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11.
We present results on using cooperative interactions to shield liposomes by incorporating multiple hydrophobic anchoring sites on polyethylene glycol (PEG) polymers. The hydrophobically-modified PEGs (HMPEGs) are comb-graft polymers with strictly alternating monodisperse PEG blocks (Mw=6, 12, or 35 kDa) bonded to C18 stearylamide hydrophobes. Cooperativity is varied by changing the degree of oligomerization at a constant ratio of PEG to stearylamide. Fusogenic liposomes prepared from N-C12-DOPE:DOPC 7:3 (mol:mol) were equilibrated with HMPEGs. Affinity for polymer association to liposomes increases with the degree of oligomerization; equilibrium constants (given as surface coverage per equilibrium concentration of free polymer) for 6 kDa PEG increased from 6.1±0.8 (mg/m2)/(mg/ml) for 2.5 loops to 78.1±12.2 (mg/m2)/(mg/ml) for 13 loops. In contrast, the equilibrium constant for distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG5k) was 0.4±0.1 (mg/m2)/(mg/ml).The multi-loop HMPEGs demonstrate higher levels of protection from complement binding than DSPE-PEG5k. Greater protection does not correlate with binding strength alone. The best shielding was by HMPEG6k-DP3 (with three 6 kDa PEG loops), suggesting that PEG chains with adequate surface mobility provide optimal protection from complement opsonization. Complement binding at 30 min and 12 h demonstrates that protection by multi-looped PEGs is constant whereas DSPE-PEG5k initially protects but presumably partitions off of the surface at longer times. 相似文献
12.
S.P. NG Z.G. LI B.W. CHEN Z.K. QIN M.M. GARCIA S.W.K. IM M.H. NG 《Journal of Rapid Methods and Automation in Microbiology》1997,5(4):285-294
We previously described an enrichment-immunoassay utilizing a T6 monoclonal antibody capture enzyme-linked immunosorbent assay. Here we evaluated it for the rapid screening for Salmonella in fishmeal obtained from the national Animal and Plant Quarantine service in the People's Republic of China. In this method, the number of Salmonella present is first expanded by appropriate enrichment cultures, and the pathogens are then directly detected by the T6 immunoassay. In a total of 94 enrichment cultures of fishmeal, we obtained an overall concordance of 98% between the results obtained in parallel by this method and by conventional test method. The positive prediction by this method was 92% and the negative prediction was 100%. The turn around time for the new test was 27 h which is a significant improvement from the turn around time exceeding 96 h required for the conventional test method. This test proved to be compatible with the routine work flow in the practical setting of a quarantine laboratory. 相似文献
13.
Eveline C van Asbeck Andy IM Hoepelman Jelle Scharringa Bjorn L Herpers Jan Verhoef 《BMC microbiology》2008,8(1):229
Background
Mannose binding lectin (MBL) is an important host defence protein against opportunistic fungal pathogens. This carbohydrate-binding protein, an opsonin and lectin pathway activator, binds through multiple lectin domains to the repeating sugar arrays displayed on the surface of a wide range of clinically relevant microbial species. We investigated the contribution of MBL to antifungal innate immunity towards C. parapsilosis in vitro. 相似文献14.
The idea of immunological surveillance against cancer has existed for nearly 100 years but as no conclusive evidence has yet
been published the importance of the cellular immune defense in the detection and removal of incipient or existing tumors
is still a hotly debated subject. However, in order to select a relevant immunotherapeutic strategy in the treatment of cancer,
a fundamental understanding of the basic immunologic conditions under which a tumor develops and exists is a prerequisite.
Therefore, a murine model was set up that we hoped would enable us to confirm or reject the theory of immunological surveillance.
A large panel of methylcholanthrene induced tumors was established in T-cell immunodeficient nude mice and congenic normal
mice to study the influence of the immune system on developing tumors. As nude mice developed tumors fastest and with the
highest incidence, we concluded that in this model the immune system constituted a ‘tumor-suppressive factor’ delaying and
sometimes abrogating tumor growth, i.e. performing immune surveillance. Immunogenicity of the tumors was assessed by transplantation
back to normal histocompatible mice. Tumors originating from the immunodeficient nude mice turned out to be far more immunogenic
than tumors from normal mice, resulting in a high rejection rate. CD8+cytotoxic T cells were found to be indispensable for
this rejection, leading to the conclusion that the cytotoxic T cells perform immune selection in normal mice, eliminating
immunogenic tumor cell variants in the incipient tumor.
