全文获取类型
收费全文 | 1810953篇 |
免费 | 50453篇 |
国内免费 | 18522篇 |
学科分类
工业技术 | 1879928篇 |
出版年
2022年 | 13119篇 |
2021年 | 25862篇 |
2020年 | 20890篇 |
2019年 | 21781篇 |
2018年 | 25464篇 |
2017年 | 26269篇 |
2016年 | 30377篇 |
2015年 | 29032篇 |
2014年 | 43720篇 |
2013年 | 105422篇 |
2012年 | 55489篇 |
2011年 | 70650篇 |
2010年 | 61719篇 |
2009年 | 68971篇 |
2008年 | 62642篇 |
2007年 | 59448篇 |
2006年 | 62097篇 |
2005年 | 55138篇 |
2004年 | 51238篇 |
2003年 | 49592篇 |
2002年 | 45624篇 |
2001年 | 42137篇 |
2000年 | 40418篇 |
1999年 | 42139篇 |
1998年 | 57652篇 |
1997年 | 47434篇 |
1996年 | 41449篇 |
1995年 | 36606篇 |
1994年 | 33470篇 |
1993年 | 32041篇 |
1992年 | 27957篇 |
1991年 | 24781篇 |
1990年 | 24834篇 |
1989年 | 23478篇 |
1988年 | 21835篇 |
1987年 | 19804篇 |
1986年 | 19160篇 |
1985年 | 22234篇 |
1984年 | 22218篇 |
1983年 | 20092篇 |
1982年 | 19157篇 |
1981年 | 19225篇 |
1980年 | 17855篇 |
1979年 | 18259篇 |
1978年 | 17541篇 |
1977年 | 17427篇 |
1976年 | 18684篇 |
1975年 | 15780篇 |
1974年 | 15279篇 |
1973年 | 15398篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
991.
Sanjeev A. Sahu 《热应力杂志》2020,43(4):489-502
AbstractPresent study deals with the scattering of a plane wave through an orthotropic thermoelastic slab sandwiched between two elastic half-spaces. Unlike the classical theory of thermoelasticity, we have employed non-classical thermoelastic theories (LS-theory and GL-theory) to analyze the scattering of plane waves. The amplitude ratios for different waves have been computed numerically for the considered generalized theories of thermoelasticity. The effect of the slab thickness on the amplitude ratios has been shown graphically. Moreover, the amplitude ratios of different waves (i.e., reflected, transmitted, forward and backward waves) are compared for different values of slab thickness under both the LS-theory and GL-theory. 相似文献
992.
993.
Yuanming Wu Xiaohua Chen Li Wang Lunjie Wu Lu Lin Wenwu Ding Zhenming Che Jianfeng Wang Jianzhou Li Yi Liu Weifeng Sun 《International Journal of Food Science & Technology》2020,55(4):1825-1832
Preparation of flavour peptides with microorganisms is an attractive choice for its large-scale production. However, beefy meaty peptide (BMP), as a research hotspot in the field of umami peptide, has been studied in few microorganisms, and furthermore, the safe preparation of BMP has not yet been reported. In this study, multi-copy BMP (8BMP) was successfully expressed and produced in the ‘generally recognized as safe’ Bacillus subtilis (B. subtilis). Firstly, 8BMP with the potentially intense umami was screened out based on molecular docking analysis. Then, it was successfully expressed in the B. subtilis 168 and verified through sensory evaluation. Finally, the scaling capacity of 8BMP was evaluated in a 5-L fermenter, with the highest yield (0.84 g L−1) 6.4 times than that of shake flask, which is conductive for industrial production of BMP and other food peptides. 相似文献
994.
995.
996.
997.
As the world moves toward more green and efficient means of modes of transport, electric vehicles are the most suitable and ideal choice to fulfill this requirement. Rapid developments in the field of battery technology are the main reason for their progress, but thermal management in such systems has been an area of concern for a long time. The work undertaken is to design and develop a battery management system (BMS) with a specific focus on the thermal behavior of the battery pack with varying vehicle loads as well as environmental conditions. To design an efficient BMS, one needs to model the battery behavior covering the thermal as well as electrical aspects of the battery. Apart from the battery model, a mathematical model of the electrical vehicle to mimic the various road load conditions for battery also needs to be modeled. Depending on the need for cooling based on battery behavior, the cooling circuit is modeled for the battery pack used. The entire study has been carried out using Dymola, a mathematical modeling software. 相似文献
998.
Mehdi Noorbakhsh Mohsen Pourfallah Seyed S. M. Ajarostaghi Mohammad Zaboli 《亚洲传热研究》2020,49(8):4678-4703
Heat exchangers are extensively used in various industries. In this study, the impact of geometric and flow parameters on the performance of a shell and double helical coil heat exchanger is studied numerically. The investigated geometric parameters include external coil pitch, internal coil pitch, internal coil diameter, and coil diameter. The influences of considered geometrical parameters are analyzed on the output temperature of the hot and cold fluid, convective heat transfer coefficient, pressure drop, and average Nusselt number. Water is considered as working fluid in both shell and tube. As an innovation, double helical coils are used instead of one in the heat exchanger. To compare the obtained results accurately, in each section, the heat transfer area (coil outer surface) is kept constant in all models. The results show that the geometrical parameters of double helical coils significantly affect the heat transfer rate. 相似文献
999.
叶片是风力机最重要的组成部分,在不同的风能资源情况下,翼型的选择对垂直轴风力机气动特性有着重要的影响。文章分别以NACA0018翼型(对称翼型)和NACA4418翼型(非对称翼型)建立3叶片H型垂直轴风力机二维仿真模型。应用数值模拟的研究方法,从功率系数、单个叶片切向力系数等方面比较两种风力机模型在不同叶尖速比下的气动特性,并采用风洞实验数据验证了流场计算的准确性。CFD计算结果表明:在低叶尖速比下,NACA4418翼型风力机气动特性优于NACA0018翼型风力机,适用于低风速区域;在高叶尖速比下,NACA0018翼型风力机气动特性较好,适用于高风速地区。而且在高叶尖速比时,NACA0018翼型在上风区时,切向力系数平均值要高于NACA4418翼型,在下风区时,NACA418翼型切向力系数平均值高。该研究可为小型垂直轴风力机翼型的选择提供参考。 相似文献
1000.
M. Sreedhar Babu Velpula V. Ramana G. Ravisankar C. S. K. Raju M. N. Bashir Sabir A. Shehzad 《亚洲传热研究》2020,49(8):4226-4245
In this investigation, the flow of an unsteady mixed convection boundary layer viscous nanofluid on a stretchable sheet is considered. The flow examination is affected by a magnetic field. The reason for the examination exhibited is to create models for nanomaterials that incorporate the Brownian movement and thermophoresis phenomena. The created nonlinear standard differential condition is illuminated numerically utilizing the Runge-Kutta-Gill technique and the start program. The different factors of speed, temperature, and concentration are reported and discussed. The examination shows that the speed, temperature, and concentration are lower in contrast with the consistent stream on account of an assisting flow, whereas the opposite situation is noticed in the opposing flow case. The effects of Brownian movement and thermophoresis in the concentration case are totally different. 相似文献