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81.
The heptasaccharide isolated from the cell wall polysaccharide of Streptococcus mitis J22 serves as an important model for the dynamics and conformation of complex polysaccharides, illustrating the nature of flexibility with rigid epitopes joined by flexible hinges. One-bond C-H residual dipolar couplings (1DCH) and long-range H-H residual dipolar couplings (nDHH) were measured for the heptasaccharide in a cetylpyridinium chloride/hexanol/brine lamellar liquid crystal medium. A method is proposed to determine the nDHH in natural abundance based on a 13C resolved 1H TOCSY pulse sequence previously published to determine the homonuclear scalar couplings. Different methods for interpretation of the 1DCH and the nDHH residual dipolar coupling data obtained were compared and combined with the NOE and long-range H,C and C,C scalar couplings available for this heptasaccharide. A flexible model of the heptasaccharide was determined in which two structurally well-defined regions involving four and two sugar residues, respectively are joined by a flexible hinge which involves two 16 glycosidic linkages. 相似文献
82.
83.
Shaw AC Larsen MR Roepstorff P Christiansen G Birkelund S 《FEMS microbiology letters》2002,212(2):193-202
The genome of the obligate intracellular bacterium Chlamydia trachomatis comprises 894 genes predicted by computer-based analysis. As part of a large-scale proteome analysis of C. trachomatis, a small abundant protein encoded by a previously unrecognized novel 204-bp open reading frame was identified by tandem mass spectrometry. No homology of this protein was observed to proteins from other organisms. The protein was conserved in C. trachomatis but not found in Chlamydia pneumoniae. Using proteomics, we show that the expression of the protein is initiated at the middle of the developmental cycle. The protein is rapidly degraded and is only present in reticulate or intermediate bodies, suggesting a possible function in the intracellular stage of C. trachomatis development. We have termed the protein '7-kDa reticulate body protein'. 相似文献
84.
Ishizuka Y Fujiwara M Kanazawa K Nemoto T Fujita K Nakanishi H 《Carbohydrate research》2002,337(19):1737-1743
The inclusion of phloridzin into beta-cyclodextrin was studied as a model of molecular recognition in membranes. Effects on 1H NMR spectra and NOE correlational peaks between phloridzin and beta-cyclodextrin were observed in the complex. Strong NOEs were observed between hydrogens of a phenol group in phloridzin and beta-cyclodextrin. The three-dimensional structure of the inclusion complex between phloridzin and beta-cyclodextrin was simulated with distance constraints estimated by the intensity of NOE peaks using the DADAS90 programs. Two inclusion possibilities were suggested-the large rim of beta-cyclodextrin as an entrance of the inclusion and the small rim of beta-cyclodextrin as the entrance. In both cases, the phenol group of phloridzin was included in the hydrophobic space of beta-cyclodextrin. 相似文献
85.
Melanoma inhibitory activity (MIA) is a small secreted protein that is implicated in cartilage cell maintenance and melanoma metastasis. It is representative of a recently discovered family of proteins that contain a Src Homologous 3 (SH3) subdomain. While SH3 domains are normally found in intracellular proteins and mediate protein-protein interactions via recognition of polyproline helices, MIA is single-domain extracellular protein, and it probably binds to a different class of ligands.Here we report the assignments, solution structure, and dynamics of human MIA determined by heteronuclear NMR methods. The structures were calculated in a semi-automated manner without manual assignment of NOE crosspeaks, and have a backbone rmsd of 0.38 Å over the ordered regions of the protein. The structure consists of an SH3-like subdomain with N- and C-terminal extensions of approximately 20 amino acids each that together form a novel fold. The rmsd between the solution structure and our recently reported crystal structure is 0.86 Å over the ordered regions of the backbone, and the main differences are localized to the most dynamic regions of the protein. The similarity between the NMR and crystal structures supports the use of automated NOE assignments and ambiguous restraints to accelerate the calculation of NMR structures. 相似文献
86.
Factors affecting the yield and properties of bacterial cellulose 总被引:12,自引:0,他引:12
Krystynowicz A Czaja W Wiktorowska-Jezierska A Gonçalves-Miśkiewicz M Turkiewicz M Bielecki S 《Journal of industrial microbiology & biotechnology》2002,29(4):189-195
Acetobacter xylinum E25 has been applied in our studies in order to find optimal culture conditions for effective bacterial cellulose (BC) production.
