全文获取类型
收费全文 | 247篇 |
免费 | 10篇 |
国内免费 | 6篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 18篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 3篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有263条查询结果,搜索用时 15 毫秒
1.
Absorbance changes induced by 25-ps laser flashes were measured in membranes of Heliobacterium chlorum at 15 K. Absorbance difference spectra, measured at various times after the flash showed negative bands in the Qy region at 812, 793 and 665 nm. The first of these bands was attributed to the formation of excited singlet states of a long-wavelength form of antenna bacteriochlorophyll g (BChl g 808). Absorbance changes of shorter wavelength absorbing antenna BChls g were at least an order of magnitude smaller, indicating rapid excitation energy transfer (i.e. within the time resolution of the apparatus) from these BChls to BChl g 808. Excited BChl g 808 showed a bi-exponential decay with time constants of 50 and 200 ps. The bands at 793 and 665 nm may be attributed to the primary charge separation and reflect the photooxidation of the primary electron donor P-798 and photoreduction of a primary electron acceptor absorbing near 670 nm, presumably a BChl c or Chl a-like pigment. The bleaching of this pigment reversed with a time constant of 300 ps at 15 K and of 800 ps at 300 K. This indicates that electron transfer from the primary to the secondary electron acceptor is approximately 2.5 times faster at 15 K than at room temperature.Abbreviations BChl
bacteriochlorophyll
- FWHM
full width at half maximum
- P-798
primary electron donor
- Tris
tris(hydroxymethyl)amino methane 相似文献
2.
The effect of chlorophyll content on changes of photochemical reactions in intact kidney bean leaves 总被引:1,自引:1,他引:0
Abstract. Activation spectra of photochemical reactions were measured by a flash spectrophotometer in leaves having varying chlorophyll contents at different stages of greening. The increase of chlorophyll concentration up to 30 nmol cm-2 elevated the rates of photochemical reactions at all wavelengths of light used, and was found to be produced by an increase in the amounts of reaction centres. Further accumulation of chlorophyll up to 40 nmol cm-2 was associated with an increase in light-harvesting chlorophyll, an improved rate of photochemical reactions around 600 nm and at 700 nm, and self-absorption and screening effects where chlorophyll absorbed maximally (400–450 nm and around 680 nm). 相似文献
3.
Shun Hirota Margareta Svensson-Ek Pia Ädelroth Nobuhito Sone Thomas Nilsson Bo G. Malmström Peter Brzezinski 《Journal of bioenergetics and biomembranes》1996,28(6):495-501
The time course of absorbance changes following flash photolysis of the fully-reduced carboxycytochrome oxidase fromBacillus PS3 in the presence of O2 has been followed at 445, 550, 605, and 830 nm, and the results have been compared with the corresponding changes in bovine cytochrome oxidase. The PS3 enzyme has a covalently bound cytochromec subunit and the fully-reduced species therefore accommodates five electrons instead of four as in the bovine enzyme. In the bovine enzyme, following CO dissociation, four phases were observed with time constants of about 10 s, 30 s, 100 s, and 1 ms at 445 nm. The initial, 10-s absorbance change at 445 nm is similar in the two enzymes. The subsequent phases involving hemea and CuA are not seen in the PS3 enzyme at 445 nm, because these redox centers are re-reduced by the covalently bound cytochromec, as indicated by absorbance changes at 550 nm. A reaction scheme consistent with the experimental observations is presented. In addition, internal electron-transfer reactions in the absence of O2 were studied following flash-induced CO dissociation from the mixed-valence enzyme. Comparisons of the CO recombination rates in the mixed-valence and fully-reduced oxidases indicate that more electrons were transferred from hemea
3 toa in PS3 oxidase compared to the bovine enzyme. 相似文献
4.
Incubation of thylakoid membranes from spinach with low concentrations of mercuric chloride induces the loss of one of the iron-sulfur centers, FB, in Photosystem I (PS I) and inhibits the electron transfer from PS I to the soluble electron carrier, ferredoxin. Reconstitution of this damaged iron-sulfur center has been carried out by incubating treated thylakoid membranes with exogenous FeCl3 and Na2S in the presence of-mercaptoethanol under anaerobic conditions. Low temperature EPR measurements indicate that center FB is largely restored. Kinetic experiments show that the restored FB can be photoreduced from P700. However, these reconstituted thylakoid membranes are still incompetent in the photoreduction of ferredoxin and NADP+, even though ferredoxin binding to the modified membranes was not impaired, indicating additional changes in the structure of the PS I complex must have occurred. 相似文献
5.
