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21.
Julius A. Kieser 《Primates; journal of primatology》1990,31(2):273-281
Static adult craniometric allometry was evaluated in a sample of 66Otolemur crassicaudatus skulls (34 males, 32 females). Although cranial measures were equally well correlated to skull length in males and females,
there were noteworthy differences in the exponential values between the sexes. These results underlined the need for caution
when allometric analyses are based on pooled data. From the cranial allometric analyses it is concluded that the longer the
skull, the shorter and the narrower the maxilla, and the broader the bizygomatic distance. Although cranial length increased
proportionately to the increase in skull length, the cranial width in females was positively allometric whilst in males it
was negatively allometric. Allometric analyses of mandibular dimensions suggest that larger animals will have proportionately
longer mandibulae, which will, in turn, be relatively wider across the gonia, yet shallower behind the first molars. It is
postulated that the disproportionate widening of the zygomata might be related to the widening across the gonia. 相似文献
22.
23.
Isolation of the putative structural gene for the lysine-arginine-cleaving endopeptidase required for processing of yeast prepro-alpha-factor 总被引:85,自引:0,他引:85
S. cerevisiae kex2 mutants are defective for the production of two biologically active secreted peptides: killer toxin and the mating pheromone, alpha-factor. Both molecules are excised from larger precursor polypeptides. In normal cells, the alpha-factor precursor is core-glycosylated and proteolytically processed intracellularly. In kex2 mutants, however, prepro-alpha-factor is not proteolytically cleaved and is secreted in a highly glycosylated form. All kex2 mutants examined (three independent alleles) lack a Zn++-sensitive membrane-associated endopeptidase with specificity for cleaving on the carboxyl side of a pair of basic residues. Absence of this activity cosegregates with the other phenotypes of a kex2 lesion in genetic crosses. The normal KEX2 gene was isolated by complementation of three of the phenotypes conferred by the kex2-1 mutation. The cloned DNA, either on a multicopy plasmid or integrated into the genome, restores both enzymatic activity in vitro and the normal pattern of proteolytic processing and glycosylation of prepro-alpha-factor in vivo. Gene dosage effects suggest that KEX2 is the structural gene for the endopeptidase. 相似文献
24.
25.
André B. Borle Takashi Uchikawa Julius H. Anderson 《The Journal of membrane biology》1982,68(1):37-46
Summary Stimulations or inhibitions by various agents of45Ca efflux from prelabeled cells or tissues display distinct and reproducible profile patterns when the results are plotted against time as fractional efflux ratios (FER). FER is the fractional efflux of45Ca from stimulated cells divided by the fractional efflux from a control unstimulated group. These profile patterns fall into three categories: peak patterns, exponential patterns, and mixed patterns. Each category can be positive (stimulation) or negative (inhibition). The interpretation of these profiles is difficult because45Ca efflux depends on three variables: the rate of calcium transport out of the cell, the specific activity of the cell compartment from which the calcium originates, and the concentration of free calcium in this compartment. A computer model based on data obtained by kinetic analyses of45Ca desaturation curves and consisting of two distinct intracellular pools was designed to follow the concentration of the traced substance (40Ca), the tracer (45Ca), and the specific activity of each compartment before, during, and after the stimulation or the inhibition of calcium fluxes at various pool boundaries. The computer model can reproduce all the FER profiles obtained experimentally and bring information which may be helpful to the interpretation of this type of data. Some predictions of the model were tested experimentally, and the results support the views that a peak pattern may reflect a sustained change in calcium transport across the plasma membrane, that an exponential pattern arises from calcium mobilization from an internal subcellular pool, and that a mixed pattern may be caused by a simultaneous change in calcium fluxes at both compartment boundaries. 相似文献
26.
Paul Nieuwenhuysen Julius Clauwaert 《Journal of biochemical and biophysical methods》1981,5(5):279-286
It is impossible to measure the diffusion coefficient of macromolecules directly and accurately by quasi—elastic light scattering, when aggregates cannot be eliminated from the solutions to be investigated. Nevertheless, a simple method can be applied to overcome this problem in many cases. Aggregates are separated from the monomeric macromolecules by rate-zonal sedimentation in a CsCl density gradient in a transparent centrifugation tube; the monomers are then located by laser light scattering intensity measurements; photon correlation spectroscopy of the scattered light finally yields their diffusion coefficient. The viscosity of aqueous CsCl solutions at different temperatures and concentrations allows a good separation by centrifugation and a low uncertainty in the reduction of the measured diffusion coefficient to standard conditions.The application of the method to eukaryotic large ribosomal subunits is described as an example. 相似文献
27.
