全文获取类型
收费全文 | 1713篇 |
免费 | 135篇 |
国内免费 | 1篇 |
专业分类
1849篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 36篇 |
2015年 | 45篇 |
2014年 | 52篇 |
2013年 | 111篇 |
2012年 | 83篇 |
2011年 | 99篇 |
2010年 | 68篇 |
2009年 | 60篇 |
2008年 | 114篇 |
2007年 | 97篇 |
2006年 | 99篇 |
2005年 | 102篇 |
2004年 | 116篇 |
2003年 | 90篇 |
2002年 | 90篇 |
2001年 | 35篇 |
2000年 | 43篇 |
1999年 | 33篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1969年 | 2篇 |
排序方式: 共有1849条查询结果,搜索用时 0 毫秒
101.
Liu T Nakashima S Hirose K Shibasaka M Katsuhara M Ezaki B Giedroc DP Kasamo K 《The Journal of biological chemistry》2004,279(17):17810-17818
A novel SmtB/ArsR family metalloregulator, denoted BxmR, has been identified and characterized from the cyanobacterium Oscillatoria brevis. Genetic and biochemical evidence reveals that BxmR represses the expression of both bxa1, encoding a CPx-ATPase metal transporter, as well as a divergently transcribed operon encoding bxmR and bmtA, a heavy metal sequestering metallothionein. Derepression of the expression of all three genes is mediated by both monovalent (Ag(I) and Cu(I)) and divalent (Zn(II) and Cd(II)) heavy metal ions, a novel property among SmtB/ArsR metal sensors. Electrophoretic gel mobility shift experiments reveal that apoBxmR forms multiple resolvable complexes with oligonucleotides containing a single 12-2-12 inverted repeat derived from one of the two operator/promoter regions with similar apparent affinities. Preincubation with either monovalent or divalent metal ions induces disassembly of both the BxmR-bxa1 and BxmR-bxmR/bmtA operator/promoter complexes. Interestingly, the temporal regulation of expression of bxa1 and bmtA mRNAs is different in O. brevis with bxa1 induced first upon heavy metal treatment, followed by bmtA/bxmR. A dynamic interplay among Bxa1, BmtA, and BxmR is proposed that maintains metal homeostasis in O. brevis by balancing the relative rates of metal storage and efflux of multiple heavy metal ions. 相似文献
102.
Tominaga Yoshito; Kuchitsu Kazuyuki; Katsuhara Maki; Tazawa Masashi; Miyachi Shigetoh 《Plant & cell physiology》1991,32(2):261-268
Rotational streaming of the cytoplasm including chloroplastswas induced by L-histidine, as well as by light, on the anticlinalface of leaf cells of Egeria densa. In the case of treatmentwith L-histidine some of the chloroplasts remained stationaryon the periclinal face of cells after rotational cytoplasmicstreaming was initiated. However, these chloroplasts were easilydislodged and translocated to the centrifugal end of the histidine-treatedcells by application of a centrifugal force that barely affectedthe location of chloroplasts in cells incubated in the darkwithout L-histidine. This result indicates that the anchoringof chloroplasts was weakened by L-histidine. Thus only the releaseof chloroplasts from anchoring was not enough for initiationof their streaming. The cytoplasmic pH (pHc) and vacuolar pH(pHv) were noninvasively monitored by in vivo 31P-nuclear magneticresonance (NMR) spectroscopy. Compared with the dark controlvalue, both illumination and treatment with L-histidine increasedthe pHc by 0.3 units. In contrast, pHv changed only a littlewith both illumination and treatment with L-histidine. Releaseof chloroplasts from anchoring and initiation of cytoplasmicstreaming are discussed in relation to the increase in pHc inducedby both light and L-histidine.
4 Present address: Department of Cell Biology, National Instituteof Agrobiological Resources, Kannondai, Tsukuba, Ibaraki, 305Japan
5 Present address: Marine Biotechnology Institute Co., Ltd.,Head Office, 2-35-10 Hongo, Bunkyo-ku, Tokyo, 113 Japan (Received July 16, 1990; Accepted December 20, 1990) 相似文献
103.
Ohtani T Nakagawa S Kurosawa M Mizuashi M Ozawa M Aiba S 《Journal of immunology (Baltimore, Md. : 1950)》2005,174(4):2412-2419
There is growing evidence that diesel exhaust particles (DEP) can induce allergic diseases with increased IgE production and preferential activation of Th2 cells. To clarify the cellular basis of the role of DEP in the induction of Th2-dominant responses, we examined the effects of DEP on the cytokine production by T cells stimulated with anti-CD3/CD28 Ab and on that by monocyte-derived dendritic cells (MoDCs) stimulated with CD40L and/or IFN-gamma. We examined IFN-gamma, IL-4, IL-5, IL-8, and IL-10 produced by T cells and TNF-alpha, IL-1beta, IL-10, and IL-12 produced by MoDCs using real-time PCR analysis or by ELISA. To highlight the effects of DEP, we compared the effects of DEP with those of dexamethasone (DEX) and cyclosporin A (CyA). DEP significantly suppressed IFN-gamma mRNA expression and protein production, while it did not affect IL-4 or IL-5 mRNA expression or protein production. The suppressive effect on IFN-gamma mRNA expression was more potent than that of DEX and comparable at 30 mug/ml with 10(-7) M CyA. The suppressive effect on IFN-gamma production was also more potent than that of either DEX or CyA. DEP suppressed IL-12p40 and IL-12p35 mRNA expression and IL-12p40 and IL-12p70 production by MoDCs, while it augmented IL-1beta mRNA expression. Finally, by using a thiol antioxidant, N-acetyl cysteine, we found that the suppression of IFN-gamma production by DEP-treated T cells was mediated by oxidative stress. These data revealed a unique characteristic of DEP, namely that they induce a Th2 cytokine milieu in both T cells and dendritic cells. 相似文献
104.