In this review, we discuss the difficulties facing immunotherapy when conclusions are drawn from the presented observations
and hypotheses. 相似文献
15.
The cytopathologic features of a malignant granular cell tumor in both exfoliative and aspiration cytopreparations included isolated cells with low nuclear-cytoplasmic ratios and abundant, diffusely granular cytoplasm. Transmission electron microscopy revealed the diagnostic secondary lysosomes in the neoplastic cells. 相似文献
16.
Hanaa F. Y. Mohamed Abeer A. Mahmoud Aishah Alatawi Mona H. Hegazy Tessema Astatkie Hussein A. H. Said-Al Ahl 《Acta Physiologiae Plantarum》2018,40(12):204
Nepeta is a perennial herbal plant that belongs to the Lamiaceae mint family. Nepta has different species that are widely used in the agriculture, medicine, and pharmaceutical industries. A field experiment was conducted in 2015 and 2016 to determine the effects of potassium humate foliar application [0 (control) and 400 ppm] on growth, essential oil and constituents of three Nepta species [Nepeta cataria (catnip), Nepeta cataria var. citriodora (lemon catnip), and Nepeta grandiflora (giant catmint)] under Egyptian conditions. In all three species, the application of potassium humate increased growth indicators, essential oil content (%) and yield (mL/plant), and flavonoids in each of the two harvests. However, the height of giant catmint was significantly higher than that of lemon catnip, which was higher than that of catnip. Lemon catnip that received potassium humate and harvested second gave the highest essential oil content and yield. The major constituents were geraniol and nepetalactone in catnip; citronellol and geraniol in lemon catnip; and o-cymene, c-terpinene, p-cymene and carvacrol in giant catmint. The highest p-cymene in giant catmint, citronellol in lemon catnip, and geraniol in catnip were obtained from the application of potassium humate, while the highest o-cymene, c-terpinene and carvacrol in giant catmint, geraniol in lemon catnip, and nepetalactone in catnip were obtained from control plants. This study demonstrated the variations among species of nepeta, and how they respond to the application of potassium humate. The findings of this study can guide the customization of potassium humate applications to the three species for achieving desired growth and essential oil production outcomes. 相似文献
17.
Early evolution of metazoan serine/threonine and tyrosine kinases: identification of selected kinases in marine sponges 总被引:14,自引:1,他引:13
The phylum Porifera (sponges) was the first to diverge from the common
ancestor of the Metazoa. In this study, six cDNAs coding for protein-
serine/threonine kinases (PS/TKs) are presented; they have been isolated
from libraries obtained from the demosponges Geodia cydonium and Suberites
domuncula and from the calcareous sponge Sycon raphanus. Sequence
alignments of the catalytic domains revealed that two major families of
PS/TK, the "conventional" (Ca(2+)-dependent) protein kinase C (PKC), the
cPKC subfamily, as well as the "novel" (Ca(2+)- independent) PKC (nPKC),
form two separate clusters. In each cluster, the sequence from S. raphanus
diverges first. To approach the question about the origin of
protein-tyrosine kinases (PTK), which are found only in Metazoa, we
analyzed two additional PS/TKs which have been cloned from S. domuncula:
the stress-responsive protein kinase (KRSvSD) and the
protein-kinase-C-related kinase (PRKvSD). The construction of the
phylogenetic tree, comprising the eight PS/TKs and the PTK cloned
previously from G. cydonium, revealed that the PTK derived from the branch
including the KRSvSD kinase. These data facilitate the first molecular
approach to elucidate the origin of metazoan PTK within the PS/TK
superfamily.
相似文献
18.
When Escherichia coli K-12 was infected with lambda phage and mutants of lambda characterized by the production of temperature-sensitive repressors, the lysogenic bacteria were significantly more resistant to normal serum than the uninfected organisms. Infection of E. coli K-12 with a lambdoid phage, phi80, whose prophage attachment site is different from that of lambda, did not result in a detectable change in serum resistance. Similarly, infection with certain Pseudomonas and Shigella phages caused no detectable differences in serum resistance. Finally, the well-known conversion of the Salmonella anatum serotype to S. newington by E(15) phage indicated that, despite the relatively greater roughness of S. anatum, S. newington was more sensitive to normal serum than S. anatum. Thus, the effects of lysogeny on the sensitivity of bacteria to the bactericidal action of serum mediated by the complement system may be quite variable. 相似文献
19.
