全文获取类型
收费全文 | 3984篇 |
免费 | 166篇 |
国内免费 | 352篇 |
出版年
2024年 | 10篇 |
2023年 | 37篇 |
2022年 | 37篇 |
2021年 | 56篇 |
2020年 | 60篇 |
2019年 | 77篇 |
2018年 | 89篇 |
2017年 | 78篇 |
2016年 | 63篇 |
2015年 | 92篇 |
2014年 | 137篇 |
2013年 | 150篇 |
2012年 | 75篇 |
2011年 | 145篇 |
2010年 | 100篇 |
2009年 | 166篇 |
2008年 | 177篇 |
2007年 | 216篇 |
2006年 | 185篇 |
2005年 | 215篇 |
2004年 | 165篇 |
2003年 | 175篇 |
2002年 | 176篇 |
2001年 | 149篇 |
2000年 | 122篇 |
1999年 | 131篇 |
1998年 | 94篇 |
1997年 | 108篇 |
1996年 | 86篇 |
1995年 | 65篇 |
1994年 | 72篇 |
1993年 | 58篇 |
1992年 | 65篇 |
1991年 | 50篇 |
1990年 | 58篇 |
1989年 | 59篇 |
1988年 | 61篇 |
1987年 | 42篇 |
1986年 | 32篇 |
1985年 | 51篇 |
1984年 | 95篇 |
1983年 | 93篇 |
1982年 | 83篇 |
1981年 | 80篇 |
1980年 | 54篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 8篇 |
排序方式: 共有4502条查询结果,搜索用时 15 毫秒
41.
In order to evaluate the aclimation of Chenopodium seedlings to different quantum fluence rates of R and BL, kinetics of Rubisco capacity, Chl content and chloroplast structure were studied. Under monochromatic light photoreceptors are stimulated selectively and their influence on biosynthetis capacities during chloroplast development can be studied.R irradiations saturate Rubisco capacity even at the lowest quantum fluence rates applied, whereas Chl a+b synthesis depends strongly upon fluence rate of R. Under BL irradiations, both Rubisco capacity and Chl content are fluence rate dependent. R irradiations favour Chl b synthesis relative to Chl a, whereas under BL Chl a content is high relative to Chl b. Under R irradiation Pfr is the main photoreceptor involved in regulation of Rubisco capacity whereas under BL a specific BL absorbing photoreceptor may control the response. From the fluence rate dependency under BL irradiations it is concluded that the blue region of the day light spectrum may be the sensor for monitoring fluence rate and causing the characteristic changes in shade and high/low WL adaptation with respect to Rubisco levels in Chenopodium. 相似文献
42.
Using isolated pea thylakoids, the relative rate of QA
- oxidation has been estimated under various conditions, from the restoration of the induction curves following a dark period and from light 1-induced changes in modulated chlorophyll fluorescence excited by light 2.Alterations of
QinfA
sup–
oxidation rates were observed under conditions which affected the degree of thylakoid stacking, the lipid fluidity and the integrity of the membranes. The results are discussed in terms of the interactions between QA
- and the plastoquinone pool with particular emphasis on lateral diffusion.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- EDTA
Ethylenediaminetetracetate
- Hepes
N-2-hydroxyethyl piperazine-N-2-ethanesulphonic acid
- NADP
nicotinamide adenine dinucleotide phosphate 相似文献
43.
44.
Abstract. Chlorophyll fluorescence emission spectra and the kinetics of 685 mm fluorescence emission from wheat leaf tissue and thylakoids isolated from such tissue were examined as a function of excitation wavelength. A considerable enhancement of fluorescence emission above 700 nm relative to that at 685 nm was observed from leaf tissue when it was excited with 550 nm rather than 450 nm radiation. Such excitation wavelength dependent changes in the emission spectrum occurred over an excitation spectral range of 440–660 nm and appeared to be directly related to the total quantity of radiation absorbed at a given excitation wavelength. Experiments with isolated thylakoid preparations demonstrated that changes in the fluorescence emission spectrum of the leaf were attributable to the optical properties of the leaf and were not due to the intrinsic characteristies of the thylakoid photochemical apparatus. This was not the case for the observed excitation wavelength dependent changes in the 685 nm fluorescence induction curve obtained from leaf tissue infiltrated with DCMU. Excitation wavelength dependent changes in the ratio of the variable to maximal fluorescence emission and the shape of the variable fluorescence induction were observed for leaf tissue. Isolated thylakoid studies showed that such changes in the leaf fluorescence kinetics were representative of the way in which the photochemical apparatus in vivo was processing the absorbed radiation at the different excitation wavelengths. The results are considered in the context of the use of fluorescence emission characteristics of leaves as non-destructive probes of the photochemical apparatus in vivo. 相似文献
45.
