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921.
Understanding chlorophylls: central magnesium ion and phytyl as structural determinants 总被引:1,自引:0,他引:1
Fiedor L Kania A Myśliwa-Kurdziel B Orzeł Ł Stochel G 《Biochimica et biophysica acta》2008,1777(12):1491-1500
Phytol, a C20 alcohol esterifying the C-17(3) propionate, and Mg2+ ion chelated in the central cavity, are conservative structural constituents of chlorophylls. To evaluate their intramolecular structural effects we prepared a series of metal- and phytyl-free derivatives of bacteriochlorophyll a and applied them as model chlorophylls. A detailed spectroscopic study on the model pigments reveals meaningful differences in the spectral characteristics of the phytylated and non-phytylated pigments. Their analysis in terms of solvatochromism and axial coordination shows how the central Mg and phytyl residue shape the properties of the pigment. Surprisingly, the presence/absence of the central Mg has no effect on the solvatochromism of (bacterio)chlorophyll pi-electron system and the hydrophobicity of phytyl does not interfere with the first solvation shell of the chromophore. However, both residues significantly influence the conformation of the pigment macrocycle and the removal of either residue increases the macrocycle flexibility. The chelation of Mg has a flattening effect on the macrocycle whereas bulky phytyl residue seems to control the conformation of the chromophore via steric interactions with ring V and its substituents. The analysis of spectroscopic properties of bacteriochlorophyllide (free acid) shows that esterification of the C-17(3) propionate is necessary in chlorophylls because the carboxyl group may act as a strong chelator of the central Mg. These observations imply that the truncated chlorophylls used in theoretical studies are not adequate as models of native chromophores, especially when fine effects are to be modeled. 相似文献
922.
Czogalla A Grzymajło K Jezierski A Sikorski AF 《Biochimica et biophysica acta》2008,1778(11):2612-2620
The region of beta-spectrin that is responsible for interactions with ankyrin was shown to comprise an ankyrin-sensitive lipid-binding site. Structural studies indicate that it exhibits a mixed 3(10)/alpha helical conformation and is highly amphipathic. These features together with the distinctively conserved sequence of the lipid-binding site motivated us to explore the mechanism of its interactions with biological membranes. A series of singly and doubly spin-labeled erythroid beta-spectrin-derived peptides was constructed, and the spin-label mobility and spin-spin distances were analyzed via electron paramagnetic resonance spectroscopy and two different calculation methods. The results indicate that in beta-spectrin, the lipid-binding domain, which is part of the 14(th) segment, has the topology of typical triple-helical spectrin repeat. However, it undergoes significant changes when interacting with phospholipids or detergents. A mechanism for these interactions is proposed in this paper. 相似文献
923.
Kremser ME Przybyło M Hoja-Łukowicz D Pocheć E Amoresano A Carpentieri A Bubka M Lityńska A 《Biochimica et biophysica acta》2008,1780(12):1421-1431
It is well documented that glycan synthesis is altered in some pathological processes, including cancer. The most frequently observed alterations during tumourigenesis are extensive expression of beta1,6-branched complex type N-glycans, the presence of poly-N-acetyllactosamine structures, and high sialylation of cell surface glycoproteins. This study investigated two integrins, alpha3beta1 and alpha(v)beta3, whose expression is closely related to cancer progression. Their oligosaccharide structures in two metastatic melanoma cell lines (WM9, WM239) were analysed with the use of matrix-assisted laser desorption ionisation mass spectrometry. Both examined integrins possessed heavily sialylated and fucosylated glycans, with beta1,6-branches and short polylactosamine chains. In WM9 cells, alpha3beta1 integrin was more variously glycosylated than alpha(v)beta3; in WM239 cells the situation was the reverse. Functional studies (wound healing and ELISA integrin binding assays) revealed that the N-oligosaccharide component of the tested integrins influenced melanoma cell migration on vitronectin and alpha3beta1 integrin binding to laminin-5. Additionally, more variously glycosylated integrins exerted a stronger influence on these parameters. To the best of our knowledge, this is the first report concerning structural characterisation of alpha(v)beta3 integrin glycans in melanoma or in any cancer cells. 相似文献
924.
Over fifty years of research data from various sources were compiled and analyzed in order to determine the effect of urbanization
on centipede diversity in the Wielkopolska-Kujawy Lowlands of western Poland. Urbanization has had a significant effect on
species composition and community structures. However, it has not reduced overall species richness and diversity in the centipede
fauna. The centipede fauna from built-up areas was found to be rich and varied. The habitats with the highest levels of species
richness were the city of Poznań and the beech forests in the surrounding region. 相似文献
925.
926.
Eighteen species of eleven lichen genera were found on driftwood and worked timber deposited on the beaches in the Hornsund
and Billefjorden regions (the west coast of Spitsbergen, Svalbard archipelago). Majority of them indicate low substrate specificity
in the high arctic regions. Only three species (Caloplaca spitsbergensis, Lecanora mughicola, L. orae-frigidae) are typical for lignum. Most of the taxa are widespread in Svalbard. Species like: Caloplaca holocarpa, C. spitsbergensis, Protothelenella sphinctrinoidella, Rinodina archaea were sporadically reported till now. Lecanora mughicola was not reported from Svalbard up to the present and this is the first record of the species for the region. 相似文献
927.
