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J. Nadarajan E. E. Benson P. Xaba K. Harding A. Lindstrom J. Donaldson C. E. Seal D. Kamoga E. M. G. Agoo N. Li E. King H. W. Pritchard 《The Botanical review》2018,84(3):295-314
Cycads are the most endangered of plant groups based on IUCN Red List assessments; all are in Appendix I or II of CITES, about 40% are within biodiversity ‘hotspots,’ and the call for action to improve their protection is long-standing. We contend that progress in this direction will not be made until there is better understanding of cycad pollen, seed and tissue biology, which at the moment is limited to relatively few (<10%) species. We review what is known about germplasm (seed and pollen) storage and germination, together with recent developments in the application of contemporary technologies to tissues, such as isotype labelling, biomolecular markers and tissue culture. Whilst progress is being made, we conclude that an acceleration of comparative studies is needed to facilitate the integration of in situ and ex situ conservation programmes to better safeguard endangered cycads. 相似文献
954.
Stephen E. Harding Arthur J. Rowe 《International journal of biological macromolecules》1982,4(6):357-361
The general triaxial ellipsoid model for the gross conformation of macromolecules in solution represents a signficiant advance over the previously, almost ubiquitously used ellipsoid of revolution model. A new method is presented which involves the graphical intersection of two triaxial hydrodynamic functions (Λ and R) involving viscosity, sedimentation and fluorescence depolarization. The method is restricted to macromolecules asymmetric enough for the functions to be sufficiently sensitive but not so asymmetric for there to be problems of internal rotations between parts of the macromolecules. The method is illustrated by application to data for neurophysin II monomers and dimers. 相似文献
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A new type of (reduced) point average molecular weight A1, is described. Several interesting properties are developed: (i) weight average molecular weight over the whole cell, number average molecular weight, An (meniscus). In addition, its usefulness in extracting the meniscus concentration, J(a), and in examining heterogeneous systems such as mucus glycoproteins, are discussed. The evaluation and application of requires only simple computational facilities, without the use for large-scale multiple data acquisition and recycling techniques. 相似文献
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We have sequenced a 1307 base pair mouse genomic DNA fragment which contains a histidine tRNA gene. The sequence of the putative mouse histidine tRNA differs from the published sequence of sheep liver histidine tRNA by a single base change in the D-loop. It does not contain an unpaired 5' terminal G residue, as reported for Drosophila and sheep histidine tRNAs. The gene does not contain introns. The 3' flanking region contains a typical RNA polymerase III termination site of 6 consecutive T residues. 523 residues after the 3' end of the his tRNA coding region, the mouse DNA contains a sequence 72% homologous to part of the consensus sequence of the B1 (alu) family. 相似文献
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Clifford Harding Philip Stahl 《Biochemical and biophysical research communications》1983,113(2):650-658
Iron uptake by rat reticulocytes is blocked by 20 mM NH4Cl, while 125I-diferric transferrin (Tf) uptake is relatively unaffected. At pH 5.0 both apo- and diferric Tf bind with high affinity; at pH 7.4 diferric Tf binds avidly, but apoTf binds very poorly. The dissociation rate (4°C) of diferric Tf is extraordinarily slow at pH 5.0 (extrapolated ) and faster at pH 7.4 (). At pH 5.0 apoTf also dissociates slowly (), but at pH 7.4 apoTf exhibits a much faster dissociation rate (). 20 mM NH4Cl slows the release of Tf from cells at 37°C, but the rate of externalization of ligand is unaffected. Ligand dissociation at 37° involves both externalization of receptor-ligand complexes and receptor-ligand separation; the NH4Cl effect may result from an increased fraction of externalized Tf in the differric form which may dissociate more slowly. Receptor-mediated movement of Tf through acid intracellular compartments provides a mechanism to remove iron from Tf and for apoTf to remain receptor-bound for externalization to the cell surface and subsequent dissociation. 相似文献
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Genetic Analysis of Phototropism of Neurospora crassa Perithecial Beaks Using White Collar and Albino Mutants 总被引:12,自引:2,他引:10 下载免费PDF全文
Positive phototropism of perithecial beaks in the fungus Neurospora crassa has been demonstrated. The effect was shown to be mediated by blue light. When mutants (white collar-1 and white collar-2) which are blocked in the light induction of enzymes in the carotenoid biosynthetic pathway were used as the protoperithecial parent in crosses, the resulting perithecial beaks did not show a phototropic response. However, when wild type, albino-1, albino-2, or albino-3 strains were used as the protoperithecial parent, phototropism occurred.
The results show that both photoinduced carotenogenesis and phototropism in N. crassa are controlled by the white collar-1 and white collar-2 loci. Thus, the sensory transduction pathways for the two photoresponses must have some steps in common. The results further support the proposal that the white collar strains are regulatory mutants blocked in the light induction process, whereas the albino-1, albino-2, and albino-3 strains can carry out light induction but have the albino phenotype because they are each defective for a different enzyme in the carotenoid biosynthetic pathway.
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