在缺钾培养条件下,高粱苗地上部单位鲜重含钾量由于地上部鲜重的增加而下降。从高梁苗钾缺乏症出现的时间、频率和程度来看,Pro培养似乎有利于缓和或减轻缺钾对植物造成的伤害。在同样含钾量情况下,以Ca(NO_3)_2为氮源的苗受到缺钾伤害要重于以Pro为氮源的苗受到的伤害,其钾缺乏症植株的百分数增加值与含钾量降低值之比为0.26,以Pro为氮源的缺钾营养液培养的苗为0.09,即下降同样量的钾前者苗的钾缺乏症的增加要大大地超过后者。Pro并不减轻在缺钾情况下叶绿素含量的下降。 相似文献
46.
D. S. Dimitrov 《The Journal of membrane biology》1984,78(1):53-60
Summary A simple viscoelastic film model is presented, which predicts a breakdown electric potential having a dependence on the electric pulse length which approximates the available experimental data for the electric breakdown of lipid bilayers and cell membranes (summarized in the reviews of U. Zimmermann and J. Vienken, 1982,J. Membrane Biol.
67:165 and U. Zimmermann, 1982,Biochim. Biophys. Acta
694:227). The basic result is a formula for the time of membrane breakdown (up to the formation of pores): =(/C)/(
m
2
0
2
U
4/24Gh
3+T
2/Gh–1), where is a proportionality coefficient approximately equal to ln(h/20),h being the membrane thickness and 0 the amplitude of the initial membrane surface shape fluctuation ( is usually of the order of unity), represents the membrane shear viscosity,G the membranes shear elasticity modules,
m
the membrane relative permittivity, 0=8.85×10–12
Fm,U the electric potential across the membrane, the membrane surface tension andT the membrane tension. This formula predicts a critical potentialU
c
;U
c
=(24Gh
3/
m
2
0
2
)1/4 (for = andT=0). It is proposed that the time course of the electric field-induced membrane breakdown can be divided into three stages: (i) growth of the membrane surface fluctuations, (ii) molecular rearrangements leading to membrane discontinuities, and (iii) expansion of the pores, resulting in the mechanical breakdown of the membrane. 相似文献
47.
Abstract The chloroplast ultrastructure, especially the thylakoid organization, the polypeptide composition of the thylakoid membranes and photosynthetic O2 evolution rate, chlorophyll (Chl) content and Chi a/b ratio were studied in leaves of nine plants growing in contrasting biotopes in the wild in South Finland. All the measurements were made at the beginning of the period of main growth on leaves approaching full expansion, when the CO2-saturated O2 evolution rate (measured at 20°C and 1500 μmol photons m?2s?1) was at a maximum, ranging from 19.2 to 6.9 μmol O2 cm?2 h?1. Among the species, the Chi a/b ratio varied between 3.75 and 2.71. In the mesophyll chloroplasts, the ratio of the total length of appressed to non-appressed thylakoid membranes varied between 1.07 and 1.79, the number of partitions per granum varied between 2.8 and 12.0 and the grana area between 21 and 42% of the chloroplast area. There was a significant relationship between the rate of O2 evolution of the leaf discs and the thylakoid organization in the mesophyll chloroplasts. The higher the O2 evolution rate, the lower was the ratio of the total length of appressed to non-appressed thylakoid membranes and also the lower the grana area. Although the relationship of the photosynthetic rate with the Chi content and the Chi a/b ratio of the leaves was not as clear, a significant negative correlation existed between the Chi a/b ratio and the ratio of appressed to non-appressed thylakoid membranes, indicating lateral heterogeneity in the distribution of different Chl- protein complexes. 相似文献
48.
