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21.
Binding, internalization and intracellular processing of 125I-epidermal growth factor purified by isoelectric focusing 总被引:1,自引:0,他引:1
B E Magun S R Planck L M Matrisian J S Finch 《Biochemical and biophysical research communications》1982,108(1):299-306
When epidermal growth factor (EGF) which had been extensively purified by HPLC was subjected to iodination with sodium 125iodide, 5 major species of differing isoelectric points were produced. Some of these species bound to rat fibroblasts with different affinities but were internalized with equal efficiency. Examination of the internalized 125I-labelled molecules revealed processing of all the 125I-EGF species to macromolecules with more acidic isoelectric points. The 125I-EGF species with a pI of 4.5 corresponded in electrofocusing behavior with intact non-iodinated EGF. Other EGF species probably represented molecules which were covalently modified as a result of the iodination procedure. 相似文献
22.
Extraction of whole lobes of normal rat liver with dimethyl sulphoxide (DMSO) under N2 gives extracts which contain 5—10 μmol/l·O?2 (50-100 nmol·O?2 per 10 ml extract per 4 g liver; 1.25-2.50 nmol·O?2 per millilitre per gram liver). Evidence for ·O?2 in the extracts is given by: (1) electron spin resonance signals (ESR), (2) differential pulse polarography (DPP), (3) chemiluminescence (CL), and (4) nitroblue tetrazolium reduction (NBT). All tests yield results identical with those obtained with authentic ·O?2. Extraction of ·O?2 is enhanced by tetrabutyl ammonium ion, and is maximal at 1-3 min. These results raise the possibility that substantial amounts of ·O?2 are normally sequestered in protective membranous sites in vivo. 相似文献
23.
A method to investigate the structure of RNA molecules within intact plant tissues has been developed. The RNA structures are analyzed using dimethyl sulfate (DMS), which modifies substituents of adenine and cytosine residues within single-stranded regions of RNA molecules. Reactive sites are identified by primer extension analysis. Using this procedure, an analysis of the secondary structure of the cytoplasmic 18S ribosomal RNA in soybean seedling leaves has been completed. DMS modification data are in good agreement with the phylogenetic structure predicted for soybean 18S rRNA. However, there are a few notable exceptions where residues thought to be involved in double-stranded regions in all 18S rRNAs are strongly modified in soybean leaf samples. These data taken together with the phylogenetic structure suggest that alternate structures may exist in vivo.The further applicability of this technique is demonstrated by comparing the modification pattern obtained in vivo to that obtained in vitro for a particular mRNA molecule encoding the small subunit of ribulose-1,5-bisphosphate carboxylase. The results obtained are compared to a predicted minimum energy secondary structure. The data indicate that the conformation of RNA molecules within the cell may not be reflected in a structural analysis of purified mRNA molecules. 相似文献
24.
K. C. Katsirdakis K. A. Roubelakis-Angelakis 《In vitro cellular & developmental biology. Plant》1992,28(2):90-96
Summary To identify possible reasons that may contribute to recalcitrance in plant protoplasts, the time course of new cell wall deposition
was studied by scanning electron microscopy in protoplasts of a recalcitrant species, the grapevine. Results showed that microfibrils
were developed after 2 days of culture, that complete cell wall formation occurred on Day 6 to 7 of protoplast culture, and
its ultrastructural appearance was identical to that of grapevine leaf-derived callus cells. In addition, a comparative study
was undertaken on [U-14C]glucose uptake and incorporation in ethanol-soluble, cellulosic, and noncellulosic polysaccharide fractions in protoplasts
of grapevine and of a readily regenerating species, tobacco, during culture. There was a significantly higher [U-14C]glucose uptake by tobacco than by grapevine protoplasts. The label distribution in the ethanol-soluble, cellulosic, and
noncellulosic fractions of newly synthesized cell walls differed quantitatively between the two species. In particular, the
labeled glucose incorporated in the noncellulosic cell wall fraction was threefold greater in tobacco than in grapevine protoplasts.
Differences were also revealed in the monosaccharide composition of this fraction between the two species. Addition of dimethyl
sulfoxide to the culture medium resulted in a dramatic increase in [U-14C]glucose uptake by grapevine protoplasts, whereas it exhibited a limited effect in tobacco protoplasts. It showed no effect
on the ultrastructural characteristics of new cell wall nor on the incorporation rate of labeled glucose in the cellulosic
and noncellulosic cell wall fractions. 相似文献
25.
