全文获取类型
收费全文 | 45922篇 |
免费 | 7161篇 |
国内免费 | 5011篇 |
专业分类
电工技术 | 5047篇 |
技术理论 | 1篇 |
综合类 | 6287篇 |
化学工业 | 3313篇 |
金属工艺 | 1885篇 |
机械仪表 | 4864篇 |
建筑科学 | 5434篇 |
矿业工程 | 1780篇 |
能源动力 | 1377篇 |
轻工业 | 898篇 |
水利工程 | 1763篇 |
石油天然气 | 1497篇 |
武器工业 | 1064篇 |
无线电 | 3902篇 |
一般工业技术 | 5171篇 |
冶金工业 | 1058篇 |
原子能技术 | 215篇 |
自动化技术 | 12538篇 |
出版年
2024年 | 127篇 |
2023年 | 805篇 |
2022年 | 1411篇 |
2021年 | 1565篇 |
2020年 | 1752篇 |
2019年 | 1446篇 |
2018年 | 1468篇 |
2017年 | 1753篇 |
2016年 | 2110篇 |
2015年 | 2166篇 |
2014年 | 2952篇 |
2013年 | 2974篇 |
2012年 | 3808篇 |
2011年 | 3740篇 |
2010年 | 2962篇 |
2009年 | 2957篇 |
2008年 | 2922篇 |
2007年 | 3492篇 |
2006年 | 3003篇 |
2005年 | 2523篇 |
2004年 | 2037篇 |
2003年 | 1681篇 |
2002年 | 1396篇 |
2001年 | 1240篇 |
2000年 | 1114篇 |
1999年 | 831篇 |
1998年 | 678篇 |
1997年 | 588篇 |
1996年 | 479篇 |
1995年 | 438篇 |
1994年 | 366篇 |
1993年 | 270篇 |
1992年 | 213篇 |
1991年 | 177篇 |
1990年 | 148篇 |
1989年 | 147篇 |
1988年 | 90篇 |
1987年 | 46篇 |
1986年 | 28篇 |
1985年 | 28篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
51.
52.
Benedetto Rocchio Claudio Chicchiero Maria Vittoria Salvetti Stefania Zanforlin 《风能》2020,23(4):915-938
The present study is focused on modeling of dynamic stall behavior of a pitching airfoil. The deep stall regime is in particular considered. A model is proposed, which has a low implementation and computational complexity but yet is able to deal with different types of dynamic stall conditions, including those characterized by multiple vortex shedding at the airfoil leading edge. The proposed model is appraised against an extensive data set of experimental (α,CL) curves for NACA0012. The results of an existing widely used model, having comparable complexity, are also shown for comparison. The proposed model is able to well reproduce not only the classic curves of deep dynamic stall but also the curves characterized by lift oscillations at high angles of attack due to the shedding of multiple vortices. Furthermore, the model appears to be robust to variations of its parameters from the optimal values and of the airfoil geometry. Finally, the model is successfully implemented in a commercial CFD software and applied to the simulation of a vertical axis wind turbine within the actuator cylinder approach. The accuracy of the prediction of the turbine power coefficient in the whole rotation cycle is very good for the optimal working condition of the turbine, for which the model parameters were calibrated. Fairly good accuracy is also obtained in significantly different working conditions without any further calibration. 相似文献
53.
This paper deals with numerical modeling of the hydraulic blade pitch actuator and its effect on the dynamic responses of a floating spar‐type wind turbine under valve fault conditions. A spar‐type floating wind turbine concept is modeled and simulated using an aero‐hydro‐servo‐elastic simulation tool (Simo‐Riflex [SR]). Because the blade pitch system has the highest failure rate, a numerical model of the hydraulic blade pitch actuator with/without valve faults is developed and linked to SR to study the effects of faults on global responses of the spar‐type floating wind turbine for different faults, fault magnitudes, and environmental conditions. The consequence of valve faults in the pitch actuator is that the blade cannot be pitched to the desired angle, so there may be a delay in the response due to excessive friction and the wrong voltage, or slit lock may cause runaway blade pitch. A short circuit may cause the blade to get stuck at a particular pitch angle. These faults contribute to rotor imbalance, which result in different effects on the turbine structure and the platform motions. The proposed method for combining global and hydraulic actuator models is demonstrated in case studies with stochastic wind and wave conditions and different types of valve faults. 相似文献
54.
55.
56.
