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991.
992.
993.
Zhenlu Cui Xiaoming Zeng & Jianbing Su 《advances in applied mathematics and mechanics.》2014,6(1):75-86
A continuum hydrodynamic model has been used to characterize flowing
active nematics. The behavior of such a system subjected to a
weak steady shear is analyzed. We explore the director structures and
flow behaviors of the system in flow-aligning and flow tumbling regimes.
Combining asymptotic analysis and numerical simulations, we extend previous
studies to give a complete characterization of the steady states for both contractile and
extensile particles in flow-aligning and flow-tumbling regimes. Another
key prediction of this work is the role of the system size on the steady
states of an active nematic system: if the system size is small, the velocity
and the director angle files for both flow-tumbling contractile and extensile
systems are similar to those of passive nematics; if the system is big, the
velocity and the director angle files for flow-aligning contractile systems
and tumbling extensile systems are akin to sheared passive cholesterics while
they are oscillatory for flow-aligning extensile and tumbling contractile systems. 相似文献
994.
I. I. Potapov 《Journal of Applied Mechanics and Technical Physics》2009,50(3):470-477
The problem of determining the specific mass flow of sediment entrained by a liquid flow passing above the sand bottom is
studied. The boundary-value problem for a two-phase mixture of the liquid and solid particles in the active bottom layer is
solved, and a general formula for determining the specific mass flow of sediment is derived. Constraints imposed on the rheological
model of a moving mixture, which allow the phenomenological parameter (concentration of particles in the active layer of the
mixture) to be eliminated from the model, are found. Within the framework of the proposed rheological model, the equation
of riverbed deformations in the case of a sand bottom is obtained.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 131–139, May–June, 2009. 相似文献
995.
An optimal control method for seismic-excited building structures with multiple time delays is investigated in this paper. The system state equation with multiple time delays is discretized and transformed into a standard discrete form without any explicit time delay by a particular augmenting for state variables. A time-delay controller is then designed based on this standard equation using the discrete optimal control method. Effectiveness of the proposed controller is demonstrated by numerical simulations. Simulation results indicate that a very small time delay may result in the instability of the control system if it is not compensated in the control design. Time delay may be compensated effectively by the proposed controller, in the mean time, an effective control may be obtained. The proposed controller is valid for both small and large time delays. 相似文献
996.
Nonlinear consensus protocols for dynamic directed networks of
multi-agent systems with fixed and switching topologies are
investigated separately in this paper. Based on the centre manifold
reduction technique, nonlinear consensus protocols are presented. We
prove that a group of agents can reach a β-consensus, the
value of which is the group decision value varying from the minimum and
the maximum values of the initial states of the agents. Moreover, we
derive the conditions to guarantee that all the agents reach a
β--consensus on a desired group decision value. Finally, a
simulation study concerning the vertical alignment manoeuvere of a
team of unmanned air vehicles is performed. Simulation results show
that the nonlinear consensus protocols proposed are more effective than
the linear protocols for the formation control of the agents and
they are an improvement over existing protocols. 相似文献
997.
带有末端集中质量的双连杆柔性机械臂主动控制 总被引:1,自引:0,他引:1
对带有末端集中质量的双连杆柔性机械臂的主动控制进行了研究,给出系统的动力学方程,采用非线性解耦反馈控制方法分别得出系统大范围运动方程和柔性臂的动力学方程,采用机械臂逆动力学方法和LQR方法分别设计大范围运动控制律和压电作动器控制律.仿真结果显示,本文控制方法能够有效地进行机械臂的轨迹跟踪,柔性臂的弹性振动可以得到有效抑制. 相似文献
998.
Recently, transition metal chalcogenides and phosphides have been increasingly reported as efficient and stable oxygen evolution reaction (OER) catalysts in alkaline medium, despite the fact that they are thermodynamically unstable under highly oxidative potentials. Here the active forms of these materials are elucidated by synthesizing a hybrid catalyst, which has a metal chalcogenide in the form of CoSe2 and metal phosphide in the form of CoP—CoSe2|CoP. Both CoSe2 and CoP in the as‐prepared catalyst are completely transformed into their respective oxyhydroxides and hydroxides, which are, in fact, the true OER‐active species in alkaline medium and not the selenide and phosphide themselves. The derived oxides from the hybrid catalyst deliver an excellent OER activity by reaching a current density of 10 mA cm−2 at a low overpotential of 240 mV (vs reversible hydrogen electrode (RHE)) and a Tafel slope of 46.6 mV dec−1. The stability of the derived oxyhydroxide/hydroxide catalyst shows no appreciable deactivation during 120 h of continuous electrolysis, displaying an extraordinary operational stability. 相似文献
999.
本文主要研究阴极脱氯协同阳极(多孔Ti/BDD 电极)电催化氧化对于对氯苯酚的电化学降解过程. 在有无阳离子交换膜电解槽体系下电化学降解对氯苯酚的实验结果表明,对氯苯酚的矿化主要在阳极区进行;无隔膜电解槽体系下,对氯苯酚在阴极还原形成的氯离子迁移到阳极,在阳极表面进一步生成了具有强催化氧化作用的活
性氯,与阳极产生的羟基自由基协同降解对氯苯酚;在阳离子交换膜电解槽体系下,阴极产生的氯离子难以通过阳离子膜迁移至阳极区,无隔膜电解槽呈现出更好的降解效率. 结合高效液相色谱技术确定阳极室的中间产物为对苯二酚、邻苯二酚、对苯醌和苯酚等,阴极室的主要产物是苯酚,并根据中间产物提出了对氯苯酚的降解路径. 相似文献
1000.
氧化还原液流电池(简称液流电池)是一种正在积极研制开发的新型大容量电化学储能装置,其活性物质是流动的电解质溶液,最显著的特点是规模化蓄电. 在广泛利用可再生能源的呼声高涨形势下,可以预见液流电池将迎来一个快速发展的时期. 氧化还原活性物质是液流电池能源转化的载体,也是液流电池中最核心的部分.传统液流电池利用无机材料作为活性物质,然而,无机材料成本高、毒性、资源有限、形成枝晶和电化学活性低等缺点限制了液流电池的大规模应用. 有机活性物质由于具有成本低、“绿色”、资源丰富、分子能级易于调节和电化学反应快等优点,引起了国内外的广泛关注. 近年来,有机液流电池的性能得到快速提升,一系列有机活性物质相继被开发出来. 本文梳理了近年来有机液流电池的研究进展. 首先简要介绍了液流电池的应用领域和技术特点;然后根据电解液种类的不同,详细讨论了有机活性物质在水系和非水系液流电池的应用情况;最后展望了有机液流电池走向实际应用所面临的挑战和潜在研究方向. 相似文献