全文获取类型
收费全文 | 7004篇 |
免费 | 411篇 |
国内免费 | 207篇 |
专业分类
电工技术 | 164篇 |
综合类 | 456篇 |
化学工业 | 1020篇 |
金属工艺 | 1565篇 |
机械仪表 | 589篇 |
建筑科学 | 825篇 |
矿业工程 | 133篇 |
能源动力 | 339篇 |
轻工业 | 236篇 |
水利工程 | 83篇 |
石油天然气 | 88篇 |
武器工业 | 26篇 |
无线电 | 233篇 |
一般工业技术 | 872篇 |
冶金工业 | 784篇 |
原子能技术 | 60篇 |
自动化技术 | 149篇 |
出版年
2024年 | 6篇 |
2023年 | 60篇 |
2022年 | 105篇 |
2021年 | 174篇 |
2020年 | 164篇 |
2019年 | 107篇 |
2018年 | 97篇 |
2017年 | 162篇 |
2016年 | 189篇 |
2015年 | 180篇 |
2014年 | 336篇 |
2013年 | 351篇 |
2012年 | 405篇 |
2011年 | 533篇 |
2010年 | 396篇 |
2009年 | 438篇 |
2008年 | 378篇 |
2007年 | 472篇 |
2006年 | 519篇 |
2005年 | 439篇 |
2004年 | 359篇 |
2003年 | 324篇 |
2002年 | 290篇 |
2001年 | 224篇 |
2000年 | 188篇 |
1999年 | 146篇 |
1998年 | 126篇 |
1997年 | 100篇 |
1996年 | 82篇 |
1995年 | 66篇 |
1994年 | 64篇 |
1993年 | 41篇 |
1992年 | 31篇 |
1991年 | 20篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1975年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有7622条查询结果,搜索用时 15 毫秒
1.
针对车身三维模型中焊枪头与焊点附近的钣金件之间空间间隙检查过程复杂、检查结果不准确等问题,提出了焊枪头与钣金件空间间隙的自动检查方法。在特征识别算法和包围盒技术的基础上获得焊点特征、钣金件特征和螺母特征等分析要素;基于三维模型的投影算法和距离测量算法计算钣金件的拓扑面与虚拟焊枪之间的距离,与安全阈值比较,筛选出与焊枪发生干涉的危险平面、孔和螺母;对焊接空间不足的焊点进行标注并截图。利用二次开发环境所提供的函数库编程实现了上述算法,通过运行实例以及企业的实际使用,验证了自动检查系统的可行性。 相似文献
2.
High Temperature Oxidation and Tribological Behaviors of NiCrAl-Graphite Self-Lubricating Composites
Nickel-graphite self-lubricating composites are a promising candidate to be used in turbine constructions that are usually exposed to high temperature oxidation and wear.However,the high-temperature stability of graphite as well as the effect that the oxide scale will play on the following wear process are still yet in debate.In this work,oxidation behavior of a NiCrAl-graphite composite and the subsequent friction and wear performances were studied.Results indicate that graphite is stable in the composites after oxidation at T≤400 ℃ for 300 h,which contributes synergistically with the thin oxide film to self-lubrication.The friction coefficient is below 0.20 and the wear rate is ~1.43×10~(-5) mm~3 N~(-1) m~(-1).The composite has the highest friction coefficient and wear rate when it was suffered from the high temperature oxidation at 500 ℃.Once it was oxidized at 600 ℃,a glaze layer would develop during the subsequent sliding.It plays a positive role in improving tribological properties though in the absence of lubricant phase of graphite,with to be exactly the friction coefficient and wear rate reduced by 13% and 21%,respectively,in comparison with the case of oxidation at 500℃. 相似文献
3.
为探索干寒地区新型波形钢腹板组合箱梁桥的温度场分布特征和温度效应,弥补现行规范中缺乏其温度梯度模式定义的不足。本文以西北干寒地区某新型波形钢腹板组合箱梁桥为研究对象,基于现场温度观测数据,分析该新型组合结构在日照作用下的温度分布规律,并运用最小二乘法拟合提出其二维温度梯度模式;建立新型波形钢腹板组合箱梁全桥精细化有限元模型,并通过实测温度梯度函数计算该桥的温度响应;探析压型钢板对新型波形钢腹板组合箱梁温度应力的影响规律。研究结果表明:基于现场实测数据拟合的竖向分段多项式和横向指数函数组成的新型波形钢腹板组合箱梁二维温度梯度,与实测温度场计算值吻合良好,可为该地区类似工程温度荷载计算提供参考;日照温度作用下,新型波形钢腹板组合箱梁顶板与腹板交界面存在明显的温度梯度;翼缘板上缘、顶板-腹板交界面和各箱室中轴线处出现的最大横向拉应力分别为2.42 MPa、1.83 MPa和1.26 MPa,可能引起桥面板开裂,在设计中应给予重视;实测温度梯度下,闭口型压型钢板可使各箱室顶板中轴线上缘横向拉应力降低0.5 MPa以上,对桥面板抗裂有利,而开口型压型钢板可使各箱室翼缘板上缘横向拉应力提高15%~18%,对桥面板抗裂不利。 相似文献
4.
