全文获取类型
收费全文 | 455篇 |
免费 | 166篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 22篇 |
综合类 | 36篇 |
化学工业 | 103篇 |
金属工艺 | 36篇 |
机械仪表 | 63篇 |
建筑科学 | 4篇 |
能源动力 | 16篇 |
轻工业 | 1篇 |
石油天然气 | 1篇 |
武器工业 | 44篇 |
无线电 | 144篇 |
一般工业技术 | 69篇 |
冶金工业 | 4篇 |
原子能技术 | 7篇 |
自动化技术 | 97篇 |
出版年
2024年 | 12篇 |
2023年 | 41篇 |
2022年 | 45篇 |
2021年 | 73篇 |
2020年 | 63篇 |
2019年 | 37篇 |
2018年 | 34篇 |
2017年 | 54篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 31篇 |
2013年 | 22篇 |
2012年 | 34篇 |
2011年 | 34篇 |
2010年 | 30篇 |
2009年 | 30篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1984年 | 1篇 |
排序方式: 共有647条查询结果,搜索用时 15 毫秒
51.
Polyamide 6 (PA6) magnetic microspheres were firstly prepared via successively in situ polymerization using phase inversion
technology of polymer pairs polyamide 6/polystyrene (PA6/PS) at extremely low PS content. The properties of PA6 magnetic microspheres,
such as morphologies, diameter size distribution, magnetic properties, thermal stability, and the functional groups of the
magnetic microspheres, were investigated by different techniques (i.e. SEM, TEM, DLS, VSM, FTIR, and DSC). The results indicated
that the diameter distribution of PA6 magnetic microspheres was narrow, and the mean diameter size was about 7.7 μm. The saturation
magnetization of magnetic microspheres reached 12.50 emu/g. Furthermore, the magnetic microspheres had abundant functional
groups and better thermal stability. 相似文献
52.
The difference in the melting points of polyamide 66 (PA66) fiber and polyamide 6 (PA6) film permits the preparation of all-polyamide
(all-PA) composites by film-packing. Good interface performance and integrated consolidation structure in this all-PA composite
are contributed to the similar chemical composition between PA66 fiber and PA6 matrix. In this paper, the non-isothermal crystallization
kinetics and melting behaviors of PA6 matrix in all-PA composite are studied by differential scanning calorimetry (DSC), in
which the modified Avrami equation, Ozawa model, and Mo equation combining Avrami and Ozawa equation are employed. It is found
that the Mo equation exhibits great advantages in treating the non-isothermal crystallization kinetics for both neat PA6 and
PA6 matrix in all-PA composite. The crystal morphologies of single PA66 fiber–PA6 composite by polarizing microscope (POM)
clearly show a transcrystallinity layer of PA6 around PA66 fiber that proves a remarkable nucleation effect of PA66 fiber
surface on the crystallization of PA6 matrix. 相似文献
53.
54.
Toluene 2, 4‐diisocyanate (TDI) functionalized multiwalled carbon nanotubes (MWNTs‐NCO) were used to prepare monomer casting polyamide 6 (MCPA6)/MWNTs nanocomposites via in situ anionic ring‐opening polymerization (AROP). Isocyanate groups of MWNTs‐NCO could serve as AROP activators of ?‐caprolactam (CL) in the in situ polymerization. Fourier transform infrared (FTIR) showed that a graft copolymer of PA6 and MWNTs was formed in the in situ polymerization. MWNTs‐PA6 covalent bonds of the graft copolymer constituted a strong type of interfacial interaction in the nanocomposites and increased the compatibility of MWNTs and MCPA6 matrix. The nanocomposites were characterized for the morphology, mechanical, crystallization, and thermal properties through field emission transmission electron microscopy (FETEM), tensile testing, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). FETEM analysis showed that MWNTs were homogeneously dispersed in MCPA6 matrix. The initial tensile strengths and tensile modulus of the nanocomposite with 1.5 wt % loading of MWNTs were enhanced by about 16 and 13%, respectively, compared with the corresponding values for neat MCPA6. DSC analysis indicated that the crystallization temperature of the nanocomposites was increased by 8°C by adding 1.5 wt % MWNTs compared with pure MCPA6. Besides, it was found that the thermal stability of MCPA6 was improved by the addition of the MWNTs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
55.
