全文获取类型
收费全文 | 48825篇 |
免费 | 5580篇 |
国内免费 | 1601篇 |
专业分类
电工技术 | 2395篇 |
综合类 | 3803篇 |
化学工业 | 9576篇 |
金属工艺 | 5360篇 |
机械仪表 | 2458篇 |
建筑科学 | 5581篇 |
矿业工程 | 818篇 |
能源动力 | 8473篇 |
轻工业 | 2516篇 |
水利工程 | 413篇 |
石油天然气 | 2286篇 |
武器工业 | 325篇 |
无线电 | 1123篇 |
一般工业技术 | 5674篇 |
冶金工业 | 3312篇 |
原子能技术 | 1063篇 |
自动化技术 | 830篇 |
出版年
2024年 | 199篇 |
2023年 | 650篇 |
2022年 | 1341篇 |
2021年 | 1495篇 |
2020年 | 1604篇 |
2019年 | 1271篇 |
2018年 | 1142篇 |
2017年 | 1336篇 |
2016年 | 1656篇 |
2015年 | 1666篇 |
2014年 | 2953篇 |
2013年 | 3023篇 |
2012年 | 3442篇 |
2011年 | 3659篇 |
2010年 | 2672篇 |
2009年 | 2819篇 |
2008年 | 2171篇 |
2007年 | 3116篇 |
2006年 | 2807篇 |
2005年 | 2477篇 |
2004年 | 2170篇 |
2003年 | 1943篇 |
2002年 | 1844篇 |
2001年 | 1485篇 |
2000年 | 1245篇 |
1999年 | 1024篇 |
1998年 | 837篇 |
1997年 | 740篇 |
1996年 | 605篇 |
1995年 | 519篇 |
1994年 | 407篇 |
1993年 | 332篇 |
1992年 | 297篇 |
1991年 | 185篇 |
1990年 | 155篇 |
1989年 | 163篇 |
1988年 | 102篇 |
1987年 | 77篇 |
1986年 | 60篇 |
1985年 | 43篇 |
1984年 | 70篇 |
1983年 | 55篇 |
1982年 | 55篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1959年 | 28篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
21.
This paper addresses the multi-objective optimization problem arising in the operation of heat integrated batch plants, where makespan and utility consumption are the two conflicting objectives. A new continuous-time MILP formulation with general precedence variables is proposed to simultaneously handle decisions related to timing, product sequencing, heat exchanger matches (selected from a two-stage superstructure) and their heat loads. It features a complex set of timing constraints to synchronize heating and cooling tasks, derived from Generalized Disjunctive Programming. Through the solution of an industrial case study from a vegetable oil refinery, we show that major savings in utilities can be achieved while generating the set of Pareto optimal solutions through the ɛ-constraint method. 相似文献
22.
The Caputo and Caputo–Fabrizio derivative are applied to study a second‐grade nanofluid over a vertical plate. A comparative analysis is presented to study the unsteady free convection of a second‐grade nanofluid with a new time–space fractional heat conduction. The governing equations with mixed time–space fractional derivatives are non‐dimensionalized and solved numerically, and a comparison between the Caputo and the Caputo–Fabrizio models is made. It is found that the temperature is higher for the Caputo–Fabrizio fractional model than the Caputo model, but the higher velocity only exists near the vertical plate for the Caputo–Fabrizio model than the Caputo model. Moreover, the velocity for the Caputo model will exceed the Caputo–Fabrizio model as y evolves. 相似文献
23.
Khalil Ghanbari Ali Akbar Golneshan Mohsen Yazdani Hesam Moghadasi Navid Malekian 《亚洲传热研究》2021,50(6):5697-5713
Nanofluids have been known as practical materials to ameliorate heat transfer within diverse industrial systems. The current work presents an empirical study on forced convection effects of Al2O3–water nanofluid within an annulus tube. A laminar flow regime has been considered to perform the experiment in high Reynolds number range using several concentrations of nanofluid. Also, the boundary conditions include a constant uniform heat flux applied on the outer shell and an adiabatic condition to the inner tube. Nanofluid particle is visualized with transmission electron microscopy to figure out the nanofluid particles. Additionally, the pressure drop is obtained by measuring the inlet and outlet pressure with respect to the ambient condition. The experimental results showed that adding nanoparticles to the base fluid will increase the heat transfer coefficient (HTC) and average Nusselt number. In addition, by increasing viscosity effects at maximum Reynolds number of 1140 and increasing nanofluid concentration from 1% to 4% (maximum performance at 4%), HTC increases by 18%. 相似文献
24.
