全文获取类型
收费全文 | 266554篇 |
免费 | 5406篇 |
国内免费 | 1044篇 |
专业分类
电工技术 | 4417篇 |
综合类 | 212篇 |
化学工业 | 40014篇 |
金属工艺 | 8454篇 |
机械仪表 | 7553篇 |
建筑科学 | 7207篇 |
矿业工程 | 575篇 |
能源动力 | 7493篇 |
轻工业 | 31538篇 |
水利工程 | 2310篇 |
石油天然气 | 1908篇 |
武器工业 | 7篇 |
无线电 | 34070篇 |
一般工业技术 | 48620篇 |
冶金工业 | 49930篇 |
原子能技术 | 3424篇 |
自动化技术 | 25272篇 |
出版年
2022年 | 1163篇 |
2021年 | 2149篇 |
2020年 | 1701篇 |
2019年 | 2051篇 |
2018年 | 3246篇 |
2017年 | 3237篇 |
2016年 | 3537篇 |
2015年 | 2689篇 |
2014年 | 4296篇 |
2013年 | 13200篇 |
2012年 | 7712篇 |
2011年 | 10476篇 |
2010年 | 8131篇 |
2009年 | 9037篇 |
2008年 | 9553篇 |
2007年 | 9540篇 |
2006年 | 8671篇 |
2005年 | 7794篇 |
2004年 | 7508篇 |
2003年 | 7373篇 |
2002年 | 6842篇 |
2001年 | 7189篇 |
2000年 | 6464篇 |
1999年 | 7020篇 |
1998年 | 17449篇 |
1997年 | 12074篇 |
1996年 | 9042篇 |
1995年 | 6792篇 |
1994年 | 5905篇 |
1993年 | 5790篇 |
1992年 | 4068篇 |
1991年 | 3836篇 |
1990年 | 3612篇 |
1989年 | 3438篇 |
1988年 | 3344篇 |
1987年 | 2649篇 |
1986年 | 2539篇 |
1985年 | 3224篇 |
1984年 | 2839篇 |
1983年 | 2596篇 |
1982年 | 2394篇 |
1981年 | 2450篇 |
1980年 | 2246篇 |
1979年 | 2071篇 |
1978年 | 1900篇 |
1977年 | 2266篇 |
1976年 | 2896篇 |
1975年 | 1597篇 |
1974年 | 1505篇 |
1973年 | 1568篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
52.
ABSTRACTThis paper presents an empirical assessment of four state-of-the-art risk-averse approaches to deal with the capacitated lot-sizing problem under stochastic demand. We analyse two mean-risk models based on the semideviation and on the conditional value-at-risk risk measures, and alternate first and second-order stochastic dominance approaches. The extensive computational experiments based on different instances characteristics and on a case-study suggest that CVaR exhibits a good trade-off between risk and performance, followed by the semideviation and first-order stochastic dominance approach. For all approaches, enforcing risk-aversion helps to reduce the cost-standard deviation substantially, which is usually accomplished via increasing production rates. Overall, we can say that very risk-averse decision-makers would be willing to pay an increased price to have a much less risky solution given by CVaR . In less risk-averse settings, though, semideviation and first-order stochastic dominance can be appealing alternatives to provide significantly more stable production planning costs with a marginal increase of the expected costs. 相似文献
53.
54.
55.
Marcela Stoia Cornelia Păcurariu Ciprian Mihali Iosif Mălăescu Cătălin Nicolae Marin Aylin Căpraru 《Ceramics International》2019,45(2):2725-2735
Magnetic MnFe2O4 nanopowders were synthesized by an original solvothermal method in the absence and in the presence of tetra-n-butylammonium bromide (TBAB) and Tween 80 (TW) as surfactants. Manganese ferrite/polyaniline (PANI) hybrid materials were synthesized by in situ polymerization of aniline on the surface of MnFe2O4 using ammonium persulfate as oxidant. The purpose of the study was to investigate the influence of the two surfactants on the properties of the MnFe2O4 powders and of their composites with PANI. The specific surface area, the cumulative surface area of pores and the cumulative volume of pores are influenced by the nature of surfactant in case of MnFe2O4 powders and are higher by comparison to those of the MnFe2O4/PANI hybrid materials. The values of saturation magnetization in case of MnFe2O4 powders are higher than those of the hybrid materials and are not influenced by the surfactant nature. These features revealed that MnFe2O4 powders can be efficiently used as adsorbents for the purification of wastewaters. The values of the electrical conductivity of the composites exhibit a significant increase in comparison to the MnFe2O4 powders and depend on the surfactant nature. The highest value of electrical conductivity was achieved by the composite obtained using Tween 80 as surfactant (σDC = 54.5·10?5S?m?1) which was close to that of PANI (σDC = 61.2·10?5 S?m?1). The fact that the magnetic and electric properties of the synthesized MnFe2O4/PANI composites can be changed by design, demonstrate the high potential of these materials to be used in magneto-electric applications. 相似文献
56.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
57.
58.
59.
60.