全文获取类型
收费全文 | 299879篇 |
免费 | 28018篇 |
国内免费 | 18217篇 |
专业分类
电工技术 | 41215篇 |
技术理论 | 25篇 |
综合类 | 34148篇 |
化学工业 | 18538篇 |
金属工艺 | 14913篇 |
机械仪表 | 27167篇 |
建筑科学 | 24876篇 |
矿业工程 | 13917篇 |
能源动力 | 13394篇 |
轻工业 | 5923篇 |
水利工程 | 10062篇 |
石油天然气 | 11698篇 |
武器工业 | 6648篇 |
无线电 | 28179篇 |
一般工业技术 | 18630篇 |
冶金工业 | 9093篇 |
原子能技术 | 3597篇 |
自动化技术 | 64091篇 |
出版年
2024年 | 746篇 |
2023年 | 3052篇 |
2022年 | 5967篇 |
2021年 | 7525篇 |
2020年 | 8090篇 |
2019年 | 5902篇 |
2018年 | 5655篇 |
2017年 | 7867篇 |
2016年 | 9497篇 |
2015年 | 10898篇 |
2014年 | 19314篇 |
2013年 | 17100篇 |
2012年 | 23037篇 |
2011年 | 24588篇 |
2010年 | 18289篇 |
2009年 | 18336篇 |
2008年 | 18299篇 |
2007年 | 23201篇 |
2006年 | 20599篇 |
2005年 | 17987篇 |
2004年 | 14829篇 |
2003年 | 12961篇 |
2002年 | 10002篇 |
2001年 | 8328篇 |
2000年 | 6843篇 |
1999年 | 5517篇 |
1998年 | 4189篇 |
1997年 | 3403篇 |
1996年 | 3008篇 |
1995年 | 2508篇 |
1994年 | 2077篇 |
1993年 | 1396篇 |
1992年 | 1161篇 |
1991年 | 865篇 |
1990年 | 705篇 |
1989年 | 585篇 |
1988年 | 408篇 |
1987年 | 223篇 |
1986年 | 177篇 |
1985年 | 149篇 |
1984年 | 138篇 |
1983年 | 111篇 |
1982年 | 94篇 |
1981年 | 75篇 |
1980年 | 67篇 |
1979年 | 63篇 |
1978年 | 40篇 |
1977年 | 34篇 |
1959年 | 39篇 |
1951年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
91.
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
92.
93.
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
94.
95.
《矿业科学技术学报(英文版)》2020,30(6):785-797
In this study, uniaxial compressive strength (UCS), unit weight (UW), Brazilian tensile strength (BTS), Schmidt hardness (SHH), Shore hardness (SSH), point load index (Is50) and P-wave velocity (Vp) properties were determined. To predict the UCS, simple regression (SRA), multiple regression (MRA), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and genetic expression programming (GEP) have been utilized. The obtained UCS values were compared with the actual UCS values with the help of various graphs. Datasets were modeled using different methods and compared with each other. In the study where the performance indice PIat was used to determine the best performing method, MRA method is the most successful method with a small difference. It is concluded that the mean PIat equal to 2.46 for testing dataset suggests the superiority of the MRA, while these values are 2.44, 2.33, and 2.22 for GEP, ANFIS, and ANN techniques, respectively. The results pointed out that the MRA can be used for predicting UCS of rocks with higher capacity in comparison with others. According to the performance index assessment, the weakest model among the nine model is P7, while the most successful models are P2, P9, and P8, respectively. 相似文献
96.
不同折流板结构螺旋折流板换热器传热性能的比较(英文) 总被引:1,自引:0,他引:1
Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as wel as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overal heat transfer coefficient K, shel-side heat transfer coefficient ho and shel-side average comprehensive index ho/Δpo. 相似文献
97.
《Measurement》2015
Structural failures (bridge or building collapses) and geohazards (landslides, ground subsidence or earthquakes) are worldwide problems that often lead to significant economic and loss of life. Monitoring the deformation of both natural phenomena and man-made structures is a major key to assessing structural dynamic responses. Actually, this monitoring process is under real-time demand for developing warning and alert systems.One of the most used techniques for real-time deformation monitoring is the Global Navigation Satellite System (GNSS) real-time procedure, where the relative positioning approach, using a well-known reference station, has been applied.This study was conducted to evaluate the actual quality of the real-time kinematic Precise Point Positioning (PPP) GNSS solution for deformation monitoring, where it can be concluded that a promise tool is under development and should be taken into account on actual and near future real-time deformation monitoring studies and applications. 相似文献
98.
The next-generation systems are expected to be largely cyber–physical systems (CPSs) that autonomously control physical processes, through sensors and actuators typically in real-time feedback and cooperative control loops distributed among physical and cyber environments. The rapid technological advancements enhance the smartness of these CPSs, pushing their boundaries of performance and efficiency by embedding new information and communication technologies. However, to what extent CPSs should be smarter so that they do not compromise safety and security of safety critical systems? is an open research question. Towards this goal, the purpose of this study is to establish a grounded theory to analyse what makes these systems smart? and eventually, how to find a balance between smartness and safety risks? In this precinct, this article aims to develop a conceptual framework, define the dimensions and derive the characteristics that make CPSs smart. The proposed approach combines an automated informetric and systematic analysis of literature pertinent to the topic of smartness across anthropology, science, engineering and technology. The analysis of a case study building and the discussions presented herein support the connection between the existing understanding of CPSs and smartness offered by the building design approach in urban environment. 相似文献
99.
针对铜冶炼工艺的特点,从门架式堆取料机对前后工序衔接、结构、原理出发,介绍了其在熔炼炉系统和吹炼炉系统中的应用情况。经过试生产期的生产实践证明,门架式堆取料机具有场地利用率高、取料量大,自动化程度高和安全环保等优点。 相似文献
100.
海洋核动力平台因其突出的安全性已成为当今核能领域热点研究问题之一,但在海洋等非惯性条件下会使一回路系统的热工特性发生变化。针对此问题,本文对几种典型的一回路系统在摇摆条件下的自然循环流量波动特性进行计算分析。分别建立典型的双环路、三环路、四环路的一回路系统模型布置方案,并同时考虑摇摆中心的位置,根据流体动量守恒方程,得到不同状态下一回路系统内的流量变化规律。对于单堆双环路系统,摇摆中心在船上/中/下部位置时,环路流量波动幅度分别为13.2%/11.2%/9.5%,堆芯流量波动幅度分别为0.9%/0.8%/0.6%;对于单堆三环路系统,摇摆中心在船下部时,环路流量和堆芯流量波动幅度分别为9.2%和0.8%;对于单堆四环路系统,摇摆中心在船下部时,布置方案1和方案2的环路流量波动幅度分别为9.5%和9.2%,堆芯流量波动幅度分别为0.9%和0.7%。计算结果表明:采用单堆双环路的设计布置方案是最有利于系统稳定性的。 相似文献