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91.
In anoxic salt marsh sediments of Sapelo Island, GA, USA, the vertical distribution of CH4 production was measured in the upper 20 cm of surface sediments in ten locations. In one section of high marsh sediments,
the concentration and oxidation of acetate in sediment porewaters and the rate and amount of14C acetate and14CO2 incorporation into cellular lipids of the microbial population were investigated. CH4 production rates ranged from <1 to 493 nM CH4 gram sediment−1 day−1 from intact subcores incubated under nitrogen. Replacement with H2 stimulated the rate of methane release up to nine fold relative to N2 incubations. Rates of lipid synthesis from CO2 averaged 39.2 ×10−2nanomoles lipid carbon cm3 sediment−1 hr−1, suggesting that CO2 may be an important carbon precursor for microbial membrane synthesis in marsh sediments under anoxic conditions. Qualitative
measurements of lipid synthesis rates from acetate were found to average 8.7 × 10−2 nanomoles. Phospholipids were the dominant lipids synthesized by both substrates in sediment cores, accounting for an average
of 76.6% of all lipid radioactivity. Small amounts of ether lipids indicative of methanogenic bacteria were observed in cores
incubated for 7 days, with similar rates of synthesis for both CO2 and acetate. The low rate of ether lipid synthesis suggests that either methanogen lipid biosynthesis is very slow or that
methanogens represent a small component of total microbial lipid synthesis in anoxic sediments.
present address: The University of Maryland,, Chesapeake Biological Laboratory, Box 38, Solomons, MD 20688, USA 相似文献
92.
P. K. Lauf 《The Journal of membrane biology》1990,118(2):153-159
Summary Hydroxylamine, a potent oxidizing agent used to reverse carbethoxylation of histidine by diethylpyrocarbonate, activated Cl-dependent K flux (KCl cotransport) of low K sheep red blood cells almost sixfold. When KCl cotransport was already stimulated by N-ethylmaleimide, hydroxylamine caused an additional twofold activation suggesting modification of sites different from those thiol alkylated. This conclusion was supported by the finding that hydroxylamine additively augmented also the diamide-induced KCl flux (Lauf, P.K. 1988.J. Membrane Biol.
101:179–188) with dithiothreitol fully reversing the diamide but not the hydroxylamine effect. Stimulation of KCl cotransport by hydroxylamine was completely inhibited by treatment with diethylpyrocarbonate also known to prevent KCl cotransport stimulation by N-ethylmaleimide, both effects being independent of the order of addition. Hence, although the effect of carbethoxy modification on KCl flux cannot be reversed by hydroxylamine and thus excludes histidine as the target for diethylpyrocarbonate, our finding reveals an important chemical determinant of KCl cotransport stimulation by both hydroxylamine oxidation and thiol group alkylation. 相似文献
93.
Nariko Kawamura 《Neurochemical research》1989,14(1):9-15
The interrelation of palmitate oxidation with amino acid formation in rat brain mitochondria has been investigated in purified mitochondria of nonsynaptic origin by measuring the formation of aspartate, -ketoglutarate, and glutamate during palmitate oxidation, and also by assaying14C-products of [1-14C]palmitate oxidation. Oxidation of palmitate (or [1-14C]palmitate) resulted in the formation of aspartate (or14C-aspartate), and the oxidation was inhibited by aminooxyacetate (an inhibitor of transaminase), Palmitate oxidation also resulted in -ketoglutarate formation, which was sensitive to the effect of aminooxyacetate. Addition of NH4Cl was found to increase14C-products and formation of -ketoglutarate, whereas glutamate formation was not increased unless the rate of palmitate oxidation was reduced by 50% by aminooxyacetate or -ketoglutarate was added exogenously. Exogenous -ketoglutarate was found to decrease14C-products, but not aspartate formation. These results indicated that palmitate oxidation was closely related to aspartate formation via aspartate aminotransferase. During palmitate oxidation without aminooxyacetate or added -ketoglutarate, however, -ketoglutarate was not available for glutamate formation via glutamate dehydrogenase. We discuss the possibility that this was because (a) oxidative decarboxylation of -ketoglutarate to form succinyl-CoA was favored over glutamate formation for the competition for -ketoglutarate in the same pool, and (b) the pool of -ketoglutarate produced in the aspartate aminotransferase reaction did not serve as substrate for glutamate formation. 相似文献
94.