Milczarek R Sokołowska E Hallmann A Kaletha K Klimek J 《The Journal of steroid biochemistry and molecular biology》2008,110(3-5):230-235
During pregnancy placenta is the most significant source of lipid hydroperoxides and other reactive oxygen species (ROS). The increased production of lipid peroxides and other ROS is often linked to pre-eclampsia. It is already proved that placental endoplasmic reticulum may be an important place of lipid peroxides and superoxide radical production. In the present study we revealed that NADPH- and iron-dependent lipid peroxidation in human placental microsomes (HPM) inhibit placental aromatase--a key enzyme of estrogen biosynthesis in human placenta. We showed that significant inhibition of this enzyme is caused by small lipid peroxidation (TBARS (thiobarbituric acid-reactive substances)<4nmol/mg microsomal protein (m.p.)). More intensive lipid peroxidation (TBARS>9nmol/mg microsomal protein) diminishes aromatase activity to value being less than 5% of initial value. NADPH- and iron-dependent lipid peroxidation also causes disappearance of cytochrome P450 parallel to observed aromatase activity inhibition. EDTA, alpha-tocopherol, MgCl(2) and superoxide dismutase (SOD) prevent aromatase activity inhibition and cytochrome P450(AROM) degradation. Mannitol and catalase have not effect on TBARS synthesis, aromatase activity and cytochrome P450 degradation. In view of the above we postulate that the inhibition of aromatase activity observed is mainly a consequence of cytochrome P450(AROM) degradation induced by lipid radicals. The role of hydroxyl radical in cytochrome P450 degradation is negligible in our experimental conditions. The results presented here also suggest that the inhibition of aromatase activity can also take place in placenta at in vivo conditions. 相似文献
928.
Mucha A Lämmerhofer M Lindner W Pawełczak M Kafarski P 《Bioorganic & medicinal chemistry letters》2008,18(5):1550-1554
Individual stereoisomers of the phosphinic pseudodipeptide hPhepsi[P(O)(OH)CH(2)]Phe were obtained by stereoselective liquid chromatographic separation as N- and C-terminally protected derivative on quinidine carbamate modified silica stationary phase. The stereoisomeric purity, exceeding 95% for each fraction, was determined before and after deprotection using two independent methods. The absolute configuration was rationally assigned by application of enantiomerically pure phosphinic acid substrates in the synthetic procedure and correlation with biological activity of the products. Substantial differences in inhibition of leucine aminopeptidase by the individual isomers revealed novel insights into potency of the recently developed and remarkably effective compound. 相似文献
929.
P. Kubeš J. Kravárik D. Klír P. Barvir M. Scholz M. Paduch K. Tomaszewski I. Ivanova-Stanik B. Bieńkowska L. Karpinski L. Juha J. Krása M. J. Sadowski L. Jakubowski A. Szydłowski A. Banaszak H. Schmidt V. M. Romanova 《Plasma Physics Reports》2005,31(5):382-391
Results are presented from experimental studies of the correlation between X-ray and neutron emissions generated in the implosion of a deuteron plasma shell onto an Al wire. The experiments were carried out on the PF-1000 facility at currents of 1.5–1.8 MA. An Al wire 80 μm in diameter and 7–9 cm in length was placed at the end of the inner electrode. During the implosion of the plasma shell, Al K-shell X-rays were first emitted at the dip of the current derivative. After the X-ray pulse, a relatively stable corona with a diameter of 2–3 mm and lifetime of a few hundred nanoseconds formed around the wire. The presence of the wire did not considerably reduce the total neutron yield (at most 1011 neutrons per shot) in comparison to discharges without a wire. As a rule, the intensity of neutron emission was maximal a few tens of nanoseconds after the peak of X-ray emission. A detailed comparison of two shots with low and high neutron yields have shown that the neutron yield depends on the configuration and dynamics of the discharge. The possible influence of the self-generated axial component of the magnetic field on the development of the plasma focus and the acceleration of fast deuterons is discussed. 相似文献
930.
Cell Cycle Activity and β-Tubulin Accumulation During Dormancy Breaking of Acer platanoides L. seeds
Cell cycle events in embryo axes of Norway maple (Acer platanoides L.) seeds were studied during dormancy breaking by flow cytometric analyses of the nuclear DNA content and by immunodetection
of β-tubulin. Most embryonic nuclei of dry, fully matured seeds were arrested in the G2 phase of the cell cycle. In addition, the lowest content of β-tubulin was detected in dry, mature seeds. Imbibition in water
and cold stratification resulted in a decrease in the number of nuclei in G2, and a simultaneous increase in β-tubulin content. In germinated seeds the content of β-tubulin was the highest and the number
of cells in G2 was the lowest. Both cell cycle events preceded cell expansion and division and subsequent growth of the radicle through
the seed coat. The anatomical investigation has proved that the main reason for decrease in the number of nuclei in G2 is mitosis, started with seeds germination (radicle protrusion). The activation of the cell cycle and the β-tubulin accumulation
were associated with embryo dormancy breaking.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献