayer peptides in lipid bilayers. The model is based on a
lattice model for the pure lipid bilayer, which accounts accurately for the most important conformational states of the lipids
and their mutual interactions and statistics. Within the lattice formulation the bilayer is formed by two independent monolayers,
each represented by a triangular lattice, on which sites the lipid chains are arrayed. The peptides are represented by regular
objects, with no internal flexibility, and with a projected area on the bilayer plane corresponding to a hexagon with seven
lattice sites. In addition, it is assumed that each peptide surface at the interface with the lipid chains is partially hydrophilic,
and therefore interacts with the surrounding lipid matrix via selective anisotropic forces. The peptides would therefore assemble
in order to shield their hydrophilic residues from the hydrophobic surroundings. The model describes the self-association
of peptides in lipid bilayers via lateral and rotational diffusion, anisotropic lipid-peptide interactions, and peptide-peptide
interactions involving the peptide hydrophilic regions. The intent of this model study is to analyse the conditions under
which the association of trans-bilayer and partially hydrophilic peptides (or their dispersion in the lipid matrix) is lipid-mediated,
and to what extent it is induced by direct interactions between the hydrophilic regions of the peptides. The model properties
are calculated by a Monte Carlo computer simulation technique within the canonical ensemble. The results from the model study
indicate that direct interactions between the hydrophilic regions of the peptides are necessary to induce peptide association
in the lipid bilayer in the fluid phase. Furthermore, peptides within each aggregate are oriented in such a way as to shield
their hydrophilic regions from the hydrophobic environment. The average number of peptides present in the aggregates formed
depends on the degree of mismatch between the peptide hydrophobic length and the lipid bilayer hydrophobic thickness: The
lower the degree of mismatch is the higher this number is.
Received: 30 December 1996 / Accepted: 9 May 1997 相似文献
132.
A. M. Arutyunyan E. R. Rafikova V. A. Drachev E. N. Dobrov 《Biochemistry. Biokhimii?a》2001,66(12):1378-1380
CD spectra in the 200 to 250 nm spectral region for small ordered aggregates (trimers-pentamers) of tobacco mosaic virus (TMV) coat protein (CP) and for long virus-like helical aggregates of TMV CP were compared. It was found that small (4S) TMV CP aggregates have a CD spectrum typical of a protein with high -helix content, which agrees well with results of X-ray diffraction studies. But in the long helical aggregates (and in the TMV virions) TMV CP gives -like CD spectra similar to those of many other aggregated proteins. From X-ray diffraction data, it is well known that TMV CP subunits do not change their secondary or tertiary structure on assembly into virions or the helical repolymerized protein. Thus, the change in the shape of 200 to 250 nm CD spectra cannot be employed as the sole criterion of the conversion of a protein to -structure in the course of aggregation. 相似文献
133.
Hydrophobic substitutions at solvent-exposed positions in two alpha-helical regions of the bacteriophage P22 Arc repressor were introduced by combinatorial mutagenesis. In helix A, hydrophobic residues were tolerated individually at each of the five positions examined, but multiple substitutions were poorly tolerated as shown by the finding that mutants with more than two additional hydrophobic residues were biologically inactive. Several inactive helix A variants were purified and found to have reduced thermal stability relative to wild-type Arc, with a rough correlation between the number of polar-to-hydrophobic substitutions and the magnitude of the stability defect. Quite different results were obtained in helix B, where variants with as many as five polar-to-hydrophobic substitutions were found to be biologically active and one variant with three hydrophobic substitutions had a t(m) 6 degrees C higher than wild-type. By contrast, a helix A mutant with three similar polar-to-hydrophobic substitutions was 23 degrees C less stable than wild-type. Also, one set of three polar-to-hydrophobic substitutions in helix B was tolerated when introduced into the wild-type background but not when introduced into an equally active mutant having a nearly identical structure. Context effects occur both when comparing different regions of the same protein and when comparing the same region in two different homologues. 相似文献
134.
There is currently great interest in the study of peptide aggregation by -sheet formation because of its relevance in pathological states or in the design of self-assembling systems of technological interest. NMR studies of -sheet aggregates are difficult because of their long correlation times and spectral degeneracy. In this communication we demonstrate the combination of a semiselective TOCSY-NOESY experiment with partial deuterium exchange of labile protons to assign inter-molecular NOE cross peaks and prove the presence of a soluble parallel -sheet in fast exchange with monomeric Ac-ASTTTNYT-NH2 (Ac-T-NH2) in solution. 相似文献
135.
Taira E Nagino T Tsukamoto Y Okumura S Muraoka O Sakuma F Miki N 《Experimental cell research》1999,253(2):697-703
Gicerin is a cell adhesion molecule in the immunoglobulin (Ig) superfamily and is expressed abundantly during development in the nervous system. It has homophilic cell adhesion activity and also has heterophilic binding activity with NOF (neurite outgrowth factor) and mediates neurite extension. There are two isoforms of gicerin, one with a short (s-gicerin) and the other with a longer cytoplasmic domain (l-gicerin). We have reported that s-gicerin possesses stronger activities than l-gicerin during cell aggregation, in NOF-binding, and in neurite extension. In this study, we established cell lines which expressed a mutant-gicerin whose cytoplasmic domain was deleted and we compared the above three biological activities of the mutant-gicerin with those of s- and l-gicerin. We found that the mutant-gicerin retained all these activities, but the activities were weaker than those of s-gicerin and almost the same as those of l-gicerin. We concluded that the cytoplasmic domain of gicerin is not essential for optimal adhesive activities of gicerin, but might be involved in the regulation of its activities. 相似文献
136.