与缓慢发展的干旱过程不同,骤旱具有发生速度快,短期内可致害的特点。目前,关于作物骤旱致害的临界阈值及其调控机制尚不清楚。以春小麦为供试作物,通过桶栽试验,模拟研究骤旱过程中小麦受旱致害的过程特征及其控制因素。结果发现,发生骤旱时土壤含水量下降呈先快后慢的变化趋势,叶片水分和叶水势则呈先慢后快的指数变化趋势。叶片光合生理指标对土壤水分的下降存在明显的阈值响应,且不同生理指标的阈值并不完全相同,其中净光合速率与表征叶片光合能力的指标(最大羧化速率)对土壤有效含水量的响应阈值为0.4,气孔导度和蒸腾速率对土壤有效含水量的响应阈值分别为0.5和0.4。而小麦光合生理指标对叶片水分和叶水势的阈值响应并不明显。同时依据各生理指标相关和通径分析结果得出,骤旱发生时引起小麦叶片净光合速率快速降低的主导因子为非气孔因素,而并不是以往作物受旱研究中的气孔因素。本研究结果有望丰富干旱影响认知,并可为科学应对干旱提供依据。 相似文献
6.
SPONTANEOUS AND STIMULATED BIOLUMINESCENCE OF THE DINOFLAGELLATE CERATOCORYS HORRZDA (PERIDINIALES)1
This is the first report of spontaneous bioluminescence in the autotrophic dinoflagellate Ceratocorys horrida von Stein. Bioluminescence was measured, using an automated data acquisition system, in a strain of cultured cells isolated from the Sargasso Sea. Ceratocorys horrida is only the second dinoflagellate species to exhibit rhythmicity in the rate of spontaneous flashing, flash quantum flux (intensity), and level of spontaneous glowing. The rate of spontaneous flashing was maximal during hours 2–4 of the dark phase [i.e. circadian time (CT)16–18 for a 14:10 h LD cycle (LD14:10)], with approximately 2% of the population flashing-min?1, a rate approximately one order of magnitude greater than that of the dinoflagellate Gonyaulax polyedra. Flash quantum flux was also maximal during this period. Spontaneous flashes were 134 ms in duration with a maximum flux (intensity) of 3.1×109 quanta-s?1. Light emission presumably originated from blue fluorescent microsources distributed in the cell periphery and not from the spines. Values of both spontaneous flash rate and maximum flux were independent of cell concentration. Isolated cells also produced spontaneous flashes. Spontaneous glowing was dim except for a peak of 6.4× 104quanta-s?1 cell?1, which occurred at CT22.9 for LD14:10 and at CT22.8 for LD12:12. The total integrated emission of spontaneous flashing and glowing during the dark phase was 4×109 quantacell?1, equivalent to the total stimulable luminescence. The rhythms for C. horrida flash and glow behavior were similar to those of Gonyaulax polyedra, although flash rate and quantum flux were greater. Spontaneous bioluminescence in C. horrida may be a circadian rhythm because it persisted for at least three cycles in constant dark conditions. This is also the first detailed study of the stimulated bioluminescence of C. horrida, which also displayed a diurnal rhythm. Cultures exhibited >200 times more mechanically stimulated bioluminescence during the dark phase than during the light phase. Mechanical stimulation during the dark phase resulted in 6.7 flashes. cell?1; flashes were brighter and longer in duration than spontaneous flashes. Cruise-collected cells exhibited variability in quantum flux with few differences in flash kinetics. The role of dinoflagellate spontaneous bioluminescence in the dynamics of near-surface oceanic communities is unknown, but it may be an important source of natural in situ bioluminescence. 相似文献
7.
