全文获取类型
收费全文 | 1854篇 |
免费 | 95篇 |
国内免费 | 71篇 |
出版年
2023年 | 19篇 |
2022年 | 24篇 |
2021年 | 49篇 |
2020年 | 44篇 |
2019年 | 38篇 |
2018年 | 63篇 |
2017年 | 49篇 |
2016年 | 33篇 |
2015年 | 56篇 |
2014年 | 94篇 |
2013年 | 92篇 |
2012年 | 56篇 |
2011年 | 60篇 |
2010年 | 50篇 |
2009年 | 74篇 |
2008年 | 62篇 |
2007年 | 102篇 |
2006年 | 66篇 |
2005年 | 54篇 |
2004年 | 84篇 |
2003年 | 71篇 |
2002年 | 61篇 |
2001年 | 48篇 |
2000年 | 54篇 |
1999年 | 48篇 |
1998年 | 42篇 |
1997年 | 41篇 |
1996年 | 43篇 |
1995年 | 40篇 |
1994年 | 31篇 |
1993年 | 29篇 |
1992年 | 35篇 |
1991年 | 28篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 8篇 |
1972年 | 7篇 |
排序方式: 共有2020条查询结果,搜索用时 15 毫秒
101.
Donald A. Drew Gretchen A. Koch Heather Vellante Ronak Talati Oswaldo Sanchez 《Bulletin of mathematical biology》2009,71(4):980-1005
Escherichia coli is a rod-shaped bacterium that divides at its midplane, partitioning its cellular material into two roughly equal parts.
At the appropriate time, a septum forms, creating the two daughter cells. Septum formation starts with the appearance of a
ring of FtsZ proteins on the cell membrane at midplane. This Z-ring causes an invagination in the membrane, which is followed
by growth of two new endcaps for the daughter cells. Invagination occurs against a cell overpressure of several atmospheres.
A model is presented for the shape of the cell as determined by the tension in the Z-ring. This model allows the calculation
of the force required for invagination. Then three possible models to generate the force necessary to achieve invagination
are presented and analyzed. These models are based on converting GTP-bound FtsZ polymeric structures to GDP-bound FtsZ structures,
which then leave the polymer. Each model is able to generate the force by relating the hydrolyzation to an irreversible molecular
binding event, resulting in a net motion of putative anchors for the structures. All three models show that cross-linking
the FtsZ protofilaments into a polymer structure allows the removal of GDP-FtsZ without interrupting the structure during
force generation, as would happen for a simple polymeric chain.
This work is a partially the result of an Undergraduate Research Project (OS and RT). The support of the National Science
Foundation Division of Mathematical Sciences and Division of Biological Sciences through Grant DMS 0214585 and a Supplement
to support Undergraduate Research in Biology and Mathematics is appreciated. 相似文献
102.
Gerald Udolph Priyadarshini Rath Joanne Toh Rahul Pandey William Chia 《Developmental biology》2009,336(2):156-168
The generation of cellular diversity in the nervous system involves the mechanism of asymmetric cell division. Besides an array of molecules, including the Par protein cassette, a heterotrimeric G protein signalling complex, Inscuteable plays a major role in controlling asymmetric cell division, which ultimately leads to differential activation of the Notch signalling pathway and correct specification of the two daughter cells. In this context, Notch is required to be active in one sibling and inactive in the other. Here, we investigated the requirement of genes previously known to play key roles in sibling cell fate specification such as members of the Notch signalling pathway, e.g., Notch (N), Delta (Dl), and kuzbanian (kuz) and a crucial regulator of asymmetric cell division, inscuteable (insc) throughout lineage progression of 4 neuroblasts (NB1-1, MP2, NB4-2, and NB7-1). Notch-mediated cell fate specification defects were cell-autonomous and were observed in all neuroblast lineages even in cells born from late ganglion mother cells (GMC) within the lineages. We also show that Dl functions non-autonomously during NB lineage progression and clonal cells do not require Dl from within the clone. This suggests that within a NB lineage Dl is dispensable for sibling cell fate specification. Furthermore, we provide evidence that kuz is involved in sibling cell fate specification in the central nervous system. It is cell-autonomously required in the same postmitotic cells which also depend on Notch function. This indicates that KUZ is required to facilitate a functional Notch signal in the Notch-dependent cell for correct cell fate specification. Finally, we show that three neuroblast lineages (NB1-1, NB4-2, and NB7-1) require insc function for sibling cell fate specification in cells born from early GMCs whereas insc is not required in cells born from later GMCs of the same lineages. Thus, there is differential requirement for insc for cell fate specification depending on the stage of lineage progression of NBs. 相似文献
103.
Mitsuhiko Kurusu Yasushi Maruyama Masataka Okabe Katsuo Furukubo-Tokunaga 《Developmental biology》2009,326(1):224-136
The intrinsic neurons of mushroom bodies (MBs), centers of olfactory learning in the Drosophila brain, are generated by a specific set of neuroblasts (Nbs) that are born in the embryonic stage and exhibit uninterrupted proliferation till the end of the pupal stage. Whereas MB provides a unique model to study proliferation of neural progenitors, the underlying mechanism that controls persistent activity of MB-Nbs is poorly understood. Here we show that Tailless (TLL), a conserved orphan nuclear receptor, is required for optimum proliferation activity and prolonged maintenance of MB-Nbs and ganglion mother cells (GMCs). Mutations of tll progressively impair cell cycle in MB-Nbs and cause premature loss of MB-Nbs in the early pupal stage. TLL is also expressed in MB-GMCs to prevent apoptosis and promote cell cycling. In addition, we show that ectopic expression of tll leads to brain tumors, in which Prospero, a key regulator of progenitor proliferation and differentiation, is suppressed whereas localization of molecular components involved in asymmetric Nb division is unaffected. These results as a whole uncover a distinct regulatory mechanism of self-renewal and differentiation of the MB progenitors that is different from the mechanisms found in other progenitors. 相似文献
104.
