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71.
72.
Hiroyuki Matsuda Yasutaka Kurata Satoshi Matsuoka Akinori Noma 《Progress in biophysics and molecular biology》2010,103(1):102-110
We aimed to study kinetics of modulation by intracellular Mg2+ of cardiac gap junction (Mg2+ gate). Paired myocytes of guinea-pig ventricle were superfused with solutions containing various concentrations of Mg2+. In order to rapidly apply Mg2+ to one aspect of the gap junction, the non-junctional membrane of one of the pair was perforated at nearly the connecting site by pulses of nitrogen laser beam. The gap junction conductance (Gj) was measured by clamping the membrane potential of the other cell using two-electrode voltage clamp method. The laser perforation immediately increased Gj, followed by slow Gj change with time constant of 3.5 s at 10 mM Mg2+. Mg2+ more than 1.0 mM attenuated dose-dependently the gap junction conductance and lower Mg2+ (0.6 mM) increased Gj with a Hill coefficient of 3.4 and a half-maximum effective concentration of 0.6 mM. The time course of Gj changes was fitted by single exponential function, and the relationship between the reciprocal of time constant and Mg2+ concentration was almost linear. Based on the experimental data, a mathematical model of Mg2+ gate with one open state and three closed states well reproduced experimental results. One-dimensional cable model of thirty ventricular myocytes connected to the Mg2+ gate model suggested a pivotal role of the Mg2+ gate of gap junction under pathological conditions. 相似文献
73.
Satoko Ito Hitoki Hasegawa Michinari Hamaguchi 《Biochemical and biophysical research communications》2010,400(2):230-235
Gap junctional communication, which is mediated by the connexin protein family, is essential for the maintenance of normal tissue function and homeostasis. Loss of intercellular communication results in a failure to coordinately regulate cellular functions, and it can facilitate tumorigenesis. Expression of oncogenes and stimulation with cytokines has been shown to suppress intercellular communication; however, the exact mechanism by which intercellular communication is disrupted by these factors remains uncertain. In this report, we show that Akt is essential for the disruption of gap junctional communication in v-Src-transformed cells. In addition, inhibition of Akt restores gap junctional communication after it is suppressed by TNF-α signaling. Furthermore, we demonstrate that the expression of a constitutively active form of Akt1, but not of Akt2 or Akt3, is sufficient to suppress gap junctional communication. Our results clearly define Akt1 as one of the critical regulators of gap junctional communication. 相似文献
74.
WILLIAM T. STANLEY JACOB A. ESSELSTYN 《Biological journal of the Linnean Society. Linnean Society of London》2010,100(3):669-680
We assess variation in morphological and molecular characters among three species of Myosorex (the mouse shrew) –Myosorex geata, Myosorex kihaulei, and Myosorex zinki– as a means to test previously proposed biogeographic hypotheses for Tanzanian ‘sky islands’ and systematic hypotheses for Tanzanian mouse shrews. We analyse 17 cranial and dental variables using multivariate statistics and perform phylogenetic and phylogeographic analyses on sequences of mitochondrial and nuclear DNA; samples are drawn from every known Tanzanian population of Myosorex. Morphometric and phylogenetic analyses reveal that M. zinki is distinct, but that currently isolated populations of M. geata and M. kihaulei are relatively similar to one another, and may not have been isolated over geological time scales. Analyses of molecular variance identify statistically significant, but limited, genetic variation within and between isolated populations of M. geata and M. kihaulei. Between two putative regional biogeographic boundaries, greater genetic variation is explained by grouping populations on either side of the Ruaha River than by grouping populations on either side of the Makambako Gap. Our results are in agreement with recent studies illustrating the close relationship between faunas of the Southern Highlands and southern Eastern Arc Mountains, diminishing the apparent importance of the Makambako Gap as a historical biogeographic barrier. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 669–680. 相似文献
75.
Gap junctions of some vertebrates are capable of passing the elongate molecule, calmodulin, with a molecular weight 8-17 times greater than the previously recognized size limits. Fluorescently labeled calmodulin (FCaM) (17.34 kDa) microinjected into oocytes of ovarian follicles from an amphibian, Xenopus laevis, and from two species of teleost fish, Danio rerio (Zebrafish) and Oryzias latipes (Medaka), is shown to transit their gap junctions and enter the surrounding epithelial cells. Passage of FCaM was terminated when follicles were first treated with 1 mM octanol, a molecule known to down-regulate gap junctions. There was no FCaM detected in the surrounding medium, nor did epithelial cells become fluorescent when follicles were incubated in medium containing dye. Calmodulin is well known to modulate many cytoplasmic reactions; thus, its passage through gap junctions opens possibilities of additional means by which cells may be supplied with this signaling molecule, and by which their supply may be regulated. 相似文献
76.
Connexin 43 (Cx43), the most widely expressed and abundant vertebrate gap junction protein, is phosphorylated at multiple
different serine residues during its life cycle. Cx43 is phosphorylated soon after synthesis and phosphorylation changes as
it traffics through the endoplasmic reticulum and Golgi to the plasma membrane, ultimately forming a gap junction structure.
The electrophoretic mobility of Cx43 changes as the protein proceeds through its life cycle, with prominent bands often labeled
P0, P1 and P2. Many reports have indicated changes in “phosphorylation” based on these mobility shifts and others that occur
in response to growth factors or other biological effectors. Here, we indicate how phosphospecific and epitope-specific antibodies
can be utilized to show when and where certain phosphorylation events occur during the Cx43 life cycle. These reagents show
that phosphorylation at S364 and/or S365 is involved in forming the P1 isoform, an event that apparently regulates trafficking
to or within the plasma membrane. Phosphorylation at S325, S328 and/or S330 is necessary to form a P2 isoform; and this phosphorylation
event is present only in gap junctions. Treatment with protein kinase C activators led to phosphorylation at S368, S279/S282
and S262 with a shift in mobility in CHO, but not MDCK, cells. The shift was dependent on mitogen-activated protein kinase
activity but not phosphorylation at S279/S282. However, phosphorylation at S262 could explain the shift. By defining these
phosphorylation events, we have begun to sort out the critical signaling pathways that regulate gap junction function. 相似文献
77.
