全文获取类型
收费全文 | 252篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
276篇 |
出版年
2021年 | 6篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 12篇 |
2011年 | 6篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1970年 | 9篇 |
1969年 | 2篇 |
1968年 | 4篇 |
1932年 | 1篇 |
1929年 | 2篇 |
排序方式: 共有276条查询结果,搜索用时 15 毫秒
71.
Kruse O Rupprecht J Bader KP Thomas-Hall S Schenk PM Finazzi G Hankamer B 《The Journal of biological chemistry》2005,280(40):34170-34177
Oxygenic photosynthetic organisms use solar energy to split water (H2O) into protons (H+), electrons (e-), and oxygen. A select group of photosynthetic microorganisms, including the green alga Chlamydomonas reinhardtii, has evolved the additional ability to redirect the derived H+ and e- to drive hydrogen (H2) production via the chloroplast hydrogenases HydA1 and A2 (H2 ase). This process occurs under anaerobic conditions and provides a biological basis for solar-driven H2 production. However, its relatively poor yield is a major limitation for the economic viability of this process. To improve H2 production in Chlamydomonas, we have developed a new approach to increase H+ and e- supply to the hydrogenases. In a first step, mutants blocked in the state 1 transition were selected. These mutants are inhibited in cyclic e- transfer around photosystem I, eliminating possible competition for e- with H2ase. Selected strains were further screened for increased H2 production rates, leading to the isolation of Stm6. This strain has a modified respiratory metabolism, providing it with two additional important properties as follows: large starch reserves (i.e. enhanced substrate availability), and a low dissolved O2 concentration (40% of the wild type (WT)), resulting in reduced inhibition of H2ase activation. The H2 production rates of Stm6 were 5-13 times that of the control WT strain over a range of conditions (light intensity, culture time, +/- uncoupler). Typically, approximately 540 ml of H2 liter(-1) culture (up to 98% pure) were produced over a 10-14-day period at a maximal rate of 4 ml h(-1) (efficiency = approximately 5 times the WT). Stm6 therefore represents an important step toward the development of future solar-powered H2 production systems. 相似文献
72.
Bao J Hunt JA Miao S Rupprecht KM Stelmach JE Liu L Ruzek RD Sinclair PJ Pivnichny JV Hop CE Kumar S Zaller DM Shoop WL O'neill EA O'keefe SJ Thompson CM Cubbon RM Wang R Zhang WX Thompson JE Doherty JB 《Bioorganic & medicinal chemistry letters》2006,16(1):64-68
Quinolinones and naphthyridinones with C7 N-t-butyl piperidine substituents were found to be potent p38 MAP kinase inhibitors. These compounds significantly suppress TNF-alpha release in both cellular and LPS-stimulated whole blood assays. They also displayed excellent PK profiles across three animal species. Quinolinone at 10 mpk showed comparable oral efficacy to that of dexamethasone at 1 mpk in a murine collagen-induced arthritis model. 相似文献
73.
Eva Fuhrmann Jelle B. Bultema Uwe Kahmann Eva Rupprecht Egbert J. Boekema Dirk Schneider 《Molecular biology of the cell》2009,20(21):4620-4628
The vesicle-inducing protein in plastids 1 (Vipp1) was found to be involved in thylakoid membrane formation in chloroplasts and cyanobacteria. In contrast to chloroplasts, it has been suggested that in cyanobacteria the protein is only tightly associated with the cytoplasmic membrane. In the present study we analyze and describe the subcellular localization and the oligomeric organization of Vipp1 from the cyanobacterium Synechocystis PCC 6803. Vipp1 forms stable dimers and higher-ordered oligomers in the cytoplasm as well as at both the cytoplasmic and thylakoid membrane. Vipp1 oligomers are organized in ring structures with a variable diameter of 25–33 nm and corresponding calculated molecular masses of ∼1.6–2.2 MDa. Six different types of rings were found with an unusual 12–17-fold symmetrical conformation. The simultaneous existence of multiple types of rings is very unusual and suggests a special function of Vipp1. Involvement of diverse ring structures in vesicle formation is suggested. 相似文献
74.
T Weidlich S M Lindsay Q Rui A Rupprecht W L Peticolas G A Thomas 《Journal of biomolecular structure & dynamics》1990,8(1):139-171
We have obtained low frequency (less than 200 cm-1) Raman spectra of calf-thymus DNA and poly(rI).poly(rC) as a function of water content and counterion species and of d(GGTATACC)2 and d(CGCGAATTCGCG)2 crystals. We have found that the Raman scattering from water in the first and second hydration shells does not contribute directly to the Raman spectra of DNA. We have determined the number of strong Raman active modes by comparing spectra for different sample orientations and polarizations and by obtaining fits to the spectra. We have found at least five Raman active modes in the spectra of A- and B-DNA. The frequencies of the modes above 40 cm-1 do not vary with counterion species, and there are only relatively small changes upon hydration. These modes are, therefore, almost completely internal. The mode near 34 cm-1 in A-DNA is mostly internal, whereas the mode near 25 cm-1 is dominated by interhelical interactions. The observed intensity changes upon dehydration were found to be due to the decrease in interhelical distance. Polymer length appears to play a role in the lowest frequency modes. 相似文献
75.
