全文获取类型
收费全文 | 345657篇 |
免费 | 27721篇 |
国内免费 | 16916篇 |
专业分类
电工技术 | 22033篇 |
技术理论 | 58篇 |
综合类 | 44084篇 |
化学工业 | 43636篇 |
金属工艺 | 11222篇 |
机械仪表 | 16075篇 |
建筑科学 | 50106篇 |
矿业工程 | 19590篇 |
能源动力 | 13106篇 |
轻工业 | 19677篇 |
水利工程 | 29395篇 |
石油天然气 | 18573篇 |
武器工业 | 2760篇 |
无线电 | 18409篇 |
一般工业技术 | 22421篇 |
冶金工业 | 18595篇 |
原子能技术 | 3577篇 |
自动化技术 | 36977篇 |
出版年
2024年 | 1091篇 |
2023年 | 3502篇 |
2022年 | 6738篇 |
2021年 | 8112篇 |
2020年 | 8705篇 |
2019年 | 7256篇 |
2018年 | 6899篇 |
2017年 | 8340篇 |
2016年 | 9797篇 |
2015年 | 10561篇 |
2014年 | 19674篇 |
2013年 | 18450篇 |
2012年 | 23521篇 |
2011年 | 24703篇 |
2010年 | 19348篇 |
2009年 | 20205篇 |
2008年 | 18611篇 |
2007年 | 24465篇 |
2006年 | 23066篇 |
2005年 | 20379篇 |
2004年 | 17006篇 |
2003年 | 15416篇 |
2002年 | 12834篇 |
2001年 | 10773篇 |
2000年 | 9080篇 |
1999年 | 7327篇 |
1998年 | 5498篇 |
1997年 | 4738篇 |
1996年 | 4256篇 |
1995年 | 3639篇 |
1994年 | 3110篇 |
1993年 | 2347篇 |
1992年 | 2059篇 |
1991年 | 1544篇 |
1990年 | 1318篇 |
1989年 | 1183篇 |
1988年 | 920篇 |
1987年 | 681篇 |
1986年 | 513篇 |
1985年 | 453篇 |
1984年 | 414篇 |
1983年 | 302篇 |
1982年 | 245篇 |
1981年 | 174篇 |
1980年 | 149篇 |
1979年 | 123篇 |
1978年 | 65篇 |
1977年 | 80篇 |
1976年 | 59篇 |
1975年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Heat transfer characteristics of a swirling impinging jet have been experimentally examined using a combined particle image velocimetry (PIV) and laser‐induced fluorescence (LIF) technique for simultaneous measurement of velocity and temperature fields. The present study shows that the radial width of the jet stretches with increasing swirl intensity, and that the stretching phenomenon contributes to the maximum local heat transfer coefficient. At the stagnation region, the flow near the heated surface is mixed intermittently by reverse flows toward upstream, and spatial distributions of temperature are correlated with instantaneous velocity vector maps. The dynamic behavior of recirculation zones, attributed to swirl number Sw and impinging distance, mainly determines the turbulent heat transfer at the stagnation region. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 663–673, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10120 相似文献
992.
形状记忆聚氨酯的结构与性能研究 总被引:1,自引:0,他引:1
以 2 ,4 -甲苯二异氰酸酯 (2 ,4 -TDI)、不同分子量的聚己二酸丁二醇酯 (PBAG)和 1,4-丁二醇 (BDO)为原料合成了具有形状记忆功能的聚氨酯材料。通过DSC、弯曲实验和力学实验 ,研究了形状记忆聚氨酯的性能 ,发现软段高度结晶和硬段聚集形成硬段微区是其具有较好形状记忆性能的必要条件。 相似文献
993.
994.
岩盐钻井水溶双井连通开采工艺的研究与推广 总被引:1,自引:0,他引:1
文章就全国井矿盐采区多年的开采工艺技术,进行了系统的研究与总结,并提出了岩盐钻井水溶开采双井连通的各种开采工艺及其关键技术,具有很强的适用性和推广价值。 相似文献
995.
