全文获取类型
收费全文 | 367618篇 |
免费 | 11784篇 |
国内免费 | 4889篇 |
专业分类
电工技术 | 10886篇 |
技术理论 | 11篇 |
综合类 | 6865篇 |
化学工业 | 55097篇 |
金属工艺 | 15856篇 |
机械仪表 | 15093篇 |
建筑科学 | 14602篇 |
矿业工程 | 4105篇 |
能源动力 | 9440篇 |
轻工业 | 29218篇 |
水利工程 | 4243篇 |
石油天然气 | 10022篇 |
武器工业 | 759篇 |
无线电 | 48220篇 |
一般工业技术 | 63713篇 |
冶金工业 | 52023篇 |
原子能技术 | 6632篇 |
自动化技术 | 37506篇 |
出版年
2022年 | 3365篇 |
2021年 | 5813篇 |
2020年 | 4473篇 |
2019年 | 4525篇 |
2018年 | 6353篇 |
2017年 | 6815篇 |
2016年 | 6574篇 |
2015年 | 6103篇 |
2014年 | 8875篇 |
2013年 | 17427篇 |
2012年 | 13054篇 |
2011年 | 15974篇 |
2010年 | 13159篇 |
2009年 | 13919篇 |
2008年 | 14743篇 |
2007年 | 14274篇 |
2006年 | 13749篇 |
2005年 | 12476篇 |
2004年 | 10503篇 |
2003年 | 9866篇 |
2002年 | 9171篇 |
2001年 | 9170篇 |
2000年 | 8990篇 |
1999年 | 9574篇 |
1998年 | 17050篇 |
1997年 | 12734篇 |
1996年 | 10315篇 |
1995年 | 8281篇 |
1994年 | 7204篇 |
1993年 | 6763篇 |
1992年 | 5481篇 |
1991年 | 4917篇 |
1990年 | 4619篇 |
1989年 | 4252篇 |
1988年 | 3989篇 |
1987年 | 3445篇 |
1986年 | 3252篇 |
1985年 | 3769篇 |
1984年 | 3472篇 |
1983年 | 3102篇 |
1982年 | 2933篇 |
1981年 | 3002篇 |
1980年 | 2778篇 |
1979年 | 2655篇 |
1978年 | 2498篇 |
1977年 | 2931篇 |
1976年 | 3559篇 |
1975年 | 2309篇 |
1974年 | 2304篇 |
1973年 | 2294篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
Automation and Remote Control - We consider multicriteria minimax optimization problems with criteria in the form of the maxima of functionals given by the induced norms of linear operators taking... 相似文献
22.
氢脆具有很强的微观组织敏感性,威胁着各类高强结构材料的安全服役.采用激光-电弧复合焊工艺对BS960E型高强钢进行焊接,并对接头在原位电化学充氢的条件下进行慢应变速率(10-5s-1)拉伸试验,结合微观组织和断裂特征进行分析并对接头的氢脆行为进行研究.结果 表明,焊接热循环所形成的富马氏体中的细晶区可以使接头表现出一定的氢脆敏感性,马氏体较大的氢扩散系数和较低的氢溶解度以及氢在晶界上的快速扩散是引起接头对氢脆敏感的主要原因,通过控制焊接工艺参数可抑制焊接热循环所引起的马氏体转变量,能够降低BS960E型高强钢激光-电弧复合焊接头的氢脆敏感性. 相似文献
23.
William M. Pitts Martin Werrel Marco Fernandez Mary A. Long Evan A. Eisenberg James Filliben Cory D. Runyon 《火与材料》2021,45(1):127-154
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF. 相似文献
24.
Zhuchkov V. I. Nazansky S. L. Frolkova A. K. Ganina K. D. 《Theoretical Foundations of Chemical Engineering》2021,55(4):786-791
Theoretical Foundations of Chemical Engineering - Using gas–liquid chromatography, the activity coefficients upon the infinite dilution of the components of the reaction mixture for obtaining... 相似文献
25.
Electric nanogenerators that directly convert the energy of moving drops into electrical signals require hydrophobic substrates with a high density of static electric charge that is stable in “harsh environments” created by continued exposure to potentially saline water. The recently proposed charge-trapping electric generators (CTEGs) that rely on stacked inorganic oxide–fluoropolymer (FP) composite electrets charged by homogeneous electrowetting-assisted charge injection (h-EWCI) seem to solve both problems, yet the reasons for this success have remained elusive. Here, systematic measurements at variable oxide and FP thickness, charging voltage, and charging time and thermal annealing up to 230 °C are reported, leading to a consistent model of the charging process. It is found to be controlled by an energy barrier at the water-FP interface, followed by trapping at the FP-oxide interface. Protection by the FP layer prevents charge densities up to −1.7 mC m−2 from degrading and the dielectric strength of SiO2 enables charge decay times up to 48 h at 230 °C, suggesting lifetimes against thermally activated discharging of thousands of years at room temperature. Combining high dielectric strength oxides and weaker FP top coatings with electrically controlled charging provides a new paradigm for developing ultrastable electrets for applications in energy harvesting and beyond. 相似文献
26.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms. 相似文献
27.
28.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
29.
30.
Zhang Qi Wang Yujing Zhang Xueling Song Jun Li Yinlei Wu Xuehong Yuan Kunjie 《Journal of Materials Science》2022,57(14):7208-7224
Journal of Materials Science - Form-stable composite phase change materials (C-PCMs) prepared by microencapsulation method and porous matrix adsorption method need for compression molding after... 相似文献