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31.
Tokio Kogoma 《Journal of molecular biology》1976,103(1):191-197
In the Escherichia coli dnaB mutant BT165/70 were observed two types of temperature sensitivity of DNA replication: one slow but irreversible, occurring before the initiation of DNA replication, and the other instant but reversible, occurring during replication. These two types of temperature sensitivity appear to result from the single dnaB mutation. The observation suggests two different states of the dnaB gene product within the cell. Interaction of the dnaB protein with other components of the hypothetical replication complex is suggested. A temperature-insensitive revertant (second site mutation) of BT165/70 was isolated whose phenotype suggests an alteration in the interacting ability of the revertant protein. 相似文献
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Toshihiko Akiba Yuichi Abe Yoshitomo Kusaka Tokio Ichimatsu Tetsuyuki Akao Eiichi Mizuki Ryuta Kanai 《Journal of molecular biology》2009,386(1):121-149
Parasporin-2 is a protein toxin that is isolated from parasporal inclusions of the Gram-positive bacterium Bacillus thuringiensis. Although B. thuringiensis is generally known as a valuable source of insecticidal toxins, parasporin-2 is not insecticidal, but has a strong cytocidal activity in liver and colon cancer cells. The 37-kDa inactive nascent protein is proteolytically cleaved to the 30-kDa active form that loses both the N-terminal and the C-terminal segments. Accumulated cytological and biochemical observations on parasporin-2 imply that the protein is a pore-forming toxin. To confirm the hypothesis, we have determined the crystal structure of its active form at a resolution of 2.38 Å. The protein is unusually elongated and mainly comprises long β-strands aligned with its long axis. It is similar to aerolysin-type β-pore-forming toxins, which strongly reinforce the pore-forming hypothesis. The molecule can be divided into three domains. Domain 1, comprising a small β-sheet sandwiched by short α-helices, is probably the target-binding module. Two other domains are both β-sandwiches and thought to be involved in oligomerization and pore formation. Domain 2 has a putative channel-forming β-hairpin characteristic of aerolysin-type toxins. The surface of the protein has an extensive track of exposed side chains of serine and threonine residues. The track might orient the molecule on the cell membrane when domain 1 binds to the target until oligomerization and pore formation are initiated. The β-hairpin has such a tight structure that it seems unlikely to reform as postulated in a recent model of pore formation developed for aerolysin-type toxins. A safety lock model is proposed as an inactivation mechanism by the N-terminal inhibitory segment. 相似文献
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Heme oxygenase inhibits human airway smooth muscle proliferation via a bilirubin-dependent modulation of ERK1/2 phosphorylation 总被引:2,自引:0,他引:2
Taillé C Almolki A Benhamed M Zedda C Mégret J Berger P Lesèche G Fadel E Yamaguchi T Marthan R Aubier M Boczkowski J 《The Journal of biological chemistry》2003,278(29):27160-27168
The aim of this study was to investigate whether the heme oxygenase (HO) pathway could modulate proliferation of airway smooth muscle (ASM) and the mechanism(s) involved in this phenomenon. In cultured human ASM cells, 10% fetal calf serum or 50 ng/ml platelet-derived growth factor AB induced cell proliferation, extracellular and intracellular reactive oxygen species (ROS) production and ERK1/2 phosphorylation. Pharmacological HO-1 induction (by 10 microm hemin or by 20 microm cobalt-protoporphyrin) and HO inhibition (by 25 microm tin-protoporphyrin or by an antisense oligonucleotide), respectively, reduced and enhanced significantly both cell proliferation and ROS production. Neither the carbon monoxide scavenger myoglobin (5-20 microm) nor the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one could reverse ASM proliferation induced by tin-protoporphyrin, making a role of the CO-cGMP pathway in HO-modulated proliferation unlikely. By contrast, bilirubin (1 microm) and the antioxidant N-acetyl-cysteine (1 mm) significantly reduced mitogen-induced cell proliferation, ROS production, and ERK1/2 phosphorylation. Furthermore, both bilirubin and N-acetyl-cysteine and the ERK1/2 inhibitor PD98059 significantly reversed the effects of HO inhibition on ASM proliferation. These results could be relevant to ASM alterations observed in asthma because activation of the HO pathway prevented the increase in bronchial smooth muscle area induced by repeated ovalbumin challenge in immunized guinea pigs, whereas inhibition of HO had the opposite effect. In conclusion, this study provides evidence for an antiproliferative effect of the HO pathway in ASM in vitro and in vivo through a bilirubin-mediated redox modulation of phosphorylation of ERK1/2. 相似文献
35.
K. Ishizeki Shintaro Nomura Masaharu Takigawa Hiroya Shioji Tokio Nawa 《Histochemistry and cell biology》1998,110(5):457-466
The localization of osteopontin (OP) was examined in Meckel’s cartilage cells that bipotentially expressed cartilage and
bone phenotypes during cellular transformation in vitro. Cultured cells were analyzed by in situ hybridization, immunostaining
followed by light and electron microscopy, electron microscopy, and electron probe microanalysis. The combination of ultrastructural
analysis and immunoperoxidase staining indicated that OP-synthesizing cells were cells that were autonomously undergoing a
change from chondrocytes to bone-forming cells at the top of nodules. Double immunofluorescence staining of 2-week-old cultures
revealed that OP was first synthesized by chondrocytic cells at the top of nodules. After further time in culture, the distribution
of OP expanded from the central toward the peripheral regions of the nodules. Electron probe microanalysis revealed that the
localization of OP was associated with matrices of calcified cartilage and osteoid nodules that contained calcium and phosphorus.
Immunoperoxidase electron microscopy revealed that, in addition to the intracellular immunoreactivity in chondrocytes and
small round cells that were undergoing transformation, matrix foci of calcospherites and matrix vesicles, in particular, included
growing crystals that were immunopositive for OP. An intense signal due to mRNA for OP in 3-week-old cultures was detected
in nodule-forming round cells, while fibroblastic cells, spreading in a monolayer over the periphery of nodules, were only
weakly labeled. These findings indicate that OP might be expressed sequentially by chondrocytes and by cells that are transdifferentiating
further and exhibit an osteocytic phenotype, and moreover, that expression of OP is closely associated with calcifying foci
in the extracellular matrix.
Accepted: 26 May 1998 相似文献
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Koichiro Saito Koji Inagaki Takahiro Kamimoto Yoko Ito Toshiaki Sugita Satoko Nakajo Akira Hirasawa Arifumi Iwamaru Takashi Ishikura Hideki Hanaoka Keisuke Okubo Tokio Onozaki Takeru Zama 《PloS one》2013,8(8)