全文获取类型
收费全文 | 2895篇 |
免费 | 56篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 169篇 |
综合类 | 6篇 |
化学工业 | 709篇 |
金属工艺 | 74篇 |
机械仪表 | 53篇 |
建筑科学 | 41篇 |
能源动力 | 110篇 |
轻工业 | 270篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 253篇 |
一般工业技术 | 547篇 |
冶金工业 | 488篇 |
原子能技术 | 71篇 |
自动化技术 | 158篇 |
出版年
2023年 | 15篇 |
2022年 | 29篇 |
2021年 | 39篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 36篇 |
2017年 | 33篇 |
2016年 | 48篇 |
2015年 | 28篇 |
2014年 | 43篇 |
2013年 | 121篇 |
2012年 | 73篇 |
2011年 | 131篇 |
2010年 | 97篇 |
2009年 | 128篇 |
2008年 | 123篇 |
2007年 | 137篇 |
2006年 | 82篇 |
2005年 | 92篇 |
2004年 | 101篇 |
2003年 | 84篇 |
2002年 | 75篇 |
2001年 | 71篇 |
2000年 | 80篇 |
1999年 | 61篇 |
1998年 | 172篇 |
1997年 | 146篇 |
1996年 | 117篇 |
1995年 | 70篇 |
1994年 | 62篇 |
1993年 | 58篇 |
1992年 | 43篇 |
1991年 | 41篇 |
1990年 | 29篇 |
1989年 | 45篇 |
1988年 | 22篇 |
1987年 | 39篇 |
1986年 | 44篇 |
1985年 | 32篇 |
1984年 | 33篇 |
1983年 | 31篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 21篇 |
1979年 | 29篇 |
1978年 | 13篇 |
1977年 | 29篇 |
1976年 | 31篇 |
1975年 | 8篇 |
1974年 | 8篇 |
排序方式: 共有2958条查询结果,搜索用时 15 毫秒
81.
Akifumi Nagatomo Kiyofumi Ninomiya Shinsuke Marumoto Chie Sakai Shuta Watanabe Wakana Ishikawa Yoshiaki Manse Takashi Kikuchi Takeshi Yamada Reiko Tanaka Osamu Muraoka Toshio Morikawa 《International journal of molecular sciences》2022,23(21)
The seed oil of Carapa guianensis Aublet (Andiroba) has been used in folk medicine for its insect-repelling, anti-inflammatory, and anti-malarial activities. This study aimed to examine the triglyceride (TG) reducing effects of C. guianensis-derived limonoids or other commercially available limonoids in human hepatoblastoma HepG2 cells and evaluate the expression of lipid metabolism or autophagy-related proteins by treatment with 7-deacetoxy-7-oxogedunin (DAOG; 1), a principal limonoid of C. guianensis. The gedunin-type limonoids, such as DAOG (% of control at 20 μM: 70.9 ± 0.9%), gedunin (2, 74.0 ± 1.1%), epoxyazadiradione (4, 73.4 ± 2.0%), 17β-hydroxyazadiradione (5, 79.9 ± 0.6%), 7-deacetoxy-7α-hydroxygedunin (6, 61.0 ± 1.2%), andirolide H (7, 87.4 ± 2.2%), and 6α-hydroxygedunin (8, 84.5 ± 1.1%), were observed to reduce the TG content at lower concentrations than berberine chloride (BBR, a positive control, 84.1 ± 0.3% at 30 μM) in HepG2 cells pretreated with high glucose and oleic acid. Andirobin-, obacunol-, nimbin-, and salannin-type limonoids showed no effect on the intracellular TG content in HepG2 cells. The TG-reducing effect of DAOG was attenuated by the concomitant use of compound C (dorsomorphin), an AMPK inhibitor. Further investigation on the detailed mechanism of action of DAOG at non-cytotoxic concentrations revealed that the expressions of autophagy-related proteins, LC3 and p62, were upregulated by treatment with DAOG. These findings suggested that gedunin-type limonoids from Andiroba could ameliorate fatty liver, and that the action of DAOG in particular is mediated by autophagy. 相似文献
82.
