全文获取类型
收费全文 | 252628篇 |
免费 | 3169篇 |
国内免费 | 867篇 |
专业分类
电工技术 | 4840篇 |
综合类 | 193篇 |
化学工业 | 36149篇 |
金属工艺 | 9509篇 |
机械仪表 | 7547篇 |
建筑科学 | 6073篇 |
矿业工程 | 880篇 |
能源动力 | 7229篇 |
轻工业 | 21095篇 |
水利工程 | 2203篇 |
石油天然气 | 3230篇 |
武器工业 | 15篇 |
无线电 | 34308篇 |
一般工业技术 | 49984篇 |
冶金工业 | 48565篇 |
原子能技术 | 5079篇 |
自动化技术 | 19765篇 |
出版年
2021年 | 2166篇 |
2020年 | 1562篇 |
2019年 | 1917篇 |
2018年 | 3276篇 |
2017年 | 3308篇 |
2016年 | 3402篇 |
2015年 | 2217篇 |
2014年 | 3958篇 |
2013年 | 11483篇 |
2012年 | 6235篇 |
2011年 | 8580篇 |
2010年 | 6912篇 |
2009年 | 7891篇 |
2008年 | 8407篇 |
2007年 | 8301篇 |
2006年 | 7368篇 |
2005年 | 6500篇 |
2004年 | 6285篇 |
2003年 | 6561篇 |
2002年 | 6043篇 |
2001年 | 6516篇 |
2000年 | 5978篇 |
1999年 | 6392篇 |
1998年 | 16494篇 |
1997年 | 11417篇 |
1996年 | 8796篇 |
1995年 | 6611篇 |
1994年 | 5907篇 |
1993年 | 5848篇 |
1992年 | 4133篇 |
1991年 | 4021篇 |
1990年 | 3860篇 |
1989年 | 3652篇 |
1988年 | 3561篇 |
1987年 | 3019篇 |
1986年 | 2943篇 |
1985年 | 3211篇 |
1984年 | 2926篇 |
1983年 | 2829篇 |
1982年 | 2636篇 |
1981年 | 2543篇 |
1980年 | 2462篇 |
1979年 | 2306篇 |
1978年 | 2107篇 |
1977年 | 2606篇 |
1976年 | 3566篇 |
1975年 | 1764篇 |
1974年 | 1729篇 |
1973年 | 1665篇 |
1972年 | 1466篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Breslavs’kyi D. V. Metel’yov V. O. Morachkovs’kyi O. K. Tatarinova O. A. 《Strength of Materials》2019,51(5):753-760
Strength of Materials - Creep constitutive equations have been derived for the materials that exhibit the properties of orthotropy (transversal isotropy) and transient creep under cyclic loading. A... 相似文献
72.
Manika Chaudhary Milan Singh Ashwani Kumar Yogendra K. Gautam Anil K. Malik Yogesh Kumar Beer Pal Singh 《Ceramics International》2021,47(2):2094-2106
The current research work presents a facile and cost–effective co-precipitation method to prepare doped (Co & Fe) CuO and undoped CuO nanostructures without usage of any type of surfactant or capping agents. The structural analysis reveals monoclinic crystal structure of synthesized pure CuO and doped-CuO nanostructures. The effect of different morphologies on the performance of supercapacitors has been found in CV (cyclic voltammetry) and GCD (galvanic charge discharge) investigations. The specific capacitances have been obtained 156 (±5) Fg?1, 168(±5) Fg?1 and 186 (±5) Fg?1 for CuO, Co-doped CuO and Fe-doped CuO electrodes, respectively at scan rate of 5 mVs?1, while it is found to be 114 (±5) Fg?1, 136 (±5) Fg?1 and 170 (±5) Fg?1 for CuO, Co–CuO and Fe–CuO, respectively at 0.5 Ag-1 as calculated from the GCD. The super capacitive performance of the Fe–CuO nanorods is mainly attributed to the synergism that evolves between CuO and Fe metal ion. The Fe-doped CuO with its nanorods like morphology provides superior specific capacitance value and excellent cyclic stability among all studied nanostructured electrodes. Consequently, it motivates to the use of Fe-doped CuO nanostructures as electrode material in the next generation energy storage devices. 相似文献
73.
