全文获取类型
收费全文 | 74821篇 |
免费 | 7160篇 |
国内免费 | 3736篇 |
专业分类
电工技术 | 5890篇 |
技术理论 | 1篇 |
综合类 | 6335篇 |
化学工业 | 19049篇 |
金属工艺 | 5861篇 |
机械仪表 | 3857篇 |
建筑科学 | 2386篇 |
矿业工程 | 2015篇 |
能源动力 | 2850篇 |
轻工业 | 4393篇 |
水利工程 | 800篇 |
石油天然气 | 5301篇 |
武器工业 | 634篇 |
无线电 | 8425篇 |
一般工业技术 | 7662篇 |
冶金工业 | 4417篇 |
原子能技术 | 1179篇 |
自动化技术 | 4662篇 |
出版年
2024年 | 246篇 |
2023年 | 987篇 |
2022年 | 1586篇 |
2021年 | 1993篇 |
2020年 | 2029篇 |
2019年 | 1836篇 |
2018年 | 1840篇 |
2017年 | 2276篇 |
2016年 | 2274篇 |
2015年 | 2256篇 |
2014年 | 4199篇 |
2013年 | 4065篇 |
2012年 | 4994篇 |
2011年 | 4468篇 |
2010年 | 3494篇 |
2009年 | 4143篇 |
2008年 | 3999篇 |
2007年 | 5465篇 |
2006年 | 5566篇 |
2005年 | 4417篇 |
2004年 | 3056篇 |
2003年 | 3297篇 |
2002年 | 2651篇 |
2001年 | 2323篇 |
2000年 | 2139篇 |
1999年 | 1764篇 |
1998年 | 1434篇 |
1997年 | 1231篇 |
1996年 | 987篇 |
1995年 | 900篇 |
1994年 | 760篇 |
1993年 | 542篇 |
1992年 | 492篇 |
1991年 | 400篇 |
1990年 | 325篇 |
1989年 | 297篇 |
1988年 | 175篇 |
1987年 | 132篇 |
1986年 | 109篇 |
1985年 | 117篇 |
1984年 | 100篇 |
1983年 | 62篇 |
1982年 | 69篇 |
1981年 | 44篇 |
1980年 | 54篇 |
1979年 | 28篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1975年 | 15篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The simultaneous flow of gas, oil, and water forms various flow patterns due to the complex interfacial relationships. Three-phase flow patterns are classified as the gas-liquid and liquid-liquid flow patterns. Pressure drop, void fraction, liquid holdup, and phase distribution are important characteristics of the three-phase flow. These characteristics are generally associated with the three-phase flow patterns. Hence, the knowledge about flow patterns can help to predict the overall behavior of the three-phase flow. Studies have been conducted to identify three-phase flow pattern and their characteristics at various superficial velocities of gas, oil, and water. The major purpose of the studies is to gather information about the three-phase co-current flow and use it for improvement of the efficiency of the flow systems. Therefore, the accuracy of the measurement technique is critical. Several types of flow pattern identification and measurement techniques have been developed to improve accuracy and provide high-quality results. In this article, classical and advanced techniques used for the three-phase flow identification and measurement have been reviewed. The survey will help the researchers working in the area of multiphase flow to choose the right technique based on the objectives of the studies. 相似文献
43.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献
44.
