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491.
492.
493.
BIOLOGICAL EFFECTS OF SURFACTANTS 总被引:2,自引:2,他引:0
494.
Some recent evidence is discussed which suggests that the controlof microtubule assembly during the formation of the mitoticapparatus in sea urchins involves three factors. These include:nucleation sites such as the kinetochores, a mechanism for regulatingintracellular calcium, and a heat stable substance which preventsspontaneous, non-nucleated microtubule polymerization. 相似文献
495.
JOSEPH FRANKEL 《The Journal of eukaryotic microbiology》1972,19(4):648-654
Cortical features were analyzed in successive samples of continuously growing stock cultures of amicronucleate strains GL-C and GL-I, and in micronucleate strain WH-6 (syngen 1, mating type I). Thirteen successive samples of strain GL-C, representing a time span of 111 months, 5 samples of WH-6 (43 months) and 2 samples of GL-I (1 month) were examined. The observed range of commonly expressed ciliary row numbers (corticotypes) was 16–20 rows in strain GL-C, 15–20 in strain GL-I, and 16–20 in strain WH-6. These ranges remained constant through time within each strain. The individual samples each included all or a large part of the total range observed in the strain, but the relative abundances of different corticotypes within this range shifted through time. The shifts appeared random, with no discernible trends. Mean contractile vacuole pore (CVP) position and number of CVP meridians were assayed in the 2 “GL” strains. Mean CVP position was an apparently stable character, with only slight fluctuations through time, while the distribution of number of CVP meridians was somewhat less constant. The CVP parameters of strains GL-C and GL-I were considerably different, and both of these strains were very different from the GL strain which had been studied by Nanney. In fact, these 3 “GL” strains have, among them, virtually the entire gamut of known CVP characteristics. The possible significance of these wide differences among strains presumed to be closely related is considered in the Discussion. 相似文献
496.
JOSEPH A. ROSEBROCK CURTIS L. PARKER TIMOTHY E. KUTE 《Differentiation; research in biological diversity》1981,19(1-3):168-178
This investigation was to study the biosynthesis of 3 H-labeled alpha-fetoprotein (AFP) by cultured mouse hepatoma (HEPA-2) cells. Both the function and regulation of this oncodevelopmental gene are unknown. However, evidence indicates that mechanisms controlling the expression of AFP involve aspects of both normal embryonic development and neoplastic transformation. The secretion of AFP was analyzed during different phases of the growth cycle to provide information on AFP production using standard culture conditions. The highest rate of secretion occurred during the stationary phase, followed by the late logarithmic and early logarithmic phases of growth, respectively. The production of AFP was then determined following the addition of glucocorticords and estrogens in an attempt to understand hormonal factors that may be involved. Studies utilizing estradiol-17β indicated that the secretion of AFP did not appear to be sensitive to this steroid even though sucrose density gradient analysis of HEPA-2 cytosol, for estrogenic receptors, revealed competitive binding moieties in the 8S and 4S regions of the gradient. In contrast, the secretion of the total complement of proteins, including AFP, was significantly stimulated by the glucocorticords, dexamethasone and corticosterone. Analysis of HEPA-2 cytosol for glucocorticord receptors revealed binding components in the 7S and 3–4S regions of the gradient. The 3 H-dexamethasone binding appeared to be stereospecific since nonlabeled dexamethasone, but not nonlabeled estradiol-17β, effectively displaced the bound radioactivity. The glucocorticoid-binding component in HEPA-2 therefore displayed characteristics reported for glucocorticord receptors in normal liver and other hepatomas. 相似文献
497.
Inhibition of RNA Polymerase by Streptolydigin 总被引:1,自引:0,他引:1
TWO antibiotics inhibit RNA synthesis by interacting directly with RNA polymerase. The rifamycin series1–3 inhibit before RNA chain initiation and are without apparent effect during polymerization. Streptolydigin, however, inhibits initiation and chain elongation4–9. Using the d(A-T)-directed reaction as a model system10, we will show that streptolydigin stabilizes the polymerase-template interaction. 相似文献
498.
499.
Bacteria have been used for years as flavor compound sources.However, little attention has been given to fungal sources forsuch compounds. This brief review was not intended to coverall aspects of flavor compound formation from all types of fungiand food systems. However, representative data are presentedto demonstrate that a wide variety of compounds possessing uniqueand potent flavor properties have been isolated as naturallyoccurring constituents of fungi. 相似文献
500.
Mature cells of several algal species (Protosiphon bo-tryoides, Chlorococcum echinozygotum, Asterococcus superbus, Chlamydomonas reinhardtii, Chlorella pyrenoidota) that will grow in a strontium-substitution for calcium are larger and more highly vacuolated than control cells in calcium. In logarithmic phase cultures average cell size of cells in strontium-replacement medium is greater than for control cells in calcium. The water content of strontium-replacement cells is indicated to be greater than of control cells. Mechanisms whereby water content and cell size differences may become established are discussed. 相似文献