全文获取类型
收费全文 | 836550篇 |
免费 | 99983篇 |
国内免费 | 438篇 |
出版年
2018年 | 6792篇 |
2016年 | 9957篇 |
2015年 | 15402篇 |
2014年 | 17681篇 |
2013年 | 24159篇 |
2012年 | 28180篇 |
2011年 | 28029篇 |
2010年 | 18890篇 |
2009年 | 17915篇 |
2008年 | 25416篇 |
2007年 | 26007篇 |
2006年 | 24523篇 |
2005年 | 23594篇 |
2004年 | 23377篇 |
2003年 | 22536篇 |
2002年 | 21799篇 |
2001年 | 34874篇 |
2000年 | 35125篇 |
1999年 | 28483篇 |
1998年 | 11192篇 |
1997年 | 11562篇 |
1996年 | 11054篇 |
1995年 | 10770篇 |
1994年 | 10606篇 |
1993年 | 10467篇 |
1992年 | 23960篇 |
1991年 | 23218篇 |
1990年 | 22771篇 |
1989年 | 22073篇 |
1988年 | 20372篇 |
1987年 | 19989篇 |
1986年 | 18326篇 |
1985年 | 18480篇 |
1984年 | 15497篇 |
1983年 | 13485篇 |
1982年 | 10895篇 |
1981年 | 9754篇 |
1980年 | 9242篇 |
1979年 | 14761篇 |
1978年 | 11915篇 |
1977年 | 10773篇 |
1976年 | 10146篇 |
1975年 | 10959篇 |
1974年 | 11811篇 |
1973年 | 11519篇 |
1972年 | 10307篇 |
1971年 | 9550篇 |
1970年 | 8172篇 |
1969年 | 7726篇 |
1968年 | 6878篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Fiona Armstrong Michael R. Blatt 《The Plant journal : for cell and molecular biology》1995,8(2):187-198
To explore the involvement of a class of seven-trans-membrane-span (7TMS) receptors in cellular signalling, a synthetic analogue (mas7) of the amphipathic tetradecapeptide mastoparan was used to mimic hormonal stimulus in guard cells of Vicia faba. The ability for mas7 to substitute for an activated receptor complex was assayed by the effect on guard cell ion channel activities in the absence of any hormonal stimulus. Currents carried by inward-(IK,in) and outward-(IK,out) rectifying potassium channels were determined under voltage clamp conditions before, during, and after exposure to mas7. The dominant effect of mas7 was to inactivate IK,in within 30 sec of application. By contrast, IK,out was largely unaffected under these conditions. The effect of mas7 on IK,in was both concentration- and voltage-dependent. At any one clamp voltage, mas7 inactivation showed Michaelian behaviour, with a mean Ki of 0.05 ± 0.02 µM at ?240 mV. Increasing mas7 concentration also shifted the voltage for half-maximal activation of the current negative, with 0.5 µM mas7 effecting a ?13 ± 2 mV displacement and lengthening the halftime for activation of the current by up to threefold. By contrast, the non-amphipathic analogue of mas7, masCP, had no appreciable effect on the steady-state current or its activation kinetics; nor was the poly-cation polylysine able to substitute for mas7 in its action on the K+ channels. Application of the non-hydrolysable analogue of GDP, GDP-β-S, either by iontophoresis or by diffusion from the microelectrode, effectively blocked mas7-induced inactivation of IK,in. These, and additional results provide in vivo evidence for the involvement of G-protein-linked 7TMS receptors in the regulation of membrane transport in a higher plant cell. 相似文献
63.
64.
65.
66.
67.
Yasuo Kobayashi Robert J. Forster Mary Alice Hefford Ronald M. Teather Masaaki Wakita Kunio Ohmiya Sadao Hoshino 《FEMS microbiology letters》1995,130(2-3):137-143
Abstract A small cryptic plasmid, pRJF2, from Butyrivibrio fibrisolvens strain OB157 was isolated and sequenced. The plasmid is similar in organisation to the previously sequenced Butyrivibrio plasmid, pRJF1, with two open reading frames, ORF1 and ORF2, flanking a region tentatively identified as the replication origin, and a region of unknown function defined by terminal 79 bp invert repeats. The sequences of ORF1, ORF2, and the presumptive replication origin are highly conserved. The sequence between the 79 bp invert repeats is not, and is therefore presumed to be of lesser functional significance, although the 5' and 3' termini are still highly conserved. The functional importance for plasmid replication of these regions was tested by constructing potential shuttle vectors, each lacking one or more of the regions of interest. When the region between the invert repeats was deleted and replaced by the erythromycin resistance gene from pAM β1 together with pUC18, to produce the 7.9 kb chimaeric plasmid pYK4, the construct was successfully transformed into E. coli and B. fibrisolvens by electroporation, and was stably maintained in both hosts. Both ORF1 and ORF2 were required for successful transformation of B. fibrisolvens . 相似文献
68.
69.
70.
In this paper the electrostatic interactions between membrane-embedded ion-pumps and their consequences for the kinetics of pump-mediated transport processes have been examined. We show that the time course of an intrinsically monomolecular transport reaction can become distinctly nonexponential, if the reaction is associated with charge translocation and takes place in an aggregate of pump molecules. First we consider the electrostatic coupling of a single dimer of ion-pumps embedded in the membrane. Then we apply the treatment to the kinetic analysis of light-driven proton transport by bacteriorhodopsin which forms two-dimensional hexagonal lattices. Finally, for the case of nonordered molecules, we also consider a model in which the pumps are randomly distributed over the nodes of a lattice. Here the average distance is equal to that deduced experimentally and the elemental size of the lattice is the effective diameter of one single pump. This latter model is applied to an aggregate of membrane-embedded Na, K- and Ca-pumps. In all these cases the electrostatic potential considered is the exact solution calculated from the method of electrical images for a plane membrane of finite thickness immersed in an infinite aqueous solution environment. The distributions of charges (ions or charged binding sites) are considered homogeneous or discrete in the membrane and/or in the external solution. In the case of discrete distributions we compare the results from a mean field approximation and a stochastic simulation. 相似文献