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331.
332.
Karita Haapasalo Hanna Jarva Tuula Siljander Wezenet Tewodros Jaana Vuopio‐Varkila T. Sakari Jokiranta 《Molecular microbiology》2012,83(6):1285-1286
The mechanisms driving bacterial chromosome segregation remain poorly characterized. While a number of factors influencing chromosome segregation have been described in recent years, none of them appeared to play an essential role in the process comparable to the eukaryotic centromere/spindle complex. The research community involved in bacterial chromosome was becoming familiar with the fact that bacteria have selected multiple redundant systems to ensure correct chromosome segregation. Over the past few years a new perspective came out that entropic forces generated by the confinement of the chromosome in the crowded nucleoid shell could be sufficient to segregate the chromosome. The segregating factors would only be required to create adequate conditions for entropy to do its job. In the article by Yazdi et al. ( 2012 ) in this issue of Molecular Microbiology, this model was challenged experimentally in live Escherichia coli cells. A Fis–GFP fusion was used to follow nucleoid choreography and analyse it from a polymer physics perspective. Their results suggest strongly that E. coli nucleoids behave as self‐adherent polymers. Such a structuring and the specific segregation patterns observed do not support an entropic like segregation model. Are we back to the pre‐entropic era? 相似文献
333.
334.
Matti Jalasvuori Jaana K. H. Bamford 《Origins of life and evolution of the biosphere》2008,38(2):165-181
Viruses and cells co-evolve due to the parasitic nature of viruses. Yet there are no models suggesting how the unicellular
organisms and their viruses might co-evolve structurally. Here, in this study, we plunge into this unexplored field from a
wide perspective and try to describe some of the intriguing ways in which viruses may have shaped the cellular life forms
on the ancient Earth. At first we propose a scenario where viruses act as a driving force in the emergence of bacterial cell
walls by providing favorable intermediates for the otherwise improbable steps in the cell wall generation. We also discuss
the role of viruses in the evolution of cell surface components such as receptors and second membranes. Finally we focus on
hypothetical proto-viruses, the selfish abusers of the RNA-world, in explaining some of the very early stages in the origin
and evolution of life. Proto-viruses may be responsible for creating the first true cells in order to support their selfish
needs. In this model we also suggest a logical pathway to explaining the emergence of modern viruses. 相似文献
335.
Jaana M. Kusnetsov Hannele R. Jousimies-Somer Aino I. Nevalainen P. J. Martikainen 《Journal of applied microbiology》1994,76(2):155-162
The efficacy of a non-selective medium and two selective media were compared for the isolation of legionellas from water samples. The effect of acid wash treatment for decontamination of the water samples on the isolation frequency of legionellas was also studied. The 236 samples were taken from cooling, humidifying and drinking water systems; 21% were legionella-positive when inoculated directly on modified Wadowsky-Yee (MWY) medium and 26% were positive when concentrated (x 200) before cultivation on MWY or CCVC media. Inoculation on MWY medium after concentration followed by decontamination by the acid-wash technique gave the highest isolation frequency (31%). The lowest frequency (8%) was found with the non-selective BCYEα medium. An isolation frequency of 28% was achieved with the BCYEα medium after concentration and acid-wash treatment of the samples. Forty per cent of the samples were positive for legionellas when the results from all the culture methods were combined. Not all the legionella-positive samples were identified by a single culture method. Ninety-three of the 95 positive samples were detected with the two best combinations of three culture methods. The best culture method for detecting legionellas depended on the source of the water sample. Some water quality characteristics, like temperature and organic matter content, affected the isolation frequency of Legionella spp. 相似文献
336.
Jaana Vormisto 《Economic botany》2002,56(1):27-40
Astrocaryum chambira Burret is a palm that provides edible fruits and fibers for making handicrafts. This study focused on the fiber products (hammocks and bags) made by the Bora in the Peruvian Amazonia. Making chambira handicrafts consists of several different phases. Handicrafts are marketed to tourists, river traders, or shopkeepers in the city of Iquitos. Villagers travel actively to sell their products because of the remote location of the village from the market. The prices received by producers were extremely low when considering the amount of work, but the prices were low also in other steps (middleman, tourist). Still, chambira works provide an important source of income for villagers. The greater abundance ofA. chambira in secondary forest compared with the primary forest indicates that it has potential for agroforestry. Agroforestry systems can provide a sustainable way to use land in the rainforest areas in NE Peru, and in this system nontimber forest products may have an important role. 相似文献
337.