Francesca R. Lamastra Mehdi Chougan Emanuele Marotta Samuele Ciattini Seyed Hamidreza Ghaffar Stefano Caporali Francesco Vivio Giampiero Montesperelli Ugo Ianniruberto Mazen J. Al-Kheetan Alessandra Bianco 《Ceramics International》2021,47(14):20019-20031
The impact of graphite nanoplatelets (GNPs) on the physical and mechanical properties of cementitious nanocomposites was investigated. A market-available premixed mortar was modified with 0.01% by weight of cement of commercial GNPs characterized by two distinctively different aspect ratios.The rheological behavior of the GNP-modified fresh admixtures was thoroughly evaluated. Hardened cementitious nanocomposites were investigated in terms of density, microstructure (Scanning Electron Microscopy, SEM and micro–Computed Tomography, μ-CT), mechanical properties (three-point bending and compression tests), and physical properties (electrochemical impedance spectroscopy, EIS and thermal conductivity measurements). At 28 days, all GNP-modified mortars showed about 12% increased density. Mortars reinforced with high aspect ratio GNPs exhibited the highest compressive and flexural strength: about 14% and 4% improvements compared to control sample, respectively. Conversely, low aspect ratio GNPs led to cementitious nanocomposites characterized by 36% decreased electrical resistivity combined with 60% increased thermal conductivity with respect to the control sample. 相似文献
5.
《Journal of the European Ceramic Society》2021,41(13):6238-6247
Ni-based alloys are believed to be the most suitable brazing fillers for SiC ceramic application in a nuclear environment. However, graphite, which severely deteriorates the mechanical property of the joint, is inevitable when Ni reacts with SiC. In this paper, Different amounts of Zr powders are mixed with Inconel 625 powders to braze SiC at 1400 °C. When Zr addition reaches 40 wt%, the brazed seam confirms the absence of graphite. This research proves that Zr can avoid the graphite’s formation by suppressing Ni’s activity. The room-temperature shear strength of the joint with graphite’s absence is tested to be 81.97 MPa, which is almost three times higher than that of the joint with graphite. The interfacial reaction process and mechanism of the SiC joint are investigated and explained in this paper using thermodynamic calculations. 相似文献
6.
7.
8.
《International Journal of Hydrogen Energy》2022,47(6):3580-3586
Renewable electricity-powered hydrogen production is an attractive alternative to unsustainable industrial processes, but the large-scale implantation of such sustainable technology still requires efficient and noble-metal-free electrocatalysts for driving cathodic hydrogen evolution reaction (HER), especially under alkaline conditions. In this paper, CoP nanowire array was in-situ developed on porous graphite felt (CoP/GF) as a new 3D electrocatalyst in facilitating hydrogen evolution electrocatalysis. This CoP/GF presents outstanding HER activity, requiring a low overpotential of 130 mV to deliver a current density of 20 mA cm?2 as tested in 1.0 M KOH. Furthermore, this free-standing catalyst exhibits impressive long-term durability of up to 50 h under working conditions. 相似文献
9.
In this study, the optimal homotopy analysis (OHAM) technique has been examined to solve the laminar magnetohydrodynamic flow (MHD flow) on the upper-convected Maxwell fluid on an isothermal porous stretch surface. A study on the effects of parameters like the relaxation time, suction/injection velocity, as well as the magnetic number on velocity over a sheet was conducted and these results are compared to the corresponding previously available results. It was observed that the thickness of the boundary layer is lowered by enhancing , , and values. Opposing this, it was observed that large values increase the magnituIIde. It is found that OHAM is an efficient method capable of giving a greater degree of accuracy in numerical values of flow parameters even after fewer approximations. 相似文献
10.
Najiba Hasan Hamad 《亚洲传热研究》2022,51(5):3794-3814
Classical Fourier's theory is well-known in continuum physics and thermal sciences. However, the primary drawback of this law is that it contradicts the principle of causality. To explore the thermal relaxation time characteristic, Cattaneo–Christov's theory is adopted thermally. In this regard, the features of magnetohydrodynamic (MHD) mixed convective flows of Casson fluids over an impermeable irregular sheet are revealed numerically. In addition, the resulting system of partial differential equations is altered via practical transformations into nonlinear ordinary differential equations. An advanced numerical algorithm is developed in this respect to get higher approximations for temperature and velocity fields, as well as their corresponding wall gradients. For validating our numerical code, the current outcomes are compared with the available literature results. Moreover, it is revealed that the velocity field is more prominent in the suction flow situation as compared with the injection flow case. It is also found that the Casson fluid is hastened in the case of lower yield stress. Larger values of thermal relaxation parameters create a lessening trend in the temperature distribution and its related boundary layer breadth. 相似文献