Detection of rapid induction kinetics with a new type of high-frequency modulated chlorophyll fluorometer 总被引:21,自引:0,他引:21
U. Schreiber 《Photosynthesis research》1986,9(1-2):261-272
A newly developed modulation fluorometer is described which operates with 1 sec light pulses from a light-emitting diode (LED) at 100 KHz. Special amplification circuits assure a highly selective recording of pulse fluorescence signals against a vast background of non-modulated light. The system tolerates ratios of up to 1:107 between measuring light and actinic light. Thus it is possible to measure the dark fluorescence yield and record the kinetics of light-induced changes. A high time resolution allows the recording of the rapid relaxation kinetic following a saturating single turnover flash. Examples of system performance are given. It is shown that following a flash the reoxidation kinetics of photosystem II acceptors are slowed down not only by the inhibitor DCMU, but by a number of other treatments as well. From a light intensity dependency of the induction kinetics the existence of two saturated intermediate levels (I1 and I2) is apparent, which indicates the removal of three distinct types of fluorescence quenching in the overall fluorescence rise from F0 to Fmax.Abbreviations QA and QB
consecutive electron acceptors of photosystem II
- PS II
photosystem II
- P 680
reaction center chlorophyll of photosystem II
- F0
minimum fluorescence yield following dark adaptation
- Fmax
maximum fluorescence yield
- DCMU
3-(3, 4-dichlorophenyl)-1, 1-dimethyl-urea
- DCCD
N,N-dicyclohexylcarbodiimide
- PQ
plastoquinone
- DAD
diaminodurene
Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement. 相似文献
49.
A chlorophyll b-less mutant of Chlamydomonas reinhardtii (Pg
27) was isolated after UV irradiation of the wild type cells. This photosynthetically competent mutant totally lacks chlorophyll b and the CP2 chlorophyll-protein complex. However, SDS-PAGE, proteolytic digestions and immunodetections demonstrated that the 24–25 Kd apoproteins of the lacking CP2 complex are still present in thylakoids of the Pg27 mutant. It is concluded that this CP2-less mutant is affected in the biosynthesis pathway of chlorophyll b.This CP2-less mutant was crossed with a CP1-less mutant (Fl5) Fluorescence emission spectra and fluorescence inductions in the presence of DCMU were analysed in the resulting (cp
2
–
, cp
1
+
), (cp
2
+
, cp
1
–
), (cp
2
+
, cp
1
+
), cp
2
–
, cp
1
–
)tetratype. Differences in PS 2 optical cross section and in the relative amplitude or localisation of fluorescence emission peaks fit well with a quadripartite model where PS1 and PS2 would each correspond to a reaction centre core complex (CP1 and CP2 respectively) associated to a light harvesting antenna (LHC1 and LHC2 respectively). The occurrence of energy transfers from PS1 peripheral antenna to PS2 in the Fl
5 mutant shows that, in absence of CP1, at least a part of its associated PS1 light harvesting antenna migrates in the PS2 containing appressed thylakoids.Abbreviations Chl
Chlorophyll
- LHC
Light harvesting chl a/b complex
- CP2
Predominant form of LHC or SDS polyacrylamide gels
- WT
Wild type
- DM
Double mutant (cp
1
–
, cp
2
–
)
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis
- DOC-PAGE
Deoxycholate polyacrylamide gel electrophoresis 相似文献
50.
In intact, uncoupled type B chloroplasts from spinach, added ATP causes a slow light-induced decline () of chlorophyll a fluorescence at room temperature. Fluorescence spectra were recorded after fast cooling to 77 K and normalized with fluorescein as an internal standard. Related to the fluorescence quenching at room temperature, an increase in Photosystem (PS) I fluorescence (F735) and a decrease in PS II fluorescence (F695) were observed in the low-temperature spectra. The change in the ratio was abolished by the presence of methyl viologen. Fluorescence induction at 77 K of chloroplasts frozen in the quenched state showed lowered variable (Fv) and initial (F0) fluorescence at 690 nm and an increase in F0 at 735 nm. The results are interpreted as indicating an ATP-dependent change of the initial distribution of excitation energy in favor of PS I, which is controlled by the redox state of the electron-transport chain and, according to current theories, is caused by phosphorylation of the light-harvesting complex. 相似文献