Timo T. My?h?nen J. Arturo García-Horsman Jofre Tenorio-Laranga Pekka T. M?nnist? 《The journal of histochemistry and cytochemistry》2009,57(9):831-848
Prolyl oligopeptidase (POP) is a serine endopeptidase that hydrolyses proline-containing peptides shorter than 30 amino acids. POP may be associated with cognitive functions, possibly via the cleavage of neuropeptides. Recent studies have also suggested novel non-hydrolytic and non-catalytic functions for POP. Moreover, POP has also been proposed as a regulator of inositol 1,4,5-triphosphate signaling and several other functions such as cell proliferation and differentiation, as well as signal transduction in the central nervous system, and it is suspected to be involved in pathological conditions such as Parkinson''s and Alzheimer''s diseases and cancer. POP inhibitors have been developed to restore the depleted neuropeptide levels encountered in aging or in neurodegenerative disorders. These compounds have shown some antiamnesic effects in animal models. However, the mechanisms of these hypothesized actions are still far from clear. Moreover, the physiological role of POP has remained unknown, and a lack of basic studies, including its distribution, is obvious. The aim of this review is to gather information about POP and to propose some novel roles for this enzyme based on its distribution and its discordant spatial association with its best known substrates. (J Histochem Cytochem 57:831–848, 2009) 相似文献
105.
Membrane fission is the last step of membrane carrier formation. As fusion, it is a very common process in eukaryotic cells, and participates in the integrity and specificity of organelles. Although many proteins have been isolated to participate in the various membrane fission reactions, we are far from understanding how membrane fission is mechanically triggered. Here we aim at reviewing the well-described examples of dynamin and lipid phase separation, and try to extract the essential requirements for fission. Then, we survey the recent knowledge obtained on other fission reactions, analyzing the similarities and differences with previous examples. 相似文献
106.
Protein phosphotase Cdc14 (Cell division cycle gene 14) is a key regulator of late mitotic events in Saccharomyces cerevisiae. However the function of human Cdc14 (HsCdc14A & B) and its regulatory network are still elusive. In this study, we identified
a new partner of HsCdc14A named Brap2 (BRCA1 associated protein 2) using yeast two-hybrid screening assay. The interaction
between these two proteins is confirmed by co-immunoprecipitation in human HEK 293T cells. Brap2 co-localizes with HsCdc14A
on mitotic spindle poles and over-expression of Brap2 causes multiple spindle poles. Furthermore, we found that Brap2, which
has intrinsic RING domain dependent E3 ligase activity, facilitates HsCdc14A Lys-63 linked ubiquitin modification, indicating
that Brap2 may be the ubiquitin E3 Ligase of HsCdc14A. Our findings imply that Brap2 plays a significant role in cell cycle
regulation besides its facilitation of HsCdc14A ubiquitination. 相似文献
107.
Adventitious roots of Primula acaulis Jacq. are characterized by broad cortex and narrow stele during the primary development. Secondary thickening of roots occurs
through limited cambial growth together with secondary dilatation growth of the persisting cortex. Close to the root tip,
at a distance of ca. 4 mm from the apex, Casparian bands (state I of endodermal development) within endodermal cells develop synchronously. During
late, asynchronous deposition of suberin lamellae (state II of endodermal development), a positional effect is clearly expressed
- suberization starts in the cells opposite to the phloem sectors of the vascular cylinder at a distance of 30 – 40 mm from
the root tip. The formation of secondary walls in endodermis (state III of endodermal development) correlates with the beginning
of secondary growth of the root at a distance of ca. 60 mm. Endodermis is the only cortical layer of primrose, where not only cell enlargement but also renewed cell division
participate in the secondary dilatation growth. The original endodermal cells additionally divide anticlinally only once.
Newly-formed radial walls acquire a typical endodermal character by forming Casparian bands and deposition of suberin lamellae.
A network of endodermal Casparian bands of equal density develops during the root thickening by the tangential expansion of
cells and by the formation of new radial walls with characteristic wall modifications. These data are important since little
attention has been paid up till now to the density of endodermal network as a generally significant structural and functional
trait of the root.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
108.
109.
衣藻质体分裂相关基因CrFtsZ2的克隆及其进化分析 总被引:5,自引:0,他引:5
FtsZ(filamentingtemperaturesensitive)是一类从大肠杆菌温度敏感型突变体中分离到的基因 .该基因与E .coli细胞分裂密切相关 .突变体由于细胞分裂受阻而呈现“长丝状”[1] .此类基因于 1980年首次被克隆[2 ] .随后的研究表明 ,FtsZ蛋白在E .coli分裂细胞的凹陷处形成环状多聚体 ,Z环 ,是E .coli细胞分裂的限制因子[3 ] .衣藻属于绿藻 ,在现存的所有单细胞真核藻类中 ,绿藻是与陆生植物亲缘关系最近的一支[4] .由于衣藻为单细胞真核生物 ,并且仅含有一个巨大的叶绿体 ,因而是研究… 相似文献
110.