The molecular weight of Artemia ribosomes, as determined from their refractive-index increment and light-scattering intensity 下载免费PDF全文
Cytoplasmic ribosomes were isolated from the cryptobiotic embryos of the brine shrimp Artemia salina. Measurements of their refractive-index increments and light-scattering intensities give a value for their molecular weight of (3.4±0.2)×106. 相似文献
28.
On integrating experimental data published previously, the following picture of the mitochondrial adenine nucleotide (AdN) translocation system is being presented: 1. The AdN translocation system serves not only to transport ATP synthesized within mitochondria into the cytosol but also to transport cytosolic ATP into the mitochondria when oxidative phosphorylation is not functioning. 2. The AdN translocator is coded for by nuclear genes and the mitochondrial protein synthesis is not involved in its formation. 3. The AdN translocation system must be preserved and functioning even in cells which could dispense with oxidative phosphorylation. It assures appropriate concentrations of intramitochondrial ATP. 4. The intramitochondrial ATP is required for normal replication of mitochondrial DNA. Tis supports the view that the mitochondrion is a self-replicating semi-autonomous organelle. 5. The appropriate concentration of ATP must be present in mitochondria to make possible cell growth or multiplication. This points to a direct or indirect role of mitochondria in the control of cell proliferation. 相似文献
29.
Elaine J. Davis Joel M. Blatt Eva K. Henderson Joseph J. Whittaker Julius H. Jackson 《Molecular & general genetics : MGG》1977,156(3):239-249
Summary Spontaneous mutants (146) of Escherichia coli K-12 were selected that were resistant to inhibition of growth by 1.2 mM L-valine (Valr). The Valr isolates, containing acetohydroxy acid synthase resistant to feedback inhibition by L-valine (AHASr), were classed according to cotransduction of the mutation with leu. Several mutations resulting in an AHASr phenotype were found to be cotransducible with glyA. However, no mutations causing a Valr phenotype were linked to ilv. AHAS activity was more closely examined in representatives of three classes of mutants with Valr linked to leu, labeled ilv-660, ilv-661, and ilv-662. The ilvE503 allele in E. coli K-12, known to cause a two- to three-fold derepression of AHAS, was found to affect regulation of synthesis of both valine-sensitive AHAS (AHASs) and AHASr in the mutants containing ilv-660 and ilv-661, whereas it affected repression of AHASs, only, in the mutant containing ilv-662. Further, both AHASs and AHASr in the ilv-661 mutant were repressed by valine, whereas valine did not repress AHASr synthesis in the strain carrying ilv-660 and only partially repressed AHASr in the strain carrying ilv-662. Unexpectedly, AHASr synthesis in strains carrying ilv-660 or ilv-662 was repressible by leucine. The ilv-660 locus appears to be similar in position to ilvH and encodes a product that confers valine-sensitivity upon AHAS activity in the wild-type E. coli K-12. The ilv-660 and ilv-662 loci may normally encode products that influence both the feedback sensitivity of AHAS and control of AHAS biosynthesis. 相似文献
30.
Identification and Properties of Methyltransferases That Synthesize Phosphatidylcholine in Rat Brain Synaptosomes 总被引:18,自引:12,他引:6
Abstract: Rat brain was found to enzymatically methylate phospholipids to form phosphatidylcholine with S -adenosyl- l -methionine serving as the methyl donor. Methyltransferase activity was localized in the microsomes and synaptosomes. In synaptosomes, at least two enzymes were found to be involved in the formation of phosphatidylcholine. The first methyltransferase which catalyzes the methylation of phosphatidylethanolamine to form phosphatidyl- N -monomethylethanolamine was found to have a pH optimum of 7.5, a low Km for 5-adenosyl- l -methionine and a partial requirement for Mg2 . Methyltransferase I is tightly bound to membranes. The second methyltransferase (II) catalyzes the successive methylations of phosphatidyl- N -monomethylethanolamine to phosphatidyl- N , N -dimethylethanolamine and then to phosphatidylcholine. In contrast to methyltransferase I, methyltransferase II has a pH optimum of 10.5, a high apparent Km for S -adenosyl- l -methionine and no requirement for Mg2 . Methyltransferase II is easily solubilized by sonication. The highest specific activity for both enzymes was found in the synaptosomal plasma membrane. 相似文献