全文获取类型
收费全文 | 335615篇 |
免费 | 31429篇 |
国内免费 | 21602篇 |
专业分类
电工技术 | 50882篇 |
技术理论 | 9篇 |
综合类 | 35859篇 |
化学工业 | 26374篇 |
金属工艺 | 14547篇 |
机械仪表 | 27268篇 |
建筑科学 | 33431篇 |
矿业工程 | 13772篇 |
能源动力 | 10125篇 |
轻工业 | 12245篇 |
水利工程 | 12428篇 |
石油天然气 | 12042篇 |
武器工业 | 4716篇 |
无线电 | 26478篇 |
一般工业技术 | 27260篇 |
冶金工业 | 13629篇 |
原子能技术 | 3907篇 |
自动化技术 | 63674篇 |
出版年
2024年 | 861篇 |
2023年 | 3711篇 |
2022年 | 6612篇 |
2021年 | 8107篇 |
2020年 | 9397篇 |
2019年 | 7762篇 |
2018年 | 7171篇 |
2017年 | 9994篇 |
2016年 | 11122篇 |
2015年 | 12065篇 |
2014年 | 21368篇 |
2013年 | 19264篇 |
2012年 | 25203篇 |
2011年 | 26418篇 |
2010年 | 20185篇 |
2009年 | 20935篇 |
2008年 | 20046篇 |
2007年 | 24823篇 |
2006年 | 22018篇 |
2005年 | 18914篇 |
2004年 | 15603篇 |
2003年 | 13539篇 |
2002年 | 11003篇 |
2001年 | 9238篇 |
2000年 | 8073篇 |
1999年 | 6682篇 |
1998年 | 5164篇 |
1997年 | 4529篇 |
1996年 | 3705篇 |
1995年 | 3149篇 |
1994年 | 2651篇 |
1993年 | 1926篇 |
1992年 | 1635篇 |
1991年 | 1181篇 |
1990年 | 935篇 |
1989年 | 887篇 |
1988年 | 629篇 |
1987年 | 380篇 |
1986年 | 288篇 |
1985年 | 192篇 |
1984年 | 250篇 |
1983年 | 166篇 |
1982年 | 169篇 |
1981年 | 140篇 |
1980年 | 87篇 |
1979年 | 102篇 |
1978年 | 65篇 |
1977年 | 62篇 |
1975年 | 26篇 |
1959年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
81.
随着对管道安全问题和降本增效理念的逐步重视,管道清管操作已成为全世界油气管道运行中必不可少的作业规程,清管器的运行速度是需要重点控制的参数之一,当其处于合理区间内时(原油管道1~5m/s,天然气管道2~7m/s),清管效果最佳。本文基于对管道清管数学模型的研究,首先论述了不同的被动控制方法,认为该方法较为灵活,应用广泛,对不同入口条件下清管器速度的准确计算是能否控制清管器速度处于合理区间的关键;然后对不同的主动控制方法进行了研究,研究表明:射流清管器速度控制的核心是旁通率的优选,其依赖于压降系数、皮碗与管壁间摩擦力的准确计算,建立简便可靠的摩擦力工程计算模型将有助于射流清管技术应用的进一步推广;最终本文对清管器智能调速技术进行综述和展望,指出发展稳定可靠的国产智能调速技术是未来重点研究方向。 相似文献
82.
弹药自动装填系统的研究已经成为火炮武器平台中机械系统设计的关键和难点,基于一种两自由度弹药提升装置,并根据该装置的工作原理构造数学模型,搭建实验平台,建立PID控制回路,同时创建该模型的虚拟样机模型,使用动力学仿真软件Recurdyn和Matlab/Simulink进行联合仿真,并通过实验与仿真的数据进行对比,验证该装置的可行性和所采用控制的有效性。 相似文献
83.
为优化液相法一步制备磷酸铁锂(LiFePO4)技术,以七水合硫酸亚铁、磷酸二氢铵、一水合氢氧化锂为原料,通过添加十二烷基苯磺酸钠(SDBS)作为表面活性剂,采用液相水热法合成技术,一步合成了LiFePO4正极材料。研究了水热法一步合成技术对LiFePO4材料的组成、结构、形貌、粒度等的影响,通过电感耦合等离子体发射光谱仪(ICP-OES)、X射线衍射仪(XRD)、扫描电镜(SEM)、粒度分析仪等对材料进行了表征分析,并测试了材料的电化学性能。研究结果表明,合成得到的LiFePO4材料为微米级球形颗粒形貌的正交晶系非化学计量比的Li1.02Fe0.994PO4材料。电化学性能测试结果表明,在0.1C倍率下首次充、放电比容量分别为162.0、159.9 mA·h/g,库伦效率达到98.7%、倍率性能(以1C/0.1C保持率计)为92.3%,0.1C倍率循环100次容量保持率为96.4%,展现出良好的电化学性能。 相似文献
84.
