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111.
112.
113.
Using photoacoustic spectroscopy, state 1-state 2 transitions were demonstrated in vivo in intact sugar maple leaves (Acer saccharum Marsh.) by following the changes in energy storage of photosystems (PS) I and II. Energy storage measured with 650 nm modulated light (light 2) in the presence of background white light indicated the total energy stored by both photosystems (ESt), and in the presence of background far-red light showed the energy stored by PSI (ESpsi). The difference between ESt and ESpsi gave the energy stored by PSII (ESpsii). While ESt remained nearly constant during state transitions, both ESpsi and ESpsii changed considerably. The ratio of ESpsii to ESpsi, an indicator of the energy distribution between the two photosystems, decreased or increased during transition to state 2 or state 1, respectively. State transitions were completed in about 20 min and were fully reversible. During transition from state 1 to state 2, the fraction of excitation energy gained by PSI was nearly equal to that lost by PSII. This fraction of excitation energy transferred from PSII to PSI accounted for about 5% of the absorbed light (fluorescence is not considered), 19% of ESt, 34% of ESpsii, and 43% of ESpsi in state 2. NaF treatment inhibited the transition to state 1. Data in the present study confirm the concept of changes in absorption cross-section of photosystems during state transitions. 相似文献
114.
Microchemical imaging of iodine distribution in the brown alga Laminaria digitata suggests a new mechanism for its accumulation 总被引:2,自引:0,他引:2
Elodie Françoise Verhaeghe Aurélien Fraysse Jean-Luc Guerquin-Kern Ting-Di Wu Guillaume Devès Charles Mioskowski Catherine Leblanc Richard Ortega Yves Ambroise Philippe Potin 《Journal of biological inorganic chemistry》2008,13(2):257-269
Brown algal kelp species are the most efficient iodine accumulators among all living systems, with an average content of 1.0%
of dry weight in Laminaria digitata. The iodine distributions in stipe and blade sections from L. digitata were investigated at tissue and subcellular levels. The quantitative tissue mapping of iodine and other trace elements (Cl,
K, Ca, Fe, Zn, As and Br) was provided by the proton microprobe with spatial resolutions down to 2 μm. Chemical imaging at
a subcellular resolution (below 100 nm) was performed using the secondary ion mass spectrometry microprobe. Sets of samples
were prepared by both chemical fixation and cryofixation procedures. The latter prevented the diffusion and the leaching of
labile inorganic iodine species, which were estimated at around 95% of the total content by neutron activation analysis. The
distribution of iodine clearly shows a huge, decreasing gradient from the meristoderm to the medulla. The contents of iodine
reach very high levels in the more external cell layers, up to 191 ± 5 mg g−1 of dry weight in stipe sections. The peripheral tissue is consequently the main storage compartment of iodine. At the subcellular
level, iodine is mainly stored in the apoplasm and not in an intracellular compartment as previously proposed. This unexpected
distribution may provide an abundant and accessible source of labile iodine species which can be easily remobilized for potential
chemical defense and antioxidative activities. According to these imaging data, we proposed new hypotheses for the mechanism
of iodine storage in L. digitata tissues.
In memory of Dr. Charles Mioskowski, “Miko,” who died on 2 June 2007. 相似文献
115.
C. Leblanc B. Kloareg S. Loiseaux-de Goër C. Boyen 《Journal of molecular evolution》1995,41(2):196-202
The entire nucleotide sequence containing the small-subunit ribosomal RNA gene (SSU rRNA) from the mitochondrial genome of Chondrus crispus was determined. To our knowledge, this is the first sequence of a mitochondrial 16S-like rRNA from a red alga. The length of this gene is 1,376 nucleotides. Its secondary structure was constructed and compared with other known secondary structures from eubacteria and from mitochondria of land plants, green and brown algae, and fungi. Phylogenetic trees were built upon SSU rRNA sequence alignment from mitochondria and eubacteria. The results show that rhodophytes and chromophytes provide additional links in the evolution of mitochondria between the green plant lineage and the nonplant lineages.Correspondence to: C. Boyen 相似文献
116.
Dehart HP Heath HE Heath LS Leblanc PA Sloan GL 《Applied and environmental microbiology》1995,61(7):2811
Volume 61, no. 4, p. 1478, Table 2, column 4: The diameters (in milliliters) of the zones of inhibition for 5-(mu)g methicillin disks given (from top to bottom), "116," "72," "107," and "32," should read "33.5," "22.6," "34.2," and "21.0," respectively. [This corrects the article on p. 1475 in vol. 61.]. 相似文献
117.
