全文获取类型
收费全文 | 1110篇 |
免费 | 11篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 15篇 |
综合类 | 32篇 |
化学工业 | 593篇 |
金属工艺 | 83篇 |
机械仪表 | 11篇 |
建筑科学 | 109篇 |
矿业工程 | 15篇 |
能源动力 | 20篇 |
轻工业 | 40篇 |
水利工程 | 12篇 |
石油天然气 | 52篇 |
无线电 | 4篇 |
一般工业技术 | 123篇 |
冶金工业 | 24篇 |
原子能技术 | 7篇 |
自动化技术 | 7篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 22篇 |
2019年 | 5篇 |
2018年 | 13篇 |
2017年 | 19篇 |
2016年 | 16篇 |
2015年 | 29篇 |
2014年 | 40篇 |
2013年 | 54篇 |
2012年 | 48篇 |
2011年 | 51篇 |
2010年 | 45篇 |
2009年 | 63篇 |
2008年 | 67篇 |
2007年 | 77篇 |
2006年 | 67篇 |
2005年 | 50篇 |
2004年 | 58篇 |
2003年 | 53篇 |
2002年 | 58篇 |
2001年 | 19篇 |
2000年 | 34篇 |
1999年 | 32篇 |
1998年 | 32篇 |
1997年 | 24篇 |
1996年 | 29篇 |
1995年 | 25篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1147条查询结果,搜索用时 31 毫秒
61.
Chloride penetration and calcium dissolution have been investigated for a saturated concrete after exposure to a 0.5 mol/L NaCl solution for a period of up to 3150 days. Simultaneous ion transport model (SiTraM) that allows the transport of chloride and calcium ions to be simultaneously simulated in a hydrated cement system has been used to verify the experimental results.Self-compacting concrete (SCC) with a water to cement ratio of 0.3 resulted in a limited chloride penetration depth while the calcium dissolution was also reduced within the near surface zone. Increased unit water content for normal concrete resulted in higher chloride penetration depth and larger dissolution front of Ca(OH)2 regardless of having the same water to cement ratio.It was revealed that the SiTraM can predict the profiles of chloride and calcium for self-compacting concrete. It was also found that the primary factor to control chloride penetration front and the dissolution front of Ca(OH)2 was the pore structure characteristic of concrete. 相似文献
62.
AM/AMPS/DMDAAC/AMC16S共聚物的合成与性能 总被引:4,自引:0,他引:4
采用氧化还原引发体系合成了丙烯酰胺(AM)/2丙烯酰胺基-2-甲基丙磺酸(AMPS)/二甲基二烯丙然氯化铵(DMDAAC)/2-丙烯酰胺基十六烷磺酸(AMC16S)四元共聚物,借助红外光谱和差热分析研究了聚合物的结构和热稳定性,初步评价了共聚物的溶液性能,结果表明,AM/AMPS/DMDAAC/AMC16S共聚物具有较好的热稳定性和耐温抗盐能力。 相似文献
63.
64.
65.
用丙烯酸丁酯(BA)和丙烯酸(AA)对醋酸乙烯酯(VAc)进行共聚改性,制备了稳定的VAc/BA/AA共聚乳液。研究了该聚合体系的动力学特征,讨论了乳化剂浓度(CE)、引发剂浓度(C1)和反应温度(T)对聚合速率和单体转化率的影响。实验结果表明,乳液聚合速率随着CE、C1和T的增加而增大;单体转化率随着CE和C1的增加而增大,在75℃时转化率有最大值;得到该共聚乳液体系的表观活化能Ea=64.4kJ·mol^-1;聚合反应速率Rp^∝CE^0.45C1^0.76该式与经典的乳液聚合动力学模型有较大偏差。 相似文献
66.
67.
The ethyl eosin/ascorbic acid photosensitized polymerization of vinyl acetate in aqueous methanol using visible radiation has been shown to occur by a mechanism in which polymerization occurs after an induction period during which the dye colour fades completely. During this period the dye is excited by incident radiation and reacts with the reducing agent to form free radical species. These react with dissolved oxygen to produce hydrogen peroxide. It is shown that the polymerization of vinyl acetate is initiated by products of the reaction between ascorbic acid and hydrogen peroxide. 相似文献
68.
The mechanism of damage occurring in NaCl contaminated materials has not been clarified yet. Apart from crystallization pressure, other hypotheses have been proposed to explain the cause of decay. Irreversible dilation has been observed in a few cases but has never been studied in a more systematic way. The aim of the research is to contribute to the modeling of this phenomenon.In the present paper the effect of NaCl on the hydric and hygric behavior of a lime-cement mortar is extensively studied. The results indicate that NaCl influences the hydric and hygric dilation behavior of the material. The material contaminated with NaCl shrinks during dissolution and dilates during crystallization of the salt. This dilation is irreversible and sufficient to damage the material after few dissolution/crystallization cycles. This behavior is not restricted to NaCl, but is observed in the presence of other salts as well (NaNO3 and KCl). Outcomes of electron microscopy studies suggest that salts causing irreversible dilation tend to crystallize as layers on the pore wall. 相似文献
69.
Evaluation of chloride penetration in high performance concrete using neural network algorithm and micro pore structure 总被引:2,自引:0,他引:2
Chloride attack is one of the major causes of deterioration of reinforced concrete structures. In order to evaluate the chloride behavior in concrete, a reasonable prediction for the diffusion coefficient of chloride ion, which governs mechanism of chloride diffusion inside concrete, is basically required. However, it is difficult to obtain chloride diffusion coefficients from experiments due to time and cost limitations.In this study, a numerical technique for chloride diffusion in high performance concrete (HPC) using a neural network algorithm is proposed. In order to collect comparative data on diffusion coefficients in concrete with various mineral admixtures such as ground granulated blast-furnace slag (GGBFS), fly ash (FA), and silica fume (SF), a series of electrically driven chloride penetration tests was performed. Seven material components in various mix designs and duration time are selected as neurons in a back-propagation algorithm, and associated learning of the neural network is carried out. An evaluation technique for chloride behavior in HPC using the obtained diffusion coefficients from the neural network algorithm is developed based on, so-called, Multi-Component Hydration Heat Model (MCHHM) and Micro Pore Structure Formation Model (MPSFM). The applicability of the developed technique is verified by comparing the analytical simulation results and the experimental results obtained in this study. Furthermore, this proposed technique using the neural network algorithm and micro modeling is applied to available experimental data for verification of its applicability. 相似文献
70.
研究了硫铵结晶系统中氯离子的来源以及对硫铵结晶系统的影响,并制定了控制氯离子含量的对策。硫铵结晶系统由于氯离子进出严重不平衡,导致母液中的氯离子含量高,造成设备腐蚀,影响产品质量和系统安全,因而必须控制氯离子的含量。 相似文献