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21.
Summary The role and importance of the redox potential phenomena in submerged citric acid production are discussed. The redox potential of the fermentation broth is the result of oxydo-reduction processes where the metabolic activity of the microorganism Aspergillus niger plays the most significant role. The course of the redox curve for a good yielding citric acid production is presented and interpreted. The experiments of submerged citric acid production were carried out on beet molasses treated with potassium hexacyanoferrate and inoculated with A. niger spores. 相似文献
22.
Inhibition of the ATPase by inorganic phosphate, Pi, was examined in terms of product inhibition of the various activities catalyzed by an enzyme preparation from rat brain, and considered in terms of the specific transport processes of the membrane Na+,K+-pump that these activities reflect. The K+-dependent phosphatase activity of the enzyme was most sensitive to Pi, and inhibition was competitive toward the substrate, nitrophenyl phosphate, as would be expected if Pi were released from the same enzyme form that bound substrate. However, this enzymatic activity does not seem to represent a transport process, and thus a cyclical discharge of K+ may not be involved. The Na+-dependent exchange activity was unaffected by Pi, in accord with the absence of Pi release in the reaction sequence. For the corresponding Na+/Na+ exchange function of the pump, which reportedly does not involve ATP hydrolysis either, prior release of Pi obviously cannot be required for Na+ discharge. With the Na+-dependent ATPase activity, measured using micromolar concentrations of ATP, Pi inhibited, but far less than with the phosphatase activity, and inhibition was not competitive toward ATP. Moreover, inhibition decreased as the Na+ concentration was raised from 10 to 100 mM. This elevated concentration of Na+ also led to substrate inhibition. For this ATPase activity, and the corresponding transport process, uncoupled Na+ efflux, the findings suggest that Na+ discharge follows Pi release, in contrast to Na+/Na+ exchange. The ATPase activity, measured with millimolar concentrations of ATP and reflecting the coupled Na+,K+-transport function, was similarly sensitive to Pi, and again inhibition was not competitive toward ATP. However, in this case inhibition did not increase as the Na+ concentration was lowered. For this activity, and the associated transport process, the site of Na+ discharge in the overall reaction sequence remains unresolved. 相似文献
23.
Frederick T. Marin 《Developmental biology》1976,48(1):110-117
Evidence is presented which indicates that amino acid starvation is the specific stimulus initiating the developmental phase of the life cycle of Dictyostelium discoideum: (i) Amoebae were washed free of complex growth medium and placed in buffer supplemented with specific nutrients; amino acids were the only nutrients that specifically inhibited the initiation of development. (ii) A partially defined growth medium allowing selective starvation for amino acids or glucose during growth is described. Amoebae initiated development only when starved for amino acids. Any effect of glucose on the primary control of the initiation of development is an indirect result of its utilization as a source of precursors for endogenously synthesized amino acids. 相似文献
24.
Thierry Brun Jean Péduzzi Manuela Marin Caniça Gérard Paul Pierre Névot Michel Barthélémy Roger Labia 《FEMS microbiology letters》1994,120(1-2):111-117
Abstract A novel procedure was used to purify a cytosolic chitinase from Candida albicans to electrophoretic homogeneity. The results represent the first demonstration of the purification of a fungal intracellular chitinase using the criterion of a single band detected following silver-staining of a polyacrylamide gel run under denaturing conditions. Purified chitinase had pH and temperature optima of 5.0 and 50°C, respectively. Inhibition of enzyme activity by allosamidin was pH-dependent occuring maximally at pH 8.0. Phospholipids had similar marked and highly specific effects on the activities of both the purified soluble enzyme and a solubilized microsomal chitinase from C. albicans . Evidence is provided for the existence of a complex chitinolytic system in this organism. 相似文献
25.
In this paper, the authors study the correlation which exists between somatic development, represented by weight, height and thorax, and the age of onset of menarche. The results indicate that girls showing early menarche have a somatic development greater than the mean. It has also been possible to show that the greatest increase in height occurs before the menarche, while the greatest increase in weight coincides with the appearance of the menarche, or occurs shortly afterwards. 相似文献
26.
Johanna Marin‐Carbonne Vincent Busigny Jennyfer Miot Claire Rollion‐Bard Elodie Muller Nadja Drabon Damien Jacob Sylvain Pont Martin Robyr Tomaso R. R. Bontognali Camille Franois Stephanie Reynaud Mark Van Zuilen Pascal Philippot 《Geobiology》2020,18(3):306-325
On the basis of phylogenetic studies and laboratory cultures, it has been proposed that the ability of microbes to metabolize iron has emerged prior to the Archaea/Bacteria split. However, no unambiguous geochemical data supporting this claim have been put forward in rocks older than 2.7–2.5 giga years (Gyr). In the present work, we report in situ Fe and S isotope composition of pyrite from 3.28‐ to 3.26‐Gyr‐old cherts from the upper Mendon Formation, South Africa. We identified three populations of microscopic pyrites showing a wide range of Fe isotope compositions, which cluster around two δ56Fe values of ?1.8‰ and +1‰. These three pyrite groups can also be distinguished based on the pyrite crystallinity and the S isotope mass‐independent signatures. One pyrite group displays poorly crystallized pyrite minerals with positive Δ33S values > +3‰, while the other groups display more variable and closer to 0‰ Δ33S values with recrystallized pyrite rims. It is worth to note that all the pyrite groups display positive Δ33S values in the pyrite core and similar trace element compositions. We therefore suggest that two of the pyrite groups have experienced late fluid circulations that have led to partial recrystallization and dilution of S isotope mass‐independent signature but not modification of the Fe isotope record. Considering the mineralogy and geochemistry of the pyrites and associated organic material, we conclude that this iron isotope systematic derives from microbial respiration of iron oxides during early diagenesis. Our data extend the geological record of dissimilatory iron reduction (DIR) back more than 560 million years (Myr) and confirm that micro‐organisms closely related to the last common ancestor had the ability to reduce Fe(III). 相似文献
27.
