全文获取类型
收费全文 | 112499篇 |
免费 | 12420篇 |
国内免费 | 5827篇 |
专业分类
电工技术 | 16322篇 |
技术理论 | 16篇 |
综合类 | 7517篇 |
化学工业 | 13004篇 |
金属工艺 | 4605篇 |
机械仪表 | 5551篇 |
建筑科学 | 11834篇 |
矿业工程 | 3512篇 |
能源动力 | 16744篇 |
轻工业 | 7007篇 |
水利工程 | 2583篇 |
石油天然气 | 3886篇 |
武器工业 | 1249篇 |
无线电 | 9713篇 |
一般工业技术 | 10827篇 |
冶金工业 | 4791篇 |
原子能技术 | 1649篇 |
自动化技术 | 9936篇 |
出版年
2024年 | 327篇 |
2023年 | 2401篇 |
2022年 | 3813篇 |
2021年 | 4485篇 |
2020年 | 4676篇 |
2019年 | 4040篇 |
2018年 | 3415篇 |
2017年 | 4075篇 |
2016年 | 4526篇 |
2015年 | 4598篇 |
2014年 | 7984篇 |
2013年 | 7186篇 |
2012年 | 8518篇 |
2011年 | 9234篇 |
2010年 | 6911篇 |
2009年 | 6865篇 |
2008年 | 6123篇 |
2007年 | 6996篇 |
2006年 | 5841篇 |
2005年 | 4702篇 |
2004年 | 4004篇 |
2003年 | 3505篇 |
2002年 | 2954篇 |
2001年 | 2489篇 |
2000年 | 2035篇 |
1999年 | 1622篇 |
1998年 | 1281篇 |
1997年 | 966篇 |
1996年 | 911篇 |
1995年 | 731篇 |
1994年 | 653篇 |
1993年 | 513篇 |
1992年 | 434篇 |
1991年 | 346篇 |
1990年 | 269篇 |
1989年 | 222篇 |
1988年 | 198篇 |
1987年 | 137篇 |
1986年 | 105篇 |
1985年 | 139篇 |
1984年 | 109篇 |
1983年 | 72篇 |
1982年 | 85篇 |
1981年 | 41篇 |
1980年 | 49篇 |
1979年 | 29篇 |
1978年 | 18篇 |
1977年 | 18篇 |
1974年 | 12篇 |
1951年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
防碰装置是起重机械重要的安全防护装置,其性能质量直接关系到人员和设备安全。常规的防碰装置性能试验方法难以保证试验数据的精度和可靠性。针对防碰装置的工作特点和试验要求,从试验原理、系统结构、运行逻辑等方面入手,设计一套能模拟防碰装置实际运行工况,自动进行性能试验和数据采集处理,精度高、重复性好的试验系统,可以有效提升防碰装置检测能力。 相似文献
82.
83.
A small-scale silica gel-water adsorption system with modular adsorber, which utilizes solar energy to achieve the cogeneration of domestic air conditioning and water heating effect, is proposed and investigated in this paper. A heat recovery process between two adsorbers and a mass recovery process between two evaporators are adopted to improve the overall cooling and heating performance. First, the adsorption system is tested under different modes (different mass recovery, heat recovery, and cogeneration time) to determine the optimal operating conditions. Then, the cogeneration performance of domestic cooling and water heating effect is studied at different heat transfer fluid temperatures. The results show that the optimal time for cogeneration, mass recovery, and heat recovery are 600 s, 40 s, and 40 s, respectively. When the inlet temperature of hot water is around 85°C, the largest cooling power and heating power are 8.25 kW and 21.94 kW, respectively. Under the condition of cooling water temperature of 35°C, the obtained maximum COPc, COPh, and SCP of the system are 0.59, 1.39, and 184.5 W/kg, respectively. 相似文献
84.
