全文获取类型
收费全文 | 41066篇 |
免费 | 3729篇 |
国内免费 | 1517篇 |
专业分类
电工技术 | 4161篇 |
综合类 | 3862篇 |
化学工业 | 3972篇 |
金属工艺 | 2384篇 |
机械仪表 | 1683篇 |
建筑科学 | 8735篇 |
矿业工程 | 1242篇 |
能源动力 | 2787篇 |
轻工业 | 2863篇 |
水利工程 | 2124篇 |
石油天然气 | 1363篇 |
武器工业 | 166篇 |
无线电 | 1984篇 |
一般工业技术 | 3477篇 |
冶金工业 | 3454篇 |
原子能技术 | 579篇 |
自动化技术 | 1476篇 |
出版年
2024年 | 165篇 |
2023年 | 533篇 |
2022年 | 998篇 |
2021年 | 1159篇 |
2020年 | 1320篇 |
2019年 | 1086篇 |
2018年 | 1033篇 |
2017年 | 1248篇 |
2016年 | 1391篇 |
2015年 | 1463篇 |
2014年 | 2552篇 |
2013年 | 2409篇 |
2012年 | 3014篇 |
2011年 | 3317篇 |
2010年 | 2428篇 |
2009年 | 2586篇 |
2008年 | 2250篇 |
2007年 | 2847篇 |
2006年 | 2588篇 |
2005年 | 2080篇 |
2004年 | 1745篇 |
2003年 | 1467篇 |
2002年 | 1260篇 |
2001年 | 1031篇 |
2000年 | 909篇 |
1999年 | 680篇 |
1998年 | 559篇 |
1997年 | 449篇 |
1996年 | 373篇 |
1995年 | 298篇 |
1994年 | 239篇 |
1993年 | 165篇 |
1992年 | 121篇 |
1991年 | 87篇 |
1990年 | 76篇 |
1989年 | 77篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 27篇 |
1985年 | 43篇 |
1984年 | 40篇 |
1983年 | 28篇 |
1982年 | 27篇 |
1981年 | 9篇 |
1980年 | 29篇 |
1979年 | 6篇 |
1975年 | 2篇 |
1959年 | 3篇 |
1955年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Elli Ntakou Ralph Masiello Farnaz Farzan Shay Bahramirad Aleksi Paaso M.A. Nayeem Maigha Maigha Daniel Kushner 《The Electricity Journal》2019,32(4):45-49
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal. 相似文献
2.
Three N-heteroleptic Pt(II) complexes, [Pt(C^C)(O^O)] [O^O = acetylacetonate, C^C = 1-phenyl-1,2,4-triazol-5-ylidene (1), C^C = 4-phenyl-1,2,4-triazol-5-ylidene (2), C^C = 2-phenylpyrazine (3)] have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). The radiative decay rate constants of complexes 1–3 have been discussed with the oscillator strength (fn), the strength of spin–orbit coupling (SOC) interaction between the lowest energy triplet excited state (T1) and singlet excited states (Sn), and the energy gaps between E(T1) and E(Sn). To illustrate the nonradiative decay processes, the transition states between triplet metal-centered (3MC) and T1 states have been optimized and were verified with the calculations of vibrational frequencies and intrinsic reaction coordinate (IRC). In addition, the minimum energy crossing points (MECPs) between 3MC and ground states (S0) were optimized. At last, the potential energy curves relevant to the nonradiative decay pathways are simulated. The results show that complex 3 has the biggest photoluminescence quantum yield because the complex 3 has the biggest radiative decay rate constant and the smallest nonradiative decay rate constant in complexes 1–3. 相似文献
3.
This paper proposes a thermoelectric-assisted vapor compression cycle (TVCC) for applications in air-source heat pump systems which could enhance the heating capacity of the system. Performances of TVCC are calculated and then compared with that of basic vapor compression cycle (BVCC). The simulation results show that when coefficients of performance (COPs) of the two cycles are almost equal, the TVCC under maximum COP condition of the thermoelectric modules still performs better than BVCC by 13.0% in heating capacity through selecting the appropriate intermediate temperature. In addition, the TVCC can also achieve an improvement of 16.4%–21.7% in both the heating COP and capacity when compared with the BVCC with an assistant electric heater that is provided with the equivalent power input of thermoelectric heat exchanger. Thus, the TVCC could be beneficial to the applications in small heat pumps if there is always need for auxiliary electric heat. 相似文献
4.
This paper presented the exergoeconomic evaluation of the developed desiccant-evaporative air-conditioning system. The developed system was evaluated based on the steady-state conditions at different regeneration and reference temperatures. The exergoeconomic evaluation method was implemented to the system components and the whole system to evaluate the exergy efficiency, exergy destruction ratios, cost rates, relative cost differences and exergoeconomic factors. The regeneration and reference temperatures affected the exergy efficiencies, exergy destruction ratios, cost rates, relative cost differences and exergoeconomic factors. The desiccant wheel, heating coil and evaporative cooler had a high cost rate (investment cost, operation and maintenance cost, and exergy destruction cost). The exit air fan, outdoor air fan and evaporative cooler had a high relative cost difference. The exit air fan, outdoor air fan and secondary heat exchanger had a high exergoeconomic factor. Replacement of the desiccant wheel with a higher dehumidification performance could decrease the high cost rate. A higher efficiency evaporative cooler and heating coil were needed. Cheaper air fans (outdoor air fans and exit air fans) were needed. 相似文献
5.
Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness. 相似文献
6.
7.
国产风机盘管空调系统常见问题分析 总被引:2,自引:1,他引:1
分析了国产风机盘管使用中常见的问题,指出机组因风量不足、冷量风量匹配不合理以及风机盘管某些设备故障,导致了风机盘管精度低、舒适性差、能耗高等一系列问题。指出应引起空调设计和运行维护人员的注意。 相似文献
8.
9.
探讨水资源承载力综合评估和多目标计算理论在城市规划中的应用。运用灰色多层次综合评估模型对惠州市水资源承载力进行定性的综合评价,应用多目标规划理论对城市经济发展规划不同方案下的惠州市水资源承载力作了定量计算。 相似文献
10.
回热损失对磁斯特林制冷循环制冷率的影响 总被引:7,自引:0,他引:7
从铁磁质的磁化强度一般表示式出发,探讨热阻和回热损失对磁斯特林制冷循环性能的影响,导出最大制冷率及其它性能参数。得到了结果适用于以顺磁质为工质的磁斯特林制冷循环。并指出在理想回热条件下的结论也适用于磁卡诺制冷循环。 相似文献