全文获取类型
收费全文 | 870篇 |
免费 | 31篇 |
专业分类
901篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 2篇 |
2016年 | 14篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 92篇 |
2012年 | 37篇 |
2011年 | 47篇 |
2010年 | 26篇 |
2009年 | 41篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 32篇 |
2005年 | 51篇 |
2004年 | 57篇 |
2003年 | 58篇 |
2002年 | 57篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 3篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有901条查询结果,搜索用时 0 毫秒
111.
Inhibitory effects of highly purified vitamin B2 (riboflavin-5'-sodium phosphate, >97%) on the interleukin (IL)-6, macrophage inflammatory protein (MIP)-2 and nitric oxide (NO) in LPS-induced shock mice were evaluated. Vitamin B2 at 20 mg/kg (protective effect on mice mortality induced by LPS), intravenously administered 6 h after LPS injection, significantly decreased the plasma elevated levels of IL-6 and MIP-2 at 9 and 12 h. In addition, vitamin B2 lowered the tissue concentration and the mRNA expression of IL-6 in lung and those of MIP-2 in liver at 9 h. Vitamin B2 also reduced concentration of MIP-2 concentration in lung, and inhibited mRNA expression in kidney, respectively. Vitamin B2 decreased the plasma elevated NO levels in accordance with a reduction in expression of inducible NO synthase (iNOS) both at 21 and 24 h. Accordingly, the reduction in elevated plasma cytokine levels and NO based on the inhibitory effect on local cytokine mRNA expression and iNOS would be responsible for the anti-septic effect of vitamin B2. 相似文献
112.
We investigated the iron release from ferritin by irradiation from a white fluorescent light in the absence or presence of ADP. Irradiation of a ferritin solution at 17,000 lx in the absence of ADP slightly induces iron release from ferritin but only at acidic pH conditions (pH 5.0 or pH 6.0). Irradiation in the presence of ADP markedly enhances iron release from ferritin under the same conditions. In the absence of irradiation, the iron release from ferritin was low even in the presence of ADP. The induction of the iron release by irradiation in the presence of ADP was also affected by various factors such as irradiation dose and acidity, but not temperature (4-47°C), oxygen concentration, or free radical generations during the irradiation. The iron release during the irradiation ceased to increase by turning off the light and was found to increase again after additional irradiation. These results suggest that visible light directly induces iron release from ferritin via the photoreduction of iron stored inside ferritin. 相似文献
113.
Miura D Norman AW Mizwicki MT Fujishima T Konno K Kittaka A Takayama H Ishizuka S 《The Journal of steroid biochemistry and molecular biology》2005,94(5):469-479
We synthesized all eight possible A-ring diastereomers of 2-methyl substituted analogs of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and also all eight A-ring diastereomers of 2-methyl-20-epi-1alpha,25(OH)2D3. Their biological activities, especially the antagonistic effect on non-genomic pathway-mediated responses induced by 1alpha,25(OH)2D3 or its 6-s-cis-conformer analog, 1alpha,25(OH)2-lumisterol3, were assessed using an NB4 cell differentiation system. Antagonistic activity was observed for the 1beta-hydroxyl diastereomers, including 2beta-methyl-1beta,25(OH)2D3 and 2beta-methyl-3-epi-1beta,25(OH)2D3. Very interestingly, 2beta-methyl-3-epi-1alpha,25(OH)2D3 also antagonized the non-genomic pathway, despite its 1alpha-hydroxyl group. Other 1alpha-hydroxyl diastereomers did not show antagonistic activity. 20-epimerization diminished the antagonistic effect of all of these analogs on the non-genomic pathway. These findings suggested that the combination of the 2-methyl substitution of the A-ring and 20-epimerization of the side chain could alter the biological activities in terms of antagonism of non-genomic pathway-mediated biological response. Based on a previous report, 2-methyl substitution alters the equilibrium of the A-ring conformation between the alpha- and beta-chair conformers. The 2beta-methyl diastereomers, which exhibited antagonism on non-genomic pathway-mediated response, were considered to prefer the beta-conformer. Further examination to elucidate the relationship between the altered ligand shape and receptors interaction will be important for molecular level understanding of the mechanism of antagonism of the non-genomic pathway. 相似文献
114.
Ando S Tachibana A Yamada S Kishimura H 《Bioscience, biotechnology, and biochemistry》2005,69(11):2258-2262
A truncated apolipoprotein (apo) A-I with a molecular weight (M(r)) of 26 kDa was first isolated from the plasma high density lipoproteins of an atypical Japanese eel (Anguilla japonica). Interestingly, this eel contained a very small amount of intact apoA-I (M(r)28 kDa) in the plasma, although serine protease inhibitors were present throughout the plasma preparation. The N-terminal sequence of 20 amino acids in truncated apoA-I was completely identical with that of intact apoA-I. Another apolipoprotein with M(r)28 kDa, whose N-terminal amino acid sequence differed from apoA-I, was also found in high density lipoprotein and low density lipoprotein. The apolipoprotein profiles of Japanese eel plasma appear to be complicated. 相似文献
115.
