全文获取类型
收费全文 | 17126篇 |
免费 | 494篇 |
国内免费 | 526篇 |
专业分类
电工技术 | 364篇 |
综合类 | 28篇 |
化学工业 | 2596篇 |
金属工艺 | 1376篇 |
机械仪表 | 604篇 |
建筑科学 | 643篇 |
矿业工程 | 23篇 |
能源动力 | 681篇 |
轻工业 | 1191篇 |
水利工程 | 138篇 |
石油天然气 | 185篇 |
武器工业 | 1篇 |
无线电 | 2072篇 |
一般工业技术 | 4355篇 |
冶金工业 | 1875篇 |
原子能技术 | 192篇 |
自动化技术 | 1822篇 |
出版年
2024年 | 16篇 |
2023年 | 90篇 |
2022年 | 198篇 |
2021年 | 316篇 |
2020年 | 201篇 |
2019年 | 288篇 |
2018年 | 392篇 |
2017年 | 359篇 |
2016年 | 483篇 |
2015年 | 318篇 |
2014年 | 492篇 |
2013年 | 1219篇 |
2012年 | 810篇 |
2011年 | 1119篇 |
2010年 | 849篇 |
2009年 | 1081篇 |
2008年 | 951篇 |
2007年 | 912篇 |
2006年 | 807篇 |
2005年 | 602篇 |
2004年 | 648篇 |
2003年 | 492篇 |
2002年 | 480篇 |
2001年 | 469篇 |
2000年 | 433篇 |
1999年 | 426篇 |
1998年 | 738篇 |
1997年 | 529篇 |
1996年 | 457篇 |
1995年 | 327篇 |
1994年 | 256篇 |
1993年 | 197篇 |
1992年 | 167篇 |
1991年 | 156篇 |
1990年 | 127篇 |
1989年 | 113篇 |
1988年 | 93篇 |
1987年 | 58篇 |
1986年 | 58篇 |
1985年 | 49篇 |
1984年 | 54篇 |
1983年 | 45篇 |
1982年 | 30篇 |
1981年 | 25篇 |
1980年 | 27篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1976年 | 13篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
In order to study the influence of cerium ion implantation on the aqueous corrosion behavior of zircaloy-4, specimens were implanted by cerium ions with a fluence range from 1×1016 to 1×1017 ions/cm2 at maximum 150°C, using MEVVA source at an extracted voltage of 40 kV. The valence and elements penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES) respectively. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the cerium ion implantation in the oxide films. Three-sweep potentiodynamic polarization measurement was employed to value the aqueous corrosion resistance of zircaloy-4 in a 1 N H2SO4 solution. It was found that a significant improvement in the aqueous corrosion behavior of zircaloy-4 implanted with cerium ions compared with that of the as-received zircaloy-4. The improvement effect will declined with raising the implantation fluence. The bigger is the fluence, the less is the improvement. Finally, the mechanism of the corrosion behavior of the cerium-implanted zircaloy-4 is discussed. 相似文献
83.
84.
B. Van de Moortéle 《材料科学技术学报》2003,19(6)
The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amo 相似文献
85.
Digital filter bank design quadratic-constrained formulation 总被引:5,自引:0,他引:5
Formulate the filter bank design problem as an quadratic-constrained least-squares minimization problem. The solution of the minimization problem converges very quickly since the cost function as well as the constraints are quadratic functions with respect to the unknown parameters. The formulations of the perfect-reconstruction cosine-modulated filter bank, of the near-perfect-reconstruction pseudo-QMF bank, and of the two-channel biorthogonal linear-phase filter bank are derived using the proposed approach. Compared with other design methods, the proposed technique yields PR filter banks with much higher stopband attenuation. The proposed technique can also be extended to design multidimensional filter banks 相似文献
86.
Novel aspects of the microstructure of PP/PA blends prepared by reactive compounding as studied by microhardness 总被引:1,自引:0,他引:1
H. G. Fritz Q. Cai M. E. Cagiao L. Giri F. J. Baltá Calleja 《Journal of Materials Science》1995,30(13):3300-3306
The microhardness of injection-moulded i-polypropylene/polyamide (iPP/PA) blends prepared by reactive compounding was determined. The formulation rules and processing technology for the preparation of these alloys was reported previously. iPP/PA compositions between 100/0 and 50/50 using functionalized PP with various degrees of mainchain grafting, were investigated. It is shown that the deviation of microhardness from the additivity law of the single components is mainly due to a decrease in the crystallinity of the iPP phase. The results are discussed in the light of the microstructural variations as revealed by X-ray diffraction methods. 相似文献
87.
88.
At strain rates greater than about 10 the deformation of polymers is an adiabatic process which can lead to the generation of very high localized temperatures. These may be well in excess of the temperatures required for thermal decomposition of the polymer to occur. It is speculated that gaseous products arising from such decomposition may act as the source of microcavities and craze initiators. Experiments are described in which the thermal decomposition reaction parameters of polyetherketone, polyetheretherketone, and polysulphone are measured using differential scanning calorimetry and thermogravimetric analysis, and the decomposition products analysed by mass spectrometry. The results indicate that the proposed mechanism could act as a source of micropores with total pore volumes amounting to several per cent of the material volume. 相似文献
89.
90.