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131.
Studies on the mechanism of photosystem II photoinhibition I. A two-step degradation of D1-protein 总被引:2,自引:0,他引:2
The role of D1-protein in photoinhibition was examined. Photoinhibition of spinach thylakoids at 20°C caused considerable degradation of D1-protein and a parallel loss of variable fluorescence, QB-independent electron flow and QB-dependent electron flow. The breakdown of D1-protein as well as the loss of variable fluorescence and QB-independent electron flow were largely prevented when thylakoids were photoinhibited at 0°C. The QB-dependent electron flow markedly decreased under the same conditions. This inactivation may represent the primary event in photoinhibition and could be the result of some modification at the QB-site of D1-protein. Evidence for this comes from fluorescence relaxation kinetics following photoinhibition at 0°C which indicate a partial inactivation of QA
--reoxidation. These results support the idea of D1-protein breakdown during photoinhibition as a two step process consisting of an initial inactivation at the QB-site of the protein followed by its degradation. The latter is accompanied by the loss of PS II-reaction centre function.Abbreviations Asc
ascorbate
- p-BQ
1, 4-benzoquinone
- DAD
diaminodurene
- DPC
diphenylcarbazide
- DQH2
duroquinole
- Fecy
ferricyanide
- MV
methylviologen
- QA
primary quinone acceptor of PS II
- QB
secondary quinone acceptor of PS II
- SiMo
silicomolybdate 相似文献
132.
When excited by ultraviolet radiation, leaves of a great number of species of higher plants exhibit emission of blue fluorescence, comparable in intensity to the red emission of chlorophyll. The fluorescence decay of the blue emission of spinach leaves recorded by single photon counting techniques is decomposed into exponential components and it is shown that at least three different components are present. The lifetime of the three components does not show significant variations with the excitation or emission wavelengths. The excitation and emission spectra of each component were determined. The nature of the chemical compounds which cause this emission is discussed in relation to these spectra. 相似文献
133.
The photosynthetic energy storage yield of uncoupled thylakoid membranes was monitored by photoacoustic spectroscopy at various measuring beam intensities. The energy storage rate as evaluated by the half-saturation measuring beam intensity (i50) was inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea, by heat inactivation or by artificial electron acceptors specific for photosystem I or photosystem II; and was activated by electron donors to photosystem I. The reactions involving both photosystems were all characterized by a similar maximal energy storage yield of 16±2 percent. The data could be interpreted if we assumed that the energy storage elicited by the photosystems at 35 Hz is detected at the level of the plastoquinone pool.Abbreviations PS
photosystem
- Tes
N-Tris [hydroxymethl] methyl-2-aminoethanesulfonic acid
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DCIP
2,6-dichlorophenolindophenol
- FeCN
potassium ferricyanide
- DCBQ
2,5-dichlorobenzoquinone
- TMPD
N,N,N-tetramethyl-p-phenilenediamine 相似文献
134.
The mechanism of excitation energy distribution between the two photosystems (state transitions) is studied in Synechocystis 6714 wild type and in wild type and a mutant lacking phycocyanin of Synechocystis 6803. (i) Measurements of fluorescence transients and spectra demonstrate that state transitions in these cyanobacteria are controlled by changes in the efficiency of energy transfer from PS II to PS I (spillover) rather than by changes in association of the phycobilisomes to PS II (mobile antenna model). (ii) Ultrastructural study (freeze-fracture) shows that in the mutant the alignment of the PS II associated EF particles is prevalent in state 1 while the conversion to state 2 results in randomization of the EF particle distribution, as already observed in the wild type (Olive et al. 1986). In the mutant, the distance between the EF particle rows is smaller than in the wild type, probably because of the reduced size of the phycobilisomes. Since a parallel increase of spillover is not observed we suggest that the probability of excitation transfer between PS II units and between PS II and PS I depends on the mutual orientation of the photosystems rather than on their distance. (iii) Measurements of the redox state of the plastoquinone pool in state 1 obtained by PS I illumination and in state 2 obtained by various treatments (darkness, anaerobiosis and starvation) show that the plastoquinone pool is oxidized in state 1 and reduced in state 2 except in starved cells where it is still oxidized. In the latter case, no important decrease of ATP was observed. Thus, we propose that in Synechocystis the primary control of the state transitions is the redox state of a component of the cytochrome b
6/f complex rather than that of the plastoquinone pool.Abbreviations DCCD
dicyclohexylcarbodiimide
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DBMIB
2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone
- EF
exoplasmic face
- PQ
plasto-quinone
- PS
photosystem
- PBS
phycobilisome 相似文献
135.