Molecular characterization of true and ectopic gene targeting events at the acetolactate synthase gene in Arabidopsis 总被引:3,自引:0,他引:3
Precise modification of plant genomes via gene targeting (GT) is important for the study of gene function in vivo. A reliable GT system using the protoporphyrinogen oxidase (PPO) gene in Arabidopsis was reported 4 years ago; however, there are no subsequent successful reports of GT in Arabidopsis. A previous study showed ectopic gene targeting (EGT) of the endogenous gene in two-thirds of GT plants, which was an obstacle to efficient true gene targeting (TGT). The endogenous acetolactate synthase (ALS) gene is involved in the biosynthesis of branched chain amino acids in plants and is the site of action of several herbicides. To confirm the generality of the GT system in Arabidopsis, and to characterize the EGT event in plants in detail, we converted ALS from a herbicide (imazapyr)-susceptible to a -resistant form by GT. We obtained two imazapyr-resistant plants following GT. One of the targeting events was TGT while the other was EGT. After detailed Southern blotting, PCR and nucleotide sequence analysis of the EGT plant, we determined the genomic position and structure of the ectopically targeted site. Based on our findings, we discuss the possible mechanisms of EGT in plants. 相似文献
116.
Three enzymes, carnosine dipeptidase I (EC 3.4.13.20, CNDP1), carnosine dipeptidase II (EC 3.4.13.18, CNDP2), and Xaa-methyl-His dipeptidase (or anserinase: EC 3.4.13.5, ANSN), are known to be capable of catalyzing the hydrolysis of carnosine (β-alanyl-l-histidine), in vertebrates. Here we report the purification and identification of two unidentified carnosine-cleaving enzymes from Japanese eel (Anguilla japonica). Two different dipeptidases were successfully purified to homogeneity from the skeletal muscle; one exhibited a broad substrate specificity, while the other a narrow specificity. N-terminal amino-acid sequencing, deglycosylation analysis, and genetic analysis clearly revealed that the former is a homodimer of glycosylated subunits, encoded by ANSN, and the latter is another homodimer of glycosylated subunits, encoded by CNDP1; that is, Xaa-methyl-His dipeptidase, and carnosine dipeptidase I respectively. This is the first report on the identification of carnosine dipeptidase I from a non-mammal. Database search revealed presence of a CNDP1 ortholog only from salmonid fishes, including Atlantic salmon and rainbow trout, but not from other ray-finned fish species, such as zebrafish, fugu, and medaka whose genomes have been completely sequenced. The mRNAs of CNDP1 and ANSN are strongly expressed in the liver of Japanese eel, compared with other tissues, while that of CNDP2 is widely distributed in all tissues tested. 相似文献
117.
Abad L Okabe S Shibayama M Kudo H Saiki S Aranilla C Relleve L de la Rosa A 《International journal of biological macromolecules》2008,42(1):55-61
The conformational associative properties of kappa-, iota-, and lambda-carrageenan and agar with irradiation dose were studied by dynamic light scattering. The random scission of the carrageenans and agar by gamma irradiation resulted in the formation of polydispersed lower molecular weight fragments. At high doses, the system moves towards uniformity. Conformational change from coil to helix was observed in all carrageenans and agar at doses up to 100 kGy. The conformational change in lambda-carrageenan may be due to the irregular and hybrid structure of this polysaccharide. Only agar and lambda-carrageenan still undergo conformational transition at a high dose of 200 kGy. Gelation is observed for kappa-, iota-carrageenan up to a dose of 50 kGy while gelation is still observed at 100 kGy for agar. Increase in the hydrodynamic radius with decreasing temperatures for the non-irradiated carrageenans follows this order: lambda-carrageenan>kappa-carrageenan>iota-carrageenan. Slight increases in hydrodynamic radius were observed with irradiation. 相似文献
118.
119.
120.
Ikeno Takeyuki Hashimoto Seiichi Kuzuya Hiroshi Nagatsu Toshiharu 《Molecular and cellular biochemistry》1977,18(2-3):117-123
1. Two different molecular forms of dopamine-beta-hydroxylase were isolated from human serum; a major component (Peak I enzyme) with a molecular weight of 368000 and with a higher specific activity and a minor component (Peak II enzyme) with a molecular weight of 188000 and with a lower specific activity. 2. Both forms require ascorbic acid for the activity, and are stimulated by fumarate. Addition of N-ethylmaleimide or copper also increased the activity. The optimal pH of both forms in the presence of 20mM tyramine as substrate is 5.0. 3. Km values toward tyramine of Peak I enzyme and Peak II enzyme were 1.67 mM and 14.2 mM respectively. 4. Both Peak I enzyme and Peak II enzyme are glycoprotein. 相似文献