Tyrosine and carboxyl protonation changes in the bacteriorhodopsin photocycle. 2. Tyrosines-26 and -64 总被引:2,自引:0,他引:2
P Roepe P Scherrer P L Ahl S K Das Gupta R A Bogomolni J Herzfeld K J Rothschild 《Biochemistry》1987,26(21):6708-6717
Low-temperature Fourier transform infrared (FTIR) and UV difference spectroscopies combined with selective tyrosine nitration and tyrosine isotopic labeling have been used to investigate the participation of tyrosines-26 and -64 in the bacteriorhodopsin (bR) photocycle. Nitration of Tyr-26 has no detectable effect on the FTIR or UV difference spectra of the BR570----K630 or BR570----M412 transitions. In contrast, nitration of Tyr-64 causes changes in both the FTIR and UV spectra of these transitions. However, this nitration does not alter tyrosine peaks in the FTIR difference spectra which have previously been associated with the protonation of a tyrosinate by K630 and the deprotonation of a tyrosine by M412 [Roepe, P., Ahl, P. L., Das Gupta, S. K., Herzfeld, J., & Rothschild, K. J. (1987) Biochemistry (preceding paper in this issue)]. Instead, Tyr-64 nitration appears to affect other tyrosine peaks. These results and changes in UV difference spectra upon Tyr-64 nitration are consistent with the deprotonation of Tyr-64 by M412 as concluded previously [Scherrer, P., & Stoeckenius, W. (1985) Biochemistry 24, 7733-7740]. Effects on chromophore vibrations caused by Tyr-64 nitration are unaltered upon reducing the nitrotyrosine to aminotyrosine with sodium dithionite. Finally, nitro-Tyr-64 causes a shift in the frequency of a positive peak at 1739 cm-1 in the BR570----M412 FTIR difference spectrum which reflects the protonation of a carboxyl-containing residue [Engelhard, M., Gerwert, K., Hess, B., Kreutz, W., & Siebert, F. (1985) Biochemistry 24, 400-407; Roepe, P., Ahl, P. L., Das Gupta, S. K., Herzfeld, J., & Rothschild, K. J. (1987) Biochemistry (preceding paper in this issue)]. The shift does not occur for samples containing amino-Tyr-64. These data suggest that Tyr-64 may interact with this carboxyl group. 相似文献
20.
Effects of amino acid substitutions in the F helix of bacteriorhodopsin. Low temperature ultraviolet/visible difference spectroscopy 总被引:6,自引:0,他引:6
P L Ahl L J Stern D Düring T Mogi H G Khorana K J Rothschild 《The Journal of biological chemistry》1988,263(27):13594-13601
Site-specific mutagenesis in combination with low temperature UV/visible difference spectroscopy has been used to investigate the role of individual amino acids in the structure and function of bacteriorhodopsin (bR). We examined the effects of eight single amino acid substitutions, all in the putative F helix, on the absorption of bR as well as formation of the K and M intermediates. Both the absorbance spectra and the photocycle difference spectra of Escherichia coli expressed bR as well as the mutants S183A, P186G, and E194Q all closely resembled the corresponding purple membrane spectra. In contrast the Pro-186----Leu substitution resulted in the loss of the normal photocycle and a large blue shift in the bR state lambda max. Thus, Pro-186 appears to play a critical role in maintaining the normal protein-chromophore interactions, although the pyrrolidine ring is not essential since proline could be replaced by glycine at this position. The mutants W182F, W189F, and S193A did not appear to be directly involved in the bathochromic shift of bR since they all had lambda max's close to that of purple membrane and produced intermediates similar to K and M. However, alterations in the UV and visible difference spectra as well as the appearance of some irreversibility in the photoreactions indicate that these mutants have altered protein-chromophore interactions during the photocycle. Unlike the other mutants examined, Y185F exhibited a red-shifted form of bR and K raising the possibility that Tyr-185 is directly involved in color regulation. In addition, UV difference peaks previously associated with a tyrosine deprotonation were absent in Y185F indicating that Tyr-185 undergoes protonation changes during the photocycle in agreement with recent Fourier transform infrared difference measurements (Braiman, M.S., Mogi, T., Stern, L. J., Hackett, N., Chao, B. H., Khorana, H.G., and Rothschild, K. J. (1988) Proteins: Structure, Function, and Genetics 3, 219-229). Our results suggest that Trp-182, Tyr-185, Pro-186, Trp-189, and Ser-193, all of which are within a 100 degrees segment of the F helix, are part of a retinal-binding pocket. 相似文献