Koizumi J Kojima T Kamekura R Kurose M Harimaya A Murata M Osanai M Chiba H Himi T Sawada N 《The Journal of membrane biology》2007,218(1-3):1-7
The epithelium of upper respiratory tissues such as nasal mucosa forms a continuous barrier to a wide variety of exogenous
antigens. The epithelial barrier function is regulated in large part by the intercellular junctions, referred to as gap and
tight junctions. However, changes of gap and tight junctions during differentiation of human nasal epithelial (HNE) cells
are still unclear. In the present study, to investigate changes of gap and tight junctions during differentiation of HNE cells
in vitro, we used primary human HNE cells cocultured with primary human nasal fibroblast (HNF) cells in a noncontact system. In HNE
cells cocultured with HNF cells for 2 weeks, numerous elongated cilia-like structures were observed compared to those without
HNF cells. In the coculture, downregulation of Cx26 and upregulation of Cx30.3 and Cx31 were observed together with extensive
gap junctional intercellular communication. Furthermore, expression of the tight junction proteins claudin-1, claudin-4, occludin
and ZO-2 was increased. These results suggest that switching in expression of connexins and induction of tight junction proteins
may be closely associated with differentiation of HNE cells in
vitro and that differentiation of HNE cells requires unknown soluble factors secreted from HNF cells. 相似文献
78.
Gap junctions are plasma membrane domains containing arrays of channels that exchange ions and small molecules between neighboring
cells. Gap junctional intercellular communication enables cells to directly cooperate both electrically and metabolically.
Several lines of evidence indicate that gap junctions are important in regulating cell growth and differentiation and for
maintaining tissue homeostasis. Gap junction channels consist of a family of transmembrane proteins called connexins. Gap
junctions are dynamic structures, and connexins have a high turnover rate in most tissues. Connexin43 (Cx43), the best-studied
connexin isoform, has a half-life of 1.5–5 h; and its degradation involves both the lysosomal and proteasomal systems. Increasing
evidence suggests that ubiquitin is important in the regulation of Cx43 endocytosis. Ubiquitination of Cx43 is thought to
occur at the plasma membrane and has been shown to be regulated by protein kinase C and the mitogen-activated protein kinase
pathway. Cx43 binds to the E3 ubiquitin ligase Nedd4, in a process modulated by Cx43 phosphorylation. The interaction between
Nedd4 and Cx43 is mediated by the WW domains of Nedd4 and involves a proline-rich sequence conforming to a PY (XPPXY) consensus
motif in the C terminus of Cx43. In addition to the PY motif, an overlapping tyrosine-based sorting signal conforming to the
consensus of an YXXϕ motif is involved in Cx43 endocytosis, indicating that endocytosis of gap junctions involves both ubiquitin-dependent and
-independent pathways. Here, we discuss current knowledge on the ubiquitination of connexins. 相似文献
79.
Glomerular mesangial cells (MCs) are specialized vascular smooth muscle cells that play a critical role in the control of
glomerular hemodynamics. One of the intriguing features of MCs is their extraordinary abundance in gap junctions (GJs). It
has long been speculated that GJs may bridge MCs together and provide the mesangium with the characteristics of a functional
syncytium. Accumulating scientific evidence supports this idea. GJs are reported to be critically involved in important physiological
processes like tubuloglomerular feedback and glomerular filtration. In addition, GJs are implicated in the control of many
cellular processes of MCs, including growth, differentiation and survival. This article summarizes the current knowledge on
the roles of GJs in glomerular pathophysiology. 相似文献
80.
茂兰喀斯特森林林隙幼苗出现的时空格局 总被引:1,自引:0,他引:1
通过4次对茂兰自然保护区喀斯特森林林隙内种子的天然萌发情况进行观测,分析了林隙内幼苗的萌发数量、存活率及幼苗出现的时空分布格局。结果发现:林隙中大多数萌发的幼苗存活率均较高,平均存活率达50%以上,林隙的形成,不但提高了喀斯特森林树种的萌发率,也提高了幼苗的存活率。林隙中心、近中心、林隙边缘各区域幼苗的密度存在显著的空间差异,山拐枣(Poliothyrsis sinensis)、多脉榆(Ulmus castaneifolia)等树种在林隙中心幼苗密度最大,圆果化香(Platycarya longipes)、翅荚香槐(Cladrastis platycarpa)、圆叶乌桕(Sapium rotundifolium)、掌叶木(Handeliodendron bodinieri)、黄连木(Pistacia chinen-sis)和云贵鹅耳枥(Carpinus pubescens)等树种在林隙近中心幼苗密度最大,而樟叶槭(Acercinnamomifolium)、球核荚蒾(Viburnumpropinquum)、小叶青冈(Cyclobalanopsis myrsinaefolia)、轮叶木姜子(Litsea verticillata)等则在林隙边缘光照较弱的地方生长良好。幼苗出现的时间分布特征明显,整个观察期幼苗都持续萌发,但大多数树种幼苗出现在第2观测期(3月),幼苗出现数目从第2次到后面的几次观察期显著下降。林隙3个区域幼苗出现不是同步的,林隙中心的幼苗出现最快,与其它两个部位相比,林隙边缘的幼苗出现有滞后现象。研究结果表明林隙中心的环境条件有利于种子萌发,但林隙近中心却更利于幼苗存活。 相似文献