Sara Marin Anaïs Gibert Juliette Archambeau Vincent Bonhomme Mylne Lascoste Benoit Pujol 《Molecular ecology》2020,29(16):3010-3021
Phenotypic divergence among natural populations can be explained by natural selection or by neutral processes such as drift. Many examples in the literature compare putatively neutral (FST) and quantitative genetic (QST) differentiation in multiple populations to assess their evolutionary signature and identify candidate traits involved with local adaptation. Investigating these signatures in closely related or recently diversified species has the potential to shed light on the divergence processes acting at the interspecific level. Here, we conducted this comparison in two subspecies of snapdragon plants (eight populations of Antirrhinum majus pseudomajus and five populations of A. m. striatum) in a common garden experiment. We also tested whether altitude was involved with population phenotypic divergence. Our results identified candidate phenological and morphological traits involved with local adaptation. Most of these traits were identified in one subspecies but not the other. Phenotypic divergence increased with altitude for a few biomass‐related traits, but only in A. m. striatum. These traits therefore potentially reflect A. m. striatum adaptation to altitude. Our findings imply that adaptive processes potentially differ at the scale of A. majus subspecies. 相似文献
28.
29.
Stéphane Guyot Laurence Pottier Lucie Bertheau Jennifer Dumont Eminence Dorelle Hondjuila Miokono Sébastien Dupont Mélanie Ragon Emmanuel Denimal Ambroise Marin John E. Hallsworth Laurent Beney Patrick Gervais 《Microbial biotechnology》2021,14(4):1445-1461
Although mechanisms involved in response of Saccharomyces cerevisiae to osmotic challenge are well described for low and sudden stresses, little is known about how cells respond to a gradual increase of the osmotic pressure (reduced water activity; aw) over several generations as it could encounter during drying in nature or in food processes. Using glycerol as a stressor, we propagated S. cerevisiae through a ramp of the osmotic pressure (up to high molar concentrations to achieve testing-to-destruction) at the rate of 1.5 MPa day-1 from 1.38 to 58.5 MPa (0.990–0.635 aw). Cultivability (measured at 1.38 MPa and at the harvest osmotic pressure) and glucose consumption compared with the corresponding sudden stress showed that yeasts were able to grow until about 10.5 MPa (0.926 aw) and to survive until about 58.5 MPa, whereas glucose consumption occurred until 13.5 MPa (about 0.915 aw). Nevertheless, the ramp conferred an advantage since yeasts harvested at 10.5 and 34.5 MPa (0.778 aw) showed a greater cultivability than glycerol-shocked cells after a subsequent shock at 200 MPa (0.234 aw) for 2 days. FTIR analysis revealed structural changes in wall and proteins in the range 1.38–10.5 MPa, which would be likely to be involved in the resistance at extreme osmotic pressure. 相似文献
30.
Aline Awad Sokhavuth Sar Ronan Barré Clotilde Cariven Mickael Marin Jean Pierre Salles Christophe Erneux Didier Samuel Ama Gassama-Diagne 《Molecular biology of the cell》2013,24(14):2171-2185
The main targets of hepatitis C virus (HCV) are hepatocytes, the highly polarized cells of the liver, and all the steps of its life cycle are tightly dependent on host lipid metabolism. The interplay between polarity and lipid metabolism in HCV infection has been poorly investigated. Signaling lipids, such as phosphoinositides (PIs), play a vital role in polarity, which depends on the distribution and expression of PI kinases and PI phosphatases. In this study, we report that HCV core protein, expressed in Huh7 and Madin–Darby canine kidney (MDCK) cells, disrupts apicobasal polarity. This is associated with decreased expression of the polarity protein Dlg1 and the PI phosphatase SHIP2, which converts phosphatidylinositol 3,4,5-trisphosphate into phosphatidylinositol 4,5-bisphosphate (PtdIns(3,4)P2). SHIP2 is mainly localized at the basolateral membrane of polarized MDCK cells. In addition, PtdIns(3,4)P2 is able to bind to Dlg1. SHIP2 small interfering RNA or its catalytically dead mutant disrupts apicobasal polarity, similar to HCV core. In core-expressing cells, RhoA activity is inhibited, whereas Rac1 is activated. Of interest, SHIP2 expression rescues polarity, RhoA activation, and restricted core level in MDCK cells. We conclude that SHIP2 is an important regulator of polarity, which is subverted by HCV in epithelial cells. It is suggested that SHIP2 could be a promising target for anti-HCV treatment. 相似文献