95.
Take-all is a world-wide root-rotting disease of cereals. The causal organism of take-all of wheat is the soil-borne fungus Gaeumannomyces graminis var tritici (Ggt). No resistance to take-all, worthy of inclusion in a plant breeding programme, has been discovered in wheat but the severity of take-all is increased in host plants whose tissues are deficient for manganese (Mn). Take-all of wheat will be decreased by all techniques which lift Mn concentrations in shoots and roots of Mn-deficient hosts to adequate levels. Wheat seedlings were grown in a Mn-deficient calcareous sand in small pots and inoculated with four field isolates of Ggt. Infection by three virulent isolates was increased under conditions which were Mn deficient for the wheat host but infection by a weakly virulent isolate, already low, was further decreased. Only the three virulent isolates caused visible oxidation of Mn in vitro. The sensitivity of Ggt isolates to manganous ions in vitro did not explain the extent of infection they caused on wheat hosts. In a similar experiment four Australian wheat genotypes were grown in the same Mn-deficient calcareous sand and inoculated with one virulent isolate of Ggt. Two genotypes were inefficient at taking up manganese and were very susceptible to take-all, one was very efficient at taking up manganese and was resistant to take-all, and the fourth genotype was intermediate for both characters. All genotypes were equally resistant under Mn-adequate conditions. 相似文献
96.
The relationship between phosphate status and cyanide-resistant respiration in bean roots 总被引:8,自引:0,他引:8
Bean ( Phaseolus vulgaris L.) seedlings were cultured on complete or phosphate-deficient nutrient medium. After 14 days of culture on phosphate-deficient medium the visible symptoms of Pi deficiency were observed only in the shoot, the fresh and dry weights of the roots were slightly higher than in control plants. The decreased Pi content in the roots had little effect on total respiration rate but had an effect on the level of inhibition of respiration by cyanide. The high resistance of respiration to cyanide observed in Pi -deficient roots was the result of the suppression of cytochrome path activity and an increased participation of the alternative, cyanide-resistant pathway. The cytochrome pathway activity increased when inorganic phosphate was supplied to Pi -deficient roots for 1 or 3.5 h. It is speculated that the suppression of cytochrome pathway in Pi -deficient roots may result from restriction of the phosphorylating capacity or a partial inhibition of cytochrome oxidase activity. 相似文献
97.
Howard Griffiths Mark S. J. Broadmeadow Anne M. Borland Clive S. Hetherington 《Planta》1990,181(4):604-610
Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO2 collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO2 exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO2 (Phase I), discrimination () ranged from 4.4 to 6.6, equivalent to an effective carbon-isotope ratio (13C) of –12.3 to –14.5 versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO2 uptake and refixation of respiratory CO2, characteristic of CAM in the Bromeliaceae. When for the relative proportion of external (p
a
) and internal (p
i) CO2 is taken into account, calculated p
i/p
a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of during Phase II, early in the light period, showed the transition between C4 and C3 pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as increased from 10.5 to 21.2 During decarboxylation in the light period (Phase III), CO2 leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of calculated from on-line measurements (64.4) showed that the CO2 lost was considerably enriched in 13C, and this was confirmed by direct analysis of the CO2 diffusing out into a CO2-free atmosphere (
13C = + 51.6 versus PDB). Instantaneous discrimination was characteristic of the C3 pathway during Phase IV (late in the light period), but a reduction in showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that double carboxylation involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.Abbreviations and Symbols CAM
Crassulacean acid metabolism
-
H+
(dawn-dusk) variation in titratable acidity
-
13C
carbonisotope ratio of plant organic material, relative to Pee Dee Belemnite (vs. PDB)
-
discrimination against 13CO2,
-
p
i, p
a
internal, external partial pressures of CO2
- Rubisco
ribulose1,5-bisphosphate carboxylase
- PAR
photosynthetically active radiation
- PEPCase
phosphoenolpyruvate carboxylase
We are grateful for financial support in respect of research grants (GR3/5360, GR3/6419) and a studentship awarded by the Natural Environment Research Council, UK. 相似文献
98.