Daniel Whittaker Andreas Geist Giuseppe Modolo Robin Taylor Mark Sarsfield Andreas Wilden 《溶剂提取与离子交换》2018,36(3):223-256
Over the last decade there has been much interest in the applications of diglycolamide (DGA) ligands for the extraction of the trivalent lanthanide and actinide ions from PUREX high active raffinates or dissolved spent nuclear fuel. Of the DGAs, the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) is the best known and most widely studied. A number of new actinide separation processes have been proposed based on extraction with TODGA. This review covers TODGA-based processes and extraction data, specifically focusing on how phase modifiers have been used to increase metal loading and thus enhance the operating process envelopes. Effects of third phase formation and the organic phase speciation are reviewed in this context. Relevant aspects of the extraction chemistry of important solvents (TODGA-modifier-diluent combinations) are described and their performances demonstrated by a consideration of the published flowsheet tests. It is seen that modifiers are successfully enabling the use of TODGA in actinide separation processes but to date the identification and testing of suitable modifiers has been rather empirical. There is a growing understanding of the fundamental chemistry occurring in the organic phase and how that affects extractant speciation and metal loading capacity but studies are still needed if TODGA-based flowsheets are to become an industrially deployable option for minor actinide (MA) recovery processes. 相似文献
45.
Fei Li Xin-Gang Wang Xiao Huang Ji-Xuan Liu Weichao Bao Guo-Jun Zhang Hongzhi Wang 《Journal of the European Ceramic Society》2018,38(14):4806-4813
We present a straightforward method via sol-gel process using polyethylene glycol (PEG) as phase separation inducer to prepare zirconium carbide/silicon carbide (ZrC/SiC) porous monoliths. Organic/inorganic hybrid gels are prepared using zirconium oxychloride, furfuryl alcohol, and tetraethyl orthosilicate as major starting materials. In the presence of PEG, crack-free hybrid monoliths are obtained by drying the wet gels under ambient pressure, whereas in the absence of PEG, the wet gels break into pieces as expected. PEG plays a key role in maintaining the macroscopic shape of the monoliths. After ceramization at 1300–1500?°C, ZrC/SiC porous monoliths are obtained. SEM and mercury intrusion porosimetry data show that PEG also has strong influence on the microstructures of the monoliths. The compressive strengths of the ceramic monoliths are in the range of 0.3 to 0.7?MPa. And their compressive behavior starts to differ due to the changes in their microstructures, especially the pore structure. 相似文献
46.
T. Galvin N.C. Hyatt W.M. Rainforth I.M. Reaney D. Shepherd 《Journal of the European Ceramic Society》2018,38(14):4585-4589
The molten salt method was used to synthesise the MAX phase compounds Ti2AlC and Ti3AlC2 from elemental powders. Between 900–1000?°C, Ti2AlC was formed alongside ancillary phases TiC and TiAl, which decreased in abundance with increasing synthesis temperature. Changing the stoichiometry and increasing the synthesis temperature to 1300?°C resulted in formation of Ti3AlC2 alongside Ti2AlC and TiC. The type of salt flux used had little effect on the product formation. The reaction pathway for Ti2AlC was determined to be the initial formation of TiC1-x templating on the graphite and titanium aluminides. 相似文献
47.
48.
49.
The present study focuses on the sintering of silicon carbide-based ceramics (SiC) by liquid phase sintering (LPS) followed by characterization of the produced ceramics. AlN/Re2O3 mixtures were used as additives in the LPS process. In the first step, the LPS-SiC materials were produced in a graphite resistance furnace in the form of discs at different temperatures. The conditions with the best results regarding real density and relative density were taken as reference for sintering in the form of prismatic bars. In the second step, these samples were evaluated regarding fracture toughness (KIC), by the Single Edge V Notch Beam – SEVNB – method, and flexural strength. KIC behavior was evaluated according to the depth and curvature radius of the notches. Reliable KIC values were presented when the ceramic displayed a small curvature radius at the notch tip. When the radius was large, it did not maintain the square root singularity of the notch tip. Tests were carried out to determine KIC values in atmospheric air and water. KIC results were lower in water than air, with a decrease ranging between 2.56% and 11.26%. The observations indicated a direct grain size correlation between KIC values and fracture strength of the SiC ceramics. 相似文献
50.
《Journal of the European Ceramic Society》2020,40(4):1644-1650
Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)3O4, (Co,Cr,Fe,Mg,Mn)3O4 and (Cr,Fe,Mg,Mn,Ni)3O4 are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient. 相似文献