全文获取类型
收费全文 | 130篇 |
免费 | 22篇 |
专业分类
152篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有152条查询结果,搜索用时 15 毫秒
1.
2.
Virtual electrodes in cardiac tissue: a common mechanism for anodal and cathodal stimulation. 总被引:6,自引:0,他引:6
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Traditional cable analyses cannot explain complex patterns of excitation in cardiac tissue with unipolar, extracellular anodal, or cathodal stimuli. Epifluorescence imaging of the transmembrane potential during and after stimulation of both refractory and excitable tissue shows distinctive regions of simultaneous depolarization and hyperpolarization during stimulation that act as virtual cathodes and anodes. The results confirm bidomain model predictions that the onset (make) of a stimulus induces propagation from the virtual cathode, whereas stimulus termination (break) induces it from the virtual anode. In make stimulation, the virtual anode can delay activation of the underlying tissue, whereas in break stimulation this occurs under the virtual cathode. Thus make and break stimulations in cardiac tissue have a common mechanism that is the result of differences in the electrical anisotropy of the intracellular and extracellular spaces and provides clear proof of the validity of the bidomain model. 相似文献
3.
4.
Cardiac tissue can be considered macroscopically as a bidomain, anisotropic conductor in which simple depolarization wavefronts produce complex current distributions. Since such distributions may be difficult to measure using electrical techniques, we have developed a mathematical model to determine the feasibility of magnetic localization of these currents. By applying the finite element method to an idealized two-dimensional bisyncytium with anisotropic conductivities, we have calculated the intracellular and extracellular potentials, the current distributions, and the magnetic fields for a circular depolarization wavefront. The calculated magnetic field 1 mm from the tissue is well within the sensitivity of a SQUID magnetometer. Our results show that complex bisyncytial current patterns can be studied magnetically, and these studies should provide valuable insight regarding the electrical anisotropy of cardiac tissue. 相似文献
5.
van Dijken JP Bauer J Brambilla L Duboc P Francois JM Gancedo C Giuseppin ML Heijnen JJ Hoare M Lange HC Madden EA Niederberger P Nielsen J Parrou JL Petit T Porro D Reuss M van Riel N Rizzi M Steensma HY Verrips CT Vindeløv J Pronk JT 《Enzyme and microbial technology》2000,26(9-10):706-714
To select a Saccharomyces cerevisiae reference strain amenable to experimental techniques used in (molecular) genetic, physiological and biochemical engineering research, a variety of properties were studied in four diploid, prototrophic laboratory strains. The following parameters were investigated: 1) maximum specific growth rate in shake-flask cultures; 2) biomass yields on glucose during growth on defined media in batch cultures and steady-state chemostat cultures under controlled conditions with respect to pH and dissolved oxygen concentration; 3) the critical specific growth rate above which aerobic fermentation becomes apparent in glucose-limited accelerostat cultures; 4) sporulation and mating efficiency; and 5) transformation efficiency via the lithium-acetate, bicine, and electroporation methods. On the basis of physiological as well as genetic properties, strains from the CEN.PK family were selected as a platform for cell-factory research on the stoichiometry and kinetics of growth and product formation. 相似文献
6.
7.
Luaine Bandounas Nick JP Wierckx Johannes H de Winde Harald J Ruijssenaars 《BMC biotechnology》2011,11(1):1-11
Background
The number of biotransformations that use nicotinamide recycling systems is exponentially growing. For this reason one of the current challenges in biocatalysis is to develop and optimize more simple and efficient cofactor recycling systems. One promising approach to regenerate NAD+ pools is the use of NADH-oxidases that reduce oxygen to hydrogen peroxide while oxidizing NADH to NAD+. This class of enzymes may be applied to asymmetric reduction of prochiral substrates in order to obtain enantiopure compounds.Results
The NADH-oxidase (NOX) presented here is a flavoenzyme which needs exogenous FAD or FMN to reach its maximum velocity. Interestingly, this enzyme is 6-fold hyperactivated by incubation at high temperatures (80°C) under limiting concentrations of flavin cofactor, a change that remains stable even at low temperatures (37°C). The hyperactivated form presented a high specific activity (37.5 U/mg) at low temperatures despite isolation from a thermophile source. Immobilization of NOX onto agarose activated with glyoxyl groups yielded the most stable enzyme preparation (6-fold more stable than the hyperactivated soluble enzyme). The immobilized derivative was able to be reactivated under physiological conditions after inactivation by high solvent concentrations. The inactivation/reactivation cycle could be repeated at least three times, recovering full NOX activity in all cases after the reactivation step. This immobilized catalyst is presented as a recycling partner for a thermophile alcohol dehydrogenase in order to perform the kinetic resolution secondary alcohols.Conclusion
We have designed, developed and characterized a heterogeneous and robust biocatalyst which has been used as recycling partner in the kinetic resolution of rac-1-phenylethanol. The high stability along with its capability to be reactivated makes this biocatalyst highly re-useable for cofactor recycling in redox biotransformations. 相似文献8.
In vivo magnetic and electric recordings from nerve bundles and single motor units in mammalian skeletal muscle. Correlations with muscle force
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Recent advances in the technology of recording magnetic fields associated with electric current flow in biological tissues have provided a means of examining action currents that is more direct and possibly more accurate than conventional electrical recording. Magnetic recordings are relatively insensitive to muscle movement, and, because the recording probes are not directly connected to the tissue, distortions of the data due to changes in the electrochemical interface between the probes and the tissue are eliminated. In vivo magnetic recordings of action currents of rat common peroneal nerve and extensor digitorum longus (EDL) muscle were obtained by a new magnetic probe and amplifier system that operates within the physiological temperature range. The magnetically recorded waveforms were compared with those obtained simultaneously by conventional, extracellular recording techniques. We used the amplitude of EDL twitch force (an index of stimulus strength) generated in response to graded stimulation of the common peroneal nerve to enable us to compare the amplitudes of magnetically recorded nerve and muscle compound action currents (NCACs and MCACs, respectively) with the amplitudes of electrically recorded nerve compound action potentials (NCAPs). High, positive correlations to stimulus strength were found for NCACs (r = 0.998), MCACs (r = 0.974), and NCAPs (r = 0.998). We also computed the correlations of EDL single motor unit twitch force with magnetically recorded single motor unit compound action currents (SMUCACs) and electrically recorded single motor unit compound action potentials (SMUCAPs) obtained with both a ring electrode and a straight wire serving as a point electrode. Only the SMUCACs had a relatively strong positive correlation (r = 0.768) with EDL twitch force. Correlations for ring and wire electrode-recorded SMUCAPs were 0.565 and -0.366, respectively. This study adds a relatively direct examination of action currents to the characterization of the normal biophysical properties of peripheral nerve, muscle, and muscle single motor units. 相似文献
9.
Lindström Irene Bontell Neil Hall Kevin E Ashelford JP Dubey Jon P Boyle Johan Lindh Judith E Smith 《Genome biology》2009,10(5):R53-17
Background
Toxoplasma gondii is a zoonotic parasite of global importance. In common with many protozoan parasites it has the capacity for sexual recombination, but current evidence suggests this is rarely employed. The global population structure is dominated by a small number of clonal genotypes, which exhibit biallelic variation and limited intralineage divergence. Little is known of the genotypes present in Africa despite the importance of AIDS-associated toxoplasmosis. 相似文献10.
Margaret?O?Nwagwu Helen?Baines Jeffrey?B?Kerr Francis?JP?EblingEmail author 《Reproductive biology and endocrinology : RB&E》2005,3(1):48