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排序方式: 共有67条查询结果,搜索用时 422 毫秒
1.
Vitamin B12 (methylcobalamin) was administered orally (3 mg/day) to 9 healthy subjects for 4 weeks. Nocturnal melatonin levels after exposure to bright light (ca. 2500 lx) were determined, as well as the levels of plasma melatonin over 24 h. The timing of sleep was also recorded. Vitamin B12 was given blind to the subjects and crossed over with placebo. We found that the 24-h melatonin rhythm was significantly phase-advanced (1.1 h) in the vitamin B12 trial as compared with that in the placebo trial. In addition, the 24-h mean of plasma melatonin level was much lower in the vitamin B12 trial than with the placebo. Furthermore, the nocturnal melatonin levels during bright light exposure were significantly lower in the vitamin B12 trial than with the placebo. On the other hand, vitamin B12 did not affect the timing of sleep. These findings raise the possibility that vitamin B12 phase-advances the human circadian rhythm by increasing the light sensitivity of the circadian clock. 相似文献
2.
The timing of sleep and sleep EEG parameters in 10 healthy male subjects were investigated in four seasons under controlled conditions. The phase of nocturnal sleep was delayed about one and a half hours in winter as compared to that in summer. The duration of stage 4 sleep decreased and REM sleep increased significantly in winter compared with summer. The seasonality in the timing of sleep can be explained by photoperiodic time cues, but the changes in sleep EEG parameters are difficult to explain in terms of photoperiod. 相似文献
3.
A. Tsukui S. Fukuda K. Shimoji 《Cellular and molecular life sciences : CMLS》1992,48(11-12):1118-1121
The responses of basilar arteries (BAs) to serotonin were attenuated by high \(P_{CO_2 } \) (86±1 mm Hg) and the pH matched acidotic solution ( \(P_{CO_2 } \) 37±1 mm Hg), whereas the responses of middle cerebral arteries (MCAs) were not. High \(P_{CO_2 } \) decreased the basal tone of both arteries, and the changes in basal tone due to high \(P_{CO_2 } \) were not influenced by 3×10?7 M imipramine, 10?5 M pargyline or 10?4 M aspirin. The responses of BAs to serotonin were attenuated by high \(P_{CO_2 } \) in the presence of imipramine, pargyline and aspirin. The responses of MCAs to serotonin were not influenced by high \(P_{CO_2 } \) in the presence of pargyline and aspirin, but attenuated by high \(P_{CO_2 } \) in the presence of imipramine. 相似文献
4.
Saitsu H Kato M Mizuguchi T Hamada K Osaka H Tohyama J Uruno K Kumada S Nishiyama K Nishimura A Okada I Yoshimura Y Hirai S Kumada T Hayasaka K Fukuda A Ogata K Matsumoto N 《Nature genetics》2008,40(6):782-788
Early infantile epileptic encephalopathy with suppression-burst (EIEE), also known as Ohtahara syndrome, is one of the most severe and earliest forms of epilepsy. Using array-based comparative genomic hybridization, we found a de novo 2.0-Mb microdeletion at 9q33.3-q34.11 in a girl with EIEE. Mutation analysis of candidate genes mapped to the deletion revealed that four unrelated individuals with EIEE had heterozygous missense mutations in the gene encoding syntaxin binding protein 1 (STXBP1). STXBP1 (also known as MUNC18-1) is an evolutionally conserved neuronal Sec1/Munc-18 (SM) protein that is essential in synaptic vesicle release in several species. Circular dichroism melting experiments revealed that a mutant form of the protein was significantly thermolabile compared to wild type. Furthermore, binding of the mutant protein to syntaxin was impaired. These findings suggest that haploinsufficiency of STXBP1 causes EIEE. 相似文献
5.
Inductive cell-cell interactions are essential for controlling cell fate determination in both plants and animals; however, the chemical basis of inductive signals in plants remains little understood. A proteoglycan-like factor named xylogen mediates local and inductive cell-cell interactions required for xylem differentiation in Zinnia cells cultured in vitro. Here we describe the purification of xylogen and cloning of its complementary DNA, and present evidence for its role in planta. The polypeptide backbone of xylogen is a hybrid-type molecule with properties of both arabinogalactan proteins and nonspecific lipid-transfer proteins. Xylogen predominantly accumulates in the meristem, procambium and xylem. In the xylem, xylogen has a polar localization in the cell walls of differentiating tracheary elements. Double knockouts of Arabidopsis lacking both genes that encode xylogen proteins show defects in vascular development: discontinuous veins, improperly interconnected vessel elements and simplified venation. Our results suggest that the polar secretion of xylogen draws neighbouring cells into the pathway of vascular differentiation to direct continuous vascular development, thereby identifying a molecule that mediates an inductive cell-cell interaction involved in plant tissue differentiation. 相似文献
6.
