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1.
2.
The fine structure of protonephridia in Gnathostomulida and their comparison within Bilateria 总被引:1,自引:0,他引:1
Volker Lammert 《Zoomorphology》1985,105(5):308-316
Summary The fine structure of the protonephridia of Haplognathia rosea (Filospermoidea) and Gnathostomula paradoxa (Bursovaginoidea) is described. Each protonephridium consists of three different cells: (1) a monociliated terminal cell which constitutes the filtration area, (2) a nonciliated canal cell showing a special protonephridial outlet system, and (3) an intraepidermal cell — the nephroporus cell — constituting the nephroporus. The protonephridia are arranged serially. There is no canal system connecting the protonephridial units.Protonephridial characters in other Bilateria are considered. The pattern of characters in the protonephridia in the last common gnathostomulid stem species and presumed apomorphies in the protonephridia of the Gnathostomulida investigated are discussed.Abbreviations used in figures
ac
acessory centriole
-
AC
additional epidermal cell
-
bb
basal body
-
bl
basal lamina
-
bm
bundle of microvilli
-
c
cilium
-
cc
cilium duct cell
-
cd
cilium duct
-
cr
ciliary rootlet
-
crs
structures resembling ciliary rootlets
-
di
diplosome
-
ds
desmosome
-
dy
dictyosome
-
f
filtration area
-
g
granules
-
m
mitochondrium
-
mv
microvillus
-
n
nucleus
-
NC
nephroporus cell
-
np
nephroporus
-
oc
outlet canal
-
TC
terminal cell
-
tl
tubules of lacunar system 相似文献
3.
Inhibition of DNA replication by transformation in a Haemophilus influenzae mutant carrying an altered Rec-1 protein. 总被引:2,自引:2,他引:0 下载免费PDF全文
In the HM5 mutant of Haemophilus influenzae, which carries a mutation in the rec-1 gene region and in which the replication of donor-recipient DNA complexes formed in transformation is inhibited, the transformation frequency could be greatly enhanced by inhibition of protein synthesis during transformation, indicating that transformation in the HM5 mutant induces the synthesis of a protein that inhibits the replication of the donor-recipient DNA complexes. This induction occurred in an early step of the recombination. Synthesis of the wild-type Rec-1 protein after transformation of the HM5 mutant with wild-type DNA could diminish the inhibiting effect on DNA replication. The HM5 mutant synthesized an altered Rec-1 protein (molecular weight, 38,000) whose pI differed from that of the wild type. As a result of the mutation in the rec-1 gene, two other proteins (molecular weights, 37,500 and 43,000) are lacking in the HM5 mutant. 相似文献
4.
Adsorptive pinocytosis of 125I-labelled lactate dehydrogenase isoenzymes H4 and M4 by rat yolk sacs incubated in vitro. 下载免费PDF全文
The pinocytic uptake of 125I-labelled porcine lactate dehydrogenase isoenzymes H4 and M4 by 17.5-day rat visceral yolk sac incubated in vitro was saturable and binding obeyed Michaelis-Menten kinetics. The uptake characteristics of the two isoenzymes were very similar. For the H4 and the M4 isoenzymes, the dissociation constants of the protein-plasma-membrane complex were 0.62 microM and 0.84 microM respectively, and the maximum rates of uptake 0.13 and 0.26 nmol/mg of yolk-sac protein per h respectively. These findings contrast with those from studies in vivo, which show the M4 form is taken up by rat liver sinusoidal cells at a much higher rate than the H4 form, and point to different recognition systems for the adsorptive pinocytosis of simple non-conjugate proteins in yolk-sac epithelial cells and liver sinusoidal cells. Competition experiments indicate that binding of the H4 isoenzyme to the yolk-sac cells is restricted to hydrophobic interactions, whereas the binding of the M4 isoenzyme involves hydrophobic as well as positively charged sites on the protein molecules. 相似文献
5.
6.
Cloning, sequencing, and expression of Bacillus subtilis genes involved in ATP-dependent nuclease synthesis. 下载免费PDF全文
The genes encoding the subunits of the Bacillus subtilis ATP-dependent nuclease (add genes) have been cloned. The genes were located on an 8.8-kb SalI-SmaI chromosomal DNA fragment. Transformants of a recBCD deletion mutant of Escherichia coli with plasmid pGV1 carrying this DNA fragment showed ATP-dependent nuclease activity. Three open reading frames were identified on the 8.8-kb SalI-SmaI fragment, which could encode three proteins with molecular masses of 135 (AddB protein), 141 (AddA protein), and 28 kDa. Only the AddB and AddA proteins are required for ATP-dependent exonuclease activity. Both the AddB and AddA proteins contained a conserved amino acid sequence for ATP binding. In the AddA protein, a number of small regions were present showing a high degree of sequence similarity with regions in the E. coli RecB protein. The AddA protein contained six conserved motifs which were also present in the E. coli helicase II (UvrD protein) and the Rep helicase, suggesting that these motifs are involved in the DNA unwinding activity of the enzyme. When linked to the T7 promoter, a high level of expression was obtained in E. coli. 相似文献
7.