Effects of the C132-methoxycarbonyl moiety on the self-assembly of chlorosomal chlorophylls (Chls) were studied. Model compounds, zinc methyl 3-devinyl-3-(1-hydroxymethyl)-pheophorbides a and a (Zn-31-OH-Chls a/a, C132-epimers) were synthesized from Chl a, and their aggregation behaviors were examined in Triton X-100 (TX-100) micellar suspensions and in 6%THF/water, in comparison with those of a pyrolized derivative, zinc methyl 3-devinyl-3-(1-hydroxymethyl)-132-demethoxycarbonyl-pheophorbide a (Zn-31-OH-pyroChl a). Zn-31-OH-Chl a formed self-aggregates in the TX-100 micellar suspension and gave a Qy absorption peak at 703 nm, while Zn-31-OH-pyroChl a aggregates of a Qy peak at 740 nm. In the Zn-31-OH-Chl a aggregate spectrum, the Qy red-shift was smaller, the band shape was broader, and the contribution of the residual monomer was more intense than that in the Zn-31-OH-pyroChl a aggregate spectrum. The bulky C132-moiety limits the ways of molecular association, and electronic interaction between the component molecules of the Zn-31-OH-Chl a aggregate is weakened. Stereoselective control of the aggregation of the C132-epimer was also examined. 相似文献
137.
138.
Purification of polyethylenimine polyplexes highlights the role of free polycations in gene transfer
Boeckle S von Gersdorff K van der Piepen S Culmsee C Wagner E Ogris M 《The journal of gene medicine》2004,6(10):1102-1111
BACKGROUND: Nonviral vectors based on polyethylenimine (PEI) usually contain an excess of PEI that is not complexed to DNA. Since unbound PEI contributes to cellular and systemic toxicity, purification of polyplexes from unbound PEI is desirable. METHODS: Size exclusion chromatography (SEC) was used to purify PEI polyplexes of free PEI. Transfection properties of purified polyplexes and the effect of free PEI on gene delivery were studied in vitro and in vivo after systemic application into mice. RESULTS: SEC did not change the size and zeta-potential of polyplexes. Independent of the amount of PEI used for complex formation, purified PEI polyplexes had the same final PEI nitrogen/DNA phosphate ratio of 2.5. Notably, purified PEI polyplexes demonstrated low cellular and systemic toxicity. High transfection efficiency was achieved with purified polyplexes at high DNA concentrations (8-15 microg/ml). At low DNA concentrations (2-4 microg/ml) gene transfer with purified particles was less efficient than with polyplexes containing free PEI both in vitro and in vivo. Mechanistic studies showed that free PEI partly blocked cellular association of DNA complexes but was essential for the following intracellular gene delivery. Adding free PEI to cells treated with purified particles with a delay of up to 4 h resulted in significantly enhanced transfection efficiency compared with non-purified particles or purified particles without free PEI. CONCLUSIONS: This study presents an efficient method to remove free PEI from PEI polyplexes by SEC. Our results from transfection experiments demonstrate that free PEI substantially contributes to efficient gene expression but also mediates toxic effects in a dose-dependent manner. Purified polyplexes without free PEI have to be applied at increased concentrations to achieve high transfection levels, but exhibit a greatly improved toxicity profile. 相似文献
139.
The purpose of this study was to investigate the effect of particle size, storage temperature, and duration of storage on
the physical stability and morphology of polylactic-co-glycolic acid (PLGA) nanospheres and microspheres. PLGA nanospheres
and microspheres containing the fluorescent dye, Bodipy, were prepared in varying sizes by controlling the method and degree
of agitation during the emulsification phase of preparation. Mean diameters of the particles were measured by dynamic light
scattering. To evaluate the effect of storage temperature and duration of storage on the extent of aggregation, nanospheres
and microspheres were stored at 4°C, 25°C, 37°C, and 50°C for 6 days and then monitored using both confocal and scanning electron
microscopy. The mean ±SD diameters of PLGA particles containing Bodipy were: 266.9±2.8, 351.6±1.8, 988.8±14.1, and 1865.9±67.0
nm. The extent of aggregation of the particulate delivery system decreased as the mean diameter increased, and increased as
the storage temperature increased. The maximum extent of aggregation was observed with the smallest (266 nm) nanospheres.
Microspheres did not aggregate. The aggregation of nanospheres was significantly reduced by introducing an additional evaporation
step during preparation, suggesting that migration of residual dichloromethane from within the nanospheres may have dissolved
the PLGA on the surface. The extent of aggregation of nanospheres increased as the temperature was increased from 4°C to 50°C,
and decreased as particle size increased. To avoid aggregation, PLGA nanospheres should be stored at 4°C. 相似文献
140.
Alpha-synuclein is the main component of the intracellular protein aggregates in neurons of patients with Parkinson's disease. The occurrence of the disease is associated with oxidative damage. Although it is known that peroxidative chemistry leads to the aggregation of alpha-synuclein in vitro, the specific amino acid types of alpha-synuclein involved in this type of aggregation have not been identified. We show, using human cytochrome c plus H(2)O(2) as the source oxidative stress, that the tyrosines of alpha-synuclein are required for aggregation. The studies reveal the chemical basis for a crucial step in the aggregation process. 相似文献