全文获取类型
收费全文 | 168篇 |
免费 | 12篇 |
专业分类
180篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 4篇 |
1967年 | 2篇 |
1966年 | 4篇 |
排序方式: 共有180条查询结果,搜索用时 0 毫秒
101.
Analysis of the chlorophyll biosynthetic system in a chlorophyll b-less barley mutant 总被引:1,自引:0,他引:1
The chlorophyll b-less barley (Hordeum vulgare L.) mutant chlorina 2807 allelic to the well-known barley mutant chlorina f2 was studied. 5-Aminolevulinic acid at saturating concentration (40 mM) was introduced into postetiolated leaves of the mutant and its wild type, and the protochlorophyllide accumulation in the dark was measured. It was found that the activity of the enzyme system transforming 5-aminolevulinic acid into protochlorophyllide was the same in both types of plants. The activity of esterifying enzymes that catalyze attachment of phytol to chlorophyllide was analyzed by infiltration of exogenous chlorophyllides a and b into etiolated leaves. The reaction was shown to have close rates in the mutant and wild-type plants. In very early stages of greening of etiolated leaves, when the apoproteins of the light-harvesting complexes are not yet formed, appearance of chlorophyll b was clearly recorded in the wild-type plants, while in the mutant chlorina 2807 no indications of chlorophyll b were detected in any stage of greening. On the other hand, in the mutant as well as in the wild type an active reverse conversion of chlorophyll b into chlorophyll a was possible. It is concluded that (a) in the mutant chlorina 2807 the ability of the biosynthetic system to transform 5-aminolevulinic acid to chlorophyll a is fully preserved, (b) in the mutant the enzymes converting chlorophyll a into chlorophyll b are most likely absent or damaged, (c) the conversion of chlorophyll a into chlorophyll b and the reverse conversion of chlorophyll b into chlorophyll a are performed by different enzymes. 相似文献
102.
Marker-Dependent Recombination in T4 Bacteriophage. III. Structural Prerequisites for Marker Discrimination 总被引:5,自引:4,他引:1 下载免费PDF全文
Distance- as well as marker-dependence of genetic recombination of bacteriophage T4 was studied in crosses between rIIB mutants with known base sequences. The notion of a "basic recombination," which is the recombination within distances shorter than hybrid DNA length in the absence of mismatch repair and any marker effects, was substantiated. The basic recombination frequency per base pair can serve as an objective parameter (natural constant) of general recombination reflecting its intensity. Comparative studies of the recombination properties of rIIB mutants with various sequence changes in the mutated sites showed that the main factor determining the probability of mismatch repair in recombination heteroduplexes is the length of a continuous heterologous region. A run of A:T pairs immediately adjoining the mismatch appears to stimulate its repair. In the case of mismatches with DNA strands of unequal length, formed by frameshift mutations, the repair is asymmetric, the longer strand (bulge) being preferentially removed. A pathway for mismatch repair including sequential action of endonuclease VII (gp49)----3'----5' exonuclease (gp43)----DNA polymerase (gp43)----DNA ligase (gp30) was proposed. A possible identity of the recombinational mismatch repair mechanism to that operating to produce mutations via sequence conversion is discussed. 相似文献
103.
D N Maianski? V I Shcherbakov Iu M Mirokhanov 《Biulleten' eksperimental'no? biologii i meditsiny》1977,84(11):616-618
In male Wistar rats, weighing 140-160 g, the block of the liver mononuclear phagocyte system (MPS) was carried out by means of "carbonyl iron" (type R-100F, particle size 1-1.5 micron). It was induced 2 hours before or 3 and 18 hours after partial hepatectomy. Iron injection previously or at the early prereplicative regeneration period led to a significant delay of the hepatocyte nucleus labeling and mitotic indices peaks against the background of an overall depression of hepatocyte proliferation. The MPS block during the intensive DNA synthesis by regenerating liver hepatocytes was less effective. The facts testify to the importance of Kupffer's cells in the regulation of the reparative liver regeneration. 相似文献
104.