A modular treatment of molecular traffic through the active site of cholinesterase 总被引:1,自引:0,他引:1 下载免费PDF全文
We present a model for the molecular traffic of ligands, substrates, and products through the active site of cholinesterases (ChEs). First, we describe a common treatment of the diffusion to a buried active site of cationic and neutral species. We then explain the specificity of ChEs for cationic ligands and substrates by introducing two additional components to this common treatment. The first module is a surface trap for cationic species at the entrance to the active-site gorge that operates through local, short-range electrostatic interactions and is independent of ionic strength. The second module is an ionic-strength-dependent steering mechanism generated by long-range electrostatic interactions arising from the overall distribution of charges in ChEs. Our calculations show that diffusion of charged ligands relative to neutral isosteric analogs is enhanced approximately 10-fold by the surface trap, while electrostatic steering contributes only a 1.5- to 2-fold rate enhancement at physiological salt concentration. We model clearance of cationic products from the active-site gorge as analogous to the escape of a particle from a one-dimensional well in the presence of a linear electrostatic potential. We evaluate the potential inside the gorge and provide evidence that while contributing to the steering of cationic species toward the active site, it does not appreciably retard their clearance. This optimal fine-tuning of global and local electrostatic interactions endows ChEs with maximum catalytic efficiency and specificity for a positively charged substrate, while at the same time not hindering clearance of the positively charged products. 相似文献
76.
Anne Rupprecht Elena A. Sokolenko Valeri Beck Olaf Ninnemann Thorsten Trimbuch Petr Jezek Elena E. Pohl 《Biophysical journal》2010,98(8):1503-1511
The molecular mechanism responsible for the regulation of the mitochondrial membrane proton conductance (G) is not clearly understood. This study investigates the role of the transmembrane potential (ΔΨm) using planar membranes, reconstituted with purified uncoupling proteins (UCP1 and UCP2) and/or unsaturated FA. We show that high ΔΨm (similar to ΔΨm in mitochondrial State IV) significantly activates the protonophoric function of UCPs in the presence of FA. The proton conductance increases nonlinearly with ΔΨm. The application of ΔΨm up to 220 mV leads to the overriding of the protein inhibition at a constant ATP concentration. Both, the exposure of FA-containing bilayers to high ΔΨm and the increase of FA membrane concentration bring about the significant exponential Gm increase, implying the contribution of FA in proton leak. Quantitative analysis of the energy barrier for the transport of FA anions in the presence and absence of protein suggests that FA− remain exposed to membrane lipids while crossing the UCP-containing membrane. We believe this study shows that UCPs and FA decrease ΔΨm more effectively if it is sufficiently high. Thus, the tight regulation of proton conductance and/or FA concentration by ΔΨm may be key in mitochondrial respiration and metabolism. 相似文献
77.
Amy T. Gilbert A. R. Fooks D. T. S. Hayman D. L. Horton T. Müller R. Plowright A. J. Peel R. Bowen J. L. N. Wood J. Mills A. A. Cunningham C. E. Rupprecht 《EcoHealth》2013,10(3):298-313
The ecology of infectious disease in wildlife has become a pivotal theme in animal and public health. Studies of infectious disease ecology rely on robust surveillance of pathogens in reservoir hosts, often based on serology, which is the detection of specific antibodies in the blood and is used to infer infection history. However, serological data can be inaccurate for inference to infection history for a variety of reasons. Two major aspects in any serological test can substantially impact results and interpretation of antibody prevalence data: cross-reactivity and cut-off thresholds used to discriminate positive and negative reactions. Given the ubiquitous use of serology as a tool for surveillance and epidemiological modeling of wildlife diseases, it is imperative to consider the strengths and limitations of serological test methodologies and interpretation of results, particularly when using data that may affect management and policy for the prevention and control of infectious diseases in wildlife. Greater consideration of population age structure and cohort representation, serological test suitability and standardized sample collection protocols can ensure that reliable data are obtained for downstream modeling applications to characterize, and evaluate interventions for, wildlife disease systems. 相似文献
78.
Optical and physical properties of wet-spun films of Na-hyaluronate. Evidence of a phase transition. 下载免费PDF全文
The refractive indices, water content, and volume of wet-spun films of Na-hyaluronate have been measured as a function of relative humidity (rh). These data are used with the Lorentz-Lorenz formula to determine the optical polarizabilities of Na-hyaluronate parallel and perpendicular to the helical axis. The analysis reveals a drop in the optical polarizabilities of approximately 20% between 80 and 88% rh, indicating a phase transition. 相似文献
79.
80.
The peripheral light-harvesting complex of Photosystem I consists of two subpopulations, LHC I-680 and LHC I-730. The latter
is composed of the two apoproteins Lhca1 and Lhca4. Recently, reconstitution of monomeric LHC I using bacterially overexpressed
Lhca1 or Lhca4 was achieved. In order to obtain insight into the structure requirements for formation of monomeric light-harvesting
complexes, we produced a series of N- and C-terminal deletion mutants and used the overexpressed proteins for reconstitution
experiments. We found the entire extrinsic N-terminal region dispensable for monomer formation in Lhca1 and Lhca4. Also at
the C-terminus, both subunits revealed similarity since all amino acids up to the end of the fourth helix could be removed
without abolishing monomer formation. In connection with former corresponding results for Lhcb1, the dispensability of these
regions appears to be a general feature in LHC-formation. In LHC I, however, a stabilising effect can be ascribed to these
regions since the yield of complexes was decreased. In the majority of the mutant LHC I versions no effect on pigment binding
was detected. However, in the LHC with the most extensively N-terminally truncated mutant of Lhca4 a dramatic shift in the
77 K fluorescence emission to shorter wavelengths was observed. This suggests that chlorophylls involved in long wavelength
fluorescence emission are located in the chlorophyll array located towards the stromal face of the thylakoid membrane assuming
a pigment arrangement corresponding to that in LHC II and CP29.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献