Kawai J Shinagawa A Shibata K Yoshino M Itoh M Ishii Y Arakawa T Hara A Fukunishi Y Konno H Adachi J Fukuda S Aizawa K Izawa M Nishi K Kiyosawa H Kondo S Yamanaka I Saito T Okazaki Y Gojobori T Bono H Kasukawa T Saito R Kadota K Matsuda H Ashburner M Batalov S Casavant T Fleischmann W Gaasterland T Gissi C King B Kochiwa H Kuehl P Lewis S Matsuo Y Nikaido I Pesole G Quackenbush J Schriml LM Staubli F Suzuki R Tomita M Wagner L Washio T Sakai K Okido T Furuno M Aono H Baldarelli R Barsh G 《Nature》2001,409(6821):685-690
The RIKEN Mouse Gene Encyclopaedia Project, a systematic approach to determining the full coding potential of the mouse genome, involves collection and sequencing of full-length complementary DNAs and physical mapping of the corresponding genes to the mouse genome. We organized an international functional annotation meeting (FANTOM) to annotate the first 21,076 cDNAs to be analysed in this project. Here we describe the first RIKEN clone collection, which is one of the largest described for any organism. Analysis of these cDNAs extends known gene families and identifies new ones. 相似文献
7.
Nishimoto S Kawane K Watanabe-Fukunaga R Fukuyama H Ohsawa Y Uchiyama Y Hashida N Ohguro N Tano Y Morimoto T Fukuda Y Nagata S 《Nature》2003,424(6952):1071-1074
The eye lens is composed of fibre cells, which develop from the epithelial cells on the anterior surface of the lens. Differentiation into a lens fibre cell is accompanied by changes in cell shape, the expression of crystallins and the degradation of cellular organelles. The loss of organelles is believed to ensure the transparency of the lens, but the molecular mechanism behind this process is not known. Here we show that DLAD ('DNase II-like acid DNase', also called DNase IIbeta) is expressed in human and murine lens cells, and that mice deficient in the DLAD gene are incapable of degrading DNA during lens cell differentiation--the undigested DNA accumulates in the fibre cells. The DLAD-/- mice develop cataracts of the nucleus lentis, and their response to light on electroretinograms is severely reduced. These results indicate that DLAD is responsible for the degradation of nuclear DNA during lens cell differentiation, and that if DNA is left undigested in the lens, it causes cataracts of the nucleus lentis, blocking the light path. 相似文献
8.
Functional architecture of an intracellular membrane t-SNARE 总被引:6,自引:0,他引:6
Fukuda R McNew JA Weber T Parlati F Engel T Nickel W Rothman JE Söllner TH 《Nature》2000,407(6801):198-202
Lipid bilayer fusion is mediated by SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) located on the vesicle membrane (v-SNAREs) and the target membrane (t-SNAREs). The assembled v-SNARE/t-SNARE complex consists of a bundle of four helices, of which one is supplied by the v-SNARE and the other three by the t-SNARE. For t-SNAREs on the plasma membrane, the protein syntaxin supplies one helix and a SNAP-25 protein contributes the other two. Although there are numerous homologues of syntaxin on intracellular membranes, there are only two SNAP-25-related proteins in yeast, Sec9 and Spo20, both of which are localized to the plasma membrane and function in secretion and sporulation, respectively. What replaces SNAP-25 in t-SNAREs of intracellular membranes? Here we show that an intracellular t-SNARE is built from a 'heavy chain' homologous to syntaxin and two separate non-syntaxin 'light chains'. SNAP-25 may thus be the exception rather than the rule, having been derived from genes that encoded separate light chains that fused during evolution to produce a single gene encoding one protein with two helices. 相似文献
9.
Location of functional regions of acetylcholine receptor alpha-subunit by site-directed mutagenesis 总被引:1,自引:0,他引:1
M Mishina T Tobimatsu K Imoto K Tanaka Y Fujita K Fukuda M Kurasaki H Takahashi Y Morimoto T Hirose 《Nature》1985,313(6001):364-369
The availability of cloned cDNAs encoding the four subunits of the Torpedo acetylcholine receptor, which can be expressed to make functional receptors in Xenopus oocytes, has made possible a detailed investigation of the functions of the different structural components of the receptor. The functional analysis of receptors with alpha-subunits altered at specific sites by site-directed mutagenesis of the cDNA has allowed the location of specific regions of the alpha-subunit molecule involved in acetylcholine binding and forming a transmembrane ionic channel. 相似文献
10.
Location of a delta-subunit region determining ion transport through the acetylcholine receptor channel 总被引:26,自引:0,他引:26
K Imoto C Methfessel B Sakmann M Mishina Y Mori T Konno K Fukuda M Kurasaki H Bujo Y Fujita 《Nature》1986,324(6098):670-674
The combination of complementary DNA expression and single-channel current analysis provides a powerful tool for studying the structure-function relationship of the nicotinic acetylcholine receptor (AChR) (refs 1-5). We have previously shown that AChR channels consisting of subunits from different species, expressed in the surface membrane of Xenopus oocytes, can be used to relate functional properties to individual subunits. Here we report that, in extracellular solution of low divalent cation concentration, the bovine AChR channel has a smaller conductance than the Torpedo AChR channel. Replacement of the delta-subunit of the Torpedo AChR by the bovine delta-subunit makes the channel conductance similar to that of the bovine AChR channel. To locate the region in the delta-subunit responsible for this difference, we have constructed chimaeric delta-subunit cDNAs with different combinations of the Torpedo and bovine counterparts. The conductances of AChR channels containing chimaeric delta-subunits suggest that a region comprising the putative transmembrane segment M2 and the adjacent bend portion between segments M2 and M3 is involved in determining the rate of ion transport through the open channel. 相似文献