Environmental concerns continue to pose the challenge to replace petroleum-based products with renewable ones completely or at least partially while maintaining comparable properties. Herein, rigid polyurethane (PU) foams were prepared using soy-based polyol for structural and thermal insulation applications. Cell size, density, thermal resistivity, and compression force deflection (CFD) values were evaluated and compared with that of petroleum-based PU foam Baydur 683. The roles of different additives, that is, catalyst, blowing agent, surfactants, and different functionalities of polyol on the properties of fabricated foam were also investigated. For this study, dibutyltin dilaurate was employed as catalyst and water as environment friendly blowing agent. Their competitive effect on density and cell size of the PU foams were evaluated. Five different silicone-based surfactants were employed to study the effect of surface tension on cell size of foam. It was also found that 5 g of surfactant per 100 g of polyol produced a foam with minimum surface tension and highest thermal resistivity (R value: 26.11 m2·K/W). However, CFD values were compromised for higher surfactant loading. Additionally, blending of 5 g of higher functionality soy-based polyol improved the CFD values to 328.19 kPa, which was comparable to that of petroleum-based foam Baydur 683. 相似文献
74.
Microsystem Technologies - The strategy for analysis of noise generated in the analog circuit is presented here. Further, methodology for optimization of noise to improve the performance of the... 相似文献
75.
Sophia X. Sui Lana J. Williams Kara L. Holloway-Kew Natalie K. Hyde Julie A. Pasco 《International journal of molecular sciences》2021,22(1)
Sarcopenia is the loss of skeletal muscle mass and function with advancing age. It involves both complex genetic and modifiable risk factors, such as lack of exercise, malnutrition and reduced neurological drive. Cognitive decline refers to diminished or impaired mental and/or intellectual functioning. Contracting skeletal muscle is a major source of neurotrophic factors, including brain-derived neurotrophic factor, which regulate synapses in the brain. Furthermore, skeletal muscle activity has important immune and redox effects that modify brain function and reduce muscle catabolism. The identification of common risk factors and underlying mechanisms for sarcopenia and cognition may allow the development of targeted interventions that slow or reverse sarcopenia and also certain forms of cognitive decline. However, the links between cognition and skeletal muscle have not been elucidated fully. This review provides a critical appraisal of the literature on the relationship between skeletal muscle health and cognition. The literature suggests that sarcopenia and cognitive decline share pathophysiological pathways. Ageing plays a role in both skeletal muscle deterioration and cognitive decline. Furthermore, lifestyle risk factors, such as physical inactivity, poor diet and smoking, are common to both disorders, so their potential role in the muscle–brain relationship warrants investigation. 相似文献
76.
Dreissenid mussel veligers compose a substantial component of pelagic biomass in the Great Lakes, yet their dynamics are poorly understood. To evaluate seasonal, spatial, and inter-annual variation in veliger density, we used a 64-μm mesh plankton net (2008, 2013–2016) and a 153-μm mesh plankton net (2007–2016) to collect dreissenid veligers at nearshore (15–25?m depth), transitional (45?m) and offshore (93–110?m) sites in southeast Lake Michigan during March–December. We also evaluated trends in density of recently settled mussels relative to veliger abundance and the density of the standing stock of adult mussels. Veliger density peaked during both summer and fall at all sites, but peak densities in summer were generally higher nearshore, whereas peak densities in the fall were generally higher offshore. The density of veligers in the 153-μm net was overall 28% of that in the 64-μm net, but there was high variability in this comparison among months. Smaller veligers were much more abundant in the 64-μm net, but there was little difference in the size distribution and abundance between nets for the 210–300?μm size classes. Thus, the 153-μm net could still be a useful tool for assessing density trends of larger veligers just prior to their settlement. Newly settled mussels (≤2?mm) were most abundant in summer or fall at the nearshore and offshore sites but were nearly absent at the transitional site despite the high density of veligers there. Factors other than veliger density must play an important role in mussel recruitment. 相似文献
77.
Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI ... 相似文献
78.
79.
80.