全文获取类型
收费全文 | 129683篇 |
免费 | 17191篇 |
国内免费 | 9433篇 |
专业分类
电工技术 | 12459篇 |
技术理论 | 5篇 |
综合类 | 11853篇 |
化学工业 | 20505篇 |
金属工艺 | 4728篇 |
机械仪表 | 10149篇 |
建筑科学 | 6050篇 |
矿业工程 | 3768篇 |
能源动力 | 8450篇 |
轻工业 | 14989篇 |
水利工程 | 6878篇 |
石油天然气 | 7176篇 |
武器工业 | 1429篇 |
无线电 | 6441篇 |
一般工业技术 | 10384篇 |
冶金工业 | 5168篇 |
原子能技术 | 1893篇 |
自动化技术 | 23982篇 |
出版年
2024年 | 830篇 |
2023年 | 2587篇 |
2022年 | 4883篇 |
2021年 | 5434篇 |
2020年 | 5437篇 |
2019年 | 4814篇 |
2018年 | 4359篇 |
2017年 | 5299篇 |
2016年 | 5874篇 |
2015年 | 6184篇 |
2014年 | 8632篇 |
2013年 | 9369篇 |
2012年 | 10052篇 |
2011年 | 10776篇 |
2010年 | 7393篇 |
2009年 | 7802篇 |
2008年 | 6978篇 |
2007年 | 8099篇 |
2006年 | 7047篇 |
2005年 | 5847篇 |
2004年 | 4824篇 |
2003年 | 4110篇 |
2002年 | 3372篇 |
2001年 | 2778篇 |
2000年 | 2371篇 |
1999年 | 1820篇 |
1998年 | 1578篇 |
1997年 | 1345篇 |
1996年 | 1173篇 |
1995年 | 1047篇 |
1994年 | 877篇 |
1993年 | 689篇 |
1992年 | 582篇 |
1991年 | 403篇 |
1990年 | 390篇 |
1989年 | 296篇 |
1988年 | 214篇 |
1987年 | 135篇 |
1986年 | 116篇 |
1985年 | 63篇 |
1984年 | 78篇 |
1983年 | 63篇 |
1982年 | 43篇 |
1981年 | 18篇 |
1980年 | 41篇 |
1979年 | 30篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1959年 | 32篇 |
1951年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Investigation on the miniaturized parallel multichannel-based devices packed with glass beads to improve the mass exchange execution is the critical focal point of the current study. One of the essential parameters to specify the miniaturized devices' flow distribution is the residence time distribution (RTD). In the present context, the RTDs of a liquid tracer were investigated for the air-water multiphase flows (concurrent) across the multichannel-based miniaturized devices (comprising of 11 similar dimensional parallel channels). The devices were variable in height and packed with glass beads. The conductivity estimations generated the RTD curves and were addressed by the axial dispersion model (ADM). The fluid-flow rates differed within the range of 5–23 ml min−1. The axial dispersion coefficients and the rate of the specific energy dispersion were investigated. The effects of pressure difference and geometry on the hydrodynamic attributes and mixing properties were well-illustrated, and the new correlations were suggested. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(8):5609-5626
The demand for clean energy use has been increasing worldwide, and hydrogen has attracted attention as an alternative energy source. The efficient transport of hydrogen must be established such that hydrogen may be used as an energy source. In this study, we considered the influences of various parameters in the transportation of liquefied hydrogen using type C tanks in shipping vessels. The sloshing and thermal flows were considered in the transportation of liquefied hydrogen, which exists as a cryogenic liquid at ?253 °C. In this study, the sloshing flow was analyzed using a numerical approach. A multiphase sloshing simulation was performed using the volume of fluid method for the observation and analysis of the internal flow. First, a sloshing experiment according to the gas-liquid density ratio performed by other researchers was utilized to verify the simulation technique and investigate the characteristics of liquefied hydrogen. Based on the results of this experiment, a sloshing simulation was then performed for a type C cargo tank for liquefied hydrogen carriers under three different filling level conditions. The sloshing impact pressure inside of the tank was measured via simulation and subjected to statistical analysis. In addition, the influence of sloshing flow on the appendages installed inside of the type C tank (stiffened ring and swash bulkhead) was quantitatively evaluated. In particular, the influence of the sloshing flow inside of the type C tank on the appendages can be utilized as an important indicator at the design stage. Furthermore, if such sloshing impact forces are repeatedly experienced over an extended period of time under cryogenic conditions, the behavior of the tank and appendages must be analyzed in terms of fatigue and brittle failure to ensure the safety of the transportation operation. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(11):6986-6995
It is clear that the entire world have to research, develop, demonstrate and plan for alternative energy systems for shorter term and also longer term. As a clean energy carrier, hydrogen has become increasingly important. It owes its prestige to the increase within the energy costs as a result of the equivocalness in the future availability. Two phase flow and hydrogen gas flow dynamics effect on performance of water electrolysis. Hydrogen bubbles are recognized to influence energy and mass transfer in gas-evolving electrodes. The movement of hydrogen bubbles on the electrodes in alkaline electrolysis is known to affect the reaction efficiency. Within the scope of this research, a physical modeling for the alkaline electrolysis is determined and the studies about the two-phase flow model are carried out for this model. Internal and external forces acting on the resulting bubbles are also determined. In this research, the analytical solution of two-phase flow analysis of hydrogen in the electrolysis is analyzed. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(10):6710-6720
