全文获取类型
收费全文 | 1014篇 |
免费 | 40篇 |
国内免费 | 106篇 |
出版年
2023年 | 18篇 |
2022年 | 11篇 |
2021年 | 27篇 |
2020年 | 17篇 |
2019年 | 28篇 |
2018年 | 30篇 |
2017年 | 31篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 42篇 |
2013年 | 70篇 |
2012年 | 28篇 |
2011年 | 42篇 |
2010年 | 29篇 |
2009年 | 37篇 |
2008年 | 44篇 |
2007年 | 80篇 |
2006年 | 55篇 |
2005年 | 41篇 |
2004年 | 73篇 |
2003年 | 41篇 |
2002年 | 34篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 16篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 9篇 |
1995年 | 20篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 5篇 |
排序方式: 共有1160条查询结果,搜索用时 15 毫秒
991.
Li J Chen H Tang MS Shi X Amin S Desai D Costa M Huang C 《The Journal of cell biology》2004,165(1):77-86
5-Methylchrysene has been found to be a complete carcinogen in laboratory animals. However, the tumor promotion effects of (+/-)-anti-5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE) remain unclear. In the present work, we found that 5-MCDE induced marked activator protein-1 (AP-1) activation in Cl41 cells. 5-MCDE also induced a marked activation of phosphatidylinositol 3-kinase (PI-3K). Inhibition of PI-3K impaired 5-MCDE-induced AP-1 transactivation, suggesting that PI-3K is an upstream kinase involved in AP-1 activation by 5-MCDE. Furthermore, we found that Akt is a PI-3K downstream mediator for 5-MCDE-induced AP-1 transactivation, whereas another PI-3K downstream kinase, p70(S6K), was not involved in AP-1 activation by 5-MCDE. Moreover, inhibition of Akt activation blocked 5-MCDE-induced activation of extracellular signal-regulated protein kinases (ERKs) and c-Jun NH(2)-terminal kinases (JNKs), whereas it did not affect p38K activation. Consistently, overexpression of a dominant-negative mutant of ERK2 or JNK1 blocked the AP-1 activation by 5-MCDE. These results demonstrate that 5-MCDE is able to induce AP-1 activation, and the AP-1 induction is specifically through a PI-3K/Akt-dependent and p70(S6K)-independent pathway. 相似文献
992.
Mammalian central nervous system trace amines. Pharmacologic amphetamines, physiologic neuromodulators 总被引:3,自引:0,他引:3
Berry MD 《Journal of neurochemistry》2004,90(2):257-271
993.
Functional identification of the gene locus (ncg12319 and characterization of catechol 1,2-dioxygenase in Corynebacterium glutamicum 总被引:2,自引:0,他引:2
Corynebacterium glutamicum assimilated phenol, benzoate, 4-hydroxybenzoate p-cresol and 3,4-dihydroxybenzoate. Ring cleavage was by catechol 1,2-dioxygenase when phenol or benzoate was used and by protocatechuate 3,4-dioxygenase when the others were used as substrate. The locus ncg12319 of its genome was cloned and expressed in Escherichia coli. Enzyme assays showed that ncg12319 encodes a catechol 1,2-dioxygenase. This catechol 1,2-dioxygenase was purified and accepted catechol, 3-, or 4-methylcatechols, but not chlorinated catechols, as substrates. The optimal temperature and pH for catechol cleavage catalyzed by the enzyme were 30 degrees C and 9, respectively, and the Km and Vmax were determined to be 4.24 micromol l(-1) and 3.7 micromol l(-1) min(-1) mg(-1) protein, respectively. 相似文献
994.
