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141.
Using EPR spectroscopy it was found that CdCl2 and HgCl2 interact (1) with the intermediates
, i.e. with the tyrosine radicals on the donor side of photosystem (PS) 2 situated in the 161st position in D1 and D2 proteins; (2) with the primary donor of PS1 (P700) whereby the oxidation of chlorophyll (Chl) a dimer in the reaction centre of PS1 occurs yet in the dark; (3) with the manganese cluster which is situated in the oxygen evolving complex. Due to these interactions of investigated metal chlorides with the photosynthetic apparatus, the interruption of the photosynthetic electron transport through photosynthetic centres occurs. Monitoring of time dependence of EPR signal I of chloroplasts treated with CdCl2 or HgCl2 after switching off the light suggests that all mechanisms, i.e. direct, cyclic, and non-cyclic reductions of P700+ are damaged. The formation of complexes between mercury or cadmium ions and amino acid residues constituting photosynthetic peptides was suggested as possible mechanism of their inhibitory action. The higher HgCl2 efficiency in comparison with that of CdCl2 was explained by higher ability of mercury ions to form complexes with amino acids, what was demonstrated by their apparent binding constants: K = 10 200 M–1 for Hg2+ ions, and K = 3 700 M–1 for Cd2+ ions. 相似文献
142.
The in vivo effects of CrCl(3) on an ergosterol-producing 33 erg(+) strain of the eukaryotic yeast Candida albicans, and on its ergosterol-deficient erg(-)2 mutant, were studied by using electron paramagnetic resonance spectroscopy. A 5-doxylstearic acid spin probe was applied to label the membranes. The absence of ergosterol, an increased accumulation of Delta(8) sterols, a decreased fatty acid chainlength and a lower proportion of unsaturated fatty acids of the erg(-)2 mutant resulted in a higher membrane rigidity and an increased sensitivity to Cr(III) than those of the parental 33 erg(+) strain. Cr(III) significantly increased the fluidity of the spin labelled membranes, this being more pronounced for the erg(-)2 mutant. The break in the slopes measured for the erg(-)2 mutant was decreased (DeltaAT approximately 4 degrees C) from 17 to 13 degrees C. Cr(III) treatment for 10 h caused a loss of metabolites adsorbing at 260 nm: this loss was 40% for 33 erg(+) and 60% for erg(-)2. This decriptification process might be the main cause of growth inhibition and cell killing by the impermeable Cr(III) ions. 相似文献
143.
Summary An NADH-specific oxidation reduction enzyme has been partially purified from rose cell microsomes by aqueous two-phase partitioning, ultracentrifugation, and ion-exchange chromatography, on the basis of the enzyme's ability to activate lucigenin chemiluminescence in the presence of NADH. The enzyme showed strong similarity to a plasma membrane NADH oxidase (superoxide synthase as assayed by lucigenin chemiluminescence; T. M. Murphy and C.-K. Auh, Plant Physiol. 110: 621–629, 1996) in its response to substrate, to Triton X-100, and to diphenylene iodonium, an inhibitor of mammalian neutrophil NADPH oxidase and other flavoenzymes. However, its fluorescence spectrum was not characteristic of flavins and instead was similar to that of pterins. Thus inhibition of an enzyme-catalyzed reaction by diphenylene iodonium does not necessarily imply that the reaction is catalyzed by NADPH oxidase or another flavoenzyme. Superoxide synthesis catalyzed by the enzyme preparation was very low but could be increased at least twofold by the addition of a quinone, menadione. This suggests the enzyme acting in conjunction with a natural quinone could produce activated oxygen species in stressed plant cells.Abbreviation DPI
diphenylene iodonium 相似文献
144.
The complex compound K2[Ni(cit)(H2O)2]2·4H2O (cit = triionized citrate ion) seems to be a good model for the investigation of Ni(II)/citrate interactions that are of
interest in relation to nickel metabolism and bioaccumulation. Its infrared and Raman spectra were recorded and analyzed on
the basis of its structural peculiarities. The magnetic susceptibility, investigated in the temperature range between 1.9
and 300 K, shows the absence of magnetic interactions between the two metal centers present in this structure. 相似文献
145.
Takaichi S 《Photosynthesis research》2000,65(1):93-99
Carotenes have attracted much attention in recent years for their biological function in processes such as photosynthesis.
The characterization of carotenes is difficult, however, because they consist of only carbon and hydrogen atoms, without oxygen.
