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排序方式: 共有305条查询结果,搜索用时 15 毫秒
1.
Ronald J.A. Wanders Carlo Van Roermund Cor Lof Alfred J. Meijer 《Analytical biochemistry》1983,129(1):80-87
A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present. 相似文献
2.
Morten Glasø Olav Hilmar Iversen Torstein Hovig 《Virchows Archiv. B, Cell pathology including molecular pathology》1988,56(1):221-235
The nature and significance of so-called dark keratinocytes in the epidermis during chemical carcinogenesis is still a matter
of concern and debate. Based on ultrastructural observations it has been suggested that dark cells most often are shrunken
cells. Reports on skin carcinogenesis, however, claim that dark cells are a sign of ongoing tumor promotion and represent
those stem cells in the epidermis from which the tumors originate. It is therefore important to find out whether these cells
are simply injured and shrunken cells, or vital cells of great importance for carcinogenesis. Dark cells are assumed to be
rich in ribosomes. There is evidence, however, that the observed number of dark cells is highly dependent on tissue fixation.
In the present ultrastructural study, morphometric methods were used to compare the effects of two different fixation procedures
on the amount of cytoplasmic ribosomes in dark cells from both untreated and carcinogen-treated hairless mouse epidermis.
The results show that the ultrastructural features of both dark and clear cells vary considerably with different fixation
procedures. In acetone-treated controls typical dark cells are only observed when the fixative has a lower osmotic activity
than the plasma. With iso-osmolal fixation typical dark cells are not observed. After an abortive two-stage carcinogenesis
treatment, in which a single application of 9,10-dimethyl-l,2-benzanthracene (DMBA) in acetone was followed by a single application
of 12-O-tetradecanoyl-13-acetate (TPA) in acetone, signs of cell injury could be found after both fixation procedures. With
DMBA/TPA and hypo-osmolal fixation the number of dark cells seemed to increase, whereas only signs of cell injury with occurrence
of some heavily altered “clear cells” dominated the picture with iso-osmolal fixation. Morphometry showed that both the numerical
and the volumetric densities of cytoplasmic ribosomes in basal keratinocytes varied most significantly with the fixation procedure
used. The cytoplasmic volumes did not vary in a way that could explain these differences. One might therefore assume that
the number of ribosomes depends on the fixative. Large swelling artifacts occurred when a fixative with low osmotic activity
was used, leading to compression of neighboring cells. Hence, an increased ribosomal density reported previously in dark cells
is probably related to such cell volume artifacts and does not reflect an actually increased quantity of ribosomes. With both
fixation procedures, a single application of DMBA followed by one of TPA appeared to produce an increased number of ribosomes
in basal keratinocytes. When hypo-osmolal fixation was used, however, treatment with DMBA/TPA did not influence the cytoplasmic
volume or the numerical density of ribosomes, in dark cells. This might indicate that so-called dark keratinocytes following
DMBA/TPA treatment are functionally inactive cells that appear more vulnerable than active cells to compression during hypo-osmolal
fixation. 相似文献
3.
Cor Dijkema Robert Pels Rijcken Harry C.M. Kester Jaap Visser 《FEMS microbiology letters》1986,33(1):125-131
Abstract The composition of the polyol pools in Aspergillus nidulans mycelium during active growth on sucrose depends strongly on pH. At pH 2.5, only mannitol is present. A comparison between nitrate- and ammonium-grown cultures shows stimulation of the arabitol content with nitrate a former nitrogen source. When starved mycelium is incubated either with natural-abundance or 13 C-enriched glucose, label appears rapidly in mannitol and arabitol, regardless of the nitrogen source or the pH used. 相似文献
4.
Cor Glas Jolanda C. Kamp Coby Jongsma H. John J. Nijkamp Jacques Hille 《Plant science》1990,70(2):231-241
Lincomycin-resistant calli were induced from both Lycopersicon esculentum and Lycopersicon peruvianum using N-mitroso-N-methylurea (NMU) mutagenesis. From these calli lincomycin-resistant plants were regenerated. For L. peruvianum it was shown that the resistant plants could be divided in two classes with respect to their resistance to lincomycin and its derivative clindamycin. The first class comprised plants which were resistant to 500 mg/l lincomycin and showed no shoot or root formation in the presence of clindamycin; the second class consisted of plants resistant to 2000 mg/l lincomycin and these plants were able to form shoots and roots on clindamycin containing media. Lincomycin is an inhibitor of peptidyltransferase; chloroplast encoded parts of this enzymatic function are sensitive for this antibiotic. Reciprocal crosses between our lincomycin resistant and wild type L. peruvianum plants indicated a maternal inheritance of the mutation. 相似文献
5.
Dog-DAT: a direct agglutination test using stabilized, freeze-dried antigen for the serodiagnosis of canine visceral leishmaniasis 总被引:2,自引:0,他引:2
Linda Oskam Rob J. Slappendel Eef G.M. Beijer Nel C.M. Kroon Cor W. van Ingen Seray Özensoy Yusuf Özbel Wiepko J. Terpstra 《FEMS immunology and medical microbiology》1996,16(3-4):235-239
Abstract We have evaluated the use of an improved direct agglutination test (DAT) based on stable, freeze-dried antigen for the detection of anti- Leishmania antibodies in canine serum samples. With a cut-off value of 1:640, the sensitivity of the DAT was shown to be 100% and the specificity of the test was 98.8%. 相似文献
6.