Pichia anomala 2.2540, isolated from soil contaminated by crude oil, degraded naphthalene, dibenzothiophene, phenanthrene and chrysene, both singly and in combination. The yeast degraded 4.5 mg naphthalene l(-1) within 24 h. Phenanthrene was degraded after a lag of 24 h. When a mixture of all four polycyclic aromatic hydrocarbons was treated at either 0.1-1.6 mg l(-1) or 3.1-5.3 mg l(-1), naphthalene was completely degraded first within 24 h, followed by phenanthrene and dibenzothiophene after 48 h. Chrysene, which remained in the mixture even after 96 h, could be degraded along with naphthalene. Chrysene at 0.7 and 1 mg l(-1), in the presence of 4.3 and 65 mg naphthalene l(-1), respectively, was removed within 96 h. 相似文献
995.
Yamamoto J Ihara K Nakayama H Hikino S Satoh K Kubo N Iida T Fujii Y Hara T 《Life sciences》2004,74(8):1039-1049
To investigate the expression of aryl hydrocarbon receptor repressor (AhRR) and related molecules in various tissues and the effects of aromatic hydrocarbons (AHs) on their expression, we developed a reliable technique of quantification of human AhRR as well as aryl hydrocarbon receptor (AhR), AhR nuclear translocator (ARNT) and cytochrome P450 1A1 (CYP1A1) mRNA by real-time TaqMan PCR method. First, we examined the expression of these genes in human adult or fetal tissues. The levels of AhRR expression were extremely high in testis, very high in lung, ovary, spleen and pancreas from adults, whereas those were low in those from fetuses. On the other hand, CYP1A1 expression was extremely high in lung, and AhR and ARNT were ubiquitously expressed in almost all tissues. Second, we compared the expression levels of these genes in mononuclear cells (MNCs) from various sources. Comparison of the basal expression levels of these genes in MNCs demonstrated that MNCs from umbilical cord blood showed higher AhRR or CYP1A1 expression than those from adults. The induction of AhRR or CYP1A1 expression by 3-methylcholanthrene (3-MC) was observed in MNCs from adults but not from umbilical cord blood. Consequently, there existed characteristic differences in the basal levels of AhRR and CYP1A1 expression in MNCs, as well as in their inducibility by 3-MC among MNCs from various types of human bloods. These results will provide basic information for a possible application of AhRR and CYP1A1 measurements to evaluate AH exposure in vivo. 相似文献
996.
Alemayehu D Gordon LM O'Mahony MM O'Leary ND Dobson AD 《FEMS microbiology letters》2004,239(2):285-293
A novel indole dioxygenase (idoA) gene has been cloned from Pseudomonas alcaligenes PA-10, based on its ability to convert indole to indigo. The chromosomally encoded idoA gene exhibits no similarity to previously cloned naphthalene dioxygenases or to aromatic oxygenases from other species at the nucleotide level. Phylogenetic analysis indicates that the idoA gene product is most similar to an acyl-CoA dehydrogenase from Novosphingobium aromaticivorans. The enzyme encoded by the idoA gene is essential for the metabolism of fluoranthene, since a mutant in which the idoA gene has been disrupted looses the ability to degrade this compound. The idoA gene appears to be constitutively expressed in PA-10, but its expression is also subject to regulation following prior exposure to salicylate and to fluoranthene degradative intermediates. 相似文献
997.
Kim YH Moody JD Freeman JP Brezna B Engesser KH Cerniglia CE 《Journal of industrial microbiology & biotechnology》2004,31(11):507-516
Polycyclic aromatic hydrocarbon (PAH) quinone reductase (PQR) and catechol-O-methyltransferase (COMT), from the PAH-degrading Mycobacterium vanbaalenii PYR-1, were demonstrated to be constitutive enzymes located in the soluble fraction of cell extracts. PQR activities for the reduction of 9,10-phenanthrenequinone and 4,5-pyrene- quinone were 1.40±0.13 and 0.12±0.01 mol min–1 mg-protein–1, respectively. The exogenous catechols alizarin, anthrarobin, 2,3-dihydroxynaphthalene and esculetin inhibited PQR activity. Anthrarobin (100 M) and esculetin (100 M) inhibited 4,5-pyrenequinone reduction by 64–92%. COMT was involved in the O-methylation of 1,2-dihydroxyphenanthrene to form 1-methoxy-2-hydroxyphenanthrene and 1,2-dimethoxyphenanthrene. Both pyrene and 1-hydroxypyrene were metabolized by M. vanbaalenii PYR-1 to form 1-methoxypyrene, 1-methoxy-2-hydroxypyrene, 1-hydroxy-2-methoxypyrene and 1,2-dimethoxypyrene. Among the catechols tested, anthrarobin showed the highest COMT activity (1.06±0.04 nmol/30 min–1 mg-protein–1). These results suggest that the PQR and COMT activities of M. vanbaalenii PYR-1 may play an important role in the detoxification of PAH catechols. 相似文献
998.
