全文获取类型
收费全文 | 6720篇 |
免费 | 1083篇 |
国内免费 | 397篇 |
专业分类
电工技术 | 462篇 |
综合类 | 858篇 |
化学工业 | 1008篇 |
金属工艺 | 291篇 |
机械仪表 | 402篇 |
建筑科学 | 444篇 |
矿业工程 | 135篇 |
能源动力 | 224篇 |
轻工业 | 578篇 |
水利工程 | 239篇 |
石油天然气 | 224篇 |
武器工业 | 97篇 |
无线电 | 834篇 |
一般工业技术 | 1067篇 |
冶金工业 | 373篇 |
原子能技术 | 42篇 |
自动化技术 | 922篇 |
出版年
2024年 | 17篇 |
2023年 | 46篇 |
2022年 | 64篇 |
2021年 | 133篇 |
2020年 | 197篇 |
2019年 | 216篇 |
2018年 | 195篇 |
2017年 | 276篇 |
2016年 | 331篇 |
2015年 | 306篇 |
2014年 | 402篇 |
2013年 | 424篇 |
2012年 | 413篇 |
2011年 | 416篇 |
2010年 | 324篇 |
2009年 | 302篇 |
2008年 | 354篇 |
2007年 | 365篇 |
2006年 | 326篇 |
2005年 | 307篇 |
2004年 | 298篇 |
2003年 | 386篇 |
2002年 | 466篇 |
2001年 | 447篇 |
2000年 | 369篇 |
1999年 | 274篇 |
1998年 | 162篇 |
1997年 | 145篇 |
1996年 | 61篇 |
1995年 | 31篇 |
1994年 | 39篇 |
1993年 | 23篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1956年 | 2篇 |
1955年 | 3篇 |
1954年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有8200条查询结果,搜索用时 15 毫秒
1.
Mehdi Hosseini Abadshapoori 《亚洲传热研究》2021,50(2):1056-1072
Increasing the heat capacity of heat exchangers is a crucial need for modern devices. The thermal conductivity of the usual fluids and the Nusselt (Nu) number of flows containing such fluids are two bottlenecks in the way of increasing heat delivery in the heat exchangers. For this reason, nanofluids have been introduced. The effect of utilizing a Cu-water nanofluid as a coolant of two hot pipes in a square cavity is investigated numerically with a two-component lattice Boltzmann method. The volume fraction of nanoparticles is assumed to be constant (0.03) while the Richardson (Ri) number varies from 0.02 to 20. Results show that the effectiveness of nanoparticles is better observed in the natural convection mode. However, sedimentation is also very probable at high Ri numbers, which significantly reduces the effectiveness of the nanoparticles. Configurations which produce a natural convection stream similar to the forced convection one as well as the configurations with high spacing and hence, low heat stream interactions, are the best choices for a uniform heat rate from the pipes. 相似文献
2.
为推进病历数字化发展,并确保其信息的安全性,将以HIS电子病历系统为基础,采用安信数字签名技术和PKI或PMI系统搭建相信并加以任用的授权服务,经过针对实际的PKC和CA的确认、委托与管控构建整体的数字签名平台,完成电子病历数字签名功能设计,以加强电子文件的完整性、真实性和不可抵赖性。最后以某医院的XML结构化的电子病历系统为基础进行项目实施,完成了医护人员通过HIS的快速身份认证,和准确地数字签名。 相似文献
3.
Yasoub Eghbali Mahmoud Ferdosizade Naeiny 《International Journal of Communication Systems》2020,33(14)
In this paper, an off‐grid direction of arrival (DoA) estimation method is proposed for wideband signals. This method is based on the sparse representation (SR) of the array covariance matrix. Similar to the time domain DoA estimation methods, the correlation function of the sources was assumed to be the same and known. A new measurement vector is obtained using the lower‐left triangular elements of the covariance matrix. The DoAs are estimated by quantizing the entire range of continuous angle space into discrete grid points. However, the exact DoAs may be located between two grid points; therefore, this estimation has errors. The accuracy of DoA estimation is improved by the minimization of the difference between the new measurement vector and its estimated values. Simulation results revealed that the proposed method can enhance the DoA estimation accuracy of wideband signals. 相似文献
4.
5.
针对现有海量点云可视化方法存在索引构建时间长、内存占用大等问题,研究一种八叉树索引结合OSG分页结点的快速可视化方法,可在占用较小内存的基础上快速建立点云索引并实时调度。采用八叉树索引结构对海量点云进行数据组织,建立各层级的八叉树结点并以文件映射的方式分块保存,对结点文件重组织转换为支持OSG渲染引擎的多分辨率点云数据。采用基于OSG分页结点的实时调度技术,对海量点云进行高质量可视化。与目前两款主流的点云数据处理商业软件进行实验对比分析,结果表明所提方法具有索引建立速度快、内存占用小等优点,同时可视化交互更加流畅,适用于各种配置计算机下海量点云数据的调度管理与实时可视化。 相似文献
6.
7.
Cellulose dissolved in ionic liquid (1‐(carboxymethyl)pyridinium chloride)/water (60/40 w/w) mixture is regenerated in various non‐solvents, namely water, ethanol, methanol and acetone, to gain more insight into the contribution of non‐solvent medium to the morphology of regenerated cellulose. To this end, the initial and regenerated celluloses were characterized with respect to crystallinity, thermal stability, chemical structure and surface morphology using wide‐angle X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. According to the results, regardless of non‐solvent type, all regenerated samples have the same chemical structure and lower crystallinity in comparison to the initial cellulose, making them a promising candidate for efficient biofuel production based on enzymatic hydrolysis of cellulose. The reduction in crystallinity of regenerated samples is explained based on the potential of the non‐solvent to break the hydrogen bonds between cellulose chains and ionic liquid molecules as well as the affinity of water and non‐solvent which can be evaluated based on Hansen solubility parameter. The latter also determines the phase‐separation mechanism during the regeneration process, which in turn affects surface morphology of the regenerated cellulose. The pivotal effect of regenerated cellulose crystallinity on its thermal stability is also demonstrated. Regenerated cellulose with lower crystallinity is more susceptible to molecular rearrangement during heating and hence exhibits enhanced thermal stability. © 2019 Society of Chemical Industry 相似文献
8.
9.
10.