The ability to simultaneously measure many long-range distances is critical to efficient and accurate determination of protein structures by solid-state NMR (SSNMR). So far, the most common distance constraints for proteins are 13C–15N distances, which are usually measured using the rotational-echo double-resonance (REDOR) technique. However, these measurements are restricted to distances of up to ~?5 Å due to the low gyromagnetic ratios of 15N and 13C. Here we present a robust 2D 13C–19F REDOR experiment to measure multiple distances to ~?10 Å. The technique targets proteins that contain a small number of recombinantly or synthetically incorporated fluorines. The 13C–19F REDOR sequence is combined with 2D 13C–13C correlation to resolve multiple distances in highly 13C-labeled proteins. We show that, at the high magnetic fields which are important for obtaining well resolved 13C spectra, the deleterious effect of the large 19F chemical shift anisotropy for REDOR is ameliorated by fast magic-angle spinning and is further taken into account in numerical simulations. We demonstrate this 2D 13C–13C resolved 13C–19F REDOR technique on 13C, 15N-labeled GB1. A 5-19F-Trp tagged GB1 sample shows the extraction of distances to a single fluorine atom, while a 3-19F-Tyr labeled GB1 sample allows us to evaluate the effects of multi-spin coupling and statistical 19F labeling on distance measurement. Finally, we apply this 2D REDOR experiment to membrane-bound influenza B M2 transmembrane peptide, and show that the distance between the proton-selective histidine residue and the gating tryptophan residue differs from the distances in the solution NMR structure of detergent-bound BM2. This 2D 13C–19F REDOR technique should facilitate SSNMR-based protein structure determination by increasing the measurable distances to the ~?10 Å range. 相似文献
105.
Alexander V. Tyakht Alexander I. Manolov Alexandra V. Kanygina Dmitry S. Ischenko Boris A. Kovarsky Anna S. Popenko Alexander V. Pavlenko Anna V. Elizarova Daria V. Rakitina Julia P. Baikova Valentina G. Ladygina Elena S. Kostryukova Irina Y. Karpova Tatyana A. Semashko Andrei K. Larin Tatyana V. Grigoryeva Mariya N. Sinyagina Sergei Y. Malanin Petr L. Shcherbakov Anastasiya Y. Kharitonova Igor L. Khalif Marina V. Shapina Igor V. Maev Dmitriy N. Andreev Elena A. Belousova Yulia M. Buzunova Dmitry G. Alexeev Vadim M. Govorun 《BMC genomics》2018,19(1):968
Background
Crohn’s disease is associated with gut dysbiosis. Independent studies have shown an increase in the abundance of certain bacterial species, particularly Escherichia coli with the adherent-invasive pathotype, in the gut. The role of these species in this disease needs to be elucidated.Methods
We performed a metagenomic study investigating the gut microbiota of patients with Crohn’s disease. A metagenomic reconstruction of the consensus genome content of the species was used to assess the genetic variability.Results
The abnormal shifts in the microbial community structures in Crohn’s disease were heterogeneous among the patients. The metagenomic data suggested the existence of multiple E. coli strains within individual patients. We discovered that the genetic diversity of the species was high and that only a few samples manifested similarity to the adherent-invasive varieties. The other species demonstrated genetic diversity comparable to that observed in the healthy subjects. Our results were supported by a comparison of the sequenced genomes of isolates from the same microbiota samples and a meta-analysis of published gut metagenomes.Conclusions
The genomic diversity of Crohn’s disease-associated E. coli within and among the patients paves the way towards an understanding of the microbial mechanisms underlying the onset and progression of the Crohn’s disease and the development of new strategies for the prevention and treatment of this disease.106.
Summary. The little-known flower mantis genus Heliomantis Giglio-Tos 1915 (Hymenopodidae) distributed in South and South-Eastern Asia is revised. All species are redescribed. New data on the morphology, distribution and ecology are given, and all known specimens are listed. The lectotype of H. elegans (Navás 1904) is designated. Due to highly divergent morphology, H. latipennis Werner 1930 from Sarawak, Borneo, is transferred to Werneriana n. gen., leaving the genus Heliomantis with the only species, H. elegans (Navás, 1904). 相似文献
107.