Natural convective flow of air inside the cubical cavity is investigated numerically. The temperature of the bottom wall is kept higher than that of top cold wall, and other four walls are assumed to be adiabatic. Attention has been paid to the convective discretization schemes, like upwind, QUICK, total variation diminishing, normalized variable diagram (NVD) schemes that are compared with respect to accuracy. The output is validated with respect to the results available in the literature. A parallel computing message passing interface code is adapted to run the simulations. From the results, it is observed that the NVD scheme gives better results among all the employed convective discretization schemes irrespective of the mesh structure. Thus, in this article, self filtered central differencing which is a family of NVD, is used. From the enormous output data, along with the streamlines, contours of isotherms, the new technique of energy pathlines, and field synergy are used to visualize the fluid flow and heat transfer mechanism arising in the system in the range of Ra from 103 to 106. Free energy streamlines are observed with small Ra, whereas trapped energy streamlines are observed with high Ra. When Ra increases, synergy angle increases and implies that the synergy between the velocity vector and temperature gradient gets reduced and leads to increasing values of average Nusselt number (Nu). 相似文献
85.
As a response to the threat of climate change, many nations are increasing their use of renewable energy, including wind energy. Large wind farms often conflict with other land uses, particularly tourism, which is a growing industry worldwide. In Iceland, tourism has recently become the largest export sector, with majority of tourists travelling to the country to experience its nature. This paper examines tourists’ opinions and perceptions of wind power development in the Southern Highlands of Iceland and compares how number, size and proximity of wind turbines, and the landscape in which they are situated, influence tourists’ perceptions. The study is based on an on-site questionnaire survey conducted in 2015. The results indicate that one-third of the travellers would be less likely to visit the Southern Highlands if a proposed wind farm were built, and two-thirds think that wind turbines would decrease the area’s attractiveness. 相似文献
86.
87.
Traditional optimization methods, which take a specific order of modal frequency as the design constraint, could fail to obtain the desired solution because of modal substitution. An improved optimization model with continuous sizing variables is established to solve this problem, in which the minimum weight and a given local modal frequency are considered as the objective and the constraint. To capture accurately the expected mode of vibration, a local mode identification technique is proposed based on the strain energy ratio between the local area and the whole structure. With that scheme, an optimization system is developed, in which the local mode can be effectively identified and the constraint can be updated with it in the iteration process. Two numerical examples, of a reinforced plate and a satellite structure, are applied to illustrate the effectiveness and efficacy of the proposed method. 相似文献
88.
89.
Yongsen Wei 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2018,40(24):3009-3018
Heat transfer has considerable applications in different industries such as designing of heat exchanger, nuclear reactor cooling, control system for spacecraft, and designing of microelectronics cooling. As the surfaces of two metals contact each other, this issue becomes so crucial. Thermal contact resistance (TCR) is one of the key physical parameters in heat transfer of mentioned surfaces. Measuring the experimental value of TCR in laboratory is highly expensive and difficult. As an alternative, numerical modeling methods could be engaged. In this study, inverse problem method solution is utilized as a proper method for estimation of TCR value. In this order, three different configurations (flat-flat, flat-cylinder, and cylinder-cylinder) were utilized in two steady and unsteady state conditions to predict the value of TCR. A comparison between the measured values and obtained values from the simulation show the errors for flat-flat, flat-cylinder, and cylinder-cylinder configuration after 10 min from starting the experiment are 4.6074%, 0.1662%, and 0.5622%, respectively. And in steady-state condition, the corresponding errors are 6.06e-3%, 1.506%, and 0.846%, respectively. In conclusion, the final results establish the fact that the inverse problem method solution can predict TCR values between contacting surfaces. 相似文献
90.
Phase change materials (PCM) have an increasingly more important role as a thermal energy storage (TES) media. However, leakage problem of PCM causes limitation during their integration in TES systems. Therefore, the encapsulation of PCMs is attracting research interest to extend usage of PCMs in real TES applications in recent years. In this study, hydroxystearic acid (HSA) was encapsulated with polymethyl methacrylate (PMMA) and different PMMA comonomer shells via emulsion polymerization method for the first time in literature. HSA with high melting temperature range (74–78°C) can widen the scope of using PCMs, and the encapsulated form can make it more versatile. The chemical structures, morphologies, and thermophysical properties of capsules were determined by FT‐IR, SEM, DSC, TGA, and thermal infrared camera. Among the produced HSA capsule candidates, PMMA‐HEMA is the most promising with latent heat of 48.5 J/g with melting range of 47 to 85°C. SEM analysis indicated that the capsules have spherical shape with compact surface at nano‐micro (100–440 nm) size range; however, some capsules exhibited agglomeration. 相似文献