Herein, molybdenum disulfide nanoflakes decorated copper phthalocyanine microrods (CuPc-MoS2) are synthesized via two step simple hydrothermal method. The as synthesized hybrid along with pure molybdenum disulfide (MoS2) nanoflower and pure copper phthalocyanine (CuPc) microrods are well characterized by various techniques that confirm phase, morphology, elemental compositions etc. Next, electrocatalytic oxygen reduction reaction towards fuel cell is investigated in alkaline medium and obtained results proclaim that our CuPc-MoS2 heterostructure outperforms the other two constituent materials. Efficient oxygen reduction is achieved following four electron pathway by CuPc-MoS2 whereas partial reduction is done through two electron process by CuPc and MoS2 separately. Long-time durability test reveals almost 97.6% retention after 8000s that eventually dictate us that CuPc-MoS2 heterostructure can be the efficient cathode electrocatalyst for future generation fuel cell. 相似文献
5.
6.
《International Journal of Hydrogen Energy》2022,47(84):35641-35654
The continuous catalytic regenerative (CCR) reforming process is one of the most significant sources of hydrogen production in the petroleum refining process. However, the fluctuations in feedstock composition and flow rate could significantly affect both product distribution and energy consumption. In this study, a robust deviation criterion based multi-objective optimization approach is proposed to perform the optimal operation of CCR reformer under feedstock uncertainty, with simultaneous maximization of product yields and minimization of energy consumption. Minimax approach is adopted to handle these uncertain objectives, and the Latin hypercube sampling method is then used to calculate these robust deviation criteria. Multi-objective surrogate-based optimization methods are next introduced to effectively solve the robust operational problem with high computational cost. The level diagram method is finally utilized to assist in multi-criteria decision-making. Two robust operational optimization problems with different objectives are solved to demonstrate the effectiveness of the proposed method for robust optimal operation of the CCR reforming process under feedstock uncertainty. 相似文献
7.
《International Journal of Hydrogen Energy》2022,47(91):38721-38735
Proper management of the liquid water and heat produced in proton exchange membrane (PEM) fuel cells remains crucial to increase both its performance and durability. In this study, a two-phase flow and multicomponent model, called two-fluid model, is developed in the commercial COMSOL Multiphysics® software to investigate the liquid water heterogeneities in large area PEM fuel cells, considering the real flow fields in the bipolar plate. A macroscopic pseudo-3D multi-layers approach has been chosen and generalized Darcy's relation is used both in the membrane-electrode assembly (MEA) and in the channel. The model considers two-phase flow and gas convection and diffusion coupled with electrochemistry and water transport through the membrane. The numerical results are compared to one-fluid model results and liquid water measurements obtained by neutron imaging for several operating conditions. Finally, according to the good agreement between the two-fluid and experimentation results, the numerical water distribution is examined in each component of the cell, exhibiting very heterogeneous water thickness over the cell surface. 相似文献
8.
A key element in solving real-life data science problems is selecting the types of models to use. Tree ensemble models (such as XGBoost) are usually recommended for classification and regression problems with tabular data. However, several deep learning models for tabular data have recently been proposed, claiming to outperform XGBoost for some use cases. This paper explores whether these deep models should be a recommended option for tabular data by rigorously comparing the new deep models to XGBoost on various datasets. In addition to systematically comparing their performance, we consider the tuning and computation they require. Our study shows that XGBoost outperforms these deep models across the datasets, including the datasets used in the papers that proposed the deep models. We also demonstrate that XGBoost requires much less tuning. On the positive side, we show that an ensemble of deep models and XGBoost performs better on these datasets than XGBoost alone. 相似文献
9.
10.