In the present study, we systematically examined the chemical structures of more than 30 carotenes, including most of the
carotenes found in phototrophic organisms, and observed their elution order using a Novapak C18 HPLC column with simple isocratic elution. The elution order of the carotenes was C30, C40,C45 then C50. The C40 carotenes with fewer conjugated double bonds (N) had longer retention times. With respect to the end groups, the carotenes eluted in the following order: φ, Ψ, ∈ then β
end groups. Furthermore, absorption spectra in the HPLC eluent used were recorded with a photodiode-array detector. A greater
N value was associated with a longer absorption maximum wavelength. Since the conjugated end groups (φ and β) influenced the
absorption spectra and the non-conjugated end groups (Ψ and ∈) did not, the number of conjugated end groups (zero, one and
two) was clearly distinguishable. Therefore, the chemical structures of carotenes can be easily determined by a combination
of the HPLC retention times and the absorption spectra.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
146.
Cláudio M. Gomes Alice Faria João C. Carita Joaquim Mendes Manuela Regalla Paula Chicau Harald Huber Karl O. Stetter M. Teixeira 《Journal of biological inorganic chemistry》1998,3(5):499-507
Seven-iron ferredoxins from the thermoacidophilic archaea Acidianus ambivalens, A. infernus, Metalosphaera prunae and Sulfolobus metallicus were extensively characterised, allowing study of their expression under aerobic and anaerobic growth conditions as well
as the putative role in thermal stability of a recently described zinc centre. The archaeon S. metallicus was found to express, under the same growth conditions, two ferredoxins in almost identical amounts, a novelty among Archaea. Most interestingly, these two ferredoxins differ at the N-terminal amino acid sequence in that one has a zinc binding motif
(FdA) and the other does not (FdB); in agreement with these findings, FdA contains a zinc ion and FdB does not. These two
ferredoxins have identical thermal stabilities, indicating that the zinc atom is not determinant in the protein thermostability.
Further, the presence of the additional zinc centre does not interfere with the redox properties of the iron-sulfur clusters
since their reduction potentials are almost identical. From the other three archaea, independently of the growth mode in respect
to oxygen, only a single zinc-containing ferredoxin was found. EPR studies on the purified proteins, both in the oxidised
and dithionite reduced states, allowed the identification of one [3Fe-4S]1+/0 centre and one [4Fe-4S]2+/1+ centre in all proteins studied. The complete sequence of A. ambivalens ferredoxin is reported. Together with the data gathered in this study, the properties of the seven-iron ferredoxins from
Sulfolobales so far known are re-discussed.
Received: 10 June 1998 / Accepted: 25 June 1998 相似文献
147.
离子注入不同辐射敏感性微生物自由基与存活关系的研究 总被引:9,自引:0,他引:9
以不同辐射敏感性微生物辐射异常微球菌和大肠杆菌为试材,用电子自旋共振波谱法研究了离子注入后在两种微生物细胞内产生的自由基及其存活的关系。 相似文献
148.
Mercedes T. Grijalba Patricm B. Andrade Andre R. Meinicke Roger F. Castilho Anibal E. Vercesi Shirley Schreier 《Free radical research》1998,28(3):301-318
In the present study we show that K+/H+ hydroxyl-containing ionophores lasalocid-A (LAS) and nigericin (NIG) in the nanomolar concentration range, inhibit Fe2+-citrate and 2,2'-azobis(2-amidinopropane) di-hydrochloride (ABAP)-induced lipid peroxidation in intact rat liver mitochondria and in egg phosphatidyl-choline (PC) liposomes containing negatively charged lipids—dicetyl phosphate (DCP) or cardiolipin (CL)—and KCl as the osmotic support. In addition, monensin (MON), a hydroxyl-containing ionophore with higher affinity for Na+ than for K+, promotes a similar effect when NaCl is the osmotic support. The protective effect of the ionophores is not observed when the osmolyte is sucrose. Lipid peroxidation was evidenced by mitochondrial swelling, antimycin A-insensitive O2 consumption, formation of thiobarbituric acid-reactive substances (TBARS), conjugated dienes, and electron paramagnetic resonance (EPR) spectra of an incorporated lipid spin probe. A time-dependent decay of spin label EPR signal is observed as a consequence of lipid peroxidation induced by both inductor systems in liposomes. Nitroxide destruction is inhibited by buty-lated hydroxytoluene, a known antioxidant, and by the hydroxyl-containing ionophores. In contrast, vali-nomycin (VAL), which does not possess alcoholic groups, does not display this protective