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61.
We used the repetitive character of transposable elements to isolate a
non-LTR retrotransposon in Drosophila subobscura. bilbo, as we have called
it, has homology to TRIM and LOA elements. Sequence analysis showed a 5'
untranslated region (UTR), an open reading frame (ORF) with no RNA-binding
domains, a downstream ORF that had structural homology to that of the I
factor, and, finally, a 3' UTR which ended in several 5-nt repeats. The
results of our phylogenetic and structural analyses shed light on the
evolution of Drosophila non-LTR retrotransposons and support the hypothesis
that an ancestor of these elements was structurally complex.
相似文献
62.
Variation of physico-chemical parameters along a river transect through the Okavango Delta,Botswana 总被引:1,自引:0,他引:1
The Okavango Delta depends on water quantity and quality to sustain its ecosystem services. Whereas many studies have been carried out on its hydrology, few have been done on water quality in the delta. Water pH, electrical conductivity (EC), dissolved oxygen (DO), turbidity, total suspended solids (TSS) and dissolved organic carbon (DOC) were monitored at 10 sites along the Okavango–Boro–Thamalakane–Lake Ngami system almost fortnightly from June 2008 to June 2010. Water quality in the delta was generally good, despite high evapotranspiration rates which would normally produce very saline waters. Electrical conductivity and water temperature increased with distance from Mohembo to Lake Ngami, the former most likely due to evapoconcentration. In contrast, pH, DO, turbidity and TSS decreased with distance from Mohembo to Boro at the lower end of the seasonal floodplain, before increasing again to Lake Ngami. Dissolved oxygen and TSS most likely declined due to biological uptake and particle sedimentation, respectively. Strong and significant relationships were observed between TSS and turbidity and between DOC and EC, indicating that turbidity and EC could be useful proxies for routine estimations of TSS and DOC, respectively, in the delta. 相似文献
63.
The suitability of using macroinvertebrates as bioindicators of stream water quality was tested in the Mkondoa River in an agricultural area at Kilosa, using the rapid bioassessment protocol. The family biotic index (FBI) showed marked variation in water quality along the stream from values ranging from 4.1 to 5.0 in the upstream reaches, indicating good water quality, 5.3 to 5.5 in the mid-reaches and 6.0 to 6.5 in the lower reaches. The water quality index (WQI) indicated that water quality was fair (77 ± 0.98) in the upstream reach of the Mkondoa, marginal (55 ± 0.86) in the midstream reach and poor (33 ± 0.45) in the downstream reach. There were significant relationships between biological oxygen demand and dissolved oxygen and the occurrence of specific taxa, mainly Chironomus and Caenis. Significant changes in macroinvertebrate abundance were mostly related to changes in water quality. As in other parts of the world, macroinvertebrate communities proved to be good biological indicators of water quality and they should be used as bioindicators in long-term monitoring of this river. 相似文献
64.
Characterization of a xylose-specific antiserum that reacts with the complex asparagine-linked glycans of extracellular and vacuolar glycoproteins 总被引:13,自引:7,他引:6 下载免费PDF全文
Antibodies were raised against carrot (Daucus carota) cell wall β-fructosidase that was either in a native configuration (this serum is called anti-βF1) or chemically deglycosylated (anti-βF2). The two antisera had completely different specificities when tested by immunoblotting. The anti-βF1 serum reacted with β-fructosidase and many other carrot cell wall proteins as well as with many proteins in extracts of bean (Phaseolus vulgaris) cotyledons and tobacco (Nicotiana tabacum) seeds. It did not react with chemically deglycosylated β-fructosidase. The anti-βF1 serum also reacted with the bean vacuolar protein, phytohemagglutinin, but not with deglycosylated phytohemagglutinin. The anti-βF2 serum reacted with both normal and deglycosylated β-fructosidase but not with other proteins. These results indicate that the βF2 antibodies recognize the β-fructosidase polypeptide, while the βF1 antibodies recognize glycan sidechains common to many glycoproteins. We used immunoadsorption on glycoprotein-Sepharose columns and hapten inhibition of immunoblot reactions to characterize the nature of the antigenic site. Antibody binding activity was found to be associated with Man3(Xyl)(GIcNAc)2Fuc, Man3(Xyl)(GIcNAc)2, and Man(Xyl) (GIcNAc)2 glycans, but not with Man3(GIcNAc)2. Treatment of phytohemagglutinin, a glycoprotein with a Man3(Xyl)(GIcNAc)2Fuc glycan, with Charonia lampas β-xylosidase (after treatment with jack-bean α-mannosidase) greatly diminished the binding between the antibodies and phytohemagglutinin. We conclude, therefore, that the antibodies bind primarily to the xyloseβ, 1→ 2mannose structure commonly found in the complex glycans of plant glycoproteins. 相似文献
65.
66.