APC mutation in the alternatively spliced region of exon 9 associated with late onset familial adenomatous polyposis 总被引:11,自引:0,他引:11
Rob B. van der Luijt Hans F. A. Vasen Carli M. J. Tops Cor Breukel Riccardo Fodde P. Meera Khan 《Human genetics》1995,96(6):705-710
Germ-line mutations in the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis (FAP). Genotype-phenotype correlation studies in patients with FAP have demonstrated associations of certain variants of the disease with mutations at specific sites within the APC gene. In a large FAP family, we identified a frameshift mutation located in the alternatively spliced region of exon 9. Phenotypic studies of affected family members showed that the clinical course of FAP was delayed, with gastrointestinal symptoms and death from colorectal carcinoma occurring on average 25 and 20 years later than usual, respectively. The numbers of colorectal adenomas differed markedly among affected individuals and the location of colorectal cancer lay frequently in the proximal colon. Our findings suggest that the exon 9 mutation identified in the pedigree is associated with late onset of FAP. The atypical phenotype may be explained by the site of the mutation in the APC gene. Analysis of the APC protein product indicated that the exon 9 mutation did not result in a detectable truncated APC protein. Given the location of the mutation within an alternatively spliced exon of APC, it is conceivable that normal APC proteins are produced from the mutant allele by alternative splicing. 相似文献
7.
Cor Dijkema Paul A.M. Michels Wil N. Konings 《Archives of biochemistry and biophysics》1980,201(2):403-410
Carotenoid difference spectra were recorded of chromatophores of Rhodopseudomonas sphaeroides energized with low light intensities versus chromatophores under dark conditions. The amplitudes of the peaks and troughs were dependent on the light intensities and the duration of illumination, but the shape of the difference spectra remained constant. Sharp isosbestic points were found at 515, 500, 481, 465, and 452 mm. When potassium-valinomycin-induced diffusion potentials (inside negative) were imposed on the chromatophores “mirror images” of the light-induced difference spectra were recorded with the same isosbestic points and the same positions but different relative amplitudes of the peaks and troughs. The results are explained in terms of changes in the shape of the vibrational splittings of the carotenoid main electronic transition. This could be the result of changes in the fluidity of the environment of the carotenoids upon energization of the membrane. Prolonged periods of illumination with low or high light intensities resulted in irreversible changes of the difference spectra. Short periods of illumination with high light intensities resulted in reversible elevations of the baseline and red shifts of peaks, troughs, and baseline crossings. 相似文献
8.
Summary The heat resistance of Klebsiella pneumoniae, an organism of widespread occurrence in nature has been determined in media containing various amounts of sucrose at temperatures between 47° and 59°C.In the presence of sucrose and at all temperatures the inactivation curves show a fast initial drop (logarithmic phase) in the number of survivors followed by a less rapid one (tail phase). The influence of the sucrose concentration can be described withln k
s = ln k
O – T [sucrose] for media with more than 0.52 mol/l sucrose for the logarithmic as well as for the tail phase of inactivation.The heat-injured cells were recovered on various media to investigate the influence of the presence of small metabolites and nutrients on the shape of the inactivation curves and on the death rate. For cells heated in media without sucrose, the recovery on a rich medium was much better than on a poor one; for cells heated in media with more than 0.26 mol/l sucrose, no difference was observed between the various recovery media.The activation energies as determined on the various media are always nearly the same, which strongly suggests that the critical sites in the heat inactivation were not enzymes playing a key role in the synthesis of small molecules such as amino acids or nucleotides. 相似文献
9.
Extra-pair paternity, testes size and testosterone level in relation to colour polymorphism in the barn owl Tyto alba 总被引:1,自引:0,他引:1
Alexandre Roulin Wendt Müller Lajos Sasvári Cor Dijkstra Anne-Lyse Ducrest Christian Riols Michael Wink Thomas Lubjuhn 《Journal of avian biology》2004,35(6):492-500
In many bird populations, individuals display one of several genetically inherited colour morphs. Colour polymorphism can be maintained by several mechanisms one of which being frequency-dependent selection with colour morphs signalling alternative mating strategies. One morph may be dominant and territorial, and another one adopt a sneaky behaviour to gain access to fertile females. We tested this hypothesis in the barn owl Tyto alba in which coloration varies from reddish-brown to white. This trait is heritable and neither sensitive to the environment in which individuals live nor to body condition. In Switzerland, reddish-brown males were observed to feed their brood at a higher rate and to produce more offspring than white males. This observation lead us to hypothesize that white males may equalise fitness by investing more effort in extra-pair copulations. This hypothesis predicts that lighter coloured males produce more extra-pair young, have larger testes and higher levels of circulating testosterone. However, our results are not consistent with these three predictions. First, paternity analyses of 54 broods with a total of 211 offspring revealed that only one young was not sired by the male that was feeding it. Second, testes size was not correlated with male plumage coloration suggesting that white males are not sexually more active. Finally, in nestlings at the time of feather growth testosterone level was not related to plumage coloration suggesting that this androgen is not required for the expression of this plumage trait. Our study therefore indicates that in the barn owl colour polymorphism plays no role in the probability of producing extra-pair young. 相似文献
10.
Maurice E. Pouw Linda M. Peelen Hester F. Lingsma Daniel Pieter Ewout Steyerberg Cor J. Kalkman Karel G. M. Moons 《PloS one》2013,8(4)