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61.
The rate of net CO2 fixation in Lemna gibba L. was decreasedto 50% by 100150 min incubation in the presence of 05mol m3 L-methionine-D,L-Sulphoximine (MSO), an irreversibleinhibitor of glutasnine synthetase (GS). The pattern of inhibitionwas similar in both 21% O2 and 2% O2. The inhibition was accompaniedby increased intracellular levels. Incubation with 10 mol m3 under the same conditions, but without MSO, resulted in even higher levels but the rate of CO2 fixation was unaffected. Additions of glutamine, glutamate, glycine or serine delayedthe MSO-induced inhibition of CO2 fixation. The same amino acidsdelayed the inactivation of GS by MSO. Thus inhibition of CO2 fixation by MSO in Lemna is neither causedby elevated levels nor closely related to photorespiration. Possibly, MSO causes shortage of amino-N formaintenance of the functional integrity of the photosyntheticapparatus. Key words: Methionine sulphoximine, CO2, fixation, Lemna 相似文献
62.
MATTSSON M; JOHANSSON E; LUNDBORG T.; LARSSON M.; LARSSON C.-M. 《Journal of experimental botany》1991,42(2):197-205
Growth and nitrate uptake kinetics in vegetatively growing barley(Hordeum vulgare L., cvs Laevigatum, Golf, and Mette) were investigatedin solution culture under long-term limitations of externalnitrogen availability. Nitrate was fed to the cultures at relativeaddition rates (RA) ranging from 0.02 to 0.2 d1. Therelative growth rate (RG, calculated for total plant dry weight)correlated well with RA in the range 0.02 to 0.07 d1.In the RA range from 0.07 to 0.2 d1 RG continued to increase,but an increasing fraction of nitrogen, added and absorbed,was apparently stored rather than used for structural growth.The RG of the roots was less affected by RA. Vmax, for net nitrateuptake increased with RA up to 0.11 d1, but decreasedat higher RA. The decline in Vmax coincided with a build-upof nitrate stores in both roots and shoots. Vmax, expressedper unit nitrogen in the plants (the relative Vmax, was higherthan required for maintenance of growth (up to 30-fold) at lowRA, whereas at higher RA the relative Vmax decreased. Kineticpredictions of steady-state external nitrate concentrationsduring N-limited growth ranged from 0.2 to 5.0 mmol m3over the RG range 0.02 to 0.11 d1. It is suggested thatthe nitrate uptake system is not under specific regulation atlow RA, but co-ordinated with root protein synthesis and growthin general. At RA higher than 0.11 d1, however, specificregulation of nitrate uptake, possibly via root nitrate pools,become important. The three cultivars showed very similar growthand nitrate uptake characteristics. Key words: Barley, growth, nitrogen limitation, nitrate uptake, kinetics 相似文献
63.
Facile labeling of oligosaccharides (acidic and neutral) in a nonselective
manner was achieved with highly fluorescent anthranilic acid (AA,
2-aminobenzoic acid) (more than twice the intensity of 2- aminobenzamide,
AB) for specific detection at very high sensitivity. Quantitative labeling
in acetate-borate buffered methanol (approximately pH 5.0) at 80 degreesC
for 60 min resulted in negligible or no desialylation of the
oligosaccharides. A high resolution high performance liquid chromatographic
method was developed for quantitative oligosaccharide mapping on a
polymeric-NH2bonded (Astec) column operating under normal phase and anion
exchange (NP-HPAEC) conditions. For isolation of oligosaccharides from the
map by simple evaporation, the chromatographic conditions developed use
volatile acetic acid-triethylamine buffer (approximately pH 4.0) systems.
The mapping and characterization technology was developed using well
characterized standard glycoproteins. The fluorescent oligosaccharide maps
were similar to the maps obtained by the high pH anion-exchange
chromatography with pulsed amperometric detection (HPAEC-PAD), except that
the fluorescent maps contained more defined peaks. In the map, the
oligosaccharides separated into groups based on charge, size, linkage, and
overall structure in a manner similar to HPAEC-PAD with contribution of
-COOH function from the label, anthranilic acid. However, selectivity of
the column for sialic acid linkages was different. A second dimension
normal phase HPLC (NP-HPLC) method was developed on an amide column (TSK
Gel amide-80) for separation of the AA labeled neutral complex type and
isomeric structures of high mannose type oligosaccharides. The
oligosaccharides labeled with AA are compatible with biochemical and
biophysical techniques, and use of matrix assisted laser desorption mass
spectrometry for rapid determination of oligosaccharide mass map of
glycoproteins is demonstrated. High resolution of NP-HPAEC and NP-HPLC
methods combined with mass spectrometry (MALDI-TOF) can provide an
effective technology for analyzing a wide repertoire of oligosaccharide
structures and for determining the action of both transferases and
glycosidases.