Hyun-Chul Kim Author VitaeDaijin KimAuthor Vitae Sung Yang Bang Author Vitae 《Pattern recognition》2003,36(5):1095-1105
Linear discriminant analysis (LDA) is a data discrimination technique that seeks transformation to maximize the ratio of the between-class scatter and the within-class scatter. While it has been successfully applied to several applications, it has two limitations, both concerning the underfitting problem. First, it fails to discriminate data with complex distributions since all data in each class are assumed to be distributed in the Gaussian manner. Second, it can lose class-wise information, since it produces only one transformation over the entire range of classes. We propose three extensions of LDA to overcome the above problems. The first extension overcomes the first problem by modelling the within-class scatter using a PCA mixture model that can represent more complex distribution. The second extension overcomes the second problem by taking different transformation for each class in order to provide class-wise features. The third extension combines these two modifications by representing each class in terms of the PCA mixture model and taking different transformation for each mixture component. It is shown that all our proposed extensions of LDA outperform LDA concerning classification errors for synthetic data classification, hand-written digit recognition, and alphabet recognition. 相似文献
996.
一种广义水驱特征曲线的建立 总被引:2,自引:0,他引:2
广义水驱特征曲线能描述综合含水储量采出程度呈多种不同的凸、S、凹曲线类型。根据油水两相渗流原理,从归一化的油水相对渗透率出发,建立起累积产油、累积产水与综合含水率的积分相关关系,进而建立了累积产油、累积产水与归一化的油水相对渗透率的关系。通过构建积分函数,利用公式形式类比,建立了更一般形式的广义水驱特征曲线。理论分析和实例计算表明,所建立的广义水驱特征曲线与实际数据线性相关性更强,结果更可靠。 相似文献
997.
本文根据电子期刊的定义、特点及图书馆期刊工作所需要面对的问题,就高校图书馆网络环境下期刊工作的设施规划、资料收集、信息开发及读者培训等多方面内容进行了简单探讨,并就如何应对网络环境下图书馆期刊工作的变化提出建议。 相似文献
998.
999.
L. S. Mazov 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):583-585
It is demonstrated that scattering of mobile charge carriers by fluctuations of local spin density in the normal state of
SC-cuprates results in anomalous contribution to the transport phenomena (Hall and Nernst effects are included). Depending
on their sign and magnitude, they can change value and sign of the corresponding effect measured. 相似文献
1000.
Mark S. MACGREGOR Sue J. CARR 《Hemodialysis international. International Symposium on Home Hemodialysis》2007,11(Z2):S1-S4
Hemodialysis was a neglected aspect of nephrology in the UK. At the request of the Renal Association, the first UK Haemodialysis Masterclass was organized in 2007. The articles in this supplement arose from that meeting. Here, an overview of UK hemodialysis services and nephrology training is presented as background. Government‐funded dialysis should be provided to all UK citizens who require it. In 2005, there were 17,645 patients receiving hemodialysis, 5057 on peritoneal dialysis and 19,074 with kidney transplants, looked after by 359 nephrologists working in 73 National Health Service renal units. Renal replacement therapy incidence and prevalence remain comparatively low, at 108 and 694 per million population, respectively. Whether this represents inadequate provision or genuinely lower need remains unclear. The Renal Association sets clinical practice guidelines for dialysis, and audits performance via the UK Renal Registry. Postgraduate medical education is undergoing radical change in the UK. This is driven by the reduction in trainee doctors' working hours to 48 hr/week (mandated by the European Working Time Directive), and the governments' wish to reduce the duration of training, but also by a desire to formalize training, Our challenge is to continue to produce talented clinical nephrologists educated in breadth and depth, despite the reduced emphasis on clinical experience and omission of period of scientific research. The future for hemodialysis services in the UK is, however, promising with an expansion in the number of specialists and dialysis centers, and a growing interest in dialysis practice and research. 相似文献