全文获取类型
收费全文 | 1006篇 |
免费 | 66篇 |
国内免费 | 39篇 |
出版年
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 26篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 24篇 |
2015年 | 18篇 |
2014年 | 29篇 |
2013年 | 51篇 |
2012年 | 28篇 |
2011年 | 24篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 32篇 |
2007年 | 39篇 |
2006年 | 27篇 |
2005年 | 25篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 37篇 |
2001年 | 27篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 30篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 30篇 |
1991年 | 34篇 |
1990年 | 16篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1973年 | 6篇 |
1970年 | 3篇 |
排序方式: 共有1111条查询结果,搜索用时 15 毫秒
41.
Jocelyn de Lara Karen L. Wydner Katherine M. Hyland W. Steven Ward 《Journal of cellular biochemistry》1993,53(3):213-221
The flat, hooked-shaped architecture of the hamster sperm nucleus makes this an excellent model for in situ hybridization studies of the three dimensional structure of the genome. We have examined the structure of the telomere repeat sequence (TTAGGG)n with respect to the various nuclear structures present in hamster spermatozoa, using fluorescent in situ hybridization. In fully condensed, mature sperm nuclei, the telomere sequences appeared as discrete spots of various sizes interspersed throughout the volume of the nuclei. While the pattern of these signals was non-random, it varied significantly in different nuclei. These discrete telomere foci were seen to gradually lengthen into linear, beaded signals as sperm nuclei were decondensed, in vitro, and were not associated with the nuclear annulus. We also examined the relationship of telomeres to the sperm nuclear matrix, a residual nuclear structure that retains the original size and shape of the nucleus. In these structures the DNA extends beyond the perimeter of the nucleus to form a halo around it, representing the arrangement of the chromosomal DNA into loop domains attached at their bases to the nuclear matrix. Telomere signals in these structures were also linear and equal in length to those of the decondensed nuclei, and each signal represented part of a single DNA loop domain. The telomeres were attached at one end to the nuclear matrix and extended into the halo. Sperm nuclear matrices treated with Eco RI retained the telomere signals. These data support sperm DNA packaging models in which DNA is coiled into discrete foci, rather than spread out linearly along the length of the sperm nucleus. 相似文献
42.
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
43.
Robin T. Clowes Wayne Boucher Colin H. Hardman Peter J. Domaille Ernest D. Laue 《Journal of biomolecular NMR》1993,3(3):349-354
Summary We recently proposed a novel four-dimensional (4D) NMR strategy for the assignment of backbone nuclei in spectra of 13C/15N-labelled proteins (Boucher et al. (1992) J. Am. Chem. Soc., 114, 2262–2264 and J. Biomol. NMR, 2, 631–637). In this paper we extend this approach with a new constant time 4D HCC(CO)NNH experiment that also correlates the chemical shifts of the aliphatic sidechain (1H and 13C) and backbone (1H, 13C and 15N) nuclei. It separates the sidechain resonances, which may heavily overlap in spectra of proteins with large numbers of similar residues, according to the backbone nitrogen and amide proton chemical shifts. When used in conjunction with a 4D HCANNH or HNCAHA experiment it allows, in principle, complete assignment of aliphatic sidechain and backbone resonances with just two 4D NMR experiments. 相似文献
44.
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
45.
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
46.
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
47.
Summary DNA containing structures (cellular, chloroplast and mitochondrial nuclei) were stained with the fluorochrome DAPI. Fluorescence intensity, as a measure of DNA content, was estimated during the mitotic cycle in synchronized populations of the chlorococcal alga,Scenedesmus quadricauda. In cells yielding eight daughter cells, three consecutive steps in chloroplast DNA increase occurred over one mitotic cycle. The first step was performed shortly after releasing the daughter cells, the second and third steps occurred consecutively during the first half of the mitotic cycle. Commitment to chloroplast DNA replication was chronologically separated from commitment to division of chloroplast nuclei, revealing that these two chloroplast reproductive steps were under different control mechanisms. The replication of chloroplast DNA occurred at a different time to that of cell-nuclear DNA. The coordination of chloroplast reproductive processes and those in the nucleocytoplasmic compartment were governed by the mutual trophic and metabolic dependency of these compartments rather than by any direct or feedback control controlled by either of them.Abbreviations DAPI
46-diamidino-2-phenylindole
- ptDNA DNA
in chloroplast nuclei
- nucDNA DNA
in cell nuclei 相似文献
48.
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
49.
50.