Tomohiro Fujii Jun Nishikawa Soichiro Fukuda Naoto Kubota Junzo Nojima Koichi Fujisawa Ryo Ogawa Atsushi Goto Koichi Hamabe Shinichi Hashimoto Aung Phyo Wai Hisashi Iizasa Hironori Yoshiyama Kohei Sakai Yutaka Suehiro Takahiro Yamasaki Taro Takami 《International journal of molecular sciences》2022,23(18)
DNA methylation of both viral and host DNA is one of the major mechanisms involved in the development of Epstein–Barr virus-associated gastric carcinoma (EBVaGC); thus, epigenetic treatment using demethylating agents would seem to be promising. We have verified the effect of , which was discovered by screening for demethylating agents. MC180295 inhibited cell growth of the EBVaGC cell lines YCCEL1 and SNU719 in a dose-dependent manner. In a cell cycle analysis, growth arrest and apoptosis were observed in both YCCEL1 and SNU719 cells treated with MC180295. MKN28 cells infected with EBV were sensitive to MC180295 and showed more significant inhibition of cell growth compared to controls without EBV infection. Serial analysis of gene expression analysis showed the expression of genes belonging to the role of BRCA1 in DNA damage response and cell cycle control chromosomal replication to be significantly reduced after MC180295 treatment. We confirmed with quantitative PCR that the expression levels of BRCA2, FANCM, RAD51, TOP2A, and CDC45 were significantly decreased by MC180295. LMP1 and BZLF1 are EBV genes with expression that is epigenetically regulated, and MC180295 could up-regulate their expression. In conclusion, MC180295 inhibited the growth of EBVaGC cells by suppressing DNA repair and the cell cycle. MC180295相似文献
83.
Horii Y Ohtsuka N Minomo K Nojiri K Kannan K Lam PK Yamashita N 《Environmental science & technology》2011,45(17):7517-7524
Distribution, characteristics, and global inventory of dioxins (polychlorinated dibenzo-p-dioxins [PCDDs] and dibenzofurans [PCDFs] and dioxin like polychlorinated biphenyls) in kaolin clays collected from 10 countries were investigated. Dioxins were found in all kaolin clay samples analyzed, at total concentrations ranging from 1.2 pg/g (Brazil) to 520,000 pg/g (USA). Dioxin concentrations in kaolin clays from a few countries (e.g., Brazil and UK) were lower than those reported for background soils in Japan. Dioxin profiles in kaolin clays were characterized by the domination of the congener octachlorodibenzo-p-dioxin (OCDD), and the concentrations of other congeners decreased in the order of reduction in the levels of chlorination. Furthermore, specific distribution of congeners, with predominant proportions of 1,4,6,9-substituted PCDDs within each homologue group, was found in most clay samples. The ratios of concentrations of PCDD to PCDF and 1,2,3,7,8,9-HxCDD to 1,2,3,6,7,8-HxCDD indicated differences in the profiles found for anthropogenic sources (including pentachlorophenol) and kaolin clays. Concentrations of PCDD/Fs in kaolin clays, except for American ball clays, did not exceed the environmental criteria set by the Law Concerning Special Measures against Dioxins in Japan. Based on the average concentrations measured in our study, inventories of PCDD/Fs from the production/usage of ball clays on a global scale were estimated to be 650 kg/yr; the corresponding value on a TEQ basis is 2400 g-TEQ/yr. More than 480 kg of OCDD is estimated to be released annually from the production of kaolin clays worldwide, suggesting that kaolin clays can be a major contributor for additional source of dioxins, especially OCDD, in the environment. 相似文献
84.
Open dumping site in Asian developing countries: a potential source of polychlorinated dibenz-p-dioxins and polychlorinated dibenzofurans 总被引:1,自引:0,他引:1
Nguyen HM Tu BM Watanabe M Kunisue T Monirith I Tanabe S Sakai S Subramanian A Sasikumar K Pham HV Bui CT Tana TS Prudente MS 《Environmental science & technology》2003,37(8):1493-1502
Open landfill dumping areas for municipal wastes in Asian developing countries have recently received particular attention with regard to environmental pollution problems. Because of the uncontrolled burning of solid wastes, elevated contamination by various toxic chemicals including dioxins and related compounds in these dumping sites has been anticipated. In this study, concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (PCBs) were determined in soils from dumping sites in the Philippines, Cambodia, India, and Vietnam. Residue concentrations of PCDD/Fs and coplanar PCBs in dumping site soils were apparently greater than those in soils collected in agricultural or urban areas far from dumping sites, suggesting that dumping sites are potential sources of PCDD/Fs and related compounds. Observed PCDD/F concentrations in soils from dumping sites in the Philippines and Cambodia were comparable or higher than those reported for dioxin-contaminated locations in the world (e.g., near the municipal waste incinerators and open landfill dumping sites). Homologue profiles of PCDD/Fs in dumping site soils from the Philippines and, to a lesser extent, from Cambodia and India reflected patterns of samples representing typical emissions, while profiles of agricultural or urban soils were similar to those of typical environmental sinks. This result suggests recent formation of PCDD/Fs in dumping site areas and that open dumping sites are a potential source of dioxins in Asian developing countries. Uncontrolled combustions of solid wastes by waste pickers, generation of methane gas, and low-temperature burning can be major factors for the formation of dioxins in dumping sites. Elevated fluxes of PCDD/Fs to soils in dumping sites were encountered in the Philippines, Cambodia, India, and Vietnam-Hanoi, and these levels were higher than those reported for other countries. Considerable loading rates of PCDD/Fs in the dumping sites of these countries were observed, ranging from 20 to 3900 mg/yr (0.12-35 mg TEQ/yr). PCDD/F concentrations in some soil samples from the Philippines, Cambodia, India, and Vietnam-Hanoi exceeded environmental guideline values, suggesting potential health effects on humans and wildlife living near these dumping sites. The estimated intakes of dioxins via soil ingestion and dermal exposure for children were higher than those for adults, suggesting greater risk of dioxin exposure for children in dumping sites. To our knowledge, this is the first comprehensive study on PCDD/Fs contamination in open dumping sites of Asian developing countries. On the basis of the result of this study, we have addressed a new environmental issue that open dumping sites are potential sources of PCDD/Fs and related compounds, and dioxin contamination in dumping sites may become a key environmental problem in developing countries. 相似文献
85.
