全文获取类型
收费全文 | 566296篇 |
免费 | 51045篇 |
国内免费 | 30666篇 |
专业分类
电工技术 | 69563篇 |
技术理论 | 55篇 |
综合类 | 59150篇 |
化学工业 | 44376篇 |
金属工艺 | 22058篇 |
机械仪表 | 44211篇 |
建筑科学 | 59965篇 |
矿业工程 | 25578篇 |
能源动力 | 19379篇 |
轻工业 | 24069篇 |
水利工程 | 20107篇 |
石油天然气 | 22261篇 |
武器工业 | 8432篇 |
无线电 | 48295篇 |
一般工业技术 | 36305篇 |
冶金工业 | 23859篇 |
原子能技术 | 5284篇 |
自动化技术 | 115060篇 |
出版年
2024年 | 980篇 |
2023年 | 6016篇 |
2022年 | 10857篇 |
2021年 | 14756篇 |
2020年 | 15448篇 |
2019年 | 11752篇 |
2018年 | 10893篇 |
2017年 | 15003篇 |
2016年 | 17949篇 |
2015年 | 20221篇 |
2014年 | 37449篇 |
2013年 | 32573篇 |
2012年 | 41393篇 |
2011年 | 44940篇 |
2010年 | 33752篇 |
2009年 | 34260篇 |
2008年 | 33583篇 |
2007年 | 41483篇 |
2006年 | 37452篇 |
2005年 | 32862篇 |
2004年 | 27398篇 |
2003年 | 24272篇 |
2002年 | 19228篇 |
2001年 | 15999篇 |
2000年 | 13610篇 |
1999年 | 10604篇 |
1998年 | 7896篇 |
1997年 | 6718篇 |
1996年 | 5766篇 |
1995年 | 4869篇 |
1994年 | 4105篇 |
1993年 | 2929篇 |
1992年 | 2358篇 |
1991年 | 1719篇 |
1990年 | 1423篇 |
1989年 | 1215篇 |
1988年 | 825篇 |
1987年 | 530篇 |
1986年 | 379篇 |
1985年 | 418篇 |
1984年 | 398篇 |
1983年 | 320篇 |
1982年 | 248篇 |
1981年 | 192篇 |
1980年 | 172篇 |
1979年 | 132篇 |
1978年 | 87篇 |
1977年 | 94篇 |
1976年 | 44篇 |
1959年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
In the present work, the heating performance of a new system combined with a new modified baseboard radiator and fan coil is investigated. Using longitudinal fins with special geometry and also forced airflow at the end of the system causes that at the lower inlet water temperature compared with the conventional models, higher heat output rate be obtained. The heat output rate of the new modified system is obtained by experimental metrology based on the European Standard No. EN-442. Temperature and velocity distribution in the room space is done by simulation of the modified system in the Flovent software. Computational fluid dynamics (CFD) results are validated against experimental results and there is a good agreement between them. Also, the energy consumption of the system during the winter season is calculated in TRANSYS software. Experimental results show that the heat output rate of a new modified heating system with inlet water temperature in the range of 45–55°C is on average 4.17 times higher compared with the conventional model. CFD simulation also showed that the combined system provides good thermal comfort conditions. Energy consumption of the new system reduced about 13% compared with conventional models. 相似文献
12.
Efficient electricity price forecasting plays a significant role in our society. In this paper, a novel influencer-defaulter mutation (IDM) mutation operator has been proposed. The IDM operator has been combined with six well-known optimization algorithms to create mutated optimization algorithms whose performance has been tested on twenty-four standard benchmark functions. Further, the artificial neural network is integrated with mutated optimization algorithms to solve the electricity price prediction problem. The policymakers can identify appropriate variables based on the predicted prices to help future market planning. The statistical results prove the efficacy of the IDM operator on the recent optimization algorithms. 相似文献
13.
14.
高面板坝的变形对面板的安全运行有着特别重要的影响,国内外已建的高面板坝工程中,因坝体变形大导致防渗面板挤压破损,坝体渗漏量大的实例较多,不得不降低水库水位进行修复处理,造成较大的经济损失乃至给大坝的长期运行留下安全隐患。通过发生挤压破损的实例分析,发现变形控制缺乏系统性是发生面板挤压破损的主要因素,为预防面板破损,系统提出了“控制坝体总变形,转化有害变形,适应纵向变形”的坝体变形控制方法,并在使用软硬岩混合料筑坝的董箐面板堆石坝中得到的应用,取得了良好效果,该工程运行至今达十余年,未见面板有挤压破损迹象,该方法对建设200 m以上乃至300 m级超高面板坝具有重要借鉴意义。 相似文献
15.
