全文获取类型
收费全文 | 11124篇 |
免费 | 1053篇 |
国内免费 | 243篇 |
专业分类
电工技术 | 56篇 |
综合类 | 306篇 |
化学工业 | 3632篇 |
金属工艺 | 646篇 |
机械仪表 | 142篇 |
建筑科学 | 374篇 |
矿业工程 | 34篇 |
能源动力 | 146篇 |
轻工业 | 4613篇 |
水利工程 | 21篇 |
石油天然气 | 369篇 |
武器工业 | 50篇 |
无线电 | 314篇 |
一般工业技术 | 1303篇 |
冶金工业 | 207篇 |
原子能技术 | 86篇 |
自动化技术 | 121篇 |
出版年
2024年 | 105篇 |
2023年 | 238篇 |
2022年 | 371篇 |
2021年 | 488篇 |
2020年 | 424篇 |
2019年 | 471篇 |
2018年 | 449篇 |
2017年 | 471篇 |
2016年 | 512篇 |
2015年 | 408篇 |
2014年 | 547篇 |
2013年 | 747篇 |
2012年 | 632篇 |
2011年 | 874篇 |
2010年 | 551篇 |
2009年 | 594篇 |
2008年 | 563篇 |
2007年 | 522篇 |
2006年 | 489篇 |
2005年 | 351篇 |
2004年 | 341篇 |
2003年 | 363篇 |
2002年 | 345篇 |
2001年 | 212篇 |
2000年 | 185篇 |
1999年 | 138篇 |
1998年 | 184篇 |
1997年 | 129篇 |
1996年 | 97篇 |
1995年 | 94篇 |
1994年 | 67篇 |
1993年 | 59篇 |
1992年 | 50篇 |
1991年 | 58篇 |
1990年 | 49篇 |
1989年 | 26篇 |
1988年 | 15篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 36篇 |
1983年 | 16篇 |
1982年 | 32篇 |
1980年 | 18篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
The group-contribution method for vapor pressures of hydrocarbons and organic compounds containing nitrogen or sulfur, based on the kinetic theory of fluids, is revised and extended to include new groups containing nitrogen or sulfur. Good representation is obtained for vapor pressure data in the region 1.30-270 kPa. The method may be used to estimate vapor pressures and enthalpies of vaporization for those organic fluids containing nitrogen or sulfur, where no experimental data are available. 相似文献
83.
Both covalent (obtained by direct fluorination at high temperature) and semi-ionic carbon fluorides (synthesized at room temperature) were reduced in order to obtain disordered carbons containing very small content of fluorine and different physical properties according to the reduction treatment (chemical, thermal or electrochemical). After a physical characterization (X-ray diffraction, electron spin resonance and FT-IR spectroscopies), the electrochemical behaviours of the pristine carbon fluorides and of the treated samples were investigated during the insertion of lithium using liquid carbonate-based electrolytes (LiClO4-EC/PC, 50:50%, v/v). Both galvanostatic and voltammetric modes were performed and revealed that the voltage profiles and the capacities differed according to the starting material and the reduction treatment. Semi-ionic carbon fluoride treated in F2 atmosphere for 2 h at 150 °C and then chemically reduced in KOH exhibits high reversible capacities (the reversible capacity is 530 mAh g−1 in the second cycle); in this case, the voltage profiles show a large flat portion at potentials lower than 0.3 V which is attributed to the insertion/deinsertion of lithium ions between the small graphene sheets and/or the absorption of pseudo metallic lithium into the microporosity of the sample. Nevertheless, a part of the lithium ions are removed at potentials higher than 0.5 V versus Li+/Li limiting the useful capacity. 相似文献
84.
