全文获取类型
收费全文 | 713篇 |
免费 | 56篇 |
国内免费 | 23篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 22篇 |
2018年 | 24篇 |
2017年 | 17篇 |
2016年 | 24篇 |
2015年 | 13篇 |
2014年 | 33篇 |
2013年 | 31篇 |
2012年 | 19篇 |
2011年 | 26篇 |
2010年 | 26篇 |
2009年 | 41篇 |
2008年 | 34篇 |
2007年 | 41篇 |
2006年 | 28篇 |
2005年 | 20篇 |
2004年 | 23篇 |
2003年 | 17篇 |
2002年 | 22篇 |
2001年 | 15篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有792条查询结果,搜索用时 15 毫秒
21.
Synchronously dividing binuclear cells were induced in root tips ofTriticum turgidum by caffeine treatment. Spindle and other microtubular configurations of such cells were studied using tubulin immunofluorescence
and electron microscopy. The binuclear cells developed one, two or three preprophase microtubule bands longitudinally, transversely
or rarely in a cross configuration. During the mitotic entry binuclear cells formed prophase spindles separately around each
nucleus. When the nuclei were located fairly apart, their spindle structures developed independently throughout all mitotic
phases. But when the nuclei were located closely together their metaphase and anaphase spindles shared a common polar region.
However, the two spindles in such cells retained their functional autonomy. They display structurally independent minipoles
in the common polar region. After anaphase the neighbouring nonsister chromosome groups of nuclei divided by a common polar
region come to lie close together and in telophase, become enclosed by a common nuclear envelope. During cytokinesis of binuclear
cells cell plates were formed only between sister nuclei. These cell plates may develop normally or may curve or branch giving
rise to aberrant daughter cell walls. The peculiar mode of spindle and spindle polar region organization of binuclear cells
and determination of the division plane in them are discussed. 相似文献
22.
The main barriers to the movement of water and ions in young roots of Zea mays were located by observing the effects of wounding various cell layers of the cortex on the roots' hydraulic conductivities and root pressures. These parameters were measured with a root pressure probe. Injury to the epidermis and cortex caused no significant change in hydraulic conductivity and either no change or a slight decline in root pressure. Injury to a small area of the endodermis did not change the hydraulic conductivity but caused an immediate and substantial drop in root pressure. When large areas of epidermis and cortex were removed (15–38% of total root mass), the endodermis was always injured and root pressure fell. The hydraulic conductance of the root increased but only by a factor of 1.2–2.7. The results indicate that the endodermis is the main barrier to the radial movement of ions but not water. The major barrier to water is the membranes and apoplast of all the living tissue. These conclusions were drawn from experiments in which hydrostatic-pressure differences were used to induce water flows across young maize roots which had an immature exodermis and an endodermis with Casparian bands but no suberin lamellae or secondary walls. The different reactions of water and ions to the endodermis can be explained by the huge difference in the permeability of membranes to these substances. A hydrophobic wall barrier such as the Casparian band should have little effect on the movement of water, which permeates membranes and, perhaps, also the Casparian bands easily. However, hydrophobic wall depositions largely prevent the movement of ions. Several hours after wounding the endodermis, root pressure recovered to some extent in most of the experiments, indicating that the wound in the endodermis had been partially healed.Abbreviations Lpr
hydraulic conductivity of root; T1/2 = half-time of water exchange between root xylem and external medium
This research was supported by a grant from EUROSILVA (project no. 39473C) to E.S., and by a Bilateral Exchange Grant jointly funded by the Deutsche Forschungsgemeinschaft and the Natural Sciences and Engineering Research Council of Canada to C.A.P. We thank Mr. Burkhard Stumpf for his excellent technicial assistance. 相似文献
23.
Organization of microtubules (MTs) in relation to the behavior of nuclei was examined in dividing binucleate cells ofAdiantum capillus-veneris L. To induce binucleate cells, caffeine, an inhibitor of formation of the cell plate, was applied at 4 mM to synchronously
dividing protonemal cells during cytokinesis (Murata and Wada 1993). Formation of the preprophase band (PPB) during the next
cell cycle was examined in non-centrifuged and centrifuged cells. The two nuclei were separated or associated with one another
in both non-centrifuged and centrifuged cells, although the location of the nuclei in the cylindrical protonemal cells was
different (Murata and Wada 1993). Irrespective of centrifugation, a single PPB was formed around the nuclei in cells with
associated nuclei. Two PPBs were formed in cells with separated nuclei in centrifuged cells. Patterns of mitosis and cytokinesis
varied, depending on the location of the PPB and the distribution of the nuclei. The role of the nucleus in formation of the
PPB is discussed. 相似文献
24.
