全文获取类型
收费全文 | 840篇 |
免费 | 59篇 |
国内免费 | 5篇 |
专业分类
904篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 18篇 |
2013年 | 51篇 |
2012年 | 21篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 19篇 |
2008年 | 35篇 |
2007年 | 38篇 |
2006年 | 40篇 |
2005年 | 16篇 |
2004年 | 23篇 |
2003年 | 42篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 31篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 24篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有904条查询结果,搜索用时 15 毫秒
811.
Tau Protein Function in Axonal Formation 总被引:2,自引:0,他引:2
Tau protein is a predominantly neuronal microtubule-associated protein that is enriched in axons and is capable of promoting microtubule assembly and stabilization. In the present article we review some of the key experiments directed to obtain insights about tau protein function in developing neurons. Aspects related to whether or not tau has essential, unique, or complementary functions during axonal formation are discussed. 相似文献
812.
Tensile Tissue Stress Affects the Orientation of Cortical Microtubules in the Epidermis of Sunflower Hypocotyl 总被引:2,自引:0,他引:2
Abstract
In turgid multicellular organs, it is convenient to differentiate between the two kinds of tensile forces acting in cell walls
as a result of turgor pressure. The primary forces occur both in situ and in cells isolated from the organ, whereas the secondary forces occur only in situ. The latter are an unavoidable physical consequence of the variation in mechanical parameters of tissues forming layers or
strands. The most rigid tissue is under maximal tensile force, whereas the least rigid is under maximal compressive force.
These forces cause tissue stresses (that is, certain tissues are under tensile stress, whereas others are under compressive
stress in the organ). The primary and secondary forces result in primary and secondary stress in cell walls, respectively.
The anisotropy of the primary stress is a function of cell shape. For instance, in cylindric cells the anisotropy expressed
as the ratio of longitudinal to transverse stresses is 0.5. The anisotropy of the secondary stress is a function of the compound
structure of the organ. For example, in the epidermis of sunflower hypocotyl, the longitudinal secondary stress is much higher
than the transverse stress. The primary and secondary stresses are superimposed, and, as a consequence, the stress anisotropy
in the outer thick walls of epidermal cells is greater than 1. These outer epidermal walls transmit most of the tissue stress.
When the epidermis is peeled but remains turgid, only primary stress remains, but loading of the peel can reestablish the
original stress anisotropy. We studied the effect of stress anisotropy changes on the orientation of cortical microtubules
(CMTs) in the sunflower hypocotyl epidermis. We showed that changes in stress anisotropy cause the CMT orientation to change
in the direction of maximal wall stress. In situ, the relatively high tensile tissue stress in the epidermis causes maximal stress in the longitudinal direction and relatively
steep CMT orientation. When the tissue stress is removed from the epidermis by peeling, the CMTs tend to reorient toward the
transverse direction, which is the direction of maximal stress in the primary component. On application of external longitudinal
stress, to substitute for tissue stress, CMTs tend to reorient in the longitudinal direction. However, a relatively high rate
of plastic strain is caused by the stress applied to the peel in an acid medium. This produces a less steep orientation of
CMTs. It appears that the change in stress anisotropy orients the CMT in the direction in which the stress is maximal after
the change, but there is also some effect of the growth rate on the orientation.
Received 4 January 2000; accepted 10 February, 2000 相似文献
813.
814.
We investigate planar cell polarity (PCP) in the Drosophila larval epidermis. The intricate pattern of denticles depends on only one system of PCP, the Dachsous/Fat system. Dachsous molecules in one cell bind to Fat molecules in a neighbour cell to make intercellular bridges. The disposition and orientation of these Dachsous–Fat bridges allows each cell to compare two neighbours and point its denticles towards the neighbour with the most Dachsous. Measurements of the amount of Dachsous reveal a peak at the back of the anterior compartment of each segment. Localization of Dachs and orientation of ectopic denticles help reveal the polarity of every cell. We discuss whether these findings support our gradient model of Dachsous activity. Several groups have proposed that Dachsous and Fat fix the direction of PCP via oriented microtubules that transport PCP proteins to one side of the cell. We test this proposition in the larval cells and find that most microtubules grow perpendicularly to the axis of PCP. We find no meaningful bias in the polarity of microtubules aligned close to that axis. We also reexamine published data from the pupal abdomen and find no evidence supporting the hypothesis that microtubular orientation draws the arrow of PCP. 相似文献
815.
816.
The unicellular green alga Micrasterias denticulata performs a two-directional postmitotic nuclear migration during development, a passive migration into the growing semicell, and a microtubule mediated backward migration towards the cell centre. The present study provides first evidence for force generation by motor proteins of the kinesin family in this process. The new kinesin specific inhibitor adociasulfate-2 causes abnormal nuclear displacement at 18 microM. AMP-PNP, a non hydrolyseable ATP analogue or the general ATPase inhibitors calyculin A and sodium orthovanadate also disturb nuclear migration. In addition kinesin-like proteins are detected by means of immunoblotting using antibodies against brain kinesin, plant derived antibodies to kinesin-like proteins and a calmodulin binding kinesin-like protein. Immunoelectron microscopy suggests a correlation of conventional kinesin-like proteins, but not of the calmodulin binding kinesin-like protein to the microtubule apparatus associated with the migrating nucleus. 相似文献
817.
818.
《Current biology : CB》2023,33(16):3522-3528.e7
819.
Monica Lindén B. Dean Nelson Dragutin Loncar Jean Francois Leterrier 《Journal of bioenergetics and biomembranes》1989,21(4):507-518
Mitochondrial movements and morphology are regulated through interactions with the cytoskeletal system, in particular the microtubules. An interaction between the microtubule-associated proteins (MAPs) and the outer surface of rat brain mitochondria has been demonstratedin vitro andin situ. One of the MAPs, MAP2, binds to specific high-affinity sites on the outer membrane. Upon binding, MAP2 is released from microtubules, and it induces a physical alteration in the outer membrane which is characterized by a tighter association of porin with the membrane. It is concluded that MAP2 either binds to porin or to a domain of the outer membrane which alters the membrane environment of porin. The possibility is raised that this domain participates in mitochondrial mobilityin situ. 相似文献
820.
Graham Purvis Cees van der Land Naoko Sano Charles Cockell Anders Barlow Peter Cumpson Elisa Lopez‐Capel Neil Gray 《Geobiology》2019,17(3):281-293
Structures in geological samples are often interpreted as fossilised life; however, such interpretations are equivocal, as abiotic processes can be invoked to explain their presence. Thus, additional lines of chemical evidence are invaluable in confirming or refuting such morphological evidence. Glass shards in tuff from the Ontong Java Plateau (OJP) contain microtubular structures that are in close proximity to functionalised nitrogen substituted aromatic compounds that may be indicative of the chemical remnants of biological activity. The organic composition of the OJP tuff containing microtubular alteration structures was compared with tuff without such features. In addition, organic matter associated with horizons with compacted remnants of woody material buried in the OJP tuff and overlying pelagic calcareous foraminifer sediment were also characterised, to ascertain the provenance of the organic matter found in the OJP tuff. As a further control, the organic material in submarine and terrestrial basalts from other locations were also characterised providing further evidence to support the view that the organic matter in the OJP tuff is authigenic. Carbon–nitrogen chemistry was detected across all OJP tuff samples irrespective of the presence or absence of microtubular features, but was not detected in either the wood material, the overlying pelagic sediments or in the basalts from other locations. The results indicate no direct link between the OJP nitrogenous organic compounds and the presence or absence of microtubular features. 相似文献