Ristic A Cichna M Sontag G 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,802(1):87-94
An analysis method was developed for the determination of trace levels of less polar heterocyclic aromatic amines (HAs) in food samples. The development started from a frequently used sample pre-treatment scheme which was slightly improved to make it applicable with high-performance liquid chromatography (HPLC) with fluorescence detection. The method was applied for the analysis of a standardised beef extract containing 5-15 ng/g of HAs and the results are compared with those of the other participants in the same European project. In addition, the method was used for the analysis of less polar HAs in cooked meat consumed in Austria. 相似文献
999.
Santos FJ Barceló-Barrachina E Toribio F Puignou L Galceran MT Persson E Skog K Messner C Murkovic M Nabinger U Ristic A 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,802(1):69-78
A feasibility study and two interlaboratory exercises on the determination of selected heterocyclic amines (HAs) in beef extract, organised in the framework of a European project, are presented. The aim of these exercises was to improve the quality of the laboratories and to evaluate the performance of a standardised analytical method and also the methods currently used by each of the participants for the analysis of these compounds. Three lyophilised portions of a commercial beef material previously spiked with HAs at different concentration levels ranging from 10 to 75 ng g(-1) were used as laboratory reference materials (lot A, B and C). Firstly, a feasibility study was carried out using a test standard solution and the beef extract (lot A), which contained only five HAs. Then, two interlaboratory exercises were carried out using the laboratory reference materials lot B and lot C, containing 10 selected HAs at two different concentration levels, 75 and 10 ng/g, respectively. The results obtained by all participant laboratories using the proposed method showed satisfactory agreement and the CV(%) between-laboratories obtained were from 8.3 to 24.1% for lot B and from 8.7 to 44.5% for lot C. The standardised method evaluated in these collaborative studies is therefore proposed for the analysis of HAs in food material. Moreover, LC-MS is recommended as the most suitable technique for the analysis of a large number of HAs in food samples. 相似文献
1000.
Kassie F Lhoste EF Bruneau A Zsivkovits M Ferk F Uhl M Zidek T Knasmüller S 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,802(1):211-215
Aim of this study was to investigate the impact of intestinal microfloras from vegetarians and non-vegetarians on the DNA-damaging activity of 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ), a carcinogenic heterocyclic amine that is found in fried meats. Floras from four vegetarians (Seventh Day Adventists) and from four individuals who consumed high amounts of meats were collected and inoculated into germfree F344 rats. The rats were kept on isocaloric diets that either contained animal derived protein and fat (meat consumers group) or proteins and fat of plant origin (vegetarian groups). IQ (90 mg/kg bw) was administered orally, after 4 h the extent of DNA-damage in colon and liver cells was determined in single cell gel electrophoresis assays. In all groups, the IQ induced DNA-migration was in the liver substantially higher than in the colon. In animals harbouring floras of vegetarians, the extent of damage was in both organs significantly (69.2% in the liver, P<0.016 and 64.7%, P<0.042 in the colon, respectively) lower than in the meat consumer groups. Our findings show that diet related differences in the microfloras have a strong impact on the genotoxic effects of IQ and suggest that heterocyclic amines are less genotoxic and carcinogenic in individuals that consume mainly plant derived foods. 相似文献