J. L. Rehspringer P. Poix A. Kaddouri D. Andriamasinoro A. Kiennemann 《Catalysis Letters》1991,10(1-2):111-120
The influence of the structure on the catalytic methane activation coupling activity has been shown for La2x
Y2–2x
O3 (0 x 1) compounds. A perovskite structure leads to total oxidation (CO, CO2) whereas a bixbyite structure results in C2 hydrocarbon formation. This change in selectivity is interpreted in terms of the difference in oxygen environment of lanthanum in the two stuctures. 相似文献
85.
The aim of this work is to analyse the possibility of using co-gasification technology to process coal mixed with wastes to take profit of its energy content and at the same time to minimize the environmental impact associated with the use of wastes and to diminish the costs of flue gas treatment. The addition to coal of different types of materials, like: pine based waste, petcoke and polyethylene (PE), was not found to give rise to any operational problems, regarding both the feeding system and gasification process and led to higher energy conversions, however, the gas presented higher tars and hydrocarbons content. Several catalysts were tested, such as, dolomite, olivine, nickel and magnesium oxides, zinc oxides and cobalt and molybdenum oxides. Catalyst action was analysed in tars release and also in ammonia compounds reduction. The presence of catalysts allowed increasing hydrogen release, whilst there was a decrease in hydrocarbons and tars contents. A nickel-magnesium oxide was the catalyst that led to the highest reduction in hydrocarbons and tars. This catalyst also led to the lowest NH3 content in the fuel gas produced, due to the catalyst efficiency in NH3 destruction. 相似文献
86.
针对固体钾碱产品中不溶性物质较多影响产品质量的问题,提出对固碱成型、包装及涮锅水处理工艺的改造,同时强化管理,优化工艺操作方法,实现了产品质量的稳步提高。 相似文献
87.
Polycrystalline Ag treated with O2 at pressures up to 1 bar and at temperatures up to 920 K was examined by TDS. It was found that the peak commonly observed at 595±25 K and assigned to adsorbed atomic oxygen (Oa) is shifted to higher desorption temperatures with rising dosing temperatures. Since saturation of the uptake was not possible either, this peak was identified as dissolved atomic oxygen (Od). The existence of a maximum for the O2 uptake after exposure at 820 K was found. Hence, under conditions of formaldehyde synthesis ( 920 K) the ability of the catalyst to dissolve oxygen is near its maximum. 相似文献
88.
Kaiguang Yang 《Desalination》2005,175(3):297-304
DNA-encapsulated polyethersulfone (PES) hollow microspheres are fabricated by means of a liquid-liquid phase separation technique; the hollow microspheres are then used to remove environmental pollutant organic compounds and heavy metal ions. The amounts of DNA encapsulated in the microspheres are dependent on the PES concentration, the DNA concentration used to prepare the particles, and the diameter of the syringe needle. The hollow microspheres can be used to remove harmful organic compounds including ethidium bromide (EB), acridine orange (AO) and endocrine disruptors. With the increase of the DNA amount encapsulated into the hollow microspheres, the removal ratios of these compounds increased. Additionally, the DNA-encapsulated PES hollow microspheres can selectively accumulate and remove heavy metal ions such as Ag+, Cu2+ and Zn2+ These results suggested that the DNA-encapsulated PES hollow microspheres have a potential to be used in environmental applications. 相似文献
89.
Model compound studies were carried out to elucidate the reaction mechanisms taking place during the liquefaction of coal with the hydrogen produced from the reaction of zinc and water. In compounds of the type Ph-(CH2)n-Ph the splitting of the aliphatic bridge was easier with higher n values. Ether type compounds such as diphenylether were unreactive although the C-O bond in dibenzylether was easily cleaved. Condensed ring aromatic compounds gave low conversion with hydrogenation being facilitated by an increase in ring number. Phenolic compounds such as phenol did not react well, but the reactivity increased with increase in aromatic ring size. The cleavage of the aliphatic bridge was accelerated by the OH group, for example, in the case of 4-hydroxydiphenylmethane bond scission was about 15 times higher than that of diphenylmethane. Heterocyclic compounds were unreactive. 相似文献
90.