全文获取类型
收费全文 | 339篇 |
免费 | 18篇 |
出版年
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 24篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 24篇 |
2009年 | 25篇 |
2008年 | 13篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 16篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
1909年 | 1篇 |
1897年 | 1篇 |
1875年 | 2篇 |
1859年 | 1篇 |
1855年 | 1篇 |
排序方式: 共有357条查询结果,搜索用时 78 毫秒
1.
Summary K+ channels in inside-out patches from hamster insulin tumor (HIT) cells were studied using the patch-clamp technique. HIT cells provide a convenient system for the study of ion channels and insulin secretion. They are easy to culture, form gigaohm seals readily and secrete insulin in response to glucose. The properties of the cells changed with the passage number. For cell passage numbers 48 to 56, five different K+-selective channels ranging from 15 to 211 pS in symmetrical 140mm KCl solutions were distinguished. The channels were characterized by the following features: a channel with a conductance (in symmetrical 140mm KCl solutions) of 210 pS that was activated by noncyclic purine nucleotides and closed by H+ ions (pH=6.8); a 211 pS channel that was Ca2+-activated and voltage dependent; a 185 pS channel that was blocked by TEA but was insensitive to quinine or nucleotides; a 130 pS channel that was activated by membrane hyperpolarization; and a small conductance (15 pS) channel that was not obviously affected by any manipulation. As determined by radioimmunoassay, cells from passage number 56 secreted 917±128 ng/mg cell protein/48 hr of insulin. In contrast, cells from passage number 77 revealed either no channel activity or an occasional nonselective channel, and secreted only 29.4±8.5 ng/mg cell protein/48 hr of insulin. The nonselective channel found in the passage 77 cells had a conductance of 25 pS in symmetrical 140mm KCl solutions. Thus, there appears to be a correlation between the presence of functional K+ channels and insulin secretion. 相似文献
2.
The effect of phloretin (20-100 M), a dipolar organic compound, on the voltage clamp currents of the frog node of Ranvier has been investigated. The Na currents are simply reduced in size but not otherwise affected. Phloretin has no effect on the slow 4-aminopyridine-resistant K channels. However, the voltage dependence and time course of the fast K conductance (g
K) is markedly altered. The g
K(E) curve, determined by measuring fast tail currents at different pulse potentials, normally exhibits a bend at –50 mV indicating the existence of two types of fats K channels. Phloretin shifts the g
K (E) curve to more positive potentials, reduces its slope and its maximum and abolishes the distinction between the two tpyes of fast K channels. The effect becomes more pronounced with time. Phloretin also markedly slows the opening of the fast K channels, but has much less effect on the closing. Opening can be accelerated again by a long depolarizing prepulse which presumably removes part of the phloretin block. It is concluded that phloretin selectively affects the fast K channels of the nodal membrane. The results are compared with similar observations on the squid giant axon.
Offprint requests to: H. Meves 相似文献
3.
4.
5.
6.
The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
7.
8.
Three types of ionic current essentially determine the firing pattern of nerve cells: the persistent Na+ current, the M current and the low-voltage-activated Ca2+ current. The present article summarizes recent experiments concerned with the basic properties of these currents. Keynes and Meves (Proc R Soc Lond B (1993) 253, 61–68) studied the persistent or steady-state Na+ current on dialysed squid axons and measured the probability of channel opening both for the peak and the steady-state Na+ current (PFpeak and PFss) as a function of voltage. Whereas PFpeak starts to rise at −50 mV and reaches a maximum at +40 to +50 mV, PFss only begins to rise appreciably at around 0 mV and is still increasing at +100 mV. This differs from observations on vertebrate excitable tissues where the persistent Na+ current turns on in the threshold region and saturates at around 0 mV. Schmitt and Meves (Pflügers Arch (1993) 425, 134–139) recorded M current, a non-inactivating K+ current, from NG108-15 neuroblastoma × glioma hybrid cells, voltage-clamped in the whole-cell mode, and studied the effects of phorbol 12,13-dibutyrate (PDB), an activator of protein kinase C (PKC), and arachidonic acid (AA). PDB and AA both decreased IM, the effective concentrations being 0.1–1 μM and 5–25 μM, respectively; while the PDB effect was regularly observed, the M current depression by AA was highly variable from cell to cell. The PKC 19–31 peptide, an effective inhibitor of PKC, in a concentration of 1 μM almost totally prevented the effects of PDB and AA on M current, suggesting that both are mediated by PKC. Schmitt and Meves (Pflügers Arch (1994a) 426, Suppl R 59) measured low-voltage-activated (l-v-a) and high-voltage-activated (h-v-a) Ca2+ currents on NG108-15 cells and investigated the effect of AA and PDB on both types of current. At pulse potentials > −20 mV, AA (25–100 μM) decreased l-v-a and h-v-a ICa. The decrease was accompanied by a small negative shift and a slight flattening of the activation and inactivation curves of the l-v-a ICa. The AA effect was not prevented by 50 μM eicosa-5,8,11,14-tetraynoic acid (ETYA), an inhibitor of AA metabolism, or PKC 19–31 peptide and not mimicked by 0.1–1 μM PDB. Probably, AA acts directly on the channel protein or its lipid environment. The physiological relevance of these three sets of observations is briefly discussed. 相似文献
9.
10.