The crack behavior of poly(trimethylene terephthalate) spherulites was studied mainly by polarizing optical microscopy, along with scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition to the effects of temperature and constraining substrate, another important factor, film thickness, on the formation of crack was first put forward and investigated. The emergence of the first crack occurred at 120°C during cooling after crystallization at 190°C for the sample with a thickness of 31.0 μm. For the spherulites growing between glass sheets, it was interesting that the sample with a thickness of 26.0 μm exhibited the largest number of cracks measured per 200 μm of radius, whereas samples thicker than 100 μm or thinner than 1 μm did not induce the formation of crack. Also, spherulites growing between two polyimide and two Teflon sheets showed no crack. Glass sheets lubricated with silicon oil restrained the number of cracks but did not eliminate cracks. SEM revealed that the cracking was about 900 nm in width. In addition, the AFM results suggest that the cracks had a depth of at least 150 nm. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
56.
57.
《Scripta materialia》2004,50(9):1203-1207
We report SiC ceramics sintered with AlN and Sc2O3 (or Lu2O3) that retain room temperature strength to 1500 °C. The intergranular glassy phase has not been observed in the ceramics due to a designed-sintering additive and, thus, the unsatisfactory effect of glassy phases on the high temperature strength is eliminated. 相似文献
58.
利用毫米波MIMO系统的稀疏特性,信道估计可以转化为稀疏信号重构的问题。解决毫米波MIMO稀疏信道估计问题时,传统的OMP方法需要信号的稀疏度作为先验信息,实际系统难以满足此需要。文中引入StOMP算法,根据信号已知的稀疏先验信息确定阈值,并结合动态的阈值调整,提出一种新的StOMP-D算法,实现了稀疏度自适应的毫米波MIMO信道估计。仿真结果表明,所提的方法与传统的LS方法比较,信道估计性能显著提高,并且与稀疏度已知的OMP方法性能十分接近,在稀疏度未知时有明显的优势。 相似文献
59.
Shear deformation that dominates elementary chip formation in metal cutting greatly relies on crystal anisotropy. In the present work we investigate the influence of crystallographic orientation on shear angle in ultra-precision orthogonal diamond cutting of single crystalline copper by joint crystal plasticity finite element simulations and in-situ experiments integrated in scanning electron microscope. In particular, the experimental cutting conditions including a straight cutting edge are the same with that used in the 2D finite element simulations. Both simulations and experiments demonstrate a well agreement in chip profile and shear angle, as well as their dependence on crystallography. A series of finite element simulations of orthogonal cutting along different cutting directions for a specific crystallographic orientation are further performed, and predicated values of shear angle are used to calibrate an extended analytical model of shear angle based on the Ernst–Merchant relationship. 相似文献
60.
Refractory metals are crucial for high-temperature applications such as fusion reactors. However, no systematic research has been reported for the influence of the impurities in refectory metals, especially at high temperatures. Our goal is an investigation of the influence of dissolved impurities on the recrystallization behavior of hot-rolled molybdenum (Mo). Two sets of 80%-rolled Mo plates with different purity levels pure Mo and non-pure Mo with the content of impurities, O, C, N, etc. are analyzed. Both isothermal and isochronous annealing experiments demonstrated that the impurities resulted in a reduction of recrystallization temperature and acceleration of texture transformation in a Mo plate. The recrystallization temperature of as-rolled non-pure Mo is about 100 °C lower than that of pure Mo. EBSD results show deformed γ-fiber texture gets weakened while {001}〈110〉 component gets strengthened at 1250 °C for pure Mo and 1150 °C for non-pure Mo, leading to the destabilization of fibrous grains. The XRD and TEM results reveal that the dislocation density of as-rolled non-pure Mo is ~2.4 times that of pure Mo. This discovery deviates from the conventional understanding of impurities or second phase particles in metals, providing better practical knowledge and opportunities to establish the technical parameters of refractory metals for high temperatures applications. 相似文献