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排序方式: 共有479条查询结果,搜索用时 31 毫秒
41.
Zakrzewski R Ciesielski W 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2005,824(1-2):327-332
The reaction between iodine and azide ions induced by thiopental was utilized as a postcolumn reaction for chromatographic determination of thiopental. The method is based on the separation of thiopental on an Nova-Pak CN HP column with an acetonitrile-aqueous solution of sodium azide as a mobile phase, followed by spectrophotometric measurement of the residual iodine (lambda=350 nm) from the postcolumn iodine-azide reaction induced by thiopental after mixing an iodine solution containing iodide ions with the column effluent containing azide ions and thiopental. Chromatograms obtained for thiopental showed negative peaks as a result of the decrease in background absorbance. The detection limit (defined as S/N=3) was 20 nM (0.4 pmol injected amount) for thiopental. Calibration graphs, plotted as peak area versus concentrations, were linear from 40 nM. The elaborated method was applied to determine thiopental in urine samples. The detection limit (defined as S/N=3) was 0.025 nmol/ml urine. Calibration graphs, plotted as peak area versus concentrations, were linear from 0.05 nmol/ml urine. Authentic urine samples were analyzed, thiopental was determined at nmol/ml urine level. 相似文献
42.
Sterol carrier protein-2 (SCP-2) facilitates cholesterol (Ch) and phospholipid (PL) transfer/exchange between membranes and appears to play a key role in intracellular lipid trafficking. Whether SCP-2 can also facilitate lipid hydroperoxide (LOOH) transfer between membranes and thereby potentially enhance dissemination of peroxidative damage was examined in this study. Transfer kinetics of photochemically generated cholesterol hydroperoxide (ChOOH) species (5alpha-OOH, 6alpha/6beta-OOH, 7alpha/7beta-OOH) and phospholipid hydroperoxide (PLOOH) families (PCOOH, PEOOH, PSOOH) were determined, using HPLC with electrochemical detection for peroxide analysis. LOOH donor/acceptor pairs employed in transfer experiments included (i) all liposomes (e.g., agglutinable SUVs/ nonagglutinable LUVs); (ii) photoperoxidized erythrocyte ghosts/SUVs or vice versa; and (iii) SUVs/mitochondria. In a SUV/ghost system at 37 degrees C, the rate constant for total ChOOH spontaneous transfer was approximately 8 times greater than that for unoxidized Ch. Purified bovine liver and human recombinant SCP-2 exhibited an identical ability to stimulate overall ChOOH transfer, 0.5 unit/mL (based on [(14)C]Ch transfer) increasing the first-order rate constant (k) approximately 7-fold. SCP-2-enhanced translocation of individual ChOOHs increased with increasing hydrophilicity in the following order: 6beta-OOH < 6alpha-OOH < 5alpha-OOH < 7alpha/7beta-OOH. Likewise, SCP-2 stimulated PCOOH, PEOOH, or PSOOH transfer approximately 6-fold, but the net k was 1/5 that of 5alpha-OOH and 1/10 that of 7alpha/7beta-OOH. Donor membrane properties favoring SCP-2-enhanced LOOH transfer included (i) increasing PL unsaturation and (ii) increasing net negative charge imposed by phosphatidylserine. Cytotoxic relevance was demonstrated by showing that SCP-2 accelerates 7alpha-OOH transfer from SUVs to isolated mitochondria and that this enhances peroxide-induced loss of the mitochondrial membrane potential. On the basis of these findings, we postulate that SCP-2, by trafficking ChOOHs and PLOOHs in addition to parent lipids, might exacerbate cell injury under oxidative stress conditions. 相似文献
43.
The effect of disease-associated mutations on the folding pathway of human prion protein 总被引:1,自引:0,他引:1
Propagation of transmissible spongiform encephalopathies is believed to involve the conversion of cellular prion protein, PrP(C), into a misfolded oligomeric form, PrP(Sc). An important step toward understanding the mechanism of this conversion is to elucidate the folding pathway(s) of the prion protein. We reported recently (Apetri, A. C., and Surewicz, W. K. (2002) J. Biol. Chem. 277, 44589-44592) that the folding of wild-type prion protein can best be described by a three-state sequential model involving a partially folded intermediate. Here we have performed kinetic stopped-flow studies for a number of recombinant prion protein variants carrying mutations associated with familial forms of prion disease. Analysis of kinetic data clearly demonstrates the presence of partially structured intermediates on the refolding pathway of each PrP variant studied. In each case, the partially folded state is at least one order of magnitude more populated than the fully unfolded state. The present study also reveals that, for the majority of PrP variants tested, mutations linked to familial prion diseases result in a pronounced increase in the thermodynamic stability, and thus the population, of the folding intermediate. These data strongly suggest that partially structured intermediates of PrP may play a crucial role in prion protein conversion, serving as direct precursors of the pathogenic PrP(Sc) isoform. 相似文献
44.
