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51.
A study has been made in everted sacs of guinea pig jejunum to see if the two transport systems of glucose analogues characterized at the brush border membrane vesicles are operative. The transport kinetics of D-galactose and alpha-methylglucoside up to 80 mM concentrations has been studied, as well as the mutual inhibitions between them at low and high concentrations of the substrate and at different concentrations of the inhibitor. Low temperature (20 degrees C) inhibits galactose transport at 0.1 mM (70%) and 40 mM (78%) concentrations. A mass transfer coefficient, KD, somewhat higher for galactose than for alpha-methylglucoside, was obtained when the transport component was abolished by phlorizin. The transport of D-galactose and alpha-methylglucoside seemed to be compatible with the function of one system shared by both substrates, which presents greater affinity for alpha-methylglucoside. The functional existence of two systems of active transport at the brush border of guinea pig was not evidenced in intestinal preparations of whole tissue, due perhaps to the effect of the unstirred water layers. However, differences in KD values and some results of the mutual inhibitions may suggest a second system. 相似文献
52.
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
53.
The secondary structure of the photosystem II (PSII) reaction center isolated from pea chloroplasts has been characterized by Fourier transform infrared (FTIR) spectroscopy. Spectra were recorded in aqueous buffers containing H2O or D2O; the detergent present for most measurements was dodecyl maltoside. The broad amide I and amide II bands were analyzed by using second-derivative and deconvolution procedures. Absorption bands were assigned to the presence of alpha-helices, beta-sheets, turns, or random structure. Quantitative analysis revealed that this complex contained a high proportion of alpha-helices (67%) and some antiparallel beta-sheets (9%) and turns (11%). An irreversible decrease in the intensity of the band associated with the alpha-helices occurs upon exposure of the isolated PSII reaction center to bright illumination. This loss of alpha-helical content gave rise to an increase in other secondary structures, particularly beta-sheets. After similar pretreatment with light, sodium dodecyl sulfate polyacrylamide gel electrophoresis reveals lower mobility and solubility of constituent D1 and D2 polypeptides of the PSII reaction center. Some degradation of these polypeptides also occurs. In contrast, there is no change in the mobility of the two subunits of cytochrome b559. In the absence of illumination, the PSII reaction center exchanged into dodecyl maltoside shows good thermal stability as compared with samples in Triton X-100. Only at a temperature of about 60 degrees C do spectral changes take place that are indicative of denaturation. 相似文献
54.
Members of the alpha-amylase inhibitors family from wheat endosperm are major allergens associated with baker's asthma 总被引:5,自引:0,他引:5
L Gómez E Martín D Hernández R Sánchez-Monge D Barber V del Pozo B de Andrés A Armentia C Lahoz G Salcedo 《FEBS letters》1990,261(1):85-88
We have identified the major antigens or IgE binding components from wheat flour. Thirty-five sera from patients with baker's asthma were used to analyze the reaction with wheat salt-soluble proteins. We found a 15 kDa SDS-PAGE band which reacted with all sera tested. Purified members of the alpha-amylase inhibitor family, which are the main components of the 15 kDa band, were recognized by specific IgE when tested with a pool of reactive sera. Immunodetection after two-dimensional electrophoretic fractionation of crude inhibitor preparations from wheat endosperms also detected several inhibitor subunits as major low-molecular-weight allergens. 相似文献
55.
A room temperature electron paramagnetic resonance potentiometric cell has been developed for the measurement of oxidation-reduction midpoint potentials of enzymes containing paramagnetic centers. Based upon an aqueous flat cell designed for use with the Varian TM high sensitivity cavity, the apparatus combines a high degree of anaerobiosis with low volume requirements. The cell is simple in design, easily constructed, and can be adapted for use with most spectrometer cavities. Tests of the cell using xanthine oxidase, in 50 mM Bicine buffer, pH 7.7, yielded midpoint potentials of -345 and -371 mV for the Mo(VI)/Mo(V) and Mo(V)/Mo(IV) couples compared with values of -373 and -377 mV obtained by electron paramagnetic resonance analysis of frozen potentiometric samples. These values indicate that shifts, of the order of 20-40 mV, may occur upon freezing poised samples. For the Mo center of xanthine oxidase, these shifts in potential are more pronounced for the Mo(VI)/Mo(V) couple and result in a destabilization of the Mo(V) intermediate during freezing. 相似文献
56.
