全文获取类型
收费全文 | 3316篇 |
免费 | 270篇 |
国内免费 | 80篇 |
专业分类
电工技术 | 43篇 |
综合类 | 335篇 |
化学工业 | 644篇 |
金属工艺 | 91篇 |
机械仪表 | 83篇 |
建筑科学 | 1639篇 |
矿业工程 | 45篇 |
能源动力 | 106篇 |
轻工业 | 90篇 |
水利工程 | 158篇 |
石油天然气 | 21篇 |
武器工业 | 8篇 |
无线电 | 53篇 |
一般工业技术 | 279篇 |
冶金工业 | 32篇 |
原子能技术 | 13篇 |
自动化技术 | 26篇 |
出版年
2024年 | 12篇 |
2023年 | 65篇 |
2022年 | 71篇 |
2021年 | 106篇 |
2020年 | 99篇 |
2019年 | 81篇 |
2018年 | 84篇 |
2017年 | 99篇 |
2016年 | 89篇 |
2015年 | 80篇 |
2014年 | 174篇 |
2013年 | 239篇 |
2012年 | 231篇 |
2011年 | 224篇 |
2010年 | 189篇 |
2009年 | 239篇 |
2008年 | 221篇 |
2007年 | 261篇 |
2006年 | 208篇 |
2005年 | 165篇 |
2004年 | 121篇 |
2003年 | 119篇 |
2002年 | 89篇 |
2001年 | 69篇 |
2000年 | 74篇 |
1999年 | 45篇 |
1998年 | 50篇 |
1997年 | 32篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有3666条查询结果,搜索用时 31 毫秒
981.
Using the epoxy-aluminum wedge specimens defined and analyzed in Part 1, we measure the number of cycles required to initiate an interfacial fatigue crack near the apex, where the stress field is predicted to be singular. The eigenvalue, λ, and the generalized stress intensity factor, Q, are varied via the wedge angle, and via the beam deflection, respectively. Crack initiation is detected using a strain gage bonded near the tip of the wedge.
Following the methodology developed in Part 1, the fatigue data are then used to construct a fatigue initiation criterion characteristic of the bimaterial interface. This criterion is a 3-D surface, with the ordinate representing the generalized stress intensity factor and the two horizontal axes representing the number of cycles to initiation and the eigenvalue, respectively. Three key assumptions of the model are found to be satisfied in the specimens tested herein: (1) geometric imperfections at the apex are smaller than the singular region, (2) the plastic zones near the apex are also smaller than the singular region, and (3) the locus of initiation is near interfacial.
Finally, a thermomechanical analysis indicates that the residual thermal stresses generated during the fabrication process make a significant contribution to the critical stress intensity factor. With high Tg adhesives and under unfavorable conditions (high modulus, high CTE, poor adhesion), we predict that the residual stresses alone could be sufficient to cause debond initiation. 相似文献
Following the methodology developed in Part 1, the fatigue data are then used to construct a fatigue initiation criterion characteristic of the bimaterial interface. This criterion is a 3-D surface, with the ordinate representing the generalized stress intensity factor and the two horizontal axes representing the number of cycles to initiation and the eigenvalue, respectively. Three key assumptions of the model are found to be satisfied in the specimens tested herein: (1) geometric imperfections at the apex are smaller than the singular region, (2) the plastic zones near the apex are also smaller than the singular region, and (3) the locus of initiation is near interfacial.
Finally, a thermomechanical analysis indicates that the residual thermal stresses generated during the fabrication process make a significant contribution to the critical stress intensity factor. With high Tg adhesives and under unfavorable conditions (high modulus, high CTE, poor adhesion), we predict that the residual stresses alone could be sufficient to cause debond initiation. 相似文献
982.
983.
针对季冻区高速铁路路基填料冻融性能问题,将水泥和水泥粉煤灰掺入级配碎石作为改良措施。为了研究水泥和水泥粉煤灰改良碎石填料的抗冻融耐久性能,对填料的水稳定性、冻融变形特性和冻融耐久性进行试验,分析改良剂的种类、掺量以及养护龄期等因素的对路基填料性能的影响规律。研究结果表明:水泥改良填料相较于水泥粉煤灰改良填料有较高的无侧限抗压强度;填料单向冻胀量随着水泥掺量的增加而降低,掺入粉煤灰后会提高填料的冻胀率;水泥粉煤灰改良填料在28 d养护后水稳定性性能较水泥改良填料更佳优异,抗冻融性能则会低于水泥改良填料。 相似文献
984.