This work describes facile synthesis of a porous polymeric material ( T-HCP ) using readily available reagents. Specifically, T-HCP is a thermally stable and hypercrosslinked polymer (HCP) that is essentially microporous with a high BET specific surface area (940 m2 g?1). Triptycene based polymers are known to feature internal free volume. Thus, the incorporation of triptycene units and extensive crosslinking by an external cross-linker in T-HCP makes it a promising adsorbent for small gas capture applications. Experimental results show that T-HCP demonstrated good CO2 capture capacity of 132 mg g?1 (273 K, 1 bar). Molecular hydrogen storage capacity of T-HCP is estimated to be 17.7 mg g?1 (77 K, 1 bar). T-HCP revealed high CO2/N2 selectivity (up to 63) as well as promising CO2/CH4 (up to 9.1) selectivity suggesting its potential applicability for CO2 separation from flue and natural gases. 相似文献
16.
《Ceramics International》2022,48(24):36835-36844
Molybdate and tungstate with scheelite-type structure are excellent self-luminescent materials, which can be used as ideal hosts for the doping of rare-earth ions. In this study, a series of Eu3+-activated SrAO4 (A = Mo and W) phosphors were successfully synthesized, and their crystal structures, photoluminescence properties, and temperature measurement performance were analyzed in detail. These phosphors were excited by UV light (291 nm and 247 nm, respectively), with clear energy transfer (ET) (MoO42?→Eu3+ or WO42?→Eu3+). According to fluorescence intensity ratio (FIR) and Judd–Ofelt (J–O) theory, compared to SrWO4:0.01Eu3+ phosphor, SrMoO4:0.01Eu3+ phosphor exhibited better thermal stability, with relatively low Sa value (maximum values were 5.082 %K?1 and 20.74 %K?1, respectively), and their Sr values were not significantly different (maximum values were 0.864 %K?1 and 0.83 %K?1, respectively). Sa value was negatively correlated to central asymmetry of Eu3+, but the optimal Sr value tended to be more suitable for central asymmetry of Eu3+. In addition, Eu3+ exhibited stronger central asymmetry as well as covalency of Eu–O bond in SrMoO4. Results reveal that SrMoO4:xEu3+ and SrWO4:xEu3+ can be used for luminescent thermometers. 相似文献
17.
18.
以“创新、协调、绿色、开放、共享”为内核的新发展理念,是对马克思主义发展理念的继承和发扬,极具时代精神,富含问题意识,为高校思想政治教育发展、教育教学改革实践提供了强大的理论支撑。本文以“通信原理”为例,阐述了新发展理念在课程改革中的思路和方法,实现了思想政治教育与专业基础课程有机融合,为深化高校教学改革、创新人才培养模式提供了思路。 相似文献
19.
Numerical simulations are performed to investigate the real gas effects on shock/expansion fan interaction. Initial perfect gas simulations at low enthalpy capture the flow structures efficiently and outcomes are found to have excellent agreement with the analytical calculations. Furthermore, the simulations with the real gas solver for different enthalpies showed that the variation in enthalpy significantly changes the flow structures. It is observed that an increase in enthalpy leads to a decrease and increase in the postshock and postexpansion fan Mach numbers, respectively. Another important observation is the decrement in the peak pressure ratio with an increment in the enthalpy. These effects are noted to be more pronounced for Mars's environment due to the higher dependency of specific heat on temperature. 相似文献
20.
《Ceramics International》2022,48(1):754-759
Thermal control coatings (TCCs) are an essential part of the thermal control systems in the spacecraft. Solar absorptance and emittance are the key performance parameters of TCCs. To develop an ultra-low solar absorption and stable inorganic TCCs for surface radiator, different TCCs were prepared by co-sintering ZnO and SiO2 nanoparticles to form Zn2SiO4/SiO2 pigment in this work, and the optical properties and radiation stability were systematically studied. It is found that the coating based on composite pigment has high reflectivity in the ultraviolet band and excellent optical performance possessing the low solar absorption of 0.06. In addition, the Zn2SiO4/SiO2 coating demonstrates the highest proton and electron radiation stability because that SiO2 between Zn2SiO4 particles acts as the relaxation center of the defects caused by radiation. 相似文献