Studies of plant protoplasts using both fluorescent dyes and electron dense probes have demonstrated endocytosis in plants. Ultrastructural work with soybean protoplasts using cationized ferritin (CF) revealed an endocytotic pathway from coated pits at the plasma membrane to coated vesicles, the partially coated reticulum, Golgi bodies, multivesicular bodies and finally the vacuole. Endocytosis may be responsible for membrane retrieval from the cell surface or degradation of elicitors or toxins during host-pathogen interactions. Immunofluorescence studies of dividing plant protoplasts have provided new information about the preprophase band (PPB) of microtubules and the shape of spindles. Studies of PPBs in soybean protoplast cultures permitted detailed examination of PPB development and an assessment of the usefulness of the PPB index for identifying morphogenic cultures. In multinucleate protoplasts the size and number of PPBs were apparently not controlled by nuclear number. Research with conifer protoplasts resulted in the discovery of new features of gymnosperm spindles. 相似文献
25.
26.
A collagen gene (Dcg1) was characterized in Drosophila melanogaster and shown to encode a peptide related to vertebrate basement membrane type IV collagen chains. To study the function of type IV collagen during Drosophila development, we transformed flies with a partially truncated Dcg1 gene under the control of a heat-shock promotor. This construct induced synthesis of shortened pro- chains which associated with normal ones and thereby caused degradation of the shortened and normal pro- chains through a process called pro-collagen suicide. A large proportion of embryos expressing the transgene developed a phenotype exhibiting absence or partial retraction of the germ band with defects in nerve cord condensation and dorsal closure. Together these results indicated that, during embryogenesis, type IV collagen was an essential guiding factor for cell-matrix interactions in morphogenetic events. 相似文献
27.
红细胞膜骨架与脂双层间存在着相互作用,其中带4.1蛋白与血型糖蛋白C/D间的相互作用对维持正常红细胞的形态和机械稳定性起着重要作用,研究表明,带4.1蛋白在血型糖蛋白C、D上的结合位点分别位于血型糖蛋白C的第82~98位氨基酸残基和血型糖蛋白D的第61~77位氨基酸残基. 相似文献
28.
Summary To examine whether preprophase microtubule band (PPB) organization occurs by rearrangement of pre-existing, or by assembly of new microtubules (Mts), we treated root cells ofTriticum turgidum with taxol, which stabilizes pre-existing Mts by slowing their depolymerization. With taxol early preprophase cells failed to form a normal PPB and PPB narrowing was prevented in cells that had already formed a wide one. The PPB became persistent in prometaphase cells and the formation of multipolar prophase-prometaphase spindles was induced. These data favour the suggestion that PPB formation and narrowing, as well as prophase spindle development, are dynamic processes depending on continuous Mt assembly at the PPB site and in the perinuclear cytoplasm.Abbreviations Mt
microtubule
- MTOC
microtubule organizing centre
- PPB
preprophase microtubule band
- DMSO
dimethyl sulfoxide 相似文献
29.
30.
Laura Chiarantini Luigia Rossi Alessandra Fraternale Mauro Magnani 《Molecular and cellular biochemistry》1995,144(1):53-59
Human and murine blood cells treated with ZnCl2 and bis(sulfosuccinimidyl)suberate (BS3) (a cross linking agent) undergo band 3 clustering and binding of hemoglobin to red blood cell membrane proteins. These clusters induce autologous IgG binding and complement fixation, thus favouring the phagocytosis of ZnCl2/BS3 treated cells by macrophages. The extension of red blood cell opsonization can be easily modulated by changing the ZnCl2 concentration in the 0.1–1.0 mM range thus providing an effective way to affect blood cell recognition by macrophages. In fact, murine erythrocytes treated with increasing ZnCl2 concentrations have proportionally reduced survivals when reinjected into the animal. Furthermore, the organ sequestration of ZnCl2/BS3 treated cells strongly resembles the typical distribution of the senescent cells. Since the ZnCl2/BS3 treatment can also be performed on red blood cells loaded with drugs or other substances, this procedure is an effective drug-targeting system to be used for the delivery of molecules to peritoneal, liver and spleen macrophages. 相似文献