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501.
502.
Exact algorithms for the kinetic analysis of multichannel patch-clamp records require hours to days for a single record.
Thus, it may be reasonable to use a fast but less accurate method for the analysis of all data sets and to use the results
for a reanalysis of some selected records with more sophisticated approaches. For the first run, the tools of single-channel
analysis were used for the evaluation of the single-channel rate constants from multichannel dwell-time histograms. This could
be achieved by presenting an ensemble of single channels by a ``macrochannel' comprising all possible states of the ensemble
of channels. Equations for the calculations of the elements of the macrochannel transition matrix and for the steady-state
concentrations for individual states are given. Simulations of multichannel records with 1 to 8 channels with two closed and
one open states and with 2 channels with two open and two closed states were done in order to investigate under which conditions
the one-dimensional dwell-time analysis itself already provides reliable results. Distributions of the evaluated single-channel
rate constants show that a bias of the estimations of the single-channel rate constants of 10 to 20% has to be accepted. The
comparison of simulations with signal-to-noise ratios of SNR = 1 or SNR = 25 demonstrates that the major problem is not the
convergence of the fitting routine, but failures of the level detector algorithm which creates the dwell-times distributions
from noisy time series.
The macrochannel presentation allows the incorporation of constraints like channel interaction. The evaluation of simulated
4-channel records in which the rate-constant of opening increased by 20% per already open channel could reveal the interaction
factor.
Received: 9 June 1997/Revised: 28 April 1998 相似文献
503.
504.
José Manuel Borrero-de Acuña Izabook Gutierrez-Urrutia Cristian Hidalgo-Dumont Carla Aravena-Carrasco Matias Orellana-Saez Nestor Palominos-Gonzalez Jozef B. J. H. van Duuren Viktoria Wagner Lars Gläser Judith Becker Michael Kohlstedt Flavia C. Zacconi Christoph Wittmann Ignacio Poblete-Castro 《Microbial biotechnology》2021,14(6):2385-2402
Lignin-based aromatics are attractive raw materials to derive medium-chain length poly(3-hydroxyalkanoates) (mcl-PHAs), biodegradable polymers of commercial value. So far, this conversion has exclusively used the ortho-cleavage route of Pseudomonas putida KT2440, which results in the secretion of toxic intermediates and limited performance. Pseudomonas putida H exhibits the ortho- and the meta-cleavage pathways where the latter appears promising because it stoichiometrically yields higher levels of acetyl-CoA. Here, we created a double-mutant H-ΔcatAΔA2 that utilizes the meta route exclusively and synthesized 30% more PHA on benzoate than the parental strain but suffered from catechol accumulation. The single deletion of the catA2 gene in the H strain provoked a slight attenuation on the enzymatic capacity of the ortho route (25%) and activation of the meta route by nearly 8-fold, producing twice as much mcl-PHAs compared to the wild type. Inline, the mutant H-ΔcatA2 showed a 2-fold increase in the intracellular malonyl-CoA abundance – the main precursor for mcl-PHAs synthesis. As inferred from flux simulation and enzyme activity assays, the superior performance of H-ΔcatA2 benefited from reduced flux through the TCA cycle and malic enzyme and diminished by-product formation. In a benzoate-based fed-batch, P. putida H-ΔcatA2 achieved a PHA titre of 6.1 g l–1 and a volumetric productivity of 1.8 g l–1 day–1. Using Kraft lignin hydrolysate as feedstock, the engineered strain formed 1.4 g l- 1 PHA. The balancing of carbon flux between the parallel catechol-degrading routes emerges as an important strategy to prevent intermediate accumulation and elevate mcl-PHA production in P. putida H and, as shown here, sets the next level to derive this sustainable biopolymer from lignin hydrolysates and aromatics. 相似文献
505.
Hany Alonso Rafael Matias José Pedro Granadeiro Paulo Catry 《Journal of Ornithology》2009,150(2):329-337
The replacement of old feathers is essential for birds, but it is also an energy-demanding task. As moult usually does not
coincide with other stressful events in its annual cycle, such as reproduction and migration, the bird can optimise its use
of time and energy allocated to different activities. There are very few studies comparing the moult strategies of populations
with similar breeding calendars but occurring in areas of different habitat quality. Cory’s Shearwaters Calonectris diomedea have a partial moult–breeding overlap, an unusual phenomenon among pelagic seabirds. We have compared the moult schedules
in Cory’s Shearwater colonies located in distinct environments (pelagic vs. coastal) and show that moult–breeding overlap
is less extensive on Selvagem Grande, situated in deep oceanic waters, than on Berlenga, situated on the continental shelf.
Colony attendance of failed breeders, most of which were moulting, was lower at Selvagem Grande than at Berlenga, which suggests
that the feeding areas of birds from the former site are more distant from the colony. Failed breeders started to moult earlier
than individuals still raising a chick, and breeding status had a stronger influence on determining the onset of wing-feather
moult than colony location. Despite published evidence that internal circannual rhythms and external cues, such as variation
in daylength, are important factors regulating moult schedules, it is clear that birds retain a considerable flexibility that
allows them to respond to external factors in order to strategically manage time and energy in a way that is thought to maximise
their fitness. 相似文献
506.
507.
The supralittoral green alga Prasiola crispa, collected in Antarctica, was grown at salinities ranging from 0.35 %o to 175 %o. Its ultrastructure was examined by electron microscopy and compared with the ultrastructure of plants grown under standard conditions (35 %o). The thalli had very thick cell walls, making up approximately 50% of the thallus volume. Most of the protoplast was occupied by a single chloroplast. Numerous starch granules in the chloroplast were enlarged under hypo-osmotic conditions and reduced in volume when subjected to hyperosmotic stress indicating a metabolic shift towards low molecular weight organic osmolytes under the latter conditions. Whilst vacuoles were lacking in plants cultured at salinities between 0.35 %o and 35 %o, they developed under hyperosmotic conditions and possibly may serve as compartments accumulating inorganic ions. Growth, photosynthesis and dark respiration were strongly inhibited under higher salinities, whilst they remained almost unaffected under lower salinities (Jacob et al., 1991). 相似文献
508.