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971.
Annemieke F. Pronk Charles Affourtit Cyril Mashingaidze Adriaan H. Stouthamer Henk W. van Verseveld Fred C. Boogerd 《FEMS microbiology letters》1995,129(2-3):149-155
Abstract The in situ method for determination of reduction levels of cytochromes b and c pools during steady-state growth (Pronk et al., Anal. Biochem. 214, 149–155, 1993) was applied to chemostat cultures of the wild-type, a cytochrome aa3 single mutant and a cytochrome aa3 /d double mutant of Azorhizobium caulinodans . For growth with NH4 + as the N source, the results indicate that (i) the aa3 mutant strains growing at a dissolved O2 tension of 0.5% possess an active alternative cytochrome c oxidase, which is hardly present during fully aerobic growth, and assuming that (i) also pertains to the wild-type, (ii) the wild-type uses cytochrome aa3 under fully aerobic conditions. For growth with N2 as the N source, it was found that the aa3 mutant strains growing at dissolved O2 tensions ranging from 0.5 to 3.0% also contain an active alternative cytochrome c oxidase. 相似文献
972.
N. Viswanathan Fred C. Davis 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(4):339-346
Pregnant Syrian hamsters with lesions of the suprachiasmatic nucleus (SCN) received single injections of melatonin or the
D1-dopamine receptor agonist, SKF 38393 on day 15 of gestation (1 day before birth). Pups were weaned on postnatal day 20
and their freerunning activity rhythms recorded for 3–4 weeks. The pups' phases on the day of weaning were significantly clustered
in both of the treatment groups, but the average phases differed by approximately 180°. The results demonstrate that a single
prenatal stimulus is sufficient to set the phases of the hamsters' rhythms and that the phase established depends on the stimulus.
Both c-fos mRNA and Fos protein were expressed in the fetal SCN after SKF 38393 injection but neither were expressed after melatonin injection. Simulations
showed that a single stimulus could produce the observed synchrony from a population of uniformally distributed phases if
the phase shifts were three to four times the magnitude of the adult hamster light phase response curve (PRC). A light pulse
PRC mimicked the effect of an SKF 38393 injection and a dark-pulse PRC mimicked the effects of a melatonin injection. Together
these results suggest that dopamine and melatonin either are, or mimic, maternal entraining signals that represent day and
night.
Accepted: 12 November 1996 相似文献
973.
Fred. J. Smith 《BMJ (Clinical research ed.)》1901,2(2134):1574-1575
974.
975.
976.
977.
978.
Fred J. Molz 《Journal of theoretical biology》1976,59(2):277-292
A detailed quantitative analysis of water flow through the apoplasm and symplasm of plant tissue is presented. The analysis results in two coupled diffusion equations which describe water transport in the two pathways. Various parameters entering the analysis identify the physical properties of the tissue which control the transport process as the resistance to water flow per cell in the two parallel pathways, the resistance per cell between pathways, and the water capacity per cell in the two pathways. Values for the several resistances and water capacities are estimated from available data, and a model problem is solved wherein a sheet of tissue at an initial water potential of — δ bars is immersed in a container of water. The resulting solutions show that depending on the values assigned to the controlling parameters, local water potential equilibrium between each cell and its cell wall may or may not obtain. In the special case of local equilibrium (water potential in the symplasm and apoplasm pathways essentially equal), the transport process can be described by a single diffusion equation which is derived along with an expression for the tissue diffusivity. It is concluded that the weakest link in the analysis is the estimated value for the permeability of the plasmodesma membrane, and that a logical extension of the theory would be to include the effects of a diffusable solute. 相似文献
979.
980.
Abstract Conformational changes in ovalbumin, a globular protein, induced by an anionic surfactant, sodium dodecyl sulfate (SDS), have been monitored by an FT-IR spectrometer using ZnSe cylindrical internal reflection optics which allows high quality IR spectra to be obtained in water solution. The most notable change, on addition of SDS, occurs in the composite band of the Amide I absorption band and the vibrational frequency of the composite C=O bond shifts from 1639 cm?1 to 1652 cm?1. On the other hand, the position of the Amide II band remains fairly unchanged. Comparison of the various peak positions in the deconvoluted spectra for the native protein and the perturbed protein clearly shows the effect of SDS on the secondary structures of the protein. SDS unfolds the protein. It increases the helix content slightly. More importantly, it alters the β sheet structure, destroying it almost completely in the Amide I region, while retaining it in its neighbourhood. In the deconvoluted spectra of the perturbed protein, a band at 1531 cm?1 indicates generation of some β turns. We used the second derivative of the deconvoluted spectra for fixing positions of minor peaks and shoulders. The results of this study indicate that the deconvolution of the normal IR spectra, consisting of composite bands, provides evidence for the specific secondary structures in a protein and for the way they are affected by changes in the environment, e.g., the addition of SDS. This makes it possible to relate conformational changes to specific secondary structures. 相似文献