Specific protection of nucleotides in the lac operator from DMS methylation and DNase I nicking by crude bacterial cell extracts 总被引:1,自引:0,他引:1
Crude bacterial cell extracts prepared from an Escherichia coli lacIq strain were shown to protect specific nucleotides in the lac operator from methylation by dimethyl sulfate (DMS) or digestion by DNase I, whereas no protection was observed using extracts prepared from a nearly isogenic lacI- strain. These experiments show that it is not necessary to use purified regulatory proteins in experiments designed to localize sequences on DNA which interact with proteins. Therefore, crude cell extracts should be useful in DNA "footprinting" experiments to define regions of DNA which bind to unknown regulatory proteins. 相似文献
26.
The genetic effects of MNNG, 4NQO and ICR-170 have been compared on 5 different UV-sensitive strains and a standard wild-type strain of Neurospora crassa with regard to inactivation and the induction of forward-mutations at the ad-3A and ad-3B loci. Whereas all UV-sensitive strains (upr-1, uvs-2, uvs-3, uvs-5 and uvs-6) are more sensitive to inactivation by MNNG and ICR-170 than wild-type, only uvs-5 shows survival comparable to wild-type after 4NQO treatment, all other strains are more sensitive to 4NQO. In contrast to the effects on inactivation, a wide variety of effects were found for the induction of ad-3A and ad-3B mutations: higher forward-mutation frequencies than were found in wild-type were obtained after treatment with MNNG or 4NQO for upr-1 and uvs-2, no significant increase over the spontaneous mutation frequency was found with uvs-3 after MNNG, 4NQO or ICR-170 treatment; mutation frequencies comparable to that found in wild-type were obtained with uvs-6 after MNNG, 4NQO or ICR-170 treatment and with upr-1 after ICR-170 treatment. Lower forward-mutation frequencies than were found in wild-type were obtained with uvs-2 after ICR-170 treatment and with uvs-5 after MNNG, 4NQO or ICR-170 treatment. These data clearly show that the process of forward-mutation at the ad-3A and ad-3B loci is under genetic control by mutations at other loci (e.g. upr-1, uvs-2, uvs-3, uvs-5 and uvs-6) and that the effect is markedly mutagen-dependent. 相似文献
27.
Identification of the predominant constituents produced by the plus and the minus strains of Blakeslea trispora is described. The occurrence of xylenes in the volatiles produced by the plus strain is reported. Additionally, production of 3-hydroxy-3-methylbutanal by the plus strain and dimethyl allyl alcohol by the minus strains were confirmed. Isoamyl alcohol, 1-octen-3-ol, 3-octanol and β-phenethyl alcohol were identified in volatiles from both strains. 相似文献
28.
W.W. Hauswirth P.J. Laipis M.E. Gilman T.W. OBrien G.S. Michaels M.A. Rayfield 《Gene》1980,8(2):193-209
Using a physical map of bovine mitochondrial DNA derived from the liver of a single Holstein cow, we have determined the location of the genes specifying the large and small riibosomal RNAs by hybridization analysis and electron microscopic observations of R-loop forms. Also, the position of the origin of DNA replication (D-loop) has been located by electron microscopy. Additionally, the direction of D-loop expansion and the polarity of the large and small ribosomal RNA genes were determined. 相似文献
29.
Collagen-induced platelet aggregation and thromboxane release is inhibited, in a concentration response relationship, by preincubation of gel-filtered platelets with melatonin in the concentration range 430 nM – 4.3 mM. Inhibition of platelet aggregation and thromboxane release also occurs in the presence of indomethacin (4.3 nM – 4.3 mM), a known potent inhibitor of prostaglandin synthesis. Arachidonic acid-induced platelet aggregation and thromboxane release was inhibited in the presence of 4.0 mM melatonin. We therefore propose that inhibition of prostaglandin synthesis maybe the mechanism by which melatonin expresses its activity. Its antigonadotropic activity may result from inhibition of PGE2 synthesis in the hypothalamus and median eminence. 相似文献
30.
An assay method for glyceraldehyde-3-phosphate dehydrogenase in which none of the primary products accumulate and which gives linear kinetics under physiological conditions has been developed. It is based on the use of the 1,3-diphosphoglycerate produced by the enzyme for the formation of NADPH, while the NADH produced is recycled with an auxiliary system. Revised Km values at pH 7.4 for the muscle (rabbit and rat) enzyme are: glyceraldehyde-3-P, 50 μM; NAD, 100 μM; Pi, 10 mM. The rat erythrocyte enzyme gave similar values except for glyceraldehyde-3-P which was 300 μM. Cooperativity for NAD+ tends to be positive but is a variable parameter. 相似文献