首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   438篇
  免费   22篇
  国内免费   3篇
  463篇
  2022年   6篇
  2021年   10篇
  2020年   8篇
  2019年   4篇
  2018年   14篇
  2017年   13篇
  2016年   13篇
  2015年   12篇
  2014年   16篇
  2013年   15篇
  2012年   26篇
  2011年   21篇
  2010年   16篇
  2009年   14篇
  2008年   17篇
  2007年   14篇
  2006年   17篇
  2005年   10篇
  2004年   13篇
  2003年   9篇
  2002年   13篇
  2001年   8篇
  2000年   14篇
  1999年   12篇
  1998年   6篇
  1997年   10篇
  1996年   6篇
  1995年   3篇
  1993年   4篇
  1992年   8篇
  1991年   6篇
  1990年   6篇
  1989年   6篇
  1988年   11篇
  1987年   13篇
  1986年   3篇
  1985年   5篇
  1984年   6篇
  1983年   9篇
  1982年   5篇
  1981年   4篇
  1980年   3篇
  1979年   2篇
  1976年   2篇
  1975年   2篇
  1973年   2篇
  1969年   6篇
  1967年   2篇
  1966年   3篇
  1965年   2篇
排序方式: 共有463条查询结果,搜索用时 15 毫秒
1.
Based on nonlinear phenomena of biophoton emission observed in the past, an interference model concerning with the mechanism of interaction between living organisms and electromagnetic fields was raised. Caused by biological nonlinearly polarizable double layer, destructive interference of incoming and reflected waves establishes in the outside. As a consequence, in the inside constructive interference takes place at the same time. The interference patterns may play an important role in biological self organization and in biological functions. We investigate the boundary conditions necessary for explaining these non-linear optical effects in terms of the phase conjugation. It turns out that there are solutions of the Maxwell equations which satisfy destructive interference of biophotons in agreement with the experimental results. Necessary provisions are nonlinearly polarizable optically active double layers of distances which are small compared to the wavelength of light. In addition, they have to be able to move into the nodal planes of the impinging waves within a small time interval compared to the coherence time. These conditions are likely fulfilled in the optically dense, but ordered and optically excited, highly polarizable living matter.  相似文献   
2.
The primary structures of the alpha chains in hemoglobins from three stocks of mice with theHba w2,Hba w3, andHba w4 haplotypes were determined to establish whether the tentative alpha-chain assignments based on the results of isoelectric focusing patterns were correct. TheseHba haplotypes were identified in laboratory descendants of feral mice captured in different parts of the world. Hemoglobin from Centreville, Maryland,Mus musculus domesticus (Hba w2) contains equal amounts of alpha chains 1 and 3. Hemoglobin from CzechMus musculus musculus (Hba w4) contains equal amounts of alpha chains 3 and 4. Amino acid analysis of the alpha-globins of Skive DanishMus musculus musculus (Hba w3) establishes that its hemoglobin is comprised of about one-third alpha chain 2 as expected plus a greater amount of a unique alpha chain that has not been described previously. This unique alpha chain has glycine at position 25, isoleucine at position 62, and serine at position 68; it is called chain 7. It may represent an intermediate in the evolution of genes that code for chain 2 (which has glycine, valine, and serine at positions 25, 62, and 68, respectively) and chain 4 (which has valine, isoleucine, and serine at positions 25, 62, and 62, respectively).This research was sponsored jointly by the National Institutes of Environmental Health Sciences under Contract 1-ES-55078 and by the Office of Health and Environmental Research, U.S. Department of Energy, under Contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.  相似文献   
3.
4.
  总被引:10,自引:0,他引:10  
J L Popp  B Kalyanaraman  T K Kirk 《Biochemistry》1990,29(46):10475-10480
Veratryl alcohol (3,4-dimethoxybenzyl alcohol) appears to have multiple roles in lignin degradation by Phanerochaete chrysosporium. It is synthesized de novo by the fungus. It apparently induces expression of lignin peroxidase (LiP), and it protects LiP from inactivation by H2O2. In addition, veratryl alcohol has been shown to potentiate LiP oxidation of compounds that are not good LiP substrates. We have now observed the formation of Mn3+ in reaction mixtures containing LiP, Mn2+, veratryl alcohol, malonate buffer, H2O2, and O2. No Mn3+ was formed if veratryl alcohol or H2O2 was omitted. Mn3+ formation also showed an absolute requirement for oxygen, and oxygen consumption was observed in the reactions. This suggests involvement of active oxygen species. In experiments using oxalate (a metabolite of P. chrysosporium) instead of malonate, similar results were obtained. However, in this case, we detected (by ESR spin-trapping) the production of carbon dioxide anion radical (CO2.-) and perhydroxyl radical (.OOH) in reaction mixtures containing LiP, oxalate, veratryl alcohol, H2O2, and O2. Our data indicate the formation of oxalate radical, which decays to CO2 and CO2.-. The latter reacts with O2 to form O2.-, which then oxidizes Mn2+ to Mn3+. No radicals were detected in the absence of veratryl alcohol. These results indicate that LiP can indirectly oxidize Mn2+ and that veratryl alcohol is probably a radical mediator in this system.  相似文献   
5.
Salmonella bacteria cause more than three million deaths each year. They hijack cells and inject among other proteins SipA via a "molecular syringe" into the cell, which can tether actin subunits in opposing strands to form mechanically stabilized filaments which rapidly reshape the cells surface into extended ruffles, leading to bacterial internalization. Exactly how these ruffles form at a single filament level remains unknown. Our real time total internal fluorescence microscopy observations show that both bidirectional elongation of actin by SipA as well as end-to-end annealing of SipA-actin filaments are rapid processes. Complementary electron microscopy investigations demonstrate that crowding agents in vitro readily induce stiff bundles of SipA-actin filaments. Taken together these three effects, rapid SipA induced actin polymerization, filament annealing and bundle formation due to molecular crowding can explain how Salmonella invades cells at molecular level.  相似文献   
6.