The high mannose oligosaccharide of phytohemagglutinin is attached to asparagine 12 and the modified oligosaccharide to asparagine 60 总被引:6,自引:2,他引:4 下载免费PDF全文
Phytohemagglutinin, the lectin of the common bean Phaseolus vulgaris, has a high mannose and a modified (fucosylated) oligosaccharide on each polypeptide. Fractionation by high performance liquid chromatography of tryptic digests of [3H]fucose or [3H]glucosamine labeled phytohemagglutinin, followed by amino acid sequencing of the isolated glycopeptides, shows that the high mannose oligosaccharide is attached to Asn12 and the modified oligosaccharide to Asn60 of the protein. In animal glycoproteins, high mannose chains are rarely found at the N-terminal side of complex chains. 相似文献
67.
The biosynthesis of ribonuclease and its accumulation in protein bodies in the cotyledons of mung bean seedlings 总被引:1,自引:0,他引:1
Germination and seedling growth of mung bean are accompanied by a 7- to 10-fold increase in the ribonuclease content of the cotyledons. The increase occurs during the first 4 days of seedling growth and precedes the senescence of the cotyledons. Separation of the RNases in the cotyledons by polyacrylamide gel electrophoresis indicates the presence of several minor bands in seeds imbibed for 24 hr. On the second day of seedling growth a new major band with an Rf of 0.76 is present. In 4- to 5-day old seedlings this major band accounts for nearly all the RNase activity in the tissue. The characteristics of this RNase show that it is a plant ribonuclease I (pH optimum of 5.0; MW 16,000; activity preferentially inhibited by purine nucleotides; no activity toward DNA; no phosphodiesterase activity). When the seedlings are grown in 66% D2O the RNase activity undergoes a density shift of 0.61% indicating that the increase in enzyme activity is due to the de novo synthesis of the enzyme molecules. A method is described for the isolation of protein bodies from protoplasts of storage parenchyma cells. Fractionation of protoplast lysates on Ficoll gradients results in the recovery of a high proportion (75%) of intact protein bodies. On these gradients RNase activity comigrates with α-mannosidase, a protein body marker enzyme indicating that the newly synthesized RNase accumulates in the protein bodies. We suggest that the synthesis of RNase in the cotyledons and its accumulation in the protein bodies indicates that protein bodies may function in the degradation of cellular macromolecules other than the reserves stored within them. 相似文献
68.
69.
Hormonal control of enzyme synthesis: on the mode of action of gibberellic Acid and abscisin in aleurone layers of barley 总被引:55,自引:43,他引:12 下载免费PDF全文
Gibberellic acid (GA) enhances the synthesis of α-amylase and ribonuclease in isolated aleurone layers and this process is inhibited by abscisin. Removal of gibberellic acid in mid-course of α-amylase production results in a slowing down of α-amylase synthesis, suggesting a continued requirement of GA for enzyme synthesis. This is paralleled by a continuous requirement for RNA synthesis. Addition of 6-methylpurine or 8-azaguanine in mid-course results in an inhibition of α-amylase synthesis within 3 to 4 hours. However, actinomycin D added in mid-course is almost without effect. This is not due to its failure to enter the cells, because it does inhibit 14C-uridine incorporation at this stage. Addition of abscisin to aleurone layers which are synthesizing α-amylase results in an inhibition of this synthesis within 2 to 3 hours. Cycloheximide on the other hand inhibits enzyme synthesis immediately upon its addition. These data are consistent with the hypothesis that the expression of the GA effect requires the synthesis of enzyme-specific RNA molecules. The similarity in the kinetics of inhibition between abscisin on the one hand and 8-azaguanine or 6-methylpurine on the other suggests that abscisin may exert its action by inhibiting the synthesis of these enzyme-specific RNA molecules or by preventing their incorporation into an active enzyme-synthesising unit. 相似文献
70.
Alpha-amylase inhibitor, not phytohemagglutinin, explains resistance of common bean seeds to cowpea weevil 下载免费PDF全文
There are claims that phytohemagglutinin (PHA), the lectin of common bean, Phaseolus vulgaris, is toxic when fed to the cowpea weevil, Callosobruchus maculatus, and that PHA serves as the chemical defense against this seed-feeding bruchid beetle (DH Janzen, HB Juster, IE Liener [1976] Science 192: 795-796; AMR Gatehouse, FM Dewey, J Dove, KA Fenton, A Pusztai [1984] J Sci Food Agric 35: 373-380). However, our studies indicate that neither PHA nor its isolectins have detrimental effects when fed to the cowpea weevil. To explain these contradictory results we characterized the commercial lectin source used by A. M. R. Gatehouse, F. M. Dewey, J. Dove, K. A. Fenton, A. Pusztai (1984, J Sci Food Agric 35: 373-380). We demonstrate here that the toxic effects of PHA to cowpea weevil are due to an α-amylase inhibitor contaminant in the commercial preparation. 相似文献