Green fluorescent protein from the jellyfish Aequorea victoria can serve as a good model protein to understand protein folding in a complex environment with molecular chaperones and other macromolecules such as those in biological cells, but little is known about the detailed mechanisms of the in vitro folding of green fluorescent protein itself. We therefore investigated the kinetic refolding of a mutant (F99S/M153T/V163A) of green fluorescent protein, which is known to mature more efficiently than the wild-type protein, from the acid-denatured state; refolding was observed by chromophore fluorescence, tryptophan fluorescence, and far-UV CD, using a stopped-flow technique. In this study, we demonstrated that the kinetics of the refolding of the mutant have at least five kinetic phases and involve nonspecific collapse within the dead time of a stopped-flow apparatus and the subsequent formation of an on-pathway intermediate with the characteristics of the molten globule state. We also demonstrated that the slowest phase and a major portion of the second slowest phase were rate-limited by slow prolyl isomerization in the intermediate state, and this rate limitation accounts for a major portion of the observed kinetics in the folding of green fluorescent protein. 相似文献
105.
106.
Induction of multiple cytokine secretion from RAW264.7 cells by alginate oligosaccharides 总被引:1,自引:0,他引:1
Yamamoto Y Kurachi M Yamaguchi K Oda T 《Bioscience, biotechnology, and biochemistry》2007,71(1):238-241
We investigated the cytokine-inducing activities of guluronate (G3-G6) and mannuronate (M3-M6) oligomers on RAW264.7 cells with the Bio-Plex assay system. Relatively high levels of tumor necrosis factor-alpha (TNF-alpha), granulocyte colony-stimulating factor (G-CSF), monocyte chemoattractant protein-1 (MCP-1), regulated upon activation normal T cell expressed and secreted (RANTES), granulocyte macrophage (GM)-CSF, and eotaxin were induced by alginate oligomers to different extents depending on the oligomer structures, and low but significant levels of interleukin (IL)-1alpha, IL-1beta, IL-6, IL-9, and IL-13 were also induced. Throughout all cytokines tested, M-oligomers tended to be more potent than G-oligomers in terms of cytokine induction, and this tendency was evident in differences between G3 and M3. 相似文献
107.
Seki M Akiyama M Sugaya Y Ohtsubo E Maki H 《The Journal of biological chemistry》1999,274(47):33313-33319
We have recently shown that single-base frameshifts were predominant among mutations induced within the rpsL target sequence upon oriC plasmid DNA replication in vitro. We found that the occurrence of +1 frameshifts at a run of 6 residues of dA/dT could be increased proportionally by increasing the concentration of dATP present in the in vitro replication. Using single-stranded circular DNA containing either the coding sequence of the rpsL gene or its complementary sequence, the +1 frameshift mutagenesis by DNA polymerase III holoenzyme of Escherichia coli was extensively examined. A(6) --> A(7) frameshifts occurred 30 to 90 times more frequently during DNA synthesis with the noncoding sequence (dT tract) template than with the coding sequence (dA tract). Excess dATP enhanced the occurrence of +1 frameshifts during DNA synthesis with the dT tract template, but no other dNTPs showed such an effect. In the presence of 0.1 mM dATP, the A(6) --> A(7) mutagenesis with the dT tract template was not inhibited by 1.5 mM dCTP, which is complementary to the residue immediately upstream of the dT tract. These results strongly suggested that the A(6) --> A(7) frameshift mutagenesis possesses an asymmetric strand nature and that slippage errors leading to the +1 frameshift are made during chain elongation within the tract rather than by misincorporation of nucleotides opposite residues next to the tract. 相似文献
108.
Maki Sato Dominika Kanikowska Satoshi Iwase Yuuki Shimizu Yoko Inukai Naoki Nishimura Junichi Sugenoya 《International journal of biometeorology》2009,53(5):443-449
We tested the hypothesis that encouraged water drinking according to urine output for 20 days could ameliorate impaired thermoregulatory
function under microgravity conditions. Twelve healthy men, aged 24 ± 1.5 years (mean ± SE), underwent −6° head-down bed rest
(HDBR) for 20 days. During bed rest, subjects were encouraged to drink the same amount of water as the 24-h urine output volume
of the previous day. A heat exposure test consisting of water immersion up to the knees at 42°C for 45 min after a 10 min
rest (baseline) in the sitting position was performed 2 days before the 20-day HDBR (PRE), and 2 days after the 20-day HDBR
(POST). Core temperature (tympanic), skin temperature, skin blood flow and sweat rate were recorded continuously. We found
that the −6° HDBR did not increase the threshold temperature for onset of sweating under the encouraged water drinking regime.
We conclude that encouraged water drinking could prevent impaired thermoregulatory responses after HDBR. 相似文献
109.
Toru Okuda Jun Kohno Noboru Kishi Yasuyuki Asai Maki Nishio Saburo Komatsubara 《Mycoscience》2000,41(3):239-253
A novel class of fungal metabolites, TMC-151, TMC-154, and TMC-171 series compounds, was found exclusively inGliocladium catenulatum, Clonostachys rosea and closely related strains. These compounds were not detected in any other fungi examined. The production spectrum of each
component was correlated to the morphology of the secondary conidiophores and the conidia. TMC-151 was limited toClonostachys rosea (formerlyG. roseum) forming navicular or reniform conidia orG. catenulatum with gray-green conidial masses, whereas TMC-154 and 171 were limited to the strains closely related toGliocladium roseum, which grew more slowly and formed more symmetrical conidia. 相似文献
110.