Wen-Quan Zou Jan Langeveld Xiangzhu Xiao Shugui Chen Patrick L. McGeer Jue Yuan Michael C. Payne Hae-Eun Kang John McGeehan Man-Sun Sy Neil S. Greenspan David Kaplan Gong-Xian Wang Piero Parchi Edward Hoover Geoff Kneale Glenn Telling Witold K. Surewicz Qingzhong Kong Jian-Ping Guo 《The Journal of biological chemistry》2010,285(18):13874-13884
45.
Lack of evidence on hybrid swarm in the sympatric population of Pinus mugo and P. sylvestris 总被引:3,自引:1,他引:2
Natural hybridisation between the taxa from Pinus mugo complex and P. sylvestris was postulated in several sympatric populations of the species in Europe. However, due to the absence of precise methods for identification of hybrid seeds and hybrid trees, the frequency of hybridisation and its influence on the genetic structure of relict P. mugo populations has not been clarified so far. In the present study, the species-specific chloroplast DNA (cpDNA) marker and isozymes were applied to test the hybridisation hypothesis in a postulated hybrid swarm population of the species from “Bór na Czerwonem” reserve at the northern foothills of Tatra Mts., Poland. The cpDNA marker was used to identify hybrids within two groups of polycormic (multi-stemmed) and monocormic (single-stemmed) pines from this population. Allelic frequencies at isozyme loci from both groups were compared to frequencies found in allopatric populations of the species. Additionally, cpDNA haplotypes of seedlings derived from open pollinated seeds were studied to detect the possibility of successful cross-pollination. The mixture of seedlings with P. sylvestris and P. mugo cpDNA haplotypes was derived from one parental tree that indicates hybridisation. However, all the mature polycormic pines had cpDNA haplotypes species specific to P. mugo and the isozyme frequencies were similar to frequencies found in three allopatric populations of P. mugo from Tatra Mts. (mean genetic distance, Dn=.027). The differences were much larger in comparisons with monocormic pines from this area (Dn=.085) and two P. sylvestris samples from distant allopatric populations (Dn=.077). Nearly all monocormic pines had cpDNA species specific to P. sylvestris and isozyme frequencies similar to other populations of this species (mean Dn=.004). Only one P. sylvestris-like monocormic tree had cpDNA of P. mugo and can be considered as a hybrid. The results do not provide evidence supporting the hybrid swarm hypothesis. Rather, the results suggest that mature hybrids have a low frequency within this population and (rare) hybridisation is not reciprocal but unidirectional with P. mugo as pollen donor. 相似文献
46.
Szukała K Sowińska A Wierzbicka M Biczysko W Szyfter W Szyfter K 《Mutation research》2006,600(1-2):67-76
BACKGROUND: Patients, who had an upper aerodigestive tract malignancy, have a high incidence of succeeding tumor development. This has been attributed to the role of "field cancerization" in carcinogenesis. The aim of this study was analysis of loss of heterozygosity (LOH) in the regions frequently lost during the course of head and neck squamous cell carcinomas (HNSCC), especially at early stages, which could answer the clinicians' question, if LOH analysis has any "predictive" value in relation to tumor occurrence. MATERIAL AND METHODS: Sixty-five larynx cancer patients were examined for loss of heterozygosity on 3p, 7q, 8p, 9p and 18q chromosomal arms with the use of 12 microsatellite markers. The material from a single patient consisted of blood, tumor, safe margin and one or two clinically unchanged mucosal samples. During follow up, the material from brush specimens (14 patients) as well as laryngeal swabs (4 patients) was also examined. RESULTS: The highest frequency of LOH was detected for marker D3S1234 in tumor tissues (29%). Analysis of margin samples (b) revealed low LOH frequencies (2-5%) and complete retention of heterozygosity for markers: D3S1234, D7S486, D8S261, D8S264, D9S171 and D18S46. Similarly, for normal appearing mucosa from upper part of larynx (c) frequencies of LOH were low (2-6%), with the complete retention of heterozygosity for markers: D3S1284, D3S1304, D3S1234, D8S264 and D9S1870. We did not detect any LOH in the material of normal appearing mucosa from tracheostoma region (d). During follow up, LOH was detected for eight markers, with the highest incidence for markers D18S46 (six cases), D7S486 (four cases) and D3S1300 (three cases). CONCLUSIONS: The data, obtained during this investigation, did not reveal the predictive value of LOH with respect to local relapse occurrence in laryngeal cancer patients. However, time of follow up did not reach 5 years, so that further clinical monitoring should be conducted. 相似文献
47.