Wouter J. Middelhoven Alex Coenen Bart Kraakman Maarten D. Sollewijn Gelpke 《Antonie van Leeuwenhoek》1992,62(3):181-187
The imperfect ascomycetous yeastsCandida parapsilosis andArxula adeninivorans degraded 3-hydroxybenzoic acid via gentisate which was the cleavage substrate. 4-Hydroxybenzoic acid was metabolized via protocatechuate. No cleavage enzyme for the latter was detected. In stead of this NADH- and NADPH-dependent monooxygenases were present. In cells grown at the expense of hydroquinone and 4-hydroxygenzoic acid, enzymes of the hydroxyhydroquinone variant of the 3-oxoadipate pathway were demonstrated, which also took part in the degradation of 2,4-dihydroxybenzoic acid byC. parapsilosis.Abbreviations HHQ
Hydroxyhydroquinone (1,2,4-trihydroxybenzene)
- GSH
reduced Glutathione 相似文献
99.
Wim van Uden Niesko Pras Esther M. Vossebeld Jos N. M. Mol Theo M. Malingré 《Plant Cell, Tissue and Organ Culture》1990,20(2):81-87
Cell suspension cultures of Linum flavum L., routinely grown on a NAA-containing medium, accumulated low levels of the phenylpropanoid-derived lignan 5-methoxypodophyllotoxin (5-MPT), up to 0.004% on a dry weight basis. Feeding experiments with the precursor L-phenylalanine resulted in a 3–5-fold increase in 5-MPT levels, but caused the levels of PAL activity to fall. Treatment of the cultures with the elicitor Nigeran, either alone or in combination with phenylalanine, caused the 5-MPT production to cease, even though PAL activity was rapidly enhanced by these treatments. Transfer of the cultures to NAA-free medium resulted in a 40–50 fold higher level of 5-MPT accumulation, the PAL activity levels being lowered compared to the routinely grown cells. With these more differentiated cultures, phenylalanine feeding and elicitor treatment, both on its own and in combination with the precursor, had no effect on 5-MPT production, even though the PAL activity levels were higher than in the untreated cells. It can be concluded that in lignan-accumulating cultures of L. flavum, PAL activity is nearly always detectable and seems to show a reciprocal relationship with 5-MPT accumulation.Abbreviations 5-MPT
5-methoxypodophyllotoxin
- PAL
phenylalanine ammonia lyase (EC 4:3:1.5)
- NAA
naphthaleneacetic acid 相似文献
100.
The green alga Chlamydomonas reinhardtii is a facultative heterotroph and, when cultured in the presence of acetate, will synthesize chlorophyll (Chl) and photosystem (PS) components in the dark. Analysis of the thylakoid membrane composition and function in dark grown C. reinhardtii revealed that photochemically competent PS II complexes were synthesized and assembled in the thylakoid membrane. These PS II centers were impaired in the electron-transport reaction from the primary-quinone electron acceptor, QA, to the secondary-quinone electron acceptor, QB (QB-nonreducing centers). Both complements of the PS II Chl a–b light harvesting antenna (LHC II-inner and LHC II-peripheral) were synthesized and assembled in the thylakoid membrane of dark grown C. reinhardtii cells. However, the LHC II-peripheral was energetically uncoupled from the PS II reaction center. Thus, PS II units in dark grown cells had a -type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS II units lack LHC II-peripheral). Illumination of dark grown C. reinhardtii caused pronounced changes in the organization and function of PS II. With a half-time of about 30 min, PS II centers were converted froma QB-nonreducing form in the dark, to a QB-reducing form in the light. Concomitant with this change, PS II units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS II form. The functional antenna of the latter contained more than 250 Chl(a+b) molecules. The results are discussed in terms of a light-dependent activation of the QA-QB electron-transfer reaction which is followed by association of the PS II unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS II) in the membrane of the grana partition region.Abbreviations Chl
chlorophyll
- PS
photosystem
- QA
primary quinone electron acceptor of PS II
- QB
secondary quinone electron acceptor of PS II
- LHC
light harvesting complex
- F0
non-variable fluorescence yield
- Fplf
intermediate fluorescence yield plateau leyel
- Fmax
maximum fluorescence yield
- Fi
initial fluorescence yield increase from F0 to Fpl (Fpl–F0)
- Fv
total variable fluorescence yield (Fm–F0)
- DCMU
dichlorophenyl-dimethylurea 相似文献