86.
Sakai Y Yoshida H Yurimoto H Takabe K Kato N 《Journal of Bioscience and Bioengineering》1999,87(1):108-111
Fructosyl amino acid oxidase (FAOD) is the enzyme catalyzing the oxidative deglycation of Amadori compounds, such as fructosyl amino acids, yielding the corresponding amino acids, glucosone, and H(2)O(2). In a previous report, we determined the primary structures of cDNAs coding for FAODs from two fungal strains Aspergillus terreus AP1 and Penicillium janthinellum and we found that both fungal FAODs included the putative peroxisome targeting signal 1 (PTS1) at the carboxyl terminal (Yoshida, N. et al., Eur. J. Biochem., 242, 499-505, 1996). In this study, we determined the intracellular localization of FAODs in these two fungi. Subcellular fractionation experiments and immuno-electronmicroscopic observations, together with the previous findings indicated that the FAODs were localized in peroxisomes of A. terreus AP1 and P. janthinellum. These FAODs were also found to belong to a new member of "peroxisomal sarcosine oxidase family protein" in eucaryotic cells. 相似文献
87.
Methyl formate synthesis during growth on methanol by methylotrophic yeasts has been considered to play a role in formaldehyde detoxification. An enzyme that catalyses methyl formate synthesis was purified from methylotrophic yeasts, and was suggested to belong to a family of alcohol dehydrogenases (ADHs). In this study we report the gene cloning and gene disruption analysis of three ADH-encoding genes in the methylotrophic yeast Candida boidinii (CbADH1, CbADH2 and CbADH3) in order to clarify the physiological role of methyl formate synthesis. From the primary structures of these three genes, CbAdh1 was shown to be cytosolic and CbAdh2 and CbAdh3 were mitochondrial enzymes. Gene products of CbADH1, CbADH2 and CbADH3 expressed in Escherichia coli showed both ADH- and methyl formate-synthesizing activities. The results of gene-disruption analyses suggested that methyl formate synthesis was mainly catalysed by a cytosolic ADH (CbAdh1), and this enzyme contributed to formaldehyde detoxification through glutathione-independent formaldehyde oxidation during growth on methanol by methylotrophic yeasts. 相似文献
88.
Two classes of Tn10 transposase mutants that suppress mutations in the Tn10 terminal inverted repeat
Tn10 transposition requires IS10 transposase and essential sequences at the two ends of the element. Mutations in terminal basepairs 6-13 confer particularly strong transposition defects. We describe here the identification of transposase mutations that suppress the transposition defects of such terminus mutations. These mutations are named "SEM" for suppression of ends mutations. All of the SEM mutations suppress more than a single terminus mutation and thus are not simple alterations of transposase/end recognition specificity. The mutations identified fall into two classes on the basis of genetic tests, location within the protein and nature of the amino acid substitution. Class I mutations, which are somewhat allele specific, appear to define a small structural and functional domain of transposase in which hydrophobic interactions are important at an intermediate stage of the transposition reaction, after an effective interaction between the ends but before transposon excision. Class II mutations, which are more general in their effects, occur at a single residue in a small noncritical amino-terminal proteolytic domain of transposase and exert their affects by altering a charge interaction; these mutations may affect act early in the reaction, before or during establishment of an effective interaction between the ends. 相似文献
89.
90.
Thermoplastic resins are typically used without any kind of physical aging treatment. For such materials, creep behavior and physical aging, which depend on time and temperature, occur simultaneously. The effects of these processes are evident after quenching and are recorded in the material as a thermal history. This history strongly influences mechanical properties and creep behavior in particular. Thus, a more thorough understanding of the physical aging process is desirable. We examined the creep deformation of polycarbonate (PC) to reveal the effects of physical aging on creep behavior. The effects were dependent on both time and temperature. The relationship between physical aging and creep behavior exemplified superposition principles with regard to time and both pre-test aging time and pre-test aging temperature. The superposition principles allowed the calculation of creep deformations at a given temperature; the calculated results were corroborated by experimental data. 相似文献