effect. Effective order parameters (Seff), determined from the spectra of an incorporated spin label are larger in the presence of salt and display a small increase upon addition of the ionophores, as a result of the increase of counter ion concentration at the negatively charged bilayer surface. This condition leads to increased formation of the ion-ionophore complex, the membrane binding (uncharged) species. The membrane-incorporated complex is the active species in the lipid peroxidation inhibiting process. Studies in aqueous solution (in the absence of membranes) showed that NIG and LAS, but not VAL, decrease the Fe2+-citrate-induced production of radicals derived from piperazine-based buffers, demonstrating their property as radical scavengers. Both Fe2+-citrate and ABAP promote a much more pronounced decrease of LAS fluorescence in PC/CL liposomes than in dimyristoyl phosphatidyl-choline (DMPC, saturated phospholipid)-DCP liposomes, indicating that the ionophore also scavenges lipid peroxyl radicals. A slow decrease of fluorescence is observed in the latter system, for all lipid compositions in sucrose medium, and in the absence of membranes, indicating that the primary radicals stemming from both inductors also attack the ionophore. Altogether, the data lead to the conclusion that the membrane-incorporated cation complexes of NIG, LAS and MON inhibit lipid peroxidation by blocking initiation and propagation reactions in the lipid phase via a free radical scavenging mechanism, very likely due to the presence of alcoholic hydroxyl groups in all three molecules and to the attack of the aromatic moiety of LAS. 相似文献
149.
Geijer Paulina Peterson Sindra Härndahl Ulrika Styring Stenbjörn Sundby Cecilia 《Photosynthesis research》1998,58(3):231-243
The Photosystem II multisubunit protein complex can be extracted from thylakoid membranes with non-ionic detergents and subjected to various spectroscopical and biochemical investigations. This paper shows that after extraction with dodecyl--D-maltoside, several Photosystem II complexes could be resolved by isoelectric focusing. Structurally, the various Photosystem II complexes differed from each other in polypeptide composition, especially with regard to the chlorophyll a/b-binding proteins, which gave rise to differing isoelectric points. Functionally, the various Photosystem II complexes differed from each other on the acceptor side, as judged by acceptor side-dependent electron transfer and electron paramagnetic resonance (EPR). The QA
- Fe2+-signal (g = 1.84), arising from QA
- spin-coupled to the acceptor-side iron, and a radical signal arising from decoupled QA
- (g = 2.0045) could be detected simultaneously in some of the Photosystem II complexes, and the amount of each of the two signals were inversely related. The results are discussed in relation to previously known heterogeneities in Photosystem II. 相似文献
150.
Irena Kruk Teresa Piechowska Paweł Berczyński Aleksandra Kładna Oya Bozdağ‐Dündar Meltem Ceylan‐Unlusoy Hassan Y. Aboul‐Enein 《Luminescence》2015,30(5):556-563
Fifteen chromonylrhodamine derivatives (CRs) were synthesized and the antioxidant activity levels were evaluated for the first time. The antioxidant activity potencies of these chromone derivatives were evaluated towards superoxide anion radicals, hydroxyl radicals and 2,2‐diphenyl‐1‐picrylhydrazyl radicals. Also, the total antioxidant capacity of the tested compounds was measured using the ferric‐ferrozine assay. The antioxidant activities were investigated using a chemiluminescence (CL) assay, spectrophotometry measurements, direct electron paramagnetic resonance (EPR) and the EPR spin‐trapping technique. The 5,5‐dimethyl‐ 1‐pyrroline‐1‐oxide (DMPO) was applied as spin trap. Eleven of the 15 chromone compounds exhibited a decrease in the CL accompanying the superoxide anion radical produced in anhydrous dimethylsulfoxide (DMSO), ranging from 71–94% at concentration of 1 mmol /L; four of these compounds enhanced light emission in the range 231–672%. Similarly, these compounds caused 28–58% inhibition in the intensity of the DMPO‐OOH radical EPR signal and the DMPO‐OH radical (from 12–48%). Furthermore, three of these compounds showed very good antioxidant response towards the DPPH radical (EC50: 0.51–0.56 µmol/L) and the high reduction potentials. These findings demonstrate that the chromone compounds tested may be considered as effective free radicals scavengers, a finding that is of great pharmacological importance. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献