全文获取类型
收费全文 | 54217篇 |
免费 | 5435篇 |
国内免费 | 2961篇 |
专业分类
电工技术 | 2233篇 |
技术理论 | 1篇 |
综合类 | 4129篇 |
化学工业 | 14979篇 |
金属工艺 | 6015篇 |
机械仪表 | 1820篇 |
建筑科学 | 3066篇 |
矿业工程 | 2025篇 |
能源动力 | 4689篇 |
轻工业 | 5365篇 |
水利工程 | 417篇 |
石油天然气 | 2911篇 |
武器工业 | 941篇 |
无线电 | 1745篇 |
一般工业技术 | 6513篇 |
冶金工业 | 4048篇 |
原子能技术 | 234篇 |
自动化技术 | 1482篇 |
出版年
2024年 | 203篇 |
2023年 | 703篇 |
2022年 | 1520篇 |
2021年 | 1727篇 |
2020年 | 1724篇 |
2019年 | 1439篇 |
2018年 | 1535篇 |
2017年 | 1916篇 |
2016年 | 1973篇 |
2015年 | 2118篇 |
2014年 | 2820篇 |
2013年 | 2764篇 |
2012年 | 3618篇 |
2011年 | 4065篇 |
2010年 | 3077篇 |
2009年 | 3246篇 |
2008年 | 2620篇 |
2007年 | 3772篇 |
2006年 | 3372篇 |
2005年 | 3021篇 |
2004年 | 2553篇 |
2003年 | 2250篇 |
2002年 | 1935篇 |
2001年 | 1587篇 |
2000年 | 1367篇 |
1999年 | 1184篇 |
1998年 | 958篇 |
1997年 | 748篇 |
1996年 | 672篇 |
1995年 | 528篇 |
1994年 | 447篇 |
1993年 | 285篇 |
1992年 | 281篇 |
1991年 | 164篇 |
1990年 | 106篇 |
1989年 | 80篇 |
1988年 | 52篇 |
1987年 | 43篇 |
1986年 | 19篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1959年 | 5篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献
73.
74.
通过对国内外大量石油套管螺纹参数的测量和全尺寸的模拟试验,以及对测量和试验数据的理论分析,找出了影响国产套管发生粘扣的原因,并在实际生产中实施验证。采取相应的措施改善了套管的抗粘结性能,同时套管的密封和抗滑脱性能并未下降。 相似文献
75.
芳烃抽提装置技术改造 总被引:3,自引:0,他引:3
由于中国石化锦西石化分公司600kt/a连续重整装置的建设,芳烃抽提装置的原料由原来的脱戊烷油变为Ce组分。为此,对抽余油水洗塔和芳烃分离部分的苯塔塔盘,以及苯塔塔顶和塔底抽出部分进行了改造,更换部分机泵和增加变频泵,并将常规仪表改为DCS控制。改造后装置实现一次开车成功,生产出合格产品。抽余油中总芳烃含量小于0.1%,苯回收率达到99%以上。 相似文献
76.
A study of the trace elements emission (As, Se, Cd, Co, Cr, Cu, Zn, Hg, Tl, Pb, Ni, Sn, Sb, V, Mn and Fe) from pulverized coal combustion has been made at six heating and power stations situated in the Czech Republic. The amount of chlorine in coal has considerable influence on volatilization of some elements such as Zn, Cu, Pb, Hg and Tl, which is explained by the formation of thermodynamically stable compounds of these elements with chlorine. Generally, the affinities for Cl follows the order Tl > Cu > Zn > Pb > Co > Mn > Sn > Hg. The experimental data indicates enrichment of some of the trace toxic elements in the emissions (Cu, Zn, As, Se, Cd, Sn, Sb, Hg and Pb) and good agreement was obtained by thermodynamic equilibrium calculations with a few exceptions. In the case of Fe, Mn, Co, Cr and Sn calculated values are overestimated in the bottom ash and there are zero predicted amounts of these elements in the fly ash. In comparison, the results from experiments show up to 80% of these elements retained in fly ash. This implies that there exist additional steps leading to the enrichment by Fe, Mn, Co, Cr and Sn of small particles. Such mechanisms could include the ejection during devolatilization of small inorganic particles from the coal of bottom ash particles, or disintegration of the char containing these metals to small particles of fly ash. On the other hand, there are slightly overestimated or similar values of relative enrichment factors for As, V, Cu, Cd, Sb, Tl and Pb in the fly ashes and zero predicted values for bottom ashes. Our experimental results show about 5% or less of these elements are retained in bottom ashes, so they probably remain in the bottom ash inside unburned parts of coal. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
77.
Here, we describe the development of a reacting flow multi-species/combustion methodology, implemented as an extension to the differential reduced ejector analysis (DREA) computer program [Mathematical and computer modeling, vol. 31, 2000, p. 21; Appl. Math. Model. 25 (2001) 427; Comput. Math. Appl. 43(10–11); NASA Contractor Report, 1998]. Use of the single fluid IVP solver framework that was developed for the original DREA model has been directly coupled into the combustion formulation. With these modifications, the analysis has an elementary single step reaction Fuel+Oxidizer→Product combustion capability. Though approximate in nature, the simplicity and efficiency of the DREA formulation make it suitable for its original niche, namely design and preliminary design environments where more complex and expensive models may be inappropriate. 相似文献
78.
燃烧及其控制技术是各种火焰炉技术核心,强调高水平燃烧系统应对燃烧全过程进行控制,着重对燃烧系统点火、火焰监测、空燃比比例调节、燃烧过程各参数监控、炉温自动控制等各个方面内容进行了讨论介绍,最后用某天然气加热炉燃烧系统原理图及应用效果进行实例说明。 相似文献
79.
杨加峰 《武汉理工大学学报(材料科学英文版)》2005,20(Z1)
1Introduction HA(hydroxyapatite)wasakindofbioactiveceram ics,whichhadexcellentbiocompatibilityandtissueaffin ityinthatitscomponentsweresimilartothoseofhuman bone[1].Soitwasthebestknownhumanbonesubstitute,andunprecedentedeffecthadbeenharvestedinrecenttwo d… 相似文献
80.
Yuanjing Zheng Anker Degn Jensen Jan Erik Johnsson 《Applied catalysis. B, Environmental》2005,60(3-4):253-264
The deactivation of a commercial type V2O5-WO3-TiO2 monolith catalyst under biomass combustion was studied at a full-scale grate-fired power plant burning straw/wood using a slip stream pilot scale reactor. The aerosols in the flue gas consisted of a mixture of potassium chloride and sulphate. Three catalyst elements were exposed at 350 °C, and one element was exposed at 250 °C for comparison. The catalyst activity was measured in the reactor at the exposure temperature by addition of NH3 and extra NO. The activity, in terms of a first-order rate constant, dropped by 52% after about 1140 h indicating a very fast deactivation compared to coal firing. It was also found that the reactor temperature was not of importance for the deactivation rate. SEM-EDX analysis showed that particle deposition and pore blocking contributed to the deactivation by decreasing the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the resulting average K/V ratio in the catalyst structure was high enough (about 0.3–0.5) for a significant chemical deactivation. Chemisorption studies carried out in situ showed that the amount of chemisorbed NH3 on the catalyst decreased as a function of exposure time, which reveals that Brøndsted acid sites had reacted with potassium compounds and thereby rendered inactive. When washed by 0.5 M H2SO4 the regenerated catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C, but even though reactivation is possible, the deactivation rate appears too high for practical use of the SCR process in straw combustion. 相似文献