混凝土耐久寿命的预测是混凝土耐久性研究的一项重要课题,本文综合介绍了目前国内外有关混凝土耐久寿命预测的重要理论方法与实践,并简要论述了各种研究方法的优缺点. 相似文献
985.
Jianzhuang XIAO Nv HAN Yan LI Zhongsen ZHANG Surendra P. SHAH 《Frontiers of Structural and Civil Engineering》2021,15(1):1-19
The quest for high-performance construction materials is led by the development and application of new reinforcement materials for cement composites. Concrete reinforcement with fibers has a long history. Nowadays, many new fibers associated with high performance and possessing eco-environmental characteristics, such as basalt fibers and plant fibers, have received much attention from researchers. In addition, nanomaterials are considered as a core material in the modification of cement composites, specifically in the enhancement of the strength and durability of composites. This paper provides an overview of the recent research progress on cement composites reinforced with fibers and nanomaterials. The influences of fibers and nanomaterials on the fresh and hardened properties of cement composites are summarized. Moreover, future trends in the application of these fibers or of nanomaterial-reinforced cement composites are proposed. 相似文献
986.
预应力混凝土试件碳化试验及碳化深度预测模型研究 总被引:5,自引:0,他引:5
进行了碳化环境下预应力混凝土试件弯曲受拉和直接受压的耐久性试验研究,阐述了碳化作用对预应力混凝土结构的损伤机理。引进拉、压应力状态影响函数χσ,以反映碳化深度和应力状态及应力水平的关系。分别假定Fick第Ⅰ定律中的碳化时间指数α为0.50或为变量,由此建立了多因素影响下的预应力混凝土结构碳化深度预测模型,且采用一次可靠性方法(FORM)对碳化深度预测模型进行了分析。研究结果表明,拉、压应力分别可加快和减缓混凝土结构的碳化速度,χσ反映了碳化速率的变化趋势。最优的碳化时间指数α=0.48,若近似取α=0.50,计算结果也是足够准确的,由此印证了Fick第Ⅰ定律的正确性,而且采用FORM计算预应力混凝土结构碳化深度的离散程度是可靠的。 相似文献
987.
对编织的八种Coolnise涤纶低弹丝纬编针织面料的热湿舒适性、顶破强力、耐磨性和透气性进行了测试,分析了纱线种类和织物结构对热湿舒适性和物理机械性能的影响。 相似文献
988.
989.
The effects of storage at 25°C in swelling solvents having different solubility parameter (δs) values of 16.8–26.0 J0.5 cm−1.5 on the physical properties and structure of as‐cast poly(L ‐lactide) (PLLA) films was investigated by the degree of swelling (DS), differential scanning calorimetry (DSC), and tensile tests. It was found that PLLA film shows durabity to swelling solvents having δs values much lower or higher than the value range of 19–20.5 J0.5 cm−1.5 and that the polymer solubility parameter (δp) for PLLA is in the value range of 19–20.5 J0.5 cm−1.5. The decrease in the glass transition temperature (Tg) and tensile properties and the increase in melting temperature (Tm) and crystallinity (xc) were larger for PLLA films swollen in solvents having a high DS at 7 days (DS7days). The slight increase in Tm and xc for PLLA films after swelling in solvents with high DS7days values was due to the crystallization of PLLA that occurred during swelling, while the small increase in Tg and elongation at break (εB) for PLLA films after immersion in the solvents having low DS7days values was ascribed to stabilized chain packing in the amorphous region. The Tg, εB, and Young's modulus of the PLLA films after swelling in the solvents varied in the ranges of 47–57°C, 4–8%, and 55–77 kg/mm2, depending on their DS7days or δs values. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1582–1589, 2001 相似文献
990.
钢筋混凝土耐久性人工气候加速退化试验的相关性研究 总被引:11,自引:1,他引:10
钢筋混凝土耐久性退化在自然气候环境中是一个比较缓慢的过程,实验室中常用人工气侯加速退化试验方法来研究钢筋混凝土耐久性。但由于目前试验中的试验方法、试验手段、加速因素的不同,使研究成果在工程中的推广应用具有较大的局限性。为了使钢筋混凝土耐久性研究与工程实际更加紧密地结合起来,本文提出了建立标准的人工气候加速退化试验的思路,认为可以通过大量人工气候试验和自然气候试验的数据,建立一种能用于工程实际的人工气候环境和自然气候环境之间的定性关系;同时,本文也探讨了基于钢筋锈蚀的钢筋混凝土耐久性失效准则和自然气候长期试验数据的获取途径。 相似文献