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121.
122.
Readthrough in vitro of the Qβ coat protein terminator codon UGA has been used as an assay for suppression by UGA-suppressor tRNATrp. When the tRNA is covalently crosslinked between 4-thiouracil(8) and cytosine(13) by irradiation at 334 nm, it is found that UGA suppression by this assay is reduced to the low level characteristic of the wild type tRNATrp. In contrast, crosslinking has little effect on incorporation of tryptophan in response to UGG codons. Thus, incorporation of tryptophan during translation of R17 messenger RNA is unaffected by photochemical crosslinking. Furthermore, dilution experiments using R17 mRNA in which tryptophan incorporation is dependent on precharged suppressor Trp-tRNA show that the crosslinked species competes well with non-irradiated tRNA. These results further emphasize the influence on tRNA-ribosome interactions of the region in tRNA around the dihydrouridine arm, where the mutation, in the suppressor is found and the photochemical crosslink is introduced. 相似文献
123.
Beneficial effect of fluorocarbon emulsion media on the function of neuromuscular preparations in vitro
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The effects of liquid fluorocarbons as bathing media were determined by use of in vitro neuromuscular preparations. Rat hemidiaphragms were bathed in either oxygenated fluorocarbon (FC) emulsion or standard oxygenated Krebs solution. Contractile force in response to simple supramaximal nerve stimuli as well as to high frequency stimulation was greater, while twitch:tetanus ratio was smaller in FC emulsion. With such medium, post-tetanic potentiation of contraction was also more consistently observed. Indirectly stimulated diaphragms survived longer in FC emulsion. After cessation of oxygenation, oxygen tension (ρO(2)) of the medium declined more rapidly with Krebs than with FC emulsion; ρO(2) directly correlated with force of contraction. Similarly, in the chick biventer cervicis preparation, FC emulsion enhanced nerve-stimulated force of contraction; returning the preparation to standard Krebs solution reversed this phenomenon. Dose-resonse curves of muscle contraction in response to acetycholine and KCl administration were shifted upward during FC emulsion superfusion. Frequency of miniature endplate potentials was lower in FC emulsion than that observed in Krebs solution, measured from the same cell of the rat diaphragm. Resting membrane potentials were also greater in muscle cells sampled from FC emulsion-bathed preparations. These data suggest that FC emulsion is superior to standard Krebs solution as a bathing medium for in vitro neuromuscular preparations by virtue of the high solubility of oxygen in it. 相似文献
124.
H. Jakob M. E. Buckingham A. Cohen L. Dupont M. Fiszman F. Jacob 《Experimental cell research》1978,114(2):403-408
The effect of temperature on testicular DNA synthesis in mice was studied in vitro. By using cultures of cryptorchid testis, DNA synthesis of differentiated germ cells, such as intermediate and type B spermatogonia and resting primary spermatocytes, was shown to be temperature-sensitive, while that of undifferentiated type A spermatogonia was not. DNA synthesis of non-germ cells was not temperature-sensitive. This temperature sensitivity of germ cells in DNA synthesis may be one cause of the thermal inhibition of germ cell differentiation. 相似文献
125.
Margaret E. Buckingham Arlette Cohen François Gros 《Journal of molecular biology》1976,103(3):611-626
Total poly(A)-containing RNA in different polysomal and supernatant cytoplasmic fractions was analysed after pulse-labelling in dividing myoblasts and fused myotubes. In particular, the peak of 26 S RNA (putative messenger for the large subunit of myosin) is located in a light region of the gradient coinciding with the monosome-trisome fractions prior to fusion, and is found in the heavy polysomes only after fusion. These heavy polysomes are free (i.e. not membrane bound). Treatment of the light part of the polysome gradient with EDTA shows that the 26 S RNA found here does not exist as part of a polysomal complex, but is present as a ribonucleoprotein particle cosedimenting in this region. Previous experiments had indicated that in actively dividing myoblasts 26 S RNA has a relatively short half-life but that it becomes “stable” after the cessation of mitosis just prior to fusion. RNA chase experiments performed in the present study show that the “short-lived” 26 S RNA from dividing myoblasts, which is present as a ribonucleoprotein particle, does not enter the heavy polysomes. In contrast, the more stable 26 S RNA also initially present as a ribonucleoprotein, just prior to and in the early stages of fusion, can be shown by chase experiments to enter the heavy polysomes later in fusion. Hence accumulation of 26 S RNA seems to precede its activation as a messenger. 相似文献
126.
127.
Vestergaard B Sanyal S Roessle M Mora L Buckingham RH Kastrup JS Gajhede M Svergun DI Ehrenberg M 《Molecular cell》2005,20(6):929-938
Bacterial class I release factors (RFs) are seen by cryo-electron microscopy (cryo-EM) to span the distance between the ribosomal decoding and peptidyl transferase centers during translation termination. The compact conformation of bacterial RF1 and RF2 observed in crystal structures will not span this distance, and large structural rearrangements of RFs have been suggested to play an important role in termination. We have collected small-angle X-ray scattering (SAXS) data from E. coli RF1 and from a functionally active truncated RF1 derivative. Theoretical scattering curves, calculated from crystal and cryo-EM structures, were compared with the experimental data, and extensive analyses of alternative conformations were made. Low-resolution models were constructed ab initio, and by rigid-body refinement using RF1 domains. The SAXS data were compatible with the open cryo-EM conformation of ribosome bound RFs and incompatible with the crystal conformation. These conclusions obviate the need for assuming large conformational changes in RFs during termination. 相似文献
128.
Cardiogenesis is an exquisitely sensitive process. Any perturbation in the cells that contribute to the building of the heart leads to cardiac malformations, which frequently result in the death of the embryo. Previously, the myocardium was thought to be derived from a single source of cells. However, the recent identification of a second source of myocardial cells that make an important contribution to the cardiac chambers has modified the classical view of heart formation. It also has an important influence on the interpretation of mutant phenotypes in the mouse, with consequences for the classification and prognosis of human congenital heart defects. 相似文献
129.
Bob?JA?Schijvenaars Barend?Mons Marc?Weeber Martijn?J?Schuemie Erik?M?van Mulligen Hester?M?Wain Jan?A?KorsEmail author 《BMC bioinformatics》2005,6(1):149
Background
Massive text mining of the biological literature holds great promise of relating disparate information and discovering new knowledge. However, disambiguation of gene symbols is a major bottleneck. 相似文献130.
Miguel L Soares Seiki Haraguchi Maria-Elena Torres-Padilla Tibor Kalmar Lee Carpenter Graham Bell Alastair Morrison Christopher JA Ring Neil J Clarke David M Glover Magdalena Zernicka-Goetz 《BMC developmental biology》2005,5(1):1-11