全文获取类型
收费全文 | 15346篇 |
免费 | 1539篇 |
国内免费 | 1373篇 |
专业分类
电工技术 | 3668篇 |
技术理论 | 2篇 |
综合类 | 1376篇 |
化学工业 | 1122篇 |
金属工艺 | 708篇 |
机械仪表 | 644篇 |
建筑科学 | 752篇 |
矿业工程 | 380篇 |
能源动力 | 891篇 |
轻工业 | 272篇 |
水利工程 | 4966篇 |
石油天然气 | 344篇 |
武器工业 | 59篇 |
无线电 | 760篇 |
一般工业技术 | 820篇 |
冶金工业 | 440篇 |
原子能技术 | 592篇 |
自动化技术 | 462篇 |
出版年
2024年 | 51篇 |
2023年 | 184篇 |
2022年 | 408篇 |
2021年 | 436篇 |
2020年 | 468篇 |
2019年 | 466篇 |
2018年 | 458篇 |
2017年 | 600篇 |
2016年 | 579篇 |
2015年 | 635篇 |
2014年 | 980篇 |
2013年 | 840篇 |
2012年 | 1155篇 |
2011年 | 1180篇 |
2010年 | 807篇 |
2009年 | 851篇 |
2008年 | 912篇 |
2007年 | 1057篇 |
2006年 | 977篇 |
2005年 | 843篇 |
2004年 | 750篇 |
2003年 | 616篇 |
2002年 | 522篇 |
2001年 | 489篇 |
2000年 | 399篇 |
1999年 | 354篇 |
1998年 | 243篇 |
1997年 | 226篇 |
1996年 | 151篇 |
1995年 | 155篇 |
1994年 | 111篇 |
1993年 | 93篇 |
1992年 | 66篇 |
1991年 | 52篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1964年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Studies were made on the thermally stimulated discharge currents (TSDCs) in pure (undoped) and Fe-doped polystyrene films as a function of polarizing field, polarizing temperature and dopant concentration. While undoped films exhibited a single peak, doped films showed two peaks one at low temperatures and another at high temperatures. The low temperature peak, which exhibits a shift towards lower temperatures with increasing dopant concentration, is attributed to the relaxation of the main chain, while the high temperature peak, which shows a tendency to shift towards higher temperatures with dopant concentration, is due to space charge polarization. The TSDCs were higher for low dopant concentrations than their undoped counterparts, while for high concentrations of the dopant, the TSDCs decreased. Formation of charge transfer complexes at low dopant concentrations and molecular aggregates at higher dopant concentrations are suggested as the possible reasons for this behaviour. 相似文献
72.
73.
74.
WU Jian-hua CAI Chang-guang JI Wei RUAN Shi-ping 《水动力学研究与进展(B辑)》2006,18(5):567-571
1. INTRODUCTION In the design of a discharge tunnel with high water head and large flow, it is important to study the cavitation and the energy dissipation, such as the prevention of cavitation for slots of various gates [1-4], the effects of entrained ai… 相似文献
75.
Annual growth increments were calculated for blue catfish (Ictalurus furcatus) and flathead catfish (Pylodictis olivaris) from the lower Mississippi River (LMR) to assess hypothesized relationships between fish growth and floodplain inundation as predicted by the Flood‐Pulse Concept. Variation in catfish growth increment was high for all age classes of both species, and growth increments were not consistently related to various measures of floodplain inundation. However, relationships became stronger, and usually direct, when water temperature was integrated with area and duration of floodplain inundation. Relationships were significant for four of six age classes for blue catfish, a species known to utilize floodplain habitats. Though similar in direction, relationships were weaker for flathead catfish, which is considered a more riverine species. Our results indicate the Flood‐Pulse Concept applies more strongly to temperate floodplain‐river ecosystems when thermal aspects of flood pulses are considered. We recommend that future management of the LMR should consider ways to ‘recouple’ the annual flood and thermal cycles. An adaptive management approach will allow further determination of important processes affecting fisheries production in the LMR. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
76.
Material removal and surface damage of Ti3SiC2 ceramic during electrical discharge machining (EDM) were investigated. Melting and decomposition were found to be the main material removal mechanisms during the machining process. Material removal rate was enhanced acceleratively with increasing discharge current, ie, working voltage, ui, but increased deceleratively with pulse duration, te. Microcracks in the surface and loose grains in the subsurface resulted from thermal shock were confirmed, and the surface damage in Ti3SiC2 ceramic led to a degradation of both strength and reliability. 相似文献
77.
I.Z. Ismagilov R.P. Ekatpure L.T. Tsykoza E.V. Matus E.V. Rebrov M.H.J.M. de Croon M.A. Kerzhentsev J.C. Schouten 《Catalysis Today》2005,105(3-4):516-2
This paper describes the optimization of three processes applied in fabrication of a microstructured reactor for complete oxidation of volatile organic compounds. The first process involves the optimization of the electro discharge machining (EDM) method to produce a set of microchannels with a high length to diameter ratio of 100, with a standard deviation from the average diameter below 0.2%, and with a surface roughness not higher than 2.0 μm. To satisfy these criteria, fabrication of microchannels must be carried out with two machining passes in the Al51st alloy. Then, the effect of several parameters on the anodization current efficiency with respect to oxide formation was studied. The best process conditions to get a 30 μm porous alumina layer in a 0.4 M oxalic acid electrolyte, were found to be a temperature of 1 °C, an anodic current density of 5 mA/cm2, and 23 h oxidation time. At last, the resulting coatings were impregnated with an aqueous solution of copper dichromate followed by drying and calcination at 450 °C to produce active catalysts. The effect of a copper dichromate concentration, number of impregnation cycles (1 or 2), and different after-treatments on catalytic activity and stability in complete oxidation of n-butane were studied. The catalytic activity of the obtained coatings is superior to that of alumina supported pelletized catalysts even at much lower loadings of active metals. 相似文献
78.
79.
80.
The hydrogen fuel cell is a promising option as a future energy resource; however, the nature of the gas is such that the conversion process of other fuels to hydrogen on board is necessary. Among the raw fuel resources, methane could be the best candidate as it is plentiful. In this experiment, the possibility of producing hydrogen with less carbon formation from methane by a dielectric barrier discharge (DBD) was investigated. Without the addition of a catalyst, the formation of hydrogen reached between 30% and 35% at methane residence time of 0.22 min and supplied powers in the range of 60-130 W. The hydrogen selectivity increased at higher supplied power, but the process efficiency, defined as a ratio of the produced hydrogen to the supplied power, decreased slightly. In order to boost the hydrogen production with less carbon formation, a mixed oxide catalyst of zinc and chromium was added to the reactor. It was shown that the production of hydrogen was ca. 40% higher than the non-catalytic plasma process. 相似文献