全文获取类型
收费全文 | 39239篇 |
免费 | 2340篇 |
国内免费 | 990篇 |
专业分类
电工技术 | 1483篇 |
技术理论 | 4篇 |
综合类 | 1553篇 |
化学工业 | 6090篇 |
金属工艺 | 1536篇 |
机械仪表 | 1669篇 |
建筑科学 | 1690篇 |
矿业工程 | 758篇 |
能源动力 | 1194篇 |
轻工业 | 2230篇 |
水利工程 | 449篇 |
石油天然气 | 1010篇 |
武器工业 | 146篇 |
无线电 | 5408篇 |
一般工业技术 | 5076篇 |
冶金工业 | 6889篇 |
原子能技术 | 388篇 |
自动化技术 | 4996篇 |
出版年
2024年 | 105篇 |
2023年 | 449篇 |
2022年 | 863篇 |
2021年 | 1197篇 |
2020年 | 927篇 |
2019年 | 800篇 |
2018年 | 898篇 |
2017年 | 945篇 |
2016年 | 861篇 |
2015年 | 1069篇 |
2014年 | 1413篇 |
2013年 | 2116篇 |
2012年 | 1986篇 |
2011年 | 2309篇 |
2010年 | 1832篇 |
2009年 | 1879篇 |
2008年 | 1930篇 |
2007年 | 1739篇 |
2006年 | 1567篇 |
2005年 | 1256篇 |
2004年 | 1109篇 |
2003年 | 1195篇 |
2002年 | 1398篇 |
2001年 | 1178篇 |
2000年 | 816篇 |
1999年 | 844篇 |
1998年 | 2362篇 |
1997年 | 1465篇 |
1996年 | 1085篇 |
1995年 | 728篇 |
1994年 | 616篇 |
1993年 | 581篇 |
1992年 | 278篇 |
1991年 | 260篇 |
1990年 | 260篇 |
1989年 | 245篇 |
1988年 | 217篇 |
1987年 | 179篇 |
1986年 | 154篇 |
1985年 | 149篇 |
1984年 | 113篇 |
1983年 | 85篇 |
1982年 | 82篇 |
1981年 | 76篇 |
1980年 | 117篇 |
1979年 | 49篇 |
1978年 | 64篇 |
1977年 | 142篇 |
1976年 | 266篇 |
1975年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Neoxanthin, a major carotenoid pigment of spinach, is found in the Chloroplast membrane and has an unknown function in plants. Neoxanthin inhibited the production of superoxide anions in an artificial xanthine and xanthine oxidase system and depressed DNA synthesis in methylcholanthrene (MCA)-initiated C3H10T1/2 fibroblasts. in two-stage carcinogenesis experiments, neoxanthin at 0.2 micrograms/0.2 ml inhibited the formation of tumors that were induced sequentially by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) in the buccal pouch of Syrian Golden hamsters. To assess the ongoing process of carcinogenesis, the activity of ornithine decarboxylase (ODC), required for cell proliferation, was analyzed. Neoxanthin inhibited the activity of ODC when animals were treated with neoxanthin one hour before the application of TPA in two-stage carcinogenesis. However, neoxanthin did not inhibit ODC activity when animals were treated with neoxanthin one hour before the application of DMBA in two-stage carcinogenesis, and there was no subsequent tumor formation. In a short-term anti-initiation experiment, neoxanthin inhibited the covalent binding of isotope-labeled DMBA to DNA by 53%. These results indicate that neoxanthin inhibits the initiation stage and the promotion stage in two-stage carcinogenesis. This suggests that neoxanthin may act as a potential chemopreventive agent. 相似文献
93.