J. De Las Rivas B. Crystall P. J. Booth J. R. Durrant S. Özer G. Porter D. R. Klug J. Barber 《Photosynthesis research》1992,34(3):419-431
A Photosystem two (PS II) core preparation containing the chlorophyll a binding proteins CP 47, CP 43, D1 and D2, and the non-chlorophyll binding cytochrome-b559 and 33 kDA polypeptides, has been isolated from PS II-enriched membranes of peas using the non-ionic detergent heptylthioglucopyranoside and elevated ionic strengths. The primary radical pair state, P680+Pheo-, was studied by time-resolved absorption and fluorescence spectroscopy, under conditions where quinone reduction and water-splitting activities were inhibited. Charge recombination of the primary radical pair in PS II cores was found to have lifetimes of 17.5 ns measured by fluorescence and 21 ns measured by transient decay kinetics under anaerobic conditions. Transient absorption spectroscopy demonstrated that the activity of the particles, based on primary radical pair formation, was in excess of 70% (depending on the choice of kinetic model), while time-resolved fluorescence spectroscopy indicated that the particles were 91% active. These estimates of activity were further supported by steady-state measurements which quantified the amount of photoreducible pheophytin. It is concluded that the PS II core preparation we have isolated is ideal for studying primary radical pair formation and recombination as demonstrated by the correlation of our absorption and fluorescence transient data, which is the first of its kind to be reported in the literature for isolated PS II core complexes from higher plants.Abbreviations CP 43 and CP 47
chlorophyll binding proteins of PS II having apparent molecular weights on SDS-PAGE of 43 kDa and 47 kDa, respectively
- D1 and D2 polypeptides
PS II reaction centre polypeptides encoded by the psbA and psbD genes, respectively
- HPLC
high performance liquid chromatography
- PS II
Photosystem two
- SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis
- P680
primary electron donor of PS II
- Pheo
phenophytin a
- SPC
single photon counting
- PBQ
phenyl-p-benzoquinone
- DPC
1,5-diphenylcarbazide
AFRC Photosynthesis Research Group, Department of Biochemistry 相似文献
8.
The thermographic method for determining specific absorption rate (SAR) in animals and models of tissues or bodies exposed to electromagnetic fields was applied to the problem of quantifying the current distribution in homogeneous bodies of arbitrary shape exposed to 60-Hz electric fields. The 60-Hz field exposures were simulated by exposing scale models of high electrical conductivity to 57.3-MHz VHF fields of high strength in a large 3.66 × 3.66 × 2.44-m TE101 mode resonant cavity. After exposure periods of 2–30 s, the models were quickly disassembled so that the temperature distribution (maximum value up to 7 °C) along internal cross-sectional planes of the model could be recorded thermographically. The SAR, W′, calculated from the temperature changes at any point in the scale model was used to determine the SAR, W, for a full-scale model exposed to a 60-Hz electric field of the same strength by the relation W = (60/ f2 · (σ′/σ) · W′ where f′ is the model exposure frequency, σ′ is the conductivity of the scale model at the VHF exposure frequency, and σ is the conductivity of the full-scale subject at 60 Hz. The SAR was used to calculate either the electric field strength or the current density for the full-scale subject. The models were used to simulate the exposure of the full-scale subject located either in free space or in contact with a conducting ground plane. Measurements made on a number of spheroidal models with axial ratios from 1 to 10 and conductivity from 1 to 10 s/m agreed well with theoretical predictions. Maximum current densities of 200 nA/cm2 predicted in the ankles of man models and 50 nA/cm2 predicted in the legs of pig models exposed to 60-Hz fields at 1kV/m agreed well with independent measurements on full-scale models. 相似文献
9.
Presence of two molecular weight forms of somatostatin in neurons from chick embryo cerebral hemispheres in culture 总被引:2,自引:0,他引:2
Vitamin D-deficiency and rickets was produced in growing chicks. The resulting decrese in mineralization of whole bone and of fractions separated by density centrifugation was accompanied by a very significant decrease in the contents of O-phosphoserine and O-phosphothreonine. Likewise, the total amount of O-phosphoserine and O-phosphothreonine and the concentrations of these phosphoamino acids in EDTA extracts and in fractions obtained by molecular sieving was also reduced. These data provide the first in vivo evidence that phosphoproteins may be critically involved in the calcification of bone. 相似文献
10.
Effect of storage, photoperiod and mechanical scarification on seed germination in Ocimum americanum
Dilip Amritphale Y. K. Mukhiya J. C. Gupta Shamanta Iyengar 《Physiologia plantarum》1984,61(4):649-652
Seeds of Ocimum americanum L. display an absolute light requirement for germination. The minimal length of the daily photoperiod required to induce a high germination decreased with increasing seed age, but the length of the photoperiod under potential control of terminal far-red light inhibition remained unchanged. There was a gradual escape from the far-red inhibition with increase in the length of the photoperiod. Seeds developed flash photosensitivity after the first 13 h photoperiod. Scarification treatment did not allow the seeds to bypass the light requirement, but it enhanced the germination considerably. Under conditions of natural day length in the field, weakening of the testa by sand may abolish the need for a second exposure to light for most of the seed population, thus rendering them non-photoperiodic. 相似文献