    
Introduction – Quality control in the pharmaceutical and phytopharmaceutical industries requires fast and reliable methods for the analysis of raw materials and final products. Objective – This study evaluates different analytical approaches in order to recognise the most suitable technique for the analysis of carbohydrates in herbal drug preparations. Methodology – The specific focus of the study is on thin‐layer chromatography (TLC), gas chromatography (GC), and a newly developed mass spectrometric method, i.e. matrix free material enhanced laser desorption/ionisation time of flight mass spectrometry (mf‐MELDI‐MS). Samples employed in the study were standards and microwave‐assisted water extracts from Quercus. Results – TLC analysis proved the presence of mono‐, di‐ and trisaccharides within the biological sample and hinted at the existence of an unknown carbohydrate of higher oligomerisation degree. After evaluation of different derivatisation techniques, GC‐MS confirmed data obtained via TLC for mono‐ to trisaccharides, delivering additionally quantified values under a considerable amount of time. A carbohydrate of higher oligomerisation degree could not be found. The application of mf‐MELDI‐MS further confirmed the presence of carbohydrates up to trisaccharides, also hinting at the presence of a form of tetrasaccharide. Besides this information, mf‐MELDI‐MS delivered further data about other substances present in the extract. Quantitative determination resulted in 1.750, 1.736 and 0.336 mg/mL for glucose, sucrose and raffinose respectively. Conclusion – Evaluation of all three techniques employed, clearly proved the heightened performance of mf‐MELDI‐MS for the qualitative analysis of complex mixtures, as targets do not need modification and analysis requires only a few minutes. In addition, GC‐MS is suitable for quantitative analysis. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
7.
A mutation that produces an absolute deficiency of normal β-major globin polypeptides has been recovered from a DBA/2J male mouse. Most mice homozygous for the deficiency survived to adulthood and reproduced but were smaller at birth than their littermates and demonstrated a hypochromic, microcytic anemia with severe anisocytosis, poikilocytosis, and reticulocytosis and the presence of inclusion bodies in a high proportion of circulating erythrocytes. Mice heterozygous for the deficiency demonstrated a mild reticulocytosis but were not clinically anemic. Analysis of globin chain synthesis in vitro by 3H-leucine incorporation revealed that β-globin synthesis was nearly normal (95%) in heterozygotes and about 75% of normal in deficiency homozygotes. Molecular characterization of the mutation by restriction analysis revealed a deletion of about 3.3 kb of DNA, including regulatory sequences and all coding blocks for β-major globin. Based on genetic and hematological criteria, mice homozygous for the mutant allele, designated Hbbth-1, represent the first animal model of β-thalassemia (Cooley's anemia), a severe genetic disease of humans.  相似文献   
8.
The influenza virus uses the hemagglutinin (HA) and neuraminidase (NA) glycoproteins to interact with and infect host cells. While biochemical and microscopic methods allow examination of the early steps in flu infection, the genesis of progeny virions has been more difficult to follow, mainly because of difficulties inherent in fluorescent labeling of flu proteins in a manner compatible with live cell imaging. We here apply sortagging as a chemoenzymatic approach to label genetically modified but infectious flu and track the flu glycoproteins during the course of infection. This method cleanly distinguishes influenza glycoproteins from host glycoproteins and so can be used to assess the behavior of HA or NA biochemically and to observe the flu glycoproteins directly by live cell imaging.  相似文献   
9.
Representative specimens of fifteen Daldinia spp. were studied for ultrastructural characteristics of their ascospores by scanning electron microscopy (SEM). The ornamentation of their outermost spore layers was found to be species-consistent, confirming the results of concurrent studies on the morphology of their teleomorphs and anamorphs, secondary metabolite profiles and PCR-based genetic fingerprints. Daldinia spp. may either show smooth or transversally striated ascospores. The spores of the species within the latter group are always ellipsoid-equilateral to ellipsoid-inequilateral with narrowly rounded ends. Smooth, broadly ellipsoid to cylindrical ascospores were observed in all species (D. caldariorum, D. fissa and D. loculata) that are known to produce their stromata on substrates damaged by fire. The ascospores of D. concentrica differed from those of D. childiae (i.e., the cosmopolitan taxon previously regarded as D. concentrica ss. auct.) and other Daldinia spp. in showing a very faint ornamentation, which only became visible at 10000× magnification by SEM. A specimen collected on the isle of Jersey (Channel Islands, UK) showed morphological similarities to the pantropical D. eschscholzii, but its ascospores appeared smooth by SEM, and it may therefore represent a previously undescribed species. Dedicated to Professor Yoshinori Asakawa, Tokushima, Japan, on the occasion of his 60th birthday PH-R Life Science Center Natural Products  相似文献   
10.
Apoptosis is a highly conserved procedure of cell death and occurs under various stimuli, including oxidative stress. A small heat shock protein, alphaB-crystallin, is found to process resistance to apoptosis in some cells and tissues. But the mechanisms under this protective role are not fully understood. In the present study, we reported the early protective role of alphaB-crystallin against hydrogen peroxide-induced apoptosis in mice myogenic C(2)C(12) cells. alphaB-Crystallin interacted with p53, a proapoptotic protein, during cell apoptosis and such protein interaction mainly occurred in the cytoplasm of the cells, suggesting that the interaction of alphaB-crystallin with p53 might prevent the translocation of p53 from cytoplasm to mitochondria. Hence, this study provides a hint that alphaB-crystallin affects on p53 mitochondrial translocation during oxidative stress-induced apoptosis.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号