118.
Catecholamine synthetic enzymes are found in many cranial parasympathetic principal neurons, and in the small intensely fluorescent (SIF) cells that populate parasympathetic as well as sympathetic ganglia. While there is evidence that the acquisition of noradrenergic properties in sympathetic neuron precursors depends on factors that these cells encounter in the trunk environment, the mechanisms that direct the development of noradrenergic traits in cranial parasympathetic neurons and SIF cells are not understood. The present study examines the time course of appearance of tyrosine hydroxylase (TH) immunoreactivity in the principal neurons and SIF cells of the rat sphenopalatine ganglion. We show that the sphenopalatine ganglion of normal adult rats contains both a small population of TH-immunoreactive principal neurons and many SIF cells. The TH-immunoreactive principal neurons do not synthesize or store detectable catecholamines, even though the majority of sphenopalatine ganglion neurons do contain 1-amino acid decarboxylase catalytic activity. Sphenopalatine ganglion principal neurons do not accumulate detectable levels of exogenous catecholamines. This observation suggests that they lack a high affinity norepinephrine uptake system. In contrast to what has been observed previously for sympathetic neurons, the appearance of TH immunoreactivity in sphenopalatine neurons is not temporally correlated with the cessation of neural crest cell migration. The first TH-immunoreactive neurons do not appear in the sphenopalatine ganglion until Embryonic Day 16.5, 2 days after the ganglion has condensed and process outgrowth has begun. The number of sphenopalatine neurons that express TH immunoreactivity increases dramatically between Embryonic Day 18.5 and Postnatal Day 1, but then decreases. In fact, the percentage of sphenopalatine neurons that express TH immunoreactivity is almost fivefold higher in newborn than in adult rats. SIF cells cannot be definitively identified in the sphenopalatine ganglion until after Embryonic Day 18.5. The time course of appearance of TH immunoreactivity in sphenopalatine ganglion cells raises the possibility that TH expression is stimulated in these cells by factors encountered either at their condensation site or at their target, such as glucocorticoids or nerve growth factor. The relatively late appearance of SIF cells in the sphenopalatine ganglion argues against the hypothesis that SIF cells are the precursors of all autonomic neurons. 相似文献
119.
The nature of the interaction between the chlorophyll a molecules in multilayer arrays obtained by the Langmuir-Blodgett technique is examined by electronic and infrared spectroscopies. Following the deposition of the multilayers, we observed a blue shift with time in the electronic spectra. This effect is monitored by infrared spectroscopy. The intensity of the coordinated ketone band is decreased while the intensity of the free ketone band is increased. These modifications are explained by the reorganization of the chlorophyll a molecules from an organized to a less organized one. The influence of H2O, D2O and SO2 vapors on the chlorophyll a multilayers give some informations on the role of water molecules in the aggregation of chlorophyll a in this ordered system. From these observations, a model is proposed for the multilayer arrangement implying two molecules of water per molecule of chlorophyll a. 相似文献
120.
Prof. J. Metuzals Y. Robitaille S. Houghton S. Gauthier C. Y. Kang R. Leblanc 《Cell and tissue research》1988,252(2):239-248
Summary Brains of nine early and four advanced Alzheimer patients have been investigated, utilizing three approaches to specify the threshold state of Alzheimer's disease (AD). Extensive thin sectioning electron microscopy (EM) of frontal lobe biopsies, correlated with stringent clinical assessment, has demonstrated that the neuronal cytoskeleton undergoes specific transformations into paired helical filament-like (PHF-like) strands, which lead to the formation of the insoluble paracrystalline paired helical filaments (PHFs). The neurofilamentous network (NFN) transformation plays an important role in this process, whereby segregation, posttranslational modifications and reassembly of the modified components through autocrosslinking, and phase transition occur. According to our data, the threshold state can be defined as the state of irreversible segregation and posttranslational modification of the NFN and the microtubule-associated proteins. At this state, therapeutic intervention to reverse the disease process may be possible. The results indicate similarities between the formation of the paracrystals of the PHFs and the formation of the tropomyosin-like crystals of the Hirano bodies. Close relationships among PHFs and smooth endoplasmic reticulum and plasma membrane do exist. Enveloped virus-like particles have been observed in neurons containing PHFs. A possible role of these virus-like particles as an etiological agent for AD is discussed. 相似文献