A. Barber 《Cell and tissue research》1982,226(2):267-273
Summary The glyoxylic acid monoamine-detecting technique of Bolstad et al. (1979) was applied to wholemounts of intact ganglia of the gastropod mollusc Philine aperta. A dense network of fluorescent varicosities was found in the sheath of the suboesophageal, visceral and genital ganglia, and most of their nerves. Drug treatment experiments suggest that these projections to the neural sheath contain serotonin. The significance of these terminals in the sheath is discussed and proposals for further work are given. 相似文献
57.
C Barber 《Microbios》1981,32(128):71-76
Immunochemical analysis of Citrobacter ballerup and Salmonella typhi Ty2 showed that the strains share native and heat-resistant proteins that are, apparently, the carriers of a common polysaccharidic determinant present in their respective somatic antigens. After the classic acetic acid hydrolysis, the somatic antigen of C. ballerup reacted, in agar gel, against the homologous antiserum by two precipitation lines, one of which also precipitated against the anti S, typhi Ty2 serum; the hydrolysis of the S. typhi Ty2 somatic antigen demonstrated that, in addition to the 'O' polysaccharide, reacting against all the S. typhi antisera, it contains a polysaccharide that precipitated against the anti-C. ballerup serum. The elusiveness in the agglutinability of only freshly isolated bacterial authorizes some doubt concerning the responsibility of the antipolysaccharide antibodies in the agglutinating Vi sera; in order to induce anitpolysaccharides hyperimmunizations are needed while antiproteins are easily induced by short immunizations. 相似文献
58.
Proteoid root morphology and function inLupinus albus 总被引:1,自引:1,他引:0
Summary Current theories of phosphorus uptake by plants imply that they can augment diffusion to their root axes by the development
of abundant root hairs or mycorrhizas. Some phosphorus efficient plants have root morphology with multi-branched roots and
localised regions of densely packed root hairs, which we suggest is better suited to the retention of substances exuded by
the roots than uptake of substances moving to the root by diffusion. Evidence of substantial exudation by the proteoid roots
ofLupinus albus is presented. 相似文献
59.
Smith Walker O. Jr.; Barber Richard T.; Huntsman Susan A. 《Journal of plankton research》1982,4(3):651-663
Chelation bioassays were conducted off the coast of northwestAfrica during two seasons. The first (winter) was characterizedby strong shelf-break upwelling and the second (spring) wascharacterized by upwelling closer to shore. Phytoplankton insamples taken from surface waters during winter showed a markedstimulation in growth upon addition of the artificial chelatorEDTA. Optimal concentrations of the ligand were 106 M.No stimulation was observed during upwelling conditions encounteredin the spring. Primary productivity in the winter season wassignificantly lower than in the spring, averaging only 35% ofthe spring rates. Ionic copper additions reduced growth in phytoplanktonassayed in the spring and the growth reductions were eliminatedby addition of EDTA. It is hypothesized that the winter growthdepression resulted from either (1) a lack of organic compoundscapable of binding ionic copper as a result of either a lackof organic input from the sediments or surface waters becauseof direct advection to the surface, or by (2) the upwellingof water from a ligand-deficient water mass whose relative importanceas a source for newly upwelled water declined and disappearedas the season progressed. 相似文献
60.
Howard R. Morris Maria Panico Michael Barber Robert S. Bordoli Robert D. Sedgwick Andrew Tyler 《Biochemical and biophysical research communications》1981,101(2):623-631
We have studied a selection of peptides using a new mass spectrometric ionisation technique - fast atom bombardment (FAB). We define the fragmentation pathways observed and comment on the utility in sequence analysis. A simple acetylation experiment is shown to aid rapid sequence assignment. 相似文献