Improving the performance of heat transfer fluids is altogether significant. The best approach for improving the thermal conductivity is the addition of nanoparticles to the base fluid. In the present study, specific heat, dynamic viscosity, and thermal conductivity of water-based Indian coal fly ash stable nanofluid for 0.1% to 0.5% volume concentration in the temperature range of 30 to 60°C has been investigated. To evaluate an average particle diameter of 11.5 nm, the fly ash nanoparticles were characterized with scanning electron microscopy and dynamic light scattering. Using zeta potential, the stability of nanofluid in the presence of surfactant Triton X-100 was tested. Thermal conductivity and viscosity of fly ash nanofluid increased, while specific heat decreased as volume concentration increased. The effect of temperature on the fly ash nanofluid was directly proportional to its thermal conductivity and specific heat and inversely proportional to viscosity. 相似文献
25.
采用四组分法从辽河减压渣油中分离出胶质、沥青质,分别考察了它们在分散型催化剂作用下的临氢热反应行为。结果表明,胶质、沥青质一方面要裂化生成较轻的产物;另一方面也要发生缩合反应生成较重的反应产物以及甲苯不溶物。渣油在临氢热反应过程中,沥青质是生焦的主要来源,其次才是胶质。比较了热反应生成的沥青质与原生沥青质之间以及热反应生成的胶质与原生胶质之间化学组成的区别,结果表明,反应生成的沥青质和胶质较原生的沥青质和胶质分子结构缩合程度高,并且反应苛刻度越高,缩合程度也越高。 相似文献
26.
利用数值模拟方法结合场协同理论,对直椭圆扁管、单向螺旋椭圆扁管和变向螺旋椭圆扁管管内传热与流动情况进行了数值模拟计算和理论分析,比较研究了不同的Re、Pr下,3种椭圆扁管的管内传热与流阻特性。结果表明,单向螺旋椭圆扁管和变向螺旋椭圆扁管与直椭圆扁管相比有很好的强化传热性能,而变向螺旋椭圆扁管要比单向螺旋椭圆扁管的强化传热性能更好。在管内流体具有高Pr及低Re的条件下,2种螺旋椭圆扁管的强化传热效果显著,可作为很好的强化传热元件应用于工程实际中。 相似文献
27.
机械力化学作用对低介硅灰石瓷料的相变和相组成的影响 总被引:1,自引:0,他引:1
采用X射线衍射仪(XRD)、差热分析(DTA)手段详细研究了由氧化物粉末制备硅灰石陶瓷时,机械力化学作用及后续热处理对硅灰石陶瓷相组成和相变过程的影响,分析了机械力化学在球磨过程中的作用机理主要是细化晶粒、使晶格畸变、晶格缺陷增多、非晶化和诱导低温化学反应。结果表明:高能球磨中的机械力化学作用能够有效地降低硅灰石陶瓷的烧成温度(11160~11220℃)。探明了经高能球磨的样品在烧成过程中的晶相转变规律。瓷料最终的晶相为单一的-硅灰石(高温变体)。 相似文献
28.
29.
30.
Thermodynamic and Transport Properties of Liquid HFC-227ea 总被引:1,自引:0,他引:1
The thermal conductivity and heat capacity of liquid 1,1,1,2,3,3,3-hepta-fluoropropane (HFC-227ea) have been studied by a high-frequency thermal-wave method over the temperature range of 294 to 345 K at pressures up to 2.8 MPa. The purity of the samples used throughout the measurements is 99.99 mol%. The experimental uncertainties of the thermal conductivity and heat capacity measurements were estimated to be within ±1.5 and ±2%, respectively. The thermal conductivity of HFC-227ea in the liquid phase decreases as temperature increases, while the pressure has an opposite effect. 相似文献