Flow cytometry was used to examine the patterns of somatic polyploidyand to determine the haploid genome sizes in Daphnia. The averageproportions of polyploid nuclei among adult animals of D.pulex,D.longispina, D.pulex x D.longispina and D.magna equalled 27,24, 24 and 24%, respectively. Both interclonal and developmentallyregulated variation were observed in the level of somatic polyploidy.Adult animals expressed more extensive polyploidy than did juveniles.The estimates of the haploid genome sizes (C values) of D.pulex,D.longispina, D.pulex x D.longispina and D.magna equalled 0.32,0.27, 0.26 and 0.37 pg, respectively. These are the smallestgenomes reported in crustaceans. Apparently, somatic polyploidycompensates for the loss of genetic material and gives riseto genetic plasticity which may contribute to the considerablelevel of phenotypic plasticity observed in Daphina. 相似文献
338.
Jaana M?nnik Daniel E. Castillo Da Yang George Siopsis Jaan M?nnik 《Nucleic acids research》2016,44(3):1216-1226
Despite extensive research over several decades, a comprehensive view of how the Escherichia coli chromosome is organized within the nucleoid, and how two daughter chromosomes segregate has yet to emerge. Here we investigate the role of the MatP, ZapA and ZapB proteins in organizing the replication terminus (Ter) region and in the chromosomal segregation process. Quantitative image analysis of the fluorescently labeled Ter region shows that the replication terminus attaches to the divisome in a single segment along the perimeter of the cell in a MatP, ZapA and ZapB-dependent manner. The attachment does not significantly affect the bulk chromosome segregation in slow growth conditions. With or without the attachment, two chromosomal masses separate from each other at a speed comparable to the cell growth. The separation starts even before the replication terminus region positions itself at the center of the nucleoid. Modeling of the segregation based on conformational entropy correctly predicts the positioning of the replication terminus region within the nucleoid. However, the model produces a distinctly different chromosomal density distribution than the experiment, indicating that the conformational entropy plays a limited role in segregating the chromosomes in the late stages of replication. 相似文献
339.
Lipid droplets are dynamic organelles that can be found in most eukaryotic and certain prokaryotic cells. Structurally, the droplets consist of a core of neutral lipids surrounded by a phospholipid monolayer. One of the most useful techniques in determining the cellular roles of droplets has been proteomic identification of bound proteins, which can be isolated along with the droplets. Here, two methods are described to isolate lipid droplets and their bound proteins from two wide-ranging eukaryotes: fission yeast and human placental villous cells. Although both techniques have differences, the main method - density gradient centrifugation - is shared by both preparations. This shows the wide applicability of the presented droplet isolation techniques.In the first protocol, yeast cells are converted into spheroplasts by enzymatic digestion of their cell walls. The resulting spheroplasts are then gently lysed in a loose-fitting homogenizer. Ficoll is added to the lysate to provide a density gradient, and the mixture is centrifuged three times. After the first spin, the lipid droplets are localized to the white-colored floating layer of the centrifuge tubes along with the endoplasmic reticulum (ER), the plasma membrane, and vacuoles. Two subsequent spins are used to remove these other three organelles. The result is a layer that has only droplets and bound proteins.In the second protocol, placental villous cells are isolated from human term placentas by enzymatic digestion with trypsin and DNase I. The cells are homogenized in a loose-fitting homogenizer. Low-speed and medium-speed centrifugation steps are used to remove unbroken cells, cellular debris, nuclei, and mitochondria. Sucrose is added to the homogenate to provide a density gradient and the mixture is centrifuged to separate the lipid droplets from the other cellular fractions.The purity of the lipid droplets in both protocols is confirmed by Western Blot analysis. The droplet fractions from both preps are suitable for subsequent proteomic and lipidomic analysis. 相似文献