全文获取类型
收费全文 | 31598篇 |
免费 | 3250篇 |
国内免费 | 1665篇 |
专业分类
电工技术 | 1722篇 |
综合类 | 3394篇 |
化学工业 | 4301篇 |
金属工艺 | 1537篇 |
机械仪表 | 1681篇 |
建筑科学 | 6119篇 |
矿业工程 | 1260篇 |
能源动力 | 1580篇 |
轻工业 | 1717篇 |
水利工程 | 1041篇 |
石油天然气 | 1990篇 |
武器工业 | 289篇 |
无线电 | 2854篇 |
一般工业技术 | 2599篇 |
冶金工业 | 1680篇 |
原子能技术 | 543篇 |
自动化技术 | 2206篇 |
出版年
2024年 | 102篇 |
2023年 | 385篇 |
2022年 | 800篇 |
2021年 | 884篇 |
2020年 | 991篇 |
2019年 | 903篇 |
2018年 | 847篇 |
2017年 | 1115篇 |
2016年 | 1256篇 |
2015年 | 1285篇 |
2014年 | 1826篇 |
2013年 | 2029篇 |
2012年 | 2415篇 |
2011年 | 2508篇 |
2010年 | 1871篇 |
2009年 | 1849篇 |
2008年 | 1784篇 |
2007年 | 2219篇 |
2006年 | 1999篇 |
2005年 | 1632篇 |
2004年 | 1305篇 |
2003年 | 1187篇 |
2002年 | 966篇 |
2001年 | 803篇 |
2000年 | 649篇 |
1999年 | 545篇 |
1998年 | 372篇 |
1997年 | 375篇 |
1996年 | 299篇 |
1995年 | 275篇 |
1994年 | 249篇 |
1993年 | 158篇 |
1992年 | 146篇 |
1991年 | 101篇 |
1990年 | 82篇 |
1989年 | 79篇 |
1988年 | 49篇 |
1987年 | 35篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
131.
132.
氨合成塔出口氨含量偏低原因分析及对策 总被引:1,自引:0,他引:1
阐述UHDE合成塔运行现状 ,分析氨净值达不到设计值的原因 ,提出相应的解决措施 相似文献
133.
A new sulfonated melamine–urea–formaldehyde (MUF) resin of relatively low melamine content, prepared according to a sequential formulation, has been shown to be highly effective when coupled with different natural vegetable tannins to produce leather with the same good characteristics of leather prepared with chrome salts. In particular, the antishrinkage effectiveness of the leather prepared according to the new approach is comparable to that obtained with chrome tanned leathers. The comparison of the traditional leather shrinkage temperatures test method with a new thermomechanical analysis (TMA) test method in tension yields thermograms presenting three major modulus of elasticity (MOE) peaks. These are closely connected to molecular level phenomena determining the shrinkage temperature of leather. The three determining parameters appear to be as follows: (1) The average value of the temperatures at which the three MOE peaks occur: the higher the value of this average, the lower is the shrinkage of leather. (2) The average of maximum MOE values of the TMA peaks: the higher this average is, the better is the leather in regard to antishrinkage effectiveness. This means the leather maximum MOE at each peak is a measure of the resistance to the contraction force induced by heat. (3) The relative intensity of the first TMA peak in relation to the second: the higher the value of the MOE for the first TMA peak is in relation to the second peak, the lower the leather shrinkage appears to be. However, it has not been possible to better define or quantify this latter effect. This new TMA test method in tension has also yielded a mathematical relationship correlating the thermogram peak temperatures and MOE averages with the traditional shrinkage temperature to a high degree of confidence. A previous TMA test method, in compression, has proven to yield more problematic and finally not very reliable results when one needs to apply it to a wide variety of different cases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1889–1903, 2003 相似文献
134.
铁元素对ZL108合金铸造性能的影响 总被引:2,自引:0,他引:2
研究了铁、锰对ZL108活塞合金铸造性能的影响。试验表明,在磷变质ZL108合金中,随着铁含量的增加,其流动性降低,体收缩、线收缩也减少。在高铁ZL108合金中加入锰后,可提高流动性,因为锰能够抑制针状β铁相的有害影响。 相似文献
135.
136.
利用小波变换去噪时小波系数方差的估计对去噪结果影响很大。自然图像小波分解后得到的系数在不同的分辨率中差异很大,所以利用邻域估计中心点方差时,不同分辨率应有不同大小的邻域。首先对在邻域中利用极大似然准则估计中心点方差进行分析,再结合自然图像小波分解后的系数在不同分辨率子带中,根据平稳性和重要性选择邻域的大小。最后进行去噪实验,并取得正交小波分解下理想的去噪性能。 相似文献
137.
介绍了AUTOCONER-338型自动络筒机空气捻接器的接头要求与影响接头质量的因素,并且就不同品种的纱线选用不同接头工艺进行了简单分析;介绍了如何评价络筒切疵有效性与影响切疵率的因素.通过以上2方面的分析介绍,及时调整设计与工艺,提高了生产效率,改善了布面质量. 相似文献
138.
139.
Hamid Javaherian Naghash Ahmad Reza Momeni Hamid Alian Ahmad Reza Massah Shahla Ataie 《Polymer International》2005,54(11):1564-1571
Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L?1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, Wg, and its equilibrium volume swelling ratio in benzene, qv, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry 相似文献
140.
An investigation of crack closure and the propagation of semi-elliptical fatigue cracks in Q1N (HY80) pressure vessel steel 总被引:1,自引:0,他引:1
The results of an experimental investigation of the effect of crack closure on the propagation of semi-elliptical fatigue cracks are presented. Load-shedding fatigue threshold tests were carried out at stress ratios of 0.2, 0.35, 0.5 and 0.7. Crack closure was measured at the surface and depth positions using backface strain gauges, near-tip gauges, and a clip gauge. Differences between the surface and depth growth behaviour are explained by considerations of the effects of the transition from plane stress conditions at the surface to plane strain conditions at the depth. The effects of stress ratios are attributed largely to differences in the crack opening displacement, which result in asperities coming into contact to induce roughness-induced crack closure. 相似文献