E. S. Lobakova I. O. Selyakh L. R. Semenova O. B. Chivkunova P. N. Shcherbakov A. E. Solovchenko 《Moscow University Biological Sciences Bulletin》2016,71(2):102-107
The growth and biomass accumulation of three microalgal strains of Desmodesmus (Scenedesmaceae, Chlorophyceae), 1Рm66В, 2Cl66E, and 3Dp86Е-1, isolated from the White Sea benthic invertebrates were studied under conditions of batch culture in different standard media (BG-11, Prat, Goldberg, Gromov, Tamiya, artificial seawater) and modified media. The culture condition, biomass accumulation, and uptake of nitrate and phosphate were recorded. A significant alkalization of the culture medium up to pH 10 has been observed during a vigorous growth of the microalgae. The most significant biomass accumulation has been recorded in BG-11 (in complete or modified medium with addition of artificial seawater), Tamiya, and Prat media. Addition of seawater did not affect the growth of Desmodesmus sp. in the nitrate-containing media, although that maintained growth of the microalgae in the nitrogen-lacking media without cell aggregation. The BG-11 medium appears suitable for isolation and cultivation of both symbiotic and free-living microalgae by all the tested features. The Prat medium is the best for maintaining the microalgal strains in living collection. 相似文献
108.
Ameres SL Shcherbakov D Nikonova E Piendl W Schroeder R Semrad K 《Nucleic acids research》2007,35(11):3752-3763
RNA chaperone activity is defined as the ability of proteins to either prevent RNA from misfolding or to open up misfolded RNA conformations. One-third of all large ribosomal subunit proteins from E. coli display this activity, with L1 exhibiting one of the highest activities. Here, we demonstrate via the use of in vitro trans- and cis-splicing assays that the RNA chaperone activity of L1 is conserved in all three domains of life. However, thermophilic archaeal L1 proteins do not display RNA chaperone activity under the experimental conditions tested here. Furthermore, L1 does not exhibit RNA chaperone activity when in complexes with its cognate rRNA or mRNA substrates. The evolutionary conservation of the RNA chaperone activity among L1 proteins suggests a functional requirement during ribosome assembly, at least in bacteria, mesophilic archaea and eukarya. Surprisingly, rather than facilitating catalysis, the thermophilic archaeal L1 protein from Methanococcus jannaschii (MjaL1) completely inhibits splicing of the group I thymidylate synthase intron from phage T4. Mutational analysis of MjaL1 excludes the possibility that the inhibitory effect is due to stronger RNA binding. To our knowledge, MjaL1 is the first example of a protein that inhibits group I intron splicing. 相似文献
109.
I. A. Nagovitsyn G. K. Chudinova D. Yu. Shcherbakov V. V. Savranskii G. G. Komissarov 《Biophysics》2007,52(2):153-155
Hydrogen peroxide is shown to change the fluorescence of β-carotene and chlorophyll a as well as various mixtures of the pigments in Langmuir films and in complex with bovine serum albumin in water solution. Similar effects were shown for zinc etioporphyrin II in the films. No shifts of the fluorescence peaks were registered in any case. 相似文献
110.
Paul A. Selden Dmitry E. Shcherbakov Jason A. Dunlop Kirill Yu. Eskov 《Pal?ontologische Zeitschrift》2014,88(3):297-307
New finds of Late Palaeozoic arachnids, based on three well-preserved carapaces from the Carboniferous of Russia and Ukraine and one complete, albeit poorly preserved, specimen from the Permian of Kazakhstan, are described. The spider genus Arthrolycosa is reported from the Late Carboniferous (Late Pennsylvanian: Kasimovian–Gzhelian) of Chunya in the Tunguska Basin of Siberia; it is the first find of a spider outside the Carboniferous tropics. Another fossil assigned to the same genus comes from the Late Carboniferous (Early Pennsylvanian: Bashkirian) of Kamensk–Shakhtinsky in the Donets Basin of Russia; it is probably the oldest fossil spider known. A thelyphonid (whip scorpion) carapace is described from the Late Carboniferous (Late Pennsylvanian: Kasimovian) of the adjacent Lugansk Province of the Donets Basin of Ukraine. 相似文献