全文获取类型
收费全文 | 17635篇 |
免费 | 2327篇 |
国内免费 | 1255篇 |
专业分类
电工技术 | 1757篇 |
技术理论 | 1篇 |
综合类 | 1819篇 |
化学工业 | 2899篇 |
金属工艺 | 619篇 |
机械仪表 | 865篇 |
建筑科学 | 1682篇 |
矿业工程 | 1185篇 |
能源动力 | 905篇 |
轻工业 | 2020篇 |
水利工程 | 638篇 |
石油天然气 | 770篇 |
武器工业 | 236篇 |
无线电 | 941篇 |
一般工业技术 | 1267篇 |
冶金工业 | 730篇 |
原子能技术 | 119篇 |
自动化技术 | 2764篇 |
出版年
2024年 | 122篇 |
2023年 | 274篇 |
2022年 | 578篇 |
2021年 | 657篇 |
2020年 | 716篇 |
2019年 | 616篇 |
2018年 | 547篇 |
2017年 | 654篇 |
2016年 | 762篇 |
2015年 | 741篇 |
2014年 | 1108篇 |
2013年 | 1096篇 |
2012年 | 1420篇 |
2011年 | 1375篇 |
2010年 | 1096篇 |
2009年 | 1060篇 |
2008年 | 962篇 |
2007年 | 1185篇 |
2006年 | 1036篇 |
2005年 | 857篇 |
2004年 | 743篇 |
2003年 | 586篇 |
2002年 | 470篇 |
2001年 | 471篇 |
2000年 | 370篇 |
1999年 | 307篇 |
1998年 | 261篇 |
1997年 | 190篇 |
1996年 | 163篇 |
1995年 | 147篇 |
1994年 | 147篇 |
1993年 | 108篇 |
1992年 | 71篇 |
1991年 | 85篇 |
1990年 | 48篇 |
1989年 | 36篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1964年 | 2篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
31.
32.
The equations for predicting the number-average molecular weight are derived on the basis of the three stage polymerization model (TSPM) in this paper. By applying the equations, a plotting approach is proposed to determine the apparent initiator efficiency defined as f[(αtd+1)/2] and the constant of chain transfer to monomer, where f is the initiator efficiency and αtd denotes the fraction of the termination rate constants by disproportionation. Using the approach to plot the experimental data in the literature, it is found that the chain transfer to monomer can be neglected for both methylmethacrylate (MMA) and styrene (St) polymerizations, but it can exert a significant effect on ethylmethacrylate (EMA) polymerization. In addition, the apparent initiator efficiency is found to be independent of reaction temperature and initiator concentration at each stage. The values of f[(αtd+1)/2] at gel effect stage are slightly reduced as compared with that at low conversion stage for MMA and EMA polymerizations. However, it decreases significantly at gel effect stage for St polymerization. Using the equations derived and the apparent initiator efficiencies obtained from TSPM plots, the number-average molecular weights at different conversions can be predicted. Comparisons show that the agreement between predictions and experimental data is satisfactory. 相似文献
33.
C. Ranganathaiah 《应用聚合物科学杂志》2002,86(13):3336-3345
I measured positron lifetime in natural polymer–cotton fibers as a function of isochronal annealing temperature in the range 27–290°C. The variations in the positron results indicated structural changes occurring in the cotton fibers and determined the glass‐transition temperature as 80°C. Activation energies were measured separately for the crystalline and amorphous regions, indicating the versatility of the technique. These values were close to the O? H bond dissociation energy, suggesting O? H bond dissociation, the most probable process occurring under thermal treatment. As an extension of the positron results, the molecular weight of the cotton fibers was determined to be 1,200,000 based on free volume, which was within the range suggested for cotton. There seemed to be an indication that crosslinking changed the spiral structure of cotton fibers to the network type. However, this needs to be validated by other measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3336–3345, 2002 相似文献
34.
本文简要地介绍了我国几个地下矿在锚喷网联合支护的硐室工程中堵漏防渗处理所取得的良好效果,可供类似矿山参考。 相似文献
35.
采用信息融合技术的IR/MMW复合导引头的目标跟踪 总被引:2,自引:0,他引:2
从误差测量环节入手,基于IR/MMW双模结构,采用信息融合处理技术提高其估计跟踪精度,最终达到降低制导误差,提高武器性能的目的,仿真结果验证了该方法的有效性。 相似文献
36.
Ioannis Arvanitoyannis John M. V. Blanshard Ioannis Kolokuris 《Polymer International》1992,27(1):7-15
Mastication of gutta percha (trans-polyisoprene) resulted in the selective scission of molecules, producing a narrower distribution of lower molecular weights. The mechanical properties of the samples also underwent a significant change due to mastication. The greater the content of incompatible substances (salts and oxides) in commercial gutta percha. the more substantial were these effects. The atmosphere (air, N2, O2) in which the experiments were conducted yielded significantly different results. The decrease in molecular weight was far greater in an O2 atmosphere than under a current of nitrogen or air, owing to the combination of double bonds with O2. 相似文献
37.
本文介绍了给水联合处理的原理及其优点以及在望亭电厂的1台300MW亚临界燃油直流炉上进行这项处理的工业性试验的过程、效果及存在问题。最后作者对给水联合处理能否取得成效的关键提出了意见。 相似文献
38.
变权组合预测模型在大坝安全监测中的应用 总被引:1,自引:1,他引:0
简要介绍了组合预测模型的基本原理,该模型改进了单一模型考虑因素的片面性,但常规的组合预测模型的权系数是固定的。考虑到各种模型的预测精度的变化,以及大坝安全监测数据存在的突变、时效等因素,固定权系数的组合预测模型有待进一步改进。文中提出了变权系数组合预测模型,并将其用于实际的大坝安全监测工程。结果表明,变权组合预测模型的预报精度高于其他模型。是一种值得推广的方法。 相似文献
39.
Design optimization of 3D steel structures: Genetic algorithms vs. classical techniques 总被引:1,自引:0,他引:1
María Belén Prendes Gero Antonio Bello García 《Journal of Constructional Steel Research》2006,62(12):1303-1309
In this paper an elitist genetic algorithm (GA) developed by the authors is compared with common commercial solutions for complex structural optimization. After its prior validation on two-dimensional (2D) structures, the GA was tuned and improved in order to obtain structural elements with minimum weights that satisfy the ultimate limit states of the applicable building code. Subsequently, the same spatial structures were optimized using a commercial structural analysis program. Finally, the cost and weight improvements obtained using the GA, although at a higher computational cost, are discussed. 相似文献
40.