全文获取类型
收费全文 | 25731篇 |
免费 | 2414篇 |
国内免费 | 1403篇 |
专业分类
电工技术 | 384篇 |
综合类 | 1548篇 |
化学工业 | 11267篇 |
金属工艺 | 1437篇 |
机械仪表 | 311篇 |
建筑科学 | 657篇 |
矿业工程 | 325篇 |
能源动力 | 3244篇 |
轻工业 | 2657篇 |
水利工程 | 123篇 |
石油天然气 | 1532篇 |
武器工业 | 241篇 |
无线电 | 901篇 |
一般工业技术 | 2787篇 |
冶金工业 | 1113篇 |
原子能技术 | 589篇 |
自动化技术 | 432篇 |
出版年
2024年 | 113篇 |
2023年 | 849篇 |
2022年 | 1072篇 |
2021年 | 1149篇 |
2020年 | 1176篇 |
2019年 | 1096篇 |
2018年 | 972篇 |
2017年 | 1023篇 |
2016年 | 916篇 |
2015年 | 812篇 |
2014年 | 1240篇 |
2013年 | 1527篇 |
2012年 | 1471篇 |
2011年 | 1608篇 |
2010年 | 1203篇 |
2009年 | 1275篇 |
2008年 | 1125篇 |
2007年 | 1448篇 |
2006年 | 1288篇 |
2005年 | 1095篇 |
2004年 | 990篇 |
2003年 | 890篇 |
2002年 | 776篇 |
2001年 | 703篇 |
2000年 | 615篇 |
1999年 | 544篇 |
1998年 | 422篇 |
1997年 | 359篇 |
1996年 | 326篇 |
1995年 | 273篇 |
1994年 | 263篇 |
1993年 | 199篇 |
1992年 | 148篇 |
1991年 | 108篇 |
1990年 | 96篇 |
1989年 | 65篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1980年 | 10篇 |
1964年 | 9篇 |
1963年 | 5篇 |
1961年 | 5篇 |
1957年 | 8篇 |
1955年 | 8篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Gang Ning 《Electrochimica acta》2006,51(10):2012-2022
A generalized first principles based charge-discharge model to simulate the cycle life behavior of rechargeable Li-ion batteries has been developed. The model is based on loss of the active lithium ions due to the electrochemical parasitic reaction and rise of the anode film resistance. The effect of parameters such as depth of discharge (DOD), end of charge voltage (EOCV) and overvoltage of the parasitic reaction on the cycle life behavior has been quantitatively analyzed. The experimental results obtained at charge rate of 1 C, discharge rate of 0.5 C, EOCV of 4.0 V and DOD of 0.4 were used to validate the cycle life model. Good agreement between the simulations and the experiments has been achieved up to 1968 cycles. Simulation of a battery subjected to multiple cycling regimes has also been demonstrated. 相似文献
132.
D. Thoenes 《Chemical engineering science》1980,35(9):1840-1853
Modelling of chemical reactors is reviewed with an emphasis on process development and scale-up. A distinction is made between modelling of chemical kinetics, of rate processes in volume elements and of whole reactors. Examples are mainly taken from papers presented at the Sixth International Symposium on Chemical Reaction Engineering. Special attention is given to the modelling of single phase reactors, fixed beds, trickle beds, fluid beds, and gas bubble reactors. 相似文献
133.
134.
本文用纤维素材料经酸分解制备具有平衡聚合度(LODP)的微晶纤维素,再分散成超细纤维素胶体(准均相纤维素体系)。用扫描电镜(SEM)观察处理前后的纤维素颗粒尺寸,并比较它们和丙烯酰胺接枝共聚的反应速率、聚合转化率、接枝率、接技效率、聚丙烯酰胺支链的分子量及其分布的情况。 相似文献
135.
3,4-亚甲二氧基苯乙胺的合成新方法 总被引:1,自引:0,他引:1
以胡椒胺为原料,通过Sandmeyer反应制得3,4-亚甲二氧基溴苯(收率75.0%),再经Grignard反应(收率74.8%)、酯化反应(收率94.0%)和Gabriel反应(收率63.0%)制备出3,4-亚甲二氧基苯乙胺,并通过红外光谱和色谱-质谱联用确定了目标产物的结构。讨论温度对各步反应的影响,确定了最佳反应条件。 相似文献
136.
137.
微波促进有机反应原理及微波有机合成仪 总被引:4,自引:0,他引:4
论述了微波促进有机反应的原理和微波加热的特点.对目前使用的家用微波炉和专用微波有机合成仪的性能进行了评价.指出微波促进有机反应需要解决的问题及我国应加强对该领域的研究. 相似文献
138.
Sn-incorporated folded sheets mesoporous materials (Sn-FSM-16) with various contents of Sn were synthesized by using a mixture of water glass, SnCl4 and NaOH as starting materials. Hexadecyltrimethyl-ammonium chloride (surfactant) was used to intercalate into the layered silicate. The reaction process was followed by measurements of XRD patterns of intermediates. The Sn-FSM-16 was formed via the following mechanism: (1) layered silicates such as - - and -Na2Si2O5 were formed as intermediates by the calcination of the mixture of the starting materials; (2) the surfactant was intercalated into the layered silicates; (3) the surfactant-silicate complex with hexagonal structure was obtained as a precursor of Sn-FSM-16; (4) the precursor was calcined to decompose the surfactant in the interlayer and was changed to Sn-FSM-16. The structural aspect of Sn in Sn-FSM-16 was studied by XPS profiles of Sn 3d
5/2 and Si2p, 29 Si MAS NMR and FTIR. The content of Sn in Sn-FSM increased with increasing concentrations of both Sn and NaOH in the starting materials. The surface area of Sn-FSM-16 decreased with an increase of Sn content in Sn-FSM (1160–620 m2/g). 相似文献
139.
碳四烷烃催化裂解制低碳烯烃的研究进展 总被引:11,自引:0,他引:11
论述了碳四烷烃催化裂解制低碳烯烃的催化剂体系、影响因素及催化裂解方式。该催化剂体系包括硅铝酸盐及锆硫酸盐,氧化铝与碱金属或碱土金属的混合物,负载型催化剂等3种类型。其中分子筛(晶体硅铝酸盐)及其改性催化剂是研究开发的主要方向。除操作条件外,稀释剂、引发和抑制剂和裂解反应方式对催化裂解反应均有影响。催化裂解反应机理与催化剂的种类和反应条件相关。对于酸性分子筛催化剂有2种比较公认的机理:正碳离子机理,自由基与正碳离子机理两种形式。研究表明碳四烷烃,特别是正丁烷催化裂解制低碳烯烃具有良好的低碳烯烃收率,收率可达50%以上。 相似文献
140.
Mitra Dadvar 《Chemical engineering science》2007,62(5):1466-1476
The question of whether effective diffusivities in porous materials under reactive and nonreactive conditions are equal is addressed. Previous studies had considered the problem with first-order reactions. We study the issue with two nonlinear reactions—a second-order reaction and one governed by the Michaelis-Menten kinetics. Pore network and continuum models of porous media are utilized to estimate the effective diffusivities under reactive and nonreactive conditions. We show that the two effective diffusivities are significantly different. The difference is due to the heterogeneities of the porous material, and the fluctuations that they cause in the spatially varying local concentrations and diffusivities, and can be as large as a few orders of magnitude. Theoretical analysis of diffusion and reactions in porous media is also presented that supports the results of the simulations. In particular, it is shown that the results of pore network simulations cannot be fitted to the classical continuum equation of diffusion and reaction, and that a more complex continuum equation should be used for this purpose. 相似文献