The load applied to a machine tool feed drive changes during the machining process as material is removed. This load change alters the Coulomb friction of the feed drive. Because Coulomb friction accounts for a large part of the total friction the friction compensation control accuracy of the feed drives is limited if this nonlinear change in the applied load is not considered. This paper presents a new friction compensation method that estimates the machine tool load in real time and considers its effect on friction characteristics. A friction observer based on a Kalman filter with load estimation is proposed for friction compensation control considering the applied load change. A specially designed feed drive testbed that enables the applied load to be modified easily was constructed for experimental verification. Control performance and friction estimation accuracy are demonstrated experimentally using the testbed. 相似文献
85.
Coupled large eddy simulation and the discrete element method are applied to study turbulent particle–laden flows, including particle dispersion and agglomeration, in a channel. The particle–particle interaction model is based on the Hertz–Mindlin approach with Johnson–Kendall–Roberts cohesion to allow the simulation of van der Waals forces in a dry air flow. The influence of different particle surface energies, and the impact of fluid turbulence, on agglomeration behaviour are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with a positive relationship observed between the two. Particle agglomeration is found to be enhanced in two separate regions within the channel. First, in the near-wall region due to the high particle concentration there driven by turbophoresis, and secondly in the buffer region where the high turbulence intensity enhances particle–particle interactions. 相似文献
86.
The main purpose of this paper is to survey some recent progresses on control theory for stochastic distributed parameter systems, i.e., systems governed by stochastic differential equations in infinite dimensions, typically by stochastic partial differential equations. We will explain the new phenomenon and difficulties in the study of controllability and optimal control problems for one dimensional stochastic parabolic equations and stochastic hyperbolic equations. In particular, we shall see that both the formulation of corresponding stochastic control problems and the tools to solve them may differ considerably from their deterministic/finite-dimensional counterparts. More importantly, one has to develop new tools, say, the stochastic transposition method introduced in our previous works, to solve some problems in this field. 相似文献
87.
《Journal of the European Ceramic Society》2020,40(13):4655-4663
As a figure-of-merit, the rising ratio of crack propagation resistance to fracture initiation resistance indicates a reduction of the brittleness and enhances the thermal shock resistance of ordinary refractory ceramics. The significant nonlinear fracture behaviour is related to the development of a fracture process zone (FPZ). The universal dimensionless load–displacement diagram method is applied as a promising graphical method for the determination of R-curves for magnesia refractories showing different brittleness. By applying digital image correlation (DIC) together with the graphical method, the problems arisen with accurate determination of the fracture initiation resistance and the crack length are overcome. Meanwhile, the R-curve is subdivided with respect to the fracture processes, viz the fracture initiation, the development of FPZ and the onset of traction free macro-crack. With the simultaneous crack lengths evaluated from DIC, the contribution of each fracture process to the crack propagation resistance at certain loading stage is quantitatively presented. 相似文献
88.
In this paper, an adaptive control approach is designed for compensating the faults in the actuators of chaotic systems and maintaining the acceptable system stability. We propose a state‐feedback model reference adaptive control scheme for unknown chaotic multi‐input systems. Only the dimensions of the chaotic systems are required to be known. Based on Lyapunov stability theory, new adaptive control laws are synthesized to accommodate actuator failures and system nonlinearities. An illustrative example is studied. The simulation results show the effectiveness of the design method. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
89.
The intermittent wind power in isolated hybrid distributed generation (IHDG) may cause serious problems associated with frequency (f) and power (P) fluctuation. Energy storage devices such as battery, super capacitor, and superconducting magnetic energy storage (SMES) may be used to reduce these fluctuations associated with f and P. This paper presents a study of IHDG power system for improving both f and P deviation profiles with the help of SMES. The studied IHDG power system is consisted of wind turbine generator and diesel engine generator. Both f and P control problems of the studied power system model are addressed in presence or absence of SMES. Fuzzy logic based proportional–integral–derivative (PID) controller with SMES is used for the purpose of minimization of f and P deviations. The different tunable parameters of the PID controller and those of the SMES are tuned by a novel quasi-oppositional harmony search algorithm. Performance study of the IHDG power system model is carried out under different perturbation conditions. The results demonstrate minimum f and P deviations may be achieved by using the proposed fuzzy logic based PID controller along with SMES. 相似文献
90.