BL Chang 《Canadian Metallurgical Quarterly》1995,32(6):556-567
Construct validity of the concepts of pain, self-care deficit and impaired mobility was examined in a study of 120 medical-surgical patients. Factors derived from a factor analysis of the empirical signs and symptoms were: pain-factor and self-care deficit/impaired mobility-factor. The pain-factor clearly showed discriminant validity by differentiating between those with and without Clinical Nurse Specialist (CNS)-identified diagnosis of pain. An overlap between the defining characteristics of the diagnoses of self-care deficit and impaired mobility has been suggested in the present sample of patients. Limitations of the study and recommendations for further research are described. 相似文献
94.
Statistical computer-aided design for microwave circuits 总被引:4,自引:0,他引:4
A useful methodology for microwave circuit design is presented. A statistical technique known as Design of Experiments is used in conjunction with computer-aided design (CAD) tools to obtain simple mathematical expressions for circuit responses. The response models can then be used to quantify response trade-offs, optimize designs, and minimize circuit variations. The use of this methodology puts the designer's intelligence back into design optimization while making “designing for circuit manufacturability” a more systematic and straightforward process. The method improves the design process, circuit performance, and manufacturability. Two design examples are presented in context to the new design methodology 相似文献
95.
本文论述了武钢新三号高炉的建设和投产,是武钢整个“八五”技术进步的新起点,指出必须进一步完善以质量为核心的生产管理体系。 相似文献
96.
Novel high voltage pumping circuits for low supply voltages are proposed. Utilising a small pumping circuit and the new substrate-connected techniques can enhance charge transfer efficiency and eliminate the body effect at low supply voltages. Furthermore, a diode-connected transistor technique can improve the reverse charge sharing phenomenon when the output has a load current. With this technique high boosted voltages can be obtained at low supply voltages 相似文献
97.
四川省电力工业局管辖的水电厂总装机容量为2617.5MW,针对受自然条件限制相当多的机组运行条件恶劣,早期建设的水电站辅助设备和控制系统质量差,自动化水平低等问题,省电力局加强了对水电厂的技术改造,进行了包括对渔子溪型水电机组和龚嘴水电站机组的改造增容,对龚嘴和映秀湾等电厂的综合自动化改造,以及部分水电厂的水工建筑物技术改造等工作,同时加强了技改管理工作,加快了技改工作的进行,提高了技改的质量,取 相似文献
98.
99.
This paper reports a new, highly integrated modular design approach for pulsewidth-modulation AC-AC converters based on a modular phase-bank structure. Novel high-power 3-in-1 integrated bi-directional power modules (IBPM) rated at 1200-V AC and 150 A and the 3-to-1 phase bank circuits have been successfully developed, fabricated and tested. This enables the modularity design of the multiphase converter systems and reduces the critical parasitic inductance. A theoretical analysis of the IBPM's silicon utilization for this new breed of direct power converters has been outlined. A lab prototype at medium power level has been successfully designed, implemented, and tested with good results. A nearly 460-VRMS out voltage at a 1:0.955 voltage transfer ratio, which, perhaps, is the highest performance reported so far in the literature, has been achieved by the novel two-side modulation control system. The converter-fed AC motor system is able to operate over the 0-240 Hz range with inherent regenerative capability and four-quadrant operation. Potential industrial applications are also briefly highlighted in this paper 相似文献
100.
A conjugative aminoglycoside resistance plasmid pST2 has been isolated from Escherichia coli K-12 14R525, which was mated with a clinical isolate of Salmonella typhimurium S24. A novel resistance gene of aminoglycoside 6'-N-acetyltransferase[AAC(6')] was cloned from plasmid pST2 on a 1,393 kilobase (kb) of SphI-SalI fragment into vector pACYC184 and pUC18. This novel AAC(6') gene in plasmid pST2 acetylated kanamycin, amikacin, dibekacin, tobramycin, gentamicin, netilmicin, and sisomicin. The complete nucleotide sequence of the novel AAC(6') gene and its neighboring sequences were also determined. Minicell experiments detected only one protein of 24.7 kilodaltons (kDa) translated from an open reading frame of the 618 base pairs (bp) gene. 相似文献