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Kubota Y Takisawa H 《BioEssays : news and reviews in molecular, cellular and developmental biology》2003,25(4):313-316
Under certain conditions, the cell cycle can be arrested for a long period of time. Vertebrate oocytes are arrested at G(2) phase, while somatic cells arrest at G(0) phase. In both cells, nuclei have lost the ability to initiate DNA synthesis. In a pair of recently published papers,[1,2] Méchali and colleagues and Coué and colleagues have clarified how frog oocytes prevent untimely DNA synthesis during the long G(2) arrest. Intriguingly, they found only Cdc6 is responsible for the inability of immature oocytes to replicate DNA. Cdc6 is a key component for replication licensing, and for G(0) cells to re-enter the proliferative stage. Strikingly similar strategies for preventing the untimely replication in both cells suggest that the suppression of replication licensing is a universal mechanism for securing the prolonged arrest of the cell cycle. 相似文献
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Gross structural changes and neuropil formation in the brain during development were described in Idiosepius paradoxus, a sepioid that we chose as a model cephalopod. The brain originates in 4 pairs of ectodermal placodes, which occur separately in the embryonic surface undergoing epiboly. In the final period of epiboly, neuroblasts internalize from the placodes and gather into 4 pairs of ganglionic masses. The ganglionic masses assemble into a ring-like cluster encircling the inner yolk and the foregut anlage, gradually integrated into the 4 domains of a massive brain, a subesophageal mass (SBM), a supraesophageal mass (SPM), and a pair of optic lobes. In the early brain, neuropil forms a framework composed of a longitudinal ladder lying in the SBM, and a transverse arch standing on the lateral sides of the SBM and crossing the SPM. Differentiation of brain lobes proceeds from ventral to dorsal along this framework; first the magnocellular lobes and the posterior pedal lobe appear first in the SBM, the other lobes in the SBM and the basal lobes follow in the proximal region of the SPM, and the accessory lobes develop last in the most dorsal zone of the SPM. In the hatchlings, the brain lobes show almost the same arrangement as in the adults, but the accessory lobes, particularly the vertical lobe, are much smaller than those in the adults. Comparison of the present results with those in the teuthoid and the octopod indicates that developmental sequences of the brain are highly conserved in the coleoid cephalopods. 相似文献
65.
Oku H Futamori N Masuda K Shimabukuro Y Omine T Iwasaki H 《Bioscience, biotechnology, and biochemistry》2003,67(10):2106-2114
It was found that the partially purified beta-ketoacyl-ACP synthase of Bacillus insolitus did not require the addition of FabD (malonyl-CoA:ACP transacylase, MAT) for the activity assay. This study therefore examined the necessity of FabD protein for in vitro branched-chain fatty acid (BCFA) biosynthesis by crude fatty acid synthetases (FAS) of Bacilli. To discover the involvement of FabD in the BCFA biosynthesis, the protein was removed from the crude FAS by immunoprecipitation. The His-tag fusion protein FabD of Bacillus subtilis was expressed in Escherichia coli and used for the preparation of antibody. The rabbit antibody raised against the expressed fusion protein specifically recognized the FabD in the crude FAS of B. subtilis. Evaluation of the efficacy of the immunoprecipitation showed that a trace of FabD protein was present in the antibody-treated crude FAS. However, this complete removal of FabD from the crude FAS did not abolish its BCFA biosynthesis, but only reduced the level to 50-60% of the control level for acyl-CoA primer and to 80% for alpha-keto-beta-methylvalerate primer. Furthermore, the FabD concentration did not necessarily correlate with the MAT specific activity in the enzyme fractions, suggesting the presence of another enzyme source of MAT activity. This study, therefore, suggests that FabD is not the sole enzyme source of MAT for in vitro BCFA biosynthesis, and implies the existence of a functional connection between fatty acid biosynthesis and another metabolic pathway. 相似文献
66.
nanos1: a mouse nanos gene expressed in the central nervous system is dispensable for normal development 总被引:2,自引:0,他引:2
Haraguchi S Tsuda M Kitajima S Sasaoka Y Nomura-Kitabayashid A Kurokawa K Saga Y 《Mechanisms of development》2003,120(6):721-731
A mouse nanos (nanos1) gene was cloned and its function was examined by generating a gene-knockout mouse. The nanos1 gene encodes an RNA-binding protein, which contains a putative zinc-finger motif that exhibits similarity with other nanos-class genes in vertebrates and invertebrates. Although nanos1 is not detected in primordial germ cells, it is observed in seminiferous tubules of mature testis. Interestingly, maternally expressed nanos1 is observed in substantial amounts in oocytes, but the amount of maternal RNA is rapidly reduced after fertilization, and the transient zygotic nanos1 expression is observed in eight-cell embryos. At 12.5 days postcoitum, nanos1 is re-expressed in the central nervous system and the expression continues in the adult brain, in which the hippocampal formation is the predominant region. The nanos1 -deficient mice develop to term without any detectable abnormality and they are fertile. No significant neural defect is observed in terms of their behavior to date. 相似文献
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A clear parallelism was demonstrated between the efficiency as substrate of the substituted oligopeptides corresponding to the carboxy-terminal (C-terminal) sequence of the precursor D1 protein (pD1) in the in vitro enzymatic assay and their competitive inhibitory capacity toward the proteolytic C-terminal processing of the full-length pD1 integrated in the intact photosystem II complex embedded in the thylakoid membrane of Scenedesmus obliquus LF-1 mutant, as shown e.g. by the influence of L343A, A345G and A345V substitutions and the effect of C-terminal fragments. This suggests that the basic mechanism for substrate recognition by the processing protease elucidated in the enzymatic analysis using synthetic oligopeptides is also effective in vivo, although it can sometimes be difficult to detect the consequence of amino acid substitution in the integrated systems. 相似文献
69.
Yumiko Nakagaito Motonobu Satoh Haruhiko Kuno Toshi Iwama Masao Takeuchi Akira Hakura Touho Yoshida 《In vitro cellular & developmental biology. Animal》1998,34(7):585-592
Summary We have established a multipotent clonal cell line, named MEB5, from embryonic mouse forebrains after the infection of a retrovirus
carrying E7 oncogene of human papillomavirus type 16. MEB5 cells proliferated in serum-free, epidermal growth factor (EGF)-supplemented
medium. They expressed markers for neural precursor cells (nestin, A2B5, and RC1) and did not express markers for neurons
(class III β-tubulin), astrocytes (glial fibrillary acidic protein), and oligodendrocytes (galactocerebroside). MEB5 cells
were stably maintained in an undifferentiated state with a diploid karyotype in the presence of EGF. When they were deprived
of EGF, about 50% of the cells died due apoptosis within 24 h. The remaining cells differentiated into neurons, astrocytes,
or oligodendrocytes within 2 wk. The newly developed cells with neuronal morphology were immunoreactive for γ-aminobutyric
acid and exhibited neuronal electrophysiological properties. When MEB5 cells were treated with leukemia inhibitory for 7 d,
they were induced to differentiate exclusively into astrocytes. These results inducate that MEB5 is a cell line with characteristics
of EGF-dependent, multipotent neural precursor cells. This cell line should provide a good model system to study the mechanisms
of survival, proliferation, and differentiation of the multipotent precursor cells in the central nervous system. 相似文献
70.
Michiya Sugimori Yumiko Hayakawa Bruce M. Boman Jeremy Z. Fields Miharu Awaji Hiroko Kozano Ryoi Tamura Seiji Yamamoto Toru Ogata Mitsuhiko Yamada Shunro Endo Masanori Kurimoto Satoshi Kuroda 《PloS one》2015,10(8)