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41.
Vojtech Ličko 《Bulletin of mathematical biology》1967,29(1):1-16
A vast number of biologically important processes are based upon bimolecular systems. In these systems intermediate complexes
are formed. Bimolecular systems in which no complex-complex interactions occur are called linear systems of complexes. A definition
and some characteristic properties of these systems are given here. There may exist a contradiction of Onsager's principle
of detailed balancing in these systems; however, no principal differences are found between the steady state behavior of an
open system and that of a closed system. It is shown that the steady state behavior of a linear system of complexes of arbitrary
complexity has some similarities with the steady state behavior of a simple bimolecular system, e.g., Michaelis-Menten enzymatic
reaction. Multiplicity of action of the substances participating in biomolecular processes may produce some qualitative differences
in the steady state behavior of the system. 相似文献
42.
43.
Vojtech Zila Erica Margiotta Beata Turoňová Thorsten G. Müller Christian E. Zimmerli Simone Mattei Matteo Allegretti Kathleen Börner Jona Rada Barbara Müller Marina Lusic Hans-Georg Kräusslich Martin Beck 《Cell》2021,184(4):1032-1046.e18
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44.
A microsomal fraction from isolated frog gastric mucosa was used to study the binding of labeled histamine, labeled metiamide (a histamine H2-antagonist), and competition between labeled histamine and unlabeled metiamide. The separation of free from bound ligand was done by gel chromatography. The acid secretion was studied in frog gastric mucosa in vitro by a pH-stat method. The binding data could be interpreted in terms of two independent binding sites for both histamine and metiamide. However, the competition between histamine and metiamide does not support the independence of the sites. Moreover, the dissociation kinetics of labeled metiamide in the presence of unlabeled metiamide is non-monotone and, thus, indicates cooperativity. In the physiological studies, the dependence of the rate of acid secretion on histamine stimulation occurs within very narrow limits, which is the result of characteristics other than related to binding. However, the total amount of acid secreted caused by a pulse of histamine does indicate two sites, of which the high-affinity site is the more effective. Metiamide inhibition of acid secretion can be interpreted as an interaction between high-affinity sites of histamine and metiamide. Overall, studies involving physiological effects provide less precise data than the direct binding studies. 相似文献
45.
Conor M. Redmond John Auga Bradley Gewa Simon T. Segar Scott E. Miller Kenneth Molem George D. Weiblen Philip T. Butterill Gibson Maiyah Amelia S. C. Hood Martin Volf Leonardo R. Jorge Yves Basset Vojtech Novotný 《Ecography》2019,42(1):162-172
Secondary succession is well‐understood, to the point of being predictable for plant communities, but the successional changes in plant‐herbivore interactions remains poorly explored. This is particularly true for tropical forests despite the increasing importance of early successional stages in tropical landscapes. Deriving expectations from successional theory, we examine properties of plant‐herbivore interaction networks while accounting for host phylogenetic structure along a succession chronosequence in montane rainforest in Papua New Guinea. We present one of the most comprehensive successional investigations of interaction networks, equating to > 40 person years of field sampling, and one of the few focused on montane tropical forests. We use a series of nine 0.2 ha forest plots across young secondary, mature secondary and primary montane forest, sampled almost completely for woody plants and larval leaf chewers (Lepidoptera) using forest felling. These networks comprised of 12 357 plant‐herbivore interactions and were analysed using quantitative network metrics, a phylogenetically controlled host‐use index and a qualitative network beta diversity measure. Network structural changes were low and specialisation metrics surprisingly similar throughout succession, despite high network beta diversity. Herbivore abundance was greatest in the earliest stages, and hosts here had more species‐rich herbivore assemblages, presumably reflecting higher palatability due to lower defensive investment. All herbivore communities were highly specialised, using a phylogenetically narrow set of hosts, while host phylogenetic diversity itself decreased throughout the chronosequence. Relatively high phylogenetic diversity, and thus high diversity of plant defenses, in early succession forest may result in herbivores feeding on fewer hosts than expected. Successional theory, derived primarily from temperate systems, is limited in predicting tropical host‐herbivore interactions. All succession stages harbour diverse and unique interaction networks, which together with largely similar network structures and consistent host use patterns, suggests general rules of assembly may apply to these systems. 相似文献
46.
Petrusová M Vojtech M Pribulová B Lattová E Matulová M Poláková M BeMiller JN Kren V Petrus L 《Carbohydrate research》2006,341(12):2019-2025
Acid-catalysed methanolysis of 3,4,5,6-tetra-O-acetyl-1,2-dideoxy-l-arabino-hex-1-enitol proceeds via a cascade set of consecutive reactions resulting in its regiospecific conversion to a mixture of alpha- and beta-C-L-arabinofuranosylmethanal dimethyl acetals and a mixed internal methyl acetal. Structures of the final products of the overall process provide unique evidence that a kinetically controlled, five-membered-ring closure precedes a six-membered-ring closure in reversible systems capable of giving both five-membered and six-membered all-sp3-atom rings. Determination of the reaction intermediate enabled extension of the Nef reaction to C-glycosylnitromethanes. Protonated aci-nitro forms of C-glycosylnitromethanes that are resistant to the Nef reaction in aqueous acidic media undergo a modified Nef reaction in acidified methanol, and the corresponding C-glycosylmethanal dimethyl acetals with alpha-L-arabinopyranosyl, beta-D-glucopyranosyl, beta-D-galactopyranosyl, beta-D-mannopyranosyl and beta-L-rhamnopyranosyl configurations were obtained in moderate yields. 相似文献
47.