相似文献
64.
MOTIVATION: Molecular biology databases hold a large number of empirical
facts about many different aspects of biological entities. That data is
static in the sense that one cannot ask a database 'What effect has protein
A on gene B?' or 'Do gene A and gene B interact, and if so, how?'. Those
questions require an explicit model of the target organism. Traditionally,
biochemical systems are modelled using kinetics and differential equations
in a quantitative simulator. For many biological processes however,
detailed quantitative information is not available, only qualitative or
fuzzy statements about the nature of interactions. RESULTS: We designed and
implemented a qualitative simulation model of lambda phage growth control
in Escherichia coli based on the existing simulation environment QSim.
Qualitative reasoning can serve as the basis for automatic transformation
of contents of genomic databases into interactive modelling systems that
can reason about the relations and interactions of biological entities.
相似文献
65.
IRMGARD BLINDOW GUNNAR ANDERSSON ERS HARGEBY STEFAN JOHANSSON 《Freshwater Biology》1993,30(1):159-167
- 1 Lake Tåkern and Lake Krankesjön, two moderately eutrophic, shallow lakes in southern Sweden, have during the past few decades shifted several times between a clear-water state with abundant submerged vegetation and a turbid state with high phytoplankton densities.
- 2 Between 1985 and 1991, Lake Takern was in a clear state, whereas Lake Krankesjon shifted from a turbid to a clear state. During this shift, the area covered by submerged macrophytes expanded, followed by an increase in water transparency, plant-associated macroinvertebrates, and piscivorous fish. Nutrient concentrations, phytoplankton biomass and abundance of planktonic cladocerans decreased.
- 3 In both lakes, water level fluctuations were the most common factor causing shifts, affecting submerged macrophytes either through changes in light availability or through catastrophic events such as dry-out or mechanical damage by ice movement.
- 4 Our data give further support for the existence of two alternative stable states in shallow lakes maintained by self-stabilizing feedback mechanisms.
66.
The inhibitory effect of 23N-alkyl-4-piperidylesters (alkyl = ethyl-butyl) (APEA) and 8N-ethyl-2-pyrrolidinylmethylesters (EPMEA) of 2- and 3-substituted alkoxyphenylcarbamic acids (alkoxy = butoxy-heptyloxy-) on photosynthetic Hill reaction activity of spinach chloroplasts and on chlorophyll (Chl) synthesis in green algaeChlorella vulgaris was investigated. Inhibitory activities of these compounds were strongly connected with the lipophilicity of the whole molecule. A lower inhibitory activity of 2-alkoxy-substituted derivatives in relation to the corresponding 3-substituted ones was confirmed. Electron spin resonance (ESR) spectra of spinach chloroplasts demonstrated that the studied compounds affected the structure of photosystem (PS) 2 with the release of Mn2+ ions into interior of thylakoid membranes. 相似文献
67.
LARA MODOLO ROBERT D. MARTIN CAREL P. VAN SCHAIK MARIA A. VAN NOORDWIJK MICHAEL KRÜTZEN 《Molecular ecology》2008,17(18):4027-4038
Barbary macaques (Macaca sylvanus), now restricted in the wild to a few isolated forested areas of Morocco and Algeria, are present in a free‐ranging colony on Gibraltar. For many decades, the Gibraltar colony was exposed to multiple bottlenecks due to highly nonrandom removal of animals, followed by repeated introductions of animals from North Africa. Moreover, because of complete isolation, Gibraltar's several social groups of macaques provide an ideal system to study the genetic consequences of dispersal in cercopithecines in situ. Predictions of genetic consequences due to male‐biased dispersal in cercopithecines will be different for autosomal and maternally inherited genetic markers, such as the control region of the mitochondrial DNA. We used a panel of 14 highly polymorphic microsatellite loci and part of the hypervariable region I of the mitochondrial control region to estimate genetic structure between five social groups in Gibraltar. Surprisingly, for autosomal markers, both classical summary statistics and an individual‐based method using a Bayesian framework detected significant genetic structure between social groups in Gibraltar, despite much closer proximity than wild Algerian and Moroccan populations. Mitochondrial data support this finding, as a very substantial portion of the total genetic variation (70.2%) was found between social groups. Using two Bayesian approaches, we likewise identified not only a small number of male first‐generation immigrants (albeit less than expected for cercopithecines) but also unexpectedly a few females. We hypothesize that the culling of males that are more likely to disperse might slow down genetic homogenization among neighbouring groups, but may also and more perversely produce selection on certain behavioural traits. This may have important repercussions for conservation, as it could lead to evolutionary changes that are not due to inbreeding or genetic drift. 相似文献
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