The strain displays significantly higher stability in BC production under stationary culture conditions. In contrast, intensive
agitation and aeration appear to drastically reduce cellulose synthesis since such conditions induced formation of spontaneous
cellulose nonproducing mutants (Cel−), which dominated in the culture. Mutation frequency strictly depends on the medium composition in agitated cultures. Enrichment
of the standard SH and Yamanaka media with 1% ethanol significantly enhanced BC production in stationary cultures. Horizontal
fermentors equipped with rotating discs or rollers were successfully applied in order to improve culture conditions. Relatively
slow rotation velocity (4 rpm) and large surface area enabling effective cell attachment are optimal parameters for cellulose
production. Physical properties of BC samples synthesized either in stationary cultures or in a horizontal fermentor revealed
that cellulose from stationary cultures demonstrated a much higher value of Young's modulus, but a much lower value of water-holding
capacity. Journal of Industrial Microbiology & Biotechnology (2002) 29, 189–195 doi:10.1038/sj.jim.7000303
Received 01 March 2002/ Accepted in revised form 18 July 2002 相似文献
87.
Conformational studies have been performed of a pentasaccharide derived from the O-polysaccharide from Escherichia coli O142. The polymer was selectively degraded by anhydrous hydrogen fluoride and reduced to yield an oligosaccharide model of its repeating unit, which in the branching region consists of four aminosugars. A comparison of (1)H and (13)C chemical shifts between the pentasaccharide and the polymer showed only minor differences, except where the cleavage had taken place, indicating that the oligomer is a good model of the repeating unit. Langevin dynamics and molecular dynamics simulations with explicit water molecules were carried out to sample the conformational space of the pentasaccharide. For the glycosidic linkages between the hexopyranoside residues, small but significant changes were observed between the simulation techniques. One-dimensional (1D) (1)H,(1)H double pulsed field gradient spin echo (DPFGSE) transverse rotating-frame Overhauser effect spectroscopy (T-ROESY) experiments were performed, and homonuclear cross-relaxation rates were obtained. Subsequently, a comparison of interproton distances from NMR experiment and the two simulation approaches showed that in all cases the use of explicit water in the simulations resulted in better agreement. Hydrogen-bond analysis of the trajectories from the molecular dynamics simulation revealed interresidue interactions to be important as a cluster of different hydrogen bonds and as a distinct highly populated hydrogen bond. NMR data are consistent with the presence of hydrogen bonding within the model of the repeating unit. 相似文献
88.
Relaxation measurements of side-chain 13CH2-groups of uniformly 13C labeled human ubiquitin were performed at 600 MHz and 800 MHz magnetic field strength at 30°C. Dipole-dipole cross-correlated relaxation effects in T1 experiments were suppressed by the combination of radio-frequency pulses and pulsed field gradients during the relaxation delay leading to monoexponential relaxation decays that allow a more accurate extraction of the 13C T1 relaxation times. Heteronuclear 1H-13C NOEs obtained by using different proton saturation schemes indicate that the influence of cross-correlation is small. The experimental T1 and NOE data were interpreted in a model-free way in terms of a generalized order parameter and an internal correlation time. 相似文献
89.
Takashi Asai Daniel K Howe Kyoko Nakajima Tomoyoshi Nozaki Tsutomu Takeuchi L.David Sibley 《Experimental parasitology》1998,90(3):277-285
Asai, T., Howe, D. K., Nakajima, K., Nozaki, T., Takeuchi, T., and Sibley, L. D.Neospora caninum: Tachyzoites Express Type-I Nucleoside Triphosphate Hydrolase1. But Lack Nucleoside Diphosphate Hydrolase Activity.Experimental Parasitology90,277–285. We have identified type I nucleoside triphosphate hydrolase (NTPase; EC 3.6.1.3) activity, previously thought to be restricted to the virulent strains ofToxoplasma gondii, in the cell extracts ofNeospora caninumtachyzoites. Sequence analysis of a complete cDNA from Nc-1 strain indicated thatN. caninumNTPases shared approximately 69% identity to the NTPases ofT. gondiiand are most similar to the NTPase-I isozyme. Southern blot analysis of genomic DNA and sequence analysis of two independentNTPclones from the Nc-1 strain revealed the presence of multiple genes, at least two of which are transcribed. Substrate specificity andKmvalues for MgATP2−and MgADP−hydrolysis for recombinant or partially purified native NcNTPase were the same as those for the type I isozyme (NTPase-I). Significantly, no type II enzyme (NTPase-II) activity for NDP hydrolysis was detected in cell extracts ofN. caninum, although it is universally present in allT. gondiistrains that have been tested. This intriguing difference between these two closely related apicomplexan parasites may provide insight into the function of the NTPases during intracellular parasitism. 相似文献
90.