Witold Diakowski Ewa Bielska Marek Langner Aleksander F. Sikorski 《生物化学与生物物理学报:生物膜》2006,1758(1):4-12
We previously showed that erythrocyte and brain spectrins bind phospholipid vesicles and monolayers prepared from phosphatidylethanolamine and phosphatidylserine and their mixtures with phosphatidylcholine (Review: A.F. Sikorski, B. Hanus-Lorenz, A. Jezierski, A. R. Dluzewski, Interaction of membrane skeletal proteins with membrane lipid domain, Acta Biochim. Polon. 47 (2000) 565). Here, we show how changes in the fluidity of the phospholipid monolayer affect spectrin-phospholipid interaction. The presence of up to 10%-20% cholesterol in the PE/PC monolayer facilitates the penetration of the monolayer by both types of spectrin. For monolayers constructed from mixtures of PI/PC and cholesterol, the effect of spectrins was characterised by the presence of two maxima (at 5 and 30% cholesterol) of surface pressure for erythroid spectrin, and a single maximum (at 20% cholesterol) for brain spectrin. The binding assay results indicated a small but easily detectable decrease in the affinity of erythrocyte spectrin for FAT-liposomes prepared from a PE/PC mixture containing cholesterol, and a 2- to 5-fold increase in maximal binding capacity (Bmax) depending on the cholesterol content. On the other hand, the results from experiments with a monolayer constructed from homogenous synthetic phospholipids indicated an increase in Δπ change with the increase in the fatty acyl chain length of the phospholipids used to prepare the monolayer. This was confirmed by the results of a pelleting experiment. Adding spectrins into the subphase of raft-like monolayers constructed from DOPC, SM and cholesterol (1/1/1) induced an increase in surface pressure. The Δπ change values were, however, much smaller than those observed in the case of a natural PE/PC (6/4) monolayer. An increased binding capacity for spectrins of liposomes prepared from a “raft-like” mixture of lipids could also be concluded from the pelleting assay. In conclusion, we suggest that the effect of membrane lipid fluidity on spectrin-phospholipid interactions is not simple but depends on how it is regulated, i.e., by cholesterol content or by the chemical structure of the membrane lipids. 相似文献
48.
Subczynski WK Raguz M Widomska J Mainali L Konovalov A 《The Journal of membrane biology》2012,245(1):51-68
The most unique feature of the eye lens fiber-cell plasma membrane is its extremely high cholesterol content. Cholesterol
saturates the bulk phospholipid bilayer and induces formation of immiscible cholesterol bilayer domains (CBDs) within the
membrane. Our results (based on EPR spin-labeling experiments with lens-lipid membranes), along with a literature search,
have allowed us to identify the significant functions of cholesterol specific to the fiber-cell plasma membrane, which are
manifest through cholesterol–membrane interactions. The crucial role is played by the CBD. The presence of the CBD ensures
that the surrounding phospholipid bilayer is saturated with cholesterol. The saturating cholesterol content in fiber-cell
membranes keeps the bulk physical properties of lens-lipid membranes consistent and independent of changes in phospholipid
composition. Thus, the CBD helps to maintain lens-membrane homeostasis when the membrane phospholipid composition changes
significantly. The CBD raises the barrier for oxygen transport across the fiber-cell membrane, which should help to maintain
a low oxygen concentration in the lens interior. It is hypothesized that the appearance of the CBD in the fiber-cell membrane
is controlled by the phospholipid composition of the membrane. Saturation with cholesterol smoothes the phospholipid-bilayer
surface, which should decrease light scattering and help to maintain lens transparency. Other functions of cholesterol include
formation of hydrophobic and rigidity barriers across the bulk phospholipid-cholesterol domain and formation of hydrophobic
channels in the central region of the membrane for transport of small, nonpolar molecules parallel to the membrane surface.
In this review, we provide data supporting these hypotheses. 相似文献
49.
EPR spin-labeling methods were used to investigate the order and fluidity of alkyl chains, the hydrophobicity of the membrane
interior, and the order and motion of cholesterol molecules in coexisting phases and domains, or in a single phase of fluid-phase
cholesterol/egg-sphingomyelin (Chol/ESM) membranes with a Chol/ESM mixing ratio from 0 to 3. A complete set of profiles for
these properties was obtained for the liquid-disordered (l
d) phase without cholesterol, for the liquid-ordered (l
o) phase for the entire region of cholesterol solubility in this phase (from 33 to 66 mol%), and for the l
o-phase domain that coexists with the cholesterol bilayer domain (CBD). Alkyl chains in the l
o phase are more ordered than in the l
d pure ESM membrane. However, fluidity in the membrane center is greater. Also, the profile of hydrophobicity changed from
a bell to a rectangular shape. These differences are enhanced when the cholesterol content of the l
o phase is increased from 33 to 66 mol%, with clear brake-points between the C9 and C10 positions (approximately where the
steroid-ring structure of cholesterol reaches into the membrane). The organization and motion of cholesterol molecules in
the CBD are similar to those in the l
o-phase domain that coexists with the CBD. 相似文献
50.
Trocha LK Kałucka I Stasińska M Nowak W Dabert M Leski T Rudawska M Oleksyn J 《Mycorrhiza》2012,22(2):121-134
Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if
native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native
tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether
the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal
root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected
only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were
all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In
addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan
and novel fungi. 相似文献