长周期扰动应力下盘区柱内巷道稳定及盘区柱整体稳定是大规模开采的关注重点。采用数值模拟方法,构建了大规模、多中段、长周期强烈开采扰动下的数值模型,建立了锚杆支护的拉伸破断、剪切破断数值力学模型,研究了不同水平、不同阶段回采过程中盘区柱内巷道锚杆支护的受力特性和盘区柱围岩的应力和塑性区发展特征。研究结果表明:不同开采阶段不同开采水平的锚杆轴力和巷道顶板变形响应明显,锚杆剪力由于变形监测部位的限制响应程度甚微,盘区柱内巷道稳定性好。盘区柱内巷道围岩偏应力场与塑性区动态演化仅在前两个中段开采时反应强烈,大规模开采结束时盘区柱仍然能够保持正常稳定。分析方法及分析结果能够对盘区柱内巷道稳定及盘区柱整体稳定做出提前预判,为盘区柱的正常使用提供安全保障。 相似文献
57.
煤层开采打破了上覆岩层原有的平衡,必然引起岩层的移动、破断,导致应力场和裂隙场的改变,工作面出现矿压显现。上覆岩层的岩性和组合结构对工作面开采覆岩损害特征分布影响显著,一般岩性越坚硬,上覆岩层应力集中程度越高,采动裂隙越发育,矿压显现也越明显;坚硬岩层尤其是关键层对覆岩的破断运动起控制作用,覆岩破断发展到一定层位后软弱岩层往往是抑制覆岩破断进一步向上发展的关键。当工作面上覆岩层同时存在远近场关键层时,近场关键层的周期性破断引起裂隙带范围内岩层的运动和工作面周期来压;而远场关键层的周期性破断导致地表裂缝或台阶下沉,工作面压力急剧上升,有时甚至导致煤矿动压灾害,尤其是远近场关键层同步破断时动力现象更明显。通过地面钻孔使远场关键层提前破断是防止此类动力灾害的关键。 相似文献
58.
采用X射线衍射仪、金相显微镜、分离式霍普金森杆和扫描电镜等手段研究了Ti-20Zr-20Al钛合金在动态压缩条件下的微观结构、力学性能和断裂机制。结果表明,Ti-20Zr-20Al铸态合金由Zr基体相和TiAl/Ti3Al针状相组成; 随着应变率增加,合金的抗压强度增加,失效应变显著增加; Ti-20Zr-20Al合金的断裂机制为解理断裂; 随着应变率增加,试验压缩断裂后碎片总数增大,平均粒径减小。采用DID模型模拟的材料碎片尺度与实验结果比较吻合,Grady模型与实验结果的偏差较大。 相似文献
59.
《中国有色金属学会会刊》2020,30(3):710-726
Cylindrical samples of Ni-based GH4037 alloy were compressed at solid temperatures (1200, 1250 and 1300 °C) and semi-solid temperatures (1340, 1350, 1360, 1370 and 1380 °C) with different strain rates of 0.01, 0.1 and 1 s−1. High temperature deformation behavior and microstructure evolution of GH4037 alloy were investigated. The results indicated that flow stress decreased rapidly at semi-solid temperatures compared to that at solid temperatures. Besides, the flow stress continued to increase after reaching the initial peak stress at semi-solid temperatures when the strain rate was 1 s−1. With increasing the deformation temperature, the size of initial solid grains and recrystallized grains increased. At semi-solid temperatures, the grains were equiaxed, and liquid phase existed at the grain boundaries and inside the grains. Discontinuous dynamic recrystallization (DDRX) characterized by grain boundary bulging was the main nucleation mechanism for GH4037 alloy. 相似文献
60.
Kai Liu Saif R. Kazi Lorenz T. Biegler Bingjian Zhang Qinglin Chen 《American Institute of Chemical Engineers》2020,66(5):e16908
The increasing penetration of unconventional gas and liquefied natural gas poses an operational challenge on existing regional gas networks for gas quality problems. A new dynamic model for natural gas pipeline network with multiple supplies is presented with a special emphasis on gas interchangeability control. Wobbe index serves as gas interchangeability indicator and is calculated by equations derived from rigorous composition-based partial differential equations. Disjunctive formulation is applied to represent different modes of gas blending due to gas reversal, and the disjunctive model is then reformulated as a nonsmooth model with min/max and absolute value functions, which is solved by a gradient-based nonlinear program solver after smooth approximation. Moreover, a heuristic algorithm is proposed to tune the penalty parameters in order to focus on different penalty terms while keeping the model well-conditioned. The developed model and strategy are first tested with a small pipeline network model and then extended to a large model. The results show that the model can effectively manage gas interchangeability issues in pipeline networks within reasonable CPU time. 相似文献