M. Engelhard K. D. Kohl K. H. Müller B. Hess J. Heidemeier M. Fischer F. Parak 《European biophysics journal : EBJ》1990,19(1):11-18
Bacteriorhodopsin (bR), converted by deionization to the blue form was reconstituted to the active purple membrane by the addition of Fe2+ or Fe3+ ions. 57Fe Mossbauer spectra of these samples were measured at different pH values (pH 3.9, pH 5.0 and pH 7.0) and at temperatures ranging from 4 K to 300 K. The hyperfine parameters reveal two iron environments with oxygen atoms in the neighbourhood of iron. Iron type 1 is in the 3+ high spin state. It is bound to acid side chains of the protein and/or the phosphate groups of the lipids. Iron type 2 is in the 2+ high spin state and is linked to carboxy groups of the protein in a rather unspecific way. Dynamics as measured by Mossbauer spectroscopy show that the purple membrane becomes flexible only above 220 K. At the interface between membrane and bulk water the mobility is comparable to that of proteins with hydrophilic surfaces. The photocycle of Fe 3+-bR is slowed down compared to native bR. 3–5 Fe3+/bR are sufficient to inhibit the photocycle turnover by one order of magnitude. This specific effect is also found with Cr3+, though it is less pronounced. Mössbauer spectra of Fe3+-bR at 4 K reveal that iron nuclei are spin-coupled, indicating their close spatial proximity. It is proposed that iron trinuclear clusters interact with the proton uptake site of bR.
Offprint requests to: M. Engelhard 相似文献
136.
K. Peng A. J. W. G. Visser A. van Hoek C. J. A. M. Wolfs J. C. Sanders M. A. Hemminga 《European biophysics journal : EBJ》1990,18(5):277-283
Fluorescent probes located in heterogeneous environments give rise to anomalous time-resolved fluorescence anisotropy. A simple analytical expression of anisotropy has been derived for the case of a small difference in local fluorescence lifetimes. The expression has the diagnostic advantage that the time dependence of the fluorescence anisotropy can be predicted from the differences in fluorescence lifetimes and residual anisotropies of the probes located in different sites. Using this model, the local fluorescence anisotropy parameters and the relative contributions of the lipid probe octadecyl rhodamine B in a lipid environment and in the vicinity of bacteriophage M13 coat protein reconstituted in phospholipid bilayers, composed of 80% 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 20% 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol have been determined experimentally. At 40°C, the correlation times for bound and free probes are 2.3 and 3.0 ns, respectively, while the corresponding order parameters are 0.85 and 0.62, respectively.Abbreviations ESR
electron spin resonance
- DMPC
1,2-dimyristoyl-sn-glycero-3-phosphocholine
- DMPC
1,2-dimyristoyl-sn-glycero-3-phosphoglycerol
- L/P ratio
phospholipid to coat protein molar ratio
- <>
average fluorescence lifetime
-
r(0)
initial anisotropy
-
r()
residual anisotropy
On leave of Shanghai Medical Equipment Research Institute, 77 Jiang Ning Rd. Shanghai, People's Republic of China
Offprint requests to: M. A. Hemminga 相似文献
137.
The effect of Ca2+ and Mg2+ on relative fluidity of phosphatidylcholine liposomes was studied by measuring the degree of chlorophyll fluorescence polarization.
An increase in the degree of fluorescence polarization was observed on incubation of liposomes with different concentrations
of Ca2+ or Mg2+. The results have been interpreted on the basis of increase in the size of liposomes which could be brought about by calcium
or magnesium induced fusion of small unilamellar liposomes to form larger vesicles. Fusion of liposomes has also been confirmed
by the experiments on efficiency of energy transfer from chlorophyll b to chlorophyll a, and transmission electron microscopy
of liposomes before and after incubation with Ca2+ and Mg2+. 相似文献
138.
The duration of one synchronous cleavage cycle (τ0 ) in Clupea harengus membras at different temperatures ( T ) was given by: (logτ0 )= 2.4349–0–0684T for T= 0.9–13°C, and (logτ0 )= 1.61010–oooit for t= 13–18–7°C. 相似文献
139.
U. Sonnewald N. Westergaard †P. Jones †A. Taylor †H. S. Bachelard A. Schousboe 《Journal of neurochemistry》1996,67(6):2566-2572
Abstract: Metabolism of [U-13 C5 ]glutamine was studied in primary cultures of cerebral cortical astrocytes in the presence or absence of extracellular glutamate. Perchloric acid extracts of the cells as well as redissolved lyophilized media were subjected to nuclear magnetic resonance and mass spectrometry to identify 13 C-labeled metabolites. Label from glutamine was found in glutamate and to a lesser extent in lactate and alanine. In the presence of unlabeled glutamate, label was also observed in aspartate. It could be clearly demonstrated that some [U-13 C5 ]glutamine is metabolized through the tricarboxylic acid cycle, although to a much smaller extent than previously shown for [U-13 C5 ]glutamate. Lactate formation from tricarboxylic acid cycle intermediates has previously been demonstrated. It has, however, not been demonstrated that pyruvate, formed from glutamate or glutamine, may reenter the tricarboxylic acid cycle after conversion to acetyl-CoA. The present work demonstrates that this pathway is active, because [4,5-13 C2 ]glutamate was observed in astrocytes incubated with [U-13 C5 ]glutamine in the additional presence of unlabeled glutamate. Furthermore, using mass spectrometry, mono-labeled alanine, glutamate, and glutamine were detected. This isotopomer could be derived via the action of pyruvate carboxylase using 13 CO2 produced within the mitochondria or from labeled intermediates that had stayed in the tricarboxylic acid cycle for more than one turn. 相似文献
140.
The effect of ozone fumigation over one season on photosynthetic processes of Quercus robur seedlings 总被引:1,自引:0,他引:1
P. K. FARAGE 《The New phytologist》1996,134(2):279-285