Hui Zhang Niko G. Gubernator Minerva Yue Roland G. W. Staal Eugene V. Mosharov Daniela Pereira Vojtech Balsanek Paul A. Vadola Bipasha Mukherjee Robert H. Edwards David Sulzer Dalibor Sames 《Journal of visualized experiments : JoVE》2009,(30)
The nervous system transmits signals between neurons via neurotransmitter release during synaptic vesicle fusion. To observe neurotransmitter uptake and release from individual presynaptic terminals directly, we designed fluorescent false neurotransmitters as substrates for the synaptic vesicle monoamine transporter. Using these probes to image dopamine release in the striatum, we made several observations pertinent to synaptic plasticity. We found that the fraction of synaptic vesicles releasing neurotransmitter per stimulus was dependent on the stimulus frequency. A kinetically distinct "reserve" synaptic vesicle population was not observed under these experimental conditions. A frequency-dependent heterogeneity of presynaptic terminals was revealed that was dependent in part on D2 dopamine receptors, indicating a mechanism for frequency-dependent coding of presynaptic selection.Hui Zhang and Niko G. Gubernator contributed equally to this work.Download video file.(112M, mp4) 相似文献
48.
Martin Hulak Vojtech Kaspar Martin Psenicka David Gela Ping Li Otomar Linhart 《Reviews in Fish Biology and Fisheries》2010,20(3):307-315
Triploidy interferes with gametogenesis in all fish species tested so far. In fish it results in complete female sterility
however, males are still able to develop testis. The reason why sterility levels in triploid fishes differ among species and
between sexes is unclear. In the present study the reproductive capacity of triploid males of tench was studied. Flow cytometry
revealed sperm cells of triploids to be largely aneuploid with high mosaic DNA, oscillating from haploid DNA to diploid DNA
content. Analysis of variance showed an insignificant influence of ploidy level on the percentage of motile spermatozoa, as
well as on spermatozoa velocity. Experimental crosses between normal diploid female and triploid males resulted in the appearance
of triploid progeny, which exhibited genotypes composed of microsatellite alleles inherited from the founder female and additional
allele derived from the donor male. We can conclude that the triploid males analysed in the present study were capable to
fertilize eggs derived from diploid females. 相似文献
49.
Juraj Balkovič Jozef Kollár Gabriela Čemanová Vojtech Šimonovič 《Folia Geobotanica》2010,45(3):253-277
A fine-scaled approach for predicting soil acidity using plant species in a spatially limited area (?epú?ky Nature Reserve, Slovakia) is presented here. This approach copes with some specific limitations: i) a limited pool of vegetation data may make the predictions too sensitive to the lack of species information, and ii) the predictions may be sensitive to the narrow pH gradient. Vegetation relevés and soil reaction (pH-H2O and pH-CaCl2) were systematically recorded. A set of species indicator values and amplitudes was calibrated with physical pH data using the Weighted Averaging (WA), HOF modelling and Non-Metric Multidimensional Scaling (NMDS) methods, along with Ellenberg indicator values. Two prediction methods were tested: i) WA and ii) Amplitude Overlap (AO). WA prediction with Ellenberg’s and WA-calibrated species indicator values were the most powerful technique (R 2?=?68.4–68.7% and 53.4–59.1% for pH-CaCl2 and pH-H2O, respectively). WA-prediction with HOF-based indicator values was less effective (R 2?=?61.7% and 50.7%) due to the decrease in species’ information because with HOF modelling many species are assumed indifferent or too rare. The NMDS method does not bring any significant gain to the calibration, though it avoids the lack of species information. The AO method was proven to be less powerful under studied circumstances, because it is sensitive both to the lack of species’ information and to the truncation of species responses. The results prove that a spatially explicit approach can provide significant indices to estimate changes in soil acidity – pH-CaCl2 better than pH-H2O. 相似文献
50.
Presence of mutated and/or structurally modified (e.g., denatured, aggregated) protein p53 form is associated with several
disorders such as Alzheimer’s disease, Parkinson’s disease, prion diseases, and many types of tumours. The aim of this work
was to distinguish native, denatured and aggregated form of full-length p53 by flow injection analysis coupled with electrochemical
detector (FIA-ED). Firstly FIA-ED method used for protein native form determination was optimized (detection limit 45.8 amol
per 5 μl injection; 3×S/N). In addition the technique was applied to identify p53 structural forms (denatured and aggregated).
It was found out that denatured form provides about three times higher electrochemical response (protein structure unfolding,
approach of more electroactive centers – aminoacid residues – towards electrode surface) in comparison with native form. On
the other hand, aggregated form offers lower response (steric eclipse of electroactive protein parts) when compared with the
signal of native form. The obtained data show that we are not only able to sensitively determine native, denatured, and aggregated
structural forms of p53 protein but also to distinguish them. 相似文献