Wolfgang Schuhmann Roland Lammert Martin H mmerle Hanns-Ludwig Schmidt 《Biosensors & bioelectronics》1991,6(8):689-697
The electrocatalytic oxidation of NADH, ascorbate, urate, xanthine and H2O2 at different polypyrrole electrodes has been investigated. The conducting polymer was grown on platinum, glassy carbon, or graphite electrodes and modified by means of enclosed redox-active anions or other redox-active compounds covalently bound to either the N- or the β-position of the pyrrole. Copolymers of pyrrole and N-substituted pyrrole derivatives of chloranil or 2,3-dicholoro-1,4-naphthoquinone showed outstanding electrocatalytic properties for the oxidation of NADH. The application of these electrodes in amperometric steady-state measurements or flow-injection systems in combination with dehydrogenase reactions has been possible. 相似文献
8.
Effect of ethylenediaminetetraacetic acid on deoxyribonucleic acid entry and recombination in transformation of a wild-type strain and a rec-1 mutant of Haemophilus influenzae 总被引:2,自引:1,他引:1 下载免费PDF全文
In transformation of Haemophilus influenzae, donor deoxyribonucleic acid (DNA) enters into competent cells in the presence of ethylenediaminetetraacetic acid (EDTA), which prevents the formation of single stranded regions in the donor DNA that has entered. If after entry of DNA the recipient cells were first incubated at 17 degrees C and then at 37 degrees C in the continuous presence of EDTA, almost no integration occurred. On the other hand, if after entry of DNA the cells were incubated first at 17 degrees C in the absence of EDTA, allowing the generation of single-stranded regions (integration is blocked at this temperature), and then at 37 degrees C in the presence of EDTA, donor-recipient DNA complexes were formed. These results suggest that single-stranded regions are required for integration. Integration to completion was strongly inhibited by EDTA. In a rec-1 mutant of H. influenzae no donor-recipient DNA complexes carrying recombinant-type activity were formed during incubation at 37 degrees C in the absence of EDTA. If rec-1 cells were incubated at 37 degrees C in the presence of EDTA, which strongly inhibited breakdown of DNA, donor-recipient DNA complexes were formed if previously single-stranded regions in the donor DNA that had entered were generated by incubation at 17 degrees C in the absence of EDTA. This suggests that the rec-1 protein protects the initial donor-recipient DNA complex against degradation, so that further steps in the recombination process can proceed. 相似文献
9.
Aspects of protein structure determining endocytosis of proteins by sinusoidal rat liver cells in vivo have been studied, using cross-linked or aggregated derivatives of bovine pancreatic ribonuclease A (labelled with 125I) as probes. Ribonuclease was cross-linked by reaction with dimethylsuberimidate, a way of modification that does not change the charge of the protein. Monomer, dimer and polymer fractions were isolated by gel filtration and characterized in respect of size and number of amino groups modified. Maintenance of enzyme activity, stability of disulfide bonds, and lack of susceptibility to endoproteases showed that the cross-linking procedure did not result in gross conformational changes of the ribonuclease molecules. Monomer, dimer and polymer fractions were injected into nephrectomized rats and plasma clearance and uptake in liver and spleen were determined. About 30% of the injected polymer fraction was found in liver 15 min after injection; for dimer and monomer fractions values of 6% and 2% of the dose were found. Similar differences were found in spleen. Autoradiography, cell isolation, and subcellular fractionation showed that in liver the radioactive proteins were taken up in lysosomes of sinusoidal cells. Similar results were obtained with fractions of aggregated ribonuclease prepared by freeze-drying the protein from 50% acetic acid. Our results demonstrate that the rate of uptake of the ribonuclease derivatives is positively correlated with the size of the molecules. Similarity of the results obtained with cross-linked and aggregated fractions suggests that the number of ribonuclease 'subunits'/molecule, rather than the procedures used to prepare the polymers, determine the rate of uptake by liver and spleen. 相似文献
10.
T Kooistra A M Duursma M K Bijsterbosch J M Bouma M Gruber 《Biochimica et biophysica acta》1979,587(2):299-311
Experiments presented in this paper suggest that sinusoidal rat liver cells recognize basic groups on proteins and that this recognition results in endocytosis of the proteins. Evidence for involvement of basic groups was obtained in two ways. Firstly, we changed the positively charged amino groups of the cross-linked ribonuclease molecules to neutral or negative by acetylation or succinylation, respectively. The modified proteins did not contain easily reducible disulfide bonds and they were not very sensitive to endoproteases, suggesting that they were not denatured by the acetylation procedures. Acetylation and succinylation reduced uptake of the injected cross-linked ribonuclease derivatives by liver and spleen and abolished their rapid clearance from plasma. In nephrectomized rats about 75% of the polymer, 36% of the acetylated polymer and 32% of the succinylated polymer were endocytosed by liver after 6 h. For the dimer fractions these values were 59%, 23% and 27%, respectively. Autoradiography and subcellular fractionation of liver 30 min post-injection localized the acetylated polymer in the lysosomal/microsomal fraction of sinusoidal liver cells, probably endothelial cells. Secondly, a positive correlation was found between binding of a number of ribonuclease derivatives to the cation exchanger SP-Sephadex G-25 and the rate of endocytosis by sinusoidal liver cells. 相似文献